Evidence that experimentally induced sleep bruxism is a consequence of transient arousal

Spontaneous rhythmic masticatory muscle activity (RMMA) during sleep occurs more frequently following spontaneous transient micro-arousal in patients with sleep bruxism (SB) and normal controls. Here, we tested the hypothesis that an experimental arousal would be followed by an increase in RMMA. We identified RMMA on polygraphic recordings taken before and after sensory stimulation to induce experimental arousal in eight SB patients and eight matched normal subjects. The rate of experimental arousal and the level of resting electromyographic activity in masseter and suprahyoid muscles during sleep did not differ between the groups. In both, muscle tone and heart rate increased during the experimental arousal. Although post-arousal RMMA occurred in all SB patients, it was seen in only one normal subject. Moreover, tooth-grinding occurred during 71% of the evoked RMMA in SB patients. These results support the hypothesis that SB is an exaggerated form of oromotor activity associated with sleep micro-arousal.     

Sleep bruxism and sleep arousal: an experimental challenge to assess the role of cyclic alternating pattern

Rhythmic masticatory muscle activity (RMMA) is the characteristic electromyographic pattern of sleep bruxism (SB), a sleep-related motor disorder associated with sleep arousal. Sleep arousals are generally organised in a clustered mode known as the cyclic alternating pattern (CAP). CAP is the expression of sleep instability between sleep maintaining processes (phase A1) and stronger arousal processes (phases A2 and A3). This study aimed to investigate the role of sleep instability on RMMA/SB occurrence by analysing CAP and electroencephalographic (EEG) activities. The analysis was performed on the sleep recordings of 8 SB subjects and 8 controls who received sensory stimulations during sleep. Baseline and experimental nights were compared for sleep variables, CAP, and EEG spectral analyses using repeated measure ANOVAs. Overall, no differences in sleep variables and EEG spectra were found between SB subjects and controls. However, SB subjects had higher sleep instability (more phase A3) than controls (P= 0·05). The frequency of phase A3 was higher in the pre-REM sleep periods (P < 0·001), where peaks in RMMA/SB activity were also observed (P = 0·05). When sleep instability was experimentally increased by sensory stimuli, both groups showed an enhancement in EEG theta and alpha power (P = 0·04 and 0·02, respectively) and significant increases in sleep arousal and all CAP variables. No change in RMMA/SB index was found within either groups (RMMA/SB occurred in all SB subjects and only one control during the experimental night). These findings suggest that CAP phase A3 may act as a permissive window rather than a generator of RMMA/SB activity in predisposed individuals.     

Sleep bruxism: an oromotor activity secondary to micro-arousal.

Spontaneous rhythmic masticatory muscle activity (RMMA) during sleep occurs in relation to transient activation in the cerebral and autonomic nervous systems of normal subjects and in patients with sleep bruxism (SB). In this study, we made a quantitative assessment of the sequential changes in cortical electroencephalographic (EEG) and autonomic-cardiac activities associated with micro-arousals preceding RMMA episodes. We matched 10 SB patients with 10 normal subjects. The onset of RMMA episodes was defined in terms of the onset of activation in the suprahyoid muscles. In SB patients, an increase in cortical EEG activity was observed 4 seconds before the onset of suprahyoid activity in 79% of episodes. A significant acceleration in heart rate was initiated one cardiac cycle before RMMA onset. A clear sequence of cortical to autonomic-cardiac activation precedes jaw motor activity in SB patients. This suggests that SB is a powerful oromotor manifestation secondary to micro-arousal.     

