A controlled daytime challenge of motor performance and vigilance in sleep bruxers

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.

Association between 5-Hydroxytryptamine Receptor 2A Gene (rs6313 and rs4941573) Polymorphism and Sleep Bruxism: A Meta-analysis

Genetic factors may influence sleep bruxism's pathogenesis. Even though the association between the, 5-hydroxytryptamine 2A (5-HTR2A) serotonin receptor gene polymorphism and sleep bruxism has been investigated, inconsistent findings have been discovered. As a result, meta-analysis was performed to gather complete results on this topic. PubMed, Web of Science, Embase, and Scopus databases were searched for all papers containing English abstracts until April 2022. Medical Subject Heading (MESH) terms plus unrestricted keywords were used in the searches. The Cochrane test and the I ² statistic were used to determine the heterogeneity percentage in numerous researches. Comprehensive Meta-analysis v.2.0 software was used to conduct the analyses. Five properly fitting papers were chosen for meta-analysis from the 39 articles acquired during the initial search. The meta-analysis revealed that the 5-HTR2A polymorphism has no link with sleep bruxism susceptibility across the models studied (P-Value > 0.05). The combined odds ratio analysis revealed no statistically significant association between the 5-HTR2A gene polymorphism with sleep bruxism. Nonetheless, these findings require confirmation through researches with large sample sizes. Identifying genetic markers for sleep bruxism may help clarify and expand our current knowledge of bruxism physiopathology.

Electromyographic analysis of the stomatognathic system of children with Molar-incisor hypomineralization

INTRODUCTION

Molar-incisor hypomineralization (MIH) is a qualitative defect of dental enamel that affects one or more permanent first molars, with or without involvement of the incisor teeth. This condition leads to challenges to dental care and treatment planning.

AIM

Based on the hypothesis that children who have MIH possibly present alterations in postural and masticatory activities and considering the absence of studies investigating these parameters, the present study evaluated the functionality of the stomatognathic system considering the mentioned aspects.

MATERIALS

The comparison of individuals with (MIHG; n = 32) and without MIH (CG; n = 32) was evaluated by electromyographic activity of the masseter and temporal muscles (right and left), as well as evaluation of the masticatory cycles during habitual mastication.

RESULTS

MIHG showed muscle hyperactivity in postural and dynamic conditions compared to the CG; higher electromyographic values for MIHG when compared to CG in the following postural conditions: at rest for the right temporal (p = 0.00) and left temporal muscles (p = 0.03); in the protrusion to the right temporal muscle (p = 0.02); in the right laterality for the right masseter (p = 0.00) and left temporal muscles (p = 0.01); in the left laterality for the right masseter (p = 0.03) and left temporal (p = 0.04) muscles. In dynamic conditions with consistent food, significance was observed for the left temporal (p = 0.01); and with soft food for the right (p = 0.01) and left temporal muscles (p = 0.04).

CONCLUSIONS

Children with MIH seem to have impaired functionality of the stomatognathic system. Children with MIH have alterations in the stomatognathic system.

A study to evaluate psychological and occlusal parameters in bruxism

Purpose

To evaluate the role of anxiety/depression and occlusal factors in bruxism using Hospital Anxiety and Depression Scale and T-Scan III respectively.

Methods

The present case control study was comprising of a group of thirty patients with bruxism (Group Br) and 30 healthy individuals as control group (Group NBr). Subjects were selected from outdoor patients visiting the dental unit with the chief complaint of wearing off/sensitivity of all the teeth due to habitual grinding. The cases were selected by using the diagnostic criteria as given by the American Academy of Sleep Medicine (AASM). Further based on similarities of age and gender, controls were selected. Tooth wear index was recorded using an index given by Ekfeldt et al. Hospital Anxiety and Depression Scale (HADS) questionnaire was administered to both the groups to evaluate anxiety and depression. Recording of occlusal parameters in both the groups was done digitally by using T-Scan III. Statistical analysis was done by using student's t-test, chi square test and Mann Whitney U test.

Results

Group Br had significantly greater mean tooth wear index (22.24 ± 11.5) than group NBr (5.17 ± 3.30). Group Br had significantly higher anxiety (9.03 + 1.87/7.17 + 1.82) and depression scores (8 + 1.93/6.17 + 1.23) as compared to NBr. The disclusion time of group Br was 0.652 ± 0.749 and that of group NBr was 0.247 ± 0.289 (p = 0.008).

