Absence of joint pain identifies high levels of sleep masticatory muscle activity in myofascial temporomandibular disorder

Abstract

Although the development of reliable diagnostic criteria for temporomandibular disorders (TMDs) has operationalised identification of a subgroup with myofascial pain (mTMD), causal mechanisms remain elusive. This study examines masticatory muscle activity (MMA) in more homogenous research subgroups of mTMD. Data from an existing case-control study of women were used to subcategorise 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. 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 towards elevated prevalence of sleep bruxism. 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 subcategorising of mTMD based on joint pain with palpation (ie 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.

Keywords: EMG; PSG; masticatory muscle activity; muscle-only pain; myofascial TMD; sleep bruxism.

Figure 1.

Comparison of Percent RDC Sleep Bruxism Across Groups P-values for comparison of sleep bruxism between mTMD subgroups and controls are based on Fisher’s exact tests. Sleep bruxism was measured using polysomnography-based Research Diagnostic Criteria for sleep bruxism. mTMD= myofascial temporomandibular disorder; M-pain= mTMD with muscle only pain; MJ-pain= mTMD with muscle and joint pain; Controls= no mTMD.

Figure 2.

Comparison of Percent High Background EMG Across Groups P-values for comparison of high background EMG between mTMD subgroups and controls were based on Fisher’s exact tests. High background EMG was defined as the 4^th quartile of the EMG root mean squared remaining after activity attributable to sleep bruxism and movement artifacts were removed. mTMD= myofascial temporomandibular disorder; M-pain= mTMD with muscle only pain; MJ-pain= mTMD with muscle and joint pain; Controls= no mTMD.