Abstract
Electromyographic (EMG) activities of the superior (SUP) and inferior heads (INF) of the lateral pterygoid muscle (LPT) were recorded in humans during voluntary stepwise changes in biting force and jaw-position. The SUP behaved like a jaw closing muscle, while the INF like a jaw opening muscle. Stretch-reflex like responses were found in the SUP, the function of which was presumed to stabilize the condyle against the biting force that pulls the condyle posteriorly. This notion was verified by examining the biomechanics on the temporomandibular joint. The EMG amplitude of the SUP showed a quasi-linear inverse relation with rotational angle of the mandible in the hinge movement during which the condyle rotated with no movement in antero-posterior direction. This finding suggests that the SUP controls the angular relationship between the articular disk and the condyle.