Conclusions

Subjects with higher level of anxiety, depression and increased disclusion time may have greater predilection towards suffering from bruxism (p < 0.05).

Bruxism, Related Factors and Oral Health-Related Quality of Life Among Vietnamese Medical Students

Although bruxism is a common issue with a high prevalence, there has been a lack of epidemiological data about bruxism in Vietnam. This cross-sectional study aimed to determine the prevalence and associated factors of bruxism and its impact on oral health-related quality of life among Vietnamese medical students. Bruxism was assessed by the Bruxism Assessment Questionnaire. Temporomandibular disorders were clinically examined followed by the Diagnostic Criteria for Temporomandibular Disorders Axis I. Perceived stress, educational stress, and oral health-related quality of life were assessed using the Vietnamese version of Perceived Stress Scale 10, the Vietnamese version of the Educational Stress Scale for Adolescents, and the Vietnamese version of the 14-item Oral Health Impact Profile, respectively. The prevalence of bruxism, sleep bruxism, awake bruxism, and both conditions in Vietnamese medical students were 51.2%, 38.2%, 23.4%, and 10.4% respectively. Stress, temporomandibular joint pain, masticatory muscle pain, and tooth attrition were associated with the presence of bruxism. Vietnamese medical students were negatively affected by bruxism in terms of oral health-related quality of life.

Dose-response association of sleep quality with anxiety symptoms in Chinese rural population: the Henan rural cohort

BACKGROUND

The epidemiological evidence on the association of sleep quality on anxiety symptoms has been inconclusive. This study aimed to explore the association between sleep quality and anxiety symptoms in rural Chinese population and investigate whether age, lifestyles, and chronic diseases modified this association.

METHODS

A total of 27,911 participants aged 18-79 years from the Henan Rural Cohort Study were included in the study. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) scale. Poor sleep quality was defined as PSQI ≥6. Anxiety symptoms were evaluated with the two-item generalized anxiety disorder scale (GAD-2). Individual with score ≥ 3 was viewed as having anxiety symptoms. Logistic regression and restricted cubic spline were conducted to examine the association of sleep quality with anxiety symptoms.

RESULTS

Altogether, 6087 (21.80%) participants were poor sleepers and 1557 (5.58%) had anxiety symptoms. The odds of anxiety were increased with increment of PSQI score after fitting restricted cubic splines. The poor sleep quality was associated with a higher possibility of anxiety symptoms [odd ratio (OR): 4.60, 95% confidence interval (CI): 3.70-5.72] in men, and (OR: 3.56, 95% CI: 3.10-4.09) in women for multivariable analysis. Further, stratified analyses showed that the effect of sleep quality on anxiety symptoms could be modified by age, marital status, smoking status, drinking status, hypertension, and type 2 diabetes mellitus.

CONCLUSIONS

A dose-response association between PSQI score and anxiety symptoms was found. In addition, the relationship between poor sleep quality and greater anxiety symptoms was observed in this rural population, especially in participants aged ≥60 years and those with unhealthy habits or had a chronic disease.

TRIAL REGISTRATION

The trial was prospectively registered on July 6, 2015 and available online at ClinicalTrials.gov ID: ChiCTR-OOC-15006699 .

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.

The correlation between sleep bruxism, salivary cortisol, and psychological status in young, Caucasian healthy adults

Objective: To analyze the association between sleep bruxism (SB), salivary cortisol, and psychological state in healthy adults.Methods: Sixty healthy students (with or without SB) were included in the study. The subjects completed a questionnaire that evaluated the presence of SB and analyzed the general and work-related psychological states and job-related frustration. Clinical examinations of TMJs and dental wear were performed. The salivary cortisol was determined using ELISA technique.Results: Subjects with SB had a general status characterized by anxiety or stress compared to subjects without SB. They also presented a work-induced depressive or anxious attitude compared to healthy individuals. The salivary cortisol levels were higher in subjects with SB and in females and were correlated with subjects' general anxiety, but not with a job-induced psychological state.Conclusion: SB is correlated with general and job-induced psychological changes. Salivary cortisol could be a non-invasive marker for the evaluation of SB severity.

