EMG Power Spectral Analysis of Jaw-Closing Muscles in Patients with Mandibular Prognathism. Comparison of Jaw Functions Before and After Orthognathic Surgery.

This study was conducted to compare pre-and post-surgical (mean 7.7 months) jaw functions in 18 patients (8 males and 10 females, mean age 23.1 years) with mandibular prognathism who underwent orthognathic surgery. Ten subjects (5 males and 5 females, mean age 26.1 years) were used as controls.EMG power spectra and integrations of jaw-closing muscles (anterior temporal and masseter muscles) were analyzed during 10 tapping strokes and during 60 seconds of continuous maximum clenching in an intercuspal position.1. TappingThe integrations of EMG in temporal and masseter muscles were increased after orthognathic surgery as compared with those before surgery, but no significant differences were found.The integrations of EMG in the patients before and after orthognathic surgery were both significantly lower as compared with the controls.The median power frequencies (MPF) were lower, though not significantly, after orthognathic surgery as compared with those before surgery.2. Continuous maximum clenchingThe integrations of EMG in temporal and masseter muscles were increased after orthognathic surgery as compared with those before surgery, but no significant differences were found.The integrations of EMG before and after orthognathic surgery were both significantly lower in the patients as compared with the controls.MPF were lower after orthognathic surgery than before, but significant differences were not found.The EMG power spectral and integration analyses during muscle fatigue were very useful to evaluate the stomatognathic function in mandibular prognathism.The results of this study suggested the necessity of carrying out long-term observation for the evaluation of the function corrected by orthognathic surgery.