Glossary of Orthodontic Terms
Abrasion
Mechanical wear of tooth structure caused by a foreign abrasive material. Toothbrush abrasion is the most common example, which may sometimes present as a sharp V-shaped notch in the gingival portion of the labial surface of the teeth.
[Compare with Attrition (Dental wear, Occlusal wear)]
Abrasive strips
(Finishing strips, Lightening strips, Coated abrasive strips)
Strips containing abrasive particles on a flexible backing material (heavyweight paper, metal or plastic). Used mainly for interproximal enamel reduction. [See Interproximal stripping (Interproximal reduction of enamel, Reproximation, Slenderizing)]
Anterior guidance
Term used to describe a particular scheme of disclusion of the dental arches during a protrusive mandibular excursion. Contacts between the maxillary incisors and the mandibular anterior teeth guide the mandible downward, to create disarticulation (separation) of all other teeth.
Achondroplasia
An autosomal dominant condition characterized by failure of the primary growth cartilages of the limbs and cranial base to grow properly. Early fusion of the sphenoethmoidal, intersphenoidal and sphenooccipital synchondroses and early closure of the epiphyseal plates of the long bones result in very short arms and legs and a characteristic midface deficiency that is most accentuated at the bridge of the nose. The anterior cranial base appears to be of approximately normal length, whereas the posterior cranial base is extremely short (i.e. the sphenooccipital synchondrosis seems to be affected more than the sphenoethmoidal). Affected patients also exhibit short bodies with thick extremities and stubby fingers, often associated with limited motion of the joints, lumbar lordosis, protruding abdomen, and inability to straighten the elbows. Correction of the midface deficiency and the resulting Class III malocclusion in achondroplasia may require a Le Fort III, or modified Le Fort II, osteotomy to advance the entire midface.
Acid etching
An enamel bonding technique invented by M. G. Buonocore in 1955. During this process a selected area of tooth substance is prepared for bonding via the application of a corrosive agent (most commonly a solution or gel of 37% orthophosphoric acid). The effect is a removal of a small amount of less mineralized, interprismatic enamel and opening of pores between the enamel prisms, substantially enlarging the surface area of the bonded part so the adhesive can penetrate into the enamel, providing micromechanical retention.
Acromegaly
Chronic metabolic disorder caused by hyperfunction of the anterior pituitary gland after maturity, usually due to an adenoma. The resulting overproduction of growth hormone induces an overgrowth of the bones, connective tissue and viscera. Skeletal changes principally involve the skull, with frontal bossing, prominent cheek bones, grossly overdeveloped mandible with a protrusive chin and consequent mandibular prognathism. The small bones of the hands and feet are also affected, and there is associated broadening of the hands, fingers and feet. Enlargement of the soft tissue usually is manifested by large ears and nose, thick lips and macroglossia. The tongue, which exhibits a lobulated margin and papillary hypertrophy, fills the oral cavity and results in associated labial and buccal tipping of the teeth. There is generalized splanchnomegaly and hypertrophy of the target organs for anterior pituitary hormones, including the adrenal cortex, thyroid gland, parathyroid glands and gonads.[See Gigantism]
Acrylic (Methyl methacrylate)
An organic resin commonly used for the construction of dental removable appliances, including appliances used during orthodontic treatment and retention. [Modified from the AAO Glossary of Dentofacial Orthopedic Terms, 1993.]
Activation
The process of storing mechanical energy into an active member of an orthodontic appliance (e.g. stretching an elastic, or compressing an open coil spring) in order for it to produce the desired force system, which will be delivered to the dentition. The force system that must be applied for activation of a spring is the opposite to the force system desired (during deactivation).
Active component
The part of an orthodontic appliance that is involved directly in tooth movement. [Compare with Reactive component]
Adaptability (Adaptive capacity, Adaptive potential)
Relative ability to adjust to the demands of the environment.
Adaptation
1. The progressive adjustive changes in sensitivity that regularly accompany continuous sensory stimulation or lack of stimulation. The process by which an organism responds to the functional demands of its environment.
2. The process by which a dental device is fitted to another structure (e.g. adaptation of a band to a tooth).
“Adenoid facies”
A long-standing descriptive term implying a relationship between mouth breathing (due to enlarged adenoids) and the development of malocclusion through altered function. The classic description of “adenoid facies” consists of narrow nasal and alar width, hypotonic musculature, “dull” or “vacant” facial expression and lips separated at rest. It is important to stress that the presence of “adenoid facies” does not necessarily mean that the patient is an obligatory mouth breather, or in other words, mouth breathing is habitual in certain patients.
Adhesion
1. Attractive force between atoms or molecules of dissimilar materials, when they are in close approximation. The attachment of one substance to another.
2. The abnormal fibrous joining of adjacent structures following an inflammatory process or as a result of injury repair. [See Bonding] [See Cohesion] SUBTERMS:
Adhesion
• Capsular adhesion
Fibrosis of the capsular tissues of a joint.
Adhesion
• Extracapsular adhesion
Fibrosis of pericapsular tissues such as muscles or ligaments.
Adhesion
• Intracapsular adhesion (Fibrous ankylosis, Pseudoankylosis)
Fibrosis between intra-articular surfaces within a joint capsule, resulting in reduced mobility of the affected joint.
Advancement (of the mandible)
An orthognathic surgical procedure aiming at sagittal (anterior) augmentation of the mandible, most often performed through a standard, or modified bilateral sagittal split ramus osteotomy (BSSO).[See Setback (of the mandible)]
[See Osteotomy, Bilateral sagittal split osteotomy (BSSO)]
Advancement (of the maxilla)
Anterior repositioning of the maxilla by orthognathic surgery. It most often involves a Le Fort I osteotomy. [See Osteotomy, Complete maxillary osteotomy]
Aesthetic
[See Cephalometric lines (planes), S-line (Esthetic plane of Steiner)]
[See Bends (Archwire bends), Artistic bends (Esthetic bends)]
[See Cephalometric lines (planes), Rees esthetic plane]
[See Facial esthetics]
[See Bracket, Esthetic bracket (Clear bracket)]
[See Cephalometric lines (planes), E-line (E-plane, Esthetic line of Ricketts)]
Agenesis
Congenital absence of a tooth.
Ala
The lateral rim of the nostril.
Alar cinch
A procedure performed during any orthognathic surgery that includes mobilization of the entire maxilla, in order to prevent excessive widening of the alar bases. It involves passing a permanent suture in a figure-eight fashion through the alar base tissues and through a bur hole placed in the region of the anterior nasal spine. This is repeated on the opposite side. Each suture is tightened independently, taking care to maintain symmetry, until the desired alar base width is attained (as determined from measurements before surgery). A situation in which an alar cinch may not be performed during maxillary orthognathic surgery is when very narrow alar bases exist preoperatively.
Alloy
A material that exhibits metallic properties (high electrical and thermal conductivity) and is composed of two or more elements, at least one of which is a metal (e.g. steel is an alloy of iron and carbon, brass is an alloy of copper and zinc).
Alpha position
The anterior component of an orthodontic spring or the anterior point of attachment of a spring. [Compare with Beta position]
Alveolar crest
The most coronal portion of the alveolar process.
Alveolar process
The U-shaped ridge of maxillary or mandibular alveolar bone that surrounds and supports the roots of the erupted teeth, as well as the unerupted tooth buds.
Anchorage
The sites that provide resistance to the reactive forces generated as a (most commonly, undesirable) consequence of the activation of an orthodontic or orthopedic appliance. [Short definition: resistance to unwanted tooth movement].
SUBTERMS:
• Cervical anchorage
Anchorage provided by the back of the neck when extraoral appliances such as a cervical pull headgear are used.
Extraoral anchorage
Anchorage provided by sites located outside the oral cavity.
Infinite anchorage
The term is commonly used when referring to implants used as anchorage in orthodontics, to indicate that they show no movement (zero anchorage loss) as a consequence of reaction forces. [See Implant, Orthodontic implant]
Intermaxillary anchorage
Anchorage for tooth movement provided by the teeth of the opposing arch.
Intramaxillary anchorage
Anchorage provided by teeth within the same arch as the ones that are to be moved.
Maximum anchorage (Type A anchorage)
A situation in which the treatment objectives require that no or very little anchorage can be lost.
Minimum anchorage (Type C anchorage)
A situation in which, for an optimal result, a considerable movement of the anchorage segment (anchorage “loss”) is desirable, during closure of space.
Moderate anchorage (Type B anchorage)
A situation in which anchorage is not critical and space closure should be performed by reciprocal movement of both the active and the anchorage segment.
Occipital anchorage
Anchorage provided by the superior and posterior portions of the head, when extraoral appliances such as a high-pull headgear are used.
Reciprocal anchorage
A situation in which the movement of one or more dental units is balanced against the movement of another, or more dental units, on which the reaction forces are placed. [The term generally means that the movement of both the active and the reactive component is desirable. ]
Anchorage loss
The undesirable movement of the reactive anchorage segment, which happens as a side effect of the movement of the active segment (e.g. mesial movement of the maxillary molars during retraction of maxillary incisors with intramaxillary mechanics).
Anchorage preparation
A procedure commonly used in the Tweed
technique, during which the molars and
premolars are tipped distally prior to
retraction of the anterior teeth. The theory
behind it is that it increases the anchorage
value of the posterior segments, allowing
further retraction of the canines and incisors
with less anchorage loss.
Anchorage reinforcement
The process of increasing the anchorage value of the reactive segment to resist anchorage loss.
This can be done in a number of ways, e.g. by incorporating more teeth into the reactive segment;
by using additional stabilizing arches such as a lingual arch, a Nance holding arch or a transpalatal
arch; or by using extraoral or intermaxillary traction.
Anchorage value
Relative resistance of a tooth (or a segment of teeth) in comparison to another, which usually is
estimated on the basis of comparison of root surface areas and density of the supporting bone.
Angle classification
• “Subdivisions” (left or right)
are used in asymmetric situations to indicate the side that deviates from a Class I molar
relationship.
Angle of activation
A measure (in degrees) of the activation placed into an orthodontic wire by bending or torsion, with
regard to its initial passive state. When the wire characteristics and the interbracket distance are
known, the clinician can estimate the magnitude of the force produced.
Angulation (Second order, “Tip”)
Angular deviation of the long axis of a tooth from a line perpendicular to the occlusal plane, in the
mesiodistal direction.
[Compare with Inclination (Third order, “Torque”)]
Ankylosis
Abnormal immobility, union or fusion that may occur between two bones at their articulation (e.g.
ankylosis of the TMJ) or between teeth and alveolar bone. In the instance of the TMJ, bony or
fibrous ankylosis can be caused by conditions such as congenital defects, trauma, inflammation,
infections, arthritis or neoplasms.
In the case of an ankylosed tooth, the periodontal ligament is obliterated in one or more localized
areas, and a “bony bridge” is formed by penetration of alveolar bone into the cementum. Dental
ankylosis eliminates the potential for both eruption and orthodontic movement. In a growing
individual, an ankylosed tooth is accompanied by a localized vertical deficiency of the alveolar
ridge, and consequently appears to “submerge” as adjacent, unaffected teeth continue to erupt.
Ankylosis of deciduous teeth (usually molars) is a more common phenomenon than ankylosis of
permanent teeth.
[See Tooth mobility, Reduced mobility (Hypomobility)]
Annealing
A heat treatment and cooling schedule used to reduce the hardness and increase the ductility of a
metal by removing residual stress.
Anomalad
A malformation, together with its subsequently derived structural changes (e.g. the Robin
anomalad).
Anodontia
A rare condition characterized by congenital absence of all teeth (both deciduous and permanent).
Most commonly related to ectodermal dysplasia.
[Compare with Oligodontia]
Antegonial notch
A depression or concavity usually present in
the inferior border of the mandible,
immediately anterior to the angle, near the
insertion of the masseter muscle. A deeper
than normal antegonial notch may be
indicative of a dolichofacial pattern or of
mandibular underdevelopment. Pronounced
antegonial notching also is a common
characteristic of some syndromes with
micrognathia of the lower jaw, such as
Treacher Collins syndrome.
Anterior component of occlusal force
A theory attempting to explain the tendency of posterior teeth to drift mesially with time. Factors
that are considered related to this phenomenon are: morphology and angulation of teeth, occlusal
and muscular forces and transseptal fibers.
Anterior cranial base
The anterior aspect of the floor of the cranial vault, commonly delimited cephalometrically by sella
turcica and nasion.
Anterior guidance
Term used to describe a particular scheme of disclusion of the dental arches during a protrusive
mandibular excursion. Contacts between the maxillary incisors and the mandibular anterior teeth
guide the mandible downward, to create disarticulation (separation) of all other teeth.
Anteroposteriorly
In a direction parallel to the sagittal plane; in radiology it denotes beam direction from front to back.
Antrum
A cavity or chamber. The term usually refers to the maxillary sinus.
Apical area (of the bone)
The apical area in the newborn child and during the
first year of life is the region in which the developing
deciduous and permanent teeth are found. In the
deciduous dentition it comprises the area occupied by
the apices of the deciduous teeth and the developing
permanent teeth. In the mixed dentition, the apical
area is the region in which lie the apices of the
deciduous and erupted permanent teeth, as well as
developing unemerged permanent teeth. In the adult,
the apical area consists of the region in which normally
the apices of the permanent teeth can be located. The
concept of the apical area was introduced by F. P. G.
M. van der Linden in 1979.
Apical base
Maxillary and mandibular bone that
supports and is continuous with the
alveolar processes, as well as with the
maxillary and mandibular bodies.
Although the demarcation between
alveolar and basal bone is not specific, it
generally is thought to lie at or slightly
above the level of the apices of the roots.
The concept of the apical base was
introduced by A. F. Lundstrцm in 1923.
[See Bone, Basal bone]
Appliance
Any device used for a particular functional, diagnostic and/or therapeutic effect.
SUBTERMS:
Appliance
• ACCO appliance
A combination of a modified maxillary removable appliance with a straight-pull J-hook headgear.
The acronym “ACCO” was suggested by H. I. Margolis (1976) and stands for ACrylic-Cervical-
Occipital.
The maxillary removable appliance includes an anterior bite plane, a labial bow, clasps for
retention and finger springs for distalization of the maxillary molars. The J-hook headgear is
attached to loops on the labial bow that are bent between the maxillary central and lateral incisors.
Its purpose is to counteract the reaction force on the maxillary anterior teeth caused by the
distalizing force of the finger springs on the maxillary molars. A cervical headgear also may be
attached on the maxillary molars to complement the action of the ACCO.
In the original design of the appliance by Margolis, molar distalization took place one side at a time.
During distalization on one side, ball clasps or passive finger springs on the other side enhanced
retention of the appliance. Once a Class I molar relationship was achieved on the active side, a
new ACCO was made. The new acrylic configuration and clasps on the completed side would
retain the correction achieved, at the same time providing anchorage to correct the residual Class
II relationship on the contralateral side of the arch.
Appliance
• Activator (Monobloc)
The first removable functional appliance, developed by V. Andresen. Historically, the term
“activator” was introduced to describe the “activation of mandibular growth,” to which the achieved
correction of a Class II malocclusion was attributed. The term currently is used in a generic sense,
referring to a family of functional appliances used to treat Class II malocclusions characterized, at
least in part, by mandibular deficiency. [For activators designed for patients with Class III
malocclusions, see Appliance, Class III functional.] These appliances position the mandible
forward, promoting a new mandibular postural position. The reactive forces from the stretch of the
muscles and soft tissues are transmitted to the maxillary dentition and through that, to the maxilla.
The acrylic body of the Andresen activator covers part of the palate and the lingual aspect of the
mandibular alveolar ridge. (Note: In its original design the appliance contacted the mandibular
anterior teeth only on the lingual side and did not extend over the incisal edges.) A labial bow fits
anterior to the maxillary incisors and carries U-loops for adjustment. On the palatal aspects of the
maxillary incisors, the acrylic is relieved to allow their retraction.
A main feature of the appliance is the faceting of the acrylic on palatal and lingual aspects of the
maxillary and mandibular posterior teeth, respectively, designed to direct their eruption. On the
palatal aspect of the maxillary posterior teeth the facets are cut so as to allow occlusal, distal and
buccal movement of these teeth. This movement is achieved by keeping the acrylic in contact with
only the mesiopalatal surfaces of the premolars and molars. On the lingual aspect of the
mandibular posterior teeth the facets only permit occlusal and mesial movement, with the acrylic
contacting the distolingual surface of these teeth.
[See Appliance, Class Class III functional appliances (Reverse functional appliances)]
[See Appliance, Functional appliance]
Appliance
• Active vertical corrector
An appliance introduced by E. L. Dellinger, attempting to correct anterior open bites by intrusion of
posterior teeth. The appliance consists of maxillary and mandibular posterior biteblocks with
incorporated repelling samarium-cobalt magnets. A commonly reported side effect of treatment
with the appliance is the creation of a posterior crossbite owing to the lateral force components of
the repelling magnets.
[See Orthodontic magnets]
Appliance
• Bass appliance
A removable functional appliance designed by N. M. Bass, consisting of a basic maxillary
expansion plate on which various other parts can be mounted. The expansion plate covers the
occlusal surfaces of all maxillary teeth and has torquing springs for the maxillary central incisors.
The appliance also carries tubes in which buccal shields can be attached, and has mandibular lip
pads extending in the vestibule in a fashion similar to the Frдnkel appliance. On the lingual side
there are specially designed flanges that can be gradually advanced. The Bass appliance also can
be combined with a high-pull headgear.
Appliance
• Begg appliance (Light-wire appliance)
Fixed multi-banded
orthodontic appliance
developed by P. R.
Begg for his light-wire technique. The appliance consists of narrow (single-wing), ribbon-arch
brackets (originally developed by E. H. Angle as the “pin and tube” appliance) and light, round
stainless steel archwires. It allows a series of tipping movements of teeth in conjunction with
intermaxillary elastics. Treatment with the Begg technique is classically divided into three stages:
The first stage includes initial alignment by simple tipping, with the exception of the anchor teeth.
Any spaces present between the anterior teeth are closed and any rotations or crossbites are
corrected. Deep anterior overbites or open bites are eliminated, and the anteroposterior occlusal
relationship between the maxillary and mandibular teeth is overcorrected. Arch forms are
coordinated and extraction spaces are reduced, to some degree, during the first stage.
During the second stage all extraction spaces are closed completely, by allowing significant lingual
tipping of the anterior teeth (incisors and canines), brought upon by a combination of intramaxillary
and intermaxillary elastic traction.
The third and final stage basically includes uprighting of the teeth by movement of the roots. This
root movement is performed by round archwires with bent-in torquing loops, in combination with
root-torquing auxiliaries of various designs. Individual tooth positioning is performed with bends
and root-tipping springs.
[See Appliance, Tip-Edge appliance]
[See Differential force theory]
[See Orthodontic wire, Australian wire]
Appliance
• Bimler appliance (Bite former, Bimler stimulator)
A modification of the activator by H. P. Bimler. There are three main kinds of Bimler appliance: type
A for patients with Class II Division 1 malocclusions, type B for those with Class II Division 2 and
type C for patients with a Class III malocclusion. All of the above appliances are flexible and carry
springs and bows on the labial and lingual side in both arches. The springs and bows are
connected together by two acrylic wings which extend toward the palatal and lingual mucosa. Each
appliance type is subdivided further into two main categories, space creation or space closure; the
space creation variety carries additional active springs.
In the type A appliance the mandible is held in its advanced position by engagement of the
mandibular incisors in a splint. The splint contacts the labial aspect of the mandibular incisors while
special springs engage on their lingual aspect. A mandibular labial wire holds the splint in place,
extending distally to connect with the maxillary part of the appliance. The maxillary part of the
appliance carries a labial arch and palatal springs for the maxillary incisors.
In the type B appliance the palate is covered by acrylic, with an incorporated midline screw. No
labial arch exists for the maxillary incisors.
In the type C appliance occlusal wires covered with plastic tubing are used to achieve bite opening.
There is no labial splint, but the mandibular incisors are retracted by a labial bow originating from
the maxillary part of the appliance.
Appliance
• Bionator
A modification of the activator, developed by W. Balters in the 1950s. Its design is significantly less
bulky compared to the activator, thus reducing interference with speech. The bionator consists of a
lingual horseshoe of acrylic, with a palatal spring shaped like a (reversed) Coffin spring. Facets are
created in the acrylic to guide the maxillary and mandibular posterior teeth and hold them in the
postured relationship. A labial bow exists anterior to the maxillary incisors that extends distally to
keep the buccal musculature away from the teeth. In the original design of the appliance, the
mandibular incisors were not capped with acrylic.
Appliance
• Crefcoeur appliance
A removable appliance designed by J. Crefcoeur, most often used to increase space at a specific
location in the dental arch. The appliance is in essence a Hawley-type acrylic plate, sectioned
(split) at the point where space creation is necessary. A heavy-gauge stainless steel wire
(Crefcoeur spring) is embedded in the acrylic at the posterior aspects of the appliance bilaterally.
This wire runs parallel to the edges of the acrylic on the lingual aspect and can be activated
appropriately to increase the separation between the two sectioned parts of the appliance. After
sufficient space has been created, the two parts of the appliance can be reconnected with rapidcuring
acrylic. The appliance also can be used to reduce a localized space in the dental arch and
to expand or constrict the dental arches. Good retention and adequate clasps are very important
for the Crefcoeur appliance, particularly in the area of the separation. The retention of the
appliance can be enhanced by creating artificial undercuts with composite on certain teeth.
Appliance
• Chin cap (Chin cup)
Extraoral orthopedic appliance that consists of a cap that fits on the patient’s chin and a headstrap
similar to that of a high-pull headgear. It is designed to deliver a superiorly and posteriorly directed
force to the mandibular condyles, via the chin. The appliance has been used for decades in an
attempt to correct mandibular prognathism in young patients by restraining or redirecting
mandibular condylar growth.
Appliance
• Class Class III functional appliances (Reverse functional appliances)
Various types of functional appliances that position the mandible posteriorly and rotate it open.
Such appliances are advocated for the correction of maxillary deficiency and/or mild mandibular
prognathism in a growing child. The mode of action of Class III functional appliances includes
correction of any anterior crossbite by labial tipping of the maxillary incisors and retroclination of
mandibular incisors (introducing an element of dental compensation for the existing skeletal
discrepancy). The prominence of the chin is decreased by causing the mandible to rotate down
and back and by increasing the lower face height. Treatment with such appliances is not indicated
for patients with excessive lower face height, as is often the case with Class III problems.
Appliance
• Combined functional/extraoral traction appliance
A functional appliance on which a facebow can be attached for extraoral traction (e.g. the Bass and
the Teuscher appliances), or on which a facebow is rigidly fixed (e.g. the Van Beek appliance).
[See Appliance, Bass appliance]
[See Appliance, Teuscher-Stцckli activator/headgear combination appliance]
[See Appliance, Van Beek appliance]
Appliance
• Crib
An interceptive appliance used for correction of deleterious habits such as a deviating tongue
position and/or digit-sucking. A crib typically consists of a fixed transpalatal [0.036-inch (0.90-mm)
or heavier gauge] wire, soldered on two maxillary first permanent molar bands. The wire extends
toward the anterior palate where it forms a crib-shaped “fence” meant to interfere with the habit. A
crib also can be incorporated in a removable appliance. Posterior (lateral) tongue cribs can be
used as part of removable appliances in patients with unilateral or bilateral posterior open bite.
[See Appliance, Habit-breaking appliance (Habit reminder)]
[See Crib]
Appliance
• Crozat appliance
Removable orthodontic appliance which was developed by G. Crozat in the early 1900s. In its
original design the appliance was fabricated entirely of precious metal. Heavy gold wires
constituted the framework and lighter gold fingersprings produced the desired tooth movement.
The Crozat appliance can be used in the maxilla and/or mandible. Tight circumferential clasps
(“cribs”) on the molars provide adequate retention to permit the use of light intermaxillary elastics
with the appliance.
[See Appliance, Crib ]
Appliance
• Delaire appliance
[See Appliance, Face mask (Reverse-pull headgear, Protraction headgear, Face frame)]
Appliance
• Edgewise appliance (Standard edgewise)
Fixed multi-banded orthodontic appliance, introduced by E. H. Angle in 1928. It involves a
rectangular labial archwire ligated into attachments (brackets) that are fixed on bands which are
cemented to individual teeth, or that are directly bonded to individual teeth. The term “edgewise”
refers to the fact that the bracket slot is fabricated in a way that permits insertion of the archwire
with its long dimension perpendicular to the long axis of the tooth, instead of parallel to it, as in the
(earlier) “ribbon arch” bracket.
Appliance
• Elastic open activator
A modification of the activator developed by G. Klammt. The appliance has reduced acrylic bulk,
facilitating increased appliance wear. The acrylic is replaced by wires which increase the flexibility
of the appliance. The flexible design allows isotonic muscular contractions (in contrast to rigid
appliances, which only allow isometric contractions).
Appliance
• Expansion appliance
An orthodontic appliance used to expand the maxillary or, less frequently, the mandibular dental
arch. An expansion appliance can be removable (e.g. split-plate appliance with a jackscrew) or
fixed on the teeth (e.g. the Hyrax appliance or the Quad-helix).
[See Expansion, Slow maxillary (palatal) expansion (SME or SPE)]
[See Expansion, Rapid maxillary (palatal) expansion (RME, RPE)]
[See Appliance, Haas appliance (Haas rapid maxillary expansion appliance, Haas palatal
separator)]
[See Expansion, Surgically assisted rapid maxillary expansion]
[See Appliance, Hyrax appliance (Hygienic rapid palatal expander)]
Appliance
• Extraoral traction appliance
An orthodontic appliance that makes use of extra-oral anchorage (e.g. headgear, face mask).
Appliance
• Face mask (Reverse-pull headgear, Protraction headgear, Face frame)
Extraoral appliance that utilizes rests on the chin and forehead (and occasionally the cheek bones)
as anchorage for elastic traction, with the purpose of orthopedically protracting the maxilla. This
maxillary protraction is performed as an early treatment modality in Class III malocclusions
associated with maxillary hypoplasia. The face mask also can be used as an orthodontic
appliance, to provide extraoral anchorage for protraction of posterior teeth. Usual side effects of
face mask treatment include elongation of the face (caused by extrusion of the teeth to which the
elastic traction is applied) and proclination of the maxillary incisors, when the traction is applied to
the maxilla. The appliance was designed by J. Delaire and subsequently modified by H. Petit and
others.
Appliance
• Fixed appliance
An appliance that is cemented or bonded to the teeth and thus cannot be removed by the patient.
The term commonly refers to fixed attachments (brackets, tubes, bands) placed on the teeth in
conjunction with archwires to move them to a new position.
Appliance
• Fixed/removable appliance
Orthodontic appliance that is fixed to the teeth but can be removed by the clinician for adjustment
and subsequently re-inserted, without taking off any brackets or bands. Fixed/removable
appliances make use of special sheaths welded on the palatal or lingual aspect of molar bands
(e.g. the fixed/removable lingual arch or transpalatal arch).
[See Sheath]
Appliance
• Frankel appliance (Function Regulator)
Group of functional appliances developed by R. Frдnkel to treat malocclusions, while aiding in the
maturation, training and reprogramming of the orofacial neuromuscular system. Four main types of
appliances have been described by Frдnkel: Function Regulator (FR)-I was designed for treatment
of Class I and Class II Division 1 malocclusions. The FR-II appliance is meant for patients with
Class II Division 1 and 2 malocclusions, the FR-III was designed for patients with Class III
malocclusions and the FR-IV for patients with hyperdivergent facial patterns and anterior open bite.
The appliances consist of acrylic buccal (vestibular) shields and lip pads, connected by wires, to
restrain and retrain aberrant musculature and to prevent the effects of restricting muscle forces on
the dentition. The extension of the buccal shields into the full depth of the vestibule is supposed to
stimulate the periosteum in order to achieve a skeletal expansion of the apical bases. Lingual
shields also are included to accomplish a gradual, stepwise advancement of the mandible.
Appliance
• Functional appliance
A removable or fixed appliance that alters the posture of the mandible and transmits the forces
created by the resulting stretch of the muscles and soft tissues and by the change of the
neuromuscular environment to the dental and skeletal tissues to produce movement of teeth and
modification of growth.
Appliance
• Haas appliance (Haas rapid maxillary expansion appliance, Haas palatal separator)
A fixed expansion appliance that was popularized by A. J. Haas. The appliance consists of bands
cemented on the maxillary first premolars and first molars that are rigidly connected to each other
with heavy-gauge wires on the buccal and palatal aspect of the teeth. Two acrylic pads encase the
palatal connecting wires and are joined with a midline jackscrew. The acrylic pads are in close
contact with the palatal mucosa. The Haas appliance was designed to expand the maxillary arch
by opening the midpalatal suture, thereby causing a skeletal expansion of the maxilla. According to
Haas, the contact of the pads with the palate allows the forces from the appliance to be dissipated
against the underlying hard and soft tissues of the palate, thus minimizing the amount of dental
tipping and maximizing the skeletal effect. Others consider this a disadvantage of the appliance
with regard to hygiene, resulting in inflammation of the palatal tissues.
[See Appliance, Expansion appliance]
[See Appliance, Hyrax appliance (Hygienic rapid palatal expander)]
[See Expansion, Rapid maxillary (palatal) expansion (RME, RPE)]
[See Expansion, Slow maxillary (palatal) expansion (SME or SPE)]
[See Expansion, Surgically assisted rapid maxillary expansion]
Appliance
• Habit-breaking appliance (Habit reminder)
Any removable or fixed appliance designed to correct undesirable habits such as digit-sucking,
tongue interposition, tongue-thrusting, or infantile swallow.
[See Appliance, Crib ]
[See Appliance, Vestibular shield (Vestibular screen)]
Appliance
• Harvold-Woodside activator
A modification of the activator developed by E. P. Harvold and D. G. Woodside. Its distinguishing
feature is the overextended vertical opening to which the appliance is constructed. The bite is
opened by 5 mm to 6 mm beyond the freeway space. The rationale is that maximum stretching of
the muscles will produce a force that will be transmitted to the bones and teeth, inducing a
compensatory anatomic correction. It is claimed that the Harvold-Woodside activator requires
minimal mandibular advancement to produce the desired sagittal correction, as the extreme
muscle stretch can cause intrusion (or inhibition of eruption) of the maxillary posterior teeth,
resulting in “closure” or counterclockwise rotation of the mandible with a relative Class II correction
(bite-block effect). Relieving the acrylic occlusally to the mandibular posterior teeth allows them to
erupt in a mesial direction, which also facilitates Class II correction.
Appliance
• Herren activator (L.S.U. activator)
A modification of the activator developed by P. Herren (also known as the Louisiana State
University modification of the same appliance). It is essentially an activator made to a construction
bite that positions the mandible forward and downward to asignificant degree. According to P.
Herren, the wearing of this appliance is not supposed to increase the activity of the lateral
pterygoid muscle.
Appliance
• Hickham protraction appliance
A modification of the face mask developed by J. H. Hickham. It consists of a chin cup with hooks
extending upwards and forwards, for application of anterior elastic traction to the maxilla and/or the
maxillary (or mandibular) dentition.
Appliance
• Harvold-Woodside activator
A modification of the activator developed by E. P. Harvold and D. G. Woodside. Its distinguishing
feature is the overextended vertical opening to which the appliance is constructed. The bite is
opened by 5 mm to 6 mm beyond the freeway space. The rationale is that maximum stretching of
the muscles will produce a force that will be transmitted to the bones and teeth, inducing a
compensatory anatomic correction. It is claimed that the Harvold-Woodside activator requires
minimal mandibular advancement to produce the desired sagittal correction, as the extreme
muscle stretch can cause intrusion (or inhibition of eruption) of the maxillary posterior teeth,
resulting in “closure” or counterclockwise rotation of the mandible with a relative Class II correction
(bite-block effect). Relieving the acrylic occlusally to the mandibular posterior teeth allows them to
erupt in a mesial direction, which also facilitates Class II correction.
Appliance
• Hyrax appliance (Hygienic rapid palatal expander)
A commonly used type of banded rapid maxillary expansion appliance developed by W. Biederman
and originally licensed to Dentaurum. The components now are available from several suppliers
internationally. The framework of the appliance is made entirely of stainless steel or cobaltchromium
alloy, with no acrylic contacting the palatal mucosa. Bands are cemented (usually) on
the maxillary first premolars and first molars. The bands are connected by means of rigid wires to a
special expansion screw which is located in the midline of the palate, in close proximity to the
palatal contour. Hyrax-type expansion screws are available in various sizes (more commonly 7
mm, 11 mm and 13 mm) depending on the application. Buccal and palatal support wires also may
be added for rigidity.
[See Expansion, Rapid maxillary (palatal) expansion (RME, RPE)]
[See Appliance, Expansion appliance]
[See Appliance, Haas appliance (Haas rapid maxillary expansion appliance, Haas palatal
separator)]
[See Expansion, Slow maxillary (palatal) expansion (SME or SPE)]
[See Expansion, Surgically assisted rapid maxillary expansion]
Appliance
• Jasper jumper appliance
A type of fixed functional appliance developed by J. J. Jasper. In essence it is a flexible version of
the Herbst appliance. The Jasper jumper is used in combination with fixed appliances for
correction of Class II malocclusions. It consists of two polyurethane-coated stainless steel coil
springs (force modules), attached at both ends to stainless steel end-caps. The force modules are
available in seven lengths (from 26 to 38 mm, in 2-mm increments). The end-caps carry holes so
they can be attached to the anchoring unit. One end-cap is attached to the distal aspect of the
headgear tube of the maxillary molar by means of a special ball pin attachment. The other end-cap
is attached to the mandibular arch, between the canine and the first premolar, either directly onto
the main archwire, or on a segment utilizing the auxiliary slot of the mandibular molar. Upon
insertion, the appliance bows out towards the cheek, promoting an anterior mandibular position.
The Jasper jumper may be used as an alternative to intermaxillary elastics and requires minimal
patient cooperation, as it is fixed on the archwires.
Appliance
• Jones jig
A fixed orthodontic appliance designed by R. D. Jones for unilateral or bilateral maxillary molar
distalization without patient cooperation. The appliance consists of a heavy-gauge wire and an
open-coil nickel-titanium spring delivering a force of approximately 0.7 to 0.8 N (70 to 80 g) over a
compression range of 1 to 5 mm. The distal end of the jig assembly carries a soldered additional
wire that is inserted into the main tube of the maxillary first molar band, whereas the heavy-gauge
wire is placed in the headgear tube. The sliding part of the jig is attached on the anchor teeth by a
stainless steel ligature so that the coil spring is compressed. The bands on the anchor teeth (which
can be either the first premolars, second premolars, or deciduous second molars) are soldered to a
large, modified Nance button to make maximal use of palatal anchorage.
Appliance
• Kinetor
A removable functional appliance developed by H. Stockfisch. The appliance consists of two acrylic
plates joined by vestibular steel loops and supported by occlusal rubber tubes. This design gives
the appliance a certain degree of flexibility, which is supposed to reinforce muscular impulses and
stimulate function.
Appliance
• Kingsley appliance (Bite-jumping appliance)
Probably the first removable functional appliance (developed by N. W. Kingsley in 1877). The
appliance consisted of a vulcanite palatal plate with an anterior inclined plane, which forced the
mandible in an anterior direction (“jumping of the bite”). It also contained a mechanism for
retraction of maxillary incisors and was retained by silk threads to the maxillary molars.
[See “Jumping of the bite”]
[See Appliance, Herbst appliance]
Appliance
• Labiolingual appliance
Early orthodontic fixed appliance system introduced by O. A. Oliver. The appliance consisted of
bands on the molar teeth in conjunction with heavy mandibular lingual and maxillary labial base
arches. Movement of individual teeth with this system was achieved by activating fingersprings and
other accessory springs soldered on the base archwires.
Appliance
• Lehman appliance (Lehman activator)
A combination activator-headgear appliance developed by R. Lehman. It consists of a maxillary
acrylic plate that carries two rigidly fixed outer bows and a mandibular lingual shield. The acrylic
plate covers the palate and it extends over the occlusal and incisal surfaces of the maxillary teeth,
up to the occlusal third of their buccal and labial surfaces.
Selective expansion of the maxillary arch is possible by appropriately activating the two transverse
expansion screws (one anterior and one posterior) that are embedded in the plate.
Occipital traction is applied through a headstrap attached on the outer bows, which are fixed at the
anterior aspect of the appliance. The mandibular lingual shield is connected to the maxillary plate
by means of two heavy S-shaped wires. Unlike many activator-type appliances which are
constructed with the mandible in a protruded position, this appliance is made from a bite
registration taken in centric occlusion. According to R. Lehman, the S-shaped wires are activated
by approximately 2 mm every 4 to 6 weeks, to achieve a gradual advancement of the mandible.
Appliance
• Lingual appliance
1. Any removable or fixed orthodontic appliance, placed on the lingual (palatal) side of the dental
arches.
2. An esthetic, “invisible” fixed orthodontic appliance consisting of special orthodontic attachments
bonded on the lingual surfaces of the teeth. The principle of a rectangular wire in a rectangular preadjusted
(straight-wire) slot is the same, but the design of the attachments is modified. The
maxillary anterior brackets have a flat surface that occludes with the mandibular incisors in patients
with deep bite and acts as an anterior bite plane. The archwire shape also is modified to fit the
configuration of the lingual surface of the dental arch (“mushroom” configuration). Accuracy of
bracket placement is critical, so indirect bonding is advocated. Disadvantages of the lingual
appliance include smaller interbracket distance, more difficult access, arguably reduced comfort for
the patient due to tongue impingement, and usually higher treatment fee.
Appliance
• Lip bumper
Intraoral removable orthodontic appliance consisting of a U-shaped 0.036-inch (0.90-mm) stainless
steel wire, which in its anterior portion may carry a plastic or acrylic pad. The ends of the lip
bumper are inserted into tubes on the mandibular first or second permanent molars. Its anterior
portion is adjusted to lie in the vestibular area, 2 to 3 mm away from the alveolar process and the
mandibular incisors (the vertical height varies).
Lip bumpers commonly are worn on a full-time basis and occasionally may be ligated in place (in
case of reduced patient compliance). They are used to control or increase the mandibular dental
arch length, to upright mesially or lingually tipped mandibular molars and to prevent the
interposition of the lower lip between the maxillary and mandibular incisors.
Depending on the anterior configuration (with or without lip pads) the appliance has two effects:
First, by removing the soft tissue forces from the labial aspect of the mandibular incisors it can
cause labial tipping of these teeth. Second, by transmitting the force from the lip to the mandibular
first molars, the lip bumper causes distal movement (mainly tipping) of these teeth. This distal
movement is accomplished more easily when the second molars are still unerupted or have been
extracted as part of the treatment plan.
Appliance
• Mouthguard
A removable appliance, usually made from flexible or rigid thermoplastic material, used to cover
and protect the teeth while engaging in contact sports.
Appliance
• Open activator
An activator with reduced acrylic coverage of the anterior palate in comparison to the classic
activator. It is meant to facilitate speech by allowing contact between the tongue and palate.
Appliance
• Pendulum appliance
A fixed orthodontic appliance introduced by J. J. Hilgers as a means for molar distalization without
patient compliance.
The appliance makes use of palatal anchorage through a large Nance button, which is retained
with bands on the maxillary first premolars and occlusal rests on the distal aspect of the maxillary
second premolars.
Two “pendulum” springs fabricated out of 0.032-inch (0.81-mm) TMA wire extend from the
posterior edge of the Nance button. Each spring contains a closed helix (close to the midline), a
small horizontal adjustment loop and a recurved portion that inserts into palatal sheaths soldered
on the bands of the maxillary first molars. The thickness of the palatal sheaths on the molar bands
is 0.036 inch (0.90 mm), so that the 0.032-inch (0.81-mm) diameter wire fits loosely in them. If
expansion of the maxillary arch is necessary, the appliance can be fabricated in a split-plate design
(“Pend-X” or “Pendex” appliance) by incorporating a midpalatal screw in the center of the Nance
button. Prior to cementation the springs are bent (preactivated) so that they lie parallel to the
midsagittal plane, and they subsequently are inserted into the sheaths.
As the molar is driven distally, it also moves palatally (on an arc). This palatal movement can be
counteracted by slightly opening the adjustment loop. Distal root movement of the molars also can
be produced by adjusting the recurved portion of the “pendulum” springs in order to avoid
distalization by mere tipping.
Appliance
• Pin-and-tube appliance
Early fixed orthodontic appliance (now archaic) consisting of vertical tubes soldered onto bands
placed on the permanent teeth. Movement of the teeth was achieved by use of an archwire with
soldered vertical pins that were forced into the tubes. The system, originally developed by E. H.
Angle, was later replaced by the ribbon-arch appliance.
Appliance
• Positioner (Tooth positioner)
A removable orthodontic appliance originally developed for closing band spaces after debanding. It
currently is used mainly to achieve fine adjustments and retain corrected positions following fixed
appliance treatment.
The positioner is fabricated of rubber or elastomeric plastic material covering the maxillary and
mandibular dental arches, as well as part of the alveolar process. For its construction, individual
teeth are cut from a plaster model and are reset subsequently in an ideal relationship.
The patient is instructed to wear the positioner immediately following fixed appliance removal and
to clench the teeth into it. The appliance functions by molding of the individual teeth into the correct
position within the arch through the forces generated by the elastic material in contact with the
teeth. When used in patients who exhibited a Class II malocclusion prior to treatment, the
positioner can be constructed in a slightly overcorrected Class I relationship, providing a “functional
appliance” component.
Advantages of the positioner include its resistance to fracture, stimulation of tissue tone and
continuous improvement of tooth position if it is worn properly. Disadvantages are its bulkiness
(making it less comfortable for the patients), and the possibility that it may keep teeth loose by
producing intermittent forces on them. Positioners are contraindicated in patients with airway
obstruction and in patients with a history of temporomandibular disorders. Their use often is
preferred in patients with minimal overbite or open bite tendency, as they tend to deepen the bite.
Appliance
• Propulsor (Mьhlemann appliance)
A removable functional appliance similar to the activator. The appliance carries a vestibular acrylic
extension over the maxillary alveolar process. The intention is to distribute the posteriorly directed
force over the basal bone to maximize the skeletal and to minimize the dentoalveolar effect.
Appliance
• Quad-helix appliance
An all-wire fixed orthodontic expansion appliance originally developed by E. Herbst and
popularized by R. W. Ricketts, among others. It typically consists of a 0.036-inch (0.90-mm)
stainless steel wire, containing four helices (two anteriorly and two posteriorly) to increase its range
and flexibility. The wire is soldered (or attached in a fixed/removable design) onto bands on the
maxillary first molars (and occasionally also on the maxillary first premolars). Various other
designs, such as a tri- or a bi-helix, also are described. The appliance is used for symmetrical or
asymmetrical expansion of the maxillary dental arch, as well as for derotation of the molars. It has
a tendency to produce buccal tipping of the teeth, and is not advocated in patients who require a
significant amount of expansion. It is considered advantageous for patients with cleft lip and palate,
in whom a localized expansion of the anterior aspect of the collapsed lesser maxillary alveolar
segment often is necessary.
Appliance
• Ribbon-arch appliance
A fixed multibanded orthodontic appliance developed by E. H. Angle, which marked another stage
towards the development of the edgewise appliance. Each band carried a vertical slot capable of
receiving a rectangular wire in a vertical orientation (with the longer dimension of the cross-section
parallel to the long axis of the tooth), hence the term ribbonwise. The archwire was retained in
place by pins. Control of buccolingual (third-order) root position was difficult with the appliance.
This problem was overcome later with the development of the edgewise appliance
[See “Ribbonwise”]
Appliance
• Sagittal appliance
An active removable appliance with expansion screws in the anteroposterior direction bilaterally
(“two-way sagittal”) or additionally in the transverse direction (“three-way sagittal”), when
expansion is also necessary. Retention is achieved by a combination of Adams clasps and
arrowhead clasps. Sagittal appliances are used mainly in patients with labially displaced canines to
increase the arch length by advancing the incisors and to apply a distalizing force on the posterior
teeth.
Appliance
• Schwarz appliance
A removable orthodontic appliance introduced by A. M. Schwarz for expansion of the maxillary and/
or the mandibular dental arch. The appliance consists of a horseshoe-shaped acrylic plate fitting
along the lingual surface of the teeth and covering a large portion of the lingual aspect of the
alveolar process or palate. A midline expansion screw is incorporated in the acrylic, and ball or
arrowhead clasps on the deciduous and permanent molars provide the necessary retention.