Investigation of neurodegenerative and inflammatory processes in sleep bruxism

Objective: The present study aimed to evaluate the anxiety and optical coherence tomography (OCT) findings in patients with sleep bruxism (SB) and to develop objective measurements to assess the neurodegenerative and inflammatory processes associated with this disease. Methods: A group of 40 SB patients were compared with a control group consisting of 40 healthy individuals (without SB). Anxiety results and the OCT measurements of retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), and choroidal thickness were assessed in both groups. Results: Anxiety values in the bruxism group were significantly higher than those in the control group. The measurements of RNFL, IPL, and GCL in the bruxism group were significantly lower than the control group, whereas the choroidal thickness was significantly higher. Conclusion: According to literature, this is the first study that analyzed the changes in the retinal structures in bruxism, which revealed that SB is a neurodegenerative and inflammatory process.

DNA is hypomethylated in circadian manifestations of bruxism

OBJECTIVE

The aim of this study was to compare the global DNA methylation levels in patients under bruxism treatment and a control group.

METHODS

Subjects undergoing bruxism treatment were classified in awake bruxism (42 patients), sleep bruxism (32 patients) and both conditions (42 patients). The control group included 42 individuals. A colorimetric assay (MethylFlash Methylated DNA 5-mC Quantification Kit, Epigenetic Group Inc., NY, USA) was used to determine the global DNA methylation levels.

RESULTS

Statistically significant differences were found in amounts of methylated DNA in all circadian manifestations of bruxism compared with a control group (sleep bruxism = 0.95% ± 2.02%; awake bruxism = 0.87% ± 2.1%; sleep and awake bruxism = 0.17% ± 0.25%; Control = 1.69% ± 1.6%; Kruskal-Wallis test [p = .0001] followed by Dunn's test [p < .05]).

CONCLUSION

Patients undergoing bruxism treatment exhibited hypomethylated DNA levels when compared to control group. Our results suggest that DNA hypomethylation might be a novel aetiologic factor in bruxism aetiology. Further researches must be performed exploring the role of epigenetics modifications in circadian manifestations of bruxism.

Sleep bruxism: Current knowledge and contemporary management

Bruxism is defined as the repetitive jaw muscle activity characterized by the clenching or grinding of teeth. It can be categorized into awake and sleep bruxism (SB). Frequent SB occurs in about 13% of adults. The exact etiology of SB is still unknown and probably multifactorial in nature. Current literature suggests that SB is regulated centrally (pathophysiological and psychosocial factors) and not peripherally (morphological factors). Cited consequences of SB include temporomandibular disorders, headaches, tooth wear/fracture, implant, and other restoration failure. Chairside recognition of SB involves the use of subjective reports, clinical examinations, and trial oral splints. Definitive diagnosis of SB can only be achieved using electrophysiological tools. Pharmacological, psychological, and dental strategies had been employed to manage SB. There is at present, no effective treatment that “cures” or “stops” SB permanently. Management is usually directed toward tooth/restoration protection, reduction of bruxism activity, and pain relief.

Genetic polymorphisms in the serotonergic system are associated with circadian manifestations of bruxism

Bruxism (BRX) is a condition of great interest for researchers and clinicians in dental and medical areas. BRX has two circadian manifestations; it can occur during sleep (sleep bruxism, SB) or during wakefulness (awake bruxism, WB). However, it can be suffered together. Recent investigations suggest that central nervous system neurotransmitters and their genes could be involved in the genesis of BRX. Serotonin is responsible for the circadian rhythm, maintaining arousal, regulating stress response, muscle tone and breathing. Thus, serotonin could be associated with BRX pathogenesis. The aim of this work was to evaluate the frequency of genetic polymorphisms in the genes HTR1A (rs6295), HTR2A (rs1923884, rs4941573, rs6313, rs2770304), HTR2C (rs17260565) and SLC6A4 (rs63749047) in subjects undergoing BRX treatment. Patients included were classified according to their diagnosis in awake bruxism (61 patients), sleep bruxism (26 patients) and both (43 patients). The control group included 59 healthy patients with no signs of BRX. Data showed significant differences in allelic frequencies for the HTR2A rs2770304 polymorphism, where the C allele was associated with increased risk of SB (odds ratio = 2·13, 95% confidence interval: 1·08-4·21, P = 0·03). Our results suggest that polymorphisms in serotonergic pathways are involved in sleep bruxism. Further research is needed to clarify and increase the current understanding of BRX physiopathology.

