Influence of voluntary teeth clenching on stabilization of posture stance

Objectives: An increasing number of studies have been made on the correlation between oral motor function and motor performance and muscle strength of the extremities. A previous study in our laboratory suggested that, in association with voluntary teeth clenching, both ankle extensors and flexors would maintain their original length against any disturbance of posture. In the present study, we investigated whether teeth clenching have influence on adaptation to the novel environments in the upright position. Methods: Subjects stood on the force plate, from which motion data were obtained in the horizontal plane, during two conditions: 1) with (CL) and 2) without voluntary teeth clenching (CO). We evoked the novel environments by supramaximal percutaneous electrical stimulation of common peroneal nerve. Subjects were instructed to maintain a position throughout experiment. Electromyograms were recorded from the masseter, the tibialis anterior (TA) and the peroneus longus (PL) muscles on both sides, with bipolar surface cup electrodes. The statistical significance of the results was assessed using Wilcoxon sighed-ranks test. Significance level was set at p=0.05. Results: When the disturbed posture stance was generated by electrical stimulation, the peak-to-peak amplitude of reaction force in the anterior-posterior direction with CL (mean=21.61mV) was significant smaller than that CO (mean=25.10mV). The anterior-posterior maximum force occurred significantly earlier in CL (mean=146.57ms) compared to CO (mean=167.75ms). Meanwhile, there was no significant difference in the electromechanical delay of TA and PL (TA; mean=9.74ms/9.81ms, PL; mean=5.54ms/5.80ms, CO/CL, respectively) during two conditions. Conclusions: Thus, the present study has shown that voluntary teeth clenching contributes to the stabilization of the posture stance perturbed transiently by electrical stimulation, not the change in the elastic component of muscle. We concluded that voluntary teeth clenching would play an important role in rapid postural adaptation to the novel environments in the upright position.