Is sleep bruxism in obstructive sleep apnea only an oral health related problem?

BACKGROUND: The etiology of sleep bruxism in obstructive sleep apnea (OSA) patients is not yet fully clarified. This prospective clinical study aimed to investigate the connection between probable sleep bruxism, electromyographic muscle tone, and respiratory sleep patterns recorded during polysomnography. METHODS: 106 patients with OSA (74 males, 31 females, mean age: 56.1 ± 11.4 years) were divided into two groups (sleep bruxism: SB; no sleep bruxism: NSB). Probable SB were based on the AASM criteria: self-report of clenching/grinding, orofacial symptoms upon awakening, abnormal tooth wear and hypertrophy of the masseter muscle. Both groups underwent clinical examination for painful muscle symptoms aligned with Temporomandibular Disorders Diagnostic Criteria (DC/TMD), such as myalgia, myofascial pain, and headache attributed to temporomandibular disorder. Additionally, non-complaint positive muscle palpation and orofacial-related limitations (Jaw Functional Limited Scale-20: JFLS-20) were assessed. A one-night polysomnography with electromyographic masseter muscle tone (EMG) measurement was performed. Descriptive data, inter-group comparisons and multivariate logistic regression were calculated. RESULTS: OSA patients had a 37.1% prevalence of SB. EMG muscle tone (N1-N3, REM; P = 0.001) and the number of hypopneas (P = 0.042) were significantly higher in the sleep bruxism group. While measures like apnea-hypopnea-index (AHI), respiratory-disturbance-index (RDI), apnea index (AI), hypopnea-index (HI), number of arousals, and heart rate (1/min) were elevated in sleep bruxers, the differences were not statistically significant. There was no difference in sleep efficiency (SE; P = 0.403). Non-complaint masseter muscle palpation (61.5%; P = 0.015) and myalgia (41%; P = 0.010) were significant higher in SB patients. Multivariate logistic regression showed a significant contribution of EMG muscle tone and JFLS-20 to bruxism risk. CONCLUSION: Increased EMG muscle tone and orofacial limitations can predict sleep bruxism in OSA patients. Besides, SB patients suffer more from sleep disorder breathing. Thus, sleep bruxism seems to be not only an oral health related problem in obstructive apnea. Consequently, interdisciplinary interventions are crucial for effectively treating these patients. TRIAL REGISTRATION: The study was approved by the Ethics Committee of Philipps-University Marburg (reg. no. 13/22-2022) and registered at the "German Clinical Trial Register, DRKS" (DRKS0002959).

The effect of sleep position on sleep bruxism in adults with obstructive sleep apnea.

BACKGROUND: Most of the respiratory events in adults with obstructive sleep apnea (OSA) occurs in supine position. It has been reported that the contraction of masseter muscles is dependent on the occurrence of arousals rather than on the occurrence of respiratory events. OBJECTIVES: This study had two aims: (1) to compare the rhythmic masticatory muscle activity (RMMA) index in supine position (RMMA_sup) and in non-supine positions (RMMA_nsup) in adults with OSA; and (2) to determine the associations between RMMA index in both supine position and non-supine positions on the one hand, and several demographic and polysomnographic variables on the other hand. METHODS: One hundred OSA participants (36 females and 64 males; mean age = 50.3 years (SD = 10.5)) were selected randomly from among patients with a full-night polysomnographic recording. RMMA_sup index and RMMA_nsup index were compared using Mann-Whitney U-test. Multivariate linear regression analyses were used to predict RMMA index both in supine and non-supine positions based on several demographic and polysomnographic variables. RESULTS: In patients with OSA, the RMMA_sup index was significantly higher than the RMMA_nsup index (p < .001). RMMA_sup index was significantly associated with the arousal index (p = .002) and arousal index in supine position (p < .001). RMMA_nsup index was only significantly associated with the arousal index in non-supine positions (p = .004). CONCLUSION: Within the limitations of this study, RMMAs occur more frequently in supine position than in non-supine positions in patients with OSA. In both sleep positions, RMMAs are associated with arousals.

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.

Influence of age and gender on sleep bruxism and snoring in non-apneic snoring patients: A polysomnographic study.