夜磨牙与微觉醒及心脏交感神经活动的关系

目的:研究夜磨牙(sleep bruxism,SB)患者睡眠期咀嚼肌节律性运动(RMMA)发生的微觉醒机制。方法 :对30名夜磨牙患者、30名正常人进行连续2夜的多导睡眠监测,研究RMMA事件与微觉醒(MA)的时间相关性;比较2组间RMMA指数及MA指数的差异;RMMA事件发生前60 s、前40 s、前20 s、前5 s,共5个时间点的各连续10个心动周期的平均心率,以及RMMA事件发生前后各5个心动周期的心率变化。结果:夜磨牙症患者微觉醒指数(7.72±1.21)与正常对照相似(7.53±1.33,P=0.5641);但咀嚼肌节律性运动频率,即磨牙指数[(6.10±1.05)次/h]约3倍于正常对照组[(1.81±0.39)次/h,P<0.0001)]。RMMA事件与MA存在高度时间相关性。夜磨牙患者RMMA事件发生前1个心动周期开始心率明显加快。结论:夜磨牙患者较正常人群有较高的RMMA频率,RMMA与睡眠微觉醒相关,磨牙事件发生时伴随明显的心脏交感神经活动增加。     

夜磨牙症患者咀嚼肌节律性运动特征与睡眠周期的关系

目的:研究夜磨牙症(sleep bruxim,SB)患者睡眠期咀嚼肌节律性运动(RMMA)的发生特征及其与睡眠周期的关系.方法:对30名SB患者、30名正常人进行连续2夜的多导睡眠监测,统计睡眠结构、睡眠效率、微觉醒指数以及磨牙指数.分析RMMA事件成群性,RMMA分布与睡眠周期的相关性.结果:SB患者微觉醒指数与正常...     

Oro-facial activities in sleep bruxism patients and in normal subjects: a controlled polygraphic and audio-video study

Summary  To our knowledge, the large spectrum of sleep motor activities (SMA) present in the head and neck region has not yet been systematically estimated in normal and sleep bruxism (SB) subjects. We hypothesized that in the absence of audio–video signal recordings, normal and SB subjects would present a high level of SMA that might confound the scoring specificity of SB. A retrospective analysis of several SMA, including oro-facial activities (OFA) and rhythmic masticatory muscle activities (RMMA), was made from polygraphic and audio–video recordings of 21 normal subjects and 25 SB patients. Sleep motor activities were scored, blind to subject status, from the second night of sleep recordings. Discrimination of OFA included the following types of activities: lip sucking, head movements, chewing-like movements, swallowing, head rubbing and scratching, eye opening and blinking. These were differentiated from RMMA and tooth grinding. The frequency of SMA per hour of sleep was lower in normal subjects in comparison with SB patients ( P  < 0·001). Up to 85% of all SMA in normal subjects were related to OFA while 30% of SMA in SB patients were related to OFA scoring ( P  < 0·001). The frequency of RMMA was seven times higher in SB patients than in normal subjects ( P  < 0·001). Several SMA can be observed in normal and SB subjects. In the absence of audio–video signal recordings, the discrimination of various types of OFA is difficult to achieve and may lead to erroneous estimation of SB-related activities.     

Sleep bruxism: a comprehensive overview for the dental clinician interested in sleep medicine

Sleep bruxism (SB) is a common sleep-related motor disorder characterized by tooth grinding and clenching. SB diagnosis is made on history of tooth grinding and confirmed by polysomnographic recording of electromyographic (EMG) episodes in the masseter and temporalis muscles. The typical EMG activity pattern in patients with SB is known as rhythmic masticatory muscle activity (RMMA). The authors observed that most RMMA episodes occur in association with sleep arousal and are preceded by physiologic activation of the central nervous and sympathetic cardiac systems. This article provides a comprehensive review of the cause, pathophysiology, assessment, and management of SB.     

