Musculature of the jaw
The masticatory muscle (M. masseter) is divided into two parts. One part is more superficial, sloping backwards and downwards (pars superficialis), one part is deeper and vertical (pars profundus), both parts originate at the zygomatic arch (Arcus zygomaticus) and are attached to the outer surface of the mandibular frame (ramus mandibulae). The temporal muscle (M. temporalis) originates as a flat muscle in an arch below the temporal line (Liniea temporalis).
It bundles and runs underneath the zygomatic arch (Arcus zygomaticus) to attach to the coronoid process of the mandible (mandibula). The inner wing muscle originates in the pterygoid fossa and moves to the inner side of the mandibular angle (angulus mandibulae). The outer wing muscle originates with a small upper part (pars superior) at the lower sleeping edge (crista infratemporalis) of the sphenoid bone (Os sphenoidale). The lower part (Pars inferior) originates at the outer surface of the pterygoid process. The upper part (pars superior) starts at the articular disc, the lower part (pars inferior) at the mandibular condylar process (mandible).
Movements of the jaw
In the jaw, chewing and grinding movements take place when the movements of both sides of the jaw are coordinated. This results in lowering (abduction), lifting (adduction), advancing (protrusion), pushing back (retrusion) and grinding movements or lateral displacement (laterotrusion). Only one temporomandibular joint is actively involved in the grinding movement.
Chewing takes place on the balance side, where the vibrating condyle (translational condyle) is located, while the resting condyle (rotational condyle) is not chewed on the working side. Lowering is performed by the front part of the diabetic muscle (digastricus venter anterior muscle), the chin hyoid muscle (geniohyoideus muscle), the mandibular hyoid muscle (mylohyoideus muscle) and the external wing muscle (pterygoideus lateralis muscle). Lifting is performed by the temporal muscle (temporalis muscle), the masticatory muscle (masseter muscle), the external wing muscle (lateral pterygoid muscle) and the internal wing muscle (medial pterygoid muscle). Advancing is performed by the outer wing muscle (lateral pterygoid muscle) and the masticatory muscle (masseter muscle). Retraction is performed by the chin hyoid muscle (geniohyoid muscle) and the posterior part of the dipterous muscle (posterior ventral digastric muscle).
