Sleep bruxism: an oromotor activity secondary to micro-arousal

The relationship between possible, probable, or definite sleep bruxism and sleep quality: A systematic review

It has been suggested that sleep bruxism may interrupt sleep continuity, hence potentially influencing sleep quality. The aim of this study was to systematically review the relationship between possible, probable, and definite sleep bruxism and sleep quality in otherwise healthy individuals. A systematic search on sleep bruxism and sleep quality was performed in seven databases until 19 December 2022. Eligible articles were screened, and quality assessment was performed via the Joanna Briggs Institute Scale. Of 3681 articles screened, 13 were included in this study. Of these, six evaluated the relationship between sleep quality and possible sleep bruxism, three with probable sleep bruxism, and four with definite sleep bruxism. An association between poor sleep quality and sleep bruxism was found among those individuals diagnosed with possible and probable sleep bruxism. However, the studies conducted in individuals with definite sleep bruxism failed to demonstrate any association. With more reliable measures to evaluate sleep bruxism, a relationship between sleep bruxism and sleep quality was not evident.

Prevalence and risk factors of sleep bruxism in adults with primary snoring: a large-scale polysomnographic study

STUDY OBJECTIVES

To determine the prevalence and risk factors of sleep bruxism (SB) in adults with primary snoring (PS).

METHODS

This study included 292 adults with PS (140 males, 152 females; mean age ± standard deviation = 42.8 ± 12.2 years; mean body mass index ± standard deviation = 26.7 ± 4.7 kg/m2) without previous treatment for snoring. SB was diagnosed based on the frequency of the biomarker of SB: rhythmic masticatory muscle activity (SB when rhythmic masticatory muscle activity ≥ 2 episodes/h). Logistic regression was performed, with SB as the dependent variable and with age, sex, body mass index, and sleep- and respiratory-related polysomnographic parameters as the independent variables to identify the risk factors for SB.

RESULTS

The prevalence of SB was 44.6% in adults with PS. Younger age (odds ratio = 0.965 [0.944, 0.987]) and shorter total sleep time (odds ratio = 0.760 [0.609, 0.948]) significantly increased the risk of SB (P < .05).

CONCLUSIONS

SB is highly prevalent in adults with PS. Younger age and shorter sleep time are significant risk factors for SB in adults with PS.

CLINICAL TRIAL REGISTRATION

Registry: onderzoekmetmensen.nl; Name: A Large Sample Polysomnographic Study on Sleep Bruxism; URL: https://trialsearch.who.int/Trial2.aspx?TrialID=NL-OMON19947; Identifier: NL8516.

CITATION

Li D, Lobbezoo F, Hilgevoord AAJ, de Vries N, Aarab G. Prevalence and risk factors of sleep bruxism in adults with primary snoring: a large-scale polysomnographic study. J Clin Sleep Med. 2024;20(8):1331-1337.

Comparison between botulinum toxin type A injection on masseter muscle only and additional injection on anterior belly of digastric muscle in sleep bruxism patients: A clinical trial

OBJECTIVE

This study aims to evaluate the effects on bite force and muscle thickness of the botulinum toxin (BoNT) injection for patients with sleep bruxism (SB) by comparing injections into the masseter muscle only and both the masseter and the anterior belly of the digastric muscle (ABDM) in a clinical trial.

METHODS

Twelve SB patients received BoNT-A injections using US-guided techniques into the masseter muscle only (Group A), while the remaining 12 SB patients received injections into both the masseter and ABDM (Group B). Bite force and muscle thickness were measured before injection, as well as 1 and 2 months after injection.

RESULTS

The bite force and masseter muscle thickness decreased in both Group A and Group B before injection, and at 1 and 2 months after injection. However, there was no significant difference (p > .05, repeated measures analysis of variance) between the two groups, and there was also no significant difference in ABDM thickness (p > .05, repeated measures analysis of variance).

CONCLUSION

This study is the first to assess the short-term effects of BoNT injected into ABDM for SB control. Results show no influence on SB reduction, suggesting the need for further research on BoNT's effectiveness in controlling intense ABDM contractions during sleep and assessing suprahyoid muscle potential impact on rhythmic masticatory muscle activity occurrence.

Effects of vibratory feedback stimuli through an oral appliance on sleep bruxism: A 14-week intervention trial

Background/purpose

Various biofeedback stimulation techniques for managing sleep bruxism (SB) have recently emerged; however, the effect of the successive application of vibratory feedback stimulation has not been clarified. This study aimed to elucidate the effect of vibration feedback stimulation via an oral appliance (OA) on SB.

Materials and methods

This prospective, single-arm, open-label intervention study included 20 participants diagnosed with "definite" SB who wore a specially designed OA for 98 nights at home. A force-based SB detection system triggered a vibrator attached to the OA. Vibratory stimulation was withheld during the first 3-week adaptation period (weeks 1-3), applied during the 9-week stimulation period (weeks 4-12), and withheld again during the post-stimulation period (weeks 13-14). The number and duration of SB events per hour of sleep were calculated based on piezoelectric signals recorded with the OA-based vibration feedback device and compared between weeks 3 and 4, 8, 12, and 14 and between weeks 12 and 14 using the Friedman test (post-hoc test with Bonferroni correction).

Results

The duration of SB events significantly decreased after vibratory stimulation (weeks 3 versus 4, 8, and 12: P < 0.001, P = 0.026, and P = 0.033, respectively) and then significantly increased upon cessation of vibratory stimulation after the stimulation period (weeks 12 versus 14: P < 0.001).

Conclusion

Contingent vibratory stimulation through an OA-based vibration feedback device may suppress SB-related masticatory muscle activity continuously for 9 weeks and may be an effective alternative for managing SB.

Sleep bruxism: The past, the present, and the future-evolution of a concept

BACKGROUND

The concept of sleep bruxism (SB) has evolved exponentially over the past several decades. Many theories and hypotheses have been proposed as to the definition, pathophysiology, and management of SB, from the early 1960s through the present. The role of peripheral factors, such as dental occlusion, in the pathogenesis of SB has been discarded.

TYPES OF STUDIES REVIEWED

The authors searched several electronic databases (ie, PubMed, Google Scholar, Web of Science, Embase, and Ovid MEDLINE) for studies on bruxism. The search was conducted from January 1961 through May 2023 and yielded 4,612 articles, of which 312 were selected for comprehensive review after eliminating duplicates and nonfocused articles.

RESULTS

There has been an evident progressive shift from the role of peripheral factors, such as dental occlusion, to more central factors, such as the involvement of a central pattern generator as well as the autonomic nervous system, in the genesis of bruxing movements. There is continued robust interest in the dental community to elucidate the contributing factors involved in SB.

CONCLUSIONS AND PRACTICAL IMPLICATIONS

The neurophysiology of SB appears to be leaning more toward central rather than peripheral factors. There is increasing evidence of the role of the autonomic nervous system, genetics, and comorbidities in the genesis of SB. The scientific literature seems to refute the role of dental occlusion in the causation of bruxing movements. As per the literature, there has been a paradigm shift in the definition and genesis of SB and its possible dental implications and management, which also highlights the need for succinct scientific studies in this regard.

Sleep bruxism and associated physiological events in children with obstructive sleep apnea: a polysomnographic study

STUDY OBJECTIVES

The aim of this study was to evaluate the physiological events associated with sleep bruxism (Sleep Bruxism [SB]; presence of mandibular movement activity) and the control window (4 minutes prior to SB event, where no mandibular movement activity was detected) in a polysomnography study in children with mild sleep apnea.

METHODS

Polysomnography data from children aged 4 to 9 years old diagnosed with mild sleep apnea were analyzed by 2 trained examiners. The mandibular movement activity (bruxism event; SB) was classified into phasic and tonic. The control window was selected 4 minutes prior to the SB event. All physiological events were recorded in both bruxism and control windows, including sleep phase (N1, N2, N3, and rapid eye movement), arousal, leg movements, tachycardia, bradycardia, oxygen desaturation, and number of obstructive and central sleep apnea events. The moment in which those phenomena occurred when associated with SB was also analyzed (before/after). Data were analyzed using 95% confidence intervals (α = 5%).

