Electromyography assessment of chewing induced fatigue in temporomandibular disorders patients - a pilot study

The purpose of this study was to evaluate the endurance time, pain and discomfort intensities, the RMS and median frequency (Fmed) in the induced fatigue by prolonged gum mastication in control and temporomandibular disorders (TMD) groups. This study evaluated 8 healthy and 11 TMD patient women (mean age 27±6 years). Each gum (18x17x4mm, weight 245mg) was put on both sides of the dental arc. The metronome set at 80 bpm indicated chewing rate. Endurance time corresponded to time ranging from beginning of mastication to the subject fatigue. Pain and discomfort intensities were evaluated by visual analogue scale (VAS) obtained after and before the prolonged gum mastication. Surface EMG was recorded from the anterior temporalis and masseter muscles using surface differential electrodes (silvers bars 10mm apart, 10mm long, 2mm wide, gain of 100x, input impedance of 10GÙ and CMRR of 130dB). The EMG signals were analogically amplified with gain of 50x, filtered (10-1500Hz bandpass) and sampled by 12 bits A/D covert board with a 2KHz frequency. The signals were digitally band-pass filtered (10-500Hz). The RMS and Fmed (PSD, FFT, 250 ms, 1024 points, Hanning window processing) were obtained from masticatory cycles in 250ms windows determined visually considering the most stable epoch. The maximal clenching RMS values were used to normalize masticatory cycles EMG amplitude. The first masticatory cycle Fmed values were used to normalize EMG frequency of masticatory cycle remains. There were no significant differences among the values of RMS and Fmed during the prolonged gum mastication (p<0.05, Friedman ANOVA). Endurance time was significantly shorter to TDM group (p<0.05, Mann-Whitney test). Pain and discomfort intensities were not different for control and TDM groups after the prolonged mastication (p<0.05, Mann-Whitney test). There was no evidence of change related to prolonged gum mastication in the investigated electromyographic parameters, in these experimental conditions.

Keywords
mastication, chewing, muscle fatigue, electromyography, visual analogue scale