To determine differences in masticatory muscle usage between temporomandibular joint disorders diagnostic groups.Setting and sample population —
Seventy-one informed and consented subjects (27 men; 44 women) participated at the University at Buffalo.Material and methods —
Research diagnostic criteria and imaging data were used to categorize subjects according to the presence/absence (+/−) of TMJ disc placement (DD) and chronic pain (P) (+DD+P, n = 18; +DD−P, n = 14; −DD−P, n = 39). Electromyographic (EMG)/bite-force calibrations determined subject-specific masseter and temporalis muscle activities per 20 N bite-force (T20N, μV). Over 3 days and nights, subjects collected EMG recordings. Duty factors (DFs, % of recording time) were determined based on threshold intervals (5–9, 10–24, 25–49, 50–79, ≥80% T20N). ANOVA and Tukey–Kramer post hoc tests identified 1) diagnostic group differences in T20N and 2) the effects of diagnostic group, gender, time and interval on muscle DFs.Results —
Mean (± SE) temporalis T20N in +DD+P subjects was significantly higher (71.4 ± 8.8 μV) than masseter T20N in these subjects (19.6 ± 8.8 μV; p = 0.001) and in −DD−P subjects (25.3 ± 6.0 μV, p = 0.0007). Masseter DFs at 5–9% T20N were significantly higher in +DD−P women (3.48%) than +DD−P men (0.85%) and women and men in both other diagnostic groups (all p < 0.03), and in +DD+P women (2.00%) compared to −DD−P men (0.83%; p = 0.029). Night-time DFs at 5–9% T20N in +DD−P women (1.97%) were significantly higher than in −DD−P men (0.47%) and women (0.24%; all p < 0.01).Conclusions —
Between-group differences were found in masticatory muscle activities in both laboratory and natural environmental settings.