The present study aimed to assess the influence of gender and age on snoring and sleep bruxism in non-apneic snoring patients. Adult participants with clinical suspicion of snoring and with no other significant medical history were recruited. Single-night video polysomnography was performed to detect snoring and sleep bruxism. Finally, 137 snoring non-apneic participants were included. Statistical analysis of gender groups showed that the total snore index and snore train were significantly higher in men than in women. Men also presented severe bruxism, with significantly more frequent episodes and higher bruxism episodes index scores. The correlation analysis showed the presence of significant linear relationships in the supine sleep position between age and snore index, snore index in non-rapid eye movement 2 (N2) sleep stage, and snore train. The analysis of groups separated according to the criterion of third age quartile showed that the average, maximum and minimum audio volume in the non-supine sleep position was significantly higher in the older group. The analysis of groups separated according to the criterion of median age showed that the bruxism episode index and bruxism phasic episodes were significantly higher in the younger group. Thus, it can be concluded that both age and gender influence snoring and sleep bruxism. Snoring and sleep bruxism seem to be more intensive in men. Older patients seem to snore more in N2 sleep and the supine sleep position and present lower bruxism episodes, especially the phasic type. The results of the present study indicate the need for further research on this topic to establish the possible relationship between snoring and sleep bruxism.

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.

Bruxism Relieved Under CPAP Treatment in a Patient With OSA Syndrome.

Bruxism is a heterogeneous condition related to various underlying mechanisms, including the presence of OSA. This case report illustrates that sleep mandibular movement monitoring and analysis could provide a useful opportunity for detection of both sleep bruxism and respiratory effort. The current case suggests that tracking of respiratory effort could enable evaluation of bruxism and its potential interactions. Successful treatment of sleep-related respiratory effort may lead to improved or resolution of bruxism in cases where such a causal relationship does exist.

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.

Evaluation of the effectiveness of infrared light-emitting diode photobiomodulation in children with sleep bruxism: Study protocol for randomized clinical trial.

BACKGROUND: Sleep bruxism is a masticatory muscle activity characterized as rhythmic (phasic) or nonrhythmic (tonic). In children and adolescents, etiological factors, such as breathing pattern and sleep quality, have recently been addressed in studies investigating sleep bruxism. New therapies for adults, such as botulinum toxin, have been investigated, but such techniques are not applicable for individuals in the growth and development phase. METHODS: The participants will be 76 children, which will be randomly allocated to a control group, that is group 1, absence of bruxism; group 2, children with bruxism treated with infrared light-emitting diode (LED); and group 3, bruxism treated with occlusal splint. All participants will be submitted to a clinical evaluation to evaluate muscle activity and salivary biomarkers, before and after treatments. Muscle activity will be verified by electromyography of muscles mastication, masseter and temporal, and salivary biomarkers observed will be cortisol and dopamine levels. DISCUSSION: Photobiomodulation therapy has piqued the interest of researchers, as this noninvasive method has demonstrated positive results in problems related to muscle tissues. This document describes the protocol for a proposed study to evaluate morphological and psychosocial aspects in children and adolescents with awake bruxism and their responses to photobiomodulation therapy with infrared LED. CLINICAL TRIALS:.

Association between sleep bruxism and anxiety symptoms in adults: A systematic review.

BACKGROUND: The purpose of this systematic review was to evaluate the association between sleep bruxism (SB) and anxiety symptoms in adults. METHODS: A systematic review was performed and studies assessing SB by means of questionnaires, clinical examination and/or polysomnography (PSG), and validated questionnaires to assess anxiety, were included. Search strategies were developed for seven main electronic databases. Risk of bias was assessed using the Joanna Briggs Institute Critical Appraisal Checklist for Analytical Cross-Sectional Studies, and confidence in cumulative evidence was evaluated using the Grading of Recommendations Assessment, Development and Evaluation criteria. RESULTS: Eight cross-sectional studies were included, of which five were judged with low and three with moderate risk of bias. No association with SB was observed in three studies that investigated generic levels of anxiety, while other two papers that evaluated generic anxiety levels through the State-Trait Anxiety Inventory (STAI) found a positive association with probable and definite SB in both STAI-1 and STAI-2 subscales. Only one study evaluated dental anxiety in particular and an association with probable SB was observed regarding very anxious or extremely anxious scores. Two studies assessed specific symptoms of anxiety using the panic-agoraphobic spectra evaluation (PAS-SR) questionnaire. Significantly higher PAS-SR total scores were observed in both studies with regard to SB. No study with definitive assessment of SB was identified. CONCLUSION: Current literature is controversial regarding an association between SB and generic symptoms of anxiety in adults. It seems that some specific symptoms of the anxiety disorders spectrum might be associated with probable SB.

