Glossary of Commonly-Used Terms in Orthodontics

anchorage	resistance to unwanted tooth movement caused by the reactive component of an orthodontic force; refers also to the intra- and extraoral structures that supply the resistance
Angle's classification of occlusion	a definition of malocclusion based on the relationships of the first permanent molars
angulation	the tilt of the long axis of a tooth in a mesial or distal direction; see inclination
anterior crossbite	one or more teeth in the maxillary anterior segment is lingual to one or more of the opposing teeth in the mandibular anterior segment in maximum intercuspation
anterior segment	all of the canine and incisor teeth in a given dental arch
arch wire	a wire applied to two or more teeth through fixed attachments to cause or guide orthodontic tooth movement
arch circumference or arch perimeter	the distance from the mesial contact of one first permanent molar to its antimere as measured through the contact points or buccal cusp tips of all of the intervening teeth, ignoring those teeth that are malpositioned or blocked out so that the measurement represents an ideal arch form; see arch length
arch depth	the perpendicular distance from a point between the central incisors to a line connecting the mesial contacts of the first permanent molars; see arch length
arch length	same as arch depth; but note that 'arch length' is often used as a synonym for arch circumference or arch perimeter
band	a circular metal strip that is adapted to fit closely around a tooth; various components of an orthodontic appliance may be welded or soldered to it
base, bracket	the part of a bracket that is attached either to a metal band or bonding pad
bimaxillary	both the upper and lower jaw
blocked out	a tooth that is positioned away from its proper position in the dental arch due to insufficient space
bonding pad	the retentive portion of a fixed orthodontic attachment which locks it mechanically to the bonding material; the pad usually has a fine mesh surface
brachycephalic	a short skull, with a cranial index of 80 or more; see cranial index This term, or a variant "brachyfacial," is sometimes used to describe a short, wide face, properly referred to as euryprosopic.
bracket	a metal, plastic, or ceramic fixed attachment which holds an arch wire
buccal tube	a fixed attachment which is open only at each end. Tubes may be round or rectangular in cross section; round tubes are usually .045 inches in diameter to receive auxiliaries such as a facebow or lip bumper, rectangular tubes are either .018 x .025 or .022 x .028 inches in order to receive arch wires and generally are placed on the most distal molar tooth in the appliance.
buccal segment	all of the premolar and molar teeth in a given quadrant
cell-free zone	descriptive term for the necrosis that occurs in a pressure zone of the periodontal ligament (PDL) as a result of excessive orthodontic force; the same as hyalinized zone
center of resistance	considering the tooth in its alveolus, it is that point through which a pure force would result in translation of the tooth without any rotational effect; for a given tooth the center of resistance is found at approximately one-third (0.3 to 0.5) of the distance from the alveolar crest to the apex, and its location does not change (unless root length or alveolar crest height changes)
center of rotation	a point around which all points on the tooth rotate; the center of rotation can change depending upon the forces and moments acting upon the tooth
cephalometer	the apparatus used to take cephalometric radiographs, consisting of an X-ray source, cephalostat and film holder
cephalometric analysis	click here to view definitions of some landmarks and measurements used in the Illnois analysis
cephalostat	the head holder used in cephalometric radiography to orient the patient in relation to the X-ray source and film holder; it usually includes a set of ear rods, an orbital pointer and a nose rest
cervical-pull headgear	a headgear that uses a cervical neck strap as anchorage, thus directing the reaction force of the headgear force module to a site that is outside the oral cavity; the direction of the force on a maxillary molar is backward and downward
Class I malocclusion (Angle)	a malocclusion with correct mesiodistal relationship of the first permanent molars
Class II malocclusion (Angle)	a malocculsion in which the lower first permanent molar is positioned distally relative to the upper; see distoclusion. To classify a unilateral Class II malocclusion, see subdivision.
Class III malocclusion (Angle)	a malocculsion in which the lower first permanent molar is positioned mesially relative to the upper; see mesioclusion. To classify a unilateral Class III malocclusion, see subdivision.
couple	a couple is produced when two equal and opposite forces act on a body; the magnitude of the couple is equal to the product of one of the forces times the perpendicular distance between the forces
cranial index	the ratio of maximum cranial breadth (measured wherever found) to maximum cranial length (glabella to opisthocranium), expressed as a percentage
crowding	exists when the sum of the mesiodistal widths of the teeth in an arch exceeds the arch circumference
dental (dentoalveolar) malocclusion	a malocclusion characterized by deviation from normal in the teeth and their supporting tissues; the size, shape and position of craniofacial bones is within the normal range
diagnostic setup	teeth are cut from a plaster cast and repositioned with wax; setups are used to evaluate alternative treatment plans
direct resorption	removal of the cortical bone of the alveolar wall by clast cells in the periodontal ligament of a tooth being moved by an orthodontic force; note that this is not possible in a cell-free zone compare to undermining resorption
distoclusion	distal position of the lower buccal teeth in relation to the upper; see Angle Class II
division 1	an Angle Class II malocclusion in which the maxillary incisors are positioned forward in relation to the lowers resulting in marked overjet
division 2	an Angle Class II malocclusion in which the maxillary incisors are in close relation to the lowers, usually with a deep overbite
dolichocephalic	a long skull, with a cranial index of 74.9 or less; see cranial index This term, or a variant "dolichofacial," has been neologized to describe a long, narrow face, properly referred to as leptoprosopic.
