The osteokinematics of the mandible

The osteokinematics of the mandible are most often described as protrusion and retrusion, lateral excursion, and depression and elevation. All of these movements occur to varying degrees during mastication. For a more detailed analysis of mandibular movements, the reader
is encouraged to consult the classic work by Posselt,61 thoroughly summarized by Okeson.

PROTRUSION AND RETRUSION
Protrusion of the mandible occurs as it translates anteriorly without significant rotation (see Figure 11-13, A). Protrusion is an important component of the mouth’s opening maximally.
Retrusion of the mandible occurs in the reverse direction (see Figure 11-13, B). Retrusion provides an important component of closing the widely opened and protruded mouth.

LATERAL EXCURSION
Lateral excursion of the mandible occurs primarily as a side-toside translation (see Figure 11-14, A). The direction (right or left) of active lateral excursion can be described as either contralateral
or ipsilateral to the side of the primary muscle action.In the adult, an average of 11 mm (about 1
2 inch) of maximal unilateral excursion is considered normal.74 Lateral excursion of the mandible is usually combined with other relatively slight translations and rotations. Normally the specific path of movement is guided by the shape of the mandibular fossa and position of the articular disc.

DEPRESSION AND ELEVATION
Depression of the mandible causes the mouth to open, a fundamental component of chewing (see Figure 11-15, A).
Maximal opening of the mouth typically occurs during actions such as yawning and singing. In the adult the mouth can be opened an average of 50mm as measured between the incisal edges of the upper and lower front teeth.2,35,74 The interincisal opening is typically large enough to fit three adult “knuckles” (proximal interphalangeal joints). Typical mastication, however, requires an average maximal opening of 18 mm—about 36% of maximum (sufficient to accept one adult knuckle). Being unable to fit two knuckles between the edges of the upper and lower incisors is usually considered abnormal in the average sized adult. Elevation of the mandible closes the mouth—an action used to grind food during mastication (see Figure 11-15, B).

TOMADO DE KINESIOLOGY OF THE  MUSCULOSKELETAL  SYSTEM .

AUTOR. DONALD NEUMANN