下颌咀嚼运动与夜磨牙症特征相关性的初步探究

目的 探讨夜磨牙症各临床诊断标准和睡眠时下颌咀嚼运动发生频率的相互关系。方法 运用视频多导睡眠监测方法,对20例健康成人,具有至少以下一项临床症状和体征且诊断为夜磨牙症的实验参与者进行记录：1）有牙齿频繁磨耗的报告;2）至少有3颗牙的咬合面有牙齿磨损与牙本质暴露;3）早晨咀嚼肌症状;4）咬肌肥大。对咀嚼肌节律性运动（RMMA）和孤立强直性咀嚼肌收缩发作事件进行评分。将这些变量与临床症状和体征存在的相关性进行比较。对孤立下颌强直运动发作的患者和RMMA受试者的颞下颌关节紊乱病（TMD）发生率进行调查。结果 20例受试者中,RMMA事件发作的频率为（5.8±3.1）次·h-1,孤立强直性发作的频率为（2.1±0.9）次·h-1。室友报告有磨牙体征的RMMA事件显著高于磨牙体征者（P<0.05）;牙齿磨耗者的RMMA事件显著高于无牙齿磨耗者（P<0.05）。但是,RMMA事件的发生与早晨咀嚼肌症状或咬肌肥大之间无差异。RMMA发生者的TMD发生率显著高于孤立下颌强直运动发作者。结论 常用于诊断夜磨牙症的临床症状和体征可体现在睡眠期间不同的临床和生理方面的下颌运动,即在睡眠期间RMMA可反映牙齿磨耗的发生,而且TMD的发生风险更大。     

Detection of sleep bruxism: comparison between an electromyographic and electrocardiographic portable holter and polysomnography

Recent polysomnographic (PSG) studies showed that the sleep bruxism (SB) event is preceded by a sudden shift in autonomic cardiac activity. Therefore, heart rate could be the simplest‐to‐record parameter for use in addition to portable home EMG monitoring to improve the accuracy in automatic detection of SB events. The aim of the study was to compare the detection of SB episodes by combined surface electromyography and heart rate (HR) recorded by a compact portable device (Bruxoff^®), with the scoring of SB episodes by a PSG recording. Twenty‐five subjects (14 ‘probable’ bruxers and 11 non‐bruxers) were selected for the study. Each subject underwent the Bruxoff and the PSG recordings during the same night. Rhythmic masseter muscle activities (RMMAs) were scored according to published criteria. Correlation coefficients and the Bland–Altman plots were calculated to measure the correlation and agreement between the two methods. Results showed a high correlation (Pearson's r = 0·95, P < 0·0001) and a high agreement (bias = 0·05) between Bruxoff and the PSG. Furthermore, the receiver operating characteristic curve analysis showed a high sensitivity and specificity of the portable device (92·3% and 91·6%, respectively) when the cut‐off was set at 4 SB episodes per hour according to published criteria. The Bruxoff device showed a good diagnostic accuracy to differentiate RMMA from other oromotor activities. These findings are important in the light of the need for simple and reliable portable devices for the diagnosis of SB both in the clinical and research settings.     

Could transient hypoxia be associated with rhythmic masticatory muscle activity in sleep bruxism in the absence of sleep‐disordered breathing? A preliminary report

Sleep bruxism (SB) is a repetitive jaw‐muscle activity characterised by clenching or grinding of the teeth during sleep. Sleep bruxism activity is characterised by rhythmic masticatory muscle activity (RMMA). Many but not all RMMA episodes are associated with sleep arousal. The aim of this study was to evaluate whether transient oxygen saturation level change can be temporally associated with genesis of RMMA/SB. Sleep laboratory or home recordings data from 22 SB (tooth grinding history in the absence of reported sleep‐disordered breathing) and healthy subjects were analysed. A total of 143 RMMA/SB episodes were classified in four categories: (i) no arousal + no body movement; (ii) arousal + no body movement; (iii) no arousal + body movement; (iv) arousal + body movement. Blood oxygen levels (SaO₂) were assessed from finger oximetry signal at the baseline (before RMMA), and during RMMA. Significant variation in SaO₂ over time (P = 0·001) was found after RMMA onset (+7 to +9 s). No difference between categories (P = 0·91) and no interaction between categories and SaO₂ variation over time (P = 0·10) were observed. SaO₂ of six of 22 subjects (27%) remained equal or slight increase after the RMMA/SB onset (+8 s) compared to baseline; 10 subjects (45%) slightly decreased (drop 0·01–1%) and the remaining (27%) decreased between 1% and 2%. These preliminary findings suggest that a subgroup of SB subjects had (i) a minor transient hypoxia potentially associated with the onset of RMMA episodes, and this (ii) independently of concomitant sleep arousal or body movements.     

