Changes in electromyographic activity of prognathism patients following orthognathic surgery

Objectives: mandibular prognathism is a dentofacial deformity that can seriously impair the masticatory function. Muscle activity is one of the important measurements. The purpose of this study was to evaluate Changes in masticatory activity before and after mandibular setback osteotomy. Methods: Muscle activity was tested by electromyography in eleven patients with mandibular prognathism before treatment and 3 months, 6 months, 1 year after mandibular surgery. A control group consisted of twelve subjects was measured at the corresponding intervals. And the electromyographic Activity of the superficial masseter , anterior temporal and anterior digastric muscles was recorded bilaterally during occluding in mandibular posture position, intercuspal position and chewing. The data were statistically compared between patients and controls by analysis one-way variance and Student-Newman-Keuls multiple range test. Results: A statistically significant difference in the mean electromyographic Activity of the masseter , anterior temporal and anterior digastric muscles was found between patients and controls during maximal bite and chewing (P <0.05). The mean decreased markedly 3 months after surgery ,and there was significant difference compared with those of the preoperative group (P <0.05). The value for the postoperative 6 months group was slightly higher than that for the postoperative 3 months group, but there was no statistical difference between the two groups(P >0.05). Although the value changes for the postoperative 1 year group increased more obviously in comparison with those of the preoperative group, the increases did not exceed those of the control group (P <0.05). Conclusions: this study suggest that, the patients before surgery have a lower level electromyographic activity than controls, which indicate decreased muscle efficiency.And showed that although the muscle activity of the masticatory system was greatly improved by Orthognathic treatment,these increases did not bring electromyographic activity up to control levels,which indicated the masticatory system still may need further adaptive rebuilding.