A quantitative electromyographic analysis of masticatory muscle activity in usual daily life

OBJECTIVE: This study was designed to investigate whether a quantitative el ectromyographic (EMG) analysis with a special reference to the EMC amplitud e at 98N bite force could reduce the influence of electrode relocation and to examine the reproducibility of masticatory muscle activity in usual dail y life within individuals. SUBJECTS AND METHODS: In the first experiment, two sessions of surface EMG recording for masseter and anterior temporal muscles during tapping, and ch ewing gum and marshmallow were performed for 10 subjects with an interval o f at least I week with electrode relocation, in the second experiment, two sessions of EMG recording during daytime (142 min, including mealtime) and sleep (142 min) were carried out for 10 subjects with an interval of at lea st 1 week. The average rectified EMG values were normalised with a special reference to the EMC amplitude induced by a 98N bite force, RESULTS: In the first experiment, high correlation coefficients and no sign ificant differences in the mean normalised values of muscle activity were f ound between two sessions. although the average rectified values showed hig h correlation coefficients, the mean masseter muscle activity while chewing gum was significantly different between two sessions. In addition, the var iation in temporal muscle activity between two sessions while chewing gum w as significantly smaller in the normalised values than in the average recti fied ones. In the second experiment, less intra-individual variation in the normalised values of masticatory muscle activity between two sessions indi cated the reproducibility, Normalised masticatory muscle activity showed le ss variation during mealtimes than during usual daytime and sleep. CONCLUSIONS: This quantitative EMG analysis could estimate the masticatory muscle activity by reducing the influences of electrode relocation, demonst rating an availability of this analysis for the evaluation of masticatory m uscle activity in usual daily life.