Motor behavior of the jaw muscles during different clenching levels

The goals of this study were to investigate whether (i) muscle activities are affected by different feedback strategies, (ii) the balancing behavior of the neuromuscular system is influenced by different force levels, and (iii) axial loading of the posterior teeth is a realistic biomechanical conception. In 10 healthy subjects, all jaw muscles were recorded bilaterally. Intra-oral force transfer and force measurement were achieved by using a measuring device simulating natural maximum intercuspation. Under visual feedback-control, the subjects generated pure vertical and directionally unrestricted force vectors with identical force magnitude at different force levels. The force transmission characteristics under experimental occlusion were investigated by calculating the reduction point (RP) of the resultant bite force. Directionally unrestricted clenching revealed a higher activation of the musculature than pure vertical clenching and was also characterized by a distinct anterior force component. Under both test conditions, the RP moved towards a posterior position with increasing clenching forces. The results indicate an essential recruitment difference of the jaw muscles between the two clenching conditions. Pure axial loading of teeth seems to be impeded by the anterior force component during bilateral clenching. The posterior movement of the RP might prevent overloading of the temporomandibular joints and anterior teeth.