Sleep bruxism and its relation to obstructive sleep apnea-hypopnea syndrome

Sleep bruxism (SB) is a known parasomnia in sleep medicine reported by approximately 8% of the adult population. Sleep bruxism is characterized mainly by rhythmic masticatory muscle activity (RMMA), often associated with powerful tooth grinding. In dentistry, SB has been thought to be associated with tooth wear, dental restoration fractures, masticatory muscle and temporomandibular joint problems. Although pathophysiology of SB remains to be elucidated, recent studies have suggested that SB is a consequence of transient arousals during sleep. Several studies have reported that SB occurs concomitantly in obstructive sleep apnea-hypopnea syndrome (OSAHS) patients. In OSAHS, abnormal respiratory events are associated with arousals. However, SB episodes seem unlikely to be associated with arousals induced by abnormal respiratory events. Compared to wakefulness, oropharyngeal activities decrease during sleep; these are preserved for maintenance of upper airway patency and for protection of the upper alimentary tract. The association between SB and oropharyngeal functions remains to be studied, while several studies have suggested altered oropharyngeal sensory and motor functions in OSAHS. Among various treatment/management strategies, oral appliances are used as an effective and relatively safe option to manage patients with light to moderate OSAHS. In some OSAHS patients undergoing oral appliance therapy, however, oromandibular and intra-oral aversive effects (e.g. orofacial pain/discomfort, oral dryness) have also been reported. Currently, little data is available to clarify the causes of these aversive effects. The aim of this review is to make an overview of SB and to present its physiological and clinical relations to OSAHS. © 2004 Japanese Society of Sleep Research.