Influence of experimental esophageal acidification on sleep bruxism: a randomized trial

The aim of this cross-over, randomized, single-blinded trial was to examine whether intra-esophageal acidification induces sleep bruxism (SB). Polysomnography with electromyogram (EMG) of masseter muscle, audio-video recording, and esophageal pH monitoring were performed in a sleep laboratory. Twelve healthy adult males without SB participated. Intra-esophageal infusions of 5-mL acidic solution (0.1 N HCl) or saline were administered. The frequencies of EMG bursts, rhythmic masticatory muscle activity (RMMA) episodes, grinding noise, and the RMMA/microarousal ratio were significantly higher in the 20-minute period after acidic infusion than after saline infusion. RMMA episodes including SB were induced by esophageal acidification. This trial is registered with the UMIN Clinical Trials Registry, UMIN000002923. Abbreviations: ASDA, American Sleep Disorders Association; EMG, electromyogram; GER, gastroesophageal reflux; LES, lower esophageal sphincter; NREM, non-rapid eye movement; REM, rapid eye movement; RMMA, rhythmic masticatory muscle activity; SB, sleep bruxism; SD, standard deviation; UES, upper esophageal sphincter.     

Changes in oxygen and carbon dioxide in the genesis of sleep bruxism: a mechanism study

PurposeRhythmic masticatory muscle activity (RMMA), a biomarker of sleep bruxism (SB), has been associated with mild hypoxia and/or big breaths in some adults with non-sleep-disordered breathing. The purpose of this study was to investigate that concurrent oxygen and carbon dioxide fluctuations are among the physiological variables that contribute to RMMA onset.MethodsTwelve subjects (5 female, 7 male, mean age: 43 ± 11) underwent polysomnography recording in a sleep laboratory. RMMA index and apnea-hypopnea index were calculated. Oxygen saturation (SpO₂) was estimated by finger pulse oximeter and end-tidal CO₂ (ETCO₂) by nasal airflow cannula before and after RMMA onset. Given the expected response time delay between actual arterial hypoxemia and fingertip pulse detection, we adjusted the SpO₂ desaturation onset to the onset of masseter muscle activity using a 17 s criterion based on ETCO₂ shifts.ResultsSpO₂ was slightly but significantly lower than at baseline (max: −0.6%) in the 6–4 s before RMMA onset and significantly higher in the 6–18 s after onset (0.9%; p < 0.05). Although ETCO₂ before RMMA onset did not differ from baseline, it decreased at 8–10 s after onset (−1.7 mmHg: p < 0.05). No changes in SpO₂ or ETCO₂ in relation to RMMA onset reached a critical clinical threshold.ConclusionsThe mild transient hypoxia observed before RMMA onset was not associated with a change in ETCO_2. The mild and brief oxygen fluctuations before RMMA onset may reflect a physiological response that seems to have little influence on SB genesis.     

The occurrence of respiratory events in young subjects with a frequent rhythmic masticatory muscle activity: a pilot study

Purpose

Concomitant occurrence of respiratory events can be often overlooked in the clinical practice of SB. This study assessed physiological characteristics of rhythmic masticatory muscle activity (RMMA) and concomitant respiratory events in young sleep bruxism (SB) subjects asymptomatic to obstructive sleep apnea (OSA).

Genesis of sleep bruxism: motor and autonomic-cardiac interactions

This is a short review paper presenting hypothesis to explain the mechanism that may be involved in the genesis of sleep bruxism (SB). In humans, SB is a repetitive sleep movement disorder mainly characterized by rhythmic masticatory muscle activity (RMMA) at a frequency of 1Hz and by occasional tooth grinding. Until recently, the mechanism by which RMMA and SB episodes are triggered has been poorly understood. It is reported that during light sleep, most SB episodes are observed in relation to brief cardiac and brain reactivations (3-15s) termed "micro-arousals". We showed that RMMA are secondary to a sequence of events in relation to sleep micro-arousals: the heart (increase in autonomic sympathetic activity) and brain are activated in the minutes and seconds, respectively, before the onset of activity in suprahyoid muscles and finally by RMMA in jaw closing masseter or temporalis muscles. In non-human primate study, we have shown that the excitability of cortico-bulbar pathways is depressed during sleep; no rhythmic jaw movements (RJM) are observed following intracortical microstimulation (ICMS) of cortical masticatory area (CMA) during sleep compared to the quiet awake state. The above results suggest that the onset of RMMA and SB episodes during sleep are under the influences of brief and transient activity of the brainstem arousal-reticular ascending system contributing to the increase of activity in autonomic-cardiac and motor modulatory networks.     

