Relationships between cortical, cardiac, and arousal-motor activities in the genesis of rhythmic masticatory muscle activity across sleep cycles in primary sleep bruxism children

Study Objectives The present study aimed to clarify the physiological relationships between rhythmic masticatory muscle activity (RMMA) and cyclic changes in cortical, autonomic, and arousal-motor activities during sleep in sleep bruxism (SB) children. Methods Polysomnographic recordings were performed on fifteen SB children (9 boys, 6 girls, 10.3 ± 2.5 years) and eighteen control children (5 boys, 13 girls, 10.7 ± 3.1 years) free from sleep and developmental disorders. Sleep and RMMA were scored by the standard rules. Sleep cycle was divided into NREM and REM sleep segments and the frequency of RMMA, transient arousal and movement, and cortical and cardiac activities were then quantitatively analyzed in relation to sleep cycles. Results Neither sleep architecture nor sleep stage distribution of RMMA significantly differed between two groups. In sleep cycles, SB children showed more frequent RMMA in all segments than controls, while cyclic changes in cortical and autonomic activities did not significantly differ between two groups. In SB children, RMMA was the most frequent in the last NREM segment before REM sleep and was associated with increases in cortical beta activity and arousal; more than 70% of RMMA time-dependently occurred with cortical and motor arousals. Conclusions This is the first study to suggest that the potentiation of RMMA occurrence was associated with transient arousal under cyclic sleep processes in primary SB children.

Sleep stage dynamics in young patients with sleep bruxism

Study Objectives We hypothesized that sleep stage dynamics are different in patients with sleep bruxism (SB) and that these changes are associated with the occurrence of rhythmic masticatory muscle activity (RMMA). Methods Fifteen healthy controls and 15 patients with SB underwent overnight polysomnography. Sleep variables and survival curves of continuous runs of each sleep stage were compared between the groups. Stage transition dynamics and the probability of stage fragmentation were analyzed for three epochs before and after the epoch with RMMA. Survival curves of continuous runs of each sleep stage, terminated with or without RMMA, were also compared. Results There were no significant differences in sleep variables between the groups, except for shorter sleep latency, shorter rapid eye movement (REM) latency, and longer total N1 duration in SB patients than in controls. REM sleep and N2 were significantly less continuous in SB patients than in controls. In the SB group, stage fragmentation probability was significantly increased for the epoch with RMMA compared with the baseline for all stages. Meanwhile, the occurrence of RMMA did not affect the continuity of N2 or REM; however, the occurrence of RMMA was preceded by more continuous N3 runs. Conclusions Sleep stage dynamics differed between SB patients and controls. RMMA does not result in sleep disruption but is likely associated with dissipation of sleep pressure. Less continuity of REM sleep in SB may provide insights into the underlying pathophysiological mechanisms of SB, which may be related to REM sleep processes such as cortical desynchronized states or brainstem activation.