This study evaluated the level of nocturnal masseter activity and the symptoms of jaw dysfunction in eighty-five subjects who varied with respect to degree of jaw dysfunction. A combined jaw dysfunction index was employed which evaluated both the patients subjective report of pain as well as the clinical examination evidence of jaw dysfunction. Using this combined index, a significant correlation was found between the level of nocturnal masseter activity and the signs and symptoms of jaw dysfunction. Tooth wear was also related to signs and symptoms of jaw dysfunction as well as high levels of nocturnal masseter muscle activity (bruxism).
The effect of a sustained (30% maximum) isometric clenching task on the maximum voluntary bite force level was evaluated on normal jaw function subjects as well as on abnormal jaw function subjects (MPD patients). The results indicate that the MPD subjects had a lower maximum voluntary bite force level and a shorter endurance time when compared to normal subjects. Neither the control subjects nor the MPD subjects demonstrated a change in their brief MVBF after a 'fatigue inducing' task. These results suggest a lack of contractile element failure in the jaw closing muscles following sustained submaximal isometric clenching on a force transducer.
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