Although Schwarz developed a variety of “split-plate” appliances, the mandibular appliance is
widely considered as the one that bears his name.
Appliance
• SPEED appliance
(Strite Industries, Ltd. ) Fixed, self-ligating orthodontic appliance system developed by H. G.
Hanson. The appliance consists of miniaturized self-ligating brackets with built-in flexible, escapeproof
spring-clips that obviate the need for conventional elastomeric or stainless steel ligatures and
permit light force delivery. The spatial relationship between the spring-loaded clip and the archwire
allows a continuous dynamic interaction between them, while maintaining three-dimensional
control of tooth position. [SPEED is an acronym of the words Spring-loaded, Precision, Edgewise,
Energy and Delivery. ]
[See Bracket, Self-ligating bracket]
Appliance
• Split-plate appliance
See Appliance, Expansion.
[See Appliance, Expansion appliance]
Appliance
• Stabilization appliance
[See Splint, Relaxation splint (Stabilization splint, Muscle relaxation splint)]
Appliance
• Straight-wire appliance (Preadjusted appliance, SWA)
A modification of the edgewise appliance, introduced by L. F. Andrews in 1972. In the standard
edgewise appliance the orientation of the bracket slot was at right angles to the long axis of the
tooth and the thickness of the bracket base was the same for all types of teeth. During treatment,
bends were placed in the archwire to individually position each tooth in the buccolingual direction
(in-out or first-order bends), as well as to idealize the angulation of the long axis of the tooth in the
mesiodistal direction (tip or second-order bends) and in the buccolingual direction (torque or thirdorder
bends).
In the straight-wire appliance this information is incorporated in the brackets and tubes for each
individual tooth, by varying the thickness of the base and the angulation of the slot relative to the
long axis of the tooth, in both the mesiodistal and buccolingual directions. As a result, a “straight”
archwire can be used to ideally position the teeth, avoiding though not completely eliminating the
need for placing such bends in the archwire. Accurate placement of the brackets on the teeth is of
paramount importance with this appliance. Straight-wire appliances of various prescriptions (sets of
characteristic values for each individual tooth) are available on the market.
[See Appliance prescription]
[See Appliance, Edgewise appliance (Standard edgewise)]
Appliance
• Teuscher-Stцckli activator/headgear combination appliance
A modified activator used in combination with a high-pull headgear. The appliance was introduced
by U. M. Teuscher and P. W. Stцckli as a means to avoid the detrimental profile effects of cervical
traction when treating Class II malocclusions in growing individuals. Buccal headgear tubes are
incorporated in the interocclusal acrylic at the level of the maxillary second premolar or first molar.
The vector of the high-pull headgear force is directed through a point midway between the
estimated center of resistance of the maxilla and that of the maxillary dentition. In this way it is
claimed that the best compromise is reached between a resulting counterclockwise rotation of the
maxillary occlusal plane and a clockwise rotation of the maxilla itself, possibly maintaining the
inclination of the maxillary occlusal plane. The design includes reduced palatal acrylic coverage to
provide more space for the tongue. The acrylic covers the occlusal and incisal surfaces of the
maxillary teeth to distribute the headgear force over the entire dentition. The labial bow can be
substituted by torquing springs to counteract palatal tipping of the maxillary incisors. Long lingual
flanges extend from the lower portion of the appliance to enhance forward positioning of the
mandible. In addition, Frдnkel-type lower lip pads may be added to enhance normal perioral
muscle function. Finally, a jackscrew is added occasionally for controlled expansion.
Appliance
• Tip-Edge appliance
Fixed orthodontic appliance developed by P. C. Kesling as a combination of the Begg and the
straight-wire appliance (marketed by TP Orthodontics). The appliance consists of specially
designed brackets with modified slots that have the shape of an asymmetric bowtie. The brackets
are equipped with auxiliary vertical slots that can receive a variety of auxiliaries, including rotation
springs, uprighting springs, power pins and position indicators to facilitate bonding. The shape of
the main slots allows tipping of the teeth during space closure (a basic principle of the Begg
technique). After space closure the angulation of the teeth is idealized by uprighting springs (sidewinders).
When a rectangular archwire is used during this uprighting process, the beveling and the
dimensions of the modified, fully programmed slot permit gradual expression of the torque to
simultaneously control tooth inclination.
[See Appliance, Begg appliance (Light-wire appliance)]
Appliance
• Tongue crib
[See Appliance, Crib ]
Appliance
• Tri-helix appliance
A modification of the quad-helix, used in situations in which the constriction of the anterior maxilla
is too severe to accommodate two helices in the anterior aspect of the appliance (e.g. in patients
with a history of cleft lip and palate).
Appliance
• Twin arch appliance (Twin wire appliance)
An early orthodontic fixed appliance introduced by J. Johnson in 1931. The appliance made use of
the resilience of two thin-gauge stainless steel wires ranging in size from 0.09 inch (0.23 mm) to
0.014 inch (0.35 mm) in diameter. Two end-tubes were soldered onto the first molar bands,
capable of receiving the twin wire strands. The bands on the remaining teeth carried special locks
forming channels with a rectangular cross-section. The twin wires were held in the locks by special
sliding caps. Differential crown or root movement was achieved by using two archwires of different
sizes (one longer than the other) and by appropriately squeezing both into the lock so that they lie
on top of each other (in a coronal-apical direction). Occasionally, a lingual arch also was used in
conjunction with the appliance.
Appliance
• Twin block appliance
Tooth-borne removable functional appliance that was developed by W. J. Clark. It consists of a
maxillary and mandibular portion, which carry inclined planes constructed in such a way that an
anterior displacement of the mandible and a certain amount of vertical separation of the arches are
effected upon closure of the mouth. Due to the two-part design, the appliance is tolerated easily by
the patient and thus increased wear is facilitated. The maxillary portion of the appliance includes
capping of the molars, with an inclined plane at its mesial end. This plane engages a similar incline
on the mandibular portion of the appliance, thus causing the mandible to assume the desired
protruded position. Retention of the maxillary portion is achieved by modified Adams clasps that
span the second premolars and first molars. A labial bow with U-loops also is included in the
maxillary portion. A headgear can be attached to the maxillary portion of the appliance by inserting
a facebow into special coils incorporated in the delta clasps. The occasional addition of a midline
expansion screw can provide compensatory maxillary arch expansion as the anteroposterior
relationship improves. The mandibular portion of the appliance carries capping in the premolar
region only and is retained by delta clasps on the first premolars and C-clasps on the canines.
[See Clasp (Retention clasp), Delta clasp]
Appliance
• Two-by-four appliance (2×4)
A term denoting partial use of fixed orthodontic appliances, only including the 2 first permanent
molars and the 4 permanent incisors. A 2×4 is most often used for treatment in the mixed dentition,
e.g. for alignment, intrusion, or proclination of the incisors.
Appliance
• U-bow activator
A removable functional appliance developed by R. Karwetzky consisting of a maxillary and a
mandibular part, which are connected by a U-shaped bow on either side. These U-bows allow
gradual displacement of the mandible from its original position in small increments. The appliance
exists in three variations, proposed for the treatment of Class II, Class III, or asymmetric
malocclusions.
Appliance
• Universal appliance
An early fixed orthodontic appliance developed by S. R. Atkinson, combining some of the principles
of edgewise and ribbon-arch appliances to achieve precise control of individual teeth in all planes
of space. The appliance consisted of bands for all the teeth in both arches. Each band carried a
bracket with two horizontal slots, of which the larger, occlusal slot opened occlusally and the
smaller, gingival slot opened buccally. The occlusal slot could accommodate a ribbon arch of up to
0.015 x 0.028 inch (0.38 x 0.70 mm) in cross-section, or alternatively up to three 0.010-inch (0.25-
mm) archwires. The wires for the gingival slot were 0.008 inch (0.20 mm) to 0.014 inch (0.35 mm)
in diameter. Special lock pins held the archwires in place. A lingual arch was used, which was
secured in horizontal sheaths soldered on the lingual aspect of the molar bands.
Appliance
• Van Beek appliance
A removable functional appliance/high-pull headgear combination, developed by H. Van Beek. The
facebow of the headgear is embedded rigidly in the acrylic at the anterior aspect of the appliance
and is its only metal part. The appliance provides labial acrylic coverage of the maxillary incisors.
Appliance
• Vestibular shield (Vestibular screen)
A simple removable appliance made of 2- to 3-mm-thick acrylic or thermoplastic material,
occupying the vestibule and extending posteriorly to the distal margin of the last erupted molar.
The appliance can be constructed with the mandible placed in an anterior position so that the
incisors are in an edge-to-edge relationship. The appliance is intended to eliminate an abnormal
sucking habit or lip dysfunction, to establish a competent lip seal and to interrupt contact between
the tip of the tongue and the lower lip, promoting maturation of the swallowing pattern. In patients
with a persistent tongue thrust, the vestibular shield can be combined with a tongue crib.
[See Appliance, Oral screen]
Appliance prescription
The set of characteristic values (in degrees) for mesiodistal tip (“angulation”), buccolingual
inclination (“torque”), and rotational offset, which are incorporated into each bracket for every
individual tooth; the “specifications” of a fixed orthodontic appliance. The prescription of an
orthodontic appliance usually is specified by the clinician at the time of placing the order with the
manufacturer or distributor.
[See Appliance, Straight-wire appliance (Preadjusted appliance, SWA)]
Appliance setup
[See Bracket setup]
Appliance trimming
Selective grinding away of acrylic from a removable appliance at areas that contact the teeth. The
purpose of this process is to guide tooth eruption and aid in the development of a proper arch form.
Trimming is an important aspect of treatment with removable and functional appliances.
Arch
A structure with a curved or bow-like outline. The term sometimes is used in orthodontics as a
synonym for archwire.
SUBTERMS:
Arch
• Alveolar arch
The arch formed by the ridge of the U-shaped maxillary and mandibular alveolar processes.
Arch
• Auxiliary arch
An accessory archwire commonly used in addition to the main or base archwire.
Arch
• Base arch
The main archwire occupying the bracket slots of a fixed orthodontic appliance system. Use of the
term “base arch” implies the presence of other auxiliary arches or springs active at the same time.
Arch
• Closing-loop arch
An archwire in which closing loops are incorporated
(unilaterally or bilaterally), commonly used for retraction
of the incisors. A closing-loop arch usually is made out
of full-dimension stainless steel wire in an attempt to
maintain the inclination and angulation of the teeth as
they are being retracted.
Arch
• Dental arch
The arch formed by the maxillary or the mandibular teeth,
when viewed from the occlusal.
Arch
• Horseshoe arch
Special type of transpalatal arch with the shape of a horseshoe, oriented in the horizontal plane.
Arch
• Intrusive arch
An archwire used as the main wire, or as an auxiliary in the
segmented arch technique, to achieve leveling of the
dental arch by intrusion of the incisors. An intrusive arch is
activated for incisor intrusion by placing tip-back bends
mesial to the molar tubes.
[See Arch, Utility arch]
Arch
• Lingual arch
A single, heavy-gauge orthodontic wire, adapted to the lingual aspect of (usually) the mandibular
arch, attached to bands on the first permanent molars. Two U-loops, often bent into the wire mesial
to the first molars, offer the possibility of adjustment in the sagittal direction. The lingual arch is
generally used for stabilization (anchorage reinforcement), as a holding arch for space
maintenance, for expansion, for increase of dental arch length or for anchorage when
intermaxillary traction is used. Lingual arches can be of fixed (soldered) or fixed/removable design.
Arch
• Nance holding arch
Maxillary fixed appliance developed by H. N. Nance, consisting of a heavy palatal wire soldered to
the palatal aspect of the first molar bands. The wire is directed from the molars anteriorly and is
attached to an acrylic button that rests against the most superior and anterior aspect of the palatal
vault. Used as a space maintainer, or as a means to reinforce anchorage.
Arch
• Overlay arch (Piggyback arch)
An auxiliary archwire added to the main (base) archwire, most commonly used to achieve
transverse changes in the dental arch or individual tooth movements. An overlay arch can be
inserted in the auxiliary slots or the headgear tubes of the molar attachments, or it may be simply
tied onto the main archwire.
[See E-arch]
Arch
• Porter arch (W-arch)
Maxillary fixed/removable appliance consisting of a heavygauge
(0.036 inch or 0.90 mm) transpalatal wire with a Wshaped
configuration, secured to the palatal aspect of the
first molar bands. It is used to achieve expansion of the
maxillary dental arch and/or derotation of the molars.
Arch
• Transpalatal arch (TPA, Palatal bar, Goshgarian-type palatal arch)
Maxillary fixed or fixed/removable appliance consisting of a 0.036-inch (0.90-mm) or higher gauge
wire that extends from one maxillary first molar, along the contour of the palate, to the maxillary
first molar on the opposite side. The arch is adapted to the curvature of the palatal vault, so that it
lies 2 to 3 mm away from the palatal mucosa. A U-loop, which usually is incorporated midway
across its span, can be activated for expansion or constriction of the intermolar width. The TPA
also is used commonly for anchorage reinforcement, for derotation of the molars, or for producing
root movements of these teeth.
Arch
• Utility arch
A maxillary or mandibular continuous archwire bypassing the canines and/or premolars to achieve
leveling of the arch and/or uprighting of the molars, or to function as a stopped arch for incisor
proclination. The utility arch,
which was introduced by R. W.
Ricketts, usually is made out of
0.016 x 0.016-inch (0.41 x 0.41-mm) or 0.016 x 0.022-inch (0.41 x 0.56-mm) stainless steel or
cobalt-chromium wire. The wire is stepped away from the occlusal plane between the first molars
and lateral incisors for convenience and comfort. Avoiding engagement of the premolars and
canines results in improved load/deflection properties because of the length of wire between the
molar and incisor segments. The stepping of the archwire in a gingival direction in the buccal
segments also reduces the risk of deformation during mastication. The utility arch can be used for
movement of the incisors in the vertical and/or sagittal plane of space.
[See Arch, Intrusive arch]
Arch
• Stopped arch (Proclination arch, Advanced arch)
An orthodontic archwire with stops or loops (usually placed
mesial to the first molar tubes) to procline the incisors, or to
maintain the existing arch length.
Arch bars
Half-round, oval, round or flat wire bars, bent to fit the labial surface of the dental arches, in the
cervical third of the crowns.
Arch bars may carry
special bases so they can
be bonded to the teeth, or
more commonly, they can
be attached to them with
interdental ligature wires.
They may contain
supporting elements,
such as hooks or eyelets,
for attaching elastic bands or tie wires. Arch bars are used to facilitate intermaxillary fixation in
orthognathic surgery, or for stabilization of fractures of the maxilla or mandible. Single arch bars
also are used sometimes for stabilization of traumatized teeth.
Arch coordination
One of the aspects of fixed appliance orthodontic treatment
by which it is made sure that the maxillary and mandibular
dental arches fit harmoniously with each other, with
corresponding arch forms and good anterior and buccal
overjet.
[See Archwire coordination]
Arch depth
The perpendicular distance in the
midsagittal plane from the most labial
midpoint between the central incisors to a
line connecting the distal surfaces of two
posterior corresponding teeth in a dental
arch, usually the second premolars (or
second deciduous molars).
Arch form
The shape of an individual dental arch, or of an archwire formed to fit or shape that arch. The arch
form can be parabolic, hyperbolic, ellipsoidal, square, tapering, V-shaped etc.
Arch length (Arch perimeter)
A measurement of space available in the
dental arch, for alignment of the teeth.
Arch length discrepancy
A difference between the space available in the dental arch and the space required to align the
teeth. An arch length discrepancy can either be in the form of a deficiency or an excess of arch
length.
SUBTERMS:
Arch length deficiency (Crowding)
Arch length excess (Spacing)
• Arch length deficiency (Crowding)
A negative difference between the
space available in the dental arch and
the space required to align the teeth.
With regard to the severity of space
deficiency, crowding is divided into
three categories: first-degree (mild)
crowding, second-degree (moderate)
crowding and third-degree (severe)
crowding.
The classification into primary,
secondary and tertiary crowding takes
into account the etiology of the space
deficiency.
Primary (hereditary) crowding is
determined genetically and is caused by disproportionately sized teeth and jaws.
Secondary crowding is an acquired anomaly caused by mesial drifting of the posterior teeth after
premature loss of deciduous teeth in the lateral segments and/or lingual or distal displacement of
the anterior teeth.
The etiopathogenesis of tertiary crowding is still under debate. This type of crowding— primarily in
the mandibular anterior teeth— occurs during and after adolescence and was previously thought to
be associated with third molar eruption. Others attribute the anomaly to differential anteroposterior
growth of the maxilla and mandible terminating at different times, in combination with differential
rotation of the maxilla and mandible with growth. Malocclusions with crowding are more common in
modern populations than those involving interdental spacing and wide arches.
• Arch length excess (Spacing)
A positive difference between the
space available in the dental arch
and the space required to align the
teeth. As with crowding, a distinction
can be made between primary,
secondary and tertiary spacing.
Primary (hereditary) spacing is
determined genetically and is
caused by disproportionately sized
teeth and jaws, including tooth
agenesis.
Secondary spacing is an acquired
anomaly caused by drifting of teeth,
subsequent to loss of a permanent
tooth.
Tertiary spacing is caused by bone
loss due to periodontal disease,
resulting in a disturbance of the equilibrium of forces acting on the teeth and associated tooth
movement.
Arch width
The breadth of the dental arch, determined
by measuring distances between
corresponding contralateral teeth (e.g.
intercanine width, intermolar width).
Archwire (Arch wire)
A wire engaged in orthodontic attachments that are affixed to the crowns of two or more teeth to
cause or guide tooth movement.
SUBTERMS:
Continuous archwire
Finishing archwire
“Full dimension” archwire
Multiloop archwire
Sectional archwire (Segmental archwire)
Stabilizing archwire
Surgical archwires
Archwire (Arch wire)
• Continuous archwire
An archwire that engages, through crown attachments (brackets and tubes), many or all of the
erupted teeth in the maxillary or mandibular dental arch (i.e. from molar to molar).
Archwire (Arch wire)
• Finishing archwire
The archwire used in the finishing stage of treatment.
Archwire (Arch wire)
• “Full dimension” archwire
A large rectangular archwire that will practically “fill” the bracket slot. Usually referring to an 0.017 x
0.025-inch (0.43 x 0.64-mm) or 0.018 x 0.025-inch (0.46 x 0.64-mm) archwire, when a 0.018 x
0.025-inch (0.46x 0.64-mm) slot size is used, or an 0.021 x 0.025-inch (0.53 x 0.64-mm) archwire
when a 0.022 x 0.028-inch (0.56 x 0.70- mm) slot is used.
Archwire (Arch wire)
• Multiloop archwire
A stainless steel archwire with loops of various configurations bent in the interbracket spaces, to
increase the flexibility of the wire to facilitate bracket engagement. The use of multiloop archwires
was very common in earlier days of orthodontics, when the only way to reduce the load/deflection
characteristics of the appliance was to increase the length of wire between brackets. It has now
been largely replaced by multistrand wires, or wires made of various superelastic materials.
[See Loop]
[See Load/deflection rate (Force/deflection rate)]
Archwire (Arch wire)
• Sectional archwire (Segmental archwire)
An archwire that engages only a few teeth within an arch (e.g. only the four incisors, or only the
teeth in a posterior dental segment. )
[See Mechanics, Segmental arch mechanics (Sectional mechanics)]
Archwire (Arch wire)
• Stabilizing archwire
A stiff, full-dimension archwire, used to maintain the actual position of the teeth (e.g. prior to
orthognathic surgery), or to consolidate a number of teeth, forming a large anchorage segment.
Archwire (Arch wire)
• Surgical archwires
The stabilizing archwires that are in place during the orthognathic surgical procedure. They usually
are rectangular stainless steel wires to which hooks have been added in the interbracket spaces to
facilitate intermaxillary fixation. Surgical archwires must fit passively to be effective. If they create
any tooth movement after the impressions are made for the model surgery and for splint
construction, the splint will no longer fit.
Archwire coordination
The process of superimposing the maxillary and mandibular archwires prior to placing them in the
patient’s mouth, to ensure that their arch form fits with each other, with the objective of achieving
coordinated dental arches.
[See Arch coordination]
Archwire cross-section
Various diameters and cross-sectional shapes of orthodontic archwires exist. The ones most
commonly used, specified by the size of the cross-section in inches (mm) are:
Round:
0.012 inch (0.30 mm),
0.014 inch (0.35 mm),
0.016 inch (0.40 mm),
0.017 inch (0.43 mm),
0.018 inch (0.46 mm),
0.019 inch (0.48 mm),
0.020 inch (0.51 mm)
Square:
0.016 x 0.016 inch (0.41 x 0.41 mm),
0.017 x 0.017 inch (0.43 x 0.43 mm),
0.018 x 0.018 inch (0.46 x 0.46 mm),
0.019 x 0.019 inch (0.48 x 0.48 mm)
Rectangular:
0.016 x 0.022 inch (0.41 x 0.56 mm),
0.017 x 0.022 inch (0.43 x 0.56 mm),
0.017 x 0.025 inch (0.43 x 0.64 mm),
0.018 x 0.025 inch (0.46 x 0.64 mm),
0.019 x 0.025 inch (0.48 x 0.64 mm),
0.020 x 0.025 inch (0.51 x 0.64 mm),
0.021 x 0.025 inch (0.53 x 0.64 mm).
Archwire locks
[See Gurin lock]
Archwire stop
A bend, auxiliary attachment, or occasionally a
drop of solder placed on an archwire to prevent it
from sliding mesially or distally through the
orthodontic attachments.
Arthritis
Inflammation of a joint, usually accompanied by pain.
SUBTERMS:
Hypertrophic arthritis
Juvenile rheumatoid arthritis (JRA, Still’s disease)
Rheumatoid arthritis
Arthrography of the TMJ
Radiographic visualization of the TMJ.
SUBTERMS:
Single-contrast arthrography
Double-contrast arthrography
Single-space arthrography
Double-space arthrography
Arthrography of the TMJ
• Single-contrast arthrography
Arthrography following injection of a radiopaque contrast medium into the joint space(s) to
determine the location and integrity of intra-articular soft tissue structures, including disc position,
soft tissue contours, presence of perforations, joint motion, intra-articular free bodies and adhesive
capsulitis.
Arthrography of the TMJ
• Double-contrast arthrography
A procedure similar to single-contrast arthrography but with injection of a small amount of
radiopaque contrast agent followed by inflation of the joint with air.
Arthrography of the TMJ
• Single-space arthrography
Contrast arthrography with injection of a radiopaque contrast medium into either the upper or the
lower synovial joint compartment of the TMJ.
Arthrography of the TMJ
• Double-space arthrography
Contrast arthrography with injection of a radiopaque contrast agent into both the upper and lower
synovial joint spaces.
Arthrokinetics of the TMJ
Temporomandibular joint motion.
SUBTERMS:
Depression of the mandible
Distraction of the mandible
Elevation of the mandible
Lateral excursion of the mandible
Protrusion of the mandible
Retrusion of the mandible
Arthrokinetics of the TMJ
• Depression of the mandible
Movement of the mandibular alveolar process away from that of the maxilla.
Arthrokinetics of the TMJ
• Distraction of the mandible
Separation of the surfaces of the TMJ by extension, without injury or dislocation of the parts.
Arthrokinetics of the TMJ
• Elevation of the mandible
Movement of the mandibular alveolar process toward that of the maxilla.
Arthrokinetics of the TMJ
• Lateral excursion of the mandible
Right or left movement of the mandible away from the median plane.
[Compare with Mediotrusion]
[See Laterotrusion]
Arthrokinetics of the TMJ
• Protrusion of the mandible
Anterior mandibular movement with bilateral forward condylar translation.
Arthrokinetics of the TMJ
• Retrusion of the mandible
Posterior mandibular movement with bilateral backward condylar translation.
Arthroscopy
Direct visualization of a joint with an endoscope.
Arthrosis
Degeneration of a joint, evidenced by bony alterations.
Articular disc (Intra-articular disc, Meniscus)
A thin biconcave pad of dense fibrous connective tissue, interposed between the temporal bone
and the mandibular condyle, that divides the articular space into an upper and a lower
compartment. It is devoid of any blood vessels or nerve fibers and its anterior and posterior
borders (bands) are thick, whereas its central part (where the condylar head fits) is thinner.
Anteriorly it may be attached to fibers of the superior head of the lateral pterygoid muscle.
Posteriorly it attaches to a structure consisting of loose connective tissue, which is richly
vascularized and innervated, known as the retrodiscal tissue (retrodiscal lamina). The medial and
lateral aspects of the disc are attached to the lateral poles of the condyle by the collateral
ligaments, which permit rotational movement of the disc on the condyle during opening and closing
of the mouth.
Articular eminence
A convex bony ridge situated immediately anterior to the glenoid fossa of the temporal bone, that
also is involved in the temporomandibular joint. The degree of convexity of the articular eminence
is highly variable but important because the steepness of this surface dictates the pathway of the
condyle when the mandible is positioned anteriorly.
Articulator
A mechanical instrument that represents the temporomandibular joints and the jaws, to which
maxillary and mandibular casts may be attached, with the intention of reproducing mandibular
movements. Depending on the amount of adjustments that an articulat or can accommodate
(which increases the accuracy and precision of the simulation of the clinical situation), there are
non-adjustable, semi-adjustable (anatomic) and fully adjustable (gnathologic) articulators.
Articulators have all the mechanical limitations imposed by their construction. The various types
and models show great variation in their function depending on the way they were constructed and
the occlusal concepts on which they were based.
SUBTERMS:
Arcon articulator
Non-arcon articulator
Association
A recognized pattern of morphological defects or malformations that currently is not considered to
constitute a syndrome or an anomalad, but that may be reclassified as a syndrome or as an
anomalad as knowledge advances.
Atherton’s patch
The small red triangular patch of thin and non-keratinized gingival epithelium often observed on the
side opposite from the direction in which a tooth is moving. The first report of this phenomenon was
made by J. D. Atherton and N. W. Kerr in 1968, associated with the mesial aspect of maxillary
canines being distalized after extraction of the first premolars.
Attachment, Gingival
The part of the gingiva that is bound down to the underlying cementum and bone.
Attachment, Orthodontic
A precision component that can be welded or soldered
to a band, or bonded directly to a tooth, to facilitate the
application of forces during orthodontic treatment. The
general term encompasses items such as brackets,
tubes, buttons, eyelets, and “pigtail” attachments.
Attrition (Dental wear, Occlusal wear)
Loss of tooth structure due to repetitive physiological or parafunctional occlusal contact between
the teeth. Attrition results in the formation of flat areas on the surface of teeth (wear facets) that
have a polished appearance and readily reflect light. Although a certain degree of attrition is
considered physiological with age, the presence of deleterious parafunctional habits such as
bruxism may accelerate it. Attrition also affects the interproximal surfaces of the teeth.
[Compare with Abrasion]
Austenite
The face-centered cubic (FCC) crystalline structure of iron and steel, or the body-centered cubic
(BCC) structure in nickel-titanium alloys, at higher temperatures. In stainless steels, certain
elements such as nickel maintain the austenitic structure at room temperature. Appropriate cooling
of nickel-titanium alloys can induce a transformation to a close-packed hexagonal martensitic
phase (martensitic transformation). The transformation from austenite to martensite and vice versa
is what gives alloys such as nickel-titanium the characteristic properties of “shape memory” and
“superelasticity” (“pseudoelasticity”).
[See Martensitic transformation]
Autorotation (of the mandible)
The rotation of the mandible around the condylar axis (or an axis in the region of the condyles),
after repositioning of the osteotomized maxilla. Mandibular autorotation can be simulated
approximately during preparation of the surgical prediction tracing by rotating the mandibular
template until the mandibular teeth contact the repositioned maxillary teeth. The same can be
accomplished during model surgery using an articulator or one of the various operation simulation
systems. This significant step in the surgical treatment planning process will determine the
feasibility of a single-jaw (maxilla only) procedure, versus the need for bimaxillary surgery.
For example, in a patient with a Class II, Division 1, anterior open bite malocclusion, it may be
feasible to achieve an ideal overjet/overbite relationship and to decrease the elongated lower
anterior face height just by a maxillary differential impaction and subsequent mandibular
autorotation, without the need for a mandibular osteotomy.
Avascular necrosis
Bone infarction not associated with sepsis, but with circulatory impairment (occlusion of blood
vessels), leading to bony necrosis.
Avulsion
The complete separation of a tooth from its alveolus as a result of trauma.
Axes, System of
[See Global reference frame]
Axis of rotation
The line about which rotation of a three-dimensional object actually occurs.
[See Center of rotation (CRot)]
Banding
The process of cementing an orthodontic band in place, which involves the selection of the
appropriate band for a certain tooth, its fitting and adaptation and, finally, its fixation on the tooth by
means of cement.
Basilar kyphosis (Kyphosis of the cranial base)
A term indicating a reduced cranial base angle (NSBa).
[Compare with Platybasia]
Behavioral therapy
An attempt to change the attitude and habits of an individual, without the use of appliances or
medications; a means to improve patient cooperation and compliance. Behavioral therapy is
performed under the assumption that all elements of behavior can be learned. Essential in this
approach is a clear explanation of the rationale of the therapy and the importance of the necessary
motivation and persistence.
Bending test
Experimental setup to determine the material properties of a specimen in bending. This involves
the measurement of angular or linear deflection of an archwire segment, resulting from a bending
moment or an applied force. A bending test designed for orthodontic wires is the American National
Standards Institute/American Dental Association (ANSI/ADA) Specification No 32.
Bends (Archwire bends)
Localized permanent
deformations, placed into an
archwire, that change its direction
and/or orientation from the
original. Bends are added to an
archwire for various reasons.
Some bends are placed without
the purpose of generating any
forces (e.g. bends placed to
account for discrepancies in
bracket positioning or tooth
anatomy, to bypass teeth that will not be included in the archwire, or to avoid possible deformation
of the archwire due to chewing). However, most bends are added with the purpose of generating a
force system necessary for a specific tooth movement. Archwire bends were an indispensable part
of treatment with the standard edgewise appliance, whereas with the straight-wire appliance they
are supposed to be either avoided or greatly reduced. According to the orthodontic coordinate
system introduced by C. H. Tweed, bends on an orthodontic wire are roughly categorized as 1storder,
2nd-order and 3rd-order bends.
SUBTERMS:
Bends (Archwire bends)
• Artistic bends (Esthetic bends)
Bends to position anterior teeth for optimal
esthetic appeal. (Usually referring to second-order
bends on anterior teeth).
Bends (Archwire bends)
• Distal-end bends (Cinching bends, Distal-end
stops)
Bends (usually in a gingival and/or medial direction) made on the archwire (after it is placed in all
the brackets), distal to the terminal attachment, to secure the archwire in place and prevent it from
shifting through the brackets and causing soft tissue impingement during the time interval between
patient visits. Distal-end bends are also useful in avoiding excessive proclination of the anterior
teeth during leveling.
[See Cinching (of the archwire)]
Bends (Archwire bends)
• First-order bends (Offsets, In-out bends, Bayonet bends)
Labiolingual offsets (step bends) in the archwire in the horizontal plane (in the plane of the wire), to
accommodate for variations in the prominence and contour of labial/buccal surfaces of individual
teeth. Typical locations along the archwire in which first-order bends were placed with the standard
edgewise appliance were mesial to the maxillary lateral incisors (insets or step-in bends), canines
(offsets, canine eminence bends, curvature or step-out bends) and first molars (offsets, step-out or
molar bayonet bends). [Note: Vertical step bends that do not change the angulation of a tooth (e.g.
step-up mesial and equal step-down distal to a bracket) are also considered first-order bends. ]
Bends (Archwire bends)
• Second-order bends (Tip bends)
Offsets in the archwire in the vertical plane, to change
the angulation (mesiodistal tipping) of a tooth.
Bends (Archwire bends)
• Step bends
Labiolingual or occlusogingival offsets in an archwire,
in such a way that the segments of the wire on either
side of the bend remain parallel to each other. A step
bend generates equal and opposite forces and
moments of equal magnitude and identical sense
between the two teeth adjacent to it (corresponding
to Burstone’s geometry I). The magnitude of these
forces and moments depends on the size of the step,
the type and size of wire and the interbracket
distance. Unlike V-bends, the force system created
by a step bend remains practically unaffected by
changing the location (mesiodistal position) of the
step bend along the span between the two brackets.
[Compare with Bends (Archwire bends), V-bends
(Gable bends)]
Bends (Archwire bends)
• Stop bends
Bends that serve as archwire stops to keep the arch length constant, or to maintain the actual
position of certain teeth.
Bends (Archwire bends)
• Third-order bends (Torquing bends)
Twists in a rectangular archwire, placed when a change of the buccolingual or labiolingual
inclination of specific teeth is desired.
Bends (Archwire bends)
• Tip-back bends
V-bends placed to tip teeth distally (as is typically done
during the anchorage preparation stage of the Tweed
technique).
Bends (Archwire bends)
• Tip-forward bends
V-bends placed to tip teeth mesially.
[Compare with Bends (Archwire bends), Tip-back bends]
Bends (Archwire bends)
• Toe-in bends
V-bends in the horizontal plane, typically placed at the ends of an archwire, to
achieve derotation or constriction of the terminal molars.
Bends (Archwire bends)
• V-bends (Gable bends)
1. “V”-shaped bends with multiple applications, such as to avoid tipping of teeth into extraction
sites during space closure. V-bends generate different force systems between two teeth, or two
segments of teeth,
depending on the location of
the “V” along the wire (in
relation to the two brackets).
When the V-bend is in the
center of the interbracket
distance, the created force
system involves equal and
opposite moments between
the teeth (corresponding to
Burstone’s geometry VI).
[Note: According to the
above definition, a V-bend
changes the orientation of
the long axis of the wire (i.e.
the segment of the wire distal to the bend is no longer parallel with that mesial to it)].
2. The term V-bend occasionally is mentioned to denote a V-shaped stop (lug) bent into the
archwire, maintaining the original wire orientation distal to it, as it is mesial to the bend.
[See Burstone’s geometry classes]
[See Archwire stop]
Bennett angle
On a lateral mandibular excursion, the non-working side condyle moves inferiorly, anteriorly and
medially. The projection of this trajectory on the horizontal plane creates an angle with the sagittal
plane, called the Bennett angle.
Bennett movement
Lateral translation (sideshift) of the working side condyle during a lateral mandibular excursion.
[See Bennett angle]
Beta position
The posterior component of an orthodontic spring, or the posterior point of attachment of a spring.
[Compare with Alpha position]
Beta-titanium alloy (TMA, b-Ti, Titanium-molybdenum alloy)
A group of titanium-based alloys in which the elevated temperature body-centered cubic beta
phase (crystalline structure) is stable at room temperature, rather than the hexagonal close-packed
alpha phase. One such alloy, made of 77.8% titanium, 11.3% molybdenum, 6.6% zirconium, and
4.3% tin, was introduced to orthodontics in 1980 by C. J. Burstone and J. A. Goldberg, under the
commercial name TMA (Ormco/Sybron). TMA has a modulus of elasticity which is approximately
40% of that of stainless steel and double that of Nitinol. As well, it has excellent resilience and
reasonably good formability, which allows stops and loops to be bent into the wire. In addition,
beta-titanium wires can be spot-welded. However,its drawback is its high friction coefficient. The
properties of TMA make it a good choice for fabrication of auxiliary springs and for intermediate
and finishing archwires.
Bidimensional technique
A fixed-appliance orthodontic treatment approach, developed by A. A. Gianelly, that is aimed at
retraction of maxillary incisors by means of sliding mechanics, with good control of their inclination.
This is attempted by using a 0.022-inch (0.56-mm) non-torqued bracket setup and a 0.016 x 0.022-
inch (0.41 x 0.56-mm) stainless steel archwire, which has ninety-degree bends immediately distal
to the lateral incisors, so as to fit into the incisor slots in a “ribbonwise” fashion. Alternatively, the
incisors are bonded with 0.018-inch (0.46-mm) brackets and the canines, premolars and molars
with 0.022-inch (0.56-mm) brackets, while an edgewise 0.018 x 0.025-inch (0.46 x 0.64- mm)
stainless steel wire is used for retraction with sliding mechanics. The filling of the slot of the incisor
brackets by the full-dimension archwire is supposed to result in good control of their root position
and minimal lingual tipping as a side effect of retraction.
Bifid uvula
A congenitally “split” uvula; a mild form of cleft palate.
Bilateral
Occurring on both sides.
[Compare with Unilateral]
Biocompatibility
The ability to exist in harmony with the surrounding biological environment. The absence of all
material properties that can harm biological tissues. In general, biocompatibility is measured on the
basis of localized cytotoxicity (such as pulpal or mucosal response), systemic responses,
allergenicity and carcinogenicity.
Biofeedback
A method of behavioral modification in which signals are relayed to the patient regarding the status
of certain physiologic functions such as muscle activity, heart rate and blood pressure.
Bite block
An interocclusal acrylic shelf that can be incorporated in a functional or other removable appliance
to contact the occlusal surfaces of (usually) the posterior teeth. Posterior bite blocks that are high
enough to impinge into the freeway space are advocated by some clinicians for the treatment of
patients with a long anterior lower facial height and an anterior open bite tendency.
[See Appliance, Harvold-Woodside activator]
Bite collapse (Posterior bite collapse)
Reduction of the occlusal vertical dimension through (partial) loss or drifting of the posterior
supporting dentition, often resulting in protrusion (flaring) of the maxillary anterior teeth.
Bite collapse (Posterior bite collapse)
Reduction of the occlusal vertical dimension through (partial) loss or drifting of the posterior
supporting dentition, often resulting in protrusion (flaring) of the maxillary anterior teeth.
Bite force
The force exerted by the masticatory musculature during biting, measured between particular
occluding teeth—a parameter that is difficult to control. For standardization purposes, research
attempts sometimes have turned to measuring “maximum bite force,” a concept of relatively little
value as it is rarely attained in everyday human masticatory function.
Bite plane
The horizontal shelf-like part of a bite plate, on which the teeth touch. Bite planes also can be used
in a fixed design (i.e. bonded to the teeth, or attached to a palatal arch).
Bite plate
A removable
orthodontic
appliance
designed to
(temporarily)
disengage the
teeth and/or
prevent
selected teeth
from occluding.
A posterior bite
plate commonly
is used to
disclude the
anterior teeth
and thus facilitate correction of an anterior crossbite. Anterior bite plates can be used to increase
the lower anterior face height, to facilitate tooth movement and to correct a deep bite by extrusion
of posterior teeth.
Bite raising
The increase of lower face height by extrusion of the posterior teeth, as can be accomplished, for
example, by a maxillary anterior bite plate contacting the incisal edges of the mandibular anterior
teeth, while the opposing posterior teeth are kept apart and are free to erupt. Alternatively,
extrusion of the posterior teeth can be obtained by using an anterior bite plane and fixed
appliances, in combination with vertical posterior elastics.
[See Opening of the bite]
Bite registration (Wax bite)
A wax record of an occlusal relationship between the maxilla and mandible, used in the trimming of
orthodontic casts or in the mounting of casts on an articulator. A wax bite usually is taken in centric
occlusion, or in centric relation (if there is a large mandibular CR-CO shift).
[See Construction bite]
Bolton analysis
A method developed by W. Bolton (1958) for the evaluation of mesiodistal tooth size discrepancies
between sets of corresponding maxillary and mandibular teeth. The analysis distinguishes between
the “overall ratio,” which involves all permanent teeth except the second and third molars, and the
“anterior ratio,” which encompasses only the six anterior teeth of each jaw. For this analysis it is
assumed that the relatively smaller tooth material is the correct one. A table of standard values lists
the tooth width value in the opposing arch that is ideally related to this given correct value. The
difference between the ideal and actual dental width in the arch with the excess value gives an
estimate in millimeters of the severity of tooth size discrepancy between the arches.
[See Tooth size discrepancy (Bolton discrepancy)]
Bolton-Brush Growth Study
The Bolton Growth Study is a longitudinal study of over 4,000 subjects from birth to adulthood,
which was started in 1929 under the direction of B. H. Broadbent, Sr. , at Case Western Reserve
University in Ohio. The records that were obtained included lateral and P-A cephalometric
radiographs, hand-wrist radiographs and dental casts, as well as nutritional, dental and medical
health status data. Approximately 2,900 of the subjects of the Bolton study were also enrolled in
the Brush study, which involved radiographs of the entire skeleton taken on a yearly basis, as well
as extensive anthropometric, nutritional, health and psychological data, also recorded annually. All
records of subjects in both studies are currently housed and curated through the Bolton-Brush
Growth Study Center at Case Western Reserve University.
Bonding
The attachment (adhesion) of a material directly onto a tooth by means of a bonding agent. In
common orthodontic use the term denotes the process by which orthodontic attachments are
affixed to the teeth, which has become a routine part of fixed appliance therapy. The most
commonly used bonding techniques involve acid etching and composite resin, or conditioning and
glass-ionomer cement.
SUBTERMS:
Direct bonding
Indirect bonding
Sequential bonding
Bone
A dense type of connective tissue, consisting of cells in a matrix of intercellular ground substance
and collagen fibers. This organic matrix is impregnated with the mineral component of bone,
consisting mainly of calcium phosphate and hydroxyapatite, which imparts rigidity to bone. Bone is
a highly dynamic type of tissue that constantly remodels. Modeling and remodeling of bone
constitutes the basis of orthodontic tooth movement.
SUBTERMS:
Alveolar bone
Basal bone
Bundle bone
Cancellous bone
Cartilaginous bone (Endochondral bone)
Compact bone (Dense bone)
Cortical bone
(Intra)membranous bone
Lamellar bone
Woven bone
Bone apposition
Addition of new bone to bony surfaces by osteoblastic activity.
Bone plate
[See Fixation plate]
Bone resorption
The removal of bone by osteoclastic activity.
SUBTERMS:
Direct resorption (Frontal resorption)
Undermining resorption (Indirect resorption)
Bonwill triangle
An equilateral triangle, each side of which
is supposed to be 4 inches (102 mm) long,
as advocated by W. G. A. Bonwill in 1858.
The triangle is formed by connecting the
medial contact point of the mandibular
central incisors (or the midline of the
residual mandibular alveolar ridge) to the
centers of the condyles.
Boot loop
[See Loop]
Border movements (of the mandible)
Movements of the mandible at the boundary or margin of the envelope of movement, as
determined by the joint anatomy and function. All other mandibular movements take place within
the limits of the border movements.
Brachycephalic
Anthropometric term used to denote an individual with a
larger than average cranial width; having a cephalic index
greater than 81. Brachycephaly may result from premature
synostosis of the coronal suture.
[Compare with Dolichocephalic]
Bracket
Precisely fabricated orthodontic attachment made of metal, plastic or ceramic material, which can
be bonded to a tooth or welded to a band. It carries a horizontal and/or a vertical channel of
standard size, called a “slot,” that can receive an archwire or other orthodontic spring as part of a
fixed orthodontic appliance. The size and shape of the slot vary with the orthodontic technique
practiced and the type of appliance used. The base of the bracket usually contains a welded mesh
or other retentive structure to increase bonding strength.
[See Bracket slot]
[See Bracket setup]
[See Bracket wings]
SUBTERMS:
Broussard bracket
Ceramic bracket
Edgewise bracket
Esthetic bracket (Clear bracket)
Extraction series bracket
Fully programmed bracket
Lewis bracket
Metal bracket
Plastic bracket
Pre-angulated bracket
Pre-torqued bracket
Self-ligating bracket
Single bracket (Single-width bracket)
Twin bracket (Siamese bracket, Double-width bracket)
Bracket position indicator
A disposable, color-coded plastic attachment that is provided by the manufacturer with some types
of brackets. It is meant to facilitate bracket identification, as well as assist with the occlusogingival
placement and axial orientation of the bracket during bonding.
Bracket prescription
[See Appliance prescription]
Bracket setup
Usually referring to the size of the bracket slot. The term “0.018-inch (0.46-mm) setup” refers to a
bracket slot size of 0.018 x 0.025 inch (0.46 x 0.64 mm) and the term “0.022-inch (0.56-mm) setup”
refers to a slot size of 0.022 x 0.028 inch (0.56 x 0.70 mm).