RESULTS

A total of 661 mandibular movements were analyzed and classified as tonic (n = 372) or phasic (n = 289). The mean apnea-hypopnea index was 1.99 (SD = 1.27) events/h. The frequency of leg movements, microarousal, and tachycardia was increased in SB events when compared with the control window (P < .05). There was an increase in bradycardia frequency in the control window when compared with SB (in both tonic and phasic events). The frequency of obstructive and central apnea during SB was lower when compared with the other physiological phenomena.

CONCLUSIONS

There is a difference in the physiological parameters evaluated in children with mild sleep apnea when comparing the 2 windows (SB and control). Sleep bruxism is associated with other physiological phenomena, such as leg movements, tachycardia, and microarousal. The use of a control window (where no mandibular activity was detected) was representative since it did not show activation of the sympathetic nervous system.

CITATION

Bonacina CF, Soster LMSFA, Bueno C, et al. Sleep bruxism and associated physiological events in children with obstructive sleep apnea: a polysomnographic study. J Clin Sleep Med. 2024;20(4):565-573.

Is there an association between sleep bruxism and obstructive sleep apnea? A case-control polysomnographic investigation

OBJECTIVES

To estimate the statistical and epidemiological association between Sleep bruxism (SB) and Obstructive sleep apnea (OSA) based on OSA severity, and to describe sleep data findings within the analyzed population.

METHODS

A case-control study (N = 37) was conducted on subjects with and without OSA. All subjects underwent a full-night polysomnographic recording at the Sleep Unit (Clinical Neurophysiology Department) of San Carlos University Hospital. The diagnosis and severity of OSA were determined using ICSD-3 and AASM-2.6 scoring. The definitive SB diagnosis was obtained through a self-report test, physical examination, and PSG recordings. Variables used to study the association between both conditions included the apnea and hypopnea episodes, the Apnea-hypopnea index (AHI), the number of SB episodes per night, and the bruxism index. Chi2, correlations, and ANOVA were calculated. The epidemiological association was calculated using the OR.

RESULTS

SB showed an epidemiological association with OSA, with an OR of 0.15 (0.036-0.68), suggesting it could be considered a protective factor (p < 0.05). OSA patients presented fewer average SB episodes (6.8 ± 12.31) than non-OSA patients (25.08 ± 31.68). SB episodes correlated negatively (p < 0.05) with the AHI and the number of hypopneas (p < 0.05). The average number of SB episodes was significantly higher in patients with mild OSA compared to those with severe OSA.

CONCLUSIONS

In this sample of patients with subclinical and mild OSA, SB may act as a protective factor. However, confirmation of these results with a larger sample size is necessary.

Short-Term Effects of 3D-Printed Occlusal Splints and Conventional Splints on Sleep Bruxism Activity: EMG-ECG Night Recordings of a Sample of Young Adults

(1) Background: This study aims to compare the effects of 3D-printed splints and conventional manufactured splints on sleep bruxism (SB) EMG activity. (2) Methods: Twenty-six patients (19 M, 7 F, 25.8 ± 2.6 years) were randomly allocated to a study group (3D splints) and a control group (conventional manufactured splints) and followed for a period of three months with night EMG-ECG recordings. Samples of the involved materials were analyzed for nanoindentation. The outcomes of interest considered were the overall SB index, the total amount of surface masseter muscle activity (sMMA), and general and SB-related phasic and tonic contractions. A statistical evaluation was performed with a confidence interval (CI) between 2.5% and 97.5%. (3) Results: Differences between groups with OAs were observed for general tonic contraction (p = 0.0009), while differences between recording times were observed for general phasic contractions (p = 0.002) and general tonic contractions (p = 0.00001). Differences between recording times were observed for the total amount of sMMA (p = 0.01), for general phasic contractions (p = 0.0001), and for general tonic contractions (p = 0.000009) during night recordings without OAs. (4) Conclusions: Three-dimensional splints seem to have a higher impact on SB-related electromyographic activity but not on the overall sleep bruxism index. The more regular surfaces offered by 3D splints could be related to phasic contraction stabilization.

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

BACKGROUND

Sleep bruxism (SB), an oral behaviour in otherwise healthy individuals, is characterised by frequent rhythmic masticatory muscle activity (RMMA) during sleep. RMMA/SB episodes occur over various sleep stages (N1-N3 and rapid eye movement (REM)), sleep cycles (non-REM to REM), and frequently with microarousals. It currently remains unclear whether these characteristics of sleep architecture are phenotype candidates for the genesis of RMMA/SB.

OBJECTIVES

This narrative review investigated the relationship between sleep architecture and the occurrence of RMMA as a SB phenotype candidate.

METHODS

PubMed research was performed using keywords related to RMMA/SB and sleep architecture.

RESULTS

In non-SB and SB healthy individuals, RMMA episodes were most frequent in the light non-REM sleep stages N1 and N2, particularly during the ascending phase of sleep cycles. The onset of RMMA/SB episodes in healthy individuals was preceded by a physiological arousal sequence of autonomic cardiovascular to cortical activation. It was not possible to extract a consistent sleep architecture pattern in the presence of sleep comorbidities. The lack of standardisation and variability between subject complexified the search for specific sleep architecture phenotype(s).

CONCLUSION

In otherwise healthy individuals, the genesis of RMMA/SB episodes is largely affected by oscillations in the sleep stage and cycle as well as the occurrence of microarousal. Furthermore, a specific sleep architecture pattern cannot be confirmed in the presence of sleep comorbidity. Further studies are needed to delineate sleep architecture phenotype candidate(s) that contribute to the more accurate diagnosis of SB and treatment approaches using standardised and innovative methodologies.

Correlations between sleep architecture and sleep-related masseter muscle activity in children with sleep bruxism

BACKGROUND

Sleep bruxism (SB) occurring during No-REM (nREM) sleep and increase in microarousals per hour have been described in adults, but not in children.

OBJECTIVE

To assess the correlation between sleep architecture and masseter muscle activity related to sleep bruxism (SB/MMA) in children.

MATERIALS AND METHODS

Forty-three children aged 7-12 years (mean age: 9.4 ± 1.3) with confirmed SB underwent a two-night polysomnographic (PSG) study in a sleep laboratory, for accommodation (first night) and data collection (second night). Data on sleep architecture (total sleep duration (TSD), sleep efficiency (SE), sleep onset latency (SOL), REM and nREM sleep duration and proportion and microarousals/hour during REM and nREM sleep) and episodes/hour of SB/MMA were recorded. Single and multiple-variable linear regression analyses were performed to assess the correlation between data on sleep architecture (predictors) and SB/MMA (dependent variable).

RESULTS

Shorter TSD, REM and nREM stage 1 sleep duration, longer SOL and more microarousals/hour during REM and nREM sleep were found to be positive predictors of SB/MMA in children in the multiple-variable regression analysis (R2  = 0.511).

CONCLUSION

Within the limitations of this study, it can be concluded that SB/MMA is correlated with altered sleep architecture in children (shorter total sleep duration (TSD), shorter nREM and REM sleep and higher microarousals during REM and nREM sleep). Nevertheless, the clinical significance of these findings need to be demonstrated in future studies.

