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labial Of or pertaining to the lip. Identifies a surface facing the lips. The same as 'facial' in the anterior portion of the dentofacial complex.

labial arch or bow A wire that traverses the labial surfaces of the teeth.

labial sulcus The furrow that lies between the lips and the alveolar process.

labial root (lingual crown) torque The third-order couple of a transverse force system applied to the crown(s) of a tooth or dental segment having the potential for rotational displacement resulting in labial movement of the root(s) and/or lingual movement of the crown(s).

labiolingual appliances A fixed orthodontic appliance that includes both facial and lingual crown attachments and archwires.

labioversion General term indicating the deviation of a tooth toward the labial.

labrale inferior Most forward point of the lower lip.

labrale superior Most forward point of the upper lip.

laminography Tomography,i.e., sectional radiography.

landmarks,cephalometric Anatomic and constructed measure points used in analysis of cephalometric radiographs.

lateral cephalometric radiograph An x-ray taken according to cephalometric conventions with the x-ray source facing the right side of the face and perpendicular to the mid sagittal plane. The x-ray film faces the left side of the face. This radiograph is used to measure and determine sagittal and verticalcraniofacial relationships. See cephalometrics.

lateral excursion Movement of the lower jaw away from the middle position.

leeway space The difference between the combined widths of the three buccal primary teeth (canine and two molars) and their permanent successors (canine and two premolars).

Le Fort surgical procedure Surgical procedures in which parts of the upper face are completely separated from their supporting structures and repositioned to effect corrective alignment.

Le Fort I surgical procedure A procedure in which the maxillary dentition and supporting alveolar process are repositioned on their bony base.

Le Fort II surgical procedure A procedure, also referred to as a pyramidal fracture, in which the maxilla are separated from their base at the junction of the nasal and frontal bones, through both orbital rims, leaving the lateral orbital rims and nasal processes intact.

Le Fort III surgical procedure A procedure in which the entire facial bone complex is separated from the cranial base.

leveling The initial phase of comprehensive orthodontic treatment using fixed appliances designed to change the line of intercuspation from a curve to a straight line; to align the teeth in the same plane.

leveling wire Orthodontic wire, ordinarily round (in cross-section) and exhibiting low flexural stiffness, used in the leveling phase of treatment.

ligament,periodontal See periodontal ligament.

ligature Typically of annealed wire, rubber, or a polymer, a tie that secures the archwire in the bracket-slot.

light-wire technique An orthodontic treatment modality in which the appliance components to be activated are relatively flexible, resulting in relatively small force values, active over long time periods.

limited treatment Orthodontic treatment with a limited objective, not involving the entire dentition. It may be directed at the only existing problem, or at only one aspect of a larger problem in which a decision is made to defer or forego more comprehensive therapy.

lingual Of or pertaining to the tongue. A term used to describe surfaces and directions toward the tongue.

lingual appliances Orthodontic appliances fixed to the lingual surface of the teeth.

lingual arch A single orthodontic wire usually located in the lower arch traversing the lingual surfaces of the teeth usually from molar to molar. Generally used for stabilization, as a holding arch for space maintenance, for expansion, or to provide anchorage for intermaxillary traction.

lingual frenum  See frenum.

lingual retainers A variation of the lingual arch traversing the lingual surfaces of the lower teeth between the cuspids. The purpose is to stabilize the teeth.

lingual root (labial crown) torque The third-order couple of a transverse force system applied to the crown(s) of a tooth or dental segment having the potential for rotational displacement resulting in lingual movement of the root(s) and/or labial movement of the crown(s).

lingual version Denotes malposition of one or more teeth to the lingual; same as linguoclusion.

linguoclusion An occlusal relationship in which the position of one or more teeth is abnormally lingual. Affected teeth must be identified when this term is used.

lip bumper An appliance designed to eliminate excessive lip pressure on the anterior teeth and transfer that force to the molars. Typically consists of a labial archwire with or without  an anterior plastic pad, fitted into tubes on the molars. The treatment objectives are to allow incisors to move forward and to distalize the molars, increasing the arch length.

lip incompetence A gap between the relaxed upper and lower lips because of a vertical hard and soft tissue imbalance.

long-face syndrome A craniofacial pattern characterized by a long and narrow face, an increased mandibular plane angle, an anterior open bite malocclusion and lip incompetence. It is thought by some to result partly from a lack of adequate airway.

long-axis rotation A nontranslational tooth movement characterized by the coincidence of the long axis and the axis of rotation.