[See Appliance prescription]
Bracket slot
A standard component of an orthodontic bracket. A precisely fabricated horizontal and/or vertical
channel, which can receive an archwire or other orthodontic mechanism as part of orthodontic
treatment. The size and shape of the slot vary with the orthodontic technique practiced and the
type of appliance used. The two bracket slot sizes most commonly used today, are 0.018 x 0.025
inch (0.46 x 0.64 mm) and 0.022 x 0.028 inch (0.56 x 0.70 mm).
SUBTERMS:
Main slot
Vertical slot
Bracket slot engagement
A measure of the play between the orthodontic archwire and bracket slot.
[See “Play” of an orthodontic wire in the bracket slot]
[See Second-order clearance]
[See Third-order clearance]
Bracket width
The mesiodistal dimension of an orthodontic bracket.
Bracket wings
Four projections (only two, in a single bracket) extending from the center of the bracket in a mesialocclusal,
distal-occlusal, mesiogingival and distogingival direction, creating undercuts that facilitate
retention of the elastic or stainless steel ligatures that secure the archwire in the bracket slot.
Bracket wings
Four projections (only two, in a single bracket) extending from the center of the bracket in a mesialocclusal,
distal-occlusal, mesiogingival and distogingival direction, creating undercuts that facilitate
retention of the elastic or stainless steel ligatures that secure the archwire in the bracket slot.
Brazing
[See Soldering]
Brittle
A material exhibiting little or no permanent deformation before fracture. In other words, a brittle
material fractures at or near its proportional limit.
Brittleness
The relative inability of a material to sustain plastic deformation before it fractures.
Bruxism
A diurnal or nocturnal parafunctional activity that includes clenching, bracing, gnashing and
grinding of the teeth. Bruxism is a common cause of dental wear, muscle hypertrophy, pain and
fatigue, and damage to the supporting tissues. It also is associated frequently with
temporomandibular joint problems. Some consider occlusal interferences as a major factor in its
etiology, whereas others believe that it is a centrally mediated phenomenon, related to emotional
tension and stress. In absence of subjective awareness, bruxism can be diagnosed from the
presence of shiny facets that are not generated by masticatory function. Bruxism can be observed
through sleep laboratory recordings.
Bruxism splint
[See Nightguard (Bruxism appliance)]
Buccally
In the direction of the cheeks.
Buccolingually
In a mediolateral direction, perpendicular to the sagittal plane (along the z-axis), for posterior teeth.
When referring to anterior teeth, the term “labiolingually” is appropriate.
[See Global reference frame]
[See Labiolingually]
Buccoversion
Buccal inclination of a tooth or a group of teeth.
Burlington Growth Study
A prospective longitudinal investigation that was started in 1952 in Burlington, Ontario, Canada, by
R. E. Moyers of the Faculty of Dentistry, University of Toronto, under the responsibility of F.
Popovitch. The 1,258 children in the Burlington sample represented 85% to 90% of the children in
Burlington, within the specified ages, at the time the study was started. By the time the data
collection was completed in 1971, the population of Burlington had risen to 90,000 (from an initial
9,000 in 1952). Records were collected annually from age 3 to 21 years. The records consisted of
medical history, periodontal evaluation, six cephalometric radiographs, one hand-wrist radiograph,
impressions for dental casts, intraoral radiographs (where necessary), height and weight records,
anthropometric data, social histories and electromyographic records for some subjects. The entire
material is currently housed at the Burlington Growth Centre, Faculty of Dentistry, University of
Toronto.
Burstone’s geometry classes
When two teeth or two toothsegments
are connected by a
straight wire fully engaged in
both brackets, the generated
force system varies depending
on the relative angulation of the two brackets. There are six different possibilities (6 geometry
classes) as described by C. J. Burstone and H. A. Koenig (1974), which are independent of the
interbracket distance. The geometries are based on the ratio between the angles (JA of the
anterior bracket and (JB of the posterior bracket with respect to a straight line passing through the
centers of the two brackets. In the description of the six geometries that follows, (JA is always (by
convention) the smaller of the two angles.
SUBTERMS:
Burstone’s geometry classes
• Geometry I
In Class I geometry both brackets are angulated in the same direction and by the same amount
(JA/JB = 1). The same situation is created when a straight wire is inserted between two brackets,
which lie at different vertical heights, with parallel slots (or equivalently, when a step bend is placed
on a wire between two aligned brackets). The force system generated in this situation consists of
two equal and opposite forces and two moments of equal magnitude and the same sense. Since
the moments at A and B are equal in magnitude, the ratio MA/MB = 1. Although the magnitude of
the moments may vary depending on the size of the vertical discrepancy (step) and the
interbracket distance (assuming the material and size of the wire segment is always constant), the
ratio MA/MB always remains +1 in Class I geometry.
Burstone’s geometry classes
• Geometry II
In Class II geometry, both brackets are angulated in the same direction but the angle of the A
bracket with the axis connecting the centers of the two brackets is half the size of that of the B
bracket (JA/JB = 0.5). As in geometry I, two equal and opposite forces are created at the positions
A and B, as well as two moments of the same sense. The magnitude of the moment at A is 0.8
times that of the moment at B (MA/MB = 0.8); thus it is reduced with respect to the value
developed in geometry I. Since the SM is reduced, the magnitudes of the forces are also reduced.
Burstone’s geometry classes
• Geometry III
This geometry is created when the slot of the bracket A is parallel to the line connecting the centers
of the two brackets (JA = 0, and consequently (JA/JB = 0). A straight wire engaged in the bracket
slot at A would thus pass through the center of the bracket B. As in the first two geometries, two
equal and opposite forces will be produced at the brackets A and B, as well as two moments of the
same sense. In this situation, the magnitude of the moment at the bracket A is only half of that at
the bracket B (MA/MB = 0.5). The magnitudes of both forces and moments are reduced with
respect to those developed in geometry II.
Burstone’s geometry classes
• Geometry IV
In this situation the ratio JA/JB is -0.5. In other words, the bracket at position A is angled one-half of
the bracket at the position B (and in the opposite direction) relative to the axis connecting the
centers of the two brackets. The wire is now said to be tied – to the A bracket – at the “point of
dissociation”. This means that forces are independent from moments at position A, where only a
force is present and no moment. The total force system that is produced by tying a straight wire
into two brackets with this geometry includes equal and opposite forces at the two brackets and a
moment at B, with no moment at A (MA/MB = 0). The SM and the magnitudes of the forces are
further reduced in this geometry compared to the previous ones.
Burstone’s geometry classes
• Geometry V
Class V geometry describes a situation with a ratio JA/JB of -0.75. In other words the two brackets
still have opposite angulation (as in geometry IV), but the bracket A is now angulated 75% as much
as the bracket B relative to the axis connecting the centers of the two brackets. In this situation the
moment at bracket A is opposite in sense to that of the moment generated at bracket B, and the
ratio between them is MA/MB = -0.4. The magnitude of MB is reduced further, as are the
magnitudes of the forces acting on the two brackets.
Burstone’s geometry classes
• Geometry VI
In this geometry the two brackets are tipped towards each other by an equal amount (JA/JB = 1).
The force system created consists of equal and opposite moments at the two brackets. No forces
are generated. SM, the sum of all the moments, is equal to zero and the ratio MA/MB is equal to 1.
Button
A small, mushroom-shaped orthodontic attachment that can be bonded directly onto a tooth or
welded on a band. Buttons are mainly used as handles for elastic traction.
[See Attachment, Orthodontic]
Calculus (Tartar)
Mineralized bacterial plaque, strongly attached to the tooth surface. According to its location there
are two general types: supragingival and subgingival.
Callus
The newly formed tissue (composed of varying amounts of fibrous tissue, cartilage and bone) that
initially connects the bony fragments where a fracture has occurred.
Camouflage orthodontic treatment
The treatment of malocclusions with underlying mild to moderate skeletal jaw discrepancies, which
achieves a good dental occlusion (Class I canine relationship and an ideal overjet and overbite),
through extraction of certain teeth, to mask the skeletal problem. This type of treatment should be
performed only if it will not have a harmful effect on facial esthetics, and if growth modification or
orthognathic surgery are not applicable or not accepted by the patient. Extraction of teeth provides
space for repositioning of the remaining teeth only in the anteroposterior plane of space. Patients
with vertical or transverse skeletal problems would not benefit from extractions for camouflage.
Similarly, if there is severe crowding, or excessive incisor protrusion in addition to a skeletal
discrepancy (so that the extraction spaces will merely be used for alignment of the remaining
teeth), camouflage treatment usually is contraindicated.
Canine guidance (Canine-protected occlusion, Canine “rise”)
A particular scheme of disclusion of
the dental arches during a lateral
mandibular excursion. The labial (or
distolabial) surface of the
mandibular canine on the working
side comes into contact with the
lingual (or mesiolingual) surface of
the maxillary canine, causing
disarticulation of all other teeth.
Canine retraction
Movement of the canine in a distal
direction, usually into an extraction
space. Individual retraction of the
canines often is performed in an attempt to preserve posterior anchorage in patients with Class II
malocclusions, and subsequently is followed by retraction of the incisors. Canine retraction can be
performed by sliding or sectional mechanics. Control of root position usually is critical, as bodily
movement of the canines generally is required.
[See Moment, Counter-moment]
Canine-to-canine retainer
See Retainer, Bonded lingual.
[See Retainer, Bonded lingual retainer]
Cartilage
A semi-rigid specialized form of supporting/connective tissue, the characteristics of which mainly
stem from the nature and predominance of ground substance in the extracellular matrix.
Proteoglycans make up the ground substance and account for the solid, yet flexible, consistency of
cartilage. Within the ground substance are embedded varying proportions of collagen and elastic
fibers giving rise to three main types of cartilage: hyaline cartilage, fibrocartilage and elastic
cartilage.
On completion of growth the cartilage mass consists of chondrocytes embedded in a large amount
of extracellular matrix. At the periphery of mature cartilage is a zone of condensed supporting
tissue called “perichondrium” containing chondroblasts with cartilage-forming potential. Growth of
cartilage occurs by interstitial growth from within and appositional growth at the periphery. Most
cartilage is devoid of blood vessels and consequently the exchange of metabolites between
chondrocytes and surrounding tissues depends on diffusion through the water of solvation of the
ground substance. This limits the thickness to which cartilage may develop whilst maintaining
viability of the innermost cells.
SUBTERMS:
Elastic cartilage
Fibrocartilage
Hyaline cartilage
Caudal
Inferior, towards the tail.
[Compare with Cephalic (Cranial)]
Cementation
The attachment of bands or a fixed orthodontic appliance on the teeth by means of a dental
cement.
Center of mass (CM)
A point in a body where its entire mass can be considered concentrated for theoretical purposes.
For homogeneous bodies with a regular geometrical shape, the CM is located at their geometric
center (i.e. the center of a sphere, or the junction point of all three-dimensional diagonals of a
cube).
Center of resistance (CRes)
The point in a body at which
resistance to movement can be
considered concentrated, for
mathematical analysis. For a free
object in non-gravitational space,
the center of resistance coincides
with the center of mass. However,
for a partially restrained object (as is
the case for a tooth that is partially
embedded in bone), the CRes is
determined by the mass, shape and
form of the tooth, as well as by the
characteristics of the constraining
elements (bone, PDL). [Other definition: CRes of a tooth is a point in the tooth on which the
application of a single force will produce bodily movement of the tooth. ] The location of the CRes
is estimated to be between halfway and two thirds along the distance between the crest of the
alveolar bone and the root apex in single-rooted teeth, and at the furcation area of multi-rooted
teeth (assuming that the periodontal support is intact).
Center of rotation (CRot)
The point around which rotation actually occurs, when an object is being moved. The location of
the CRot is variable and depends on the movement performed. The actual CRot of a tooth for a
specific movement is almost impossible to determine and can be estimated only by the initial and
final positions of the tooth. In orthodontics, the approximate location of the CRot can be controlled
by varying the moment-to-force ratio at the bracket. The CRot during bodily movement is
considered to lie at infinity. [For three-dimensional objects, the term “axis of rotation” is more
accurate. ]
Centric relation (CR)
A gnathological term that has been used in dentistry for many years, especially in prosthodontics
(as it was meant as a reproducible reference mandibular position, mainly in the construction of
complete dentures). Although CR has had a variety of definitions (which has led to great
confusion), it generally is considered to designate the relation of the mandible to the maxilla when
the condyles are in a physiologically stable position, independent of tooth contacts. Centric relation
has been described as:
1. The relation of the mandible to the maxilla when the mandible is in its most retruded, unstrained
position from which lateral movements can be performed, at any given degree of jaw separation;
also termed the “ligamentous” position, as it is determined mainly by the ligaments of the TMJ.
2. The maxillomandibular relationship in which the condyles articulate with the thinnest avascular
portion of their discs, with the disc-condyle complex in the anterior-superior position against the
slope of the articular eminence.
3. The most superoanterior position of the condyles in the articular fossae with the discs correctly
interposed. Centric relation may be impossible to record in the presence of dysfunction of the
masticatory system.
Cephalic (Cranial)
Towards the head.
[Compare with Caudal]
Cephalometer (Cephalostat)
A head-holding device introduced in 1931 by B. H. Broadbent in the USA and by H. Hofrath in
Germany. The original design included two ear rods for insertion into the external auditory canals,
an infraorbital pointer and a forehead clamp, to achieve parallelism of the Frankfort plane with the
floor. The cephalometer is used to obtain standardized and comparable craniofacial images on
radiographic film.
Cephalometric analysis
The process of evaluating skeletal, dental and soft tissue relationships of a patient, by comparing
measurements performed on the patient’s cephalometric tracing with population norms for the
respective measurements, to come to a diagnosis of the patient’s orthodontic problem. Refers also
to the various standardized sets of cephalometric measurements (e.g. Downs’ analysis, Steiner
analysis) commonly used in the evaluation.
SUBTERMS:
Burlington cephalometric analysis
Di Paolo (Quadrilateral) cephalometric analysis
Downs cephalometric analysis
Harvold cephalometric analysis
McNamara cephalometric analysis
Sassouni cephalometric analysis
Steiner cephalometric analysis
Tweed cephalometric analysis
Wylie cephalometric analysis
Cephalometric landmarks
Readily recognizable points on a cephalometric radiograph or tracing, representing certain hard or
soft tissue anatomical structures (anatomical landmarks) or intersections of lines (constructed
landmarks). Landmarks are used as reference points for the construction of various cephalometric
lines or planes and for subsequent numerical determination of cephalometric measurements.
In the definitions of the specific landmarks the following convention is used: “midsagittal” identifies
landmarks lying on the midsagittal plane, “unilateral” identifies landmarks corresponding to
unilateral structures and “bilateral” applies to landmarks corresponding to bilateral structures.
SUBTERMS:
A-point (Point A, Subspinale, ss)
Anterior nasal spine (ANS)
Articulare (Ar)
B-point (Point B, Supramentale, sm)
Basion (Ba)
Bolton (Bo)
Condylion (Co)
Crista galli
Dacryon
Glabella (G)
Gnathion (Gn)
Gonion (Go)
Incision inferius (Ii)
Incision superius (Is)
Infradentale (Id, Inferior prosthion)
L-point
Menton (Me)
Nasion (N, Na)
Opisthion (Op)
Orbitale (Or)
Pogonion (Pog, P, Pg)
Porion (Po)
Posterior nasal spine (PNS)
Prosthion (Pr, Superior prosthion, Supradentale)
Pterygomaxillary fissure (PTM, Pterygomaxillare)
R-point (Registration point)
Sella (S)
Cervical point (C)
Inferior labial sulcus (Ils)
Labrale inferior (Li)
Labrale superior (Ls)
Pronasale (Pn)
Soft tissue glabella (G’)
Soft tissue menton (Me’)
Soft tissue nasion (N’, Na’)
Soft tissue pogonion (Pg’, Pog’)
Stomion (St)
Stomion inferius (Sti)
Stomion superius (Sts)
Subnasale (Sn)
Superior labial sulcus (Sls)
Trichion (Tr)
Soft tissue gnathion (Gn’)
Cephalometric lines (planes)
Most analyses utilize one or more cephalometric lines that are joining two landmarks, are tangent
to an outline from a landmark, or are perpendicular to another line from a landmark.
SUBTERMS:
A-B plane
Basion-Nasion line (Ba-N)
Bolton plane
Camper’s base plane
De Coster line
E-line (E-plane, Esthetic line of Ricketts)
Facial axis of Ricketts
Facial plane (FP, Facial line)
Frankfort horizontal plane (FH, Frankfort horizontal line, Auriculo-orbital plane, Eye-ear plane)
H-line (Harmony line of Holdaway)
Intergonial line
Mandibular plane (MP, Mandibular line, ML)
Nasion-perpendicular
Occlusal plane (OP)
Palatal plane (ANS-PNS, PP, Nasal line, Nasal floor, Spinal plane)
Rees esthetic plane
Reference line
Riedel plane
S-line (Esthetic plane of Steiner)
Sella-Nasion line (SN, Nasion-Sella line, NSL)
True horizontal line
True vertical line
Y-axis (Growth axis)
Z-line (Profile line of Merrifield)
Cephalometric radiograph (Cephalogram)
A radiograph of the head obtained under standardized conditions, introduced simultaneously in the
United States and Germany (1931), by B. H. Broadbent and H. Hofrath, respectively.
Cephalometric radiographs are taken on a cephalometer, which dictates a standardized orientation
of the head and a precisely defined relationship among x-ray source, subject and film. By
convention, the dis-tance between x-ray source and the midsagittal plane of the subject is either 5
feet (152.4 cm) or 150 cm. The distance between the midsagittal plane of the subject and the film
may vary between 10 cm and 18 cm, depending on head size. Measurement of the subject-film
distance and the source-subject distance allows calculation of the image magnification. The
standard projections are lateral (profile), posteroanterior (P-A) and oblique projections.
SUBTERMS:
Lateral cephalometric radiograph
Oblique cephalometric radiograph
Posteroanterior (P-A) cephalometric radiograph
Cephalometric tracing
An overlay drawing produced from a
cephalometric radiograph by copying
specific outlines from it with a lead
pencil onto acetate paper, using an
illuminated view-box. Tracings are
used to facilitate cephalometric
analysis, as well as in
superimpositions, to evaluate
treatment and growth changes.
Chief complaint (CC)
The patient’s statement of the main problem or primary concern.
Chronic pain disorders
Persistent pain that lasts more than six months, with associated behavioral and psychosocial
factors.
Cinching (of the archwire)
Placing a sharp bend on the archwire distal to the terminal attachments in an arch. Cinching is
done to avoid excessive proclination of the anterior teeth during leveling or to prevent the archwire
from sliding in an anterior direction during the interval between patient visits.
[See Bends (Archwire bends), Distal-end bends (Cinching bends, Distal-end stops)]
Circumferential supracrestal fibrotomy (Edwards’ procedure)
An adjunctive periodontal surgical procedure developed by J. G. Edwards to reduce the relapse
tendency of corrected individual tooth rotations. The procedure consists of inserting the sharp point
of a fine blade into the gingival sulcus, down to the crest of the alveolar bone, to sever the gingival
fibers around the tooth (including the transseptal fibers between it and the adjacent teeth).
Clasp (Retention clasp)
An element of a removable appliance made of metal that serves to secure the appliance in place
by engaging on undercuts provided by the morphology and inclination of the teeth.
SUBTERMS:
Clasp (Retention clasp)
• Adams clasp (Modified arrowhead clasp)
A clasp made of stainless steel wire, which was designed by
C. P. Adams to retain removable appliances, by means of
point contact with the mesio- and distobuccal undercuts of
individual posterior teeth. The clasp is bent from a single
piece of round wire and crosses the occlusal table at the
mesial and distal embrasures of a posterior tooth (typically
first permanent molar). Itconsists of a mesial and a distal retentive U- or V-shaped loops, which are
pointed in a gingival direction and joined by a buccal bridge.
[See Clasp (Retention clasp), Arrowhead clasp (Arrow clasp)]
Clasp (Retention clasp)
• Arrowhead clasp (Arrow clasp)
Clasp made from stainless steel wire, bent in the shape
of an arrowhead. It is meant to engage the distobuccal
and mesiobuccal undercuts of adjacent teeth (in a
fashion similar to a ball clasp). Two or more arrowhead
clasps may be combined, joined by a buccal bridge.
[See Clasp (Retention clasp), Adams clasp (Modified
arrowhead clasp)]
Clasp (Retention clasp)
• Ball clasp
Clasp bent from round stainless steel wire, with a
ball-shaped end. The clasp crosses the occlusal table
at the embrasure between two adjacent teeth and
engages their mesiobuccal and distobuccal
undercuts.
Clasp (Retention clasp)
• Circumferential clasp (Three-quarter clasp, C-clasp)
A single-tooth cast or bent stainless
steel wire clasp that engages the
cervical region of the canines and
posterior teeth. The clasp usually
crosses the occlusal table at an
interproximal embrasure between two
teeth, then progresses gingivally toward
the other interproximal surface,
engaging in the interproximal gingival undercut, thus traversing three surfaces of the tooth.
The diameter of the wire used for its fabrication typically is 0.024 inch (0.60 mm) for deciduous
canines; 0.028 inch (0.70 mm) for deciduous molars, premolars and permanent canines; and 0.032
inch (0.80 mm) for permanent molars. Circumferential clasps function well on maxillary teeth as the
morphology and the inclination of the posterior teeth provide adequate undercuts. In the
mandibular dental arch this is not always the case. By creating artificial undercuts with composite,
circumferential clasps can provide firm retention of mandibular removable appliances. An
advantage of the circumferential clasp is the possibility of avoiding occlusal interference of the part
of the clasp that crosses the occlusal table.
Clasp (Retention clasp)
• Claw clasp
A clasp introduced by F. P. G. M. van der Linden
for retention on maxillar incisors. It is made of a
0.024-inch (0.60-mm) stainless steel springhard
wire crossing the incisal edge and forming
a small rectangular box on the labial surface of
those teeth. The addition of composite at that
point, to create an artificial undercut, greatly
enhances retention.
Clasp (Retention clasp)
• Delta clasp
A modification of the standard Adams clasp by W. J.
Clark, for retention of the twin block appliance. The
major difference is the shape of the retentive loops,
which in the case of the delta clasp are shaped in a
closed triangle, unlike the open V- or U-shaped loops, of
the Adams clasp. Subsequent modification of the delta
clasp produced circular loops, which are easier to
construct and have similar retentive properties. The
advantage of the delta clasp, according to its designer,
is that the loops do not open with repeated insertion and
removal of the appliance. Delta clasps, which are
constructed from 0.028-inch (0.70-mm) or 0.030-inch
(0.75-mm) stainless steel wire, can provide good
retention on mandibular premolars and can be used on
most posterior teeth.
[See Appliance, Twin block appliance]
Class I, II, III malocclusion
[See Angle classification]
Classification of gingival recession
[See Miller classification]
Cleft lip and/or palate (CLP)
The most common craniofacial anomaly (approximately 1 in 600 to 1 in 700 live births higher in
some populations), characterized by failure of fusion between certain embryological processes
(swellings) during facial morphogenesis. Failure of fusion between the medial and lateral nasal and
the maxillary swellings results in a cleft of the lip and/or alveolar process. Failure of fusion between
the lateral palatine swellings results in a cleft of the palate. These problems are thought to result
from a deficiency of mesenchyme in the facial region, brought about by failure of neural crest cells
to migrate or failure of the facial mesenchyme to proliferate. A cleft can be complete or incomplete,
and it can occur unilaterally or bilaterally. Cleft lip may occur without clefting of the alveolar process
or the palate, and cleft palate also can occur as an isolated phenomenon. A useful classification
divides the anatomy into primary and secondary palates. An individual thus may have clefting of
the primary palate, the secondary palate, or both. In addition, a CLP may be an isolated
phenomenon, or may occur as part of a syndrome.
The etiology of cleft lip and palate is thought to be multifactorial. Genetics is implicated in 20% to
30% of patients. Even in those individuals whose genetic background may verify familial
tendencies for clefting, the mode of inheritance is not understood completely. Environmental
factors that have been shown in experimental animals to result in clefting include nutritional
deficiencies, radiation, several drugs, hypoxia, viruses, and vitamin excesses or deficiencies. In
complete unilateral or bilateral clefts of the lip, alveolus and palate, the maxillary arch typically is
collapsed in the transverse direction, especially in the area of the cleft. The maxillary permanent
lateral incisors may be congenitally missing or malformed, and many atypically shaped
supernumerary teeth may be present in the area of the cleft.
The treatment of patients with cleft lip and/or palate is a long and involved process, requiring many
stages of intervention by many different specialists, forming a “cleft lip and palate team. ” The
involvement of the team orthodontist starts a few days after the baby is born, with presurgical infant
orthopedic treatment (if applicable), in preparation for the initial repair.
Repair of the lip usually is performed within the first three months after birth, and the palate
subsequently is repaired within the first year. The scar tissue created from these and other surgical
procedures is considered responsible for variable degrees of maxillary growth inhibition which is
commonly seen during subsequent growth.
When the cleft involves the alveolar process, a bone graft may be necessary to restore the alveolar
anatomy. Alveolar bone grafting usually is performed prior to the eruption of the permanent
maxillary canine on the side of the cleft.
Phase I of orthodontic treatment, in preparation for the alveolar bone graft, may consist of
expansion of the constricted maxilla and correction of any crossbites. Following alveolar bone
grafting, and when the patient is in the permanent dentition, phase II of orthodontic treatment is
performed to idealize the occlusion, or if a severe skeletal discrepancy is present, to prepare the
arches for orthognathic surgery.
[See Graft, Alveolar bone graft]
[See Palate, Secondary palate]
[See Palate, Primary palate]
Cleidocranial dysplasia (Cleidocranial dysostosis, CCD)
Inheritable disorder (autosomal dominant) affecting both intramembranous and endochondral bone
formation. The clinical features include a characteristic brachycephalic skull (cephalic index
commonly in excess of 81), with frontal and parietal bossing and the appearance of a small face.
Paranasal sinuses and mastoids often are underdeveloped or absent. Clavicles are hypoplastic or
aplastic, and closure of fontanels and cranial sutures is delayed, sometimes for life.
The palate is highly arched, and there may be a submucous or complete cleft palate. The maxilla is
underdeveloped and a skeletal Class III malocclusion usually is present. The dentition often
presents a chaotic appearance with multiple supernumerary teeth, multiple crown and root
abnormalities, ectopic development, retention of deciduous teeth and failure of eruption of
permanent teeth. Extraction of retained deciduous teeth usually does not facilitate the eruption of
their permanent successors. The molecular pathology of this condition was shown to be associated
with mutations of a gene called CBFA. This gene is a transcription factor essential for osteoblast
differentiation and bone formation, which explains the general bone dysplasia in the condition.
Clenching
Parafunctional activity characterized by hyperactivity of the elevator masticatory muscles, with the
teeth in contact. Clenching is considered to be stress-related and, together with bruxism, is thought
to be part of the predisposing/initiating/perpetuating factors in the development of
temporomandibular joint disorders.
Clicking
Brief, sharp sound (distinct snapping or cracking), audible with or without a stethoscope, or
detectable by palpation, emanating from one or both temporomandibular joints during mandibular
movements. The most common cause for clicking is anterior or antero-medial displacement of the
articular disc. Clicking may or may not be associated with internal derangement of the TMJ, and it
may occur only during the opening or closing movement of the mandible (single click), or during
both (reciprocal click).
SUBTERMS:
Clicking
• Early closing clicking
A clicking noise that occurs at the initiation of retrusive condylar translation.
Clicking
• Early opening clicking
A clicking sound from the TMJ that occurs at the initiation of protrusive condylar translation.
Clicking
• Late closing clicking (Terminal closing clicking)
A click that occurs before the end of retrusive condylar translation.
Clicking
• Late opening clicking (Terminal opening clicking)
A click that occurs just before the end of protrusive condylar translation.
Clicking
• Mid-closing clicking
A clicking noise that occurs midway along the condylar translatory path during closing.
Clicking
• Mid-opening clicking
A clicking noise that occurs midway along the condylar translatory path during opening.
Clicking
• Reciprocal clicking
A pair of clicking noises from the temporomandibular joint, heard during the mandibular opening
movement and again just before the teeth occlude during the closing movement. Reciprocal
clicking is a common characteristic of disc displacement with reduction. From a closed mouth
position, the temporarily misaligned disc reduces or improves its structural relation with the condyle
when mandibular translation occurs, which produces the first clicking noise. The closing noise is
usually of less magnitude and is thought to be produced by a displacement of the disc to its
previous position.
[Compare with Clicking, Single clicking]
Clicking
• Single clicking
An individual clicking noise, occurring either during the opening, or during the closing stage of
mandibular movement.
[Compare with Clicking, Reciprocal clicking]
Closed bite
Excessive vertical overlap of the anterior teeth; extremely deep bite.
Closed lock
[See Disc displacement (Disc derangement, Disc prolapse, Disc interference disorder), Disc
displacement without reduction]
Cobalt-chromium alloy (Co-Cr, Cobalt-chromium-nickel alloy, Chromium-cobalt alloy)
Highly corrosion-resistant alloys based on cobalt and chromium, used for fabrication of orthodontic
wires or clasps. Cobalt-chromium orthodontic wires are very similar in appearance, mechanical
properties, and joining characteristics to stainless steel wires, but have a significantly different
composition and considerably greater heat treatment response.
One of the most widely known alloys, introduced to orthodontics under the trademark
“Elgiloy” (Rocky Mountain Orthodontics), consists of approximately 40% cobalt, 20% chromium,
15% nickel, 15.8% iron, 7% molybdenum, 2% manganese, 0.15% carbon, and 0.04% beryllium.
Concerns about the toxicity of beryllium have led to the development of beryllium-free cobaltchromium
alloys such as “Remaloy” (Dentaurum).
Cobalt-chromium wires are available in different tempers. The soft-temper wires are popular with
clinicians because they are more easily formable and subsequently they can be hardened by heat
treatment. Cobalt-chromium alloys have a modulus of elasticity (E) equivalent to that of stainless
steel. However, they “feel” softer in the not-hardened state, as their yield strength and elastic range
are lower compared to the more resilient stainless steel alloys.
Cohesion
The property of a material by which its constituent molecules are attracted to each other, resisting
separation.
[Compare with Adhesion]
Collateral ligaments
Ligaments attaching the medial and lateral borders of the articular disc of the temporomandibular
joint to the respective poles of the condyle. These ligaments permit the disc to rotate anteriorly and
posteriorly on the articular surface of the condyle during mandibular movements.
Collimator
A diaphragm, cone or tube containing a lead disk with an aperture, designed to fit on an x-ray
source so as to restrict the size and shape of the primary beam, by eliminating its peripheral (more
divergent) portion. The aperture of the collimator may be circular or rectangular.
Coloboma
A congenitally occurring lack of continuity (“cleft”) in the orbital region. The defect may be restricted
to the eyelids or extend into the globe from the iris to the retina. Lower lid and/or lateral canthal
colobomas are commonly seen in patients with Treacher Collins syndrome.
[See Treacher Collins syndrome (Mandibulofacial dysostosis)]
Columella
The small fleshy column connecting the upper lip and the tip of the nose, between the nares; a
continuation of the nasal septum.
Comprehensive orthodontic treatment
Coordinated treatment aiming at improving a patient’s craniofacial dysfunction and/or dentofacial
deformity, taking into account anatomical, functional and esthetic factors. Treatment may
incorporate several phases, with specific objectives at various stages of dentofacial development.
Adjunctive procedures such as extractions, dentofacial orthopedic treatment, orthognathic surgery,
myofunctional or speech therapy, and restorative or periodontal treatment may be performed
concurrently to achieve the best attainable result. Typically, at the end of active comprehensive
orthodontic treatment each tooth is in its ideal position and the achievable optimum in occlusion
has been obtained. Long-term periodic reevaluation following active treatment is important for
maintenance of the achieved result. [Modified from the AAO Glossary of Dentofacial Orthopedic
Terms, 1993.]
[Compare with Limited orthodontic treatment]
Compressive deformation (Compressive strain)
The shape change of a body when it is subjected to compressive stress (e.g. the shortening of an
orthodontic open coil upon compression).
Computerized cephalometrics
The process of entering cephalometric data in digital format into a computer for cephalometric
analysis. Depending on the software and hardware available, the incorporation of data can be
performed by digitizing points on a tracing, by scanning a tracing or a conventional radiograph, or
by originally obtaining computerized radiographic images that are already in digital format, instead
of conventional radiographs. Computerized cephalometrics offers the advantages of instant
analysis; readily available race-, sex- and age-related norms for comparison; as well as ease of
soft tissue change and surgical predictions.
Concrescence
Union of the cellular cementum of two teeth that have developed from
two separate tooth buds.
[Compare with Fusion]
[Compare with Gemination]
[See Twinning]
Condylar growth
Proliferation of condylar cartilage, followed by endochondral ossification. The condyle, the coronoid
process and the ramus are the principal sites of growth of the mandible. As condylar growth
occurs, the mandible is translated inferiorly and anteriorly, which can be visualized by inspection of
cephalometric superimpositions using the cranial base as a reference. The upward and backward
direction of condylar growth is seen clearly by mandibular superimposition. Condylar growth
normally stops shortly after that of the rest of the face, although it may continue well beyond
adolescence, particularly in males.
[See Growth center]
[See Growth site]
Condylectomy
Surgical removal of the entire mandibular condyle.
Condylar guidance
The functional guidance of the mandibular excursions, as determined by the relationship between
the mandibular condyles and the contours of the glenoid fossae, articular eminences and articular
discs.
Condylar hyperplasia
Excessive growth of the condyle, usually unilateral, resulting in facial asymmetry and an
associated malocclusion. Such malocclusions often are associated with an open bite on the
affected side and/or a crossbite on the non-affected side, with a corresponding midline
discrepancy. The condition typically appears in the late teens, but may begin at an earlier age. A
bone scan (scintigram) with Tc99m, an isotope that is concentrated in areas of active bone
deposition, can be used to distinguish between an actively growing (“hot”) condyle and an enlarged
condyle that has ceased growing. The treatment for severe cases of condylar hyperplasia is
usually surgical.
Condylar growth
Proliferation of condylar cartilage, followed by endochondral ossification. The condyle, the coronoid
process and the ramus are the principal sites of growth of the mandible. As condylar growth
occurs, the mandible is translated inferiorly and anteriorly, which can be visualized by inspection of
cephalometric superimpositions using the cranial base as a reference. The upward and backward
direction of condylar growth is seen clearly by mandibular superimposition. Condylar growth
normally stops shortly after that of the rest of the face, although it may continue well beyond
adolescence, particularly in males.
[See Growth center]
[See Growth site]
Condylysis
Idiopathic resorption or dissolution of the condyle.
“Cone-funnel” mechanism
The mechanism by which it is theorized that interdigitation of posterior teeth is achieved in the late
stages of their eruption. Occlusal contacts between the maxillary and mandibular posterior teeth
dictate a series of adjustments in mesiodistal angulation and buccolingual inclination over a
relatively short period of time, leading to their final interdigitation.
Construction bite
A bite registration at the desired occlusal relationship, to permit articulator mounting of the casts for
fabrication of an (most commonly functional) appliance. The construction bite is sent to the
orthodontic laboratory, together with the impressions (or casts) and a prescription with the required
specifications of the appliance.
[See Bite registration (Wax bite)]
Contralateral
Referring to the side opposite to the one that is being considered.
[Compare with Ipsilateral]
Conversion (of a tube into a bracket)
The process of removing the buccal cap of a convertible tube of a molar attachment to transform
the tube into a bracket.
[See Tube (Molar tube), Convertible tube]
[See Orthodontic instruments, Conversion instrument]
Corrosion
A chemical or electrochemical degrading process, through which a material is attacked by
corrosive agents, such as acids (but also air and saliva, in the case of the intraoral environment),
resulting in partial or complete dissolution, deterioration, or weakening. Although glasses and other
nonmetals also are susceptible to environmental degradation, metals generally are more prone to
such an attack because of electrochemical reactions.
SUBTERMS:
Galvanic corrosion
Pitting corrosion
Stress corrosion
Cortical drift
All bone structures have one
growth principle in common,
which was termed “drift” by D.
H. Enlow. The cortical plate can
be relocated by simultaneous
apposition and resorption
processes on the opposing
periosteal and endosteal
surfaces (cortical drift). The
bony cortical plate drifts by
apposition and resorption of
bone substance on its outer and
inner surfaces, respectively, in the
direction of growth. If resorption and deposition take place at the same rate, the thickness of the
bone remains constant. Should more bone be deposited than resorbed, the thickness of the
structure increases, as during growth. The teeth follow the drift of the alveolar processes while the
jaw is growing, and thus they maintain their position within the surrounding bony structure, despite
the displacement of the entire bone.
[See Displacement, Displacement (of a bone)]
Cortical plate
The dense layer of cortical bone covering the buccal and lingual aspects of the alveolar process.
[See Bone, Cortical bone]
Corticotomy (Cortical osteotomy)
A partial osteotomy, involving only the cortical plate, to weaken the resistance of the bone to the
application of forces. Such a procedure is routinely performed prior to distraction osteogenesis for
elongation of the mandible or the maxilla.
[See Distraction osteogenesis (Distraction osteosynthesis, Ilizarov technique, Callus distraction,
Callotasis)]
Costen’s syndrome
Condition involving dizziness, tinnitus, earache, stuffiness of the ear, dry mouth, burning in the
tongue and throat, sinus pain and headaches, described by the otolaryngologist J. B. Costen in
1934. He attributed the symptoms to overclosure of the bite and posterior displacement of the
mandibular condyle. [Term formerly used for “temporomandibular joint disorders. “]
Cortical plate
The dense layer of cortical bone covering the buccal and lingual aspects of the alveolar process.
[See Bone, Cortical bone]
Cranial base
The bones of endochondral origin that form the antero-inferior aspect of the brain case. Because
the bones of the cranial base stop growing relatively early, they often are used in the
superimposition of se-rial cephalograms or tracings as reference structures to assess growth of the
jaws or treatment results.
Craniofacial clefts
Rarely occurring clefts that are not limited to the lip and palate, but also involve the facial soft
tissues and underlying bone. They result from problems in the migration of neural crest cells and
failure of fusion between facial processes (swellings), or from differentiation defects of facial
tissues of mesodermal origin in the first trimester of pregnancy. Some craniofacial clefts produce
extensive facial defects with severe tissue deficits. There are many kinds of craniofacial clefts,
commonly classified under a system described by P. Tessier, which involves numbers from 0 to 14,
centered around the eye.
Craniometry
A branch of anthropometry dealing with the measurements of dimensions and angles of the bony
skull.
Craniosynostosis
A birth defect that may occur as an isolated phenomenon or as part of a syndrome, consisting of
premature fusion of one or more skull sutures. Craniosynostosis results in craniofacial deformity
and potentially in increased intercranial pressure, which can be deleterious to brain function. For
this reason, surgical release of the fused sutures sometimes is undertaken quite early in life. A
number of craniofacial syndromes sharing the clinical feature of craniosynostosis (such as Crouzon
syndrome, Pfeiffer syndrome and Apert syndrome) have been found to result from mutations in the
genes for fibroblast growth factor receptors (FGFR gene mutations).
Crefcoeur spring
[See Appliance, Crefcoeur appliance]
Crepitus (Crepitation, Grating sound)
Rough, sandy, diffuse noise or vibration, produced by the rubbing together of irregular bone or
cartilage surfaces, usually identified with osteoarthritic changes when heard in joints.
Crimpable attachments
A number of different orthodontic attachments (e.g. hooks, stops) that can be fixed on an archwire
by squeezing their base with special sharp-beaked pliers or cutters.
Crossbite
An abnormal relationship of one or more teeth to one or more teeth of the opposing arch, in the
buccolingual or labiolingual direction. A crossbite can be dental or skeletal in etiology. [Note: The
appropriate type of crossbite can be specified by identifying the teeth or jaws that deviate the most
from their ideal position (e.g. when a crossbite is mainly due to a narrow maxillary arch the correct
term is “maxillary posterior lingual crossbite” as opposed to “mandibular posterior buccal
crossbite”). ]
SUBTERMS:
Crossbite
• Anterior crossbite
Situation in which one or more primary or permanent mandibular incisors are labial to their
antagonists (or one or more maxillary incisors are lingual to their antagonists) in habitual occlusion.
Crossbite
• Buccal crossbite
A crossbite due to buccal displacement of the affected tooth (or group of teeth) from its (their) ideal
position relative to its (their) antagonist(s).
Crossbite
• Complete mandibular buccal crossbite
A situation in which the mandibular dental arch is wide and lies entirely buccal to (contains) the
maxillary dental arch. This rare situation is sometimes seen in extreme Class III anomalies
associated with mandibular hyperplasia.
[Compare with Crossbite, Complete maxillary palatal crossbite]
Crossbite
• Complete maxillary buccal crossbite (Brodie syndrome)
A situation in which the maxillary dental arch is
wide and lies entirely buccal to (contains) the
mandibular dental arch (named after A. G. Brodie).
This rare situation sometimes is seen in extreme
Class II anomalies associated with maxillary
hyperplasia.
[Compare with Crossbite, Complete mandibular
lingual crossbite]
Crossbite
• Complete maxillary palatal crossbite
A situation in which the maxillary
dental arch is narrow and lies
entirely lingual to (contained within)
the mandibular dental arch. This rare
situation sometimes is seen in
extreme Class III anomalies
associated with maxillary
hypoplasia.
[Compare with Crossbite, Complete
mandibular buccal crossbite]
Crossbite
• Dental crossbite
An abnormal relationship between antagonist teeth that is due to deviations in the position or
inclination of one or a few teeth (i.e. the relationship between the maxilla and mandible is
harmonious). Such crossbites usually are treatable by means of tooth movement alone.
[Compare with Crossbite, Skeletal crossbite]
Crossbite
• Functional crossbite (Pseudo-crossbite)
A crossbite that is due to a shift of the mandible (i.e. forced bite) into a faulty habitual occlusion
(CO) because of a premature occlusal interference in centric relation (CR). The shift may occur in
an anterior and/or in a lateral direction. Such crossbites often are seen in children, typically
because of interferences caused by lack of wear of their deciduous canines. The treatment
advocated for such problems may be enameloplasty of the deciduous canines or expansion of the
maxillary dental arch.
[See Lateroclusion]
[See Mandibular shift (CR-CO shift, Mandibular slide, Forced bite, Slide in centric)]
Crossbite
• Lingual crossbite
A crossbite mainly due to lingual displacement of the affected mandibular tooth (or group of teeth)
from its (their) ideal position relative to its (their) antagonist(s).
Crossbite
• Palatal crossbite
A crossbite mainly due to palatal displacement of the affected maxillary tooth (or group of teeth)
from its (their) ideal position relative to its (their) antagonist(s).
Crossbite
• Posterior crossbite
A type of crossbite in which one or more deciduous or permanent posterior teeth occlude in an
abnormal buccolingual relation with their antagonists. Posterior crossbites may occur unilaterally or
bilaterally. They may be maxillary or mandibular, buccal or lingual, and may be accompanied by a
lateral functional shift of the mandible (especially in the case of unilateral posterior crossbites).
Crossbite
• Skeletal crossbite
Anterior or posterior (unilateral or bilateral) crossbite that is due to a sagittal or transverse
incoordination in the size or shape of the maxilla and/or mandible. The treatment of such
crossbites usually requires a skeletal expansion by means of rapid maxillary expansion or
orthognathic surgery.
[See Crossbite, Dental crossbite]
Crossbite
• Telescoping bite
A term denoting either a complete
mandibular lingual, or a complete
maxillary buccal crossbite. The
opposite (i.e. a complete maxillary
palatal or a complete mandibular
buccal crossbite) sometimes is called a
reverse telescoping bite.
Cross-section of orthodontic wires
[See Archwire cross-section]
Curettage
Soft tissue periodontal procedure aiming at removal of necrotic tissue lining the soft tissue wall of
periodontal pockets by means of a curet.
SUBTERMS:
Closed curettage
Open curettage
Curve of Monson
A three-dimensional combination of the curves of Spee and
Wilson. According to G. S. Monson, who introduced this
concept (1920), all cusps and incisal edges in a natural
dentition are tangent to a surface of a sphere, approximately 4
inches (10.2 cm) in radius, with its center in the area of the
glabella.
Curve of Spee (Compensating curve)
The curve displayed in the sagittal plane (or
rather, in a plane parallel with the body of the
mandible on either side) by the cusps and incisal
edges of the mandibular teeth. The convex
aspect of the curve of Spee is pointing inferiorly.