Masticatory muscle sleep background electromyographic activity is elevated in myofascial temporomandibular disorder patients

Despite theoretical speculation and strong clinical belief, recent research using laboratory polysomnographic (PSG) recording has provided new evidence that frequency of sleep bruxism (SB) masseter muscle events, including grinding or clenching of the teeth during sleep, is not increased for women with chronic myofascial temporomandibular disorder (TMD). The current case–control study compares a large sample of women suffering from chronic myofascial TMD (n = 124) with a demographically matched control group without TMD (n = 46) on sleep background electromyography (EMG) during a laboratory PSG study. Background EMG activity was measured as EMG root mean square (RMS) from the right masseter muscle after lights out. Sleep background EMG activity was defined as EMG RMS remaining after activity attributable to SB, other orofacial activity, other oromotor activity and movement artefacts were removed. Results indicated that median background EMG during these non‐SB event periods was significantly higher (P < 0·01) for women with myofascial TMD (median = 3·31 μV and mean = 4·98 μV) than for control women (median = 2·83 μV and mean = 3·88 μV) with median activity in 72% of cases exceeding control activity. Moreover, for TMD cases, background EMG was positively associated and SB event‐related EMG was negatively associated with pain intensity ratings (0–10 numerical scale) on post‐sleep waking. These data provide the foundation for a new focus on small, but persistent, elevations in sleep EMG activity over the course of the night as a mechanism of pain induction or maintenance.     

Rhythmic masticatory muscle activity during sleep in humans

Rhythmic Masticatory Muscle Activity (RMMA) is frequently observed during sleep in normal subjects and sleep bruxers. We hypothesized that some normal subjects exhibit RMMA at a lower frequency than sleep bruxers. Polysomnographic data from 82 normal subjects were compared with data from 33 sleep bruxers. RMMA episodes were defined as three or more consecutive bursts of masseter EMG activity, with or without tooth-grinding. Such episodes were observed in nearly 60% of normal subjects. A lower frequency of episodes was noted in normal subjects than in bruxers. Sleep organization was similar between groups. Bruxers had twice as many masseter muscle bursts per episode and episodes of higher amplitude compared with controls with RMMA. The high prevalence of RMMA observed in normal subjects suggests that this activity is related to certain sleep-related physiological functions, including autonomic activation.     

The effect of oral splint devices on sleep bruxism: a 6-week observation with an ambulatory electromyographic recording device

This study investigated the effect of stabilization splint (SS) and palatal splint (PS), which had the same design as SS except for the elimination of the occlusal coverage, on sleep bruxism (SB) using a portable electromyographic (EMG) recording system. Sixteen bruxers participated in this study. The EMG activities of the right masseter muscle during sleep were recorded for three nights each in the following five recording periods: before, immediately after, and 2, 4 and 6 weeks after the insertion of the splint. The crossover design, in which each splint was applied to each subject for 6 weeks with an interval of 2 months for a washout period, was employed in this randomized-controlled study. The number of SB events, duration and total activities of SB were analysed. The number of SB events before the insertion of splints (baseline) was 2.98 +/- 1.61 times h(-1). Both splints significantly reduced SB immediately after the insertion of devices (P < 0.05, one-way repeated-measures anova followed by Dunnett); however, no reduction was observed in 2, 4 or 6 weeks (P > 0.05). There was no statistical difference in the effect on SB between the SS and PS (P > 0.05, two-way repeated-measures anova). Both splints reduced the masseter EMG activities associated with SB; however, the effect was transient.     

