A pilot study of ambulatory masticatory muscle activities in temporomandibular joint disorders diagnostic groups

Objective: 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 (T_20N, 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% T_20N). anova and Tukey-Kramer post hoc tests identified 1) diagnostic group differences in T_20N and 2) the effects of diagnostic group, gender, time and interval on muscle DFs. Results: Mean (± SE) temporalis T_20N in +DD+P subjects was significantly higher (71.4 ± 8.8 μV) than masseter T_20N 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% T_20N 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% T_20N 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.