Effect of foot position and Jaw function on body sway

Objective: The present study evaluated the effect of foot position on body sway. Dentulous patients confirmed to have bite force asymmetry were measured. Methods: Seven patients with bite force asymmetry (mean age 25.1) as defined by the Dental Prescale System Index were selected in this study. Seven other patients without bite force asymmetry (mean age, 24.4) were also measured as a control. Body sway was measured using a body sway measuring system (WinPDM, Zebris) as following conditions: three foot positions of Romberg parallel (RP), toe-out (RT), and natural standing posture (NS), with subject eyes open (-o) and closed (-c). For the analysis, three items were selected as indices of bodily sway: total length of trajectory (LNG), maximum amplitude of sway in the direction X (XD) and Y (YD). An analysis of variance and Tukey's multiple comparison test were used to analyze the measurements for each condition (p<0.05). Results: The mean LNG value for each condition was largest for NS-o, and smallest for RP-o. A significant difference was noted between RP and NS (p<0.05). There was no significant difference of corresponding foot positions in the two groups. The mean XD value was largest for RP-c, and smallest for NS-c; all foot positions were significantly different from each other. In the control group, RP-c had largest mean XD value, and NS-c had smallest. All foot positions showed significant differences (p<0.05). A significant difference between eyes open and closed was observed only in the RP position (p<0.05). Similarly, the mean YD value was largest for RP-c, and smallest for NS-o; RP-c, RT-o and -c, and NS-o were significantly different (p<0.05). Conclusions: The above results suggest a trend in both groups, as was the case for XD, toward an increased sway in the lateral direction for RP and RT, compared to that for NS.