Chew the Pain Away: Oral Habits to Cope with Pain and Stress and to Stimulate Cognition

The acute effects of chewing gum on cognitive performance, stress, and pain have been intensively studied in the last decade. The results have been contradicting, and replication studies proved challenging. Here, we review some of the recent findings of this topic and explore possible explanations for these discrepancies by incorporating knowledge derived from studies into oral habits and bruxism. Both stress and cerebral functional specialization (i.e., the involvement of specific brain structures in distinctive cognitive processes) are hypothesized to play a major role in the underlying physiological mechanisms of the diverse effects of chewing gum on cognition, stress, and pain.

Interactions between sleep disorders and oral diseases

Dental sleep medicine is a rapidly growing field that is in close and direct interaction with sleep medicine and comprises many aspects of human health. As a result, dentists who encounter sleep health and sleep disorders may work with clinicians from many other disciplines and specialties. The main sleep and oral health issues that are covered in this review are obstructive sleep apnea, chronic mouth breathing, sleep-related gastroesophageal reflux, and sleep bruxism. In addition, edentulism and its impact on sleep disorders are discussed. Improving sleep quality and sleep characteristics, oral health, and oral function involves both pathophysiology and disease management. The multiple interactions between oral health and sleep underscore the need for an interdisciplinary clinical team to manage oral health-related sleep disorders that are commonly seen in dental practice.

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.

No effect of conscious clenching on simple arithmetic task in healthy participants

PURPOSE

This study aimed to investigate whether clenching aids performance in a task requiring mental concentration in healthy participants.

MATERIALS AND METHODS

Twenty healthy participants (an average of 26.8 ± 2.0 years, nine females and 11 males) were recruited from our department. Participants performed four sets of hundred-square calculations as a mental arithmetic task. Among these sets, the third and the fourth sets were randomly divided into two conditions: one condition where participants made an effort to not allow their teeth to touch ('no tooth-contact' condition), and another where they made a conscious effort to rhythmically clench their teeth ('clenching' condition) during the task. Surface EMG was recorded from the left masseter muscle. Arithmetic performance was compared between the tooth-contact and clenching conditions using paired t-tests. In addition, we computed Pearson product-moment coefficients of the correlations between the difference in EMG activity and arithmetic performance in the two conditions.

RESULTS

No significant change in arithmetic score was found between the no tooth-contact (68.8 ± 12.2) and clenching conditions (66.5 ± 12.7; P=0.27). No significant correlation was found between the difference in EMG activity and changes in arithmetic performance (r=0.32, P=0.17).

CONCLUSION

In healthy participants, conscious clenching was not associated with any benefit in arithmetic performance. Although our study was limited by only measuring the short-term effects of clenching on a simple arithmetic task, the results indicate that it may not be harmful for clinicians to encourage their patients to refrain from clenching their teeth.

Controlled clinical, polysomnographic and psychometric studies on differences between sleep bruxers and controls and acute effects of clonazepam as compared with placebo

The pathogenesis, pathophysiology, and pharmacotherapy of sleep bruxism (SB) are still not fully understood. We investigated symptomatology, objective and subjective sleep and awakening quality of middle-aged bruxers compared with controls and acute effects of clonazepam 1 mg compared with placebo by polysomnography and psychometry. Twenty-one drug-free bruxers spent 3 nights in the sleep lab, 21 age- and sex-matched controls 2 nights. Clinically, bruxers exhibited deteriorated PSQI, SAS, SDS and IRLSSG measures, polysomnographically impaired sleep maintenance, increased movement time, stage shift index, periodic leg movements (PLM) and arousals and psychometrically deteriorated subjective sleep and awakening quality, evening/morning well-being, drive, mood, drowsiness, attention variability, memory, and fine motor activity. As compared with placebo, clonazepam significantly decreased the SB index in all patients (mean: -42 +/- 15%). Sleep efficiency, maintenance, latency, awakenings and nocturnal wake time, the stage shift index, S1, PLM, the arousal index, subjective sleep and awakening quality, and fine motor activity improved.