E space	the difference between the mesiodistal widths of the primary second molar and the second premolar; generally the second premolar is smaller than the primary second molar
ectopic eruption	any tooth can erupt ectopically; when applied to the maxillary first permanent molar it describes a condition wherein the permanent molar erupts with excessive mesial angulation, resulting in resorption of the second primary molar and lack of full eruption of the first permanent molar
elastic limit	the maximum stress a wire or spring can withstand without permanent deformation
euryprosopic	a low, wide face, with a facial index of 84.9 or less; see facial index
extrusion	displacement of a tooth along its long axis out of the alveolus; sometimes called forced eruption
facebow	the wire portion of an orthodontic headgear, consisting of an inner and outer bow; the inner bow is connected to the teeth by means of a round tube on an orthodontic band, or by a 'J' hook to an arch wire, the outer bow is connected to a neck strap or headcap by an interposed force module
facial index	the ratio of facial height (nasion to gnathion) to zygomatic breadth ( zygion to zygion), expressed as percentage
functional shift	the mandible moves excessively from initial contact position to maximum intercuspation, usually resulting in an anterior (forward shift) or posterior (lateral shift) crossbite
glabella	most anterior point on the midsagittal plane between the superciliary arches; on the living it is found above the root of the nose between the eyebrows
headcap	that portion of an orthodontic headgear that rests on a portion of the occipital part of the cranium, thus directing the reaction force of the headgear force module to a site that is outside the oral cavity; the direction of the force on the maxillary molar is backward or backward and upward (see neck strap)
headgear	an apparatus that is used to deliver force to the teeth from outside the oral cavity; it consists of three parts: a facebow, a headgear force module and a neck strap or headcap (see high-pull, occipital-pull, and cervical pull headgear)
headgear force module	the source of force for an orthodontic headgear; it may consist of an elastic strap or rubber bands, but modern "safety" headgear typically use a small plastic part with an internal spring that is designed to "breakaway" if the facebow is pulled forward
high-pull headgear	a headgear that is arranged so that the direction of the force is markedly upward and backward; this apparatus uses a headcap as anchorage
hyalinized zone	a term which describes the sometimes glassy appearance of a cell-free zone in the light microscope; see cell-free zone
ideal occlusion	no malocclusion present
impacted	a tooth that has failed to erupt into the oral cavity; in orthodontics this often describes maxillary canines and third permanent molars that occupy a position from which normal eruption is highly unlikely
inclination	the tilt of the long axis of a tooth in the buccolingual or faciolingual direction; see angulation
infraocclusion	a tooth or teeth positioned below the plane of occlusion
intermaxillary	between the upper and lower jaws
intrusion	displacement of a tooth along its long axis into the alveolus
leeway space	the difference between the mesiodistal widths of the primary canine, first and second primary molars and the permanent canine, first and second premolars
leptoprosopic	a high, narrow face with a facial index of 90 or more; see facial index
ligature	a tie used to secure the brackets on individual teeth to an orthodontic arch wire; usually made of wire or elastic material -- ligatures may also be used to secure removable lingual arches, lip bumpers, etc. in their respective attachments.
