Electromyographic activity of the jaw-closing muscles before and after unilateral coronoidectomy performed on a...

There have been few reports analyzing the activity of the jaw-closing muscles after coronoidectomy performed on a patient with coronoid hyperplasia. This paper presents a case study using electromyograms (EMGs) to evaluate the effects of unilateral coronoidectomy on the activity of masseter and temporal muscles. The patient was a 25-year-old male whose maximal range of jaw opening was 24 mm. After coronoidectomy of the left region, the range improved to 43 mm. EMGs were recorded in the center of the masseter muscles and the anterior part of the temporal muscles during gum chewing. Preoperatively, no abnormal EMG activity was observed. Eight months after surgery, increase in the ratio of the bilateral temporal muscle activity and a decrease in the ratio of the right masseter muscle activity were observed, and the proportion of activity of jaw closing muscles was out of the normal range. Eighteen months after surgery, there was slight return to the preoperative EMG activity. It was concluded that unilateral coronoidectomy could result in EMG changes of masseter and temporal muscles with a gradual return.