Factors Influencing Human Masticatory Performance
Callaghan, Kathryn X.
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Mastication is a highly complex and integrative chewing process that is performed by humans and other mammals involuntarily. Combinations of fixed and adaptive factors have the potential to determine how well one masticates. In coordination with video recording of jaw movements and electromyographic (EMG) recording of masseter and temporalis muscle activity, twenty-three subjects (9 male and 14 female) performed a series of seven different chewing tasks five times in random order, five tasks of which required chewing to a metronome (0.5x, 0.75x, lx, 2x, and 3x natural rate). An artificial test food was chewed for each trial and then the expectorated test food material was run through a series of fractional sieves as a means of measuring performance. Demographics, jaw and skull anatomical measurements, dental occlusion, and facial muscle activity were considered with the adjustment of chewing rate in determining what primary factor or combination of factors produced maximum performance. Decreased chewing rate resulted in significantly lower median particle sizes (MPS) and thus, better performance. In addition, performance by measuring the broadness of the particle distribution was the best at the lx chewing rate. Subjects compensated for the change in chewing rate by adjusting the EMG chewing burst duration of masseterand temporalis muscles in proportion with the prescribed chewing rate. Performance analysis, via MPS and distribution, in congruence with EMG data analysis suggested that chewing rate overpowered the effects of demographics, cephalometric measurements and occlusal contact area with the muscles responding by altering burst duration for voluntary chewing rates.