The concept was first introduced by F. Graf von
Spee in 1890, who theorized that the extension
of this curve would be tangent to the anterior
surface of the mandibular condyles, bilaterally.
SUBTERMS:
• Reverse curve of Spee
In many patients with a deep overbite, the curve formed by the cusps and incisal edges of the
maxillary teeth is reverse to the curve of Spee, namely having its convex aspect pointing
superiorly. When using continuous archwire mechanics for leveling of the mandibular arch, some
clinicians incorporate a reverse curve of Spee in the mandibular archwire. Conversely, during
leveling of the maxillary arch in a patient with a reverse curve of Spee, the opposite curve (i.e.
accentuated curve of Spee) is incorporated into the maxillary archwire.
Curve of Wilson
When looking at a coronal section of the mandibular
dentition one can see that the long axes of the
mandibular molars and premolars converge towards
the midline (i.e. they are tipped lingually). From this
view the occlusal surfaces of these teeth bilaterally
form a curve in a buccolingual direction. This
imaginary curve that is defined by a line tangent to
the buccal and lingual cusps of the mandibular
posterior teeth bilaterally, is termed the curve of
Wilson.
Cusp
A conical-shaped, pointed or rounded eminence, on or near the occlusal surface of posterior teeth
and on the lingual surface of anterior teeth, which may come into occlusal contact with a tooth of
the opposing dental arch.
SUBTERMS:
Cusp
• Functional cusps (Supporting cusps)
The palatal cusps of the maxillary posterior teeth and the buccal cusps of the mandibular posterior
teeth that come into occlusal contact in intercuspal position, maintaining the occlusal vertical
dimension.
Cusp
• Non-functional cusps (Non-supporting cusps)
The buccal cusps of the maxillary posterior teeth and the lingual cusps of the mandibular posterior
teeth that do not directly contact the opposing teeth in intercuspal position. They act like the rim of
a pestle to prevent food from escaping from the occlusal table, and they protect the buccal mucosa
and the tongue by keeping them away from the functional cusps.
Cusp
• Plunger cusp
A cusp that tends to forcibly wedge food into the interproximal area of two teeth of the opposing
arch.
Cuspid
[See Canine guidance (Canine-protected occlusion, Canine “rise”)]
[See Canine-to-canine retainer]
[See Canine rise]
[See Canine retraction]
Cyclosporine
A pharmacological substance that can cause gingival hyperplasia. It is an immunosuppressant and
antifungal agent, sometimes used to prevent rejection in recipients of organ transplants.
Cytokines
A family of growth factors that mediate considerable roles in growth, differentiation and tissue
damage by cellular receptors.
Deactivation
The process following the activation of an appliance (or an appliance part), during which the stored
force is delivered to the dentition.
Debanding
The removal of cemented orthodontic bands.
Debonding
The removal of bonded orthodontic attachments.
Decalcification
The removal of various minerals from a bone or tooth.
[See White spot lesion (Decalcification)]
Decompensation
The process of removing the dentoalveolar compensations that
may be present (by re-establishing the correct tooth position
with regard to the skeletal base), usually prior to surgical
correction of a skeletal malocclusion.
[See Dentoalveolar compensation]
Decompression
Force delivered by a component of an appliance that has been activated previously by elastically
constricting its characteristic shape (e.g. the compression of an open coil spring).
[Compare with Traction]
Decompression of a joint (Unloading of a joint)
Removal or release of pressure (stress) from a joint.
Deep bite
Excessive overbite. Type of malocclusion in which the vertical overlap of the anterior teeth is
increased beyond the ideal relationship; it is frequently associated with decreased vertical facial
dimensions. Impingement of the mandibular incisors in the mucosa palatal to the maxillary incisors
commonly is seen in malocclusions with extremely deep bite. As well, in some Class II, Division 2
malocclusions with minimal overjet the retroclined maxillary incisors may impinge in the keratinized
tissue labial to the mandibular incisors, causing gingival recession.
Deflection
A bending type of deformation, such as the deviation from the straight line (curving or arching) of a
beam under an applied load.
Deflection (of the mandible on opening)
Eccentric displacement of the mandible away from the midsagittal plane on mouth opening, without
return to the centered position upon full opening.
[Compare with Deviation (of the mandible on opening)]
Deformable body
A body that changes its shape when subjected to external forces, as opposed to a rigid body (an
ideal concept).
Deformation
A change in geometry (size and/or shape) of a body produced by the application of a mechanical
force: an adaptive process of materials to stress.
SUBTERMS:
Deformation
• Elastic deformation
A temporary change of shape brought about on a body by the application of a mechanical force,
within the elastic limit of the material from which the body is made. Upon removal of the deforming
force there is full recovery to the original configuration, as the atoms in the crystalline structure of
the body that were temporarily displaced resume their original position.
Deformation
• Permanent (Plastic, Inelastic) deformation
A permanent change of shape or dimension brought about on a body by a mechanical force that
exceeds the proportional limit of the material from which the body is made. The material will not
recover its original shape on removal of the deforming force, as a permanent change has occurred
in its crystalline structure.
Deformable body
A body that changes its shape when subjected to external forces, as opposed to a rigid body (an
ideal concept).
Degeneration
Deterioration of soft tissue, cartilage and bone into a tissue of inferior quality. When referring to a
complex structure such as a joint or articulation, it describes the failure to adapt to loading forces,
resulting in impaired function.
Deglutition
[See Swallow]
Degrees of freedom
The number of independent coordinates required to specify the complete position of a body. For
example, a body pivoting about a fixed axis has a single degree of freedom, reflecting the fact that
motion is permitted in only one plane. A rigid body in space (such as a tooth) has six degrees of
freedom, corresponding to its six possible motions: linear motion along the x-, y- and z- axes and
angular motion (rotation) about the three axes x-, y- and z-.
Dehiscence
An isolated vertical soft tissue and bony defect, exposing a part of the root of a tooth. It occurs
more commonly on the vestibular aspect of anterior teeth, especially mandibular incisors.
Delaire face mask
[See Appliance, Face mask (Reverse-pull headgear, Protraction headgear, Face frame)]
Dens evaginatus (Leong’s premolar)
A dental anomaly characterized by a supernumerary cusp on the occlusal aspect of an otherwise
normal tooth. It is thought to be the reverse of dens invaginatus and occurs in approximately 2% of
the Asian and Native American population. Histologically, the extra cusp is composed of a thin
pulpal extension surrounded by dentin and enamel. Dens evaginatus occurs most commonly in
premolars as an extra cusp which may be large enough to cause occlusal interferences. Any
attempt at occlusal equilibration, or simply occlusal wear or trauma, can result in pulpal
degeneration and periapical inflammation. The teeth with the anomaly typically are caries-free, and
may have an immature root. If extractions are indicated as part of the orthodontic treatment plan,
the premolars with the anomaly typically are given preference, as endodontic treatment may have
a poor prognosis due to the immature root or arrested root formation of these teeth.
De-impaction
Any process aiming at bringing an impacted tooth into the dental arch.
Dens invaginatus (Dens in dente)
A developmental defect resulting in invagination of a pit or fissure in the crown, before it is calcified,
into the future pulp space, giving the appearance of “a tooth within a tooth”. The invagination is
partially or completely lined with enamel and may extend all the way to the apex. Dens invaginatus
is occasionally seen in (peg-shaped) maxillary lateral incisors. In the presence of caries an acute
or chronic pulpal inflammation could rapidly occur, and thus these teeth should be preferred when
extractions are indicated, especially since their crowns and/or roots typically are malformed.
Dental compensation
[See Dentoalveolar compensation]
Dental mobility
[See Tooth mobility]
Dentinogenesis imperfecta
A hereditary disorder that can appear in several different types, which affects the development of
dentin and may be accompanied by a similar disturbance of the bones. Clinically the teeth may
appear opalescent or gray with bulbous crowns; attrition is rapid and enamel chips easily. Usually,
extensive prosthetic restorations are indicated.
Dentition
The complement of teeth.
SUBTERMS:
Dentition
• Deciduous dentition (Primary dentition)
The deciduous teeth.
Dentition
• Mixed dentition (Transitional dentition)
The dentition in the period spanning from the eruption of the first permanent tooth until the
shedding of the last deciduous tooth, during which both permanent and deciduous teeth are
present in the mouth.
Dentition
• Permanent dentition
The permanent teeth.
Dentoalveolar
Concerning the teeth and the alveolar bone. [The term often is used to indicate a correction that is
achieved by adaptation of the teeth and alveolar processes, without any skeletal effect. ]
Dentoalveolar compensation
The natural adaptive changes of the dentition, which tend to mask the severity of any skeletal
discrepancy that may be present between the maxilla and mandible (e.g. proclination of the
maxillary incisors and retroclination of the mandibular incisors resulting in a positive overjet in a
skeletal Class III malocclusion).
Dento-periosteal fibers
[See Gingival fibers]
Depression of the mandible
[See Arthrokinetics of the TMJ]
Derotation of molars
The term usually is meant to describe the procedure aimed at correction of the mesiolingual
rotation (about the large palatal root) of the maxillary first permanent molars, a common finding in
Class II malocclusions. Derotation of molars can be achieved with various treatment modalities,
e.g. by using a transpalatal arch.
Development
In the normal youngster, growth and development are processes that work in concert with one
another and actually are inseparable. It is helpful, however in understanding the contributions that
each one makes to the progress of individual change to divide them arbitrarily into their actual
areas of manifestation. Therefore development is considered the area of differentiation and
maturation that leads to increase in skill, more comprehensive function and sexual dimorphism in
progress towards maturity.
Growth, arbitrarily separated from development, relates to the changes in physical size, which may
be measured in increments of weight or linear change.
Through this artificial separation of these two elements one is able to note individual changes that
may exhibit an increase in size but be lacking in maturational evolution, whereas, on the other
hand, one may observe conditions in which the natural maturational processes toward adulthood
take place without a significant or measurable increase in size.
[See Growth]
Developmental guidance
An orthodontic and orthopedic effort to influence changes in the dentition, growth of the jaws, and
functional conditions with the objective of guiding abnormal development into a normal situation.
This generally requires a combination of carefully timed interceptive procedures or appliance
therapies based on supervisory examinations, involving radiographic and other diagnostic records
at various stages of development. This may be required from the earliest date of detection of a
developing malformation until the craniofacial skeleton is mature. [Modified from the AAO Glossary
of Dentofacial Orthopedic Terms, 1993.]
Deviation (of the mandible on opening)
Eccentric displacement of the mandible on mouth opening, away from the midsagittal plane, with
correction to the centered position upon full opening.
[Compare with Deflection (of the mandible on opening)]
Diagnostic setup (Kesling setup)
A laboratory procedure first described by H. D. Kesling. The teeth are cut from a duplicate study
model and realigned in the desired position using wax to evaluate the predicted occlusal result of a
specific orthodontic treatment plan or diagnose a tooth size discrepancy.
Diastema
A space between two adjacent teeth in the same arch.
[See Midline diastema]
Differential force theory
A theory proposed by P. R. Begg (1956), which constitutes the basic philosophy behind the Begg
technique. According to this, the force applied for space closure should be light enough to exceed
the “critical threshold of stress” necessary for tooth movement on the active segment of teeth, but
still be below the “critical stress threshold” for movement of the anchorage segment, so that no
anchorage loss occurs. The area of root surface over which the force is dissipated is a determining
factor for the amount of movement that will be experienced by a specific tooth (or segment of
teeth). Incorporating more teeth in the anchorage segment increases the root surface area,
reducing the stress in the periodontal ligament for the same magnitude of force.
According to the same theory, it is hypothesized that there is a certain level of stress in the
periodontal ligament beyond which hyalinization will occur. If a force of such a high magnitude is
used during space closure, there may be no or little movement of the active segment because of
hyalinization, but the resulting stress over the larger root surface area of the anchorage segment
could exceed its threshold for tooth movement, resulting in anchorage loss.
[See Appliance, Begg appliance (Light-wire appliance)]
Differentiation
The change from generalized cells or tissues to more specialized ones during development. It is a
change in quality or kind.
Digitization (of radiographs)
Conversion of landmarks on a radiograph or tracing to numerical values on a two- (or three-)
dimensional coordinate system, usually for the purpose of computerized cephalometric analysis.
The process allows for automatic measurement of landmark relationships.
[See Computerized cephalometrics]
Dilaceration
A developmental distortion of the form of a tooth, whereby the root or the apex forms an angle with
the long axis of the tooth (i.e. the tooth appears sharply “curved” or “bent”). Dilacerations can occur
as a result of trauma or mechanical impedance of tooth eruption. In the latter situation, the
developing apical part of the erupting tooth is forced to move in a direction opposite to that of
eruption, inducing resorption of bone in an area where it usually does not occur. Teeth with severe
dilaceration may be impossible to align in an ideal way and in severe cases extraction may be
indicated.
Dillon dimple
A latching indentation on the palatal
wall of a sheath, in which the doubled
end of the palatal arch fits tightly,
providing a “lock” to retain the palatal
arch in position. Named after its
innovator, C. F. S. Dillon.
[See Sheath]
Direction (Line of action)
One of the four characteristics of vectorial quantities (the other three are point of application, sense
and magnitude). Direction refers to the line on which the specific vector lies. It can be defined by
specifying the angular deviation (in degrees) of the vector from a given reference line or axis.
Disc-condyle complex
The condyle and its disc articulation, which functions as a simple hinge joint.
Disc displacement (Disc derangement, Disc prolapse, Disc interference disorder)
The dislocation of the articular disc of the temporomandibular joint from its physiologic position on
the head of the condyle. It most often occurs in an anteromedial direction. Disc displacements are
a common etiologic factor for joint sounds (clicks or pops) and often result in an unusual opening
and closing trajectory of the mandible, or in limitation of maximal opening.
SUBTERMS:
Disc displacement (Disc derangement, Disc prolapse, Disc interference disorder)
• Disc displacement with reduction
A situation in which the articular disc of the temporomandibular joint is displaced (usually in an
anteromedial direction) when the mandible is in the intercuspal position, but resumes a normal
anatomic relationship with the condyle (is “re-captured” by the condyle) on mandibular movement.
[See Clicking, Reciprocal clicking]
Disc displacement (Disc derangement, Disc prolapse, Disc interference disorder)
• Disc displacement without reduction
A situation in which the articular disc of the temporomandibular joint is displaced when the
mandible is at the intercuspal position and does not resume a physiologic anatomic relationship
with the condyle upon mandibular movement.
Disc locking
[See Disc displacement (Disc derangement, Disc prolapse, Disc interference disorder), Disc
displacement without reduction]
Disc perforation
A circumscribed tear in the articular disc of the TMJ, usually as a result of a degenerative thinning
in its central portion, permitting communication between the superior and inferior joint spaces and
direct contact between the articular surfaces of the condyle and temporal bone.
Disc-repositioning surgery
Arthrotomy of the TMJ with the purpose of reestablishing a physiologic anatomic disc-to-condyle
relationship.
[See Plication]
Discectomy (Meniscectomy)
Surgical removal of the articular disc of a joint.
“Dished-in” profile
A profile with severely reduced lip prominence. The term originally referred to the side effect of
early orthodontic treatment attempts to “camouflage” an underlying skeletal discrepancy (usually a
Class II malocclusion) by removing premolar teeth (a routine treatment method up until the 1970’s).
More recently, the advancement of orthognathic surgical techniques as well as the rise in
popularity of growth modification in North America have led to increased awareness of the esthetic
facial changes brought upon by various orthodontic treatment options.
[See Camouflage orthodontic treatment]
Dislocation of the condyle (Luxation, Open lock)
Non-reducible displacement of the mandibular condyle in an anterior direction, past the articular
eminence.
Disruption
A morphological defect of an organ, part of an organ, or a larger region of the body resulting from a
breakdown of, or interference with, an originally normal developmental process. An example is an
amputation of a digit in utero, or a atypical facial cleft caused by an amniotic band.
[Compare with Malformation]
[Compare with Deformity]
Dissociation, Point of
[See Burstone’s geometry classes, Geometry IV]
Distal
Away from a point of reference. In the case of teeth, away from the dental midline, along the dental
arch (in a right or left direction when referring to anterior teeth, or in a posterior direction when
referring to posterior teeth).
[Compare with Mesial]
Dissociation, Point of
[See Burstone’s geometry classes, Geometry IV]
Discrepancy
Inconsistency, incongruency or disagreement.
[See Midline discrepancy (Midline shift, Midline deviation)]
[See Tooth size discrepancy (Bolton discrepancy)]
[See Arch length discrepancy]
Disclusion (Disocclusion, Disarticulation)
Separation of the mandible from the maxilla through tooth-guided contacts during mandibular
excursive movements.
Distal tipping
Tipping of the crown of a tooth in the distal direction.
Distalization
The movement of teeth to the distal.
SUBTERMS:
Distalization
• Molar distalization
A treatment procedure designed to provide space for alignment of teeth and achievement of ideal
overjet and overbite, as an alternative to premolar extraction. The procedure can be performed
with or without extraction of the second molars. Various appliances are designed for this purpose,
including the ACCO and pendulum appliances, appliances with compressed coils or repelling
magnets, and extraoral traction appliances.
Distortion
Deviation of a radiographic image from the true outline or shape of the object or structure.
Distoversion
Distal tipping (angulation) of a tooth or group of teeth.
Distraction (of the condyle)
Separation or forced downward movement of the condyle from the articular fossa.
Distraction (of the mandible)
[See Arthrokinetics of the TMJ]
Distraction osteogenesis (Distraction osteosynthesis, Ilizarov technique, Callus distraction,
Callotasis)
A technique for lengthening of long bones of the extremities attributed to G. A. Ilizarov, although it
was first described by A. Codivilla in 1905. Other applications of the method in orthopedics are in
the treatment of fractures or malunions. It also is used in the craniofacial area for the correction of
bone defects in the skull and for the treatment of hypoplasias of the maxilla or the mandible. It
involves a corticotomy followed by gradual distraction of the segments, with formation of new bone
(“regenerate” bone) between them. The distraction can be performed by an extraoral or an
intraoral device containing some type of screw that can be wound gradually, in a manner similar to
rapid maxillary expansion.
The advantage of the technique is that it allows simultaneous expansion of the surrounding soft
tissue envelope and generates bone without the need for a graft. The disadvantages include the
facial scars and inconvenience in the case of an extra-oral procedure, as well as the lack of
adequate control of the direction of movement (mainly in the case of the proximal segments in
mandibular distraction). Furthermore, little is known about the potential implications of a
mandibular distraction procedure on the TMJs.
Dolichocephalic
Anthropometric term denoting an individual with a long, narrow cranial
form; having a cephalic index smaller than 76. Severe dolichocephaly may
result from premature synostosis of the sagittal suture.
[Compare with Brachycephalic]
Donor site
The area of the body from which a graft is taken.
[Compare with Recipient site (Host site)]
Down-fracture (of the maxilla)
An orthognathic procedure in which all or part of the maxillary alveolar and basal bone is separated
from the more superior elements of the midfacial skeleton. The procedure usually involves a Le
Fort I or sometimes a Le Fort II osteotomy.
Down-fracture (of the maxilla)
An orthognathic procedure in which all or part of the maxillary alveolar and basal bone is separated
from the more superior elements of the midfacial skeleton. The procedure usually involves a Le
Fort I or sometimes a Le Fort II osteotomy.
Drift (of bones)
A term established by D. H. Enlow to signify the movement of a bony structure in relation to
adjacent structures, caused by simultaneous bone apposition and resorption processes on
opposing surfaces.
[See Cortical drift]
Drift (of teeth)
Spontaneous movement of teeth without the direct application of orthodontic forces.
SUBTERMS:
Drift (of teeth)
• Distal drift
1. The occasional tendency of teeth mesial to an edentulous space to move distally into it.
2. The spontaneous distal movement of teeth associated with active distalization of adjacent teeth
(e.g. the distal drift of the maxillary premolars following molar distalization. )
Drift (of teeth)
• Mesial drift (Mesial migration, Approximal drift)
A term applied to either a natural developmental phenomenon whereby the posterior teeth
continually move in a mesial direction as a result of interproximal surface wear, or to the tendency
of teeth distal to an edentulous space to move mesially into it.
[See Physiologic tooth movement, Post-eruptive tooth movement]
Dual bite
A situation in which a patient has two positions of habitual occlusion (intercuspal position) that
differ by more than 2 mm.
Ductility
The ability of a material to sustain a large permanent deformation under a tensile load without
rupture. A metal that can be drawn readily into a wire is said to be ductile. Ductility is heavily
dependent on strength.
[Compare with Malleability]
Dynamic friction
[See Friction]
Dynamics
The branch of mechanics that considers forces on bodies which are being accelerated positively or
negatively. Dynamics plays a relatively minor role in orthodontics, where accelerations or
decelerations are practically negligible. Dynamics is comprised further of “kinematics” and
“kinetics.”
SUBTERMS:
Kinematics
Kinetics
Dysfunction
Abnormal, impaired or altered function.
Dysostosis
A pathological condition characterized by defective ossification, especially involving fetal cartilages.
Dysplasia
Abnormality of development.
Eccentric extraoral traction
[See Headgear, Asymmetric headgear (Eccentric headgear)]
Ectopic eruption
The eruption of a tooth in an abnormal position. In the
permanent dentition, this condition occurs most often in
maxillary first molars and maxillary or mandibular incisors and
canines. A typical example is the eruption of a maxillary first
permanent molar in a mesial position under the distal part of the
crown of the adjacent second deciduous molar.
Edge bevel
Rounding of the edges of orthodontic wires with square or
rectangular cross section, as part of their manufacturing process. A certain amount of edge
beveling is desirable to prevent discomfort of the soft tissues and to facilitate engagement of the
archwire in the bracket slot. If the amount of rounding is excessive, it can be of clinical significance
for control of the buccolingual inclination of the teeth provided by the archwire-bracket combination.
Edge-to-edge bite (End-to-end bite)
A situation in which the maxillary and mandibular incisors meet with contact of their incisal edges.
This type of occlusal relationship is most commonly seen in malocclusions with a Class III
component.
Edgewise bracket
[See Appliance, Edgewise appliance (Standard edgewise)]
Elastic limit
The maximum deformation that a body (e.g. orthodontic wire or appliance part) can undergo before
permanent (plastic) deformation occurs. Precise experimental distinction between the proportional
limit and the elastic limit is difficult, and for all practical purposes they can be considered
indistinguishable.
Elastic material
A material that undergoes no permanent deformation (fully recovers its original shape), after it has
been subjected to a certain stress.
[See Elasticity]
Elastic modulus (E)
S. Modulus of elasticity.
[See Modulus of elasticity E (Young’s modulus of elasticity, E-modulus)]
Elastic range
The strain up to which no plastic deformation occurs. [On a stress/strain diagram, the horizontal
(strain) coordinate of the elastic limit. ]
Elastic strength
The load (stress) up to which no plastic deformation occurs. [On a stress/strain diagram, the
vertical (stress) coordinate of the elastic limit. ]
Elasticity
The property of a material to exhibit reversible deformation under load (i.e. changing its shape
without undergoing permanent deformation). An elastic material regains its original shape when the
load is removed.
[See Modulus of elasticity E (Young’s modulus of elasticity, E-modulus)]
Elastomer (Elastomeric material)
A polymer (soft, rubber-like material) containing large molecules with weak interaction among
them, cross-linked at certain points to form a three-dimensional structure. Elastomers may be
stretched when their chains are pulled apart and uncoiled, but on removal of the stress they snap
back to their relaxed state and practically their original dimensions.
Elastomeric modules
Different configurations of elastomeric material in the shape of small circles (ligatures), chains or
threads, with various orthodontic applications.
SUBTERMS:
Elastomeric modules
• Elastomeric chain
A chain of connected elastomeric rings used as a force-producing mechanism for orthodontic tooth
movement. Elastomeric chains can be open or closed, depending on whether or not there is a
distance between the rings at its passive state.
Elastomeric modules
• Elastomeric ligature (“Donut,” “O-ring”)
Small round band of elastomeric material that is stretched around the tie-wings of an orthodontic
bracket for the purpose of preventing disengagement of an archwire or auxiliary from a bracket
slot.
Elastomeric modules
• Elastomeric thread
A stretchable thread made of elastomeric material available in various cross-sectional thicknesses.
It is used as a force-producing mechanism for tooth movement.
Electromyography (EMG)
Detection and recording of changes in the intrinsic electric potentials of skeletal muscles, by means
of surface (“surface EMG”) or needle electrodes (“deep EMG”).
Elevation of the mandible
[See Arthrokinetics of the TMJ]
Elevator masticatory muscles
Paired masseter, medial pterygoid and temporalis muscles, the main action of which is to elevate
the mandible.
Elgiloy wire
[See Cobalt-chromium alloy (Co-Cr, Cobalt-chromium-nickel alloy, Chromium-cobalt alloy)]
Elongation
Overall deformation (elastic and plastic) of a material as a result of tensile force application.
Emergence
The stage of the eruption process involving the initial penetration of the gingiva by the erupting
tooth and its first appearance in the oral cavity. The term sometimes is used to signify breaking
through the alveolar bone during eruption.
Eminectomy
Surgical removal of part of the articular eminence of the temporomandibular joint or recontouring of
its surface. Eminectomy occasionally is contemplated as a treatment modality for some types of
TMD.
Emission scintigraphy (Planar scintigraphy)
Two-dimensional imaging process in which the area of interest is scanned with a gamma camera 2
to 4 hours after the administration of a radio-labeled material. When bone is to be assessed,
technetium 99m is the radioisotope of choice due to its tendency to accumulate in areas of
osteoblastic activity. Increased uptake of the radioisotope in the tissue scanned is indi-cative of
increased cellular activity (as for instance an active area of growth in children, neoplasia or
inflammation).
“En masse” retraction
Retraction of a number of teeth (usually the four incisors, or all six anterior teeth) together, as a
group.
“End-on”
Anteroposterior deviation of an occlusal relationship from the ideal (Angle Class I) by one half cusp
(half the mesiodistal width of a premolar). The term can be used for either Class II or Class III
occlusal relationships.
Enucleation
Surgical removal of a bone cyst together with its lining, or of a
tooth that has not yet emerged into the oral cavity. Enucleation of
premolars sometimes is contemplated as part of a serial extraction
protocol, but depending on the technique and the situation, it
carries a chance of creat-ing a residual bony defect at the site.
Enucleation of the mandibular third molars sometimes is
advocated as a means to increase the available space in a
severely crowded mandibular arch.
Envelope of discrepancy
A diagram devised by W. R. Proffit and J. L. Ackerman to illustrate
graphically the amount of change that can be produced by
orthodontic tooth movement alone (inner envelope), orthodontic
tooth movement combined with growth modification (middle
envelope), and orthognathic surgery (outer envelope) in the
sagittal and vertical planes of space, based on the authors’ clinical
judgment.
Envelope of motion
The three-dimensional space circumscribed by border mandibular movements and by the incisal
and occlusal contacts of a given point of the mandible.
Epicanthal folds
Excess skin and subcutaneous tissue lateral to the nasal bridge, concealing the medial canthi.
Epicanthal folds may be a result of racial phenotype (common in Asians), nasal bridge hypoplasia,
orbital hypotelorism, surgery, or trauma.
Epidemiology
The science concerned with the frequency and distribution of a disease or state. Its focus is on the
total population rather than the individual, and its purpose is disease classification and prevention.
Equilibrium
The state of a body (i.e. a tooth or dental segment) or a system when the sum of all the forces and
the sum of all the moments acting on it is equal to zero. The assumption that a system is in static
equilibrium at a given point is the basis for static analysis of all mechanical systems.
Eruption path
The path traversed by a tooth, through surrounding tissues, from the initiation of its eruptive
movement until its arrival at its functional position in the mouth.
Eruption theories
[See Tooth eruption mechanisms]
Etiologic factors
Factors that may be involved in, or cause the development of a disease or condition.
Euryprosopic
Having a wide and short facial form.
Excursion of the mandible
Movement of the mandible away from the median position or the intercuspal occlusion position.
[See Arthrokinetics of the TMJ]
SUBTERMS:
Excursion of the mandible
• Lateral excursion
Right or left move-ment of the mandible away from the midsagittal plane (to the side).
[Compare with Mediotrusion]
[Compare with Laterotrusion]
Excursion of the mandible
• Protrusive excursion
Anterior movement of the mandible from the intercuspal position.
Exfoliation (Shedding)
Physiological loss of a deciduous tooth prior to the eruption of its successor.
Exostosis
A hyperplastic osseous overgrowth projecting outward from the surface of a bone (e.g. torus
palatinus, torus mandibularis).
Expansion
Enlargement; increase in volume, surface or extent. The term often is used to refer to the process
of widening of the dental arches.
SUBTERMS:
Expansion
• Asymmetric expansion
At the level of the dental arch, asymmetric expansion can be attempted by pitting the segment of
teeth that primarily needs to be expanded against an anchorage segment of increased size. In
practice this is done by incorporating more teeth or a larger palatal surface in the anchorage
segment (anchorage reinforcement) and/or by expanding the teeth on the active segment one at a
time. In any case, some buccal displacement of the teeth in the anchorage segment will be
observed as a side effect.
Expansion
• Rapid maxillary (palatal) expansion (RME, RPE)
A method of increasing the maxillary arch width by opening the midpalatal suture, thereby
achieving some degree of skeletal expansion. The method, which was popularized by A. J. Haas,
involves the use of a fixed (cemented or bonded) maxillary appliance of several possible designs,
using an expansion screw of the same type as in the Hyrax appliance. The screw typically is
activated by at least 0.20 to 0.25 mm (one quarter turn) daily and may produce a force as high as
100 N (10 kg or 20 lb). Expansion usually is continued until the lingual cusps of the maxillary
posterior teeth come into contact with the lingual inclines of the buccal cusps of the mandibular
posterior teeth. A diastema commonly
appears between the central incisors
as the midpalatal suture separates,
which closes spontaneously in the few
weeks following the procedure due to
the pull of the supracrestal fibers.
When active expansion has been
completed, a 3- to 5-month retention
period is recommended with the
appliance in place. It is advocated that
this type of expansion may have more
of a skeletal effect and may minimize
the amount of dental tipping, which is
a common (usually undesirable) side
effect of orthodontic arch expansion.
[See Appliance, Haas appliance
(Haas rapid maxillary expansion
appliance, Haas palatal separator)]
[See Appliance, Hyrax appliance
(Hygienic rapid palatal expander)]
[See Appliance, Expansion appliance]
[See Expansion, Slow maxillary (palatal) expansion (SME or SPE)]
[See Expansion, Surgically assisted rapid maxillary expansion]
Expansion
• Slow maxillary (palatal) expansion (SME or SPE)
A method of increasing the maxillary dental arch width by using a maxillary removable appliance
that normally carries an expansion screw in the midline. The appliance commonly is activated by
0.20 to 0.50 mm (one or two quarter turns) per week and is advocated in patients that require
limited expansion, since it produces expansion mainly
by dental tipping.
[See Appliance, Expansion appliance]
[See Appliance, Haas appliance (Haas rapid maxillary
expansion appliance, Haas palatal separator)]
[See Appliance, Hyrax appliance (Hygienic rapid palatal expander)]
[See Expansion, Rapid maxillary (palatal) expansion (RME, RPE)]
[See Expansion, Surgically assisted rapid maxillary expansion]
Expansion
• Surgically assisted rapid maxillary expansion
In adult patients in whom the midpalatal suture is fused, the resistance to suture separation can be
decreased by bilateral osteotomies of the lateral maxillary buttress, with or without a midpalatal
osteotomy. After the lateral osteotomies are performed, the screw is turned a few times in the
operating room to achieve separation of the suture and is subsequently turned back. The patient
can begin activating the appliance the following day. If correction of a unilateral maxillary palatal
crossbite is necessary, the lateral osteotomy can be made only on one side, thus creating a
differential anchorage situation.
[See Appliance, Expansion appliance]
[See Appliance, Haas appliance (Haas rapid maxillary expansion appliance, Haas palatal
separator)]
[See Appliance, Hyrax appliance (Hygienic rapid palatal expander)]
[See Expansion, Rapid maxillary (palatal) expansion (RME, RPE)]
[See Expansion, Slow maxillary (palatal) expansion (SME or SPE)]
Expansion screw (Jackscrew or Glenn Ross screw)
A mechanical device incorporated in a removable or fixed appliance used to enlarge the dental
arch, usually in the transverse dimension. Expansion screws also can be used as part of a
removable appliance for individual tooth movement or for incisor proclination, as well as in a bone
distraction device for distraction osteogenesis.
Expansion screw key
An instrument used to turn the jackscrew of an expansion appliance.
Extraction
Removal of teeth.
Extraction therapy
Orthodontic treatment requiring the extraction of one or more permanent teeth.
Extraction vs. non-extraction debate
A long-standing controversial issue in orthodontics, over whether or not extraction of permanent
teeth is advisable and necessary as part of orthodontic treatment. This debate started in the early
1900s between E. H. Angle and his former student C. S. Case, and has been continuing, on and
off, ever since. Angle’s thesis was that “there shall be a full complement of teeth and each tooth
shall be made to occupy its normal position. ” He believed in the universal applicability of the
“normal occlusion theory” in which every tooth must have its ideal position and serve its specific
function. Case, on the other hand, defended the judicious use of extraction as a practical
procedure. Following his own precisely set rules, he claimed to extract in only 12% to 15% of his
cases.
The climax of this conflict was a fierce debate in 1911 between Case and M. Dewey (who
represented Angle’s views) at the annual meeting of the National Dental Association (former name
of the ADA). It took many years after this episode for the problem to become a matter of calm and
objective evaluation and respectful appreciation of various points of view, each of which has made
its contribution to orthodontics.
Extraoral traction
The use of extraoral anchorage to apply forces to the dentition or the jaws.
Eyelet
A small orthodontic attachment in the shape of a closed helix soldered onto a bonding base or
welded directly on an orthodontic band. Eyelets mainly are used as handles for elastic traction.
[See Attachment, Orthodontic]
Facebow (of an articulator)
An instrument used to enable the mounting of dental casts on an articulator. The facebow is used
to record the relationship of the patient’s maxillary arch with respect to the opening axis of the
temporomandibular joint and the Frankfort horizontal plane and subsequently to transfer this
relationship to the articulator.
Facebow (of a headgear)
The rigid wire component of a headgear used to transfer extraoral forces to the maxilla (or
occasionally the mandible) and the teeth. A facebow consists of two coplanar metal bows, brazed
or (laser-)welded at the midline. The smaller of the two bows (inner bow) inserts intraorally into
specially manufactured tubes that usually are attached to the bands of the maxillary first molars, or
incorporated into the acrylic of a removable orthodontic appliance. The hooks at both ends of the
larger, outer bow attach to the headgear strap, which produces an extraoral force of variable
direction, depending on the type of headgear (cervical, occipital, etc. ).
Facial asymmetry
A term denoting a dissimilarity or disproportionality between the right and left sides of the face,
usually meant as an undesirable lack of balance. The asymmetry can be due to the underlying
facial skeleton or to the soft tissue drape.
Facial concavity
A term commonly used in profile analysis. A concave facial profile is one in which an inwardly
rounded curve is formed from the forehead to the lips to the chin, as often associated with a Class
III malocclusion (Downs’ angle of convexity (NAPg) has anegative value). [Modified from the AAO
Glossary of Dentofacial Orthopedic Terms, 1993.]
Facial esthetics
A term pertaining to the beauty and appeal of the face. It is an entity which carries a great deal of
subjectivity and is impossible to describe and quantify accurately, but it generally is believed that
symmetry, balance and proportion play a major role.
Facial form
The term usually refers to the configuration (shape) of the face from an anterior (frontal) view.
Facial growth
The physiological process of enlargement and change of the facial skeleton and overlying soft
tissues over time.
Facial pattern
A term generally used to describe the facial configuration, or the directional tendency of facial
growth, from a lateral (profile) view.
Facial type
1. When referring to the lateral (profile) view the facial type can be described as: retrognathic
(opisthognathic), mesognathic (orthognathic) or prognathic.
2. When referring to the frontal view, the three facial type options are: brachycephalic or
euryprosopic (wide and short), mesocephalic or mesoprosopic (average) and dolichocephalic or
leptoprosopic (long and narrow).
Facies
A distinctive facial appearance characteristic of certain disorders (i.e. Down syndrome).
Fatigue
Degradation of materials subjected to a number of load changes. Tendency to fracture under cyclic
stresses.
Fatigue failure
The phenomenon in which stress values well below the ultimate tensile stress of a material can
produce a premature fracture because microscopic flaws grow slowly over many cycles of stress.
Depending on the type of loading situation, a material can exhibit either static or dynamic fatigue
failure.
SUBTERMS:
Fatigue failure
• Dynamic fatigue failure
Most prosthetic and restoration fractures develop progressively over many cycles of periodic
occlusal loading after initiation of a crack from a critical flaw and subsequently by propagation of
the crack until a sudden fracture occurs.
Fatigue failure
• Static fatigue failure
Fracture of a material attributed to the interaction of a constantly applied stress with structural flaws
over time.
Fenestration
Round or oval perforation of the buccal or lingual cortical plate of the alveolar process over the root
of a tooth, which does not involve the alveolar crest.
Ferrite
One of the three possible lattice structures of iron, on which the different classes of steels also are
based.
The body-centered cubic (BCC) structure that pure iron has at room temperature. This phase is
stable in temperatures as high as 912° C.
[See Martensite]
[See Austenite]
FGF
[See Growth factors]
Fibrosis
Formation of fibrous connective tissue to replace normal tissue lost through injury or infection.
Figure-eight ligature
A stainless steel ligature tied around two or more brackets on teeth of the same arch, so that its
two ends cross over each other at the interproximal spaces, forming a figure of eight. It is used to
prevent closed spaces from reopening and to consolidate teeth together, forming a multi-tooth
anchorage segment.
[See Laceback (Lace)]
Finishing
The final stage of fixed appliance orthodontic treatment, during which final detailing takes place to
idealize individual tooth position.
Finite element analysis
An engineering technique of stress analysis, the basic concept of which is the visualization of a
structure as an assemblage of a finite number of discrete structural elements connected at a finite
number of points. The finite elements are formed by figuratively “cutting the original structure into
segments. ” For two-dimensional applications, triangles of various sizes and shapes usually are
the finite elements of choice. Each element retains the mechanical characteristics of the original
structure. Some characteristics of the material have to be specified (depending on whether it is
isotropic or not).
Additionally, a numbering system is required to identify the elements and their connecting points,
called “nodes. ” A coordinate system also must be established to identify uniquely the location of
the nodal points. A large number of simultaneous linear equations are computer-generated, which
establishes compatibility within each element.
The technique has some very distinct advantages as a research tool, among which is the ability to
obtain an estimate of the stresses throughout the structure under consideration. Further, the
inclusion of any type of anisotropy and inhomogeneity conceptually is possible by inserting the
appropriate distribution of material properties at the nodes of the elements. However, when it is
applied to structures such as a tooth, there are some practical limitations, as relatively little is
known about the mechanical properties of dental and especially periodontal tissues.
First transitional period
The period during which the deciduous maxillary and mandibular incisors are replaced by the
permanent incisors (starting from the time of exfoliation of the first deciduous incisor, or from the
time of emergence of the first permanent molar in the mouth, and ending with the eruption of the
last incisor).
Fistula
An abnormal passage or communication between two anatomical cavities, or between an
anatomical cavity and the external body surface.
SUBTERMS:
Fistula
• Oronasal fistula
A fistula connecting the nasal and oral cavities, a common finding in patients with a history of cleft
lip and palate.
Fixation, Surgical
Immobilization of bones following a fracture or a surgical procedure to facilitate and accelerate the
healing process.
SUBTERMS:
Fixation, Surgical
• Intermaxillary fixation (IMF, Maxillo-mandibular fixation)
Traditional method of fixation utilizing stainless steel wires between the maxillary and mandibular
teeth to immobilize the mandible. The wires can be ligated on special hooks soldered or crimped
on the orthodontic archwires, or on arch bars if no fixedorthodontic appliances are present. Typical
duration of IMF is between 6 and 8 weeks, during which the patient is fed liquid diet through the
retromolar area. Intermaxillary fixation is sometimes combined with RIF, in which case its duration
is shorter.
Fixation, Surgical
• Rigid internal fixation (RIF)
Fixation technique in which bony segments are
immobilized by use of small titanium bone plates (fixation
plates) and/or screws across the osteotomy or fracture line.
Bone plates must be contoured carefully to adapt to the
bony surfaces prior to their application. By directly and
rigidly fixing bony segments together, the period of
intermaxillary fixation can be reduced or completely
eliminated after surgery. Rigid internal fixation occasionally
is combined with IMF following orthognathic surgery.
Fixation plate
Titanium plates of various configurations that carry holes
for placement of osseous screws, used for rigid internal
fixation.
Fixation screws
Titanium osseous screws (2.0 to 3.5 mm in diameter or larger) used for stabilization of the bone
plates in rigid internal fixation.
SUBTERMS:
Fixation screws
• Bicortical (Position) screw
Fully threaded screw that binds in both cortices of the two bony segments to which it is applied. As
the screw is tightened, no compression is possible because with the screw
threads engaging both segments, the distance between them is maintained.
Fixation screws
• Lag screw
Partially threaded screw (only has threads close to its tip) that is placed so that
its threads only bind the cortex of
the bony segment that lies farthest
away from the point of entry (i.e. the
medial/distal segment in the case of
a BSSO). The same size hole is
drilled in both segments. As the lag
screw is tightened, it engages the
medial/distal cortex but is free to
rotate in the lateral/proximal cortex,
which eventually produces compression of the
segments against each other.
[See Segment, Distal segment]
Fixture
A device that is firmly fastened in place in a mechanical sense, often used to secure other devices.
[In implantology the term commonly is used to denote the body of an osseointegrated dental
implant (i.e. the portion of the implant that is placed into the bone surgically). ]
Flange
A projecting rim of a removable orthodontic appliance, usually consisting of an acrylic extension of
its main body. Flanges commonly are used in functional appliances to dictate the desired
mandibular position. Vestibular and lingual flanges also serve to remove the pressures from the
surrounding soft tissues on the alveolar processes and teeth.
Flap
A loosened section of tissue, separated from its surrounding tissues except at its base.
SUBTERMS:
Flap
• Repositioned flap
A flap that is moved laterally, coronally or apically to a new position.
Flared teeth
A term used to indicate generalized labial tipping of the maxillary and/or mandibular anterior teeth,
or generalized buccal tipping of posterior teeth.
Flexibility
The property of certain materials that can undergo a larger strain or deformation under the
influence of a relatively small stress. The maximum flexibility is defined as the strain that occurs
when the material is stressed to its proportional limit. It is desirable that orthodontic wires and
springs have a high flexibility as well as a high value for the elastic limit (the stress above which a
wire will not recover its original shape).
Flexion-extension injury (Whiplash)
Sudden, exaggerated traumatic movement of joints through the extremes of their range of motion
with hyperflexion and then hyperextension, resulting in ligamentous sprain, muscular strain,
inflammation and subsequent reflex muscle splinting.
Flux
A substance that promotes the flow of solder over two metal parts by preventing the production of
oxides.
Force
The action of one body on another body that tends to change the state of rest or motion of the
latter. Orthodontics is based on the application of forces on teeth, under the influence of which
tooth movement can be achieved. Force is a vectorial quantity. This means that to adequately
describe a force, its magnitude, direction (line of action), sign (sense) and point of application have
to be defined. Forces are depicted in a coordinate system as vectors. The inclination of the vector
(or the angle between it and a specified reference line or axis) shows the direction of the force, the
length of the vector is proportional to the magnitude of the force, and the arrowhead denotes the
sense of the force. Force, though defined in Newtons, commonly (but, strictly speaking,
inaccurately) is reported in mass units (grams or ounces).
SUBTERMS:
Force
• Component forces
The constituent forces (two or more) of a certain force system.
Force
• Concurrent forces
Two or more forces that have the same point of application.
Force
• Constant force
A force whose magnitude
remains the same as at
the time of activation, for
a certain time interval
(e.g. from one patient visit
to the next). This is a
theoretical concept, as in
clinical reality a true
constant force cannot be
generated, but only
approximated.
Force
• Continuous force
A force that is maintained
between certain intervals
(e.g. does not drop to zero
between patient visits).
Force
• Coplanar forces
Two or more forces whose vectorial direction is on the same plane of space (regardless of their
sense).
