Sleep Bruxism （SB）, which has been thought to have various harmful influences to stomatognathic system, is a disease with jaw movement accompanied by excessive occlusal force during sleep. The physiological masticatory muscle activity, which can be observed several times at night even in healthy people, is recently referred to as rhythmic masticatory muscle activity （RMMA） as a biomarker to diagnose SB. Patients who exhibit RMMA over 4 times per hour are diagnosed with SB. It has been suggested that RMMA might be caused by primary factor （brain activation） and/or secondary factor （e.g. sleep apnea, REM behavioral disorder）. During RMMA event, phasic or/and tonic masticatory muscle contractions are performed and jaw movement, such as clenching at eccentric jaw position and grinding exceeding canine edge to edge, are specifically observed by recent studies. These jaw movements may cause various signs （e.g. tooth attrition, masticatory muscle pain）. However, these signs can be due to other multiple factors（ e.g. tooth, daytime oral habits）, so it is hard to establish a causal link between SB and the signs. SB has been diagnosed by electromyography, clinical signs and questionnaire. In order to improve the validity of SB diagnostic methods, grading system is recently applied; polysomnography with audio-video recordings, clinical signs, and questionnaire define “definite,” “probable,” and “possible” SB respectively. Since there is still no definitive treatment for SB, dental clinicians have been performing symptomatic therapy such as splint therapy, pharmacotherapy, and behavioral therapy. Splint therapy is the most commonly used therapy on SB patients, but its potential side effects, e.g. worsening sleep breathing disorder, have been reported. Therefore, behavioral therapy, such as sleep hygiene measure and relaxation, needs to be performed first. Unlink the primary SB, the secondary factor might lead to not only negative effect but also positive influences such as activating secretion or diffusion of saliva in gastroesophageal reflux disease patients and releasing stress. Therefore, for the case caused by the secondary factor, dentists should consult with medical specialists from different fields to review and examine the case.
