Characteristics of muscle architecture in human lateral pterygoid muscle and relationgships between it and attachments of tempo-romandibular joint

Objective To explore characterisics of muscle architecture in human lateral pterygoid muscle and relationships between it and attachments of temporomandibular joint (TMJ), and to confirm properties of biomechanics in superior and inferior heads of the pterygoid muscle.Methods Muscle architecture indexes were determined for ten specimens of the pterygoid muscles, and figured out as well as analyzed by a mechanical formula.Results Superior and inferior heads of the pterygoid muscle appeared as short muscle bundles, muscle fibers of which ran parallel to tendon axle. A part of them in the supperior head penetrated TMJ capsule, firmly attaching to the anterior medial portion of the capsule. And the rest of them mingled with muscle fibers of the inferior head, in turn, all attaching to the joint pterygoid fovea on the condyle. The ratios of physiological cross- sectional area/muscle weight and of muscle fiber length/physiological cross- sectional area in the superior head were obviously higher than in the inferior head.On the contrary, the rest indexes in the inferior head were significantly higher than in the superior head.Conclusions These results demonstrate that the superior head of the pterygoid muscle is mainly involved in force and velocity production,playing an important role in the trusion of TMJ disc and the control of TMJ's location. The inferior head of the pterygoid muscle, however, serves as a mainbody and initiator for TMJ's movements.