Force
• Extraoral force
Force generated by (elastically) deforming an activating element of an orthodontic or orthopedic
appliance, located outside the oral cavity.
[See Anchorage, Extraoral anchorage]
Force
• Heavy force
A force of high magnitude.
[Compare with Force, Light force]
Force
• Intermittent force
A force whose magnitude abruptly drops to zero, as is the case when an orthodontic appliance is
removed by the patient and then resumes again, as when the appliance is re-inserted into the
mouth. Intermittent forces are produced by all appliances that require patient cooperation, such as
removable appliances, headgear, and elastics.
Force
• Interrupted force
A force whose magnitude declines to zero between activations. Most conventional orthodontic
force-producing mechanisms (with the exception of super-elastic wires and coils) generate
interrupted forces that sharply or smoothly decline as some tooth movement occurs, and require
re-activation after a certain time period.
Force
• “Jiggling” forces
Interrupted forces causing the teeth to move in one and then in another direction. Occlusal forces
are thought to be of the “jiggling” type, especially in cases of occlusal trauma. No clear-cut
pressure and tension zones can be identified histologically in affected teeth, but rather there is a
combination of pressure and tension.
[See “Jiggling” (of a tooth)]
[See Round-tripping]
Force
• Light force
A force of low magnitude. The term is used freely and arbitrarily, as there is neither universal
consensus nor sound scientific evidence regarding specific numeric values of magnitude. As well, it
is application-dependent: a force that is considered too high for a certain application may be ideal
for another.
Force
• Normal force (FN)
Any force acting in a direction perpendicular to the plane under consideration. In the case of friction
between two bodies, the force acting in a direction perpendicular to the contacting surfaces. The
magnitude of the normal force is directly proportional to the magnitude of the frictional force.
[See Frictional coefficient (μ)]
Force
• Orthodontic force
Force applied to teeth for the purpose of effecting tooth movement, generally having a magnitude
lower than an orthopedic force. There is no clear distinction between orthodontic and orthopedic
forces in terms of magnitude, but rather many widely variable, arbitrary suggestions exist in the
literature.
Force
• Orthopedic force
Force of higher magnitude in relation to an orthodontic force that, when delivered via the teeth for
12 to 16 hours a day, is supposed to produce a skeletal effect on the maxillofacial complex. Little
scientific evidence exists regarding the magnitude that a force should have in order to produce a
skeletal effect.
Force
• Reaction force
A force identical in magnitude and direction to the active force that is used for a certain orthodontic
application, but of opposite sense.
[See Newton’s laws, III. Law of action and reaction]
Force
• Resultant force
A single force that can substitute two or more individual
forces (component forces) acting on a body, and produce
the same effect on it. It can be expressed as the vector
sum of all component forces. The resultant force can be
determined by one of two methods: the geometric method
or the analytical (trigonometric) method. The analytical
method is preferred when the calculation of a resultant of
coplanar, non-concurrent forces is to be performed.
[See Force composition (Combination of forces)]
Force composition (Combination of forces)
Determination of a resultant force by combination of two or more component forces. When two
component forces have a common point of application, the resultant force is determined by
considering the two vectors to be sides of a parallelogram (geometric method). The resultant force
then is the diagonal of the parallelogram. Its length indicates the magnitude of the resultant force
on the same scale as the original forces. It is important to understand that the resultant force will
have the identical effect on movement of the tooth as the two separate forces. A tooth or a set of
teeth moves in response to the net effect of all forces. If the resultant force is the same, the
movement will be the same, regardless of how many individual forces are applied to the tooth and
regardless of their direction.
To determine the resultant of more than two forces that have a common point of application, a
series of successive parallelograms is constructed. Each time, the resultant from any two forces
replaces those forces and is used to construct the next parallelogram. The sequence in which
forces are combined is of no consequence. However, different forces on a tooth usually are not
applied at the same point, as was assumed previously. According to the law of transmissibility of
force, the point of application of a force may be considered to be anywhere along its line of action.
Consequently, the resultant of two forces with different points of application can be determined by
extending their lines of action to construct a common point of application.
[See Law of transmissibility of force]
Force couple
[See Couple]
Force delivery
A force produced by an orthodontic wire, spring or other auxiliary against a tooth.
Force resolution (Decomposition of forces)
Rather than combining two or more forces into a single resultant, it often is useful to divide a single
force into components at right angles to each other (in two or three dimensions). In this instance,
the parallelogram procedure for composition of forces is reversed. Every force can be considered
as the diagonal of a parallelogram and its components can be drawn along the orthogonal axes.
With more than one force on a tooth, there are two methods for determining the overall component
forces. First, the applied forces can be combined into a single resultant , and then this resultant
can be resolved into its components. Alternatively, the components for each force can be
determined separately, and these components then can be combined to determine the net
component vectors.
[See Force composition (Combination of forces)]
[See Global reference frame]
Force system
Combination of all the forces and moments acting on a body. A 3-dimensional force system
consists of three forces in the principal dimensions of space (Fx, Fy, Fz) and three moments
considered about the three axes (Mx, My, Mz).
SUBTERMS:
Force system
• Applied force system
The force system acting at the point of application of the forces (usually the bracket of a tooth).
Force system
• Consistent force system
A force system that only includes forces and moments that are
desirable for the intended tooth movement.
Force system
• Effective force system
The combination of forces and moments considered at the center
or resistance (CRes) of a body (tooth). It can be used to predict
the type of movement that will occur.
Force system
• Equivalent force systems
Two force systems are equivalent if they cause the same effect on a body. In such a case, the sum
of all the forces and the sum of all the moments in system A have to be equal to those in system B
in all three principal dimensions of space.
Force system
• Inconsistent force system
A force system that contains one or more components
(forces or moments) which are not com-patible with the
intended tooth movement and thus would lead to
unwanted side effects.
Force system
• Statically determinate/indeterminate force system
As stated by the first law of Newton, when a body is in
static equilibrium then the sum of all the forces and the
sum of all the moments acting on it must be equal to
zero (SF = 0 and SM = 0). This generates a total of six
equations in 3 dimensions. When the number of static
equilibrium equations is larger than or equal to the
number of unknowns, then the force system is
determinate, which allows calculation of the applied
forces and moments and prediction (to an extent) of
the resulting tooth movement. This is done by
considering the system at one specific instant in time
and by assuming that it is, at that time, in static
equilibrium.
When a wire connects two teeth (or two segments of teeth that have been joined together so that
they can be assumed to be rigid bodies and their CRes can be estimated) then specific equilibrium
equations may be formulated for them, which allow a description of the force system and an
approximate prediction of the tooth movement that will occur (determinate force system).
Conversely, when a continuous wire engages more than two teeth, the forces and moments acting
on each tooth will interact with the force systems on the adjacent teeth. The result is a situation
with more unknowns than available equilibrium equations, which does not permit analysis of the
resulting forces and moments. The force system then is said to be statically indeterminate.
Mandibular shift (CR-CO shift, Mandibular slide, Forced bite, Slide in centric)
A deflection of the mandible in an anterior, posterior and/or lateral direction, as a result of a
premature contact occurring when the mandible is in centric relation.
[See Occlusal interference (Premature occlusal contact, Supracontact, Deflective occlusal contact,
“Prematurity”), Centric interference]
Forced bite
• Anterior forced bite
A mandibular shift in an anterior direction from CR to CO. An
anterior forced bite may result in an anterior functional
crossbite.
[See Crossbite, Functional crossbite (Pseudo-crossbite)]
Forced bite
• Lateral forced bite
A mandibular shift in a
lateral direction after an
occlusal interference in CR.
A lateral forced bite may be
the cause a posterior functional crossbite.
[See Lateroclusion]
Forced eruption (of a tooth)
The application of orthodontic traction to guide an unerupted or
impacted tooth into its proper position in the dental arch, usually following its surgical exposure.
[See Surgical exposure (of a tooth)]
Formability
The amount of permanent deformation that a material can withstand before failing. In the case of
an orthodontic wire, it represents the amount of permanent bending the wire will tolerate (e.g. while
being formed into a clinically useful spring or loop) before it breaks. High formability is a property
that an ideal wire alloy for orthodontic purposes should possess.
Forme fruste
An atypically mild or incomplete manifestation of a disease or anomaly (e.g. forme fruste cleft lip).
Fracture
Break or discontinuity of an entity (pertaining to a fractured bone, tooth, cartilage, but also wire,
appliance part, ceramic bracket etc. ).
SUBTERMS:
Fracture
• Comminuted fracture
A fracture resulting in multiple small segments, fragments or splinters.
Fracture
• Complex fracture
A fracture involving vital structures adjacent to the fracture site.
Fracture
• Compound (open) fracture
A fracture that has communication with the external surface (e.g. when a bony segment per-forates
the skin or penetrates the oral mucosa).
Fracture
• Displaced fracture
A fracture leading to gross discontinuity of the segments involved, as compared with the normal
anatomy.
Fracture
• Greenstick fracture
An incomplete fracture, in which one side of a bone (one cortical plate) is broken and the other side
is bent (usually the fracture only involves the convex side of the curve).
Fracture
• Intracapsular fracture
A fracture occurring within the capsule of a joint. In the case of the mandibular condyle, an
intracapsular fracture involves the portion of the condylar head that is enclosed by the
temporomandibular joint capsule.
Fracture
• Pathologic fracture
A fracture due to the weakening of bone structure by pathologic processes such as osteomalacia,
osteomyelitis, tumors or osteogenesis imperfecta. In instances of severe destruction of bone,
fractures of the jaws can occur spontaneously during chewing,yawning or talking.
Fracture line
Linear radiolucency seen on a radiograph indicating a break in a bone or tooth.
Free body diagram
A depiction of an object (e.g. a tooth) or system as a free body, upon which all the acting forces
and moments can be considered, and the Newtonian laws of static equilibrium can be applied, for
purposes of mechanical analysis.
Free vector
A vector whose action is not confined to or associated with a unique line in space. A free vector can
produce the same effect on a body regardless of the point on the body where it is applied. The
moment of a couple is an example of a free vector commonly encountered in orthodontics.
Freeway space (Interocclusal clearance, Interocclusal separation)
The distance between the occlusal surfaces of the ma-xillary and mandibular teeth when the
mandible is in its rest position.
Fremitus
Vibration of a tooth due to a premature contact with its antagonist in centric occlusion, which can
be clinically detected by palpation.
Frenectomy
The surgical repositioning or excision of a (labial) frenum in cases where it is felt that its fibers may
interfere with the stability of an orthodontically corrected midline diastema, or with its spontaneous
closure during and after eruption of the maxillary canines. Frenectomy also is indicated when a
frenum is involved in causing localized gingival recession or in cases of ankyloglossia.
[See Ankyloglossia (Tongue-tie)]
Frenum (Frenulum)
A fold of mucous membrane and underlying fibrous tissue.
SUBTERMS:
Buccal frenum
Labial frenum
Lingual frenum
Friction
A force resisting the relative dis-placement of two contacting bodies, in a direction tangent to the
plane of contact. Because of friction, part of the mechanical energy intended for movement of the
two bodies relative to each other is dissipated as thermal energy.
Static friction is the component of frictional force that has to be overcome to initiate motion.
Dynamic (kinetic) friction is the component of frictional force that has to be overcome to maintain
motion. The static frictional force usually is somewhat higher than the dynamic frictional force.
Frictional coefficient (μ)
The law of friction theorized by Coulomb states that the magnitude of the frictional force F is equal
to the product of the normal force FN acting perpendicular to the contact surface, multiplied by the
frictional coefficient μ (F = FN x μ). The frictional coefficient μ depends on the surface roughness
and the combination of the materials involved. It does not depend on the area of the contacting
surfaces and varies only slightly with the velocity of movement. With respect to the type of friction,
a static and a dynamic frictional coefficient can be distinguished.
[See Friction]
Frontal plane (Coronal plane)
Any plane passing longitudinally through the body from side to side, at right angles to the median
plane and dividing the body into front and back parts.
Function
The specialized, normal or proper physiologic activity of an organ or part.
Functional jaw orthopedics
Treatment with functional appliances, making use of forces created by the musculature of the
patient to bring about the desired dentofacial and functional changes.
Functional matrix theory
A hypothesis put forth by M. L. Moss to provide a theoretical explanation of the interrelationship
between osteogenesis and local functional demands. According to Moss, each function in the head
is controlled by a specific functional cranial component. The size, shape and spatial position of the
individual cranial components are relatively independent of one another. Each cranial component
consists of two parts: a “functional matrix” that actually carries out the function and a “skeletal unit,”
whose role is to protect and/or support its specific functional matrix.
Skeletal units may be composed of bone, cartilage or ligaments, but they are not the equivalent of
the “bones” of classic osteology. Skeletal units are distinguished as microskeletal or macroskeletal
units. The sum of all microskeletal units of a skull component makes up the macroskeletal unit. For
example, the mandible is a macroskeletal unit consisting of the condylar, coronoid, angular,
alveolar and basal microskeletal units.
The functional matrix includes the functioning spaces and the soft tissue components required for a
specific function. Teeth also are a functional matrix. When a functional matrix grows, or changes in
size, shape or spatial position, the related skeletal unit will respond accordingly. Movement of teeth
with orthodontic treatment induces changes on the alveolar skeletal unit. In a similar fashion, the
blood vessels and nerves of the mandibular canal have an effect on the mandibular basal
microskeletal unit.
There are two types of functional matrices, the “periosteal” matrix and the “capsular” matrix (their
designation indicates the sites of their activity). The periosteal matrices include muscles and teeth,
whereas the capsular matrices are conceived of as volumes enclosed and protected by both the
neurocranial and the orofacial capsules. In the neural skull the capsular matrix is the neural mass.
In the facial skull this matrix consists of the functioning spaces of the oronasopharyngeal and
orbital cavities.
The capsular and periosteal matrices have completely different effects on the growth process.
Periosteal matrices act upon skeletal units in a direct fashion by the processes of osseous
deposition and resorption (or by the processes of cartilaginous and fibrous tissue manipulation).
Their net effect is to alter the form (size and shape) of their respective skeletal units. On the other
hand, capsular matrices act upon functional cranial components as a whole, in a secondary and
indirect manner, by altering the volume of the capsules within which the functional cranial
components are embedded. The effect of such growth changes is to cause a passive translation of
these cranial components in space.
Cranial growth is a result of combined activity of both types of matrix. Growth is accomplished by
both spatial translation and changes in form.
Fusion
Abnormality of dental morphology involving a union of the
dentin (and enamel) of two teeth, from two separate tooth
buds.
[Compare with Twinning]
[See Concrescence]
[See Gemination]
Genial
Of or pertaining to the chin.
Gemination
Abnormality of dental morphology due to incomplete division of a
single tooth bud.
[Compare with Twinning]
[See Fusion]
[See Concrescence]
Genioplasty
An orthognathic surgical procedure designed to reshape the contour of the chin, giving it a more
esthetic appearance. The procedure is performed intraorally by a vestibular incision and,
depending on the situation, can augment or reduce the prominence of the chin in the
anteroposterior, vertical or transverse plane of space. This can be performed by various
approaches, such as by sliding the distal (genial) segment on the proximal (mandibular) segment
and/or by removal of a wedge of bone. Alloplastic grafts to increase the prominence of the chin are
no longer widely performed, due to their side effects.
Gingiva
The fibrous investing tissue, covered by keratinized epithelium, that immediately surrounds a tooth
and is contiguous with its periodontal ligament and with the mucosal tissues of the oral cavity. Two
types of gingiva can generally be distinguished, attached and free gingiva.
SUBTERMS:
Attached gingiva
Free gingiva
Marginal gingiva
Gingival col
A valley-like depression of the interdental gingiva that connects facial and lingual papillae and
conforms to the shape of the interproximal contact area.
Gingival fibers
Collagen (predominantly), reticulin and elastic fibers, which together with the different cells (e.g.
fibroblasts, macrophages) and the ground substance (proteoglycans and glucoproteins) make up
the connective tissue content ofthe gingiva. Depending on their orientation, they are organized into
five principal groupings: the dento-gingival, alveolo-gingival, dento-periosteal, circular and
transseptal fibers.
SUBTERMS:
Alveolo-gingival fibers
Circular fibers
Dento-gingival fibers
Dento-periosteal fibers
Transseptal fibers
Gingival fibrotomy
[See Circumferential supracrestal fibrotomy (Edwards’ procedure)]
Gingival hyperplasia
An enlargement of the gingiva owing to an increase in the number of cells.
Ginglymoid joint
Hinging joint with one convex and one concave surface, with movement in only one plane of
space.
Glenoid fossa (Mandibular fossa, Temporal fossa, Articular fossa of the temporal bone)
A depression on the inferior surface of the squamous portion of the temporal bone at the base of
the zygomatic process, in which the mandibular condyle is situated. Posterior to the glenoid fossa
is the squamotympanic fissure, which extends mediolaterally. Medially the fossa is limited by the
spine of the sphenoid and laterally by the root of the zygomatic process of the temporal bone.
Anteriorly, the fossa is bounded by the articular eminence. The middle part of the glenoid fossa is
separated from the middle cranial fossa and temporal lobe of the brain by a fairly thin plate of
bone.
Global reference frame
A coordinate system of three mutually perpendicular, intersecting axes (x = sagittal/anteroposterior,
y = vertical/occlusogingival, and z = transverse/mediolateral), used as a reference for various
measurements or vector analysis within a dental arch, or in relation to the entire dentofacial
complex. The x-axis is defined as the intersection of the sagittal and occlusal planes, the y-axis as
the intersection of the sagittal and coronal planes and the z-axis as the intersection of the coronal
and occlusal planes.
Glycosaminoglycans (GAGs)
One of the types of macromolecules that constitute the extracellular matrix. Glycosaminoglycans
are long, unbranched polysaccharide chains composed of repeating disaccharide units. Examples
of GAGs include hyaluronic acid, dermatan sulfate and heparin.
The major characteristic of GAGs is that they are strongly hydrophilic and have the capacity to
withhold water. Thus, GAGs tend to adopt highly extended, so-called random coil conformations,
which occupy a large volume relative to their mass (as their polysaccharide chains are too
inflexible to fold into more compact structures), and they form gels even at very low concentrations.
These gels osmotically absorb large amounts of water into the matrix, enabling the matrix to
withstand compressive forces (in contrast to collagen fibrils, which resist stretching forces).
Cartilage matrix, for example, resists compression by this mechanism.
Goldenhar syndrome
A variant of hemifacial microsomia which additionally may include epibulbar dermoids (soft tissue
tumors on the cornea of the eyes), lipomas around the orbits and vertebral abnormalities.
[See Hemifacial microsomia (First and second branchial arch syndrome)]
Graft
Any material or tissue that is not normally part of an organ or tissue, implanted or transplanted for
the purpose of reconstructing or repairing.
SUBTERMS:
Allogenic graft (Allograft, Allogeneic graft)
Alloplastic graft (Alloplast)
Alveolar bone graft
Autologous (Autogenous) graft
Costochondral graft
Free graft
Free gingival graft (Epithelialized free soft tissue graft)
Full thickness periodontal graft (Mucoperiosteal periodontal graft)
Heterologous (Xenogenic, Heterogenous) graft
Homologous (Homogenous) graft
Isologous (Syngeneic) graft
Split thickness periodontal graft (Partial thickness periodontal graft, Mucosal periodontal graft)
Subepithelial connective tissue graft
Grating joint sound
[See Crepitus (Crepitation, Grating sound)]
Grinding (of teeth)
[See Bruxism]
Group function
Term used to describe a particular scheme of disclusion of the dental arches during a lateral
mandibular excursion. The maxillary and mandibular canines, premolars and, on occasion, molars
on the working side come into contact as the mandible moves laterally, causing disarticulation of
the remaining teeth.
Growth
The age-related increase in size or mass, involving changes in amount of living substance. Growth
is the quantitative aspect of biologic development and is measured in units of increase per units of
time (e.g. inches per year or grams per day). Enlargement of living matter with growth may be the
direct result of cellular division or the indirect product of biologic activity (e.g. bones and teeth).
Although growth typically is equated with enlargement, there are instances in which it results in
normal decrease in size (e.g. the thymus gland after puberty).
[See Development]
Growth center
A location at which independent (genetically controlled) growth occurs, as opposed to a growth
site, which is merely a location at which growth occurs. All growth centers also are growth sites,
whereas the reverse is not true. For example, as a result mainly of transplantation studies, it is now
known that the sutures between the membranous bones of the cranium and the maxilla that
previously were considered as primary growth centers, actually are mere sites of growth.
Conversely, the epiphyseal plates of the long bones are considered to be growth centers, as they
continue to grow when transplanted to a new location or even in culture, indicating an innate
growth potential.
Growth factors
Highly specific serum polypeptides that are directly and specifically involved in stimulating cell
division and/or differentiation. Growth factors act in complex manners in regulating a certain
function: most cell types probably depend on a specific combination of growth factors rather than a
single specific growth factor. Some growth factors are present in the circulation, but most act as
local chemical mediators.
Examples of growth factors include the platelet-derived growth factor (PDGF), which stimulates
proliferation of connective tissue cells and is involved in wound-healing; the insulinlike growth
factors I and II (IGF-I and IGF-II), which stimulate proliferation of fat cells and connective tissue
cells; the transforming growth factor b (TGF-b), which potentates or inhibits the response of most
cells to other growth factors and regulates differentiation of some cell types; and the fibroblast
growth factor (FGF), which stimulates proliferation of many cell types, including fibroblasts,
endothelial cells and myoblasts.
Growth potential
The amount of growth yet to occur.
Growth prediction
In general, an estimation of the amount of growth to be expected. In orthodontics, the term refers
to the estimation of the amount and direction of growth of the bones of the craniofacial skeleton
and the overlying soft tissues. Due to the large inter-individual variation, growth prediction
generally is considered a procedure with relatively low accuracy.
Growth site
A location at which growth occurs.
[Compare with Growth center]
Guidance of eruption
A planned sequence of selective, timed extraction of deciduous teeth with the objective of
facilitating the eruption of the permanent successors into improved positions. Guidance of eruption
involves no extractions of permanent teeth.
[Compare with Serial extraction]
Guide plane
An acrylic surface of a removable or functional appliance that contacts a tooth and transmits the
desired intermittent forces to it. A guide plane also may be the part of the functional appliance that
serves to induce the desired anterior (or posterior) mandibular position.
Guided tissue regeneration (GTR)
Periodontal surgical procedure attempting to regenerate lost periodontal structures through
differential tissue responses. Such procedures make use of barrier techniques, where membranes
made of materials such as expanded polytetrafluoroethylene, polyglactin, polylactic acid and
collagen are employed to exclude the epithelial tissue from the root surface and bone, in the belief
that it interferes with regeneration.
“Gummy” smile
Excessive amount of gingival exposure upon smiling.
[See Tooth-to-lip relationship]
Gurin lock
Adjustable archwire attachment that can be locked
onto an archwire to serve as a stop, without the need
for bending, welding or soldering. A Gurin lock
consists of a small screw that is split along its long
axis, allowing it to be positioned “riding” the archwire
and is secured in place by a hexagon-head lock-nut.
Its advantage is that it can be easily removed or
repositioned along the archwire at any time, and with
no consequences for the archwire. Gurin locks also
are available with hooks, used for attachment of
elastics directly on the archwire (instead of a
Kobayashi hook on a certain tooth).
Hand and wrist radiograph
A radiograph of the carpal, metacarpal and phalangeal bones of the hand and wrist, traditionally
used to determine the skeletal maturation status of children, as skeletal or developmental age does
not always correspond with chronological age. The procedure involves the appraisal of the degree
of development of various carpal, metacarpal and epiphyseal centers of ossification, in comparison
with standards provided from growth studies. The standards are published in an atlas format,
based on the average appearance of a hand and wrist radiograph at various chronological ages.
Hardening
A process used to increase the yield strength and resistance to indentation of a metal.
SUBTERMS:
Hardening
• Work-hardening (Cold-working)
Hardening of a wire by repetitive plastic deformation in the cold state. Placing repetitive bends on
an orthodontic wire increases its strength and hardness because of work-hardening, but also
makes the wire more brittle.
Hardness (of a material)
Resistance to indentation on the surface. Depending on the type of indentor used for the hardness
test, one can distinguish between Brinell hardness, Rockwell hardness and Vickers hardness.
Among the properties that are important to the hardness of a material are strength, proportional
limit, and ductility.
Hawley wire
The labial bow of the Hawley retainer.
[See Labial bow]
[See Retainer, Hawley retainer]
Headgear
Extraoral appliance making use of cervical or cranial anchorage to apply forces to the jaws and
teeth, with the purpose of growth modification or tooth movement. The choice of direction of pull of
the headgear usually is based on the patient’s facial pattern: the more vertically excessive growth
is present, the higher the direction of pull and vice versa. It should be kept in mind, however, that
considerable variation in growth response can occur. [Note: To apply Newton’s laws for theoretical
biomechanical consideration on use of different types of headgears, the facebow is assumed to be
completely rigid. ]
SUBTERMS:
Headgear
• Asymmetric headgear (Eccentric headgear)
A modification in the design of a cervical or straight-pull headgear to
achieve differential magnitude of force between the two sides, when
attempting asymmetric molar distalization. This is usually performed using
a facebow with an asymmetric outer bow. One of the arms is kept longer
(and/or more laterally offset) on the side that requires the greater
distalization to generate a higher force magnitude. The disadvantage of
asymmetric headgear traction is the creation of transverse (buccolingual)
forces, which are difficult to control and may have detrimental effects on the
maxillary arch and the occlusion, especially if an asymmetric headgear is
used for a prolonged period.
Headgear
• Cervical headgear (Kloehn-type headgear, Low-pull headgear)
A type of headgear consisting of a standard facebow inserting into the headgear tubes of the
maxillary first permanent molar attachments and a cervical neckstrap. The cervical headgear,
which was made popular by S. Kloehn, is used to restrict anterior growth of the maxilla and to
distalize or maintain the sagittal position of the maxillary molars. Because of the cervical
anchorage, the direction of the traction with this type of headgear produces an extrusive force on
the maxillary first molars, in addition to the distal force. Depending on the orientation and length of
the outer bow, as well as the number of teeth included, the vector of the force can be made to pass
through, below or above the center of resistance of the unit, resulting in a bodily or tipping
movement.
Headgear
• High-pull headgear (Occipital headgear)
This consists of a high-pull headstrap and a standard facebow, the outer arms of which are cut
shorter and/or bent upwards slightly, so that the force vector is directed through, below or above
the center of resistance of the maxillary first permanent molars, or that of the entire maxilla. The
line of action of the force forms an angle of approximately 45° with the occlusal plane. A high-pull
headgear also can be attached to a removable or functional appliance. When a high-pull headgear
is used directly on the maxillary first permanent molars without any fixed appliances on the
remaining teeth, the insertion of a transpalatal arch on the first molars can serve to prevent
undesirable buccal tipping. The objectives of high-pull headgear treatment are restriction of
anterior and downward maxillary growth and/ or molar distalization, intrusion, or control of their
eruption. The high-pull headgear is commonly used in the treatment of growing patients with Class
II malocclusions, increased vertical dimension, minimal overbite and increased gingival exposure
on smiling.
Headgear
• J-hook headgear
A type of headgear consisting of a high-pull or straight-pull headstrap, attaching to hooks or loops
on the archwire by means of a J-hook assembly through the commisures (i.e. without a facebow).
A J-hook headgear also may be used to provide the necessary force for distal movement of teeth
(such as retraction of canines) with sliding mechanics, by attaching to a sliding jig or directly to the
archwire, mesial to the teeth that are to be retracted. Use in conjunction with a removable
appliance again is feasible.
Headgear
• Mandibular headgear
A headgear directing extraoral forces to the mandibular arch by means of a standard facebow and
a cervical neckstrap. Because of the mobility of the mandible, the line of action of the force
produced by a mandibular headgear changes depending on the degree of opening.
Headgear
• Straight-pull headgear (Combination headgear, Horizontal-pull headgear)
A headgear with a modified headstrap designed to produce a horizontal
force (approximately parallel to the occlusal plane). A similar direction of
force can be produced by simultaneously attaching a high-pull
headstrap and a cervical neckstrap on the same facebow. Varying the
proportions of the total force derived from the two straps, as well as
varying the length and inclination of the outer bow, allows the resultant
vector to be altered.
Headgear
• Vertical-pull headgear
A type of headgear consisting of a standard facebow and a modified headcap, capable of
generating a force vector passing at approximately 65° to the occlusal plane (force vectors passing
anteriorly to that would dislodge the headcap, unless a special custom made headcap is used).
This type of headgear is used when intrusion of the buccal segments is attempted. The headcap of
a vertical-pull headgear is usually versatile, in that it has multiple notches allowing variation in the
direction of the traction force.
Headstrap (Headcap)
The component of an extraoral traction appliance that distributes and transfers reaction forces to
the cranium. The headstrap allows a posterior and upward force vector. It usually carries safetyrelease
force modules to reduce the chance of accidental injury. Modified headstraps also are used
with straight-pull (combination) headgears or with vertical-pull headgears.
[Compare with Neckstrap]
Helix
A spiral bend placed in an orthodontic wire in the shape of a
closed circle. Used as a stop along the archwire, or for the
attachment of various modules such as elastics or J-hooks.
Additionally, helices can be added in the design of various
orthodontic springs to lower their force/deflection rate.
Hemifacial microsomia (First and second branchial arch syndrome)
An umbrella term denoting a family of congenital anomalies characterized by malformation,
underdevelopment or absence of certain structures which are derived from the first and second
branchial arches during embryological development. Variations of the condition have been named
Goldenhar syndrome, oculoauriculovertebral spectrum, necrotic facial dysplasia, otomandibular
dysostosis, and craniofacial microsomia.
The disorder can involve the maxilla, mandible, ears, eyes, orbits, nose, frontonasal structures,
zygoma, facial soft tissue and musculature, parotid gland and the facial nerve. Unilateral or
bilateral cleft lip and/or palate can be co-existing in 7% to 15% of the cases. Cardiac, renal,
vertebral and central nervous system abnormalities also have been reported.
The exact mechanism of its etiology remains unknown; however, vascular abnormalities,
disturbance of neural crest cell migration, chromosomal abnormalities and certain teratologic
agents have been hypothesized. The frequency is approximately 1:5600 live births and there
seems to be a male predominance of about 3:2 and a predominance of 3:2 of right-sided versus
left-sided involvement in truly unilateral cases.
The disorder is expressed to varying degrees, ranging from a mild facial asymmetry to involvement
of many facial structures, unilateral or bilateral, which can be functionally and psychologically
debilitating. The clinical appearance most often involves a unilateral hypoplasia of the mandibular
condyle and ramus, leading to deviation of the chin to the affected
side. Depending on the severity, a number of mandibular posterior
teeth may be missing ipsilaterally. Canting of the maxillary occlusal
plane (up on the affected side) is a common finding, as are
preauricular tags of skin and cartilage.
Treatment of patients with hemifacial microsomia often includes
multi-stage procedures such as reconstruction of the mandibular
condyle and/or fossa, microvascular free-flap transfer for soft tissue
augmentation, auricular reconstruction, facial reanimation,
functional appliance treatment, ramus lengthening by distraction
osteogenesis or bimaxillary orthognathic surgery.
Hemisection (of a tooth)
The surgical separation of an endodontically treated multi-rooted
tooth (most commonly a mandibular molar) through the furcation.
“High-angle” patient (“Vertical” patient, Long face syndrome, Hyperdivergent face)
A general term used to describe a patient with a predominantly vertical growth pattern, a long lower
face height and a steep mandibular plane. A Class II malocclusion with an anterior open bite
tendency may be associated, typically with excessive gingival exposure on smiling, vertical
maxillary excess and lip incompetence. (Referring to the mandibular plane angle. )
[Compare with “Low-angle” patient (“Horizontal” patient, Hypodivergent face)]
Hinge axis
The theoretical single horizontal axis about which the pure rotational movement of the mandible
occurs, during the initial phase of jaw opening.
Holding arch
[See Arch, Lingual arch]
[See Arch, Nance holding arch]
Homeostasis of the dentition
The state of equilibrium of the position of the teeth, as determined by their morphology, the
relationship between their supporting bones, the occlusion, the periodontium and forces from
muscles and other structures involved.
Hooks
Attachments soldered, welded or crimped onto an orthodontic
archwire, to aid in placement of elastics, headgear (i.e. J-hook), elastic
chains, etc. , or to facilitate intermaxillary fixation during orthognathic
surgery.
Howes’ analysis
A plaster cast analysis aimed at evaluating the relationship of the maxillary and mandibular dental
arch width to the width of the respective apical bases, taking into account the existing tooth
material.
According to A. E. Howes, the ratio of the premolar width (the linear distance between the tips of
the buccal cusps of the first premolars bilaterally) over the existing tooth material (the sum of the
mesiodistal widths of the first permanent molars, premolars, canines and incisors), in either the
maxillary or the mandibular arch, should be approximately 43%. Correspondingly, the ratio of the
canine fossa width (the width of the apical base measured on the plaster cast at the level of the
apex of the first premolars) over the existing tooth material (the sum of the mesiodistal widths of all
the teeth anterior to the second molars, as explained previously) for the same arch should be
approximately 44%, whether this concerns the maxillary or the mandibular arch.
When the former ratio is much smaller than the latter, the arch can be expanded to eliminate any
existing crowding. If the opposite is true, then according to Howes, extractions are indicated in the
presence of crowding.
Howship’s lacunae
Small pits or hollow depressions in bone undergoing resorption, containing osteoclasts. Similar
lacunae also can be found in cementum, in which cementoclasts may or may not be located.
Hyalinization
A term describing the loss of cells from an area of the PDL because of trauma, as seen by light
microscopy. Hyalinization occurs often on the compression side of the PDL during tooth movement.
When this happens, no remodeling of the alveolar bone can occur because no cells are present;
therefore hyalinization causes tooth movement to cease. Only after the hyalinized portion of the
ligament is removed by osteoclasts coming from the bone marrow on the endosteal side, does
tooth movement start again.
[See Bone resorption, Undermining resorption (Indirect resorption)]
[See Bone resorption, Direct resorption (Frontal resorption)]
Hyperdivergent
A facial pattern that is characterized by a steep mandibular plane angle, a long anterior lower facial
height with an open bite tendency, a retrognathic mandible with an associated Class II
malocclusion and lip incompetence. Named so because of the cephalometrically observed
excessive divergence of the skeletal planes (mandibular, occlusal and palatal) in relation to each
other or to the cranial base.
[See Hypodivergent]
[See “High-angle” patient (“Vertical” patient, Long face syndrome, Hyperdivergent face)]
Hypernasality (Rhinolalia aperta)
The defective voice quality that is characteriz-ed by excessive nasal resonance during speech. It
can result from a structural (i.e. hypomobility or shortness of the soft palate in cleft palate patients)
or a functional problem of the velopharyngeal mechanism.
[Compare with Hyponasality (Rhinolalia clausa)]
Hyperplasia
Excessive enlargement of a tissue or structure due to increase in the number of cells.
Hypertrophy
Excessive enlargement of an organ or structure due to increase in the size but not the number of
its individual constituent cells, as well as increase of intercellular matrix.
Hypodivergent
A facial pattern characteriz-ed by relative parallelism of the skeletal planes (mandibular, occlusal
and palatal) in relation to each other or to the cranial base, as observed cephalometrically. This
facial pattern often is associated with a Class II,Division 2 malocclusion typically exhibiting a
decreased gonial angle, short anterior lower facial height, deep overbite, strong chin and retrusive
lips.
[See “Low-angle” patient (“Horizontal” patient, Hypodivergent face)]
[See Hyperdivergent]
Hypodontia
Congenital absence of one or more, but not all teeth.
[Compare with Supernumerary teeth (Hyperodontia)]
[Compare with Anodontia]
Hyponasality (Rhinolalia clausa)
Phonation with insufficient nasal resonance, usually due to a blockage of the nasal airway.
[Compare with Hypernasality (Rhinolalia aperta)]
Hypoplasia
Incomplete or defective development of a tissue or structure. [The term implies fewer than the
usual number of cells. ]
Iatrogenic
An unfavorable response or condition, caused by medical or dental personnel, diagnostic tests or
treatment procedures.
Ideal occlusion
A theoretical concept of an ideal arrangement of the teeth within the dental arches, combined with
an ideal interarch relationship, which concentrates optimal esthetics, function, and stability of the
dentition and supporting structures.
[See Six keys of occlusion]
Idiopathic
Pain, disease or disorder of unknown etiology.
Imbrication
The overlapping of incisors and canines in the same arch, usually due to crowding.
Immobilization
[See Fixation, Surgical]
[See Splinting (of teeth)]
Impaction (of food)
The forceful wedging of food into the interproximal space during mastication.
Impaction (of the maxilla)
An orthognathic surgical procedure involving superior repositioning of the maxilla, usually by
means of a Le Fort I osteotomy. A maxillary impaction is used for correction of a high smile line,
associated with vertical maxillary excess. In the instance of surgical correction of a skeletal open
bite, a differential maxillary impaction is performed, whereby the anterior aspect of the maxilla is
moved superiorly to a lesser extent than its posterior aspect.
Implant
An alloplastic material or device that is surgically placed into the body. In dentistry, implants are
placed beneath the mucosal or periosteal layer or within bone for functional, therapeutic or esthetic
purposes. Root-form, endosseous, screw-threaded implants are the most commonly used implants
in clinical practice.
SUBTERMS:
Endosseous implant
Orthodontic implant
Subperiosteal implant
Transosteal implant
Impression
An accurate negative imprint of the maxillary or mandibular dental arch and surrounding structures,
from which a positive reproduction (cast, model) can be made. When taking an impression for
orthodontic purposes the flanges of the impression tray are extended to allow maximum
reproduction of the alveolar process. Alginate is by far the most commonly used impression
material in orthodontics.
[See Orthodontic casts (Orthodontic models)]
[See Orthodontic impression trays]
Incidence
The number of new patients acquiring a disease or condition over a predetermined time period, as
generated by an analytic epidemiological investigation of a prospective longitudinal nature.
[Compare with Prevalence]
Incisal
Pertaining to, or in the direction of, the incisal edge of the anterior teeth.
Inclination (Third order, “Torque”)
Angular deviation of the long axis of a tooth from a line
perpendicular to the occlusal plane, in the labiolingual, or
buccolingual direction.
[Compare with Angulation (Second order, “Tip”)]
Inclined plane
An oblique surface (slope) used to correct a crossbite of one or more incisors.
The inclined plane can be part of a removable appliance or it can be fixed on the
teeth of the opposing arch. Inclined planes also have been used as part of
functional appliances to induce an anterior or posterior mandibular position.
Index
A relative or arbitrary system of measurement used to describe or quantify a condition. The
purpose of an index is to reduce the multitude of variables that enter into a diagnosis and influence
the assessment of the severity and prognosis of a condition, to a format (numerical or categorical)
that permits direct comparison.
Many indices have been advocated in orthodontics; some have been developed to classify
malocclusion into types (the Angle classification being a prime example), others to record
prevalence of malocclusion in epidemiological studies. In addition, certain occlusal indices (such as
the IOTN and PAR index) are meant mainly as methods of determining the need for treatment, or
as indicators of the clinical outcome of treatment.
SUBTERMS:
Index
• Cephalic index
A numerical expression of the ratio between biparietal diameter
and fronto-occipital diameter of a living person’s head.
[Compare with Index, Cranial. ] The cephalic index is calculated
by the formula “maximum head width x 100/maximum head
length. ” It is used in anthropometry to classify skulls as
dolichocephalic (cephalic index up to 75.9), mesocephalic
(between 76 and 80.9) or brachycephalic (81 or larger).
[Compare with Index, Cranial index]
Index
• Cranial index
The equivalent of the cephalic index in a dry skull; a craniometric measurement.
Index
• Facial index
A numerical expression of the proportionality of the face. The facial index is calculated by the
formula: “facial height x 100/zygomatic width. ” It is used in anthropometry to classify faces as
euryprosopic, mesoprosopic or leptoprosopic.
Index
• Index of orthodontic treatment need (IOTN)
An index developed by P. H. Brook and W. C. Shaw in 1989. The IOTN ranks malocclusions in
terms of the significance of their various components for the individual’s dental health and
perceived esthetic impairment. The intention is to identify those individuals who would most likely
benefit from orthodontic treatment. It incorporates a dental health and an esthetic component. The
dental health component can be applied either clinically or on study casts, by categorizing each
occlusal trait contributing to the malocclusion into one of five grades (grade 1 = no need for
treatment, grade 5 = great need). The measurements are facilitated by a specially designed ruler.
The esthetic component consists of a 10-point scale illustrated by a series of numbered
photographs to which the patient’s situation is compared.
Index
• Irregularity index
An index introduced by R. M. Little in 1975 for standardized assessment of mandibular anterior
crowding. It involves measuring the linear displacement of the anatomic contact points (as
distinguished from the clinical contact points) of each mandibular incisor from the respective points
of the adjacent teeth. The sum of these five displacements represents the relative degree of
anterior irregularity. Perfect alignment from the mesial aspect of the left to the right canine would
yield a score of 0, with increased crowding represented by greater displacement, and thus a higher
index score. The measurements are performed with a caliper, parallel to the occlusal plane.
Vertical discrepancies between adjacent contact points are not taken into account, as it is assumed
that correction of such discrepancies would not appreciably affect anterior arch length. Mesiodistal
interdental spacing also is disregarded, provided the teeth in question are in proper arch form. If
spacing as well as rotations are present, only the labiolingual displacement from the proper arch
form is recorded.
Index
• Peer assessment rating (PAR) index
An index for recording the severity of a malocclusion in the mixed and permanent dentition,
developed in 1987 by a group of 10 orthodontists in Great Britain (British Orthodontic Standards
Working Party). The index consists of a scoring system of study casts, facilitated by a ruler.
Individual scores for the components of alignment and occlusion finally are summed to calculate an
overall score. Thus, a score of zero would indicate perfect alignment and occlusion, with scores
above zero (but rarely beyond 50) indicating increasing levels of irregularity. The index is applied to
both the start and end of treatment study casts, and the change in the total score reflects the
success of treatment with regard to the alignment and occlusion.
Inelastic
Deviating from a proportional relationship of stress and strain.
Inertia
The property of matter that causes it to resist change in motion.
Inferior joint space (Inferior joint compartment)
The intra-articular space between the head of the mandibular condyle and the inferior surface of
the articular disc of the TMJ. During the early opening stage of mandibular movement, only the
inferior joint space is involved (by rotational movement of the condyle).
[See Joint, Temporomandibular joint (TMJ, Craniomandibular articulation)]
[See Superior joint space (Superior joint compartment)]
Informed consent
The outline by any health professional, including the orthodontist, of the patient’s problems along
with the possible solutions, in a simplified fashion comprehensible to the reasonable layman, in
order to obtain the patient’s consent to treatment. The health professional is supposed to establish
treatment priorities through discussion with the patient. Reasonable treatment alternatives and the
risks and benefits of each alternative should be provided, including that of no treatment. In this
way, the patient is able to make an informed decision. Informed consent is a legal requirement
prior to treating patients and is encouraged by the American Association of Orthodontists.
Infraorbital pointer
The component of an articulator facebow that records the position of the infraorbital rim to facilitate
alignment of the plane of the facebow with the Frank-fort horizontal plane.
Infraposition (Infraocclusion)
A situation in which a tooth or group of teeth is positioned below the occlusal plane; commonly due
to a deleterious habit or to ankylosis. Infraposition is a more general term that contains
undereruption.
[Compare with Undereruption (Infraeruption)]
Initiating factors
Factors that cause the onset of a disease or disorder.
Intensifying screen (Rare-earth screen)
A screen used to intensify the latent images on an x-ray film. It usually consists of a thin sheet of
plastic coated with a fluorescent material, which is mounted in the cassette in close contact with
the film. The x-rays cause the screen to produce visible light, which intensifies the generation of
the latent images on the film, greatly reducing the exposure of the patient to radiation.
Interbracket span (Interbracket distance)
The distance between orthodontic brackets (measured between adjacent slot ends) that
determines the length of a straight wire connecting them. The smaller the width of the brackets, the
longer the interbracket span, the lower the load/deflection rate of the wire and vice versa.
[See Load/deflection rate (Force/deflection rate)]
Interceptive orthodontic treatment
Intervention in the incipient stages of a problem to lessen its severity or possible future adverse
effects and to eliminate its cause. Such treatment may take place in the deciduous or transitional
dentition and may include redirection of ectopically erupting teeth, slicing or extraction of deciduous
teeth, correction of isolated dental crossbites or recovery of minor space loss. The presence of
complicating factors such as skeletal disharmonies, overall space deficiency, or other conditions
requiring present or future comprehensive therapy are beyond the realm of interceptive therapy.