Secondary bruxism: A valid diagnosis or just a coincidental finding of additional masticatory muscle activity? A narrative review of literature

INTRODUCTION

Bruxism is defined as a repetitive masticatory muscle activity that can manifest it upon awakening (awake bruxism-AB) or during sleep (sleep bruxism-SB). Some forms of both, AB and SB can be associated to many other coexistent factors, considered of risk for the initiation and maintenance of the bruxism. Although controversial, the term 'secondary bruxism' has frequently been used to label these cases. The absence of an adequate definition of bruxism, the non-distinction between the circadian manifestations and the report of many different measurement techniques, however, are important factors to be considered when judging the literature findings. The use (and abuse) of drugs, caffeine, nicotine, alcohol and psychoactive substances, the presence of respiratory disorders during sleep, gastroesophageal reflux disorders and movement, neurological and psychiatric disorders are among these factors. The scarcity of controlled studies and the complexity and interactions among all aforementioned factors, unfortunately, does not allow to establish any causality or temporal association with SB and AB. The supposition that variables are related depends on different parameters, not clearly demonstrated in the available studies.

OBJECTIVES

This narrative review aims at providing oral health care professionals with an update on the co-risk factors and disorders possibly associated with bruxism. In addition, the authors discuss the appropriateness of the term 'secondary bruxism' as a valid diagnostic category based on the available evidence.

CONCLUSION

The absence of an adequate definition of bruxism, the non-distinction between the circadian manifestations and the report of many different measurement techniques found in many studies preclude any solid and convincing conclusion on the existence of the 'secondary' bruxism.

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

BACKGROUND

Sleep 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.

OBJECTIVE

The 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.

METHODS

Polysomnographic 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.

RESULTS

Sleep 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.

CONCLUSION

Discrepancies 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.

Self-reported sleep bruxism and mortality in 1990-2020 in a nationwide twin cohort

BACKGROUND

The association of sleep bruxism with mortality has not been studied.

OBJECTIVES

Altogether 12 040 subjects from the nationwide Finnish twin cohort were included in the analyses. We examined whether self-reported sleep bruxism is associated with increased risk of mortality, and if so, whether the effect is independent of known common risk factors. The time span of the follow-up was 30 years.

METHODS

Cox proportional hazards regression models (Hazard Ratios and their 95% Confidence Intervals) adjusted by age, sex and covariates were used to assess the effect of baseline bruxism status in 1990 on future mortality in 1990-2020.

RESULTS

The risk of mortality among all participants (n = 12 040), independent of missing covariates and adjusted by age and sex, was 40% higher in weekly bruxers than in never bruxers (HR 1.40, 95% CI 1.16-1.68, p < .001). However, when adjusted by all studied covariates, (n = 11 427) the risk was no longer observed (HR 1.04, 95% CI 0.86-1.25, p = .717). Despite the overall lack of between bruxism and mortality after adjustment for covariates, we examined the cause-specific risks for major cause-of-death groups. There were no substantial associations of weekly bruxism with major disease outcomes by the fully adjusted hazard ratios for them.

CONCLUSION

Bruxism does not kill-in line with its definition of being rather a behaviour (with all its phenotypes) than a disease.

Sleep apnea pathophysiology

OBJECTIVE

The purpose of this study is to examine the pathophysiology underlying sleep apnea (SA).

BACKGROUND

We consider several critical features of SA including the roles played by the ascending reticular activating system (ARAS) that controls vegetative functions and electroencephalographic findings associated with both SA and normal sleep. We evaluate this knowledge together with our current understanding of the anatomy, histology, and physiology of the mesencephalic trigeminal nucleus (MTN) and mechanisms that contribute directly to normal and disordered sleep. MTN neurons express γ-aminobutyric acid (GABA) receptors which activate them (make chlorine come out of the cells) and that can be activated by GABA released from the hypothalamic preoptic area.

METHOD

We reviewed the published literature focused on sleep apnea (SA) reported in Google Scholar, Scopus, and PubMed databases.

RESULTS

The MTN neurons respond to the hypothalamic GABA release by releasing glutamate that activates neurons in the ARAS. Based on these findings, we conclude that a dysfunctional MTN may be incapable of activating neurons in the ARAS, notably those in the parabrachial nucleus, and that this will ultimately lead to SA. Despite its name, obstructive sleep apnea (OSA) is not caused by an airway obstruction that prevents breathing.

CONCLUSIONS

While obstruction may contribute to the overall pathology, the primary factor involved in this scenario is the lack of neurotransmitters.

Associations between signs of sleep bruxism and insomnia: A polysomnographic study

Sleep bruxism (SB) is a repetitive jaw-muscle activity characterised by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible. Sleep bruxism has been linked with insomnia symptoms. Moreover, it has been suggested that there is a positive association between distress and the occurrence of sleep bruxism. However, the occurrence of sleep bruxism and its association with distress have not been studied in patients with insomnia. Therefore, we hypothesised that: (1) the occurrence of sleep bruxism is higher in patients with insomnia than in healthy controls; and (2) the occurrence of sleep bruxism in insomnia patients with moderate to high distress (IMHD) is higher than that in insomnia patients with slight distress (ISD). A total of 44 controls (34 females, 10 males, mean ± SD age = 46.8 ± 14.4 years) and 42 participants with insomnia (35 females, 7 males, mean ± SD age = 51.3 ± 12.1 years) were enrolled in this study. Among 42 participants with insomnia, 20 participants were subtyped as IMHD, 17 participants as ISD. Another five participants were not subtyped due to insufficient information. Group differences in rhythmic masticatory muscle activity (RMMA), a biomarker of sleep bruxism, were evaluated with Mann-Whitney U tests. The medians and interquartile ranges of the RMMA indices were 0.8|1.8|3.3 in controls, 1.1|1.6|2.3 in IMHD and 1.2|1.9|2.9 in ISD. There was no significant difference in the RMMA index, neither between participants with insomnia and controls (P = 0.514) nor between IMHD versus ISD (P = 0.270). The occurrence of RMMA indicators of possible sleep bruxism is not significantly different between individuals with insomnia and controls, nor between IMHD versus ISD.

Primary headache management in a multidisciplinary team - a pilot study

Tension-type headaches and migraines are bidirectionally related to dysfunctions of the cervical and masticatory muscles and some psychosocial factors. Our pilot study aimed to investigate the connections between primary headaches, bruxism, and psychosocial issues. In addition, we aimed to assess the effectiveness of a multidisciplinary approach in decreasing the intensity and frequency of headache episodes and bruxism. Sixty-seven patients previously diagnosed with primary headache and bruxism were divided into two similar groups. One group benefited from manual therapy alone, while the other received manual therapy and counseling sessions for three months. Statistical data analysis was conducted using SPSS, Version 24, using the paired Student's t-tests and McNemar's tests. After the three-month intervention period, we observed substantial improvements across various parameters. Some demonstrated statistically significant differences, while others did not reach statistical significance. When comparing the outcomes, the combined therapy proved more effective than manual therapy alone.

Understanding the pathophysiology of sleep bruxism based on human and animal studies: A narrative review

BACKGROUND

Sleep bruxism (SB) is a common sleep disorder that affects approximately 20% of children and 10% of adults. It may cause orodental problems, such as tooth wear, jaw pain, and temporal headaches. However, the pathophysiological mechanisms underlying SB remain largely unknown, and a definitive treatment has not yet been established.

HIGHLIGHT

Human studies involving polysomnography have shown that rhythmic masticatory muscle activity (RMMA) is more frequent in otherwise healthy individuals with SB than in normal individuals. RMMA occurs during light non-rapid eye movement (non-REM) sleep in association with transient arousals and cyclic sleep processes. To further elucidate the neurophysiological mechanisms of SB, jaw motor activities have been investigated in naturally sleeping animals. These animals exhibit various contractions of masticatory muscles, including episodes of rhythmic and repetitive masticatory muscle bursts that occurred during non-REM sleep in association with cortical and cardiac activation, similar to those found in humans. Electrical microstimulation of corticobulbar tracts may also induce rhythmic masticatory muscle contractions during non-REM sleep, suggesting that the masticatory motor system is activated during non-REM sleep via excitatory inputs to the masticatory central pattern generator.

