Study of EMG postural activity in mandibular muscles at different body positions

The purpose of this work was to study the influence of the gravitational force on the postural tonic activity of the masseter, anterior and posterior temporalis muscles in different body positions. This study was made in 8 male subjects with normal functional occlusion and no dysfunction of the stomatognathic system. All muscles studied showed the highest EMG activity in the upright position and progressively decreasing to supine position. The masseter muscle compared with AT and PT, presents the highest decrease of EMG activity from 90° toward 0°. On the other hand the AT presents the lowest decrease from inclined backward position (45°) toward supine. All the muscles showed a gradual decrement of activity from the record performed immediately, 1 min and 2 min after shifting, in each body position. The results support the essential role of the gravitational forces in the control of the postural mandibular position, as well as, the propioceptive muscular mechanism represented by the neuromuscular spindle and its miotatic reflex activity.