Electromyographic study of the superior and inferior heads of the lateral pterygoid muscle at basic jaw positions with the mandible in closed lock

Abstract

We recorded electromyograms at basic jaw positions at the superior and inferior heads of the lateral pterygoid muscle, the anterior belly of the digastric muscle, the temporal muscle, the masseter muscle and the sternocleidomastoid muscle, together with incisal movements, in 8 healthy controls and 9 persons with their mandibles in closed lock. In the healthy subjects, the superior head showed powerful activity during intercuspal clenching, and displayed reciprocal activity with the inferior head during tapping, protrusion and lateral movement. Persons with closed lock had decreased activity of the superior and inferior heads. They also had spontaneous activity of the temporal muscle, and activity of the sternocleidomastoid muscle during opening. The superior and inferior heads often displayed inconsistent patterns during various jaw movements These results suggest that electromyographic examination of the lateral pterygoid muscle and other masticatory muscles in various jaw positions may be useful in the diagnosis of closed lock. Shika Igaku (J Osaka Odontol Soc) 1997 Jun； 60(2)：141-151．