The purpose of this study was to clarify the effects of various masticatory movements on the sway of the center of gravity of the body. The sway of the center of gravity of 20 healthy dentate subjects (10 men, 10 women, average age 28.5±4.2 years) was measured using a foot pressure distribution measurement system (Footview Clinic^®, Nitta Corporation) and the total trajectory length was used as a quantitative parameter. The total trajectory length at rest with eyes open and closed (maintaining the mandibular rest position in an upright posture) and the total trajectory length at rest with eyes open and during various masticatory movements were measured. The masticatory movements were performed under three conditions: free chewing before softening, free chewing after softening, and unilateral chewing after softening. First, the total trajectory length was compared between the measurements during eyes open and eyes closed at rest using a pairedt-test. Bonferroni’s multiple comparison test was performed among the four conditions of rest, free chewing before softening, free chewing after softening, and unilateral chewing after softening. The total trajectory length was significantly shorter with the eyes open than with the eyes closed at rest. Upon comparing the four conditions of rest and the three masticatory movements, the total trajectory length of free chewing before softening was the longest, and shortened in the order of rest, free chewing after softening, and unilateral chewing after softening was significantly shorter. From these results it was suggested that the sway of the center of gravity was more stable when the eyes were open than when the eyes were closed, and more stable when chewing softened chewing gum, especially on the unilateral side; moreover, unilateral chewing was optimal when investigating the effect of masticatory movements on the sway of the center of gravity of the body.

The purpose of this study was to clarify the presence or absence of gender difference in movement velocity during mastication. Forty healthy dentate adults (20 males, 20 females, average 25.1±3.7 years) were asked to chew softened chewing gum on their habitual chewing side and the mandibular movements were recorded using a Mandibular Kinesiograph (MKG). For 10 cycles from the 5th cycle of mastication, the opening maximum velocity, closing maximum velocity, opening mean velocity, and closing mean velocity were calculated and compared between males and females. The opening maximum velocity and closing maximum velocity were both larger in males than in females, and significant differences were observed between the two groups. The opening mean velocity and closing mean velocity were larger in males than in females, similar to the maximum velocity, and significant differences were observed between the two groups. From these results it was suggested that there was a gender difference in the movement velocity during mastication, and that the gender difference should be noted when analyzing the masticatory movement velocity.