[Modified from the AAO Glossary of Dento facial Orthopedic Terms, 1993.]
Interdental spacing
Spacing between the teeth.
Interdigitation (Intercuspation)
The interlocking of the cusps of the posterior teeth in the fossae and embrasures of their
antagonists.
Interlabial gap
The vertical separation of the lips at rest. A 2- to 3-mm interlabial gap generally is considered to be
esthetically pleasing.
[See Cephalometric measurements, Interlabial gap]
Intermaxillary
Between the maxilla and the mandible.
[Compare with Intramaxillary]
Intermediate splint
[See Splint, Surgical splint (Surgical wafer)]
Internal derangement
Disturbed arrangement of intracapsular joint components that interferes with smooth joint
movements. In the TMJ it can be associated with elongation, tear or rupture of the ligaments or
capsule, causing altered disc position or morphology. Although this is not always the case, chronic
dysfunction of internally deranged TMJs generally is thought to follow a progression to more
severe stages of breakdown, eventually leading to degenerative joint disease.
Interocclusal splint
[See Splint]
Interproximal stripping (Interproximal reduction of enamel, Reproximation, Slenderizing)
Reduction of the mesiodistal width of the teeth by removal of interproximal enamel. This procedure
can be achieved by means of handheld or motor-driven abrasive strips, or handpiece-mounted
abrasive discs, or by means of a tapered fissure carbide bur. It most commonly is performed in the
mandibular or maxillary incisor area in patients with a tooth-size discrepancy. Generalized stripping
of the entire arch is advocated by J. J. Sheridan to relieve crowding without extractions. According
to him, up to 0.3 or 0.4 mm of enamel can be removed per tooth surface, depending on the size
and shape of the teeth.
It has been advocated that interproximal stripping, if carried out to an extreme, may cause the
mandibular incisor roots to approximate excessively, resulting in thinning of the interradicular
alveolar bone, perhaps making it more prone to later periodontal bone loss. Another potential side
effect is the resulting enamel roughness that may contribute to increased plaque accumulation.
Interproximal stripping (Interproximal reduction of enamel, Reproximation, Slenderizing)
Reduction of the mesiodistal width of the teeth by removal of interproximal enamel. This procedure
can be achieved by means of handheld or motor-driven abrasive strips, or handpiece-mounted
abrasive discs, or by means of a tapered fissure carbide bur. It most commonly is performed in the
mandibular or maxillary incisor area in patients with a tooth-size discrepancy. Generalized stripping
of the entire arch is advocated by J. J. Sheridan to relieve crowding without extractions. According
to him, up to 0.3 or 0.4 mm of enamel can be removed per tooth surface, depending on the size
and shape of the teeth.
It has been advocated that interproximal stripping, if carried out to an extreme, may cause the
mandibular incisor roots to approximate excessively, resulting in thinning of the interradicular
alveolar bone, perhaps making it more prone to later periodontal bone loss. Another potential side
effect is the resulting enamel roughness that may contribute to increased plaque accumulation.
Interpupillary line
A line connecting the pupils of the eyes, used as a
reference in the evaluation of frontal facial asymmetry.
Intersegmental
Between segments of teeth (usually within the same dental arch).
[Compare with Intrasegmental]
Interstitial growth
Growth within a tissue. Histologically, a characteristic type of growth of soft tissues and cartilage
occurring by a combination of cellular hyperplasia and hypertrophy. Interstitial growth does not
occur in calcified tissues such as teeth or bone.
Intracapsular
Located within the capsule of a joint.
Intracoronal retainer
[See Retainer, Bonded lingual retainer]
Intramaxillary
Within the same dental arch.
[Compare with Intermaxillary]
Intrasegmental
Within the same segment of teeth.
[Compare with Intersegmental]
Invisible braces
A lay term applied to lingual orthodontic appliances, or to those made of a clear material (ceramic
or plastic brackets).
[See Appliance, Lingual appliance ]
Ion implantation
A surface modification technique involving a ballistic process through which an element is
imbedded into the surface of a substrate. The main advantage of this process is that the surface
properties of the substrate are improved, while the bulk properties and tolerances remain
unchanged. Ion implantation is used in orthodontics to optimize the frictional characteristics of b-Ti
archwires.
Isometric contraction
Muscle contraction without change in length.
Isotonic contraction
Muscle contraction with shortening of the muscle length, without appreciable change in magnitude
of the produced force.
Jaw
Either of the two bony structures (maxilla or mandible) in most vertebrates that border the mouth
and bear teeth.
SUBTERMS:
Jaw
• Lower jaw
[See Mandible]
“Jiggling” (of a tooth)
Repetitive limited movement of a tooth in one and then in the opposite direction, as is commonly
thought to occur under the influence of occlusal forces. Most types of orthodontic tooth movement
in reality take place as a series of minute “jiggling” movements. This translates into continuous
reversal of the root surfaces that sustain compression and tension which is, at the histological
level, equivalent to round-tripping.
[See Round-tripping]
Joint
The place of union between two or more bones.
SUBTERMS:
Joint
• Arthrodial joint
A joint that permits gliding movements (translation).
Joint
• Cartilaginous joint
A joint in which cartilage is interposed between the implicated bones and the fibrous tissue (in the
sequence: bone-cartilage-fibrous tissue-cartilage-bone). Examples are the costochondral joint and
the pubic symphysis. Cartilaginous joints permit little if any movement of the bones involved.
Joint
• Fibrous joint
A joint in which the bones are connected by fibrous tissue. Three types are described:
Suture, a joint that permits little or no movement. Its function also is to permit bone growth.
Gomphosis, a joint such as the one that connects a tooth to its surrounding bone by the fibrous
periodontal ligament.
Syndesmosis, a joint in which the two bony components are some distance apart, but are
connected by a ligament that permits limited movement (e.g. the joint between the fibula and tibia,
or that between the radius and ulna).
[See Suture]
Joint
• Ginglymoid joint
A joint that permits hinging movement (rotation) in one plane.
Joint
• Synovial joint
A type of joint by which two bones are united and surrounded by a fibrous capsule, thus creating a
joint cavity. [Note: The name comes from the latin word ova (egg) because the opposing bones of
such joints are separated by an enclosed space filled with fluid which, when examined with the
naked eye, resembles egg white. ] The capsule is continuous with periosteum of the bones
involved in the joint and is lined on its inner surface by a synovial membrane. The synovial
membrane secretes synovial fluid that fills the joint cavity. The articulating surfaces of the bones
are covered with hyaline cartilage (the temporomandibular, acromioclavicular and ster-noclavicular
joints are exceptions in that their articulating surfaces are covered by fibrous tissue). The cavity
may or may not possess a fibrous articular disc, separating it into two compartments. Various
ligaments are associated with synovial joints to strengthen the articulation and limit excess
movement.
Synovial joints are classified further by the number of axes in which the bones involved can move
(uniaxial or multiaxial) and by the shapes of the articulating surfaces (planar, ginglymoid, pivot,
condyloid, saddle, and ball-and-socket). Movements in a synovial joint are initiated and performed
by muscles working together in a highly coordinated manner.
Joint
• Temporomandibular joint (TMJ, Craniomandibular articulation)
Paired synovial joint capable of both gliding (translation) and hinge (rotation) movements; thus
considered a ginglymoarthrodial joint. The TMJ is formed by the mandibular condyle fitting into the
glenoid fossa of the temporal bone. Separating these two bones from direct contact is the articular
disc. In the healthy joint, the articular portion of the disc is composed of dense fibrous connective
tissue, devoid of any nerves or vessels. Conversely the posterior attachment of the disc is richly
vascularized and innervated.
The disc also is attached to the condyle both medially and laterally by collateral (discal) ligaments.
These ligaments permit rotational movement of the disc on the condyle during opening and closing
of the mouth. This so-called condyle-disc complex translates out of the fossa during over-extended
mouth opening.
Surrounding the joint is a fibrous capsule (capsular ligament) that extends from the margins of the
glenoid fossa, including the articular eminence anteriorly, to envelop the head of the condyle before
fusing inferiorly with the periosteum of the condylar process. Other ligaments reinforcing the joint
are the lateral (temporomandibular) ligament, which reinforces the lateral wall of the capsule,
preventing lateral dislocation of the condyle, as well as the sphenomandibular and stylomandibular
ligaments.
In the healthy joint, rotational movement occurs between the condyle and the inferior surface of the
disc (the inferior joint space) during early opening. During later stages of opening, translation takes
place in the space between the superior surface of the disc and the fossa (the superior joint
space). The synovial fluid serves as a lubricant and also acts as a medium for transporting
nutrients to and waste products away from the joint components.
Unlike most synovial joints the articulating surfaces of the TMJs are lined with dense fibrous
connective tissue, not hyaline cartilage. This is an important feature because fibrous connective
tissue has a greater ability to repair itself than does hyaline cartilage. Movement and stability of the
TMJs is achieved by the muscles of mastication. These include the masseter, medial pterygoid and
temporal muscles, which predominantly elevate the mandible; the digastric muscles, which assist
in mandibular depression; the inferior lateral pterygoid muscles, which assist in protruding the
mandible; and the superior lateral pterygoid muscles, which provide stabilization for the condyle
and disc during function.
Joint noises
[See Clicking]
[See Crepitus (Crepitation, Grating sound)]
Joint symptoms
Symptoms of TMD.
“Jumping of the bite”
1. An expression credited to N. W. Kingsley in the late 1800s, referring to the avoidance of the prior
intercuspal position by anterior repositioning of the
mandible. Such an effect can be brought up by a
functional-type appliance for the correction of mandibular
retrognathism.
2. The same expression also is used to connote correction
of an anterior crossbite by movement of the affected tooth
over the opposing dental arch.
[See Appliance, Kingsley appliance (Bite-jumping
appliance)]
[See Appliance, Herbst appliance]
Junctional epithelium (Epithelial attachment)
A single or multiple layer of non-keratinized cells adhering to the tooth surface at the base of the
gingival crevice.
Key ridge
The radiographic image of the zygomatic process of the maxilla as commonly seen on a lateral
cephalometric radiograph.
“Keystoning”
The reshaping of the interproximal aspects of the mandibular
incisors to provide an interlocking pattern to resist rotational
relapse. “Keystoning” is done by oblique interproximal
stripping, so that rotational tendency of one tooth would be counteracted by the reverse rotational
relapse tendency of its adjacent tooth.
Kinesiograph
Instrument used to record and provide graphic representation of mandibular movements.
Kinetic friction
[See Friction]
Kobayashi hook (Kobayashi tie, Kobayashi ligature)
A ligature fabricated from 0.012-inch (0.30-mm) or 0.014-inch (0.35-
mm) annealed stainless steel wire, whose legs are welded onto each
other, forming a helical “hook” at its end. It is placed on a bracket
below the archwire or in the same way as a regular stainless steel
ligature and it is used for the attachment of orthodontic elastics.
Labial
Of or pertaining to the lips, or in a direction towards the lips. Also identifies a surface facing the lips.
[Compare with Lingual]
Labial bow
A part of a removable orthodontic appliance, typically consisting of a stainless steel wire that lies
on (or at a distance from) the labial surface of the maxillary or mandibular anterior teeth, usually at
the mid-crown level. A labial bow may be embedded in the acrylic of the appliance and cross the
occlusal table at the embrasures mesial or distal to the first premolars, or it may be soldered
directly onto the molar clasps. It is used to enhance retention of the appliance, to relieve pressure
from the lips as well as (when activated) to tip the incisors lingually and close spaces. A labial bow
can be covered with clear acrylic in the case of some retainers.
[See Retainer, Hawley retainer]
[See Retainer, Spring retainer (Barrer retainer)]
Labiolingual tipping
Tipping of a tooth in a labiolingual direction.
[See Inclination (Third order, “Torque”)]
Labioversion
Labial inclination of one or more teeth.
Laceback (Lace)
Stainless steel ligature placed passively in a figure-eight
mode (usually from the terminal molar to the canine of the
same quadrant), as part of the leveling and alignment
stage of treatment with the straight-wire appliance. For
example, when a canine is slightly upright at the time of
insertion of the initial archwire, a laceback serves to
maintain the sagittal position of its crown, so that the
angulation of the tooth is improved by distal movement of
the root.
[See Figure-eight ligature]
Lacunae
Small pits or hollow cavities.
[See Howship’s lacunae]
Lateroclusion
A functional posterior cross-bite associated with a lateral shift of the mandible that occurs only in
centric occlusion (CO or ICP). In centric relation (CR) the mandible is centered in the midsagittal
plane. This type of crossbite is caused by dental interferences and can be treated by maxillary
expansion and/or by occlusal equilibration.
[See Crossbite, Functional crossbite (Pseudo-crossbite)]
[See Laterognathia]
[See Forced bite, Lateral forced bite]
Laterognathia
A posterior crossbite in CO, associated with a lateral shift of the mandible that does not improve
when the mandible is in CR (a true skeletal asymmetry). In severe situations the only treatment
option is orthognathic surgery.
[Compare with Lateroclusion]
Laterotrusion
The movement away from the median of the ipsilateral (working) half of the mandible and the
respective condyle, during a lateral mandibular excursion.
[Compare with Mediotrusion]
Lavage
The process of washing out or irrigating a cavity or an organ.
Law of transmissibility of force
According to this law, the point of application of any force applied to a rigid body can be considered
to lie anywhere along the line of action of the force.
For example, a single retraction force on the crown of a maxillary incisor will have the same effect
on the tooth whether it is applied on the labial or on the palatal aspect of the crown, provided the
line of action is the same. Similarly, the outer arms of a facebow used with a high-pull headgear
can be cut short or bent upwards without changing the force system “felt” by the molars, provided
the line of force from the headstrap is the same.
The law of transmissibility of force is applied when combining two or more
forces with different points of application to construct their resultant force.
Leeway space
The difference between the combined width of the deciduous canine, first
and second molars in each quadrant, and their successors (permanent
canine, first and second premolars). The term was introduced by H. N. Nance (1947). The average
value is approximately 1.0 mm for each maxillary quadrant and 1.7 mm for each mandibular
quadrant, although there are large individual variations. These “spaces” normally are closed by
mesial drift of the first permanent molars as the deciduous teeth are replaced.
Le Fort I, II and III surgical procedures
[See Osteotomy, Complete maxillary osteotomy]
Leptoprosopic
Having a narrow and long facial form.
Leveling
The phase of comprehensive orthodontic treatment
aiming at flattening the curve of Spee until the marginal
ridges of all the teeth in the arch lie more or less in the
same horizontal plane. Thus, leveling refers to correction
in the vertical plane.
Leveling wire
Any archwire used for leveling.
Ligament
Flexible band of fibrous tissue composed of parallel collagenous bundles, binding joints together,
as well as connecting various bones and cartilages.
Ligature
A tie that secures an archwire or other auxiliary in the bracket slot, by being placed under the tiewings
of the bracket. Ligatures are typically made of stainless steel wire, rubber, or elastomeric
material.
SUBTERMS:
Stainless steel ligature
Limited orthodontic treatment
Orthodontic treatment with a limited objective, not involving the entire dentition. It may be directed
at the only existing problem, or at only one aspect of a larger problem in which a decision is made
to defer or forego more comprehensive therapy. Examples of this type of treatment would be
single-arch treatment to improve alignment, partial treatment to close or to open space, or to
upright a tooth in preparation for prosthodontic treatment. [Modified from the AAO Glossary of
Dentofacial Orthopedic Terms, 1993.]
Lingual
Of or pertaining to the tongue; or in a direction towards the tongue. Also identifies a surface facing
the tongue.
[Compare with Labial]
Lingual cleat
A low-profile attachment that can be bonded directly to a tooth
or welded on a band. Its functions are to accommodate the
attachment of elastics, to aid as a seating lug during band
fitting, and to facilitate band removal.
Lingual crown torque
[See Torque, Root torque]
[See Torque, Crown torque]
Linguoversion
Lingual inclination of one or more teeth.
Lip exercises
Exercises aiming at stimulating the musculature of the lips, with the objective of achieving a
competent lip seal. A key component of functional appliance treatment, stressed by R. Frдnkel.
Lip incompetence (Incompetent lip seal)
Excessive separation of the lips at rest.
Lip interposition
The habit of placing the lower lip between the maxillary and mandibular
anterior teeth, or between the mandibular anterior teeth and the palate
(often seen in patients with an increased overjet).
Lisping
Incorrect pronunciation of a sibilant or affricate sound, most commonly
heard on /s/ and /z/.
Load/deflection rate (Force/deflection rate)
A mechanical characteristic of orthodontic springs or wires, describing
the dependence of the magnitude of the generated force on the amount of deflection (deformation,
activation). It expresses force per unit displacement of the spring, and is measured in cN/mm (g/
mm). A spring with a low load/deflection rate is capable of generating forces that approximate
constancy and do not depend very much on the amount of activation. The five major parameters
available to the clinician for varying the load/deflection rate are:
1. Wire cross-section
The load/deflection rate varies directly with the fourth power of the diameter of a round wire and
with the third power of the width (large dimension) of a rectangular wire. Therefore, reducing the
cross-section of the wire can reduce the load/deflection characteristics of an orthodontic appliance
significantly.
2. Wire length
The load/deflection rate varies inversely with the third power of the length of a wire segment (or
cantilever); thus small increases in wire length can reduce the load/deflection rate dramatically. In
continuous archwire multi-attachment appliances, the wire length is, to a great extent, dictated by
the interbracket span between adjacent teeth. The addition of loops to the wire can serve in
increasing the length, lowering the load/deflection rate.
3. Wire material
The load/deflection rate is proportional to the modulus of elasticity (E) of the material. For the same
size and cross-sectional shape, a wire material with a low E will deliver less force for an equal
deflection, than a wire with a high E.
4. Wire configuration
Bending loops of various shapes into an archwire reduces its load/deflection rate by increasing the
wire length.
5. Constraint conditions
The load/deflection rate of a wire segment depends on its mode of ligation between two teeth. A
wire segment tightly ligated in two edgewise brackets delivers a much higher load, for a standard
deflection, than a cantilever of the same material, length and cross-section ligated in only one of
the brackets (one fixed end).
[See Orthodontic springs, Cantilever spring]
[See Archwire cross-section]
[See Loop]
[See Interbracket span (Interbracket distance)]
[See Archwire (Arch wire), Multiloop archwire]
[See Modulus of elasticity E (Young’s modulus of elasticity, E-modulus)]
Lock, Archwire
[See Gurin lock]
Locking of a joint
[See Disc displacement (Disc derangement, Disc prolapse, Disc interference disorder), Disc
displacement without reduction]
Long-axis rotation
[See Orthodontic tooth movement, Pure rotation]
Long face syndrome
[See “High-angle” patient (“Vertical” patient, Long face syndrome, Hyperdivergent face)]
Loop
Orthodontic spring of various shapes and configurations. Loops are used for a number of
purposes, such as to lower the load/deflection rate by addition of more wire, to achieve frictionless
tooth movement, to avoid the inconsistency of the force system delivered by a straight wire, and to
achieve dissociation of forces and moments in the created force system (i.e. changes in forces do
not automatically alter the moments)
[See Archwire (Arch wire), Multiloop archwire]
[See Load/deflection rate (Force/deflection rate)]
SUBTERMS:
Loop
• Box loop
A rectangular or square-shaped loop bent into a continuous
archwire (the loop has no free end). It is used to increase
the flexibility of the wire at a certain localized point where
this is necessary (e.g. when there is only one tooth that is
not well aligned within the arch), while maintaining rigidity of
the archwire in the remainder of the arch for anchorage
purposes. A box loop offers flexibility in both the horizontal
and vertical plane.
[Compare with Loop, Rectangular loop]
[See Loop, Closed loop (Reverse loop)]
Loop
• Closed loop (Reverse loop)
A loop bent in such a way that the separation between its vertical
legs is reduced when activated by traction (the base of the loop
remains closed–”safety-pin” principle), in contrast to an open loop.
[See Loop, Box loop]
Loop
• Closing loop
Any loop which, upon mesiodistal-pulling activation, is
capable of generating a force in the direction of the
activation. A closing loop can be open or closed and can
have various configurations. Closing loops are used for
space closure, either by movement of an individual tooth
(e.g. canine retraction), or as part of a closing loop arch for
“en masse” movement of teeth.
[See Arch, Closing-loop arch]
[See Loop, L-loop (Boot loop)]
[See Loop, Vertical loop]
[See Loop, T-loop]
[See Loop, Teardrop loop]
Loop
• L-loop (Boot loop)
An orthodontic loop in the shape of an “L” (or a “boot”). It combines
flexibility in both horizontal (mesiodistal and buccolingual) and
vertical dimension. The L-loop delivers a force system that is
different at the two sides of the loop. As a simple rule, the smaller
moment is developed at the bracket that faces the L-loop.
[See Loop, Closing loop]
[See Loop, T-loop]
Loop
• Omega loop
An W-shaped loop used primarily for space closure, or for attachment of intermaxillary elastics.
Loop
• Open loop
A loop whose vertical leg separation increases when activated by
traction (the base of the loop is open), in contrast to a closed loop.
[Compare with Loop, Closed loop (Reverse loop)]
[See Loop, Vertical loop]
Loop
• Opening loop
A loop used to create space, in a fashion comparable to an open coil spring. The loop is
compressed to engage the archwire in the brackets, so deactivation of the loop will tend to
increase the arch length.
[See Orthodontic springs, Coil spring, Open]
[Compare with Loop, Closing loop]
Loop
• Rectangular loop
A rectangular-shaped loop bent into a segmental wire (the
posteriorly directed, horizontal end of the loop is free). The
rectangular loop is used to overcome problems of inconsistency
of force system delivered by a straight wire, where either the
forces or the moments are in an undesirable direction. The
desired combination of forces and moments can be reached by
varying the point of ligation along the horizontal free end of the
loop, and by controlling the horizontal dimension of the loop.
[Compare with Loop, Vertical loop]
[Compare with Loop, Box loop]
Loop
• T-loop
Orthodontic loop in the shape of a “T. ” A T-loop is basically a double L-loop, but is more flexible in
the vertical plane than an L-loop of the same dimensions that is made from the same orthodontic
wire. Used primarily as a force-producing mechanism for space closure or alignment.
[See Loop, L-loop (Boot loop)]
[See Loop, Rectangular loop]
[See Loop, Closing loop]
Loop
• Teardrop loop
A modified version of a vertical loop with its legs touching each
other at its base, giving it the shape of an inverted teardrop. Its
advantage is that it required less interbracket space than a
regular closed or open loop of the same dimensions.
[See Loop, Open loop]
[See Loop, Vertical loop]
[See Loop, Closing loop]
Loop
• Vertical loop
A simple U-shaped loop that can be bent into a continuous
archwire or used as a segmental spring. The greatest
degree of flexibility of a vertical loop is in the mesiodistal
dimension, somewhat less in the buccolingual, and very
little in the vertical dimension. When preactivation bends
are placed in the wire on either side of a vertical loop, it
behaves according to the V-bend principle. Although it
does reduce the force/deflection rate, when placed
between two misaligned brackets a vertical loop produces
a force system corresponding to that of a straight wire.
[Compare with Loop, Rectangular loop]
[See Loop, Teardrop loop]
[See Loop, Closing loop]
[See Loop, Open loop]
Loop
• Wilson loop
A U-shaped loop, similar in shape, but smaller than a Coffin spring, often incorporated in a
transpalatal arch (midway between the maxillary first molars), or in a lingual arch (mesial to the
mandibular first molars, bilaterally), to facilitate adjustment in the transverse or sagittal direction,
respectively.
“Low-angle” patient (“Horizontal” patient,
Hypodivergent face)
A general term used to describe a patient with a
predominantly horizontal growth pattern, a short
lower face height and a flat mandibular plane. A
Class II malocclusion with a deep, occasionally
impinging overbite may be associated. (Referring to
the mandibular plane angle. )
[Compare with “High-angle” patient (“Vertical”
patient, Long face syndrome, Hyperdivergent face)]
Luxation (of a tooth)
Partial or complete detachment of a tooth from its socket.
[See Subluxation (of a tooth)]
Macrodontia
A term denoting larger than normal tooth size. Although no standardization is agreed upon, two
standard deviations above the mean of the general population can be considered a cut-off point
beyond which a diagnosis of macrodontia can be established.
[Compare with Microdontia]
Macroglossia
Abnormally large tongue, commonly associated with the presence of an open bite and spacing of
teeth. Indentations may be evident on the side of the tongue. Macroglossia is a common finding in
certain pathologic conditions such as Down syndrome, Beckwith-Wiedemann syndrome,
myxedema, cretinism, or hypophyseal gigantism. A partial glossectomy is advocated by some
clinicians as a means of treatment in severe situations.
Magnetic resonance imaging (MRI)
Non-invasive, non-ionizing imaging technique that uses a combination of magnetic fields and
radiofrequency waves. As with computerized tomography, the images can be restricted to narrow
planes and in this way multisectional views of the body can be obtained.
Human tissues consist of molecules contain hydrogen nuclei (protons). Each proton has an axial
spin and because of its charge, behaves like a small magnet. Normally the protons are arranged
randomly; however, when the patient is placed in a strong magnetic field the direction of the spin of
the protons aligns with that of the field. In addition, the protons precess or wobble with a frequency
determined by the strength of the magnetic field, but out of phase with each other. The application
of a pulsed, resonant radiofrequency causes the protons to be deflected from their alignment and
to precess in phase. With cessation of the radiofrequency, the protons realign with the applied
magnetic field by transferring their acquired energy to their surroundings and revert to precessing
out of phase. The rate at which the protons realign is referred to as the “T1 relaxation time”; the
“T2 relaxation time” is the period in which protons remain in phase before returning to a random
pattern. The energy released by the relaxation of the hydrogen nuclei is converted by a computer
into a visual image.
Diagnostic MRI allows multiplanar imaging and offers better soft tissue contrast compared with CT.
Additionally, it has no known harmful effects to the tissues. On the other hand, it does not display
bone as well, since bone has a low signal intensity. Magnetic resonance imaging may be
contraindicated in patients with ferromagnetic surgical clips and cardiac pacemakers.
Magnification
The enlargement of the image of an object on a radiograph in relation to the actual object due to
divergence of the x-ray beam (depending on the object-film distance).
Magnitude
A characteristic of both scalar and vectorial quantities, denoting size or amount, in physical units of
measurement.
Main archwire
[See Arch, Base arch]
Malar midfacial augmentation
Augmentation of the malar and of the infraorbital and paranasal areas, which may be
accomplished by a modified Le Fort I or II osteotomy, or with alloplastic materials or onlay cortical
bone grafts placed simultaneously with a Le Fort I osteotomy.
[See Osteotomy, Complete maxillary osteotomy]
Malformation
A morphological structural defect of an organ, part of an organ, or a larger area of the body
resulting from an intrinsically abnormal developmental process (e.g. cleft lip, or polydactyly).
Malformations may be relatively simple or complex. The later the defect is initiated, the simpler the
malformation. Malformations initiated earlier during organogenesis tend to have more far-reaching
consequences.
[Compare with Disruption]
[Compare with Deformity]
Malformation syndromes
Recognized patterns of malformation presumably having the same etiology and currently not
interpreted as the consequence of a single localized error in morphogenesis (e.g. Down
syndrome).
[See Down syndrome (Trisomy 21)]
Malleability
The ability of a material to sustain considerable permanent deformation without rupture, under
compression (as in hammering, or rolling into a sheet). Malleability is not as dependent on strength
of the material as ductility is. Gold is the most ductile and malleable pure metal and silver is
second.
[Compare with Ductility]
Malocclusion
Any deviation from the normal or ideal occlusion.
[See Angle classification]
Mandible
The lower jaw, consisting of a curved, horizontal portion, the body, and two perpendicular portions,
the rami. Each of the rami carries a coronoid and a condylar process. The condyles articulate with
the temporal fossae by means of the temporomandibular joint. Fifteen pairs of muscles attach on
the mandible. Its embryological development is guided by Meckel’s cartilage. At birth, the bone
consists of two halves united by a synchondrosis (mandibular symphysis), which ossifies during
the first postnatal year.
Mandibular rotation
To visualize the following concepts, one has to imagine the core of the mandible as the bone that
surrounds the inferior alveolar nerve. The rest of the mandible consists of its various functional
processes. If implants are placed in areas of stable bone away from the functional processes, it
can be observed that in most individuals the core of the mandible rotates during growth, in a sense
that would tend to decrease the mandibular plane angle (i.e. counterclockwise, with the standard
head orientation toward the right side). The concept of mandibular rotation during growth was
elucidated mainly by the metallic implant experiments of A. Bjцrk in the 1960s. Following are the
most commonly encountered terms on components of mandibular rotation (the terminology varies
greatly depending on the source):
SUBTERMS:
Mandibular rotation
• Clockwise rotation (Backward rotation, Posterior
rotation)
Displacement of the mandible in the direction of mouth
opening (clockwise, with the patient facing to the right),
due to increased posterior vertical growth. Clockwise
mandibular rotation also can occur as a consequence
of orthodontic treatment, when posterior teeth are
extruded in a non-growing patient. Clockwise rotation
of the mandible usually is accompanied by an increase
of the anterior lower face height and a reduction of the
overbite.
Mandibular rotation
• Counterclockwise rotation (Forward rotation,
Anterior rotation)
Rotation of the mandible in the direction of mouth
closing (counterclockwise, with the patient facing to
the right), due to increased posterior, compared to
anterior growth. Counter-clockwise rotation of the
mandible would tend to cause a relative reduction in
the anterior lower face height and a deepening of the
overbite.
Mandibular rotation
• Intramatrix rotation (External rotation)
Rotation within the body of the mandible, due to angular remodeling of the inferior border relative
to the core of the mandible (which affects the orientation of the mandibular plane with regard to the
cranial base).
Mandibular rotation
• Matrix rotation (Apparent rotation)
Rotation of the entire mandible around its condylar axis (which affects the orientation of the
mandible as a whole relative to the cranial base).
Mandibular rotation
• Total rotation (True rotation, Internal rotation)
The actual rotation of the core of the mandible (the part of the bone that surrounds the inferior
alveolar nerve) relative to the cranial base, which is a combination of the intramatrix and matrix
rotation.
Mandibular shift (CR-CO shift, Mandibular slide, Forced bite, Slide in centric)
A deflection of the mandible in an anterior, posterior and/or lateral direction, as a result of a
premature contact occurring when the mandible is in centric relation.
[See Occlusal interference (Premature occlusal contact, Supracontact, Deflective occlusal contact,
“Prematurity”), Centric interference]
Mandibular symphysis (Mental sym-physis)
The line of fusion of the lateral halves of the anterior portion of the mandible at the median plane. It
is wide open during fetal life and ossifies by intramembranous ossification in the first year of life,
usually before the emergence of the mandibular deciduous central incisors.
Marking pencil (Arch marker)
Wax pencil usually in white or red for marking archwires intraorally to indicate the desired location
for adjustment bends or loops.
Martensite
A body-centered cubic phase in stainless steels, or a monoclinic, triclinic or hexagonal crystalline
structure of nickel-titanium alloys. The martensitic phase of nickel-titanium exists at lower
temperatures and is characterized by high ductility. It is formed as a result of quenching (rapid
cooling) or cold working the austenite phase. [See also Austenite; Martensitic transformation. ]
[See Martensitic transformation]
[See Austenite]
Mandibular shift (CR-CO shift, Mandibular slide, Forced bite, Slide in centric)
A deflection of the mandible in an anterior, posterior and/or lateral direction, as a result of a
premature contact occurring when the mandible is in centric relation.
[See Occlusal interference (Premature occlusal contact, Supracontact, Deflective occlusal contact,
“Prematurity”), Centric interference]
Masticatory muscles
A group of skeletal muscles providing movement of the mandible and safeguarding the stability of
the TMJs. The masticatory muscles involve the masseter, medial pterygoid and temporal muscles,
which predominantly elevate the mandible (mouth closing); the digastric muscles, which assist in
mandibular depression (mouth opening); the inferior lateral pterygoid muscles, which assist in
protrusion and in contralateral movements of the mandible; and the superior lateral pterygoid
muscles, which provide stability for the condyle and disc during function. The masticatory muscles
are recruited during talking, swallowing and masticating, as well as during nonfunctional
(parafunctional) actions such as grinding and clenching. Motor innervation of the muscles of
mastication is supplied by the trigeminal nerve (CV).
[See Muscle]
Materia alba
White accumulation or aggregation of microorganisms, desquamated epithelial cells, blood cells
and food debris, loosely adhered to surfaces of teeth, soft tissues, dental restorations and
orthodontic appliances.
Maturation
The qualitative changes that occur with ripening or aging. Rapid maturation as well as accelerated
physical growth occurs during puberty.
Maxilla (Upper jaw)
An irregularly shaped paired bone that makes up a major part of the bony framework of the facial
skeleton. It consists of the body of the maxilla and the zygomatic, nasal, palatine and alveolar
processes. The suture between the right and left portions of the maxilla persists into adulthood.
Maxillary
Of or pertaining to the upper jaw.
Maxillary incisor-lip line relationship
See Tooth-to-lip relationship.
[See Tooth-to-lip relationship]
Mechanics
The physical science that deals with the state of rest or motion of bodies under the action of forces.
Mechanics includes two sub-disciplines, statics and dynamics, and is also associated very closely
with materials science. In orthodontics the term often is used as a synonym for mechanotherapy.
SUBTERMS:
Mechanics
• Cantilever mechanics
Orthodontic mechanotherapy using
cantilever springs to generate the
appropriate force systems for specific
types of tooth movement. Because full
bracket engagement is allowed only at
the fixed end of the cantilever with onepoint
contact at the other end, a
statically determinate force system is
achieved. This allows determination of
the produced forces and moments at
both ends of the cantilever by simple
measurements and calculations.
Moreover, the cantilever offers the
possibility of a low load/deflection rate
and a relatively long range of
deactivation, generating an almost
continuous force that generally is
considered desirable for tooth
movement.
[See Orthodontic springs, Cantilever spring]
Mechanics
• Class I mechanics
Orthodontic mechanotherapy utilizing intramaxillary anchorage for tooth movement.
Mechanics
• Class II mechanics
Orthodontic mechanotherapy making use of intermaxillary anchorage (e.g. elastics) between the
anterior aspect of the maxillary and the posterior aspect of the mandibular arch.
Mechanics
• Class III mechanics
Orthodontic mechanotherapy utilizing intermaxillary an-chorage (e.g. elastics) between the anterior
aspect of the mandibular and the posterior aspect of the maxillary arch.
Mechanics
• Continuous archwire mechanics
Orthodontic mechanotherapy utilizing continuous archwires in the entire dental arch (as opposed to
segments of archwires encompassing segments of teeth).
Mechanics
• Frictionless mechanics
The use of strategies or appliances that do not involve friction between archwire and bracket
during tooth movement (e.g. retraction of a tooth by means of a segmental spring).
Mechanics
• Intermaxillary mechanics
The application of forces and/or moments from one arch to the other.
Mechanics
• Intersegmental mechanics
The application of forces and/or moments from one segment of teeth to another.
Mechanics
• Intrasegmental mechanics
The application of forces and moments between teeth that belong to the same segment of an arch.
Mechanics
• Segmental arch mechanics (Sectional mechanics)
Orthodontic mechanotherapy in which not all teeth within an arch are included in the same
archwire, but rather anchorage and active segments are created by consolidating teeth together
using wire segments. Various orthodontic loops and springs (e.g. cantilever springs) and different
types of arches (e.g. intrusive arches) are used to generate the force systems required for
movement of the active segments. Advantages of segmental arch mechanics include the
avoidance of friction and the ability to design statically determinate force systems.
Mechanics
• Sliding mechanics
Mechanotherapy involving sliding of brackets along the archwire during tooth movement (i.e. the
classic “pearls on a chain” example). The archwire generates the counter-moment necessary for
bodily movement of the teeth. Frictional forces are present when tooth movement is performed by
sliding mechanics.
Mechanotherapy
Collective term encompassing all procedures, appliances, and strategies adopted in specific
phases of orthodontic treatment.
[See Mechanics]
Meckel’s cartilage
A curved cylindrical rod of cartilage derived from the first branchial arch that embryologically has a
close positional relationship and guides the development of the mandible. The greater part of
Meckel’s cartilage disappears without contributing directly to the formation of the bone of the
mandible. Only a small part of the cartilage between the future mental foramen and the midline
contributes to the mandible by endochondral ossification. The cartilage at the mandibular
symphysis is not derived from Meckel’s cartilage but differentiates from the connective tissue in the
midline. After the 10th embryonic week, by which time the rudimentary mandible is formed (almost
entirely by intramembranous ossification), Meckel’s cartilage forms the malleus and incus of the
inner ear, the anterior ligament of the malleus, and the sphenomandibular ligament.
[Compare with Reichert’s cartilage]
Median plane (Midsagittal plane)
The imaginary plane passing longitudinally through the middle of the body, dividing it into left and
right halves.
[See Sagittal plane (Parasagittal plane)]
Mediolaterally
In a direction perpendicular to the sagittal plane of the dentofacial complex (along the z-axis). For
incisor teeth this coincides with the mesiodistal direction. For all other teeth, it signifies a
buccolingual direction.
[See Global reference frame]
Mediotrusion
Movement in a medial direction of the contralateral (non-working) half of the mandible and the
respective condyle during a lateral mandibular excursion.
[Compare with Laterotrusion]
Mentolabial fold (Labiomental sulcus)
The shallow groove created where the curvature of the lower lip merges with that of the chin.
Mesial
Toward the midline, following the dental arch. The term is used to describe surfaces of teeth as
well as direction.
[Compare with Distal]
Mesial tipping
Tipping of the crown of a tooth in the mesial direction.
Mesiodens
A supernumerary tooth in the midline of the maxillary alveolar
process. A mesiodens often is unerupted, and it may interfere
with the eruption and position of the maxillary permanent
central incisors.
Mesiodistally
In a direction along the dental arch. For incisor teeth this term signifies a direction approximately
perpendicular to the sagittal plane (along the z-axis), whereas for all other teeth it actually indicates
a direction approximately parallel to the sagittal plane (along the x-axis).
[See Global reference frame]
Mesocephalic
Anthropometric term used to denote a cranial form of average proportions (cephalic index between
76.0 and 80.9).
Michigan Growth Study (University of Michigan Growth Study)
The University of Michigan Elementary and Secondary School Growth Study was founded by Dean
W. Olsen in 1935. It consists of 714 subjects, primarily of Northern European ancestry, on whom
anthropometric, psychometric and craniofacial growth data were obtained on an annual basis while
they were enrolled as students in the University School, a laboratory school located within the
School of Education on the Ann Arbor campus. Collection of cephalometric and other data of
orthodontic interest started in 1953 under the direction of R. E. Moyers. The number of annual
records was variable among subjects and depended on the number of years that each student
attended the University School. Major data collection ended in 1970, but several long-term recall
studies have been conducted since that time. The Michigan Growth Study material is currently
housed at the Schools of Education and Dentistry, University of Michigan in Ann Arbor.
Microdontia
A term denoting smaller than normal tooth size.
[Compare with Macrodontia]
Micrognathia
Abnormally small jaw size.
Midline
A central reference line of a structure about which symmetry between the right and left halves can
be evaluated.
SUBTERMS:
Midline
• Facial midline
An imaginary line splitting the face in two approximately equal right and left halves. In the ideal
situation of absolute symmetry, the facial midline can be considered as a perpendicular to the
interpupillary line from glabella, passing through the tip of the nose, the midpoint of the philtrum of
the upper lip and the midline of the chin.
Midline
• Mandibular dental midline
A line perpendicular to the mandibular occlusal plane, passing through the interproximal contact
point between the mandibular central incisors (or, in absence of contact, the midpoint of the
diastema between them).
Midline
• Maxillary dental midline
A line perpendicular to the maxillary occlusal plane, passing through the interproximal contact point
between the maxillary central incisors (or, in absence of contact, the midpoint of the diastema
between them).
Midline
• Midline of the chin
A line drawn perpendicular to the mandibular plane, dividing the chin in two (right and left) halves.
Midline diastema
A space between the central incisors of the maxillary (common) or mandibular arch (relatively
rare), which may be associated with the presence of a hyperplastic labial frenum, or tongue frenum
in the case of a mandibular diastema.
Midline discrepancy (Midline shift, Midline deviation)
Incongruency between the midlines of the maxillary and mandibular dental arch and/or between
them and the facial midline.
Migration, Pathologic
Spontaneous movement of a tooth out of its natural position, usually as a result of periodontal
disease.
Miller classification
A classification of gingival recession, widely used in periodontology, introduced by P. D. Miller
(1985) as follows:
Class I
Gingival recession in which the marginal tissues have not receded beyond the mucogingival
junction and there is no loss of interproximal soft tissue or bone. In such recessions 100% root
coverage is possible.
Class II
Gingival recession in which the marginal tissues have receded beyond the mucogingival junction,
still with no loss of the interproximal soft tissue or bone. Again, 100% root coverage is possible in
such recessions.
Class III
Class I or Class II gingival recession, combined with loss of interproximal bone, such that the soft
tissue now is apical to the cementoenamel interproximal junction but coronal to the marginal tissue.
100% root coverage is not possible.
Class IV
Gingival recession combined with loss of interproximal bone that is such that one or both of the
adjacent interdental areas is level with the marginal gingiva. No root coverage is possible in Class
IV recessions.
Mixed dentition analysis
The analysis of space available for alignment of the permanent teeth, when the patient is in the
mixed dentition (which involves estimation of the size of the unerupted permanent teeth). There are
three basic approaches to this:
1. Measurement of the size of the unerupted teeth on radiographs. This method is best performed
with individual periapical films, but the accuracy is still limited by the inevitable presence of
distortion, especially in the case of the canines. In addition appropriate compensation for
enlargement is required, which dictates the use of a proportionality ratio (e.g. true width of
deciduous molar/radiographically measured width of deciduous molar = true width of unerupted
premolar/radiographically measured width of unerupted premolar).
2. Estimation from proportionality tables, without the use of radiographs. These data have been
tabulated for white American children by R. E. Moyers based on the combined mesiodistal width of
the mandibular permanent incisors, which is used to predict the size of both the mandibular and
maxillary unerupted canines and premolars. The size of the mandibular incisors correlates better
with the size of the maxillary canines and premolars than does the size of the maxillary incisors,
because maxillary lateral incisors show great variability in size and shape. This method shows a
tendency to overestimate the size of unerupted teeth. An alternative method for predicting the size
of the unerupted canines and premolars by using the width of the mandibular incisors is the
method developed by M. M. Tanaka and L. E. Johnston, Jr. According to that, the width of the
mandibular canine and premolars in one quadrant can be calculated by adding 10.5 mm to half of
the measured mesiodistal width of the four mandibular incisors. Similarly, the width of the maxillary
canine and premolars in one quadrant can be determined by adding 11.0 mm to half of the
measured mesiodistal width of the four mandibular incisors. The method shows a small tendency
toward overestimating the unerupted tooth sizes. Its advantage is that it does not require
radiographs or reference tables.
3. Combination of the radiographic and prediction table methods. Since the major problem with
using radiographic images comes in evaluating the canine teeth, another option is to use the size
of the permanent incisors measured from the dental casts and the size of the permanent premolars
measured from the films to predict the size of the unerupted canines. Graphs are available (such
as that by R. N. Staley and R. E. Kerber) that allow determination of the mandibular canine from
the sum of incisor and premolar widths. The technique is limited to the mandibular arch and
requires periapical radiographs.
Mode of force application (Force regime)
The time-related aspect of orthodontic
force application: the magnitude of a
continuous force is more or less
maintained between activations, that of
an intermittent force declines with time
until a reactivation is performed, whereas
that of an interrupted force drops to zero
between activations (the force is
removed temporarily).
[See Force]
Model surgery
A simulation of the actual surgical
procedure using the patient’s presurgical casts, which are mounted on an articulator. The purposes
of this simulation are to verify that the movements planned by the surgical prediction tracing
actually can be performed and to relate the casts in the position where the surgical splints will be
fabricated. If both jaws are to be repositioned, the maxillary cast is moved first and fixed on the
articulator. In this position, the first surgical splint (intermediate splint) is made. Then the
mandibular cast is repositioned to simulate the occlusion at the completion of surgery. The final
surgical splint is made with the casts in this position. The model surgery is based on a combination
of the surgical prediction and the presurgical clinical diagnostic information.