Specific increase in non-functional masseter bursts in subjects aware of tooth-clenching during wakefulness

Previous studies have reported that subjective awareness of a tooth-clenching habit is associated with increased jaw motor activity (Rao SM, Glaros AG, J Dent Res. 1979;58:1872). The aim of this study was to test the hypothesis that subjects with clenching awareness exhibit different motor expressions specific to non-functional oromotor activity under laboratory conditions without psychological or sensory effects. Polygraphic and audio-video recordings were made for a 30-min period of silent reading by 33 subjects without oro-facial pain. Oro-facial behaviours (e.g. swallowing, lip movements) were scored according to the polygraphic and audio-video records and masseter bursts were quantitatively analysed. Subjective psychological/sensory measures were also recorded before and/or after the polygraphic recording using a visual analogue scale. The subjects were classified into two groups one with 15 subjects who were aware of having a tooth-clenching habit and another with 18 who were not aware of any such habit. There were no differences between the groups with respect to the number of functional oro-facial behaviours or subjective psychological/sensory measures. Masseter bursts unrelated to functional oro-facial behaviours occurred more frequently in subjects with awareness [median (range) = 23 (2-187) bursts] than in those without [9.0 (0-36); P = 0.01], while neither burst activity [12.3 (1.8-34.5) % of maximum voluntary clenching and 10.1 (6.5-25.1) %, respectively] nor duration [1.17 (0.2-2.2) s and 1.28 (0.3-4.1) s, respectively] differed between the groups. The occurrence of functional oro-facial behaviours or other body behaviours (e.g. limb and body movements) did not differ between the two groups. These findings suggest that the increased masseter activity in subjects with tooth-clenching awareness is characterized by a specific increase in non-functional masseter bursts.     

Sleep Bruxism and Sleep‐Disordered Breathing

Sleep bruxism (SB) is a repetitive jaw muscle activity with clenching or grinding of the teeth during sleep. SB is characterized by what is known as rhythmic masticatory muscle activity (RMMA). RMMA is the laboratory polysomnographic finding that differentiates SB from other oromandibular movements seen during sleep. Most often RMMA episodes are associated with sleep arousal. Some patients will report similar complaints related to both SB and sleep disordered breathing (SDB). There are some reports that would suggest that SB is a result of SDB. It has has been postulated that SB is a compensatory mechanism to re establish muscle tone of the upper airway. While these disorders do in fact often present concomitantly, the relationship between the two is yet to be fully elucidated. This Critical Appraisal reviews 3 recent publications with the intent to better define what relationships may exists between SDB and SB. While the current evidence appears to support the notion that these are often concomitant disorders, it also makes clear that evidence to support the hypothesis that SDB is causative for SB is currently lacking. (J Esthet Restor Dent 00:000–000, 2016)     

Influence of psychological symptoms on home-recorded sleep-time masticatory muscle activity in healthy subjects

The present investigation attempts to describe the correlation between sleep-time masticatory muscle activity (MMA) and psychological symptoms by the use of a four-channel electromyography (EMG) home-recording device in a group of 15 healthy volunteers completing a battery of psychometric questionnaires for the assessment of anxiety, depression and anger. The integrated EMG signal was adopted to quantify the work (μV × s) produced by each of the four muscles (bilateral masseter and temporal) during the 5-h recording span and per each 1-h increment. The duration of MMA events and the muscle work during the first hour of sleep was related to trait anxiety scores for both masseter (P = 0·007) and temporalis muscles (P = 0·022). Trait anxiety was also significantly correlated to the total amount of MMA duration (in seconds) of the temporalis muscles (r = 0·558; P = 0·031). The present investigation provides support to the hypothesis that the duration of sleep-time masticatory muscle activity, especially during the early phases of a night's sleep, may be related to anxiety trait and not to anxiety state, depression or anger. These findings may support the view that features related to the individual management of anxiety, viz. trait, are likely to be more important than acute episodes of anxiety, viz. state, in the aetiology of sleep-time masticatory muscle activity. The role of other psychological symptoms is likely to be less important.