Research and Education Section Editor

A lthough there have been a number of studies that involved the function of jaw muscles, due to its deep placement, the action of the superior belly of the lateral pterygoid (SLP) muscle has not been studied widely. The electromyographic (EMG) activities of the superior and inferior bellies of the lateral pterygoid muscles have been shown to be reciprocal in humans’-‘,+ and rhesus monkeys. *-lo The SLP muscle is of particular interest because it attaches to the anterior border of the mandibular disk anterior to the point where it inserts at from the pterygoid fovea. Activity of this muscle in relation to the function of other jaw muscles seems to be important in mandibular condyle-disk discoordination and in temporomandibular joint (TMJ) and muscle pain. A previous article from our laboratory’ described the EMG activities of the superior and inferior bellies of the lateral pterygoid muscles during basic jaw positions and clenching the teeth. The present article describes the activities of SLP and the inferior belly of the lateral pterygoid (ILP) in relation to masseter, temporal, anterior belly of the digastric, and medial pterygoid muscles during some basic jaw positions and movements. Understanding the relationship of muscle functions during basic jaw movements is an important step in understanding muscle function during preconscious chewing, swallowing, and speech.