The present study was designed to evaluate how typical Japanese staple foods - rice and rice cake - with different physical properties influence the patterns of muscle activity during chewing. Six normal adults were asked to eat rice and rice cake freely in a natural manner. Surface electromyographic recordings of the masseter and suprahyoid muscles were performed. There were large differences between the foods in terms of masticatory duration. The masseter activity per cycle was significantly greater for rice cake than for rice. The masseter activity gradually decreased as chewing progressed, although the suprahyoid activity did not change throughout the sequence of rice cake chewing. The results suggest that the process of bolus formation with rice cake is very different from that with rice in terms of jaw-closing and jaw-opening muscle activities. Practical Applications: This study aimed to examine how the masticatory sequence adapts to variations in the initial properties of foods. This research may enhance our understanding of the oral physiology of bolus formation and changes in the physical properties of foods during chewing.
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