The changes in electrical activity of the postural muscles of the mandible upon varying the vertical dimension.

The relation between BT-EMG activity and variations of VD (1 to 41 mm of interocclusal distance) was studied in the masseter, anterior temporal, and posterior temporal muscles of eight normal experimental subjects. EMG activity was recorded with surface electrodes, and the VD was measured with a specially designed device. Recordings were performed with dynamic variations (series A) and with static variations (series B) of VD. Series A shows a gradual decrease of EMG activity starting from the occlusal position, passing through a range of maximum reduction at a certain interocclusal distance, and gradually increasing to the highest values close to maximum jaw opening. Series B shows the same progression, although it points out the exact VD at which minimum basal EMG activity is observed in each muscle studied (10 mm for the masseter muscle, 13 mm for the anterior temporal muscle, and 16 mm for the posterior temporal muscle).