Effects of a contingent vibratory stimulus delivered by an intra-oral device on sleep bruxism: a pilot study.

PURPOSE: Although sleep bruxism (SB) is one of the most important clinical problems in dental practice, there is no definitive method for controlling it. This pilot study evaluated the effects of contingent vibratory feedback stimuli using an occlusal splint for inhibition of sleep bruxism. METHODS: Thirteen subjects with clinically diagnosed SB participated after providing an informed consent. Portable polysomnographic recordings were conducted in the subjects' home environment to make a definitive SB diagnosis and to evaluate the effects of the vibratory stimuli on SB. A force-based bruxism detection system, which used a pressure-sensitive piezoelectric film embedded in the occlusal splint, was utilized to trigger vibration feedback stimuli, which was scheduled to be applied intermittently for 30 min, at 30-min intervals. RESULTS: The number of SB episodes (times/hour), the total SB duration (seconds/hour), the mean duration of SB episodes (seconds/episode), and the micro-arousal index (times/hour) were scored for each time period (with and without vibration). The effects of the vibration on these scores were tested (paired t test; p < 0.05). The number of SB episodes tended to decrease with the vibration stimuli, and the decrease in the total SB duration was statistically significant (14.3 ± 9.5 vs. 26.0 ± 20.0, p = 0.03). No substantial change was found in terms of the micro-arousal index. CONCLUSIONS: These study results suggested that the SB inhibitory system employing a vibratory stimulus might be able to suppress the total SB duration without disturbing sleep.

The effectiveness of an occlusal disclosure sheet to diagnose sleep bruxism: A pilot study.

OBJECTIVE: To evaluate the utility of vacuum-pressed, BruxChecker® sheets for the diagnosis of sleep bruxism. METHODS: Twenty subjects participated in this study. Tooth contact during sleep was recorded using a 0.1 mm-thick polyvinyl chloride sheet called BruxChecker®. The area of the BruxChecker® in which the red dye was removed was measured. In addition, the EMG activity of the masseter muscle during sleep was recorded. The numbers of bruxism bursts and episodes were counted, and their correlations with the peeled area of the red dye on the BruxChecker® were evaluated. RESULTS: The number of bruxism bursts and episodes/hr significantly correlated with the peeled area at all cut-off values. The peeled area significantly correlated with the number of phasic type bruxism episodes but not with tonic or mixed type bruxism episodes. DISCUSSION: Since the BruxChecker® peeled area reflected phasic type sleep bruxism, the sheets may be useful in sleep bruxism screening.

Chronic stress and temporalis muscle activity in TMD patients and controls during sleep: a pilot study in females.

OBJECTIVES: The aim of this study was to assess the correlation between chronic stress and temporalis muscle activity during four nights. MATERIAL AND METHODS: Forty-four female subjects were recruited in five dental practices located in different areas of the federal state of Saarland, Germany (dental practice network in Saarland). The following inclusion criteria were used: female, aged between 18 and 65, no somatization or depression, and no pain medication, graded chronic pain status < 3. Both subjects reporting about sleep bruxism and subjects negating sleep bruxism during anamnesis were included. Anamnestic issues, sleep bruxism, anxiety, and chronic stress were assessed using validated questionnaires. Temporalis muscle activity was measured for four nights using a portable electromyographic device. Correlation coefficient was used to assess the correlation (Spearman-correlation) between chronic stress and number of temporalis muscle episodes/hour and between anxiety and the number of episodes/hour. RESULTS: The analysis showed that the factors "work overload" (adulthood chronic stress because of too many demands at work) and "pressure to perform" (necessity to be successful at work) were significantly correlated with the number of temporalis muscle episodes per hour. In contrast, anxiety was not correlated with temporalis muscle episodes per hour. CONCLUSIONS: Work-related chronic stress seems to be associated with an increased level of temporalis muscle activity during sleep. CLINICAL RELEVANCE: During anamnesis, work-related aspects should be assessed in females presenting with sleep-bruxism.

Periodontal mechanoreceptors and bruxism at low bite forces.

