The relationship between selective sleep deprivation, nocturnal jaw-muscle activity and pain in healthy men

The relationship between nocturnal jaw-muscle activity and temporomandibular disorders (TMD) is still controversial. The aim of this study was to investigate the effect of selective slow wave sleep (SWS = non-rapid-eye-movement (NREM) stage 3 + 4) deprivation on jaw-muscle activity using a new automatic system. Ten healthy men without signs of symptoms of TMD participated. The subjects slept in the laboratory for six continuous nights including one adjustment night, one baseline night, three nights with experimental sleep deprivation and one recovery night. Polysomnographic recordings of electroencephalography (EEG) and electromyography (EMG) were obtained for recognition of sleep stages and masseter muscle activity. During the three experimental nights, computer-controlled sound stimulation (60--90 dB(A), 1000 Hz) were given as long as the subjects were in SWS. Maximum voluntary occlusal force (MVOF), pain pressure threshold (PPT) and visual analogue scales (VAS) were used to assess the state of the masseter muscles every morning and evening during the study period. The results showed that the time spent in SWS was significantly decreased during the first sleep deprivation night, but there were no significant effects on nocturnal EMG activity (i.e. the numbers of bruxism episodes per hour of sleep, bruxism bursts per episodes bruxism bursts per hour of sleep), MVOF, VAS or PPT. Furthermore, the automatic system only deprived the SWS in five subjects for the following two nights although the sound stimulation was given at the maximum intensity. These results suggest that deprivation of SWS may not interact immediately with nocturnal jaw-muscle activity and jaw-muscle pain.