Functions of masseter and temporalis muscles in the control of temporomandibular joint loading--a static analysis using a two-dimensional rigid-body spring model.

Masticatory forces or bite forces applied to the teeth are known to generate a compressive force on the temporomandibular joint (TMJ). This intra-articular force is referred to as TMJ loading. TMJ loading is considered to be controlled to a certain extent by the stomatognathic system, so as not to exceed a certain limit. In order to clarify the control mechanism of the TMJ during biting, the controllability of TMJ loading through coordinated activities of the masticatory muscles has been numerically analyzed using a static two-dimensional jaw model. This model consists of a rigid-body model of the jaws and a spring model of the articular disk, which includes three dominant muscle force vectors representing the masseter, temporalis and lateral pterygoid muscles. The bite force vector is assumed to be applied solely at the first molar. Static equilibrium analyses suggest that coordinated activities of the masseter muscle and anterior portion of the temporalis muscle can minimize TMJ loading and concentrate the stress within the articular disk to the intermediate zone of the disk, and that the activity of the posterior portion of the temporalis muscle has the possibility of reducing TMJ loading.