[See Splint, Surgical splint (Surgical wafer)]
Model trimmer
A device used for trimming plaster and stone casts. Its main component is a large rotating grinding
wheel, which is kept wet by a stream of water to reduce dust and keep the cutting wheel clean.
Modeling (of bone)
A process involving independent sites of resorption and formation that change the intrinsic form
(shape and/or size) of a bone, in contrast to the term “remodeling,” which signifies a specific
coupled sequence of resorption and formation events to replace previously existing bone. Bone
modeling is the dominant process in growth as well as in adaptation to applied loads such as those
produced with headgear, rapid palatal expansion, functional appliances, etc. Traumatic or surgical
wounding usually results in intense but localized modeling and remodeling responses. Following
fractures, osteotomies or placement of endosseous implants, the processes of callus formation and
resorption of necrotic osseous margins are modeling processes. In contrast, replacement of the
devitalized cortical bone surrounding these sites is a remodeling activity.
[See Remodeling (of bone)]
Models, Plaster
[See Orthodontic casts (Orthodontic models)]
Modulus of elasticity E (Young’s modulus of elasticity, E-modulus)
The slope of the stress/strain curve in its linear portion (below the elastic limit) (E = s/e). It is an
inherent property of the material, which measures its stiffness. A material with a high modulus of
elasticity deforms less than a material with a low modulus, when subjected to identical loads. The
modulus of elasticity of a certain material is not influenced by its geometrical shape (length and
cross-sectional area) and it cannot be altered appreciably by heat treatment, work-hardening, or
any other type of conditioning. The modulus of elasticity of an orthodontic wire determines its load/
deflection rate, and it can be changed only by changing the wire material.
[See Stress/strain diagram (Stress/strain curve)]
[See Load/deflection rate (Force/deflection rate)]
Moment
Rotational tendency.
SUBTERMS:
Moment
• Counter-moment
When a single force is applied at the bracket of a tooth, uncontrolled tipping probably will result,
due to generation of a moment (since the force is applied at a distance from the center of
resistance of the tooth). This will tend to move the crown in the direction of the force and the apex
in the opposite direction. If bodily movement of the tooth is desired, a reverse moment (countermoment)
must be applied simultaneously to prevent the unwanted movement of the apex.
This counter-moment can be generated either by a second force or, more commonly, by a couple.
When sliding mechanics is used for retraction of a canine, the counter-moment is generated by a
couple, formed by contact of the archwire with the mesial-gingival and distal-occlusal wings of the
canine bracket, following a small initial unopposed distal tipping movement. When a segmental
spring (loop) is used for canine retraction, the counter-moment is generated by the spring itself.
[See Canine retraction]
[See Moment-to-force ratio]
Moment of a couple
Unlike the curvilinear motion produced by a
moment of a force, the moment of a couple
produces a tendency to pure rotation around
the center of mass (when applied on a free
body), or around the center of resistance
(when a partially constrained body, e.g. a
tooth, is involved).
The moment produced by a couple is a
vectorial quantity. It has a magnitude equal to
the product of the magnitude of one of the two
forces F, times the perpendicular distance d
between the two forces (Mcouple = F x d);
thus it is measured in units of force x distance
(i.e. N mm, or g mm). Its direction is
perpendicular to the plane of the pair of the
forces, and its sense is either clockwise or
counterclockwise, as viewed looking into the plane of the couple. A couple can be applied
anywhere on a rigid object, creating the same rotational effect. This is why the moment of a couple
is said to be a free vector.
[See Couple]
Moment of a force
The moment of a force about a specified point or line is a measure of
the potential of that force to rotate the body, upon which the force
acts, about the particular point or line.
The moment M of a force F about a point is also a vectorial quantity.
Its magnitude is given by the formula M = F x d (where d is the
“moment arm”). A moment of a force is also measured in units of
force x distance (i.e. N mm, or g mm). The direction of the moment
vector is perpendicular to the plane defined by the force vector and
the point about which the moment is considered. The sense of the
vector is determined by a rule associated with the rotational
tendency, as viewed from above the plane of the force vector and the
point about which the moment is considered. By convention,
counterclockwise moments (out of the plane) are said to be positive,
whereas clockwise moments (into the plane) are considered
negative.
The shorter the moment arm, the smaller the moment of a force. A
moment of a force acting on a body can be considered about any
specific point on the body; in orthodontics the center of resistance is
commonly used. A force passing through an arbitrary point obviously
produces no moment about it.
Moment arm
The perpendicular distance (d) of the point about which the moment is determined to the line of
action of the force producing the moment.
Moment-to-force ratio
The ratio of magnitudes of the uprighting (counter-)moment applied at the bracket of a tooth to
control the location of the center of rotation, to the tooth-moving force that is applied at the same
point (the bracket).
The counter-moment usually is the moment of a couple. In terms of sense, the counter-moment
always is opposite to that of the moment of the force, relative to the center of resistance. Since
moments are measured in gram millimeters and forces in grams, the ratio of the two has units of
millimeters; this represents the distance away from the bracket that a single force will produce the
same effect. [However, it has become conventional in orthodontics to ignore these units and just
speak of the moment-to-force ratio as a pure number. ]
The moment-to-force ratio is used in two-dimensional analysis as an indicator of the type of tooth
movement that will occur. C. J. Burstone and R. J. Pryputniewicz estimated the different momentto-
force ratios required for various types of tooth movement for a 3-D model of an ideal maxillary
central incisor with intact periodontium. When only a force is applied at the bracket of a tooth (M/F
ratio of zero), the center of rotation is at, or just apical to, its center of resistance. The resulting
tooth movement is uncontrolled tipping. The more the counter-moment increases, the more the
center of rotation moves in an apical direction. With a distance from the bracket to the center of
resistance of 10 mm, the center of rotation approaches infinity as the M/F ratio approaches 10:1.
As soon as the M/F ratio exceeds 10:1, the net moment at the center of resistance changes
direction, since the magnitude of the counter-moment is now greater than that of the moment
produced by the applied force. The center of rotation is slightly incisal to the center of resistance.
When the M/F ratio becomes 12:1 or 13:1, the center of rotation is displaced at the incisal edge,
resulting in pure root movement. Further increase of the M/F ratio up to about 20:1 causes the
center of rotation to gradually move to a location just incisal to the center of resistance. It is
obvious that small changes in the M/F ratio have major effects on the clinically observed tooth
movement.
As mentioned previously, it is the ratio between the applied counter-moment and force (and not
their absolute magnitudes) that determines the type of tooth movement. However, this mechanical
principle does not take into account the fact that the magnitudes of forces and couples are
important in determining the biologic response to an orthodontic force system.
[See Orthodontic tooth movement]
Mouth breathing
The habit of breathing primarily through the oral cavity, which traditionally has been associated with
some detrimental dentofacial changes and associated malocclusion. Specifically, the theory is that
breathing through the mouth, rather than the nose, could bring about some postural changes,
namely tipping of the head back and lowering of the mandible and tongue, in order to facilitate
respiration. If these postural changes are maintained, face height may increase and the posterior
teeth may overerupt, with resulting downward and backward rotation of the mandible, steep
mandibular plane and open bite tendency. As well, the change in equilibrium between the soft
tissues and the jaws and teeth could result in compensatory dental changes, such as a constricted
maxillary arch, tendency to a crossbite and upright mandibular incisors. In addition, mouth
breathing creates xerostomia, which can predispose to gingival hyperplasia and inflammation, as
well as caries, at least in the anterior aspect of the dental arches.
The possible association of mouth breathing and the above described craniofacial pattern, as well
as its relationship to nasal airway obstruction, is yet another controversial issue, which has led to
many referrals of orthodontic patients for adenoidectomy over the years.
[See “Adenoid facies”]
Mucogingival junction (MGJ)
The junction between the keratinized gingiva and the non-keratinized oral mucosa.
Mucosa
The epithelial lining of body cavities opening to the outside, consisting of a mucous membrane.
SUBTERMS:
Alveolar mucosa
Masticatory mucosa
Oral mucosa
Multidisciplinary treatment
Coordinated collaboration of multiple specialties in the treatment of a single individual.
Multifactorial
Resulting from the combined action of several factors.
Muscle
Tissue composed of contractile fibers that effect movements of an organ or body part. Muscle
types include striated (skeletal and cardiac) muscles and non-striated, smooth (visceral) muscles.
SUBTERMS:
Buccinator muscle
Digastric muscle
Lateral (External) pterygoid muscle
Masseter muscle
Medial (Internal) pterygoid muscle
Orbicularis oris
Scalene muscles
Sternocleidomastoid muscle
Suprahyoid muscles
Temporalis muscle
Trapezius muscle
Muscle contraction
The development of tension or shortening of a muscle.
Muscle spasm (Myospasm, Muscle cramp)
Spasmodic continuous involuntary contraction of a muscle or group of muscles, typically
associated with acute pain and dysfunction.
[Compare with Protective muscle splinting (Reflex muscle splinting)]
Myalgia
Muscle pain.
Myofascial
Pertaining to the muscle and its attaching fascia.
Myofascial pain (Myofascial pain dysfunction syndrome, MPDS)
Regional pain referred from or emanating around active myofascial trigger points.
Myofascial trigger point
Hyperirritable spot, usually within a taut band of skeletal muscle or in the muscle fascia that is
painful on compression and can give rise to characteristic referred pain, tenderness and autonomic
phenomena. Myofascial trigger points are subdivided into active and latent.
SUBTERMS:
Myofascial trigger point
• Active myofascial trigger point
Myofascial trigger point responsible for local or referred current pain, or symptoms without
stimulation through palpation.
Myofascial trigger point
• Latent myofascial trigger point
Myofascial trigger point with all the characteristics of an active myofascial trigger point, including
referred pain with palpation, but not currently causing spontaneous clinical pain or symptoms.
Myofunctional therapy (Muscle exercises)
Therapy aiming at improvement of muscle function and the habitual position of soft tissues (e.g.
therapy for correction of a tongue-thrust habit) to prevent or maintain the correction of any occlusal
or dental abnormalities associated with them. The concept was introduced to orthodontics by A.
Rogers in 1918.
Nasal obstruction
Inhibition of normal nasal breathing due to a mechanical impediment of the nasopharyngeal airway.
Nasal obstruction generally induces mouth breathing, but the reverse is not always true (i.e. the
presence of mouth breathing does not necessarily suggest nasal obstruction), as mouth breathing
could be habitual.
[See “Adenoid facies”]
Natural head position
A standardized orientation of the head that is reproducible for each individual and is used as a
means of standardization during analysis of dentofacial morphology. The concept of natural head
position was introduced by C. F. A. Moorrees and M. R Kean in 1958 and now is a common
method of head orientation for cephalometric radiography.
To accomplish natural head position, the patient is asked to look into a mirror placed in front of him/
her at eye level (as if he/she were looking at the horizon), with the interpupillary line parallel to the
floor. Advocates of this method maintain that registration of the head in its natural position while
obtaining a cephalogram has the advantage that an extracranial line (the true vertical or a line
perpendicular to that) can be used as a reference line for cephalometric analysis, thus bypassing
the difficulties imposed by the biologic variation of intracranial reference lines.
[Compare with Natural head posture]
Neckstrap
The component of an extraoral appliance (e.g. cervical headgear) that distributes and transfers
reaction forces to the cervical area.
Neuralgia
Paroxysmal or constant pain, typically with sharp, stabbing, itching or burning character, in the
distribution of a nerve.
Newton’s laws
All principles of mechanics are based on three physical laws presented in 1686 by Sir I. Newton in
his “Philosophea Naturalis Mathematica. ” The laws of Newton are:
SUBTERMS:
Newton’s laws
• I. Law of inertia
When the sum of all the external forces acting on a body is zero, the motion of the body is
unchanged (the body either remains at rest, or continues its motion at a straight line with a
constant velocity).
Newton’s laws
• II. Law of acceleration
If the sum of all the forces acting on a body is not equal to zero, the motion of the body is
accelerated along the line of action of the resultant force. The acceleration is proportional to the
resultant force and inversely proportional to the mass of the body.
Newton’s laws
• III. Law of action and reaction
To every force (action) in a given system, there is an equal and opposite reaction force, so that the
sum of all the forces (SF) and the sum of all the moments (SM) in the system always is equal to
zero.
Neurotrophism
The hypothesis that skeletal growth is under control of the nervous system, assumedly by
transmission of substances through the axons of the nerves, much like neural activity controls
muscle growth and activity.
Neutral position
During the activation process of an orthodontic spring, the position of the spring with only the
activation moments placed on it (but with zero force).
Nickel-titanium alloy (Ni-Ti)
Family of alloys primarily consisting of nickel (approximately 55%), titanium (approximately 45%)
and optionally of third elements such as cobalt or copper. Nickel-titanium alloys were first reported
in the orthodontic literature by G. F. Andreasen in 1971. The name of the first commercially
available product was Nitinol. Nitinol was developed originally for the U. S. Navy, in the early
1960s, by W. F. Buehler, a research metallurgist at the Naval Ordnance Laboratory in Maryland.
[The name “nitinol” is an acronym derived from nickel and titanium composition, along with the
suffix -nol which stands for Naval Ordnance Laboratory. ] Although the original nitinol wire (Unitek/
3M) did not exhibit superelastic behavior, it possessed two features of considerable importance for
clinical orthodontics:
1. A very low elastic modulus (E), corresponding to about one-fifth of the force delivery of stainless
steel wires, and half the force delivery of beta-titanium archwires of the same length and crosssectional
dimensions.
2. An extremely wide working range. A “second generation” superelastic Chinese nickel-titanium
alloy (marketed as “Ni-Ti” by Ormco/Sybron) exhibits non-linear loading and unloading
characteristics more pronounced than those of the original nitinol wire.
A “third generation” Japanese nickel-titanium alloy (marketed as “Sentalloy” by GAC International)
was subsequently introduced, which also exhibits superelastic behavior. [The name Sentalloy is an
acronym of the words superelastic nickel titanium alloy. ] The unloading characteristics of this type
of Ni-Ti alloys exhibit initial and final regions of relatively steep slope, along with an extensive
intermediate region where there is little or no change in stress.
The superelastic behavior and shape memory characteristics of nickel-titanium alloys are based on
a reversible transformation between the austenitic and martensitic Ni-Ti phases. Some of the
available nickel-titanium wires are termed “thermally activated” wires due to the fact that their
transition temperature is close to the level of body temperature.
Nickel-titanium alloys have characteristic properties that are very useful in orthodontics, namely
superelasticity, excellent springback, large working range and low stiffness. However, Ni-Ti wires
cannot be soldered or welded without losing their properties, and their friction coefficient is higher
than that of stainless steel (although still lower than that of beta-titanium). Ion-implantation may aid
in reducing the frictional resistance of nickel-titanium wires.
[See Martensitic transformation]
[See Shape memory]
Nickel-titanium wire
[See Nickel-titanium alloy (Ni-Ti)]
Nightguard (Bruxism appliance)
A removable acrylic interocclusal appliance worn at night to prevent or reduce dental wear resulting
from bruxism.
Nitinol
[See Nickel-titanium alloy (Ni-Ti)]
Nociception
Stimulation of specialized nerve endings designed to transmit information to the central nervous
system concerning potential or actual tissue damage (painful sensation).
Non-extraction therapy
Orthodontic treatment without any extractions of permanent teeth (wisdom teeth generally
excluded).
Non-invasive
Denoting any diagnostic or therapeutic procedure that does not require penetration of the skin or
entrance into a cavity or organ of the body.
Non-occlusion
Any situation in which teeth do not have maximal contact with their antagonists in habitual
occlusion. Non-occlusion may be caused by disturbances in tooth eruption (e.g. ankylosis) or by
factors that inhibit further eruption, such as digit-sucking or tongue interposition. According to its
localization, non-occlusion can be classified as anterior, posterior or total non-occlusion.
[Compare with Open bite (Negative overbite)]
SUBTERMS:
Non-occlusion
• Anterior non-occlusion
Non-occlusion in the incisor area, which may be combined with some degree of vertical overlap of
the incisors, as frequently seen in Class II, Division 1 malocclusions.
Non-occlusion
• Posterior non-occlusion
Non-occlusion in the premolar or molar area, with great variation in the number of teeth and in the
occlusal surfaces involved.
Non-occlusion
• Total non-occlusion
A situation characterized by absence of maximal occlusal contact of all posterior teeth, combined
with an anterior non-occlusion. In total non-occlusions the tongue usually is positioned between all
opposing teeth most of the time.
Non-steroidal anti-inflammatory drug (NSAID)
Class of anti-inflammatory medications that also provide analgesia, but lack the detrimental side
effects associated with steroid use.
Non-working side (Mediotrusive side, Non-functioning side, Balancing side)
The side opposite to the functioning (working) side on a lateral excursion of the mandible. The side
the mandible is moving away from, during a lateral excursion.
Normal occlusion theory of Angle
[See Extraction vs. non-extraction debate]
Obstructive sleep apnea (OSA, Obstructive sleep apnea syndrome, OSAS)
Breathing abnormality occurring during sleep, characterized by repeated collapse of the upper
airway, producing hypopnea, apnea and, ultimately, desaturation of hemoglobin. The hypopneic
and apneic episodes produce frequent arousal from sleep patterns. The effects of repeated
desaturation significantly alter normal cardiovascular and pulmonary function, resulting in
pulmonary and systemic hypertension as well as arrhythmias, which if untreated can lead to death.
The etiology of OSA appears to be neurogenic failure to preserve the patency of the pharyngeal
airway during sleep. The condition often is combined with airway obstruction at various anatomic
locations, such as the nasal cavity, adenoids, soft palate, tonsils or base of the tongue. Obesity is
considered a predisposing factor in the etiology. In the adult OSA population, males are affected 10
to 20 times more often than females. Almost all apneic patients snore loudly at night. The diagnosis
of OSA is made by polysomnography (multiphysiologic sleep recording).
Various treatment modalities advocated include weight loss (if patient is obese), nasal continuous
positive air pressure (nasal CPAP), or surgical uvulo-palato-pharyngoplasty (UPPP). Removable
intra-oral appliances that advance the mandible sometimes are used to re-establish the patency of
the airway, as well as to determine whether an orthognathic surgical correction is indicated.
Obturator
A dental prosthesis or appliance used to close a congenital or acquired opening. Sometimes used
to cover a remaining oronasal fistula or to facilitate the velopharyngeal mechanism in a patient with
a history of cleft lip and palate.
Occlusal
Pertaining to the masticatory surfaces of the posterior teeth. (Also may be used to identify a
coronal direction. )
Occlusal contact
A contact between maxillary and mandibular teeth during occlusion.
SUBTERMS:
Occlusal contact
• Non-working side contact (Mediotrusive contact, Balancing contact)
A contact between maxillary and mandibular teeth on the side opposite to the working side during a
lateral mandibular excursion. [Note: The term “non-working contact” is used when there is at least
one simultaneous contact on the working side. If the occlusal contact on the non-working side
causes disclusion of the teeth on the working side, the term “non-working interference” is used. ]
[See Occlusal interference (Premature occlusal contact, Supracontact, Deflective occlusal contact,
“Prematurity”), Non-working side interference (Mediotrusive side interference, Balancing
interference)]
Occlusal contact
• Working side contact (Laterotrusive occlusal contact)
A contact between maxillary and mandibular teeth on the ipsilateral side during guided lateral
excursive movement of the mandible.
Occlusal dysfunction
A malocclusion with impaired function.
Occlusal equilibration (Occlusal adjustment)
Selective grinding of occlusal surfaces of the teeth in an effort to eliminate premature contacts and
occlusal interferences, to achieve balancing of the functional occlusal load on the teeth, to
eliminate occlusal trauma, to address muscle tension and associated pain, to improve functional
relations or to aid in the stabilization of orthodontic results.
Occlusal equilibrium
The stage of eruptive tooth movement starting at the point that a tooth reaches the occlusal level
and is in complete function. Occlusal equilibrium is divided into juvenile and adult phases.
SUBTERMS:
Occlusal equilibrium
• Adult occlusal equilibrium
The final phase of tooth eruption after the end of the pubertal growth spurt. During this phase the
rate of tooth eruption is extremely slow.
[See Physiologic tooth movement]
[See Post-emergent spurt]
Occlusal equilibrium
• Juvenile occlusal equilibrium
The phase of tooth eruption after the post-emergent spurt and during the period of the pubertal
growth spurt. During the juvenile equilibrium, teeth that are in function erupt at a rate that parallels
the rate of vertical growth of the mandibular ramus. The rate of tooth eruption during this stage is
much slower than during the post-emergent spurt, but faster than during the adult equilibrium.
[See Post-emergent spurt]
[See Physiologic tooth movement]
Occlusal guidance
The contact pattern between teeth during dentally guided mandibular movement away from or
toward maximum intercuspation.
Occlusal interference (Premature occlusal contact, Supracontact, Deflective occlusal
contact, “Prematurity”)
Undesirable occlusal contact that may produce mandibular deviation during closure to maximum
intercuspation or may hinder smooth passage to and from the intercuspal position.
SUBTERMS:
Occlusal interference (Premature occlusal contact, Supracontact, Deflective occlusal contact,
“Prematurity”)
• Centric interference
A premature contact occurring when the mandible closes with the condyles in their optimum
position in the glenoid fossae (centric relation), which causes a deflection (shift) of the mandible in
an anterior, posterior and/or lateral direction.
Occlusal interference (Premature occlusal contact, Supracontact, Deflective occlusal contact,
“Prematurity”)
• Non-working side interference (Mediotrusive side interference, Balancing interference)
A contact between maxillary and mandibular teeth on the non-working side that causes disclusion
of the teeth on the working side during a lateral mandibular excursion.
[Compare with Occlusal contact, Non-working side contact (Mediotrusive contact, Balancing
contact)]
Occlusal interference (Premature occlusal contact, Supracontact, Deflective occlusal contact,
“Prematurity”)
• Protrusive interference
An occlusal contact between maxillary and mandibular posterior teeth discluding the incisors
during a protrusive mandibular excursion.
Occlusal plane (OP)
An imaginary surface that passes through the occlusion of the teeth. This surface usually is curved
and is, strictly speaking, not a plane, but commonly is approximated by one (straight line in the
lateral view), based on specific reference points with in the dental arches. The maxillary occlusal
plane passes through the occlusal cusps of the posterior teeth and the incisal edges of the
maxillary incisors. The mandibular occlusal plane is tangent to the occlusal cusps of the posterior
teeth and the incisal edges of the mandibular incisors.
[See Cephalometric lines (planes), Occlusal plane (OP)]
Occlusal rest (Occlusal lug, Occlusal stop)
The part of a removable appliance that rests on the occlusal surface of a tooth and prevents
movement of the appliance toward the soft tissue. Occlusal rests sometimes are soldered on fixed
appliances, such as a “band and loop” space maintainer, to resist dislodgment of the appliance as
a result of the forces of mastication.
Occlusal trauma (Traumatic occlusion, Trauma from occlusion, Periodontal trauma)
1. Injury to the periodontium resulting from occlusal forces in excess of the reparative capacity of
the periodontal attachment. The affected teeth usually exhibit widening of the PDL space, wear
facets and some degree of hypermobility.
2. The same term sometimes is used to denote a palatally impinging overbite.
[See Tooth mobility, Increased mobility (Hypermobility)]
[See Impinging overbite]
SUBTERMS:
Primary occlusal trauma
Secondary occlusal trauma
Occlusion
The relationship of the maxillary and mandibular teeth, as they are brought into functional contact.
SUBTERMS:
Occlusion
• Centric occlusion (CO, Intercuspal position, ICP, Habitual occlusion)
Mandibular position dictated by maximum and habitual intercuspation of the maxillary and
mandibular teeth. It is a dentally determined position, independent of condylar position.
Occlusion
• Functional occlusion (Physiological occlusion)
A static and dynamic relationship of the teeth combining minimum stress on the
temporomandibular joint, optimal function of the orofacial complex, stability and esthetics of the
dentition and protection and health of the periodontium.
Occlusion
• Optimal occlusion (Ideal occlusion)
An ideal relationship of maxillary and mandibular teeth combining a functional occlusion with the
absence of malocclusion (as described by the six keys of occlusion).
[See Ideal occlusion]
[See Occlusion, Functional occlusion (Physiological occlusion)]
Occlusal trauma (Traumatic occlusion, Trauma from occlusion, Periodontal trauma)
1. Injury to the periodontium resulting from occlusal forces in excess of the reparative capacity of
the periodontal attachment. The affected teeth usually exhibit widening of the PDL space, wear
facets and some degree of hypermobility.
2. The same term sometimes is used to denote a palatally impinging overbite.
[See Tooth mobility, Increased mobility (Hypermobility)]
[See Impinging overbite]
SUBTERMS:
Primary occlusal trauma
Secondary occlusal trauma
Occlusogingivally (Occlusoapically)
In a direction perpendicular to the occlusal plane, along the y-axis.
[See Global reference frame]
Occlusogram
A graphic representation of the arches from the occlusal view. Occlusograms are mainly used as
treatment planning aids to assist in defining the specific tooth movements required within and
between arches (in the sagittal and transverse planes) to achieve treatment goals. An occlusogram
is essentially a two-dimensional diagnostic setup and is directly correlated with the Visual
Treatment Objective (VTO). It can be constructed from tracings of photographic or photostatic
copies of the occlusal aspects of the maxillary and mandibular study casts. The tracings of the
teeth of both arches are superimposed on each other to reproduce the existing occlusal
relationship, using index points that are marked on the models and subsequently transferred to the
tracings. Anticipated movements of individual teeth as well as the need for extractions then can be
determined, to simulate the desired treatment goal.
[See Visual treatment objective (VTO)]
[See Diagnostic setup (Kesling setup)]
Occult cleft
[See Submucous cleft palate]
Oculoauriculovertebral spectrum
[See Hemifacial microsomia (First and second branchial arch syndrome)]
Oligodontia
The congenital absence of multiple teeth (a severe form of hypodontia). In many such patients, the
existing teeth are smaller than normal and can be shaped atypically.
[Compare with Anodontia]
Open bite (Negative overbite)
Inherited, developmental or acquired malocclusion whereby no vertical overlap exists between
maxillary and mandibular anterior teeth (anterior open bite), or no vertical contact is exhibited
between maxillary and mandibular posterior teeth (posterior open bite). An open bite may be
localized and thus involve only a few teeth due to a digit-sucking habit or other local factors (dental
open bite), or it may be caused by divergence of the skeletal planes (skeletal open bite or
apertognathia).
[Compare with Non-occlusion]
Opening of the bite
The correction of a deep bite. This can be performed by extrusion of posterior teeth, often resulting
in clockwise rotation of the mandible (increased separation between the mandibular and palatal
planes); by intrusion of the anterior teeth; or by a combination of the two methods (relative intrusion
of the anterior teeth).
[See Bite raising]
Optimal force theory
The hypothesis that there exists a force of certain magnitude and temporal characteristics
(continuous vs. intermittent, constant vs. declining, etc. ) that is capable of producing a maximum
rate of tooth movement with no tissue damage and maximum patient comfort. The optimal force for
tooth movement may differ for each tooth, or for each individual patient.
Orbital hypertelorism
The increased distance between the medial orbital walls, reflecting an increased distance between
the orbits (greater than 2 standard deviations from the norm). The anatomic landmarks used
commonly for the measure-ment of interorbital distance are the dacryon points (bilaterally).
Hypertelorism is described on the basis of skeletal measurements, because the presence of
epicanthal folds or strabismus (exotropia), or other soft-tissue variations such as increased
distance between the medial canthi (telecanthus) clinically may give a false impression of
hypertelorism. Orbital hypertelorism is common in a number of craniofacial malformations such as
Crouzon syndrome and frontonasal dysplasia.
[Compare with Telecanthus]
[Compare with Orbital hypotelorism]
Orbital hypotelorism
The decreased distance between the medial orbital walls, a common finding in patients born with
malformations such as a median cleft. A patient with orbital hypotelorism has a much greater
chance of severe brain abnormality than does one with hypertelorism.
[Compare with Orbital hypertelorism]
Orofacial
Pertaining to the mouth and face.
Oronasal communication
[See Fistula, Oronasal fistula]
Orthodontic attachment
[See Attachment, Orthodontic]
[See Button]
[See Eyelet]
[See “Pigtail” attachment (Coil eyelet)]
[See Tube (Molar tube)]
Orthodontic band
A ring, usually made of a thin strip of stainless steel, that serves to secure orthodontic attachments
to a tooth. Bands are prefabricated in varying shapes to fit closely around the crowns of specific
teeth. Each shape comes in different sizes to accommodate individual tooth size variation. Most
bands have an occluso-gingival taper to fit the tooth, with the incisal edge straight and the cervical
edge contoured, similar to the cementoenamel junction. Orthodontic bands can be plain or have
buccal (brackets or tubes) or lingual (buttons, sheaths, cleats, seating lugs) attachments welded or
brazed on them. The inner surface of the band can be conditioned by various methods such as
pattern rolling, sandblasting, photo- or laser-etching to increase retention.
Orthodontic cement
Dental cement used for fixation of orthodontic bands to the teeth.
SUBTERMS:
Glass-ionomer cement
Resin-modified glass-ionomer cement (Dual-cured glass-ionomer cement)
Zinc oxide-eugenol (ZOE) cement
Zinc phosphate cement
Orthodontic elastics (Rubber bands)
Flexible bands, usually made of elastomeric material, used to produce forces for tooth movement.
SUBTERMS:
Orthodontic elastics (Rubber bands)
• Anterior diagonal elastics (Anterior oblique elastics)
Anterior intermaxillary elastics crossing the midline (e.g.
extending from the maxillary right canine to the
mandibular left lateral incisor), often used to facilitate the
correction of non-coinciding maxillary and mandibular
dental midlines.
Orthodontic elastics (Rubber bands)
• Asymmetric elastics
Various combinations of intermaxillary elastics (e.g. Class III elastics on one side and Class II
elastics on the other) used to correct an asymmetry in the buccal segment occlusion, with or
without an associated midline discrepancy.
Orthodontic elastics (Rubber bands)
• Class II elastics
Intermaxillary elastics extending unilaterally or
bilaterally from the anterior aspect of the maxillary
dental arch to the posterior aspect of the mandibular
one (e.g. from the maxillary canines to the mandibular
first molars). They are used to aid in Class II correction,
to reduce the overjet, to minimize anchorage loss
during maxillary incisor retraction by taking advantage
of intermaxillary anchorage, etc. In addition to the
desired sagittal force, Class II elastics create vertical
forces (especially when the patient opens their mouth)
as well as certain transverse forces, both of which often
are undesirable.
Orthodontic elastics (Rubber bands)
• Class III elastics
Intermaxillary elastics with the opposite orientation to
Class II elastics (from the anterior aspect of the
mandibular dental arch to the posterior aspect of the
maxillary one). As in the instance of Class II elastics,
Class III elastics can be used unilaterally or bilaterally.
They have various applications: to facilitate protraction
of maxillary posterior teeth, to improve the incisor
relationship in an edge-to-edge or anterior crossbite situation, or to make use of intermaxillary
anchorage during mandibular incisor retraction. In addition to the desired sagittal force, Class III
elastics create vertical forces (especially when the patient opens their mouth), as well as certain
transverse forces, both of which often are undesirable.
Orthodontic elastics (Rubber bands)
• Crossbite elastics (Criss-cross elastics, Through-the-bite elastics)
Elastics extending from the palatal (lingual) aspect of one or more maxillary teeth,
to the buccal aspect of one or more mandibular teeth (or the reverse), to aid in
correction of a crossbite. Crossbite elastics create vertical forces in addition to the
desirable trans-verse or anteroposterior forces; they therefore should be used with
caution, especially in patients with minimal overbite and long anterior lower facial
height.
Orthodontic elastics (Rubber bands)
• Intermaxillary elastics (Intermaxillary traction)
Elastics running between maxillary and mandibular teeth for sagittal, transverse or
vertical coordination of the arches, or a combination of the above. Class II, Class
III and crossbite elastics are all examples of intermaxillary traction. Intermaxillary elastics generate
forces in all three planes of space, only some of which are usually desirable. They therefore should
be used with caution, especially in patients with minimal overbite and long anterior lower facial
height.
Orthodontic elastics (Rubber bands)
• Intramaxillary elastics (Class I elastics, Intramaxillary
traction)
Elastic traction between teeth or groups of teeth of the same
arch. For example, patients sometimes are requested to
wear such elastics during canine retraction using sliding
mechanics.
Orthodontic elastics (Rubber bands)
• Transpalatal elastics
Intramaxillary form of elastic traction extending across the palatal vault (e.g. between two lingual
cleats on the second molar bands) in an attempt to constrict the maxillary arch form, or to
reciprocally move buccally displaced teeth into the arch.
Orthodontic elastics (Rubber bands)
• Vertical elastics (Up-down
elastics, Box elastics,
Triangular elastics, Zig-zag
elastics, “Spaghetti” elastics)
Intermaxillary elastics in various configurations, aiming at extrusion of teeth. They are used to aid
in settling (improve the interdigitation) in the final stages of active treat-ment, to achieve closure of
a localized open bite, or to aid in postsurgical leveling of the mandibular curve of Spee by premolar
extrusion (e.g. in Class II, Division 2 patients with short lower facial height).
Orthodontic impression trays
Stainless steel, aluminum or plastic trays used to receive the impression material (usually alginate)
during orthodontic impression taking. An orthodontic impression tray consists of a main body and a
handle, which is either welded or riveted to the body. The maxillary tray allows for coverage of the
maxillary alveolar process and the palate, whereas the mandibular tray allows for coverage of the
mandibular alveolar process. Some tray bodies are perforated to increase retention of the
impression material. Trays are available in various sizes and shapes. The flanges of the tray are
usually extended with rope wax to achieve representation of the full depth of the vestibule during
taking of impressions for orthodontic study models.
Orthodontic instruments
Orthodontic procedures demand the use of many specialized instruments, along with several also
used in other areas of dentistry.
SUBTERMS:
Orthodontic instruments
• Adams pliers (Universal pliers)
Heavy wire pliers with sharply tapered beaks forming a four-sided pyramid when closed. Used for
bending heavy-gauge wires and adjusting removable appliances.
Orthodontic instruments
• Arch-forming pliers (Arch-contouring pliers, De la Rossa
pliers)
Pliers with straight, thick, parallel beaks; the concave beak
fits around the opposing cylindrical one. The cylindrical beak
may have grooves of varying sizes or may be non-grooved.
Used to form and contour archwires, either round or
rectangular, as well as to incorporate (reverse) curve of Spee into an archwire.
Orthodontic instruments
• Band burnisher (Beaver-tail burnisher)
Stainless steel instrument with a heavy, hollow handle
for palm grip, similar to a Mershon band pusher. The
shank ends in an angled beaver-tail-shaped tip that
can be smooth or serrated and flattened for easier
access to band margins under buccal tubes or bracket
wings. Used for burnishing and adapting margins of
bands to the tooth contour.
Orthodontic instruments
• Band-contouring pliers
Pliers with two long, tapering and slightly bowed
beaks. The convex tip at the end of the one beak fits
into the opposing concave tip in a ball- and-socket
manner. The diameter and shape of the tips vary with
the manufacturer. Used for adaptation and contouring
of stainless steel orthodontic bands.
Orthodontic instruments
• Band pusher (Mershon band pusher)
Stainless steel instrument with a large, tapering handle
for palm grip and a long shank with an angled tip. The
tip is rectangular and serrated to prevent slippage of
the instrument during use. Used for positioning and
seating the band properly, as wellas for burnishing or
adapting the edges of the band around the tooth.
Orthodontic instruments
• Band-removing (Debanding) pliers, Anterior
Pliers with a longer, flat-sided curved beak placed on the
incisal edge of teeth, opposing a shorter, sharper beak
positioned under the gingival aspect of the band or
attachment. The longer incisal beak may have a
replaceable plastic or rubber tip to prevent
fractures of the incisal edge of the teeth. The
beaks generally do not make contact when the
handles are closed fully. Used to remove bands
from anterior teeth.
Orthodontic instruments
• Band-removing (Debanding) pliers, Posterior
Pliers with two beaks, one longer than the other. The longer beak, which carries a replaceable
plastic cap, is placed on the occlusal surface of a tooth, while the shorter, sharpened beak
engages and lifts the gingival margin of the band. Anterior and posterior band removing pliers can
be combined in a “Universal” design.
Orthodontic instruments
• Band seater (Band biter)
Plastic or metal instrument consisting of a handle
and a bite stick that makes use of the patient’s
biting force to aid the clinician in seating a band.
The tip of the bite stick has two sides. The one
that is placed on the occlusal margin of the band
is made of stainless steel and is available in
several sizes and shapes. As well, it usually is
serrated to minimize slippage of the instrument
during use. The opposite side of the tip, which
comes in contact with the patient’s teeth during biting, usually consists of a plastic bite shelf.
Orthodontic instruments
• Bird-beak (no. 139) pliers
Pliers with two short beaks (one of which is
conical and the other pyramidal in shape) used
for bending small wires and springs.
Orthodontic instruments
• Bracket-positioning instrument (Bracket-height gauge)
Device of various designs used to facilitate the
placement of brackets at standard distances from
the incisal edges or occlusal surfaces of specific
teeth. It usually has a ledge that rests on the
incisal edge (occlusal surface) of the tooth, while
a shorter arm is inserted into the bracket slot.
Orthodontic instruments
• Bracket-removing pliers (Debonding pliers)
Pliers used to remove brackets bonded to teeth.
There are various designs depending on the type
of bracket (e.g. stainless steel, ceramic, plastic).
The standard design for stainless steel brackets
has two mirror-image jaws with the sharp cutting
tips formed around a cylindrical opening. The
cutting tips generally do not make contact when
the handles are closed fully. The bracket is
removed by peel and shear forces by placing the
cutting tips at the bracket-adhesive junction and
squeezing.
Orthodontic instruments
• Conversion instrument
An orthodontic instrument that is inserted into the mesial opening of a convertible tube and
functions in a “can-opener” fashion to remove its convertible cap and thus turn it into a bracket.
[See Tube (Molar tube), Convertible tube]
[See Conversion (of a tube into a bracket)]
Orthodontic instruments
• Coon ligature-tying pliers
Reverse-action pliers
(squeezing the handles
increases the separation of the
tips), consisting of two opposing
mirror-image parts (handle,
shank and tip, all one piece)
joined just below the shank by a
round metal cylinder with a
channel. The opposing handles
are attached by a spring that
holds them apart, causing the
tips to touch when the
instrument is passive. It is used
for tying metal ligatures. The opposing tips are blunted and forked to facilitate retention of the
ligature wire. As the handles are compressed, spreading the tips, the channel locks the ligature
wire automatically. Because of the reverse action, the initial twist and the pressure are exerted at
the bracket-archwire junction and then twisted away from the bracket. This gives the ligature a
tighter fit around the bracket, forcing the archwire further into the slot.
Orthodontic instruments
• Distal-end cutter
A special wire cutter with the juxtaposed
cutting edges set at right angles to the
long axis of the instrument to facilitate
cutting of the distal end of the archwire,
intraorally. May have a safety hold
mechanism provided either by a thick wire
running parallel to the cutting edges, or by
a rectangular shoulder immediately below
the cutting edges. This mechanism serves
to grip the loose end of the cut archwire
and prevent it from being lost in the
mouth, so that it can be discarded easily.
It can be used to cut round wires up to
0.020 inch or 0.51 mm in diameter and
rectangular wires up to 0.022 x 0.028 inch
or 0.56 x 0.70 mm.
Orthodontic instruments
• Elastic separator pliers (Separator pliers)
Reverse-action pliers
(squeezing the handles
increases the separation of
the beaks) with two long
beaks that are angled for
better access. The beaks are
connected with a circular
hinge and carry tapered,
grooved, blunted tips, which
can retain elastic separators
(modules). They are used to
stretch, hold and place elastic separators.
Orthodontic instruments
• Facebow-adjusting pliers
Heavy-duty pliers with a box-jointed pivot construction, having two parallel beaks and an opposing
one that fits between the former when the pliers are closed. Each beak has a rounded notch at a
right angle to the beak near the tip on the opposing surfaces. Used for adjusting the inner and
outer arches of facebows, or for contouring wires of large diameter (up to 0.062 inch or 1.55 mm).
Orthodontic instruments
• Hard wire cutter
Cutter of design similar to a pin and ligature wire cutter, only larger, and capable of cutting fulldimension
archwires.
Orthodontic instruments
• Hemostat (Mosquito pliers)
Small and light pliers with scissor-like design, provided with a mechanical locking mechanism
located between the handles. The handles are available in various lengths. The serrated beaks
ligatures. Used for placement of elastomeric ligatures
(donuts).
Orthodontic instruments
• Howes utility pliers
Pliers with two long, round beaks tapered to a
pyramid shape and bowed, terminating in
juxtaposed flat round serrated pads. The pads
are positioned at right angles to the long axis
of the beaks; their diameter varies with the
manufacturer. The beaks may be straight or
offset at a 45° angle. Used mainly for gripping
and handling archwires and stainless steel
ligatures during placement in the mouth.
Orthodontic instruments
• Ligature director (Pitchfork instrument)
Stainless steel instrument carrying a straight or angled tip with a notch capable of engaging wires.
Available in double-ended versions or in combination with amalgam-pluggers, scalers or other tips.
Used to tuck and direct stainless steel ligatures under the archwire or bracket wings, or to push
archwires or auxiliaries into position.
Orthodontic instruments
• Light-wire pliers
Essentially identical to bird-beak pliers, only with longer
and more slender beaks. Some designs have one or
more grooves at the tip of the pyramidal beak to aid in
making reproducible loops and helices. Used mainly to
form various loop designs in orthodontic wires
(generally light, round wires), to make minor adjustment
bends in archwires or to place metal spring separators.
[See Orthodontic wire, Australian wire]
Orthodontic instruments
• Mathieu-style ligature-tying pliers
Pliers with long, thin handles equipped with a positivelocking
ratchet and spring for instant opening and closing. The opposing tips are serrated and may
have tungsten carbide inserts for longer instrument life. The tips vary in length and taper by the
manufacturer. The pliers are available in various sizes. Used mainly for tying stainless steel
ligatures as well as for placing elastomeric ligatures (donuts).
Orthodontic instruments
• Parallel-action pliers with cutter (Sargent’s heavy-duty pliers)
Heavy-duty pliers with parallel, flat, serrated opposing
beaks. One of the beaks carries a wire cutter on its nonserrated
side. Used mainly for bending, cutting or holding
large-diameter wires in laboratory procedures.
Orthodontic instruments
• Pin and ligature wire cutter
Cutter with two tapered and pointed opposing beaks,
terminating in delicate and sharp cutting edges. The
cutting edges may have carbide inserts that can be
sharpened or replaced when dull or damaged, without
replacing the entire instrument. It is available in various
angles, the straight and 15° to the long axis being the
most common. The tape and size of the tips vary with
the manufacturer. Used to cut soft ligature wires
(generally up to 0.016 inch or 0.41 mm) and archretaining
pins.
Orthodontic instruments
• Serrated amalgam-plugger
A single-ended or double-ended (in combination with a
ligature director or other tip) stainless steel instrument,
sometimes used to seat and position bands or to tuck
steel ligatures. The tip is available in various lengths,
angles and diameters and usually is serrated for better
control in pushing motion.
Orthodontic instruments
• Steiner ligature-tying pliers
Identical to the Coon ligature-tying pliers, differing
only in that the round metal cylinder at the shank of
the instrument does not carry the special channel to
engage the end of the ligature wire. The ligature
wire is retained on the instrument by manually
wrapping its free ends around the round metal
cylinder.
Orthodontic instruments
• Torquing key
Usually a cross-shaped stainless steel instrument, each of the four ends of which carries a milled
slot to engage the wire for placement of torque. Each slot is a different size to accommodate
various gauge wires. Used to place torque in an archwire or to assist full engagement of a wire into
a bracket slot. Various other kinds of torquing keys are used in combination with special pliers to
place torque for an individual tooth.
Orthodontic instruments
• Triple-beaked pliers (Three-jaw pliers, Clasp-adjusting
pliers)
Pliers similar to but smaller than the facebow-adjusting
pliers, with a box-jointed pivot construction. The
double-sectioned beak is opposed by a single beak, so
that a squeezing motion can produce a sharp bend in
the wire. Used for adjusting wires, particularly labial
bows or clasps on retainers, as well as for placing a curve on flexible or heavier wires, or stainless
steel tubing.