OBJECTIVE: In this study, we examined if 6-9 Hz jaw tremor, an indirect indicator of Periodontal Mechanoreceptor (PMR) activity, is different in bruxists compared to healthy participants during production of a low-level constant bite force. METHODS: Bite force and surface EMG from the masseter muscle were recorded simultaneously as participants (13 patients, 15 controls) held a force transducer between the upper and lower incisors very gently. RESULTS: Tremor in 6-9 Hz band for bruxists was greater on average compared to controls, but the difference was not significant, both for force recordings and EMG activity. CONCLUSIONS: The low effect sizes measured with the current protocol contrast highly with those of our previous study, where larger, dynamic bite forces were used, and where jaw tremor was markedly different in bruxists compared with controls. SIGNIFICANCE: We have now gained important insight into the conditions under which abnormal jaw tremor can be elicited in bruxism. From a scientific standpoint, this is critical for understanding the 'abnormality' of PMR feedback in bruxism. From a clinical perspective, our results represent progress towards the development of an optimal protocol in which jaw tremor can serve as a biological marker of bruxism.

Salivary cortisol levels and biological rhythm in schoolchildren with sleep bruxism.

OBJECTIVE: Salivary cortisol levels and biological rhythms could be hypothesized as part of the multifactorial framework that explains bruxism etiology. The objective of this study was to examine salivary cortisol levels and biological rhythms in schoolchildren with sleep bruxism (SB). METHODS: This is a cross-sectional study with a school-based sample. The Biological Rhythms Interview for Assessment in Neuropsychiatry for Kids (BRIAN-K) was used to evaluate biological rhythms. Salivary samples were collected by the spitting method. The salivary cortisol level was measured by electrochemiluminescence. The criteria proposed by the American Academy of Sleep Medicine (AASM) were used to evaluate SB. RESULTS: The SB prevalence was 16%. The SB presence was associated with belonging to families of lower economic status (p = 0.003). In addition, children with SB showed greater difficulty in maintaining biological rhythm (p = 0.002) and had higher levels of salivary cortisol (p = 0.034) compared with children without SB. CONCLUSIONS: Higher levels of cortisol and disruption of biological rhythm was associated with SB in schoolchildren.

Characterisation of the relationships between rhythmic masticatory muscle activities and limb movements in patients with sleep bruxism.

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.

Transcranial Magnetic Stimulation: Potential Use in Obstructive Sleep Apnea and Sleep Bruxism.

The aim of this article is to introduce transcranial magnetic stimulation (TMS) to dental practitioners and to explain its use in obstructive sleep apnea (OSA) and sleep bruxism (SB). In these 2 sleep disorders, TMS has proven to be a useful tool to explore pathophysiological pathways and disease mechanisms, and in a more limited way, to recruit upper airway muscles in OSA and reduce muscle activity and pain intensity in SB. Although promising, research using TMS in these conditions is still very limited and future investigations should be conducted before its clinical application can be considered.

Study of Associated Factors With Probable Sleep Bruxism Among Adolescents.

STUDY OBJECTIVES: To evaluate the prevalence of probable sleep bruxism (SB) and its association with sleep features, orthodontic fixed appliance wearing, and extraoral and intraoral clinical signs and symptoms in a population of adolescents. METHODS: Two hundred thirty-nine 12-year-old adolescents enrolled in private and public schools in Brumadinho, southeast Brazil, and their parents were invited to participate. They answered a questionnaire containing information regarding adolescents' sleep features and history of SB. Extraoral and intraoral examination was performed to identify some clinical signs (ie, absence of lip competence, presence of mouth breathing, clicks in the temporomandibular joint [TMJ], tooth wear) and symptoms (ie, pain in the masseter muscle upon palpation), and ongoing orthodontic treatment with fixed appliances. Parental report and clinical examination were used to determine probable SB. Descriptive statistics and logistic regression were performed to identify association of probable SB with independent variables. RESULTS: Of 239 adolescents initially selected, 231 (96.6%) participated in the study. Prevalence of probable SB was 16.9%. Adolescents who snored during sleep (odds ratio [OR] = 3.14; 95% confidence interval [CI] = 1.47-6.70), adolescents who did not have clicks in the TMJ (OR = 3.37; 95% CI = 1.11-10.15), and those who wore orthodontic appliances (OR = 2.72; 95% CI = 1.04-7.14) were more likely to be in the group with probable SB. CONCLUSIONS: Snoring, absence of clicks in the TMJ, and fixed appliance wearing were associated with probable SB among adolescents. This study adds to the ongoing research on SB in adolescents and its associated factors. COMMENTARY: A commentary on this article appears in this issue on page 1281.

Home Polysomnography Reveals a First-Night Effect in Patients With Low Sleep Bruxism Activity.

