Evaluation of muscle activity and maximum voluntary clenching force in patients with unilateral temporomandibular joint replacement

Objectives: Total alloplastic temporomandibular joint replacement (TMJR) requires detachment of the masseter muscle and often resection of the coronoid process. The present study investigated masticatory muscle activity and maximum voluntary clenching (MVC) force after insertion of a unilateral TMJR.
Materials and methods: Muscle activity of the masseter and temporalis anterior muscles (surface electromyographic – sEMG) and MVC as well as muscle symmetry (POC) were determined on both sides preoperatively (T0) and 1-year postoperatively (T3).
Results: 28 patients (18 females, 10 males; aged 47.25 ± 17.54 years) with preservation of the mandibular angle (MA) (n = 15) and with resection of the MA (n = 10) were studied. In patients with MA, muscle activity increased bilaterally at a constant POC from T0 to T3. In patients without MA, activity increased contralaterally in both muscles. Ipsilaterally, muscle activity increased in the temporalis muscle and remained constant in the masseter muscle. POC showed an increase in the temporalis muscle and a decrease in the masseter muscle. Both groups showed an increase in MVC ipsilaterally and a constant MVC contralaterally.
Conclusion: The anterior fibers of the temporalis muscle were preserved despite resection of the coronoid process. Reattachment of the masseter muscle was likely. In the group with resection of the MA, residual activity/the mimic muscles were probably derived ipsilaterally.