An electromyographic study of the human lateral pterygoid muscles.

An electromyographic investigation of the lateral pterygoid muscles was undertaken to determine their activity relative to isolated and functional movements of the mandible. Daerally in the lateral and medial pterygoid muscles. Surface electrodes were placed bilaterally on the skin over the temporalis and masseter muscles. Our data strongly suggest that separate roles for the superior and inferior heads of the lateral pterygoid cannot be supported electromyographically. In addition, the lateral pterygoid is active in protrusive movements, including an incisor clench, and not active in retrusion or a molar clench. Both lateral pterygoid muscles initiate depression of the mandible and the contralateral muscle initiates a lateral transversion. The ipsilateral activity present is not sufficient to be an active stabilizer of the temporomandibular joint. In the chewing cycle, the lateral pterygoids are bilaterally active, both in alternation with and overlapping the elevating musculature. The sequence of the lateral pterygoid activity in the chewing cycle is led by the ipsilateral lateral pterygoid muscle.