Relationship between mean power frequency and potential of human masticatory muscles at rest position and clenching.

The EMG signals from left and right masseter and anterior temporal muscles of 40 healthy subjects were sampled at rest position and through gradually increased clench level to maximum voluntary contraction (MVC) at intercuspal position. A visual sense feedback of masseter muscle potential value was used for the subject to control clench level. The relationship between mean power frequency (MPF) and potential of EMG was investigated by a curvilinear regression of the second order. It was found that the relationship was of the second order logarithmic curve with maximum value of MPF. With the raising of the potential levels of EMG, the MPF increased at the lower clench levels and decreased at higher clench levels. The results indicate that controlling an identical clench level is necessary for using MPF to describe the functional state of masticatory muscles in the clinical situation.