The Timing and Amplitude of Masticatory Muscle Activity

Previous studies have demonstrated that the left and right-sided chewing movements mirror each other in asymptomatic subjects with good occlusions.

Objectives: We hypothesized that left and right-sided masticatory muscle activity patterns of normal subjects should mirror each other, both in terms of amplitude and also in timing.

Methods: 12 asymptomatic subjects (5 f, 7 m) masticated a tough bolus in a standardized portion. Each subject masticated one bolus with left-sided chewing and an equal bolus on the right side. We measured; 1) the Peak rms amplitude, 2) the time from onset of contraction to peak rms amplitude and 3) the Integral of the chewing burst, for the superficial masseters (Mm), the anterior temporalis (Ta) and the anterior belly of the digastrics (Da) bilaterally.

Results: We used Student's 2-tailed paired t test to compare; 1) peak rms amplitudes, 2) time to peak rms amplitude and 3) integrated amplitude from the onset of contraction to the end of the chewing burst for all muscles. We found no significant differences (p>0.05) in any of the 3 (Working Vs Working) measurements. After pooling the (L + R) elevators we found a significant difference between the Working Vs Nonworking peak amplitudes of Ta (p<0.023) and Mm (p<0.0001) and a significant difference (p<0.00015) in the Integrated amplitudes of the same masseters. We saw a trend (p<0.052) toward a difference in the Working Vs Nonworking Da in the time to peak amplitude.

Conclusion: We found no statistically significant difference in the mastication activity of the mirrored left/right (Working Vs Working) temporalis, masseter or digastric muscles with respect to peak amplitude, time to peak amplitude or the integral of the chewing burst. Differences were found between the Working and Nonworking peak activity and Integral of the chewing burst.