Evaluation of biting performance with standardized test-foods.

Human masseter muscle is the main power source used for crushing or grinding the foods. Its size is regarded as an determining factor of chewing force and function. A system of measuring the masseter muscle volume from MR images was developed in this study. For a better understanding of the masseter muscle function, a standardized test-food developed in our laboratory was used. Twelve male subjects having complete dentition and healthy masticatory function were used to chew the test-foods. The EMG muscle activity of the masseter muscle during breaking and chewing the test-foods was observed. It was found that the muscle volume was positively related to the body size. The increase of the muscle activity during breaking and chewing was almost parallel to the increase of the test-food hardness, and the increase was mostly in the duration of muscle contraction. It was concluded that the measurement of masseter muscle volume is possible, and our test-foods can be used for chewing function examination with high reliability. Within a certain level of hardness, harder food requires longer muscle contraction time instead of stronger muscle force to break and chew the food.