The Human Chewing Pace is Subject-Specific and Stable over time

Objectives: It is widely accepted that masticatory function is a result of an intrinsic pattern generated by a central pattern generator, which is modified by peripheral sensory feedbacks. However, current knowledge regarding chewing frequency (i.e. pace) has been mostly derived from laboratory findings, and little information currently exists on the chewing function in the natural environment during habitual daily activities. The aim of this study was to investigate the features of the chewing activity and the variability of the human chewing pace, as assessed in the natural environment, using a repeated-measurement study design. It was hypothesized that there is a chewing frequency that is relatively stable within-subjects but variable across subjects. Methods: Electromyographic surface activity was recorded unilaterally from the masseter in 16 subjects for three hours over three recording days in the natural environment using portable recorders. The time-frequency properties of chewing episodes were automatically extracted off-line using a previously validated algorithm (Farella et al., Muscle Nerve 39: 828-836). Repeated-measurements ANOVA, intraclass correlation coefficient (ICC), and hierarchical cluster analysis were used for statistical analysis. Results: Overall, 2376 chewing episodes could be detected, with a mean frequency of 1.54 Hz (5th and 95th percentiles: 0.75-2.17 Hz). Variability of chewing frequency between-individuals was much greater than that of within-individual (F=18.4; p<0.001). The individual chewing paces were stable across different days with an ICC of 0.90 (95% confidence interval: 0.81 – 0.96). By using a hierarchical cluster analysis on chewing frequencies, subjects could be allocated to three non-overlapping groups – fast, normal, and slow chewers. Conclusions: Our findings provide evidence that each individual has a specific chewing pace in the natural environment, which is stable across different days. Supported by the RC Tonkin Summer Research Scholarship (New Zealand Dental Association Research Foundation).