Mandibular occlusal stability in patients undergoing orthognathic surgery

OBJECTIVES The aim of this study is to evaluate the activity of the right and left an-terior masseter and temporalis muscles in patients before and af-ter orthognathic surgery. 19 pa-tients, 9 males and 10 females, aged between 17 and 34 years, were included in the study. Among the selected patients, 4 had a skeletal class II with man-dibular retrusion and were candi-dates for bilateral sagittal mandib-ular osteotomy (BSSO), while 15 had a skeletal class III with man-dibular protrusion and were can-didates for bimaxillary surgery.MATERIALS AND METHODS Electromyographic examinations were performed in all the 19 pa-tients before surgery and 6-8 months after surgery, sufficient period to allow optimal adaptation to the new occlusal situation. To check the neuromuscular bal-ance, the superficial bundle of the right and left masseter and ante-rior temporalis muscles were evaluated by placing the surface bipolar electrodes parallel to the fibers of the muscles in the study and analyzing and calculating the following parameters: percentage overlap coefficient (POC, index of the symmetric distribution of muscle activity determined by the occlusion) and torque coefficient (TC, torque and mandibular pres-ence index).RESULTS After surgery, there was a ten-dency for improvement in POC and TC indices with little variabili-ty within the group. This result indicates that after surgical treatment a better bal-ance was achieved between the right and left masseter and the anterior temporal muscles.CONCLUSIONS The electromyographic evalua-tion permitted to quantify the in-fluence of occlusion on neuro-muscular balance and showed that the improvements obtained after surgery were mainly due to occlusal stability and not to bio-mechanical advantages.CLINICAL SIGNIFICANCE The comparison of electromyo-graphic analysis obtained before and after orthognathic surgery is an excellent instrumental exam-ination in order to assess the new neuromuscular pattern ob-tained after surgery and allows to quantify the improvements ob-tained through surgery and to highlight patients who have not obtained the expected benefits of the treatment.