A new method for evaluating smoothness of the jaw movement

Objectives: Movement smoothness has been used as a measure of motor performance. Smoothness measures have most often been based on minimizing jerk, the time integral of squared jerk, where jerk is defined as the rate of change in acceleration. The routine technique for measuring the jaw movement has been scanning the transducer which was attached to the surface of the dentition. However, this method suffers from the complicatedness in measurement, and evaluates the jaw movement under the peculiar situation. The aims of this study were:1) to demonstrate the simple and non-invasive method for recording human jaw movements using 3-axis accelerometer; 2) to verify the hypothesis that the adhesive nature of the gum affects smoothness of opening phase. Methods: This project was approved by the Institutional Review Board for Human Subjects (H18-0226). Five young healthy subjects (2 women, 3 men) participated in this study. A calibrated 3-axis piezoelectric accelerometer (Matsushita AGS61231) was attached to the body surfaces at the mentum, and the acceleration of the jaw movement was measured. Each subject chewed a piece of chewing gum with the posterior of the habitual chewing side at a frequency. The chewing data of each cycle were divided into open, close, and intercuspal phases. Finally using the five strokes after the third strokes, the meanings of 3D-jerk-cost for each chewing phase were calculated as described with following formula. The Friedman test was carried out to see if the data indicate a significant difference in the distributions of jerk-cost measurements for each chewing phase. P-Values<0.05 was considered significant. Results: Opening phase had the highest jerk-cost and a highly significant difference was shown among chewing phases (N=5, Chi-square=10, df=2, p=0.007). Conclusion: Using the simple and non-invasive system, our hypothesis that the adhesive nature of the gum may affect smoothness of opening phase was confirmed.