Experimental pain reduces jaw-movement smoothness during gum chewing

Objectives: Pain has been reported to result in smaller and slower jaw movements. The objective of this investigation was to determine whether experimental jaw muscle (masseter) pain had an effect on jaw movement smoothness. Methods: An accelerometer was attached to the skin of the mentum of 5 asymptomatic subjects and acceleration was recorded during chewing of softened gum. Vertical jaw displacement, acceleration, the jerk, and the time differential of jerk, namely jerk cost (an inverse measure of jaw movement smoothness) during the gum chewing were obtained as a function of time. Chewing was performed under two conditions: control pain-free condition, and test condition (induced pain of moderate intensity) during which 4.5% hypertonic saline was continuously infused into right masseter to achieve 40–60 mm pain intensity on a 100-mm visual analog scale. Jerk cost was calculated on the opening and closing phase of each chewing cycle and was compared between control and test 1 with paired student t-test (2-tailed). The mean jerk cost of five strokes after an initial three strokes was used for the calculation. Results: In the opening phase, there was a significantly higher jerk cost (5044.9 ± 2098.1 m2s-5) during the test (pain) condition than that of control (3166.2 ± 1169.4 m2s-5; n=5, p<0.05). There was also a higher jerk cost during the test (pain) condition in the closing phase (1994.3 ± 1150.2 m2s-5) than that of control (1105.4 ± 965.1 m2s-5; n=5, p<0.1 ). Conclusion: This is the first characterization of the effect of experimental pain on jaw movement smoothness and the data suggest that experimental pain may decrease movement smoothness which may reflect a decrease in movement skillfulness. Supported by the NHMRC of Australia (Grant #512309), the Australian Dental Research Foundation, Inc.