Masseter muscle activity during the whole day in young adults.

This study was conducted to evaluate the biting function during the entire day in young adults by measuring the masseter muscle activity with a 24-hour electromyography (EMG) system. With this system, the masseter muscle activity for 24 hours was recorded in 20 male and 10 female young adult subjects with acceptable occlusion. For the male subjects, means of the number and total duration of bursts over level 2, which is one-fourth of the maximum discharge voltage during maximum clenching, were 1938 times and 357 seconds. For the female subjects, the values were 2356 times and 419 seconds. A large percentage of such high amplitude bursts as level 3 or 4 was observed during meals in both groups. These results indicated that most of the strong bursts of the masseter muscle appeared only during meals and a number of low amplitude bursts were observed during the entire day, although masseter muscle activity during the entire day in young adults was less than expected. It is anticipated that the nature of masticatory muscle activity revealed in this study might provide valuable information about the association between the biting function and the craniofacial structure or malocclusion.