INTRODUCTION SLEEP BRUXISM IS DEFINED AS A STEREOTYPED MOVEMENT DISORDER CHARACTERIZED BY TOOTH GRINDING DURING SLEEP AND HAS BEEN PLACED IN THE PARASOMNIA SEC- TION ACCORDING TO THE INTERNATIONAL CLASSIFICATION OF SLEEP DISORDERS.1 Bruxism

SLEEP BRUXISM IS DEFINED AS A STEREOTYPED MOVEMENT DISORDER CHARACTERIZED BY TOOTH GRINDING DURING SLEEP AND HAS BEEN PLACED IN THE PARASOMNIA SECTION ACCORDING TO THE INTERNATIONAL CLASSIFICATION OF SLEEP DISORDERS.1 Bruxism has also been considered to be a parafunction2 because it afflicts approximately 10% of the general population, causing abnormal tooth wear, fracture, and hypersensitivity; masticatory muscle discomfort; and pain or temporomandibular disorders.3,4 However, the mechanism that generates bruxism remains unknown. In order to study sleep bruxism, Lavigne et al5-7 focused their attention on rhythmic masticatory muscle activity (RMMA) during sleep. In patients with bruxism, approximately 90% or more of sleep bruxism episodes are RMMA episodes.5-7 Rhythmic masticatory muscle activity is also commonly observed in normal healthy subjects, but its frequency in normal subjects is significantly lower than in patients with bruxism.5-7 In addition, it has been recently reported that RMMA is secondary to micro-arousal6,8,9; RMMA often occurs in the supine position and is often associated with swallowing during sleep.7 Interestingly, among various phenomena occurring during sleep in humans, nocturnal gastroesophageal reflux (GER) has been found to be closely associated with sleep arousal such as micro-arousal,10,11 supine position,12 and swallowing for esophageal lubrication (ie, acid clearance).11,13-15 Furthermore, sleep bruxism and GER are known to have several common features. For example, sleep bruxism and GER have been separately reported to be more prevalent in children than in adults3,16; bruxism and GER disease (GERD) also have separately been reported to be associated with obstructive sleep apnea,17,18 smoking,18,19 drinking of coffee18,20 and alcohol,18,21 and psychologic stress.18, 22 In addition, the concordance rate for sleep bruxism in monozygotic twins has been reported to be higher than in dizygotic ones,23 and a similar finding has also been reported for GERD. 24 The purpose of this study was to test the hypothesis that nocturnal bruxism is associated with nocturnal GER by examining the relationship between RMMA and GER episodes and by performing a double-blind, placebo-controlled, clinical trial with a gastric–acid-inhibiting drug (ie, a drug commonly used for the treatment of GERD).