CONCLUSION

This review article summarizes the pathophysiology of SB and putative origin of RMMA in both human and animal studies. Physiological factors contributing to RMMA in SB have been identified in human studies and may also be present in animal models. Further research is required to integrate the findings between human and animal studies to better understand the mechanisms underlying SB.

Nutrients Associated with Sleep Bruxism

Background: The purpose of the present research was to identify nutrients related to sleep bruxism and to establish a hypothesis regarding the relationship between sleep bruxism and nutrients. Methods: We recruited 143 Japanese university students in 2021 and assigned them to sleep bruxism (n = 58) and non-sleep bruxism groups (n = 85), using an identical single-channel wearable electromyography device. To investigate nutrient intakes, participants answered a food frequency questionnaire based on food groups. We assessed differences in nutrient intakes between the sleep bruxism and non-sleep bruxism groups. Results: Logistic regression modeling showed that sleep bruxism tended to be associated with dietary fiber (odds ratio, 0.91; 95% confidence interval, 0.83–1.00; p = 0.059). In addition, a subgroup analysis selecting students in the top and bottom quartiles of dietary fiber intake showed that students with sleep bruxism had a significantly lower dietary fiber intake (10.4 ± 4.6 g) than those without sleep bruxism (13.4 ± 6.1 g; p = 0.022). Conclusion: The present research showed that dietary fiber intake may be related to sleep bruxism. Therefore, we hypothesized that dietary fiber would improve sleep bruxism in young adults.

Sleep bruxism is highly prevalent in adults with obstructive sleep apnea: a large-scale polysomnographic study

STUDY OBJECTIVES

The aim was to determine the prevalence and risk factors of sleep bruxism (SB) and to investigate the relationships between SB episodes, arousals, and respiratory events in adults with obstructive sleep apnea (OSA).

METHODS

This prospective study included 914 adults with OSA (305 females, 609 males; age = 53 years [interquartile range = 17]; apnea-hypopnea index = 13.9 events/h [interquartile range = 21]). The diagnosis of SB was made when the rhythmic masticatory muscle activity (RMMA) index was at least 2 episodes/h of sleep based on a full polysomnographic recording. Binary logistic regression was performed to identify risk factors for SB. Network analysis was performed to determine the relations between RMMA, respiratory event, sleep arousal, and other factors. Further, the percentage of RMMA time-related to arousal was calculated.

RESULTS

The prevalence of SB in adults with OSA was 49.7%. Male sex, lower body mass index, and higher percentage of N1 sleep increased the odds of having SB (odds ratios = 1.425, 0.951, and 1.032, respectively; all P < .05). Network analysis showed that there were no direct associations between RMMA and apnea-hypopnea index, nor between RMMA and arousal, although 85.7% of RMMA was time-related to arousals.

CONCLUSIONS

Nearly half of adults with OSA have comorbid SB. Male sex, lower body mass index, and a higher percentage of light sleep increase the risk of having SB. Although RMMAs do not directly correlate with respiratory events and arousals, most RMMAs are time-related to arousals in adults with OSA.

CLINICAL TRIAL REGISTRATION

Registry: Netherlands Trial Register; Name: A Large Sample Polysomnographic Study on Sleep Bruxism; URL: https://trialsearch.who.int/Trial2.aspx?TrialID=NL8516; Identifier: NL8516.

CITATION

Li D, Kuang B, Lobbezoo F, de Vries N, Hilgevoord A, Aarab G. Sleep bruxism is highly prevalent in adults with obstructive sleep apnea: a large-scale polysomnographic study. J Clin Sleep Med. 2023;19(3):443-451.

Effectiveness of Botulinum Toxin Injection on Bruxism: A Systematic Review and Meta-analysis of Randomized Controlled Trials

OBJECTIVE

The present study compiled evidence on the efficacy of botulinum toxin A (BTX) for management of bruxism.

METHODS

A literature review that included randomized control, cohort, as well as observational studies published between January 2000 and November 2022 was conducted. All studies related to BTX injections administered into the masseters of patients with bruxism were included. Primary outcomes were measured by performing a meta-analysis of changes in maximal biting forces and pain severity and meta-regression of the effects of the BTX dose.

RESULTS

Ten studies were included for quantitative analysis. The analysis of the maximal biting force after BTX injections demonstrated a significant reduction at 1 month or less compared with both oral splints (P < 0.000001) and saline injections (P = 0.01). BTX continued to outperform oral splinting (P = 0.001) and saline placebos (P = 0.03) at 3 months. Between 3 and 6 months, a significantly higher maximal biting strength was observed in the BTX group than the oral splinting group (P < 0.00001). No significant differences in the maximal biting force were observed between the BTX and saline placebo groups (P = 0.50). A similar trend was observed in the analysis of pain reduction after botulinum treatment. Additionally, for every unit increase in the BTX dose, pain severity decreased by 0.0831 points (P = 0.0011).

CONCLUSION

BTX is effective in reducing biting strength and pain severity. BTX effects are evident at less than 4 weeks, peak between 5 and 8 weeks, and last for up to 24 weeks. Higher BTX doses result in greater improvement in pain. Although BTX benefits manifest earlier, they gradually diminish, and oral splinting exerts a more enduring effect, especially after 9-12 weeks. BTX injections into masseters are recommended as management options for bruxers, especially for those having difficulties complying with wearing oral splints or those seeking earlier symptom relief. However, future studies should determine BTX effects beyond 24 weeks and after repetitive injections and how bruxers of different ages or genders respond to treatment.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Relationships between respiratory and oromotor events differ between motor phenotypes in patients with obstructive sleep apnea

Purpose

The present study investigated the relationship between sleep bruxism (SB) and obstructive sleep apnea (OSA) in relation to the sleep architecture.

Methods

We conducted a cross-sectional study. Polysomnographic recordings were performed on 36 patients. Sleep, respiratory, and oromotor variables, such as rhythmic masticatory muscle activity (RMMA) and non-specific masticatory muscle activity (NSMA), were compared between OSA patients with or without SB. A correlation analysis of the frequency of respiratory and oromotor events in NREM and REM sleep was performed. The frequency of oromotor events following respiratory events was also assessed.

Results

The proportion of REM sleep was higher in OSA patients with SB than in those without SB (p = 0.02). The apnea-hypopnea index (AHI) did not significantly differ between the two groups; however, AHI was approximately 8-fold lower during REM sleep in OSA patients with SB (p = 0.01) and the arousal threshold was also lower (p = 0.04). Although the RMMA index was higher in OSA patients with than in those without SB (p < 0.01), the NSMA index did not significantly differ. The percentage of RMMA following respiratory events was significantly higher in OSA patients with than in those without SB, whereas that of NSMA did not significantly differ. The frequency of oromotor events throughout the whole night positively correlated with AHI. However, regardless of the sleep state, AHI did not correlate with the RMMA index, but positively correlated with the NSMA index.

Conclusion

In consideration of the limitations of the present study, the results obtained indicate that OSA patients with SB have a unique phenotype of OSA and also emphasize the distinct relationship of respiratory events with RMMA and NSMA.

Managements of sleep bruxism in adult: A systematic review

This systematic review aimed to update the management of sleep bruxism (SB) in adults, as diagnosed using polysomnography (PSG) and/or electromyography (EMG). Management methods covered were oral appliance therapy (OAT) with stabilization splints, cognitive-behavioral therapy (CBT), biofeedback therapy (BFT), and pharmacological therapy. A comprehensive search was conducted on MEDLINE, Cochrane Library, and Web of Science up to October 1st, 2021. Reference list searches and hand searches were also performed by an external organization. Two reviewers for each therapy independently performed article selection, data extraction, and risk of bias assessment. The reviewers resolved any disagreements concerning the assortment of the articles by discussion. Finally, 11, 3, 14, and 22 articles were selected for each therapy. The results suggested that OAT tended to reduce the number of SB events, although there was no significant difference compared to other types of splints, that the potential benefits of CBT were not well supported, and that BFT, rabeprazole, clonazepam, clonidine, and botulinum toxin type A injection showed significant reductions in specific SB parameters, although several side effects were reported. It can be concluded that more methodologically rigorous randomized large-sample long-term follow-up clinical trials are needed to clarify the efficacy and safety of management for SB.