Bruxism physiology and pathology: an overview for clinicians

Awake bruxism is defined as the awareness of jaw clenching. Its prevalence is reported to be 20% among the adult population. Awake bruxism is mainly associated with nervous tic and reactions to stress. The physiology and pathology of awake bruxism is unknown, although stress and anxiety are considered to be risk factors. During sleep, awareness of tooth grinding (as noted by sleep partner or family members) is reported by 8% of the population. Sleep bruxism is a behaviour that was recently classified as a 'sleep-related movement disorder'. There is limited evidence to support the role of occlusal factors in the aetiology of sleep bruxism. Recent publications suggest that sleep bruxism is secondary to sleep-related micro-arousals (defined by a rise in autonomic cardiac and respiratory activity that tends to be repeated 8-14 times per hour of sleep). The putative roles of hereditary (genetic) factors and of upper airway resistance in the genesis of rhythmic masticatory muscle activity and of sleep bruxism are under investigation. Moreover, rhythmic masticatory muscle activity in sleep bruxism peaks in the minutes before rapid eye movement sleep, which suggests that some mechanism related to sleep stage transitions exerts an influence on the motor neurons that facilitate the onset of sleep bruxism. Finally, it remains to be clarified when bruxism, as a behaviour found in an otherwise healthy population, becomes a disorder, i.e. associated with consequences (e.g. tooth damage, pain and social/marital conflict) requires intervention by a clinician.

Freqüência de relatos de parafunções nos subgrupos diagnósticos de DTM de acordo com os critérios diagnósticos para pesquisa em disfunções temporomandibulares (RDC/TMD)

INTRODUÇÃO: as disfunções temporomandibulares (DTM) podem ser definidas como um conjunto de condições dolorosas e/ou disfuncionais, que envolvem os músculos da mastigação e/ou as articulações temporomandibulares (ATM). Um dos meios usados para o diagnóstico é o "Critério Diagnóstico para Pesquisa em Disfunções Temporomandibulares" (RDC/TMD). Hábitos parafuncionais são aqueles não relacionados à execução das funções normais do sistema estomatognático. O bruxismo é caracterizado por atividade parafuncional noturna involuntária dos músculos mastigatórios, enquanto o apertamento dentário é considerado uma parafunção diurna envolvendo esta musculatura, embora possa ocorrer também à noite. OBJETIVOS: o objetivo do presente estudo foi avaliar a freqüência do relato de parafunções orais diurna e/ou noturna em pacientes com DTM nos diferentes subgrupos diagnósticos do RDC/TMD. METODOLOGIA: foram utilizados dados provenientes de 217 pacientes que procuraram tratamento na Clínica de DTM e Dor Orofacial da Faculdade de Medicina de Petrópolis, sendo avaliados através do questionário e exame físico que compõem o RDC/TMD. RESULTADOS: dos 182 pacientes com DTM estudados, 76,9% relataram algum tipo de parafunção, podendo ser diurna, noturna ou a associação de ambas. A parafunção diurna foi a mais freqüentemente relatada entre os subgrupos de DTM, sendo encontrada em 64,8% dos casos contra 55,5% dos casos com relato de bruxismo. O relato de ambas as parafunções foi constatado em 43,4% dos pacientes com DTM. CONCLUSÕES: considerando cada subgrupo diagnóstico, os relatos de parafunções diurna e noturna foram mais freqüentes nos pacientes com dor miofascial.

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.

Anxiety symptoms in clinically diagnosed bruxers

The present work was an attempt to investigate for the existence of an association between anxiety psychopathology and bruxism. The presence of bruxism was investigated according to validated clinical criteria in 98 subjects, who also filled out a self-report questionnaire (PAS-SR) for the assessment of panic-agoraphobic spectrum. 34.7% (n = 34) of participants were diagnosed as bruxers. The prevalence of anxiety psychopathology was similar between bruxers and non-bruxers, but Mann-Whitney U-test revealed significant differences in total PAS-SR (P = 0.026) score, indicating that subclinical symptoms of the anxiety spectrum might differentiate bruxers from controls. In particular, significant differences emerged in scores of domains evaluating panic (P = 0.039), stress sensitivity (P = 0.006) and reassurance sensitivity symptoms (P = 0.005) of panic-agoraphobic spectrum. Support to the existence of an association between bruxism and certain psychopathological symptoms has been provided.

