TMJ (temporomandibular joint) One of the two paired articulations between the temporal bones of the skull and the mandible; the condylar process of the mandible articulates on the eminence of the glenoid fossa of the temporal bone.
therapeutic diagnosis An assessment of the objectives and available methods of treatment in light of conditions existing in the individual patient.
threshold force The minimum magnitude of force needed to produce a desired orthodontic displacement (a theoretical concept).
thumb (or finger) sucking A normal infantile activity that sometimes extends into middle or late childhood. In certain situations, it may produce or exacerbate malocclusion.
tie-backAn omega loop, soldered or welded hook on an archwire anterior to the molar tubes which is tied to an attachment distal to it in order to fixate archwires in place.
tinnitus Noise in the ears, such as buzzing, ringing, roaring, clicking; a symptom often reported in TMJ dysfunction problems.
tomograph A radiograph of a selected layer of the body produced while shifting the film and x-ray source in opposite directions around an axis located in the region of interest. This movement blurs outside structures while maintaining sharpness in the region of interest.
tongue crib An appliance used to control undesirable and potentially deforming tongue movements, i.e., a posturing or thrusting of the tongue between the anterior teeth.
tongue thrust Interposition of the tongue between the anterior teeth, especially in the initial stage of swallowing. This action, often combined with a resting position of the tongue between the teeth, can inhibit normal eruption and produce an open bite.
tonsils Areas of lymphoid tissue on either side of the throat. The term tonsils most commonly refers to the palatine or the faucial tonsils. An infection of the tonsils is called tonsillitis.
tooth positioner See positioner.
tooth size discrepancy Lack of proportional harmony in the width (mesiodistal diameter) of various tooth crowns and the available space in the dental arch, causing relative spacing or crowding in different parts of the dentition.
torque A third order couple that moves the crown in one direction and the root in the opposite direction.
torsiversion A tooth malposition characterized by rotation around the long axis of the root (not related to torque as described above).
torus An exostosis on the palatal midline or low on the lingual alveolar surface of the mandible in the canine-premolar area. (torus palatinus/torus mandibularis)
toughness The maximum amount of energy, referenced to a passive state, transferred to a body in the form of mechanical work, that the body can absorb prior to structural failure (ordinarily by fracture or rupture); the total area under the load-deformation plot.
tracing (cephalometric) An overlay drawing made from a cephalometric radiograph that shows specific structures and landmarks that may provide a basis for a variety of measurements.
traction Pertaining to a force-delivering component of an appliance that is mechanically activated by elastically extending its characteristic length (e.g., as in the stretching of an elastic module or a coiled spring).
transitional dentition See dentition.
translation The movement of a body as a whole such that the displacements of all particles of that body are alike (equal) in magnitude, direction, and sense. The angulation of the long axis must remain unchanged for a tooth movement to be translational. Any movement of a body that is not a translation in a rotation.
transposition Teeth positioned out of their normal position in the dental arch, specifically describes an anomaly where adjacent teeth have switched positions.
transseptal fibers Gingival fibers traversing the septum between teeth that provide a fibrous connection between the teeth.
transverse displacement An orthodontic tooth movement characterized by displacements of points of the tooth at right angles (perpendicular) to the long-axis orientation.
trauma Tissue damage caused by an external force, such as a blow in an accident or abnormal clenching or grinding of the teeth.
trismus Muscle spasm (cramp).
tuberosity The posterior aspect of the maxillary alveolar process.
Tweed triangle A constructed triangle on the lateral cephalogram or tracing which is formed by the mandibular plane, Frankfurt plane and the long axis of the mandibular incisor. Used as a diagnostic aid by C.H. Tweed.
twin block appliance A functional appliance developed by William Clark, with inclined planes on maxillary and mandibular components, to guide the mandible forward.
twin bracket An edgewise bracket formed by two single brackets side by side on one base. (B. Swain)
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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. B.H. Broadbent “coined” the term.
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.
unilateral Relating to one side.
universal appliance An orthodontic appliance developed by S.R. Atkinson which combined some of the principles of edgewise and ribbon arch appliances with very light archwires.
uprighting Tipping inclined teeth to a more normal vertical axial inclination.
utility arch Used in the edgewise technique to upright molars and depress anterior teeth similar to a step-down or by-pass arch, developed by R. Ricketts.
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velopharyngeal insufficiency (VPI) Anatomic or functional deficiency in the soft palate or superior pharyngeal constrictor muscle which affects closure of the opening between the mouth and the nose in speech. The result is in a 'nasal' speech quality.
veneer A protective or ornamental facing. Often used as a restoration to alter the shade and shape of the teeth for esthetics.
vertex (anatomy) The most superior point on the top of the skull.
vertical dimension The vertical distance between two selected anatomic or marked points; specifically relates to the vertical relationship of the mandible to the maxilla.
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.
vestibule The portion of the oral cavity that is bounded on the medial side by the gingiva, alveolar process, teeth and on the lateral side by the lips or cheek.
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 that consists of a cephalometric tracing or computerized projection which is modified to show anticipated changes in the course of treatment.
voxel A three-dimensional version of a pixel. Voxels are generated by computer-based imaging systems, such as CT and MRI. Using voxels, three-dimensional simulations of objects can be reconstructed by imaging systems.
vulcanite An obsolete material that was used to fabricate removable appliances. It is a combination of caoutchouc and sulfur. It hardens in the presence of certain heat and pressure.
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w arch W-shaped maxillary expansion arch, usually soldered to the lingual of the maxillary molars. (Also known as Porter arch.)
Waldeyer’s ring(Waldeyer's tonsillar ring) Anatomical term that describes the lymphoid tissue ring located in the pharynx.The ring consists of (from superior to inferior) the adenoids, tubal tonsils, palatine tonsils and the lingual tonsils.
wear facet A flat, polished surface on a tooth which is produced by physiologic or parafunctional occlusal contact.
weld A joint between pieces of metal at faces that have been made plastic by heat or pressure.
Wilson, curve of See curve of Wilson.
Wolff’s Law Eponym for the principle that a bone, either normal or abnormal, will develop the structure most suited to resist those forces acting on it.
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 at 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.
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x-bite Abbreviation for crossbite.
x-ray Electromagnetic radiation produced when electrons strike a target under high voltage in a vacuum. The term is sometimes used incorrectly as a synonym for radiograph.
xerostomia A symptom in which too little saliva is produced in the mouth. Also called ‘dry mouth’.
- Y –
yield strength The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of .2% is commonly used.
Youngs modulus (modulus of Elasticity, E) The ratio of stress to corresponding strain below the proportional limit. It is a measure of stiffness.
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zygoma The 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.