The function of the disco-muscular apparatus in the human temporomandibular joint

The morphology and function of the disco-muscular apparatus of the human TMJ is a controversial subject. Connections between the muscles which move the mandible and the "disco-capsular complex" have been described in a contradictory way. The disco-muscular apparatus is also described as being more extensive than that of the M. pterygoideus alone to include to the Mm. temporalis and masseter. However, the involvement of the latter is considered to be a peripheral variation of the normal anatomy and of little, if any, functional significance. The existence of independent relationships between the deep portions of the masseter and temporal muscles and the disco-capsular apparatus of the human TMJ is rarely discussed or explained. The morphologic findings were derived from fixed and unfixed human temporomandibular joints (TMJ) of varying ages and both sexes, whereby the functional maturity of the masticatory apparatus was taken into consideration. The results of the study show that aside from fibers originating from the superior venter of the M. pterygoideus lateralis, additional muscle or connective tissue fibers from the perimysium of the M. masseter are inserted to varying extents into the disc. The same is true for the M. temporalis, which is also directly connected to the disc via muscular or fibrous elements, or indirectly via fibers from the M. masseter. The insertion of the M. pterygoideus lateralis is always in the medial portion of the Discus articularis and those of the Mm. temporalis and masseter in the middle and lateral portions of the disc respectively. It is highly probable that a direct force transfer through the Mm. temporalis and masseter to the articular disc takes place, and that these muscles contribute to the movement of the disc during jaw movement, whereas the size and form of the muscle insertions are subject to a great deal of individual variation.