Sleep Bruxism Contributes to Motor Activity Increase during Sleep in Apneic and Nonapneic Patients-A Polysomnographic Study

Background: Jaw motor activity (MA) in sleep bruxism (SB) has been demonstrated to accompany lower limb movements. However, it remains unknown whether SB activity coexists with other types of movements and what the possible underlying mechanisms of such temporal coexistence are. In obstructive sleep apnea (OSA), increased movement activity is also reported, including SB activity; however, no studies have compared MA in apneic and nonapneic SB patients. Aim: This cross-sectional study focused on the phenomenon of “big body movements” in patients with either SB or OSA (or both) and intended to identify the primary factors contributing to their appearance, using polysomnography (PSG) recording. Methods: A whole-night videoPSG was carried out in 287 participants, and 124 apneic and 146 nonapneic participants were selected for the study. In both groups, participants were further divided into no SB, moderate SB, and severe SB (SSB) subgroups based on their bruxism episode index (BEI). MA was recorded using a built-in sensor of the central PSG unit located on the participant’s chest during the examination. Results: The presence of SB was related to the higher intensity of MA in both apneic and nonapneic participants, though in general the MA level was higher in apneic participants, with the highest level observed in SSB apneic participants. Conclusions: SB might contribute to MA. The prevalence of SB might be higher in nonapneic patients due to phasic and mixed SB activity, whereas the SB phenotype seems to be less relevant in apneic patients. SB activity is likely to increase MA in non-REM 1 sleep.

Relationship Analogy between Sleep Bruxism and Temporomandibular Disorders in Children: A Narrative Review

Sleep bruxism (SB) is a condition characterized by repetitive clenching or grinding teeth and/or by bracing or thrusting of the mandible during sleep. Although SB is not considered a disorder in children, SB can be a potential physical and psychological hazard or consequence, and this study examines whether SB is a risk factor for TMD as it is in adults. A narrative review on the topic of inferring the relationship between sleep bruxism and TMD in children was performed based on a search in the PubMed and Google Scholar databases for articles published between 1999 and 2022. A total of 76 articles were included in this review. SB is very common in children, may be related to psychological distress or sleep breathing disorder, with a prevalence of up to 49%, and mainly occurs in the non-rapid eye movement stage in the sleep structure. SB may be one cause of TMD. The prevalence of TMD in children is 16–33%. Compared to the female-dominant TMD prevalence in adults, the sex-differences in TMD prevalence in children are less pronounced. However, TMD-related pain is more prevalent in girls than in boys. Given the complex etiology of each of SB and TMD in children, it can be inferred that the explanation of the relationship between the two conditions is very challenging. Ultimately, their relationship should be understood in the individual biopsychosocial model in the process of special physical growth and mental development of children. Moreover, appropriate clinical guidelines for a definitive diagnosis of SB and TMD in children and more research with a high scientific evidence level, which is comprehensive, considering physical, psychological, genetic, and social cultural factors, are required.

Polysomnographic Evaluation of Sleep Bruxism Intensity and Sleep Architecture in Nonapneic Hypertensives: A Prospective, Observational Study

Sleep bruxism (SB) is a repetitive jaw muscle activity characterized by clenching or grinding of the teeth, which is classified under sleep-related movement disorders in the International Classification of Sleep Disorders—Third Edition. Because the potential common pathomechanism of SB and arterial hypertension is the activation of the sympathetic system as well as an increase in inflammatory factors, we aimed to examine the intensity of SB and the sleep architecture among patients with arterial hypertension. The study included a total of 91 Caucasian adult patients, among whom 31 had arterial hypertension diagnosed according to the current European Society of Cardiology/European Society of Hypertension (ESC/EHS) hypertension guidelines. The control group consisted of 61 normotensive patients. Patients with obstructive sleep apnea were excluded. A single full-night polysomnographic examination was conducted in the Sleep Laboratory, and then the results were analyzed based on the guidelines of the American Academy of Sleep Medicine. Bruxism episode index (BEI) was higher in the hypertensive group compared to normotensives. The groups also showed statistically significant differences in polysomnographic sleep indexes. Similar to BEI, arousal index, apnea–hypopnea index, and snoring were higher in hypertensives compared to normotensives. On the other hand, the mean and minimal oxygen saturation were lower in hypertensives compared to normotensives. A statistically significant positive correlation was observed between oxygen desaturation index and BEI in the hypertensive group, whereas this correlation was not statistically significant in the case of normotensives. In summary, nonapneic hypertensives had higher SB intensity, altered sleep architecture, decreased mean oxygen saturation, and increased snoring compared to normotensives. The results suggest that dental screening is necessary for patients with arterial hypertension, especially those presenting with the symptoms of SB.

Oral appliances reduce masticatory muscle activity-sleep bruxism metrics independently of changes in heart rate variability

OBJECTIVES

Sleep bruxism (SB) is associated with physiological activities including sympathetic autonomic system dominance and sleep micro-arousal. While oral appliances (OA) are used to prevent SB harmful effects, the influence of OAs physiological mechanisms during sleep is unknown. The aim of this study is to assess whether heart rate variability (HRV) changes, as a marker of autonomic nervous system activity, would be associated with the OA mechanism of action on SB using occlusal splint (OS) and mandibular advancement splint (MAS).

MATERIALS AND METHODS

A retrospective analysis, from data previously collected in 21 participants with SB (25.6 ± 4.5 years) with polysomnographic recordings, was done. HRV data were compared between a reference night (no-device) and ones during which OS or MAS was used in a crossover study design. Rhythmic masticatory muscle activity (RMMA) index was compared between nights. HRV was evaluated using autoregressive model analysis for three sections: baseline (distance from RMMA), immediately before, and after RMMA period.

RESULTS

A significant reduction in RMMA index, when wearing OA during sleep, was observed (P < 0.01), but was not associated with HRV parameters change. HRV significantly changed after RMMA onset for nights with OA during non-REM sleep in comparison with baseline (P < 0.02).

CONCLUSIONS

The usage of OAs for SB participants reduced RMMA, but most likely independently of changes in HRV linked to the mechanism associated with SB genesis.

CLINICAL RELEVANCE

Wearing OA seems to reduce grinding noise and protect from dental injuries but does not seem to influence SB genesis.

The effects of mandibular advancement appliance therapy on the sequence of jaw-closing muscle activity and respiratory events in individuals with obstructive sleep apnea

Purpose

To determine the effects of a mandibular advancement appliance (MAA) on sequences of jaw-closing muscle activity (JCMA) and apneic or hypopneic event (AHE) in individuals with obstructive sleep apnea (OSA).

Methods

Individuals with OSA were included in a secondary analysis of a randomized controlled crossover trial, in which two ambulatory polysomnographic recordings were performed: one with MAA in situ and the other without MAA. A time span of 16 s between JCMA and AHE was applied to classify JCMAs into four sequences: (1) JCMA occurs before AHE (B-type); (2) both events occur simultaneously (S-type); (3) JCMA occurs after AHE (A-type); and (4) JCMA is time-unrelated to AHE (U-type). The effects of MAA on the distribution of these sequences were analyzed by Wilcoxon signed-rank test.

Results

Among 16 individuals (10 men, mean age 51.3 ± 8.5 years) baseline apnea–hypopnea index and JCMA index were 23.8 ± 16.0 events/h and 10.8 ± 10.3 events/h, respectively. In both conditions, i.e., without and with MAA, most JCMAs were U-type (48% and 65%, respectively), followed by A-type (41% and 22%), B-type (25% and 21%), and S-type (2% and 1%). With MAA in situ, only the A-type JCMA index decreased significantly (P = 0.005), while B-type, S-type, and U-type JCMA indices did not change significantly (all P > 0.05).