On the pharmacotherapy of sleep bruxism: placebo-controlled polysomnographic and psychometric studies with clonazepam

OBJECTIVES

Sleep bruxism (SB) is a parasomnia defined as a stereotyped movement disorder characterized by grinding or clenching of the teeth during sleep. Pathophysiologically, SB is the result of biological and psychosocial influences. Treatment comprises behavioral, orthodontic and pharmacological interventions. While benzodiazepines and muscle relaxants have been reported by clinicians to reduce bruxism-related motor activity, placebo-controlled studies are lacking. Thus, the aim of the present study was to investigate the acute effects of clonazepam (Rivotril) as compared with placebo, utilizing polysomnography and psychometry.

METHOD

Ten drug-free outpatients (6 females, 4 males), aged 46.5 +/- 13.1 years, suffering from SB (ICD-10: F45.8; ICSD: 306.8) and having been treated by bite splints were included in the trial. Comorbidity was high: 7 patients presented nonorganic insomnia related to adjustment or anxiety disorders (5 patients) or depression (2 patients); all patients had a concomitant movement disorder (6 restless legs syndrome, 4 periodic leg movement disorder). After one adaptation night, patients received placebo and 1 mg clonazepam 1/2 hour before lights out in a single-blind, nonrandomized study design. Objective sleep quality was determined by polysomnography, subjective sleep and awakening quality by rating scales, objective awakening quality by psychometric tests. Clinical evaluation was based on the Pittsburgh Sleep Quality Index (PSQI), the Zung Depression (SDS) and Anxiety (SAS) Scales, the Quality of Life Index, the Epworth Sleepiness Scale and the International Restless Legs Syndrome Study Group (IRLSSG) Scale.

RESULTS

On admission, SB patients exhibited deteriorated PSQI, SAS, SDS and IRLSSG measures. As compared with placebo, 1 mg clonazepam significantly improved the mean bruxism index from 9.3 to 6.3/h of sleep. Furthermore, it significantly improved the total sleep period, total sleep time, sleep efficiency, sleep latency and time awake during the total sleep period, and increased stage 2 sleep and movement time. Periodic leg movements decreased significantly, while the apnea index and apnea-hypopnea index increased marginally, but remained within normal limits. Subjective sleep quality improved as well, while in mood, performance and psychophysiology no changes were observed.

CONCLUSION

Acute clonazepam therapy significantly improved not only the bruxism index but also objective and subjective sleep quality, with unchanged mood, performance and psychophysiological measures upon awakening, suggesting good tolerability of the drug.

Psychic and occlusal factors in bruxers

BACKGROUND

The aim of this study was to investigate the existence of associations between bruxism and psychic and occlusal factors.

METHODS

Participants in this study (n=85) were recruited from the Section of Odontostomatology, Deparent of Neuroscience, University of Pisa, Italy. They were split into two groups, bruxers (n=34) and non-bruxers (n=51), on the basis of the presence of both clinical and anamnestical indicators of bruxim. All participants were administered two self-reported validated questionnaires to evaluate (MOODS-SR) and panic-agoraphobic (PAS-SR) spetra. A number of occlusal variables (deep-bite: cross-bite, open-bite, mediotrusive and laterotrusive interferences, slide RCP-ICP, laterotrutsive guides, canine and molar classes) were also recorded.

RESULTS

With regards to occlusal factors, the only association was revealed between bruxism mediotrusive interferences (p < 0.05). As for psychiatric investigation, significant differences between bruxers and controls emerged for the presence of both depressive (p < 0.01) and manic symptoms (p < 0.01) in MOODS-SR, and for stress sensitivity (p < 0.01), anxious expectation (p < 0.05), and reassurance sensitivity symptoms (p < 0.05) in PAS-SR. In particular, both mood (p < 0.01) and panic-agoraphobic (p < 0.05) spectra symptoms seem to differentiate bruxers from controls in males, while in females strong differences emerged for stress sensitivity symptoms (p < 0.05).

CONCLUSIONS

It can be confirmed that certain psychic traits are present in bruxers, while occlusal factors are not useful parameters to discern bruxers from non-bruxers.

