Purpose: To investigate the relationships among occlusion time (OT), disocclusion time (DT), occlusal load distributions, and simultaneous electromyographic (EMG) recordings of the anterior temporalis (AT) and masseter (MM) muscles during centric and lateral movements in patients with unilateral temporomandibular disorder (TMD) pain and in asymptomatic control subjects.
Materials and Methods: Twelve healthy and 13 unilateral TMD subjects participated in the present study. The diagnosis of unilateral TMD was verified with joint vibration analysis (JVA) of the temporomandibular joints (TMJs) using BioJVA software. Simultaneous computerized digital occlusal analysis using T-Scan III (Tekscan) and recording of the EMG activity of the MM and TA using BioEMG III (BioResearch Associates) were performed in the intercuspal position and during right and left lateral movements. In intercuspation and lateral movement records, EMG activity of the masticatory muscles, OT, DT, and bite-force distribution ratios were evaluated.
Results: No statistically significant differences were observed in OT, DT, or EMG activity of the MM and TA muscles between controls and patients with unilateral TMD in the intercuspal position. In unilateral TMD patients, DT of the painful side was significantly higher than in the control group and compared to the nonpainful side (P < .05). For lateral movements, bite-force distribution on the nonworking side in TMD patients showed statistically significantly higher values than in control subjects. In controls, the EMG activity of the working-side AT was higher than on the nonworking side and compared to the nonpainful side in TMD patients (P < .05). However, EMG activity of the MM and AT muscles did not show a difference between the working side and nonworking side in the painful side of TMD patients.
Conclusion: In the intercuspal position, there was no difference in OT, distribution of force, or EMG activity of the masticatory muscles observed between the control group and unilateral TMD pain patients. However, in lateral movements, the painful side of the unilateral TMD patients revealed increased nonworking-side AT activity and distribution of force with higher DT.