Conclusion

MAA therapy only significantly reduces the jaw-closing muscle activities that occur after apneic or hypopneic events in individuals with OSA.

Trial registration

www.clinicaltrials.gov (NCT02011425); December 13, 2013.

Polysomnographic characteristics of sleep-related bruxism: What are the determinant factors for temporomandibular disorders?

This study aimed to evaluate the clinical and polysomnographic characteristics of sleep bruxism (SB) and delineate the determinant factors for temporomandibular disorders (TMD). Forty-six patients were allocated into the SB group (n = 26) and control group (n = 20). The signs and symptoms of TMD were recorded using the Research Diagnostic Criteria for TMD. Patients underwent a full-night polysomnographic recording and masseter and temporal muscle electromyographic recordings. Clinical and polysomnographic data in patients with SB were analyzed in relation to TMD. The presence of TMJ sounds was significantly correlated with the number of bruxism bursts. Intra-articular pain in the TMJ was neither correlated with clinical nor polysomnographic parameters in patients with SB. Lower sleep efficiency in patients with SB was caused by a higher number of bruxism episodes. Morning headaches were associated with the severity of SB during rapid eye movement sleep.

Is there an association of genetic polymorphisms of the catechol-O-methyltransferase gene (rs165656 and rs174675) and the 5-hydroxytryptamine receptor 2A gene (rs4941573 and rs6313) with sleep bruxism in individuals with obstructive sleep apnea?

OBJECTIVE

To evaluate the association of single-nucleotide polymorphisms within the catechol-O-methyltransferase and 5-hydroxytryptamine receptor 2A genes with sleep bruxism in individuals diagnosed with obstructive sleep apnea.

DESIGN

Sixty-nine individuals with suspected sleep-related problems were evaluated by polysomnography, following the recommendations of the American Academy of Sleep Medicine. Deoxyribonucleic acid (DNA) samples were collected only from 48 of the study participants because of missing polysomnographic data. DNA samples were collected and two single-nucleotide polymorphisms in the 5-hydroxytryptamine receptor 2A encoding HTR2A gene (rs4941573 and rs6313) and two in the catechol-O-methyltransferase gene (rs165656 and rs174675) were selected to be genotyped using real-time polymerase chain reaction. The association between sleep bruxism and genetic polymorphisms was investigated by recessive and dominant models. Association analyses were performed using a 95% confidence interval and the level of statistical significance was p < 0.05.

RESULTS

From the 69 study participants, 48 were included in the polymorphism analysis and sleep bruxism was present in 35.4%. No significant differences were observed in the dominant and recessive models (p > 0.05). Haplotype and diplotype analyses revealed the predicted four haplotypes and two diplotypes were not associated with sleep bruxism.

CONCLUSION

Polymorphisms rs174675 and rs165656 in the catechol-O-methyltransferase gene and rs4941573 and rs6313 in the 5-hydroxytryptamine receptor 2A gene were not significantly associated with sleep bruxism in individuals with obstructive sleep apnea.

Associations between sleep bruxism and other sleep-related disorders in adults: a systematic review

OBJECTIVE

Systematic reviews on sleep bruxism (SB) as a comorbid condition of other sleep-related disorders are lacking. Such reviews would contribute to the insight of sleep clinicians into the occurrence of SB in patients with other sleep-related disorders, and into the underlying mechanisms of such comorbid associations. This systematic review aimed: 1. to determine the prevalence of SB in adults with other sleep-related disorders; and 2. to determine the associations between SB and other sleep-related disorders, and to explain the underlying mechanisms of these associations.

METHODS

A systematic search on SB and sleep-related disorders was performed in PubMed, Embase, Cochrane Library, and Web of Science to identify eligible studies published until May 15, 2020. Quality assessment was performed using the Risk of Bias Assessment tool for Non-randomized Studies.

RESULTS

Of the 1539 unique retrieved studies, 37 articles were included in this systematic review. The prevalence of SB in adult patients with obstructive sleep apnea, restless leg syndrome, periodic limb movement during sleep, sleep-related gastroesophageal reflux disease, REM behavior disorder (RBD), and sleep-related epilepsy was higher than that in the general population. The specific mechanisms behind these positive associations could not be identified.

CONCLUSIONS

SB is more prevalent in patients with the previously mentioned disorders than in the general population. Sleep arousal may be a common factor with which all the identified disorders are associated, except RBD and Parkinson's disease. The associations between SB and these identified sleep-related disorders call for more SB screening in patients with the abovementioned sleep-related disorders.

Temporal relationship between sleep-time masseter muscle activity and apnea-hypopnea events: A pilot study

BACKGROUND

Obstructive sleep apnea (OSA) is the most common sleep disorder due mainly to peripheral causes, characterized by repeated episodes of obstruction of the upper airways, associated with arousals and snoring. Sleep bruxism (SB) is a masticatory muscle activity during sleep that is characterized as rhythmic (phasic) or nonrhythmic (tonic) and is not a movement disorder or a sleep disorder in otherwise healthy individuals. Given the potentially severe consequences and complications of apnea, the concurrent high prevalence of SB in daily dental practice, getting deeper into the correlation between these phenomena is worthy of interest..

STUDY OBJECTIVES

The aim of this study was to investigate the correlation between SB-related masseter muscle activity (MMA) and apnea-hypopnea events as well as to assess their temporal sequence.

METHODS

Thirty (N = 30) patients with sleep respiratory disorders and clinical suspicion of sleep bruxism (SB) were recruited. Ambulatory polygraphic recording was performed to detect apnea-hypopnea events (AHEs) and sleep bruxism episodes (SBEs). Pearson test was used to assess the correlation between apnea-hypopnea index (AHI) and SB index (SBI). A 5-s time window with respect to the respiratory events was considered to describe the temporal distribution of SBEs. Furthermore, SBI was compared between groups of patients with different AHI severity (i.e., mild, moderate and severe) using ANOVA.

RESULTS

On average, AHI was 27.1 ± 21.8 and SBI 9.1 ± 7.5. No correlation was shown between AHI and SBI. Most of SBEs (66.8%) occurred without a temporal relationship with respiratory events. Considering OSA, 65.7% of SBEs occurred within 5 s after AHEs, while in the case of central apnea (CA) 83.8% of SBEs occurred before the respiratory event. The participants with severe apnea (N = 9) show a tendency to have higher bruxism indexes when compared to patients with mild (N = 11) and moderate apnea (N = 10).

CONCLUSIONS

Findings suggest that: 1. At the study population level, there is no correlation between AHI and SBI, as well as any temporal relationship between SBEs and respiratory events. 2. Specific patterns of temporal relationship might be identified with future studies focusing on the different types of apnea-hypopnea events and bruxism activities.

A lack of specific motor patterns between rhythmic/non-rhythmic masticatory muscle activity and bodily movements in sleep bruxism

Purpose The aims of the present study were to investigate the temporal relationships between jaw and bodily movements and clarify motor processes in the genesis of rhythmic masticatory muscle activity (RMMA) in sleep bruxism (SB).Methods Video-polysomnography recordings were obtained from ten subjects with SB (mean age: 23.4 ± 1.6 years) and ten matched normal controls (CTL) (mean age: 24.4 ± 3.2 years). RMMA and nonspecific masseter activity (NSMA) were scored in association with bodily movements in the leg, arm, head, and trunk using electromyography and video recordings. The relationship between oromotor episodes and bodily movements was assessed in terms of sleep stage distributions and temporal relationships. Cardiac changes preceding oromotor episodes in stage N2 were assessed.Results Approximately 80% of RMMA and NSMA were associated with movements in one or more body sites. RMMA and NSMA were more frequently associated with movements of the leg (70-75%) and arm (40-55%) than movements of the head (17-22%) and trunk (5-25%). The relationship between oromotor episodes and bodily movements did not significantly differ among sleep stages. Oromotor episodes and bodily movements did not show a consistent temporal pattern in the SB and CTL groups. Regardless of the temporal relationship between oromotor episodes and bodily movements, the mean heart rate significantly increased by 5 beats before the onset of oromotor episodes.Conclusions No specific temporal motor patterns were found between RMMA and bodily movements. RMMA and NSMA represent a repertoire of arousal-related autonomic motor responses during sleep.