Neurobiological mechanisms involved in sleep bruxism

Sleep bruxism (SB) is reported by 8% of the adult population and is mainly associated with rhythmic masticatory muscle activity (RMMA) characterized by repetitive jaw muscle contractions (3 bursts or more at a frequency of 1 Hz). The consequences of SB may include tooth destruction, jaw pain, headaches, or the limitation of mandibular movement, as well as tooth-grinding sounds that disrupt the sleep of bed partners. SB is probably an extreme manifestation of a masticatory muscle activity occurring during the sleep of most normal subjects, since RMMA is observed in 60% of normal sleepers in the absence of grinding sounds. The pathophysiology of SB is becoming clearer, and there is an abundance of evidence outlining the neurophysiology and neurochemistry of rhythmic jaw movements (RJM) in relation to chewing, swallowing, and breathing. The sleep literature provides much evidence describing the mechanisms involved in the reduction of muscle tone, from sleep onset to the atonia that characterizes rapid eye movement (REM) sleep. Several brainstem structures (e.g., reticular pontis oralis, pontis caudalis, parvocellularis) and neurochemicals (e.g., serotonin, dopamine, gamma aminobutyric acid [GABA], noradrenaline) are involved in both the genesis of RJM and the modulation of muscle tone during sleep. It remains unknown why a high percentage of normal subjects present RMMA during sleep and why this activity is three times more frequent and higher in amplitude in SB patients. It is also unclear why RMMA during sleep is characterized by co-activation of both jaw-opening and jaw-closing muscles instead of the alternating jaw-opening and jaw-closing muscle activity pattern typical of chewing. The final section of this review proposes that RMMA during sleep has a role in lubricating the upper alimentary tract and increasing airway patency. The review concludes with an outline of questions for future research.

Prevalence of bruxism awareness in a Sardinian population

1014 subjects on the island of Sardinia (Italy) were interviewed regarding the habit of clenching and grinding their teeth. They had to specify if this activity occurred during the day, during the night, or both. Other information recorded was their age, gender, marital status, and occupation. Overall prevalence of bruxism was 27.2% (276 subjects). No association was found between bruxism and age, gender and job. Even differentiating diurnal, nocturnal, diurnal and nocturnal bruxism, associations were non-significant. Marital status seems to make some difference: divorced people reported higher parafunctional activity compared to widows and widowers who reported the least. Although awareness of bruxism is not a precise measure of parafunction, based on the results we cannot support the role of stress on bruxism etiology.

The significance of saliva during sleep and the relevance of oromotor movements

Saliva is an essential component of the oroesophageal milieu and allows for normal speech, taste, mastication, food bolus formation and swallowing. Saliva has important functions in protecting the hard and soft tissues of the oral cavity from acids and pathogenic microbes. A large number of people suffer either subjective or objective alterations in quantity and/or quality of their saliva that may be secondary to disease, medications, medical treatments or emotional events. Sleep-related xerostomia is a sensation of dry mouth associated with a report of either mouth and/or throat discomfort that induces awakenings for water intake. The prevalence of self-reported dry mouth complaint during sleep (associated with awakening and water intake) in a Canadian survey was estimated at 23%. The biological significance of decreased saliva during sleep is unknown and it is unclear how the oral cavity compensates for this period of relative dryness. The amount of saliva produced is greatest during the waking hours of the day and diminishes dramatically during sleep and may represent another process in the human body that displays a circadian rhythmicity. Salivary secretion during wakefulness is, in part, associated with oromotor activity involving the masticatory muscles. Rhythmic masticatory muscle activity and swallowing are non-disruptive events that occur during normal sleep. We hypothesize herein that lubrication from saliva is necessary during sleep to protect tissue integrity and health of oroesophageal structures.

Lower number of K-complexes and K-alphas in sleep bruxism: a controlled quantitative study

OBJECTIVES

Although patients with sleep bruxism (SB) show a higher incidence of rhythmic masticatory muscle activity (RMMA) during sleep than matched normal controls, they are good sleepers. Sleep macrostructure (e.g. total sleep time, sleep latency, number of awakenings or sleep stage shifts and sleep stage duration) is similar between groups. Differences in sleep microstructure between SB patients and normals have been investigated only in few studies. The aim of the present study was to quantify number of microarousals, K-complexes, K-alphas, EEG spindles, and the density of slow wave activity, in both groups, in order to better understand the pathophysiology of SB.

