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technique (appliance) A method or procedure based on the use of certain appliances in specific ways. There are numerous variations and combinations.

telescoping bite Total lingual crossbite of the lower arch.

temporomandibular articulation The bony articulation between the mandible and the temporal bones, consisting of the right and left temporomandibular joints.

TMD Temporomandibular dysfunction.

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 sometimes extending into middle or late childhood. In certain situations, may produce or exacerbate malocclusion. 

tie-back An omega loop, soldered or welded hook on an archwire, usually anterior to the molar tubes 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 also between the teeth, can inhibit normal eruption and so produce an open bite.

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 moving 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 traced from a cephalometric radiograph, showing 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 remaining unchanged is necessary 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. (Teeth which have switched positions).

transseptal fibers Gingival fibers traversing the septum between teeth, providing 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, 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.