Objectives: Recently, some polysomnographic studies reported that bruxers with masticatory muscle pain have less sleep bruxism activities than bruxers without pain (Lavigne 1997, Arima 2000). The aim of this study was to compare the severity of tooth wear, which is normally used as indicator of bruxism, between myofacial pain patients and bruxers without pain verifying the previous studies from the other aspect. Methods: Forty-seven female participated in this study. All subjects were divided into the following three groups according to the guideline (LeResche 1992): healthy subjects (Control: n=19, age 22-26), myofacial pain patients (Patient: n=12, age 21-27), and bruxers without pain in craniomandibular region (Bruxer: n=16, age 21-27). A set of maxillomandibular study casts was obtained from each individual. The severities of tooth wear on the casts were scored by a calibrated-blinded examiner using five point ordinal scale (Seligman 1988). Sum totals of scores in maxillomandibular tooth were calculated and compared between the groups. Furthermore, the scores were subdivided into the parts of arch (molar, premolar, canine, and incisor) and were compared between the groups. The data were analyzed with one-way analysis of variance. Significance was accepted at p
<0.05. Results: The sum total of scores in maxillomandibular teeth in Bruxer (67.7
±7.1) showed significantly higher score compared to the other two groups (Control: 60.7
±7.7, p
=0.028, Patient: 60.8
±8.5, p
=0.025). However, Control and Patient was not significantly different (p
=0.968). From the sum total of scores in each part of arch, Bruxer showed significantly higher score especially in molar and premolar (18.6
±2.0 and 18.9
±3.2, respectively) compared to Control (16.9
±1.5 and 15.9
±1.6, respectively: p
<0.009). Conclusion: This cast-quantitative investigation showed that bruxism activities in myofacial pain patients and healthy subjects were less quantity than bruxers without pain. It is, therefore, suggestive that sleep bruxism activity does not always cause masticatory muscle pain supporting the previous studies.