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

Purpose Rhythmic 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. Methods Twelve 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. Results SpO2 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 Conclusions The mild transient hypoxia observed before RMMA onset was not associated with a change in ETCO2. The mild and brief oxygen fluctuations before RMMA onset may reflect a physiological response that seems to have little influence on SB genesis.

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). Methods Twenty-two subjects (age: 24.1 ± 1.9 years; F 8: M 14; BMI: 20.2 ± 1.9 kg/m2) were polysomnographically diagnosed as moderate-severe SB. Sleep architecture, oromotor (RMMA and non-specific masseter activity [NSMA]) and apnea/hypopnea events were scored. Results All subjects showed normal sleep architecture whereas 6 exhibited respiratory events at a mild level of OSA. In all subjects, RMMA predominantly occurred in Stage N1 + N2 while NSMA occurred in Stage N1 + N2 (approximately 60 %) and in Stage R (up to 30 %). Up to 50 % of respiratory events were scored in Stage R. RMMA occurred more frequently in close association (e.g., within 10 s) with respiratory events in 6 subjects with OSA than those without. The percentage of RMMA occurring closely to respiratory events was positively correlated with apnea–hypopnea index (AHI) in Stage N1 + N2 only while that of NSMA was positively correlated with AHI in Stage N1 + N2 and Stage R. A sub-analysis in 6 subjects with OSA, RMMA after respiratory events was followed to arousals while those before respiratory events were mostly associated with central apnea. Conclusions A subpopulation of young SB subjects can show concomitant respiratory events. Further large sample studies are needed to demonstrate that the occurrence of subclinical respiratory events represents a clinical subtype of SB.

Occlusal overload during sleep is a significant clinical issue that has negative impacts on the maintenance of teeth and the longevity of dental prostheses. Sleep is usually viewed as an ‘out-of-functional’ mode for masticatory muscles. However, orodental structures and prostheses are not free from occlusal loads during sleep since masticatory muscles can be activated at a low level within normal sleep continuity. Thus, an increase in masticatory muscle contractions, by whatever the cause, can be associated with a risk of increased occlusal loads during sleep. Among such conditions, sleep bruxism (SB) is a type of sleep-related movement disorders with potential load challenge to the tooth and orofacial structures. Patients with SB usually report frequent tooth grinding noises during sleep and there is a consecutive increase in number and strength of rhythmic masticatory muscle activity (RMMA). Other types of masticatory muscle contractions can be non-specifically activated during sleep, such as brief contractions with tooth tapping, sleep talking, non-rhythmic contractions related to non-specific body movements, etc.; these occur more frequently in sleep disorders. Studies have shown that clinical signs and symptoms of SB can be found in patients with sleep disorders. In addition, sleep becomes compromised with aging process, and a prevalence of most sleep disorders is high in the elderly populations, in which prosthodontic rehabilitations are more required. Therefore, the recognition and understanding of the role of sleep disorders can provide a comprehensive vision for prosthodontic rehabilitations when prosthodontists manage complex orodental cases needing interdisciplinary collaborations between dentistry and sleep medicine.

Purpose Dentists may encounter patients who present with a sense of a malocclusion but in whom no objective findings can be detected. For the patient who insists that there is occlusal discomfort, in the absence of evidence some dentists elect to perform an occlusal adjustment that not only fails to alleviate symptoms, and may, in fact, exacerbate the discomfort. The patient–dentist relationship is then likely compromised because of a lack of trust. Study selection In 2011, the Clinical Practice Guidelines Committee of the Japan Prosthodontic Society formulated guidelines for the management of occlusal discomfort. When formulating clinical practice guidelines, the committee bases their recommendations on information derived from scientific evidence. For "occlusal dysesthesia," however, there are an insufficient number of high-quality papers related to the subject. Therefore, a consensus meeting was convened by the Japan Prosthodontic Society to examine evidence in the Japanese- and English-language literature and generate a multi-center survey to create an appropriate appellation for this condition. Results As a result of the consensus meeting and survey findings, this condition may be justifiably termed "occlusal discomfort syndrome." Conclusions The Japan Prosthodontics Society believes that identification of an umbrella term for occlusal discomfort might serve as a useful guide to formulating clinical practice guidelines in the future. This position paper represents summary findings in the literature combined with the results of a multicenter survey focused on dental occlusal treatment and the condition of patients who present with occlusal discomfort syndrome.