Sleep stage-dependent changes in tonic masseter and cortical activities in young subjects with primary sleep bruxism

STUDY OBJECTIVES

The present study investigated the hypothesis that subjects with primary sleep bruxism (SB) exhibit masseter and cortical hyperactivities during quiet sleep periods that are associated with a high frequency of rhythmic masticatory muscle activity (RMMA).

METHODS

Fifteen SB and ten control participants underwent polysomnographic recordings. The frequencies of oromotor events and arousals and the percentage of arousals with oromotor events were assessed. Masseter muscle tone during sleep was quantified using a cluster analysis. Electroencephalography power and heart rate variability were quantified and then compared between the two groups and among sleep stages.

RESULTS

The frequency of RMMA and percentage of arousals with RMMA were significantly higher in SB subjects than in controls in all stages, while these variables for non-rhythmic oromotor events did not significantly differ between the groups. In SB subjects, the frequency of RMMA was the highest in stage N1 and the lowest in stages N3 and R, while the percentage of arousals with RMMA was higher in stage N3 than stages N1 and R. The cluster analysis classified masseter activity during sleep into two clusters for masseter tone and contractions. Masseter muscle tone showed typical stage-dependent changes in both groups, but did not significantly differ between the groups. Furthermore, no significant differences were observed in electroencephalography power or heart rate variability between the groups.

CONCLUSION

Young SB subjects exhibited sleep stage-dependent increases in the responsiveness of RMMA to transient arousals, but did not show masseter or cortical hyperactivity during sleep.

The neurophysiological basis of bruxism

Mesencephalic trigeminal nucleus (MTN) neurons innervate the stretch receptors of the jaw elevator muscles and periodontal ligament mechanoreceptors, Bruxism activates the MTN. We analyzed how MTN cells are structured, their anatomy and physiology, and the effects of their activation.

To induce and maintain sleep, gamma-aminobutyric acid (GABA), an inhibitor neurotransmitter, is released from the ventro-lateral preoptic area of the hypothalamus and acts on the ascending reticular activating system (ARAS) nuclei. The GABA neurotrasmitter induces the entry of chlorine into cells, hyperpolarizing and inhibiting these. MTN cells, on the contrary, are depolarized by GABA, as their receptors are activated upon GABA binding. They “let out” chlorine and activate ARAS cells. MTN cells release glutamate, an excitatory neurotransmitter onto their target cells, in this case onto ARAS cells. During wakefulness, ARAS activation causes cerebral cortex activation; instead, during sleep (sleep bruxism), ARAS activation avoids an excessive reduction in ARAS neurotransmitters, including noradrenaline, dopamine, serotonin, acetylcholine and glutamate. These neurotransmitters, in addition to activating the cerebral cortex, modulate vital functions such as cardiac and respiratory functions. Polysomnography shows that sleep bruxism is always accompanied by cardiac and respiratory activation and, most importantly, by brain function activation. Bruxism is not a parafunction, and it functions to activate ARAS nuclei.

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.

Cardiovascular Implications of Sleep Bruxism-A Systematic Review with Narrative Summary and Future Perspectives

Sleep bruxism is a common sleep-related behavior characterized as repetitive masticatory muscle activity. Genetic vulnerability to stress and anxiety is considered a basal component in the pathogenesis of bruxism events. Dysfunction of the autonomic nervous system related with an arousal during sleep is considered an underlying cause of the cardiovascular implications of sleep bruxism. Increased cardiovascular risk was previously linked with sleep conditions: for example, obstructive sleep apnea and insomnia, and sleep bruxism. The aim of present systematic review was to evaluate the current arguments on the relationship between sleep bruxism and cardiovascular diseases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We have reviewed the Embase, PubMed (Medline) and Scopus databases to identify applicable articles (1994-2021). A total of 127 records in English language were identified, then after screening and exclusion of nonrelevant records, 19 full-text articles were evaluated. Finally, we included 12 studies for synthesis. Due to the heterogeneity of the compared studies, only a qualitative comparison and narrative summary were performed. In the majority of studies, increased sympathetic activity was successfully established to escalate heart rate variability, the inflammatory process, oxidative stress, endothelial remodeling and hormonal disturbances, leading to hypertension and other cardiovascular complications.

Sleep Bruxism: An Integrated Clinical View

The vision of adult sleep bruxism (SB) has changed over time. Thus, among the most important concomitant factors of SB noted are the pathophysiological aspect, namely sleep arousal, obstructive sleep apnea, gastroesophageal pH/gastroesophageal reflux disease, and the use or abuse of certain substances. The aim of this article was to review the main clinically relevant pathophysiological SB-associated factors and a proposal for a diagnostic process.

Functional (Psychogenic) Movement Disorders Presenting During Sleep

Background:

Functional (psychogenic) movement disorders are involuntary movements that seems to originate from activation of voluntary motor pathways in the brain. The movements typically present during the waking hours with variable frequency.

Case presentation:

We present the case of a 24-year-old woman with FMDs during the waking state, but also during stages 1 and 2 of non-REM sleep and REM sleep, recorded with polysomnography. Such movements caused arousal leading to excessive daytime sleepiness and fatigue.

Conclusions:

FMDs may disrupt sleep causing day time somnolence, adding morbidity to the disorder.

Determinants of probable sleep bruxism in a pediatric mixed dentition population: a multivariate analysis of mouth vs. nasal breathing, tongue mobility, and tonsil size

OBJECTIVES

This study aims to identify structural and functional craniofacial characteristics that correlate with higher incidence of 'probable' sleep bruxism in children.

METHODS

From March 2018 until March 2019, a cross-sectional clinical study was performed with ninety-six healthy children ages 6-12 years who presented for routine dental examination at the UCLA pediatric dental clinic. Variables of interest included: (1) assessment of probable bruxism based on parental awareness on the frequency of tooth grinding during sleep and clinical signs of bruxism based on tooth wear; (2) parental reports of mouth breathing while awake and asleep, snoring during sleep, difficulty breathing and/or gasping for air during sleep; (3) parental reports of psychosocial distress; (4) assessment of tonsil hypertrophy, tongue mobility, and nasal obstruction. Three pediatric dental residents were calibrated to perform the clinical data collection. All dental residents were graduated dentists with licensure and at least one year of experience examining children. The methodology to take the specific measurements administered in the manuscript were calibrated between the data-collectors under the supervision of a board-certified pediatric dentist and orthodontist (AY).

RESULTS

The mean age of individuals was 8.9 (SD = 1.9) years with a gender distribution of 46 males and 50 females. There were 23 out of the 96 (24%) individuals who met the diagnostic criteria for probable sleep bruxism (PSB). Sleep Disturbance Scale for Children (SDSC) scores were significantly elevated among children positive for PSB, indicating that they are at higher risk for sleep disturbances (PSB-positive: 45.1 ± 13.0, PSB-negative: 34.8 ± 5.5; p < 0.0001). Impaired nasal breathing, parental reports of mouth breathing when awake or asleep, restricted tongue mobility, and tonsillar hypertrophy were found to be significant risk factors for PSB. Exploratory analysis further suggests a synergistic effect between tonsil hypertrophy, restricted tongue mobility, and nasal obstruction. The incidence of probable sleep bruxism among individuals without any of the exam findings of tonsillar hypertrophy, restricted tongue mobility, and nasal obstruction was 5/58 (8.6%), whereas the incidence of PSB among individuals with all three exam findings was 10/11 (90.9%), p < 0.0001. Among the 23 individuals with PSB, however, there were n = 5 (21.7%) who did not have any of the three exam findings, suggesting an additional role of psychosocial distress, postural maladaptation, malocclusion, or other factors in the etiology of sleep bruxism.