METHODS

Ten normal sleepers were matched for age and gender with 10 patients who exhibited frequent tooth-grinding during sleep. Using quantitative polysomnographic measures, we compared the above-mentioned sleep variables in both groups. Data are presented as indices for total sleep and for consecutive non-rapid eye movement (non-REM) episodes over non-REM to rapid eye movement (REM) cycles and per hour of sleep.

RESULTS

SB patients showed 6 times more RMMA episodes per hour of sleep than normals (P<0.001), with a higher frequency in the second and third non-REM to REM cycles. SB patients presented 42.7% fewer K-complexes per hour of stage 2 sleep, but only normals showed a decline from the first to fourth non-REM episode. Only 24% of SB-RMMA episodes were associated with K-complexes in 60 s. The number of K-alphas was 61% lower in SB patients, no change across non-REM episodes was noted. While no difference in electroencephalographic (EEG) spindles or slow wave activity (SWA) was observed between groups, EEG spindles increased and SWA decreased linearly over consecutive non-REM to REM cycles.

CONCLUSIONS

According to our observations, good sleep in SB patients is characterized by a low incidence of K-complexes or K-alphas and by the absence of any difference in other sleep microstructure variables or SWA.

Variability in sleep bruxism activity over time

Sleep bruxism (SB) is an oral activity associated with jaw movements and tooth grinding. Sleep bruxism is believed to be highly variable over time, with subjects showing no activity on some nights and intense activity on others. Assessment of SB variability in individual patients is necessary for clinical trials designed to estimate the efficacy of SB management strategies. The present study analysed SB night-to-night variability over time in nine moderate to severe SB patients. Excluding the first night for habituation, a total of 37 nights were analysed, with a range of 2-8 nights per subject. The interval between the first and the last recording was between 2 months and 7.5 years. The outcomes were the number of SB episodes per hour, number of SB bursts per hour and number of SB episodes with grinding noise. The within subject variability of the three SB oromotor outcomes was evaluated using standard deviation (SD) and coefficient of variation. To verify the diagnosis of subjects over time, the values of the oromotor outcomes were compared with a standard research diagnostic cut-off: (1) Number of SB episodes per hour >4, (2) Number of SB bursts per hour >25, (3) Number of SB episodes with noise per night >1 (Lavigne et al. 1996). The mean coefficient of variation for the nine subjects was 25.3% for SB episodes per hour, 30.4% for SB bursts per hour and 53.5% for episodes with noise. Linear regression showed that the number of SB episodes per hour of stages 1 and 2 explains a large proportion of the variability. The SB diagnosis remained constant over time for every subject: 35 nights over 37 respected criteria 1 and 2, while grinding was present every night. These results indicate that while the SB diagnostic remains relatively constant over time in moderate to severe sleep bruxers, individual variability could be important in some SB patients.

Double-blind, crossover, placebo-controlled trial of bromocriptine in patients with sleep bruxism

This study was designed to assess the effects of bromocriptine, a dopamine D2 receptor agonist, on sleep bruxism. Seven otherwise healthy patients with severe and frequent sleep bruxism participated in this randomized, double-blind, placebo-controlled study. The study used a crossover design that included 2 weeks of active treatment or placebo with a washout period of 1 week. To further evaluate whether bromocriptine influences striatal D2 receptor binding, we used iodine-123-iodobenzamide single photon emission computed tomography (SPECT) under both placebo and bromocriptine regimens. Bromocriptine did not reduce the frequency of episodes of bruxism during sleep (mean +/- SEM, 9.0 +/- 1.0 and 9.6 +/- 1.5 bruxism episodes per hour for placebo and bromocriptine, respectively) or the amplitude of masseter muscle contractions (root mean square values, 48.2 +/- 15.5 microV and 46.9 +/- 12.7 microV for placebo and bromocriptine, respectively). SPECT also failed to reveal that either treatment had any influence on striatal D2 binding (values for total binding in counts/pixel, 1.80 [1.72-1.93] and 1.79 [1.56-1.87] for placebo and bromocriptine, respectively). This study shows that a nightly dose of bromocriptine does not exacerbate or reduce sleep bruxism motor activity.