GUM CHEWING AND JAW MUSCLE FATIGUE AND PAINS

To study possible associations between gum chewing and fatigue and pai ns in the jaw muscles, eight healthy adults performed prolonged idling , prolonged unilateral chewing of gum, and brief vigorous clenching of the teeth (MVC). Through surface electromyography (EMG), the authors monitored the cumulative (mu V.s(-1)) as well as the average rates (mu V.s(-1)) of contractile activities in the right and left masseter mus cles. During 10 min of idling there was an absence of muscle fatigue a nd muscle pains when the EMG rates of the right and left masseter musc les were 2% and 3%, respectively, of those required to elicit isometri c muscle pains through MVC. During 10 min of right-sided gum chewing a ta rate of 1.2 Hz, the majority of subjects (75%) experienced weak jaw muscle fatigue-not jaw muscle pains-when the EMG rates of the right a nd left masseter muscles were 38% and 19%, respectively, of those requ ired to elicit isometric pains through MVC. In comparison with 10 min of idling, the weak muscle fatigue of 10 min of unilateral gum chewing appeared when the total contractile activities of the right and left masseter muscles were increased by 1664% and 519%, respectively. It se emed as if prolonged unilateral gum chewing and previous pain-releasin g MVC caused some sensitization of muscle nociceptors which, in turn, aggravated subsequent isometric jaw muscle pains elicited through MVC. Even though the right masseter muscle was the most frequent site of c linical fatigue and pains, the authors found no evidence supporting th e theoretical foundation of the myofascial pain/dysfunction syndrome.