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A See Point A (subspinale).

AAO See American Association of Orthodontists.

AAOF See American Association of Orthodontists Foundation.

AAOIC See American Association of Orthodontists Insurance Company.

AAOSI See American Association of Orthodontists Services, Inc.

ABO See American Board of Orthodontics.

acromegaly A disease caused by increased activity of the anterior pituitary and characterized in part by a marked lengthening of the mandible.

acrylic Methyl methacrylate, an organic resin commonly used for the construction of dental appliances, including orthodontic treatment and retention appliances.

activation The process of deforming an appliance part from its passive state (e.g.,the stretching of an elastic) and completing its engagement to produce a force system transmitted by the appliance to the dentition.

activation site The intraoral location of the activating process,often where the orthodontic force system is to be transmitted to the dentition.

activator A removable growth guidance orthodontic appliance, originally developed by Pierre Robin, Viggo Andresen and Karl Haupl, with later modifications by Schwarz, Bimler,Balters, Franker,Fleischer, Peters, etc.Also called a functional appliance.

Adams clasp A circumferential retention clasp (see crib) designed by C. Philip Adams to stabilize removable appliances by means of point contact with the mesio- and disto-buccal undercuts of individual buccal teeth.

adolescent dentition  See dentition.

adult dentition See dentition.

alveolar bone The bone that surrounds and supports the roots of the teeth.

alveolar process The unshaped ridge of maxillary or mandibular alveolar bone that surrounds and supports the roots of the teeth.

American Association of Orthodontists (AAO) The AAO is a professional association of educationally qualified orthodontic specialists dedicated to advancing the art and science of orthodontics and dentofacial orthopedics, improving the health of the public by promoting quality orthodontic care, and supporting the successful practice of orthodontics.

American Association of Orthodontists Foundation (AAOF) The AAOF, a 501(c)(3) organization, is the charitable arm of the AAO. The AAOF raises money for an endowment the earnings from which are used to support orthodontic research and teaching fellowships.

American Association of Orthodontists Insurance Company (a Risk Retention Group) (AAOIC) The AAOIC provides professional liability insurance for eligible United States members of the AAO. AAOIC is unique in that coverage is only available to AAO members and only orthodontists are insured by the company. The policyholders are also the shareholders of the Company. AAOIC is governed by a group of dedicated orthodontists and other experts who have one goal in mind: to provide a stable, efficiently run professional liability insurance company designed specifically to meet the unique needs of the AAO member orthodontists. See Risk Retention Group.

American Association of Orthodontists Services, Inc. (AAOSI) The AAOSI is the for-profit subsidiary of the AAO, dedicated to the evaluation and management of services that benefit the members? pursuit of professional success and financial security through quality insurance products and other services.

American Board of Orthodontics (ABO) The ABO is recognized by the American Dental Association as the official certifying body for the specialty of orthodontics.  Though sponsored by the American Association of Orthodontists, it is a separate and autonomous entity.  The mission of the ABO is to establish and maintain the highest standards of clinical excellence in orthodontics.

anchorage Resistance to activation force.  Anchorage may come from any of the following sources: intraoral ? teeth, bone and soft tissue; extraoral ? cervical = back of the neck, occipital = back of the head, cranial = top of the head.

Andresen appliance See activator.

Angle classification of malocclusion A classification of malocclusion introduced by Edward H. Angle. The governing criterion is the anteroposterior relationship of upper and lower first molars.

Class I malocclusion (neutroclusion) A malocclusion in which the mesiobuccal cusp of the maxillary first molar occludes in the buccal groove of the mandibular molar. "Class I" is sometimes incorrectly used as a synonym for normal occlusion, whereas it signifies only a normal sagittal relationship of upper and lower posterior teeth as they meet.

