Abstract
The weakening of the biting force restrains growth of the jaw area, and creates the risk not only of disease of the jaw and face region but may also cause ill health and dysfunction of the whole body. The purpose of this study was to investigate the functions of the masseter muscle, which, morphologically, is known to be the largest structure with the greatest biting force among the masticatory muscles. First, the functions of the masseter muscle were investigated, using ultrasonography to measure the muscle cross sectional area, where both the right and left masseter muscle are slackened and strained. Second, through the use of a strain gauge, the strength of occlusion at the location where one top tooth and one bottom tooth were occluded was measured. Third, the relationship between the cross sectional area of the masseter muscle and biting force was examined. Results showed that when the tension in the masseter muscle increased as a result of the biting force, the value of muscle thickness and the cross sectional area increased while the value of muscle width decreased. Furthermore, the maximum biting force was 683.7±204.9N (CV=0.299) on the right side and 693.6±208.7N (CV=0.300) on the left side. A comparison of right and left did not reveal a significant difference. However, from standard deviation and a variation index of the biting force value, it was shown that individual differences were large. In addition, a significant and positive correlation between the biting force and all masseter morphometry values for the right and left sides was found. Finally, results showed that the size of the masseter form influences the expression of the biting force.
