- U -
ugly duckling stage A stage of dental development during the incisor transition, characterized generally by linguoversion of mandibular lateral incisors, malalignment and flaring of maxillary lateral incisors, and a median diastema between the maxillary central incisors. These aberrations may be self-corrective, but could persist and require treatment. First recognized by B.H. Broadbent.
underbite An ambiguous non-technical term for negative overjet. (archaic)
undermining resorption A microscopic local condition in which resorption may occur beyond the active area, undermining bone spicules and so leading to their more rapid removal.
universal appliance An orthodontic appliance developed by S.R. Atkinson, combining some of the principles of edgewise and ribbon arch appliances with very light arch wires.
uprighting Tipping inclined teeth to a more normal vertical axial inclination.
utility arch Similar to a step-down or by-pass arch, used in the edgewise technique to upright molars and depress anterior teeth, developed by R. Ricketts.
- V -
velopharyngeal insufficiency Anatomic or functional deficiency in the soft palate or superior pharyngeal constrictor muscle affecting closure of the opening between mouth and nose in speech, resulting in a 'nasal' speech quality.
vertex (anatomy) The most superior point on the top of the skull.
vertical dimension The vertical relationship of the mandible to the maxilla in the rest or occluded position.
vertical elastic traction Pertaining to forces occlusally directed and delivered through orthodontic attachments to tooth crowns as the result of the (stretching) activation of an 'up-and-down' elastic band.
vestibular screen (oral screen) A removable appliance, used to deflect or eliminate muscle forces on certain teeth. Commonly placed in the vestibule between the lips, cheeks and the teeth.
visceral swallowing The term used to describe the swallowing pattern in which the tongue is thrust between the teeth (i.e., infantile swallowing pattern).
Visual Treatment Objective (VTO)A diagnostic and communication aid consisting of a cephalometric tracing or computerized projection, modified to show anticipated changes in the course of treatment.
- W -
w arch W-shaped maxillary expansion arch, usually soldered to the lingual of the maxillary molars. (Also known as Porter arch.)
wear facet A flat, polished surface on a tooth produced by physiologic or parafunctional occlusal contact.
Wilson, curve of See curve of Wilson.
working side The lateral segment of the dentition toward which the mandible is moved during masticatory function.
World Federation of Orthodontists (WFO) An organization of orthodontic specialists formed initially by 69 orthodontic organizations from 62 countries participating in the 4th International Congress in San Francisco, CA, USA on May 15, 1995. The purpose of the WFO is to advance the art and science of orthodontics throughout the world.
- X -
x-bite Abbreviation for crossbite.
x-rayElectromagnetic radiation produced when electrons strike a target under high voltage in a vacuum. The term is sometimes used incorrectly as a synonym for radiograph.
- Y -
no entries at "Y."
- Z -
zygomaThe bone that articulates with the maxilla to form the lateral wall of the orbit and the cheek bone itself. Its posterior extension, the processus temporalis, articulates with the zygomatic process of the temporal bone, and together they provide major support for the muscles of mastication. 
