Comparison between the rhythmic jaw contractions occurring during sleep and while chewing.

The masticatory central pattern generator (CPG) may be implicated in the pathophysiology of sleep bruxism (SB). The aim of this study was to compare rhythmic masticatory muscle activity (RMMA) occurring during sleep related to SB with that of natural voluntary chewing in a sample of sleep bruxers. It was hypothesized that the pace of RMMA during sleep is correlated with the chewing pace. Electromyographic (EMG) surface activity was recorded unilaterally from the masseter muscle of 13 participants diagnosed with SB (mean age ± standard deviation =26.1 ± 9.0 years) by means of portable recorders. For each participant, recordings were carried out in the natural environment setting, always including the dinner time and the entire sleeping period. The time-frequency features of RMMA episodes were extracted automatically offline using a previously validated algorithm. Comparisons between chewing and SB activity indicated that chewing RMMA episodes almost doubled sleep RMMA in duration and power. The mean frequency of SB episodes was 1.0 ± 0.3 Hz, whereas the mean frequency of chewing episodes was 1.5 ± 0.4 Hz. The pace of SB and that of chewing were not correlated significantly (R = -0.13; P = 0.96). We conclude that sleep RMMA is not related to that of chewing. Despite both activities being accompanied by rhythmic jaw contractions, the pace-generating mechanism of SB may be independent from that of chewing.