LAUSR

BACKGROUND Although development of reliable diagnostic criteria for temporomandibular disorders (TMD) have operationalized identification of a subgroup with myofascial pain (mTMD), causal mechanisms remain elusive. OBJECTIVES This study examines masticatory muscle activity (MMA) in more homogenous research subgroups of mTMD. METHODS Data from an existing case-control study of women were used to subcategorize mTMD cases based on joint pain with palpation to isolate muscle-only pain (M-pain) vs muscle and joint pain (MJ-pain). Differences in laboratory indicators of MMA, specifically research diagnostic criteria for sleep bruxism (SB) and high background EMG activity, and other clinical and sociodemographic indicators were examined between groups. RESULTS Compared to controls, the MJ-pain subgroup did not show elevated background EMG or sleep bruxism. In contrast, the M-pain subgroup showed significantly higher background EMG and a trend toward elevated prevalence of sleep bruxism. CONCLUSIONS These results may explain why it has been difficult for studies of SB in mixed TMD and even mTMD samples to find a consistent positive association, since a positive association may be limited to mTMD without joint pain. The subcategorizing of mTMD based on joint pain with palpation (i.e., M-pain, MJ-pain) appears to reveal subgroups with relatively high and low sleep masticatory muscle-specific activity. Findings need replication in a larger study with updated mTMD diagnostic criteria, but may prove useful for understanding mechanism of pain maintenance in mTMD with and without joint pain. This article is protected by copyright. All rights reserved.