Reciprocal first night effect on rhythmic and non‐rhythmic oromotor episodes in moderate to severe primary sleep bruxism: A retrospective physiological study

Abstract

BackgroundSleep on the first night in a sleep laboratory is characterized by a lower sleep quality and frequency of rhythmic masticatory muscle activity (RMMA) than that on the second night in moderate to severe sleep bruxism (SB) patients.ObjectiveThe aims of this study was to clarify the physiological factors contributing to the first night effect on oromotor activity during sleep and investigate whether physiological factors involved in the first night effect differed between rhythmic and non‐rhythmic oromotor activities.MethodsPolysomnographic data collected on two consecutive nights from 15 moderate to severe SB subjects (F 7: M 8; age: 23.2 ± 1.3 [mean ± SD] years) were retrospectively analysed. Sleep variables, RMMA and non‐specific masticatory muscle activity (NSMA) were scored in relation to episode types (i.e. phasic or tonic and cluster or isolated), sleep architecture and transient arousals. The relationships between nightly differences in oromotor and sleep variables were assessed. The distribution of oromotor events, arousals, cortical electroencephalographic power, RR intervals and heart rate variability were examined in relation to sleep cycle changes. These variables were compared between the first and second nights and between RMMA and NSMA.ResultsSleep variables showed a lower sleep quality on Night 1 than on Night 2. In comparisons with Night 1, the RMMA index increased by 18.8% (p < .001, the Wilcoxon signed‐rank test) on Night 2, while the NSMA index decreased by 17.9% (p = .041). Changes in the RMMA index did not correlate with those in sleep variables, while changes in the NSMA index correlated with those in arousal‐related variables (p < .001, Spearman's rank correlation). An increase in the RMMA index on Night 2 was found for the cluster type and stage N1 related to sleep cyclic fluctuations in cortical and cardiac activities. In contrast, the decrease in the NSMA index was associated with increases in the isolated type and the occurrence of stage N2 and wakefulness regardless of the sleep cycle.ConclusionDiscrepancies in first night effect on the occurrence of RMMA and NSMA represent unique sleep‐related processes in the genesis of oromotor phenotypes in SB subjects.

A case–control study on the effect of rhythmic masticatory muscle activity (RMMA) clusters on sleep fragmentation and severity of orofacial muscle pain in sleep bruxism

“…Previous studies have proposed different pathogenesis for tonic events compared with phasic and mixed events, as well as a relationship between the TERT gene polymorphism and phasic events but not tonic events (Macek et al, 2022). The positive correlation between hypoxia and phasic events, but not tonic events, supports the hypothesis that phasic and tonic types of bruxism exhibit distinct features and roles (Michalek-Zrabkowska, Wieckiewicz, Haraki et al, 2023;Okura et al, 2023). Recently, Toyota et al (2022) demonstrated a significantly higher frequency of RMMA and percentage of arousals with RMMA in subjects with sleep bruxism compared with controls, with no significant differences observed for nonrhythmic promotor events.…”

“…However, there are also limitations to consider. We did not conduct an adaptation night, which prevented us from accounting for the first-night effect and may result a bias related adaptation and environment (Haraki et al, 2023). Another limitation is the lack of data on other TMD disease entities in the studied group.…”

Sleep architecture as a candidate for phenotyping sleep bruxism: A narrative physiological review

“…and microstructure (e.g., more frequent microarousals) also significantly differed between the two nights. 71 In other words, the first night effect on SB is paradoxical; the occurrence of RMMA does not positively correlate with that of microarousals 73 . It is important to note that daily fluctuations in the occurrence of RMMA are a significant factor when diagnosing SB and assessing treatment effects on SB.…”