load-deflection rate	force per unit displacement of a spring; the lower the rate, the smaller the force developed for a given amount of displacement, and vice versa
mesioclusion	mesial position of the lower buccal teeth in relation to the upper; see Angle Class III
mesocephalic	a skull that is neither long nor short, with a cranial index that ranges from 75 to 79.9; see cranial index
mesognathic	jaws slightly forward to the normal position in relation to other facial structures
mesoprosopic	a face that is neither wide nor narrow, with a facial index that ranges from 85.0 to 89.9; see facial index
moment of a couple	an applied couple tends to produce a turning effect or rotation on the body on which it acts; the center of rotation is always coincident with the center of resistance regardless of where the couple is applied to the body
moment of a force	an applied force tends to produce a turning effect or rotation on the body on which it acts; the magnitude of the moment is equal to the product of the force times the perpendicular distance from the line of action of that force to the point around which the rotation occurs (see center of rotation)
neck strap	that portion of an orthodontic headgear that rests on the back of the neck, thus directing the reaction force of the headgear force module to a site that is outside the oral cavity; see cervical-pull headgear
neutroclusion	normal mesiodistal occlusal relationships of the buccal teeth
nickel-titanium or Ni-Ti	arch wires made of a nickel-titanium alloy which deliver a much lower force for a given amount of deflection than comparable wire made of resilient stainless steel; see load-deflection rate
normal occlusion	optimal occlusion as it exists in real life; minor irregularities may be present
occipital-pull headgear	a headgear that is arranged so that the direction of the force is mostly backward; this apparatus uses a headcap as anchorage
open bite	a malocclusion in which some teeth cannot be brought into contact with opposing teeth and no vertical overlap is present
open bite, functional	failure of incisors to contact in maximum intercuspation even though vertical overlap is present
opisthocranium	the point on the midline of the skull which projects the farthest backward
orthodontic appliance	any device used to move teeth or influence the shape of the jaw
orthognathic	normal position of the jaws in relation to other facial structures
orthognathic surgery	surgical repositioning of one or both jaws; usually done concurrently with orthodontic repositioning of the teeth
overbite	vertical overlap of upper teeth over lower teeth; usually refers to incisors
overjet	horizontal projection of upper teeth beyond the lower teeth; usually refers to incisors; in Class III malocclusion incisor overjet may be recorded as negative
posterior crossbite	one or more teeth in the maxillary buccal segment is lingual to one or more of the opposing teeth in the mandibular buccal segment in maximum intercuspation
pressure zone	that part of the periodontal ligament that is compressed as a result of an applied orthodontic force; see cell-free zone
primate space	in the primary dentition, a space mesial to the maxillary primary canines and distal to the mandibular primary canines
proclined	a forward inclination of an incisor tooth, usually determined from a cephalometric analysis; see inclination
prognathic	a forward position of the mandible relative to other facial structures
protraction	anterior movement of teeth
protrusive or procumbent	a forward position of an incisor tooth, usually determined from a cephalometric analysis
reproximation	see stripping
retraction	posterior movement of teeth
retroclined	a backward inclination of an incisor tooth, usually determined from a cephalometric analysis; see inclination
retrognathic	a backward position of the mandible relative to other facial structures
retrusive or recumbent	a backward position of an incisor tooth, usually determined from a cephalometric analysis
rotation	turning of a tooth by movement around its long axis; a tooth is said to be rotated if turning it around its long axis is required in order to bring it into its proper position
separator	a device inserted between teeth which are to be fitted with orthodontic bands; usually made of elastomeric material or small metal springs, separators will push the teeth apart so that the band material passes freely through the contact area.
sheath	a fixed attachment, welded or soldered to a band, which is specifically designed to receive removable auxiliaries such as lingual arches, etc.
skeletal malocclusion	a malocclusion characterized by deviations from the normal in the size, shape, or position of craniofacial bones; there may or may not be a concomitant dentoalveolar malocclusion
slot, bracket	that portion of a bracket which receives an arch wire; Edgewise bracket slots are rectangular in cross section, either 0.018 x 0.025 or 0.022 x 0.028 inches in dimension with the shorter dimension open to the buccal or labial
source	the tube which supplies X-rays in a cephalometer ; see target
spacing	exists when the sum of the mesiodistal widths of the teeth in an arch is less than the arch circumference
Spee, curve of	the extent to which the cusp tips of the lower dental arch describe a curve, concave upwards in the lateral view; some authors define this curve as extending only from the canine through the molars; others include the incisors
stripping	reduction of mesiodistal tooth width by removal of interproximal enamel
subdivision	an Angle Class II or Class III malocclusion that is unilateral; the designation of the subdivision as 'right' or 'left' indicates the side which is Class II or Class III
supraocclusion	eruption of a tooth or teeth beyond the normal level
target	the target anode which is bombarded by a stream of electrons from a heated cathode in an X-ray tube; is used as one factor in calculating magnification ratios in cephalometry
tension zone	that part of the periodontal ligament that is tensed as a result of an applied orthodontic force
tie wing	that portion of a bracket which retains a ligature
tipping	the tendency of a tooth to turn or rotate in either the mesio-distal or bucco-lingual direction when a force is applied to the crown; thus, tipping can change either the inclination or angulation of a tooth
tipping, uncontrolled	the application of a force to the crown will cause a tooth to rotate around a center near the middle of the root; thus, the apex will move in the opposite direction to the crown as the tooth tips
tipping, controlled	the application of a force plus a moment to the crown which is designed to cause the tooth to rotate around a center that is at the apex; thus, the crown moves the greatest distance and the apex moves the least as the tooth tips
torque	with respect to the Edgewise appliance, it is the force system created when a rectangular arch wire is engaged in a bracket slot in torsion, and which has the effect of changing the inclination of the tooth; also refers to torsion bends (twisting) deliberately placed in a rectangular arch wire which are intended to change the inclination of the tooth
translation	all points on a tooth move in a parallel straight line; the center of rotation is at infinity
twin bracket	an arrangement in which two Edgewise brackets are attached to the same base in order to effect better control of individual tooth rotations; also referred to as a Siamese bracket.
undermining resorption	removal of the cortical bone of the alveolar wall by clast cells in the marrow spaces adjacent to a cell-free zone; compare to direct resorption
zygion	the most lateral point on the zygomatic arch