Chewing behavior observed at different stages of mastication for six foods, studied by electromyography and jaw kinematics in young and elderly subjects

The chewing patterns measured with jaw kinematics and electromyography (EMG) of ten young adults and ten healthy elderly subjects chewing six food products (rice, beef, cheese, crispy bread, apple, and peanut) were compared. The chewing sequence was divided into five periods by number of chewing cycles, each corresponding to 20% of the entire chewing sequence. Elderly subjects exhibited lower EMG amplitudes and longer jaw-closing duration than younger subjects, but the maximal vertical and lateral displacements of the jaw were not significantly different at any period of mastication. EMG amplitudes, muscle activities during the jaw-closing phase, duration of contraction, and vertical jaw movements decreased in the mastication process. Muscle activities during occlusion and inter-burst duration increased in the later period. Food properties modified EMG activities and jaw-kinematics more significantly in the earlier stage of mastication, but the food effects continued until the latest stage. Generally, the effects of the mastication period and the food type on the masticatory variables except maximal EMG amplitude were similar for both ages. The amplitude decreased significantly while mastication proceeded for young subjects but stayed unchanged for elderly. This suggests that the elderly found it more difficult to adapt their chewing force to changing the food texture during in mouth degradation.