EMG versus force relationship in painful masseter muscles before and after intramuscular anesthetics and saline injections.

Electromyographic (EMG) activity of masseter and anterior temporal muscles, and bite force were analyzed in 28 young, fully dentate women with painful and tender masseter muscles before and after intramuscular injection of either lidocaine or saline in superficial masseter muscle. EMG-activity of the descending part of the trapezius muscle during increased bite force was also analyzed. As regards the mandibular elevators, the intraindividual relationship between slopes for EMG-force regression at low and high contraction levels before injection were the same as for healthy women investigated previously. Intramuscular injection of lidocaine reduced postural EMG-activity of the masseter muscles and EMG-force regression curve became less steep at low contraction levels. After saline injections no changes in EMG-activity were found. The EMG-activity of the descending part of the trapezius muscle was increased significantly for the total group during the strongest bite.