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Sleep bruxism (SB) is characterised by rhythmic (phasic) or non-rhythmic (tonic) masticatory muscle activities during sleep and is not a movement disorder or sleep disorder in otherwise healthy individuals. 1 SB prevalence rate has been reported about 14%-20% 2 in children and 8%-12% in adolescents and adults with a decrease with age. 3 Most SB patients complain of tooth wear, locked jaw, temporomandibular pain and temporal headache. Previous studies showed psychological (eg stress and anxiety) and genetic factors as well as smoking, oesophageal reflux and drugs (such as selective serotonin AbstractMost sleep bruxism (SB) episodes are accompanied by an increase in sympathetic tone and heart rate (HR). To characterise heart rate (HR) changes in relation to rhythmic masticatory muscle activities (RMMAs) in SB patients, polysomnographic recordings were performed on 10 SB patients and 11 normal controls. The duration of movement events, amplitude and duration of HR increases, and time to reach HR peak associated with RMMAs and limb movements (LMs) were determined, and the relationships of the parameters of HR increases with types of movements and RMMAs were analysed. All of the parameters of HR increases associated with three types of movements (RMMAs, RMMAs + LMs and LMs) and masseter activities (phasic, tonic and mixed) were significantly different (two-way ANOVA, P < .001 for all) in both SB patients and controls. The duration of RMMAs/LMs was positively correlated with the parameters (SB patients: R 2 = .24-.85, P < .0001; controls: R 2 = .23-.68, P < .0001).The amplitude of HR increases was also positively correlated with respiration changes in the SB patients (R 2 = .3258, P < .0001) and controls (R 2 = .09469, P < .05). The proportions of phasic RMMAs associated with awakenings, microarousals and no cortical arousals were significantly different and so were the proportions of tonic and mixed RMMAs (Friedman's tests, P < .05-.001). The HR increases associated with RMMAs may be intrinsic to the cortical arousal response and autonomic activation, and differences in HR increases associated with different types of movements and RMMAs might be related to the changes in respiration and differences in cortical arousal levels. K E Y W O R D Scortical arousal, heart rate, limb movements, respiration, rhythmic masticatory muscle activities, sleep bruxism

Summary Background Most rhythmic masticatory muscle activities (RMMAs) have been shown to be accompanied with limb movements (LMs) in sleep bruxism (SB) patients during sleep. Objectives To compare the relationships between RMMAs and LMs in SB patients and normal subjects. Methods Polysomnographic recordings were performed on eight SB patients and nine normal subjects and the frequencies and durations of RMMAs as well as LMs were determined. Linear regression and correlation analysis were performed to study the relationship between durations of RMMAs and LMs when RMMAs occurred with LMs. Results Most LMs in SB patients, but not in normal subjects, were accompanied with RMMAs. RMMAs in SB patients were more likely to be isolated, phasic or mixed, while RMMAs in normal subjects were more likely to be tonic. The frequencies of LMs, isolated RMMAs and RMMAs accompanied with LMs in SB patients were significantly higher than those in normal subjects. Furthermore, linear regression and correlation analysis showed that duration of RMMAs was significantly associated with that of LMs when RMMAs occurred with LMs. The duration of RMMAs, when accompanied with LMs, in SB patients was significantly longer than that in normal subjects. Conclusions Close relationships between LMs and RMMAs exist in SB patients and normal subjects, and SB episodes may be part of cortical arousal responses and the increased cortical activities associated with SB episodes may not just be localised to the central nervous system (CNS) that controls jaw movements but may also include other parts of CNS that controls LMs.