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sagittal split osteotemy A surgical procedure in which the rami of the mandible are split parallel with the sagittal plane to allow repositioning of the mandibular body either anteriorly or posteriorly into a more favorable relationship with the maxilla.

screen (intensifying) See intensifying screen.

second-order clearance The angle through which an engaged arch wire may be tipped within the bracket slot, relative to the 'slot-parallel' configuration, before making contact with the occlusogingival slot surfaces.

second-order rotation A tooth as a whole rotates about a faciolingual axis. The angulation/orientation of the long axis of the tooth changes.

sella-nasion(S-N) A frequently used cephalometric reference line connecting the center of the sella turcica with nasion.

sella turcica (sella; S) The pituitary fossa. The center is used as a cephalometric landmark.

separation An orthodontic procedure for slightly separating teeth to facilitate placing bands.

serial extraction A program of selective or guided extraction of primary and sometimes permanent teeth over a period of time, with the objective of relieving crowding and facilitating the eruption of remaining teeth into improved positions.

sheath A synonym for a tube used as an orthodontic attachment.

shield See vestibular screen.

soft palate See palate.

space maintainer A prosthetic replacement for prematurely lost primary teeth intended to prevent closure of the space before eruption of the permanent successors. Often an urgent necessity in the buccal segment to prevent impaction of the permanent teeth and other complications.

space regainer Correction of tooth displacement resulting from premature loss of one or more primary teeth without timely space maintenance. Effective when the space loss is recent and small. May be accomplished with varying types of corrective appliances. Often most efficiently accomplished as a part of a comprehensive orthodontic treatment plan.

specialist 1.A person with practice limited to diagnosis and treatment of one specific discipline.2. A healthcare practitioner who devotes attention to a particular class of diseases, patients, etc.

spee,curve of  See curve of spee.

splint A rigid appliance used to connect and mutually support teeth or bones. A removable form is often used to temporarily relieve occlusal interferences in functional disorders of the temporomandibular joint and related musculature.

spring-back The recovery exhibited by a beam, shaft, wire, or wire loop upon its unloading (deactivation). stabilizing wire A stiff rectangular arch wire that fills the bracket slot and is used ordinarily to distribute a responsive force system throughout a dental segment.

stiffness The ratio of change in load to accompanying change in deformation of a member fabricated of a Hookean material and activated within its elastic limit; the slope of the load-versus-deformation plot beneath the elastic limit.

stomatognathic system Literally, the mouth-jaw system; the entire complex of structures of the head and neck involved in the functions of mastication, swallowing, respiration and speech.

stomion Intersection of the closed upper and lower lips.

stop A bend or auxiliary attachment placed on a wire to limit its sliding into a tube or in other orthodontic attachments.

straight wire appliance A variation of the edgewise appliance in which brackets are angulated to minimize multiple archwire bends. Brackets and molar tubes have specific orientation in three planes of space.

strain Local unit volumetric or distortional deformation experienced by a nonrigid body or structure subjected to external force.

stress (mechanical) Local intensity of distributed internal force experienced by a body or structure as a response to the application of external force to that body or structure.

stress-relief A heat-treatment process intended to reduce the magnitudes of residual ('locked-in') stresses induced by inelastic deformation.

stripping of teeth Term used for reproximating or slenderizing mesiodistal width of teeth, usually incisors.

subnasale The intersection of the columnella of the nose and the upper lip.

subspinale (Downs Point A) The most posterior point in the concavity between the anterior nasal spine and prosthion, i.e., apical base.

subtraction radiography A darkroom technique in radiology which makes important radiographic information easier to see because it subtracts less important information from the image.

succedaneous teeth Those permanent teeth that replace (succeed) the primary teeth, which include all permanent teeth except the permanent molars.

superelastic Refers to a metallic alloy having a relatively substantial elastic range; within a specific range of temperatures, the elastic portion of the force-deformation relationship for the alloy has two distinct, sequential parts because of a (submicroscopic) metallurgic phase-change that occurs as the force-magnitude is increased; a reversal of the phase-change occurs as the magnitude of force is subsequently decreased toward the passive state.

superimposition Useful to evaluate the changes brought about as a result of a growth and/or treatment.  Change is determined by placing two roentgenographic tracings upon each other, registering on structures that remain relatively stable during the time period separating the two images.

superoinferior The global direction perpendicular to the transverse plane of the dentofacial complex or the occlusal plane of one dental arch; the superior direction/sense is upward, and the inferior direction/sense is downward.

supernumerary teeth Teeth in excess of the normal number. Often malformed or erupting abnormally.

supramentale (Downs point B) The deepest point on the profile curvature from Pogonion to infradentale (i.e., apical base).

supraocclusion Overeruption of a tooth or teeth beyond the normal level, often as a result of tooth-loss or irregularity in the opposing arch.

surgical fixation Stabilization of two bony segments for purposes of improving healing.

suture In anatomy a fibrous junction between bones, as in the face and skull.

symphysis (mental) The union in the median plane of the two halves of the mandible.