STUDY OBJECTIVES: To examine the presence of a first-night effect (FNE) and the level of internight variability in sleep bruxism (SB) activity when a self-applicable electrode set is used in home polysomnography (PSG) in a sample of subjects with possible SB. METHODS: Fourteen females and two males aged 38.3 ± 9.1 years (mean ± standard deviation) with self-reported SB underwent home-PSG on three consecutive nights. The subjects applied PSG sensors themselves, including self-applicable electrode sets used to record sleep and masseter muscle activity. Repeated-measures analysis of variance was used to compare SB and sleep variables between the nights. RESULTS: Surprisingly, there were statistically significant elevations in the rhythmic masticatory muscle activity (RMMA) episode index (P = .009), burst index (P = .016), and bruxism time index (P = .049) throughout the course of 3 nights. More bruxers were diagnosed on the second (6 bruxers, ≥ 2 episodes/h) and third night (7 bruxers) compared to the first night (2 bruxers). Most subjects (14/16) had their highest RMMA index on the second or third night. The mean coefficient of variation for RMMA episode index was 50.7%. No statistically significant differences were detected in other sleep variables. CONCLUSIONS: The results indicate that a FNE may be present in SB activity, possibly lasting several nights in some subjects. Furthermore, FNE appears to be combined with high internight variability of SB activity without indications of internight changes in sleep macrostructure. To confirm the level of ongoing SB activity, several nights of PSG may be required, especially in subjects with low first-night SB activity. COMMENTARY: A commentary on this article appears in this issue on page 1281.

Effect of sleep bruxism duration on perceived sleep quality in middle-aged subjects.

Sleep-related bruxism may directly impact sleep quality. This study aims to evaluate potential relationships between sleep bruxism events and related daytime symptoms. We investigated 22 patients (42.1 ± 11.6 yr of age) with sleep bruxism in comparison with 12 good sleeper control subjects of similar age (41.0 ± 11.5 yr). Sleep bruxism was visually analyzed and categorized according to sleep stage, bruxism type (tonic/phasic) and duration. Clinical instruments comprised the Epworth Sleepiness, the Brugmann Fatigue Scale, and the Hospital Anxiety and Depression Rating Scale. Sleep quality was measured using the Pittsburgh Sleep Quality Index. Controls and patients with sleep bruxism presented similar sleep architecture. However, patients with sleep bruxism displayed significantly decreased sleep efficiency and higher sleep fragmentation. Perceived sleep quality was significantly worse in patients with sleep bruxism than in control subjects. Additionally, patients presented with significantly greater fatigue intensity and more affective symptoms than controls. The cumulative durations of sleep bruxism events (phasic, tonic, and combined) were significantly correlated with deterioration of sleep quality, whereas neither the event index per hour of sleep nor the count of event types (phasic/tonic) were related to sleep quality. Patients with sleep bruxism present with higher levels of daytime fatigue and sleepiness than control subjects who experience good sleep and may also exhibit impairments of sleep quality which are related to the duration of bruxism occurrence rather than to its frequency.

Masticatory muscle stretching for the management of sleep bruxism: A randomised controlled trial.

BACKGROUND: Sleep bruxism is a phenomenon associated with masticatory muscle hyperactivity. While stretching of limb and trunk muscles has been extensively studied for musculoskeletal disorders, little is known about the effectiveness of stretching of masticatory muscles in the management of bruxism. OBJECTIVE: The aim of this study is to determine the effectiveness of stretching of the masticatory muscles for sleep bruxism. METHODS: Twenty four pain-free individuals with sleep bruxism were randomly assigned to either an intervention group or a control group. Both groups were given sleep hygiene advice and the intervention group additionally received muscle-stretching exercises for 10 days. Primary outcome measures, bruxism bursts and episodes per hour of sleep, were measured by ambulant polysomnography. Secondary outcome measures were among others pain-free active maximum mouth opening (MMO) and masseter pressure pain threshold (PPT). RESULTS: The number of bruxism episodes per hour of sleep increased more in the intervention group than in the control group (by 1.1 episodes, P = 0.066), as did the number of bruxism bursts per hour of sleep (by 8.6 bursts, P = 0.049). MMO and PPT increased significantly more in the intervention group (by 3.2 mm, P = 0.020; and by 1.0 kg/cm2 , P = 0.036, respectively). CONCLUSION: Static stretching of the masticatory muscles resulted in a minor increase in sleep bruxism episodes (not significant) and bursts (significant). It also led to a significant increase in MMO and PPT. Therefore, masticatory muscle stretching was not effective in reducing sleep bruxism in the absence of pain and/or dysfunction.