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obturator A prosthesis used to close an opening. Frequently used to close the defect caused by a cleft palate.

occlusal Pertaining to the chewing surfaces of the posterior teeth. May be used to identify those tooth surfaces, as well as the direction (upward in the lower arch, downward in the upper).

occlusoapical The local direction perpendicular to the occlusal plane; also termed 'occlusogingival.'

occlusal dysfunction A term often used to describe abnormal functional forces and improper contact of upper and lower teeth. Untoward reaction beyond the teeth and investing tissues is claimed by some dentists, with the possibility of enhancing a multifactorial TMD etiology.

occlusal index A rating or categorizing system that assigns a numeric score or alphanumeric label to an individual's occlusion. There are five types: diagnostic, descriptive-epidemiological, treatment need or priority, treatment outcome, treatment complexity.

occlusal plane The imaginary surface on which upper and lower teeth meet in occlusion. It is actually a compound curved surface, but is commonly approximated by a plane (straight line in the lateral view) based on specific reference points within the dental arches.

occlusion The relationship of the maxillary and mandibular teeth as they are brought into functional contact.

onplant An anchorage fixture integrated to a bony surface beneath the soft tissue

open bite A malocclusion in which some teeth cannot be brought into contact with opposing teeth.

oral screen See vestibular screen.

orbitale The most inferior point on the lower border of the left orbit. A craniometric and cephalometric landmark.

ortho- A prefix denoting straight or correct.

orthodontic (orthopedic) Relating to correction of abnormal dental relationships, including facial structures and neuromuscular abnormalities.

orthodontic attachment The element affixed to the tooth crown that transmits force from the arch wire or auxiliary to the dentition (e.g., a bracket).

orthodontic displacement Tooth movement achieved through biomechanical remodeling of the periodontal ligament and/or the alveolar bone.

orthodontic force Force generated by the orthodontic appliance that contributes to the correction of a malocclusion.

orthodontics/dentofacial orthopedics That dental specialty which includes the diagnosis, prevention, interception, guidance and correction of malrelationships of the developing or mature orofacial structures.

orthodontist A dental specialist who has completed an advanced post-doctoral course, accredited by the American Dental Association of at least two academic years in the special area of orthodontics.

orthognathic Normal relationships of the jaws.

orthognathic surgery Surgery to alter relationships of teeth and/or supporting bones, usually accomplished in conjunction with orthodontic therapy.

orthopedic Correction of abnormal form or relationship of bone structures. May be accomplished surgically (orthopedic surgery) or by the application of appliances to stimulate changes in the bone structure by natural physiologic response (orthopedic therapy).

osseous Of or pertaining to bone.

ostectomy Surgical removal of a bone or part of a bone.

osteogenesis See distration osteogenesis.

osteotomy Surgical procedure involving the cutting of bone. 

overbite Vertical overlapping of upper teeth over lower teeth, usually measured perpendicular to the occlusal plane.