Orthodontic instruments
• Turret
Tubular metal device of various circumferences carrying grooves of various calibrated sizes, used
to shape straight lengths of orthodontic wire into
an arch form. Some turrets are equipped with
angulated grooves to place torque into rectangular
wire during shaping of the arch form.
Orthodontic instruments
• Tweed arch-adjusting (no. 142) pliers
Pliers used exclusively for handling or adjusting
square or rectangular wires. The beaks are
symmetrically flattened blades that are parallel at a
separation of 0.020 inch (0.51 mm).
Orthodontic instruments
• Tweed loop-forming pliers (Omega pliers,
Optical pliers)
Pliers with two opposed parallel beaks, one with
concave and one with round cross-section. The
round beak generally is stepped, having three
sections of different diameters (most commonly
0.045, 0.060, and 0.075 inch or 1.12, 1.50 and
1.90 mm). The tip of the round beak may be
replaceable. Used to form various loops or short
curved sections in orthodontic wire.
Orthodontic instruments
• Weingart utility pliers
Pliers with two long, slender beaks with opposing, serrated tips. The tips are oblong and pointed
and can be straight or curved from the long axis of the pliers to provide a better working angle for
intraoral adjustments. Used for holding or
gripping the archwire to place it and remove it
from the mouth, or to make adjustment bends.
Orthodontic magnets
Magnets have had various applications in medicine (mainly to aid in fracture healing) and in
dentistry (mainly for retention of prostheses). The miniaturization of magnets as a result of the
introduction of rare-earth or lanthanide elements facilitated their intraoral applications. In
orthodontics, magnetic forces from repelling or attracting poles have been utilized to achieve
palatal expansion, intrusion of posterior teeth, molar distalization, forced eruption of unerupted
teeth, anterior repositioning of the mandible during treatment with some functional appliances,
retraction or alignment of teeth, as well as retention of diastema closure. Neodymium-iron-boron
(Nd2Fe14B) and samarium-cobalt (SmCo5) are the types of rare-earth magnets most commonly
used. The greatest disadvantage of magnets is their low corrosion resistance in the presence of
saliva. Corrosion products are toxic to the tissues, for which reason magnets must be coated with
appropriate materials (usually parylene or acrylic), or be enclosed in a stainless steel casing, when
intended for intraoral use. The possibility of adverse effects of magnetic fields on cells and tissues
is an issue of controversy.
Orthodontic springs
Force-producing modules or appliance components, made of metal.
SUBTERMS:
Orthodontic springs
• Cantilever spring
In principle, any piece of wire, one end of which is
inserted fully into a bracket or tube, while the
other end is ligated to another unit with only a
one-point contact. The advantage of using
cantilever mechanics is that the created force
system can be estimated easily at both units
(statically determinate force system) by knowing
the length of the cantilever and by measuring the
force exerted at its ligated end with a force
gauge. Moreover, the relatively long range of
deactivation of the spring results in a low
magnitude continuous force (low load/deflection
ratio) that generally is considered desirable for
tooth movement.
[See Mechanics, Cantilever mechanics]
Orthodontic springs
• Closed spring
A spring (usually part of a removable appliance) having both ends attached.
Orthodontic springs
• Coffin spring
An omega-shaped (_) spring made of heavygauge
wire, spanning across the palate as part
of some removable orthodontic appliances
(e.g. the Bimler or the Crozat appliance). The
function of a Coffin spring is to offer the
possibility of expansion or constriction of the
maxillary dental arch.
Orthodontic springs
• Coil spring, Closed
Spring made of fine (typically 0.010 to 0.012 inch, or 0.25 to 0.30 mm) orthodontic wire wound into
a coil whose helices tightly contact each other; thus it cannot be compressed. A closed coil spring
usually comes in a spool and is cut to the appropriate length according to the intended application.
It most commonly is used to maintain a space during fixed appliance orthodontic treatment (e.g.
the space of a missing tooth that eventually will be replaced prosthetically).
Orthodontic springs
• Coil spring, Open
Spring made of fine (typically 0.010 to 0.012 inch, or 0.25 to 0.30 mm) orthodontic wire wound into
a coil whose helices are spaced, so it can be compressed along its long axis. An open coil spring
comes in a spool and usually is cut to a length larger than the interbracket distance between the
teeth that are intended to be moved away from each other. It is compressed prior to insertion,
generating equal and opposite forces on either end.
Orthodontic springs
• Coil spring, Retraction (Pletcher spring, Closing coil spring)
Spring made of fine (typically 0.010 to 0.012 inch, or 0.25 to
0.30 mm) orthodontic wire wound into a coil with tightly
contacting helices. The coils are prefabricated from
superelastic or stainless steel wire and come in
predetermined lengths with two eyelets on either end.
Retraction coil springs are used to generate forces for
retraction of teeth or space closure by extending them beyond their initial length.
Orthodontic springs
• Finger spring
A free-end spring usually incorporated in removable orthodontic appliances to produce various
tipping movements of teeth. Finger springs can contain helices to increase the effective wire length
for added flexibility.
Orthodontic springs
• Free-end spring (Open spring)
A broad category of springs (usually part of a removable appliance) having only one end
embedded in acrylic.
Orthodontic springs
• PG spring (Gjessing spring)
A universal retraction spring made of 0.016 x 0.022-inch
stainless steel wire, introduced by P. Gjessing. The spring
consists of a 10 mm-long, double, ovoid-shaped, closed
loop extending gingivally, continuing with a small (2 mm in
diameter) occlusal helix. This configuration was designed to reduce the load/deflection rate to
approximately 45 g per millimeter of activation. The spring also has an anti-tip moment-to-force
ratio of approximately 11:1 and an anti-rotation moment-to-force ratio of approximately 7:1.
It is meant to be used as a segmental spring for frictionless segmental canine retraction by
translation, or for “en masse” retraction of the maxillary incisors without undesirable lingual tipping.
The spring is supposed to be activated every 4 to 6 weeks, to the point where the double loop is
separated, which is calibrated to produce approximately 100 g of force.
Orthodontic springs
• Root spring
An orthodontic spring that can cause movement of the root of a tooth with relatively little movement
of the crown. Uprighting springs and torquing springs both are subcategories of root springs.
Orthodontic springs
• Rotation spring
Auxiliary orthodontic spring, commonly used with single
brackets (usually inserted into the vertical slot) to generate
the moment required for rotation of a tooth around its long
axis.
Orthodontic springs
• Torquing spring
Auxiliary orthodontic spring used to move the root of a tooth in
the labiolingual or buccolingual direction.
Orthodontic springs
• Uprighting spring
Auxiliary orthodontic spring used to move
the root of a tooth in the mesiodistal
direction. Uprighting springs commonly
are used in the bracket vertical slot with
the Begg technique and its modifications
(e.g. the side-winder springs of the Tip-
Edge appliance).
Orthodontic springs
• Z-spring (Recurved spring)
A spring bent in the form of a “Z,” commonly incorporated into a
removable appliance to tip an individual tooth or groups of teeth buccally
or labially.
Orthodontic tooth movement
Movement of a tooth under the influence of a mechanical force.
Orthodontic tooth movement is possible because of the regenerative
and remodeling capacity of the alveolar bone and the periodontal
ligament. The mechanism regulating the transduction of a mechanical
stimulus into specific cellular activity is not yet entirely understood.
SUBTERMS:
Orthodontic tooth movement
• Extrusion
A translational type of tooth movement parallel
to the long axis of the tooth in the direction of
the occlusal plane.
Orthodontic tooth movement
• Intrusion
A translational type of tooth movement parallel
to the long axis of the tooth in an apical
direction.
Orthodontic tooth movement
• Pure crown movement
The type of tooth movement for which the
center of rotation is at the apex of a tooth.
[Note: the term is somewhat misleading, as
this type of movement also affects part of the root. ]
[See Orthodontic tooth movement, Tipping, Controlled]
Orthodontic tooth movement
• Pure root movement
The type of tooth movement for which the center of rotation is at the incisal edge (or for all practical
purposes, at the bracket) of a tooth. For an average maxillary central incisor with intact
periodontium the M/F ratio for this type of movement is estimated to be 12:1 to 13:1. Pure root
movement is the intended type of movement when “torquing” incisor teeth, when uprighting canine
roots following extraction space closure, or when uprighting mesially tipped molars. [Note: the term
is somewhat misleading, as this type of movement also affects part of the crown. ]
Orthodontic tooth movement
• Pure rotation
Rotation of a tooth about its long axis, most evident when viewing the tooth from an occlusal
perspective. To achieve this type of tooth movement, the application of a couple is required.
Orthodontic tooth movement
• Tipping, Controlled
A type of tooth movement consisting of rotation about the apex of the tooth. It is achieved clinically
by the application of a force at the level of the bracket (as in uncontrolled tipping) as well as a
counter-moment to prevent movement of the root apex in the opposite direction. For an average
maxillary central incisor with no periodontal loss, the M/F ratio for controlled tipping is estimated to
be between 7:1 and 8:1.
[See Orthodontic tooth movement, Pure crown movement]
Orthodontic tooth movement
• Tipping, Uncontrolled (Simple)
A single horizontal force applied to the crown of the tooth at the level of the bracket will cause
movement of the crown and the apex of a tooth in opposite directions. The center of rotation for
this movement is approximately at (or slightly apical to) the center of resistance of the tooth. This is
the simplest type of tooth movement, but it often is undesirable. The moment-to-force ratio for
uncontrolled tipping is 0:1 (no counter-moment is applied, but only a single force).
Orthodontic tooth movement
• Translation (Bodily movement)
The type of tooth movement during which all points on a tooth move in the same direction by the
same amount. During bodily movement, the center of rotation can be assum-ed to lie at infinity. A
single force passing through the center of resistance canproduce translation of a tooth along its
line of action. Alternatively, a force and a (counter-)moment have to be applied at the bracket of a
tooth. For an average maxillary central incisor tooth with intact periodontium, a moment-to-force
ratio of approximately 10:1 at the level of the bracket is typical of translation.
Orthodontic wire
In orthodontics, wires of various alloys having various cross-sectional shapes and dimensions are
used.
SUBTERMS:
Orthodontic wire
• Australian wire
A round austenitic stainless steel wire, introduced by the A. J. Wilcock Co. in Australia, and
selected by P. R. Begg as the main material from which archwires were made for his light-wire
technique. The wire is heat-treated and cold-drawn down to its proper diameter from round wire of
larger diameter. It exhibits high toughness and tensile strength, combined with increased
resilience, but low corrosion resistance because of the presence of copper as an alloying element
of the steel. There are various grades of Australian wire, but Begg mainly used the 0.016-inch
(0.41-mm), so-called “Special Plus” wire. Another characteristic of the wire is its brittleness. It is
recommended that when bending Australian wire, the flat rather than the round beak of the pliers
be used and that the bend be placed very slowly, to avoid breakage. Following bending, the
archwire can be heat-treated, which makes it harder and more resistant to permanent deformation.
[See Appliance, Begg appliance (Light-wire appliance)]
Orthodontic wire
• Multistrand wire (Braided wire, Coaxial wire)
Orthodontic wire fabricated by braiding multiple strands of wire of the same material and usually of
the same diameter. This method of combining a number of strands of wire that individually would
not be strong enough for a particular application is used to achieve a wire with high flexibility and
adequate strength. Multistrand archwires can be round or rectangular and commonly are used for
initial alignment.
Orthodontic wire
• Nickel-titanium wire
[See Nickel-titanium alloy (Ni-Ti)]
Orthodontic wire
• Rectangular wire
An orthodontic wire with rectangular cross-section.
[See Archwire cross-section]
Orthodontic wire
• Round wire
An orthodontic wire with round cross-section.
[See Archwire cross-section]
Orthodontic wire
• Square wire
An orthodontic wire with square cross-section.
[See Archwire cross-section]
Orthodontic wire
• TMA wire
[See Beta-titanium alloy (TMA, b-Ti, Titanium-molybdenum alloy)]
Orthognathic (Mesognathic)
A facial type with normal anteroposterior relationship of the maxilla and mandible in relation to each
other and to the cranial base.
[See Facial type]
Orthognathic surgery
Surgical reposition-ing of all or parts of the maxilla and/or mandible to correct malpositions or
deformities. Usually accomplished in conjunction with orthodontic treatment.
[See Osteotomy]
SUBTERMS:
Orthognathic surgery
• Bimaxillary surgery (Two-jaw surgery)
Orthognathic surgical procedure involving repositioning of both the maxilla and the mandible.
Orthognathic surgery
• Single-jaw surgery (One-jaw surgery)
Orthognathic surgical procedure during which either the mandible or the maxilla are surgically
repositioned.
Osseointegration
A direct structural connection between bone and the surface of an implant. The host bone
responds in a safe, predictable and versatile manner to the placement of an implant, with a healing
cascade leading to interfacial osteogenesis and immobility of the implant.
Ossification
Formation and development of bone. Histologically two types of ossification are distinguished:
endochondral and intramembranous.
SUBTERMS:
Ossification
• Endochondral ossification
Bone formation taking place on a cartilage matrix; the cartilage immediately preceding bone in
development. This type of ossification occurs embryologically as the chondrocranium ossifies at
the epiphyses of all long bones, vertebrae and ribs, at the head of the mandibular condyle, and at
the synchondroses of the base of the skull.
Ossification
• Intramembranous ossification
Bone formation directly within a connective tissue membrane, without any intermediate formation
of cartilage. This type of ossification occurs embryonically at many sites, such as the cranial vault,
the maxilla, the body of the mandible, and at the diaphyses (midshaft) of long bones, initially by
proliferation and condensation of mesenchymal cells. As vascularity increases at these sites of
condensed mesenchyme, osteoblasts differentiate and begin to produce bone matrix de novo.
Ostectomy
Surgical removal of a bone, or part of a bone.
Osteoarthritis (Degenerative joint disease, DJD, Degenerative arthritis)
Chronic disease resulting in joint deformity caused by degenerative changes in the articular
cartilage, fibrous connective tissue and/or disc. In its late stage it is accompanied by proliferation of
new bony tissue at the margins of the joint surface, known as marginal osteophytes, lipping, spurs,
or ridges. The fibrillation and breakdown of cartilage is not an inflammatory process, but the
breakdown is accompanied by inflammation. The most common etiologic factor that either causes
or contributes to osteoarthritis is overloading of the joint structures. In the case of the TMJ it often
is painful, and symptoms are accentuated by jaw movement. Crepitation is a common finding.
Osteoarthrosis
Chronic non-inflammatory joint disorder characterized by progressive deterioration and loss of
articular cartilage and subchondral bone.
Osteoblast
Uninucleated cell that synthesizes both collagenous and noncollagenous bone proteins (the
organic matrix, osteoid). Osteoblasts are responsible for mineralization and are thought to derive
from multipotent mesenchymal cells or, alternatively, from perivascular cells. The osteoblast
generally is considered to differentiate through a precursor cell, the preosteoblast. Osteoblasts
secrete, in addition to Type I and Type V collagen, small amounts of several noncollagenous
proteins and a variety of cytokines. Under physiologic conditions supporting resorption rather than
formation of bone, osteoblasts can be stimulated by lymphokines and by prostaglandins to produce
interleukin 6, a factor that increases the resorbing activity of the osteoclast.
Osteoclast
Large multinucleated type of cell involved in the degradation and removal of hard tissue.
Osteoclasts are derived from monocytes and typically are found against the bone surface,
occupying shallow depressions called “Howship’s lacunae.” To break down hard tissue, osteoclasts
attach to mineralized tissue and create a sealed environment that is first acidified to cause
demineralization. Following that, the organic matrix is broken down through the secretion of
proteolytic enzymes.
Osteoconductive material
A material that acts as a scaffold for new bone formation.
[Compare with Osteoinductive material]
Osteocyte
As osteoblasts secrete bone matrix, some of them become entrapped in bone and are then called
osteocytes. The number of osteoblasts that become osteocytes depends on the rate of bone
formation: the more rapid the formation, the more osteocytes are present per unit volume. As a
general rule, embryonic (woven) bone has more osteocytes than does lamellar bone.
Osteogenesis imperfecta
As a diagnostic term, osteogenesis imperfecta represents a heterogeneous group of inherited
disorders characterized by defects in both mineralized and non-mineralized connective tissues,
resulting from mutations in Type I collagen. Males and females are affected equally, and the
incidence is between 1 in 5,000 and 1 in 14,000 live births. The classification of the clinical features
of the various types of osteogenesis imperfecta according to D. O. Sillence is as follows:
Type I:
Normal stature, increased frequency of fractures prior to puberty and after menopause, little or no
deformity following fracture repair, hearing loss in about 50% of families, blue sclerae,
dentinogenesis imperfecta is uncommon.
Type II:
Death in the perinatal period due to extreme bone fragility, poor mineralization of the calvarium,
intrauterine fractures of endochondral and membranous bones, blue/black sclerae in virtually all
affected individuals, long bone and rib deformities.
Type III:
Short stature, characteristic facies, long bone deformity following fracture repair, scoliosis,
dentinogenesis imperfecta common, hearing loss common, scleral discoloration variable, reduced
lifespan.
Type IV:
Mild to moderate short stature, mild to moderate long bone deformity following fracture repair,
normal scleral hue, dentinogenesis imperfecta is common, hearing loss occurs in some families.
Osteoinductive material
A material that causes the conversion of mesenchymal cells into bone progenitor cells.
[Compare with Osteoconductive material]
Osteomyelitis
Inflammation of bone, especially of the marrow, caused by pathogenic organisms.
Osteophyte
Bony outgrowth. Marginal adaptation of a joint, formed by bony tissue. In the case of the TMJ, the
anterior aspect of the mandibular condyle (in the region of the attachment of the lateral pterygoid
muscle) is a relatively common location where osteophytes can be found.
Osteotomy
Surgical procedure involving the cutting of bone.
SUBTERMS:
Osteotomy
• Anterior maxillary segmental (subapical) osteotomy
Osteotomy of the anterior maxillary segment, usually from canine to canine, with displacement in a
posterior, inferior, superior or rotational manner. Most commonly a combination of posterior and
inferior repositioning of the anterior segment is performed, into the space created by simultaneous
extraction of the maxillary first premolars. Anterior repositioning of the segment is almost
impossible because of difficulties in stabilization and fixation, even with bone grafting, and because
the soft tissue pedicles often are insufficient to cover the surgical defects. The most popular
techniques for this type of osteotomy are the Wassmund and Wunderer techniques.
Wassmund technique
An approach to anterior maxillary segmental osteotomy described by M. Wassmund (1927), which
relies on maintaining both the labial and palatal pedicles for vascular supply to the anterior
maxillary segment. The osteotomies are carried out through mucosal tunnels created on the
vestibular side by vertical incisions at the midline and at the level of the first premolar and through
palatal tunnels created by connecting the extraction sockets of the first premolars to a midpalatal
incision.
Wunderer technique
An alternative approach to anterior maxillary segmental osteotomy described by S. Wunderer
(1963). The technique relies on the vestibular pedicle for vascular supply to the anterior maxillary
segment, together with some blood supply from the incisive canal. Bilateral vertical incisions are
performed on the vestibular side at the level of the first premolars. These are connected by a
transpalatal horizontal incision, allowing reflection of the palatal flap posteriorly.
Osteotomy
• Bilateral sagittal split osteotomy (BSSO)
A mandibular orthognathic surgical procedure first reported in the English literature by R. Trauner
and H. L. Obwegeser (1957), and subsequently modified by others. In this procedure the rami of
the mandible are split parallel with the sagittal plane to allow repositioning of the mandibular body
into a more favorable relationship with the maxilla and the face. The procedure currently is
routinely performed through an intraoral approach and can be used for advancement, setback and
rotation of the distal (mandibular) segment.
When the distal segment is advanced, a gap is created in the buccal plate. When it is set back, a
section of the buccal plate is removed to allow good approximation of the buccal cortex of the
proximal segment against the lingual cortex of the distal segment on each side. The osteotomy
design spares the mandibular nerve and provides a broad interface of the bony segments to aid
with fixation and healing. Fixation is achieved by bone screws or bone plates, or through
circumosseous fixation wires in combination with IMF.
[See Segment, Proximal segment]
[See Segment, Distal segment]
Osteotomy
• Complete maxillary osteotomy
Maxillary osteotomies traditionally are described in comparison with the common fracture patterns
of the midfacial skeleton, named after the work of R. Le Fort (1900). The Le Fort I, II and III
fractures indicate the general levels at which the maxilla may be sectioned selectively from the rest
of the skull, although the osteotomies are tailored to the individual patients and may deviate from
the known fracture patterns.
Le Fort I osteotomy
The most frequently performed of all midfacial osteotomies. It sections the midface through the
walls of the maxillary sinuses, the lateral nasal walls and the nasal septum, at a level just superior
to the apices of the maxillary teeth. Starting at the inferior-lateral margin of the pyriform aperture of
the nose, the osteotomy line traverses the lateral walls of the maxillary sinus approximately 3 to 4
mm above the apices of the canine, premolars and molars. It passes across the canine fossa to
the base of the zygomatic buttress and curves around and above the maxillary tuberosity to the
lowest part of the pterygomaxillary fissure, where it crosses the posterior wall of the sinus at the
same level. It then turns anteriorly through the lateral wall of the nose below the inferior turbinate to
join the point of origin. The cut is made bilaterally. Following this, the pterygomaxillary plates are
separated from the posterior aspects of the maxillary tuberosities, and the nasal septum is
detached from the superior aspect of the hard palate by dividing it along its length with a chisel, so
that the maxillary segment is freed. The Le Fort I osteotomy offers a great number of options as
the freed maxilla can be reoriented in all spatial planes. Further segmentation of the maxilla can be
performed to correct transverse, anteroposterior and vertical discrepancies between the maxilla
and the mandible.
Le Fort II osteotomy
A pyramid-shaped osteotomy that is identical to the Le Fort I procedure from the pterygoid column
to the zygomatic buttress. From that point, instead of continuing anteriorly to the pyriform aperture
of the nose, the cut is directed superiorly, towards the orbit. The cut is kept anteromedial to the
infraorbital foramen and crosses the inferior orbital margin at a point halfway between the lacrimal
duct medially and the infraorbital canal laterally. It then is continued posteriorly along the floor of
the orbit and at right angles to the orbital rim until past the lacrimal groove and its contained
lacrimal sac. The cut then is turned medially and anteriorly across the apex of the lacrimal groove
and emerges medially to the orbit, just below the midpoint of the medial canthal attachment. The
frontal process of the maxilla then is crossed and the cut becomes continuous with the osteotomy
of the other side across the nasal bones. The nasal septum is divided at a higher level than during
the Le Fort I osteotomy, passing from the nasal bones anteriorly in a downward and backward
direction to the posterior part of the septum just above the posterior nasal spine. The lateral nasal
walls are fractured during mobilization of the maxilla at levels corresponding to the septal cut.
Le Fort III osteotomy
The basic Le Fort III osteotomy, as originally described by P. Tessier (1971), was designed to
achieve anteroposterior movement of the whole facial mass, establishing normal dental occlusion
and increasing orbital capacity, enlarging both the height and the depth of the orbits. The aim is to
separate the facial mass from the cranial base along the inter-frontofacial and the interpterygomaxillary
planes. To do this, the osteotomy traverses, on each side, the medial orbital wall,
the orbital floor and the lateral orbital wall to reach the region of the frontozygomatic suture. The
frontal process of the zygomatic bone then is split sagittally (effectively splitting the lateral wall of
the orbit) and the cut is continued inferiorly to complete division of the zygoma. The two sides are
connected centrally through the frontona-sal area, as in the Le Fort II osteotomy. Pterygomaxillary
and septal separation then are completed as in the Le Fort II operation and the central facial block
is mobilized. Many variants of Le Fort III procedures exist that can be applied in the treatment of a
variety of craniofacial problems and can be combined with surgery of the cranial vault.
Kьfner osteotomy
A modification of the Le Fort II osteotomy originally described by J. Kьfner (1971). It is intended for
patients with good nasal bridge and projection, but exhibiting retrusion of the infraorbital region and
maxillary dentoalveolar area, with zygomatic flatness. The difference is that the osteotomy does
not involve the nasal bridge, but is extended laterally to include the infraorbital rim and zygomatic
process.
Osteotomy
• Multiple-piece maxillary osteotomy
When a severe transverse discrepancy between the maxillary and mandibular arches exists, a twoor
a three- and sometimes even a four-piece maxillary procedure is performed, following a Le Fort I
osteotomy, to reposition each segment separately to an ideal relationship with the mandibular arch.
Due to the increased risks entailed in the segmental procedures, most clinicians prefer to limit the
number of segments into which they divide the maxilla.
[Compare with Osteotomy, One-piece maxillary osteotomy (Single-piece maxillary osteotomy, Total
maxillary osteotomy)]
Osteotomy
• One-piece maxillary osteotomy (Single-piece maxillary osteotomy, Total maxillary osteotomy)
Any osteotomy that mobilizes the maxilla as a whole.
[Compare with Osteotomy, Multiple-piece maxillary osteotomy]
Osteotomy
• Transoral vertical ramus osteotomy (TOVRO, Intraoral vertical ramus Osteotomy, IVRO)
A vertical osteotomy of the mandibular ramus performed via a transoral approach for correction of
mandibular prognathism. It commonly is carried out in conjunction with a coronoidectomy. The
coronoid fragment with attached temporalis tendon is allowed to retract. The line of the osteotomy
extends from an area in front of the condyle to a point at or near the angle of the mandible.
This osteotomy is reserved for patients who require a mandibular setback, as it necessitates fullthickness
overlap between the mandibular segments. After the setback the condylar segment lies
laterally to the distal mandibular segment. Stabilization can be provided by a circumramus suture
or wire, by rigid fixation screws, or alternatively no stabilization is used. In the latter case, patients
are left in intermaxillary fixation for 4 to 6 weeks. The TOVRO is advocated to be less likely than
the BSSO to produce neurosensory changes.
Overbite (Vertical overbite)
The degree of vertical overlap of the mandibular incisors by their maxillary antagonists, usually
measured perpendicular to the occlusal plane. It is reported either in millimeters, or as a
percentage of the total crown length of the mandibular incisors that is overlapped by the maxillary
incisors.
[Compare with Overjet (Sagittal overbite)]
SUBTERMS:
Overbite (Vertical overbite)
• Impinging overbite
Extremely deep bite with impingement of the mandibular incisors in the mucosa palatal to the
maxillary incisors; commonly seen in patients with severe Class II, Division 2 malocclusions.
Overbite (Vertical overbite)
• Positive overbite
A term indicating the presence of vertical overlap between the maxillary and mandibular anterior
teeth. Positive overbite is a characteristic of the ideal occlusion, but also of deep bite
malocclusions.
Overclosure
Reduced vertical dimension with the teeth in occlusion.
Overcorrection
The notion of continuing a certain type of treatment even after an ideal relationship has been
achieved, in anticipation of some degree of relapse after the end of active treatment. For example,
the overcorrection of a typical Class II deep bite malocclusion to an end-to-end anterior relationship
sometimes is advocated.
Overeruption (Supraeruption, Supraposition, Supraocclusion)
The situation whereby an unopposed or non-occluding tooth
extends beyond the occlusal plane.
Overjet (Sagittal overbite)
The distance between the labial surface of the mandibular
incisors and the labial aspect of the incisal edge of the
maxillary incisors, usually measured parallel to the occlusal
plane. When not otherwise specified, the term is generally
assumed to refer to the most prominent central incisors.
The extent of overjet is determined primarily by the differences of labiolingual
position and inclination of the maxillary and mandibular central incisors. Only in a
minority of cases is the anteroposterior skeletal relationship reflected directly in
the amount of overjet.
[Compare with Overbite (Vertical overbite)]
SUBTERMS:
Overjet (Sagittal overbite)
• Buccal overjet
The distance between the buccal surfaces of the maxillary posterior teeth and the buccal surfaces
of their mandibular antagonists. An unofficial term sometimes used to indicate whether or not there
is a tendency for a posterior crossbite.
Overjet (Sagittal overbite)
• Negative overjet(Reverse overjet)
A situation usually associated with Class III malocclusions in which the maxillary
incisors occlude lingually to the mandibular incisors.
Overjet (Sagittal overbite)
• Positive overjet
A term denoting that the maxillary incisors occlude labially to the mandibular
incisors, as is seen commonly in Class I or Class II malocclusions.
Palatal rugae
The irregular ridges in the masticatory mucosa covering the anterior hard palate.
Palate
The structure that serves as the roof of the oral cavity and the floor of the nasal cavity, consisting
anteriorly of the hard palate and posteriorly of the soft palate.
SUBTERMS:
Palate
• Hard palate
The anterior part of the palate, the osseous framework of which consists of the palatine processes
of the maxilla and the horizontal parts of the palatine bones.
Palate
• Primary palate
The embryological structure that forms during the 5th to 7th weeks of human intrauterine life,
originating from the fused medial nasal and maxillary processes. The primary palate eventually
forms the upper lip, the anterior portion of the maxillary alveolar process and the hard palate
anterior to the incisive canal.
[See Premaxilla]
Palate
• Secondary palate
The embryological structure that forms during the 6th-9th weeks of human intrauterine life by
fusion of the palatine processes (of the maxillary process) at the midline. The anterior parts of the
palatine processes (palatal shelves) also unite with the nasal septum, eventually forming the hard
palate. In the posterior region, where there is no attachment to the nasal septum, the soft palate
and uvula eventually develop.
Palate
• Soft palate (Velum)
The posterior mobile part of the palate, which is suspended anteriorly from the hard palate. Its
sides blend with the pharynx and its posterior portion forms the uvula. In its relaxed position the
soft palate is continuous with the roof of the mouth. During the process of deglutition or sucking, as
well as during production of certain speech sounds, it is elevated, thus separating the nasal cavity
and nasopharynx from the posterior part of the oral cavity and the oral portion of the pharynx.
Palate-splitting appliance
[See Appliance, Expansion appliance]
[See Appliance, Hyrax appliance (Hygienic rapid palatal expander)]
[See Appliance, Haas appliance (Haas rapid maxillary expansion appliance, Haas palatal
separator)]
Pantograph
A tracking device attached to the mandible and maxilla that enables recording of mandibular
movements in three planes of space.
Parafunction (Parafunctional activity, Parafunctional habit)
Non-physiological activity, including clenching and bruxing, nail-biting, and lip- or cheek-chewing.
Paresthesia
Diminished or abnormal sensation, such as burning, prickling, tingling, or numbness; a common
finding following orthognathic surgery. Almost all patients have some degree of paresthesia of the
lower lip over the distribution of the mental nerve immediately following mandibular ramus surgery
(e.g. bilateral sagittal split osteotomy). Return of sensation may be rapid, may occur over a few
weeks, or may occur gradually over 12 to 18 months. In some instances a permanent degree of
paresthesia remains.
Pathognomonic
Specifically distinctive characteristic (sign or symptom) of a disease or pathologic condition, on the
basis of which a diagnosis of the disease can be made.
“Peg-shaped” lateral incisors
Atypical, undersized, pointed and tapered crown form of the maxillary permanent lateral incisors.
Perikymata
The numerous small transverse ridges and grooves on the surface of the enamel of permanent
teeth, representing the rhythmic deposition of enamel. With continued abrasion the surface of the
enamel becomes eroded and the perikymata eventually disappear.
Periodontal ligament (PDL)
A dense, highly specialized connective tissue situated between the root of a tooth and the alveolar
bone. Its principal function is to connect the tooth to the bone while resisting the stress created by
the various forces exerted on the teeth. This is achieved by the masses of collagen fiber bundles
that follow an undulated course between the bone and the tooth, and by an incompressible gel-like
matrix consisting of 70% water (ground substance). The second function of the PDL is to provide
sensory input (proprioception) on the level and type of strain that it experiences, partially through
specialized sensory receptors. Other than fibers and ground substance, the PDL contains many
cells (mainly fibroblasts, epithelial cells and undifferentiated mesenchymal cells), blood vessels
and nerves.
Fibers of the PDL
The majority of fibers of the periodontal ligament are collagen fibers, mainly a mixture of Type I and
Type III. The greatest proportion of the collagen fibers in the PDL are arranged in definite and
distinct fiber bundles. The principal groups of bundles are as follows:
1. The alveolar crest group, attached to the cementum just below the cementoenamel junction and
running downward to insert into the rim of the alveolus.
2. The horizontal group, occurring just apical to the alveolar crest group and running at right angles
to the long axis of the tooth from cementum to bone just below the alveolar crest.
3. The oblique group, by far the most numerous in the PDL, running from the cementum in an
oblique direction, to insert into bone coronally.
4. The apical group, radiating from the cementum around the apex of the root to the bone, forming
the base of the socket.
5. The interradicular group, found only between the roots of multirooted teeth and running from the
cementum into the bone, forming the crest of the interradicular septum.
At each end, all the principal fibers of the PDL are embedded in cementum or bone. The
embedded portion is called a Sharpey’s fiber. Other than collagen, the PDL also contains some
elastic fibers, consisting of two types of immature elastin, namely oxytalan and eluanin.
Width of the PDL
In humans the width of the PDL ranges from 0.15 to 0.38 mm, with its narrowest aspect at the
middle third of the root and its widest aspect cervically. Occlusal loading in function affects the
width of the PDL. If occlusal forces are within physiologic limits, increased function leads to an
increase in width through a thickening of the fiber bundles and an increase in diameter and number
of Sharpey’s fibers. Unphysiologic situations such as traumatic occlusion typically cause widening
of the PDL. Conversely, when function is diminished or absent, the width of the PDL decreases.
The fibers are reduced in number and density and they show a tendency to become oriented
parallel to the root surface. A widening of the PDL also typically is associated with active
orthodontic tooth movement.
Perpetuating factors
Factors that interfere with resolution of, or enhance the progression of, a disease or disorder.
Pharyngeal flap operation
A surgical procedure for lengthening the soft palate by attaching a flap from the posterior
pharyngeal wall to it. Depending on the way that the pharyngeal flap is raised, a superiorlybased
and an inferiorlybased pharyngeal flap can be distinguished.
[See Velopharyngeal insufficiency (Velopharyngeal incompetence, VPI)]
[See Hypernasality (Rhinolalia aperta)]
Philtral columns
Normal ridges in the skin of the central portion of the upper lip, extending bilaterally from the
vermilion border of the upper lip to the columella of the nose, and containing the philtrum.
Photoelasticity
Engineering technique of stress analysis based on the property of some transparent materials to
exhibit patterns of color when viewed with polarized light. These patterns occur as the result of
alteration of the polarized light by the internal stresses into waves that travel at different velocities.
The patterns that develop consequently are related to the distribution of internal stresses and are
called the photoelastic effect. A research technique with many orthodontic applications.
Physiologic migration
[See Drift (of teeth)]
Physiologic rest position (of the mandible)
The mandibular position assumed when the head is in an upright position and the involved
muscles, particularly the elevator and depressor groups, are in equilibrium in tonic contraction, and
the condyles are in a neutral, unstrained position.
Physiologic tooth movement
Movement of the teeth taking place as part of the natural process from their early stages of
development until they become functional at the level of the occlusal plane, and extending to the
end of their lifespan in the mouth. The movements teeth make are complex and may be
distinguished as “pre-eruptive,” “eruptive” and “post-eruptive.” Superimposed on these is a
progression from deciduous to permanent dentition, involving the exfoliation of the deciduous
dentition. This categorization of tooth movement merely serves descriptive purposes; it must be
recognized that what is being described is a continuous series of events.
SUBTERMS:
Physiologic tooth movement
• Eruptive tooth movement
This includes “pre-emergent” and “post-emergent” tooth movement. The mechanism of eruption of
deciduous and permanent teeth is thought to be similar, bringing about the axial and occlusal
movement of the tooth from its developmental position within the jaw to its final functional position
within the occlusal plane. Pre-emergent tooth movement seems to be controlled by a different
mechanism than post-emergent tooth movement.
Eruptive movement begins soon after the root begins to form. The PDL also develops only after
root formation has been initiated, and once established, it must be remodel-ed to permit eruptive
tooth movement. The remodeling of the PDL fiber bundles is achieved by fibroblasts, which
simultaneously degrade and synthesize the collagen fibers as required across the entire extent of
the ligament. As the tooth moves occlusally, bone is resorbed occlusal to it and new bone is formed
apical to the tooth.
At the time of emergence of the tooth into the oral cavity, its dental follicle fuses with the oral
epithelium. Following emergence the tooth erupts rapidly until it approaches the occlusal level
(post-emergent spurt). Environmental factors such as muscle forces from the tongue, cheeks and
lips, as well as forces of contact of the erupting tooth with other erupted teeth, help determine the
final position of the tooth in the dental arch. The effect of thumbsucking onthe dentition is an
obvious example of environmental determination of tooth position.
[See Post-emergent spurt]
[See “Cone-funnel” mechanism]
Physiologic tooth movement
• Post-eruptive tooth movement
Movement of the teeth after they have reached their functional position in the occlusal plane. The
same mechanisms that control post-emergent tooth movement seem to regulate post-eruptive
tooth movement in the vertical plane. Post-eruptive tooth movement can be divided into three
categories:
1. Vertical movement occurring in concert with jaw growth (“juvenile occlusal equilibrium”). This
movement is completed toward the end of the second decade, when jaw growth ceases, and it
occurs earlier in girls than in boys. It is related to the growth of the mandibular ramus, which
causes the maxilla and mandible to grow apart from each other, permitting further eruptive
movement of the teeth.
2. Movement to compensate for the continuous occlusal wear of the teeth (“adult occlusal
equilibrium”). This axial post-eruptive movement occurs even after the apices of the teeth are fully
formed. It is demonstrable by the tendency of teeth to overerupt when their antagonist is lost, at
any age.
3. Movement to compensate for interproximal wear. Wear also occurs at the contact points
between teeth on their proximal surfaces, and its extent can be considerable (more than 7 mm in
the mandibular dental arch). This interproximal wear is compensated for by a process known as
“mesial drift.” The mechanism of this mesial drift is multifactorial and is attributed to the anterior
component of the occlusal force, to contraction of the transseptal fibers and/or pressure from the
perioral and intraoral soft tissues (cheeks and tongue).
[See Drift (of teeth), Mesial drift (Mesial migration, Approximal drift)]
[See Occlusal equilibrium, Juvenile occlusal equilibrium]
[See Occlusal equilibrium, Adult occlusal equilibrium]
Physiologic tooth movement
• Pre-eruptive tooth movement
Movement of the deciduous and permanent tooth germs within the tissues of the jaw before they
begin to erupt. As the deciduous tooth germs grow, the space for them in the developing jaw
becomes less, and initially they are “crowded” in the anterior region. This “crowding” usually is
alleviated before emergence by growth of the jaws, mainly in the midline, which permits mesial
movement of the anterior tooth germs.
The deciduous molar germs gradually increase in size and become displaced distally in
association with sagittal growth of the jaws. At the same time, the tooth germs are moving
occlusally with the increase in height of the jaws. The permanent anterior tooth germs initially
develop on the lingual aspect of their predecessors. From this position they shift considerably as
the jaws develop (e.g. the incisors eventually come to occupy a position on the lingual aspect of
the roots of their predecessors, and the premolar germs are positioned between the divergent
roots of the deciduous molars). In the maxilla, the permanent molar germs initially develop with
their occlusal surfaces facing distally, and swing into position only when the maxilla has grown
sufficiently to provide space for such movement. In the mandible, the permanent molars develop
with their axes showing a mesial inclination, which gradually becomes more vertical.
“Pigtail”
The twisted, cut end of a stainless steel ligature or brass separator that is tucked under the
archwire, under a bracket wing, or in the interproximal area for patient comfort.
“Pigtail” attachment (Coil eyelet)
A small orthodontic attachment consisting of a pigtail-shaped wire soldered onto a bonding base.
“Pigtail” attachments are used mainly as handles for elastic traction.
[See Attachment, Orthodontic]
Pin
T-shaped orthodontic auxiliary, used mainly in the Begg technique and its modifications. The pins
are inserted in the vertical slots of the brackets, and their primary purpose is to retain the archwire
in the main slot.
SUBTERMS:
Pin
• Bi-level pin
Used to create an additional slot for a second archwire, which can be inserted between the bi-level
pin and the gingival tie-wing of the bracket.
Pin
• Power pin
Used as an attachment to anchor orthodontic elastic bands for the application of traction.
Placebo
Inactive substance, device or measure that is believed by the patient to have an active therapeutic
value, but in fact, does not. Placebos sometimes are used in controlled studies to determine the
effect of drugs without the influence of bias.
Plagiocephalic
An individual with an asymmetric skull shape. Plagiocephaly may be produced by unilateral
synostosis of the coronal or the lambdoidal suture.
[Compare with Trigonocephalic]
Plate
A non-specific term implying a removable orthodontic appliance constructed at least partially of
acrylic.
Platybasia
A term denoting a more obtuse than normal cranial base angle (saddle angle, BaSN).
[Compare with Basilar kyphosis (Kyphosis of the cranial base)]
“Play” of an orthodontic wire in the bracket slot
The amount of freedom allowed at the bracket-to-wire interface due to the difference in size
between the wire and the bracket slot. The amount of “play” varies depending on the relative size
of the bracket and wire and refers to the type of individual movement intended (usually a distinction
is made between second-order and third-order clearance). For example, to achieve a certain
amount of torquing movement of an individual tooth, more activation (in degrees) is necessary
when using a 0.016 x 0.022-inch (0.41 x 0.56-mm) archwire, compared to using an 0.018 x 0.025-
inch (0.46 x 0.64-mm) archwire, because of the increased torsional play in the former case.
[See Second-order clearance]
[See Third-order clearance]
Plication
The stitching of folds or tucks in a tissue to reduce its size, as in the retrodiscal tissue of the
temporomandibular joint, in an attempt to reposition an anteriorly displaced articular disc and reestablish
a physiologic anatomic disc-to-condyle relationship. A type of disc-repositioning surgery.
Point of application
One of the four characteristics of vectorial quantities (the other three are line of action, sense and
magnitude). The point on a body where the vector is applied.
Point of application
One of the four characteristics of vectorial quantities (the other three are line of action, sense and
magnitude). The point on a body where the vector is applied.
Point of dissociation
[See Burstone’s geometry classes, Geometry IV]
Pontic
The part of a restoration that replaces a missing natural tooth.
Post-emergence eruption
[See Physiologic tooth movement, Eruptive tooth movement]
Post-emergent spurt
The phase of relatively rapid eruptive movement, from the time a tooth first penetrates the gingiva
until it reaches the occlusal level.
[See Occlusal equilibration (Occlusal adjustment)]
Postural
Related to position.
Post-emergence eruption
[See Physiologic tooth movement, Eruptive tooth movement]
Predisposing factors
Factors that increase the risk of developing a disease or condition.
Preferred provider organization (PPO)
A formal agreement between a purchaser of a health benefits program and a defined group of
health care practitioners for the delivery of services to a specific patient population, usually as an
adjunct to a traditional plan, using discounted fees for cost savings. Preferred provider
organizations provide a reduced fee for each service, rather than a fixed fee for all services.
Preferred provider organizations allow treatment by a non-PPO physician or dentist, for a higher
fee. [Modified from the AAO Glossary of Dentofacial Orthopedic Terms, 1993.]
[Compare with Health maintenance organization (HMO)]
Premature loss
Loss of a deciduous tooth prior to its normal time of exfoliation, due to extraction or undue
resorption of its root. An example of the latter is the situation in which there is severe lack of space
in the dental arch for eruption of a permanent incisor, which sometimes results in resorption of the
root of not only its predecessor, but also of that of the adjacent deciduous tooth.
Premaxilla
The triangular part of the hard palate anterior to the incisive foramen, including the four maxillary
incisor teeth, extending in the midline up to the piriform rim. The premaxilla is derived
embryologically from the primary palate. It is a separate bone in most animals; however, in humans
it generally is not independent of the maxilla, even in the early developmental stages.
[See Segment, Premaxillary segment]
Presurgical infant orthopedics (PSIO, Presurgical orthopedic treatment, PSOT, Neonatal
maxillary orthopedics)
Any orthopedic manipulation of the segments of the clefted maxilla in a newborn with complete
unilateral or bilateral CLPaiming at establishing a more normal maxillary alveolar arch form or at
retracting a protruding premaxilla to facilitate the surgical repair of the lip. This procedure, the value
of which is under investigation, usually involves the use of plates
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