Index of electromyographic activity patterns in the lateral pterygoid muscle

Abstract

Electromyography (EMG) has long been used for the objective evaluation of muscule function. However, no clear activity pattern has been established for EMG during normal mandibular function. We attempted to determine an index of EMG muscular activity patterns in the lateral pterygoid muscle. Mandibular movements of the bilateral lateral pterygoid muscles were simultaneously recorded with their electromyographs in healthy subjects who had no orthognathic abnormalities in the jaw or oral system. We examined anteroposterior movement (AP) and opening and closing (OC) of the mandible. In addition the subjects were instructed to move their mandibles horizontally and vertically for 40 seconds to the rhythm of a metronome at 0.5, 0.65, and 0.8Hz. The muscular activity per unit time was calculated from the integrated value of muscular activity for a single back and forth movement. AP displacement, OC displacement, and mean muscular activities during AP and OC movements were calculated for each subject, and the ratios of EMG activity during OC and AP movements were calculated and compared. The OC/AP ratio was approximately 1 in healthy subjects, indicating that muscular activity of the lateral pterygoid muscle during AP and OC movements were similar in healthy subjects.