Class II malocclusion (distoclusion) A distal (posterior) placement of the mandibular (lower) molar, mesial (anterior) relationship of the maxillary (upper), or a combination of the two. The mesiobuccal cusp of the upper first molar occludes mesial to the buccal groove of the lower, usually near the embrasure between the lower molar and second bicuspid.

Class II, Division 1 A Class II molar relationship with proclined upper incisors with respect to the lower incisors.

Class II, Division 2 A Class II molar relationship, usually with the upper central incisors tipped lingually, the upper lateral incisors tipped labially, and an excessive overbite.

        Subdivision Denotes a unilateral malocclusion classification(e.g. Class II, division 2, subdivision).

Class III malocclusion (mesioclusion) Mesial (anterior) relationship of the lower first molar to the upper, a retruded relationship of the upper first molar to the lower, or a combination of the two. The mesiobuccal cusp of the upper first molar will typically occlude near the embrasure between the lower first and second molars.

ankylosis Abnormal immobility, union or fusion. May occur between two bones at their articulation (i.e., TMJ) or between teeth and alveolar bone. In such a case, the periodontal ligament is obliterated by a 'bony bridge' and the tooth root is fused to the alveolar bone.Dental ankylosis prevents both eruption and orthodontic movement. In a growing child, an ankylosed tooth appears to 'submerge' as adjacent unaffected teeth and alveolar bone continue their normal pattern of growth occlusally.

anodontia Congenital absence of teeth.

antegonial notch A concavity usually present in the lower border of the mandible, immediately anterior to the angle of the mandible. A deeper than normal antegonial notch may be indicative of mandibular underdevelopment.

anterior cranial base The anterior aspect of the floor of the cranial vault, commonly delimited cephalometrically by sella turcica and nasion.

anterior guidance Contact of maxillary incisors and mandibular incisors to guide mandible downward to create disarticulation of the posterior teeth.

anterior nasal spine Pointed bony process at the inferior margin of the piriform aperture. In cephalometric radiography, the tip is often used to define the anterior end of the palatal plane.

anteroposterior The global direction perpendicular to the coronal plane of the dentofacial complex; the anterior direction/sense is forward, and the posterior direction/sense is rearward.

anthropometry Measurement of the human body and its parts.

apical base Maxillary and mandibular bone that supports and is continuous with the alveolar processes (see basal bone). Although the demarcation between alveolar and basal bone is not specific, it is generally consideredto lie at the level of the apices of the roots.

appliance Any device designed to influence the shape and/or function of the stomatognathic system.

fixed appliance A bonded or banded appliance affixed to individual teeth or groups of teeth.

orthodontic appliance Any device used to influence growth or the position of teeth and jaws.

removable appliance An appliance not attached to teeth and removable from the mouth.

orthopedic appliance Any device used to influence the growth or position of bones.

functional appliance Any device, removable or fixed, designed primarily to effect skeletal and/or dental changes by modifying and utilizing the neuromuscular forces of the stomatognathic system (i.e., activator, bionator).

arch Collectively,the teeth or basal bone of either jaw.

alveolar arch The U-shaped alveolar bone that surrounds the dentition of either jaw.

dental arch The composite structure of the dentition and alveolar ridge basal arch. The U-shaped basal bone of either jaw.

arch form The shape of an individual dental arch or of an arch wire formed to fit or shape that arch.

arch length A measurement of available and required space needed to align the teeth.

arch length deficiency Difference between available and required space to align the teeth (see discrepancy).

archwire or arch wire A wire engaged in orthodontic attachments, affixed to the crowns of two or more teeth, and capable of causing or guiding tooth movement.

continuous arch wire A wire that engages or could engage, through crown attachments, all of the erupted teeth in the maxillary or mandibular dental arch.

sectional or segmental arch wire An arch wire that engages, through crown attachments, only a few teeth (e.g., only the four incisors or only a posterior dental segment).

articulare The point of intersection of the dorsal contour of the mandibular condyle and the temporal bone, as viewed on the lateral cephalometric film. (A. Bjork)