CONCLUSION

This study shows that tonsil hypertrophy, restricted tongue mobility, and nasal obstruction may have a synergistic association on the presentation of PSB. Dentists should evaluate for tonsillar hypertrophy, restricted tongue mobility, and nasal obstruction in the evaluation of PSB, as these exam findings are highly prevalent in the majority of cases.

The effects of mandibular advancement appliance therapy on jaw-closing muscle activity during sleep in patients with obstructive sleep apnea: a 3-6 months follow-up

STUDY OBJECTIVES

The main aim of this study was to investigate the effects of mandibular advancement appliance (MAA) therapy on jaw-closing muscle activity (JCMA) time-related to respiratory arousals, and on JCMA time-related to nonrespiratory arousals in patients with obstructive sleep apnea.

METHODS

Eighteen patients with OSA (mean ± standard deviation = 49.4 ± 9.8 years) with a mean ± standard deviation apnea-hypopnea index of 22.0 ± 16.0 events/h of sleep participated in a randomized controlled crossover trial in which two ambulatory polysomnographic recordings, 1 with an MAA in situ and another without the MAA in situ, were performed. JCMA was quantified as the sum of rhythmic masticatory muscle activities and other orofacial activities.

RESULTS

Significant reductions in the apnea-hypopnea index (Z = -2.984; P = .003), in the respiratory arousal index (Z = -2.896; P = .004), and in the JCMA time-related to respiratory arousal index (Z = -3.434; P = .001) were found with MAA in situ. On the nonrespiratory arousal index, and on the JCMA time-related to nonrespiratory arousal index, MAA had no significant effect (T = 2.23; P = .82; and Z = -0.66; P = .51, respectively).

CONCLUSIONS

This study shows that effective mandibular advancement appliance therapy significantly reduces jaw-closing muscle activities time-related to respiratory arousals in OSA patients. Future studies are needed to confirm these findings in obstructive sleep apnea patients with comorbid sleep bruxism.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Name: The Effects of Oral Appliance Therapy on Masseter Muscle Activity in Obstructive Sleep Apnea; Identifier: NCT02011425.

Genetic basis of sleep bruxism and sleep apnea-response to a medical puzzle

Sleep bruxism (SB) and obstructive sleep apnea (OSA) are co-occurring sleep conditions. The study aimed to evaluate the association of selected single-nucleotide polymorphisms (SNPs) occurring within the genes of the serotonin and dopamine pathways in SB and OSA and investigate the relationship between them. The study group included 100 Caucasian patients. SB and OSA were diagnosed in 74 and 28 patients, respectively. In addition, 125 unrelated Caucasian healthy blood donors served as randomly selected controls to enable comparison of polymorphisms. The following SNPs were analyzed: rs2770304 and rs6313 within the serotonin receptor encoding gene (HTR2A), rs4680 polymorphism of the catechol-O-methyltransferase (COMT) gene, and rs686 within the dopamine receptor (DRD1) encoding gene. The prevalence of the DRD1 rs686 G variant (GG homozygosity) was found to be high in the study group compared to the control group. Bruxism episode index (BEI) was found to be significantly increased in the HTR2A rs6313 TT homozygotes compared to the heterozygous patients. Moreover, within a group of the HTR2A rs2770304 TT homozygous cases, a statistically significant correlation was observed between BEI and apnea-hypopnea index. These results indicate that DRD1 rs686 may potentially affect predisposition to SB, that HTR2A rs6313 SNP may be involved in SB pathogenesis, and that HTR2A rs2770304 polymorphism might contribute to the association between SB and OSA. This suggests a possible genetic contribution to the etiology of primary SB.

Effect of laterotrusive occlusal scheme on chewing duration, external intercostal muscular activity, heart rate, and oxygen saturation

Objective: To evaluate the effect of the laterotrusive occlusal scheme on chewing duration, external intercostal (EIC) electromyographic (EMG) activity, heart rate (HR), and oxygen saturation (OS) during different tasks in the upright seated position.Methods: Fifty young participants, 25 with canine guidance and 25 with group function, were included. Chewing duration, bilateral EIC EMG activity, HR, and OS were recorded during the following tasks: 1) chewing until swallowing threshold; 2) laterotrusive teeth grinding.Results: Chewing duration, bilateral EIC EMG activity, HR, and OS showed no significant differences between the two laterotrusive occlusal schemes during the tasks studied.Conclusion: These results suggest that chewing duration, EIC muscle activity, HR, and OS were not significantly influenced by the laterotrusive occlusal scheme. Therefore, when a modification of the laterotrusive occlusal scheme is needed during oral rehabilitation or orthodontic treatment, canine guidance or group function should not significantly change EMG activity of EIC muscles.

Botulinum Toxin Therapy for Managing Sleep Bruxism: A Randomized and Placebo-Controlled Trial

The purpose of this study is to evaluate the effects of botulinum toxin type A (BoNT-A) for managing sleep bruxism (SB) in a randomized, placebo-controlled trial. Thirty SB subjects were randomly assigned into two groups evenly. The placebo group received saline injections into each masseter muscle, and the treatment group received BoNT-A injections into each masseter muscle. Audio-video-polysomnographic recordings in the sleep laboratory were made before, at four weeks after, and at 12 weeks after injection. Sleep and SB parameters were scored according to the diagnostic and coding manual of American Academy of Sleep Medicine. The change of sleep and SB parameters were investigated using repeated measures analysis of variance (RM-ANOVA). Twenty-three subjects completed the study (placebo group 10, treatment group 13). None of the SB episode variables showed a significant time and group interaction (p > 0.05) except for electromyography (EMG) variables. The peak amplitude of EMG bursts during SB showed a significant time and group interaction (p = 0.001). The injection decreased the peak amplitude of EMG bursts during SB only in the treatment group for 12 weeks (p < 0.0001). A single BoNT-A injection cannot reduce the genesis of SB. However, it can be an effective management option for SB by reducing the intensity of the masseter muscle.

Associations between sleep bruxism, sleep quality, and exposure to secondhand smoke in Japanese young adults: a cross-sectional study

OBJECTIVE

Sleep bruxism, a major sleep disorder that causes serious harm to oral health, is considered a multifactorial disease. Sleep bruxism can be induced by smoking, which also adversely affects sleep quality. The objective of present study was to clarify the associations between sleep bruxism, sleep quality, and exposure to secondhand smoke (SHS).

METHODS

To assess the prevalence of sleep bruxism, sleep quality, and SHS exposure, we conducted oral examinations and self-report questionnaires on university students in Japan. Sleep bruxism and quality were screened using the Japanese version of the Pittsburgh Sleep Quality Index (PSQI) and the third edition of the International Classification of Sleep Disorders (ICSD-3). The inclusion criteria were adults aged between 18 and 19 years, non-smokers and non-alcohol drinkers. The exclusion criteria was failing to complete the questionnaire in full.

RESULTS

We analyzed a total of 1781 Japanese young adults. Young adult females who had been exposed to SHS had worse sleep quality (p = 0.019) than those who had not. Young adult female with worse sleep quality showed a higher prevalence of sleep bruxism (p = 0.034) than those with better sleep quality. Using structural equation modeling, direct associations were identified between SHS exposure and poor sleep quality (standardized coefficients, 0.153; p = 0.008) and between sleep bruxism and poor sleep quality (standardized coefficients, 0.187; p = 0.022) in young adult females. However, no association was found among young adult males.

CONCLUSION

SHS exposure is indirectly associated with sleep bruxism through poor sleep quality in Japanese young adult females.