Methods: Surface EMG (2 Khz sampling rate) was used to measure bilateral masseter, temporalis, and suprahyoid muscles in 27 TMD cases and 26 controls during “baseline”, tongue up, and tongue down experimental conditions. Experimental conditions were measured during block one (2 trials) and, after 30 minutes of induced parafunctional behaviors, during block two (1 trial). Data were reduced off-line, sides were averaged, and trial and block reliability was assessed, followed by 2-way (experimental conditions, groups) repeated-measures ANOVA of the EMG collapsed across the two blocks (alpha 0.05;).
Results: Test-retest EMG reliability within the first block revealed high consistency (r > 0.9) for each muscle, for each of the two controlled tongue conditions in each group. In contrast, between-block EMG reliabilities for the two tongue conditions, while notably lower overall, exhibited generally higher values for the controls (r≈0.7) vs cases (r≈0.5), and both groups exhibited better reliability during instructed tongue conditions (r≈0.7) compared to baseline (r≈0.4). Compared to both tongue positions, the baseline mean for both groups, averaged across muscles, was 10 microvolts higher (p<.05), and the baseline variance was greater (3 to 8 fold, p<.05).
Conclusions: Both tongue positions confer equal advantage for organizing jaw posture and reducing activity, compared to the apparent “normal” state of disorganized postural control of the jaw. Typical jaw posture motor control appears to be more influenced in TMD vs control by other factors that vary across time. Research supported by NIH-DE-13331 and T-35-DE-07106.