Introduction
Temporomandibular disorders (TMDs) are neuromuscular and musculoskeletal disorders affecting the jaw and muscles of mastication, with pain being the most common complaint. Hyperactivity of masticatory muscles is a common background in TMD, which led to the hypothesis that muscle relaxation with botulinum toxin may be a treatment of choice. Botulinum toxin type A (BoNT-A) blocks the release of acetylcholine from the presynaptic membrane, leading to abridged muscle contraction. BoNT-A has also been suggested to have analgesic properties by blocking the release of substance P, glutamate, and calcitonin gene-related peptide (CGRP) [1,2].
Abundant research has shown that BoNT-A injections reduce pain in patients with TMD, providing a new means for treating patients with refractory symptoms [3]. Nevertheless, some studies have reported no improvements of symptoms after treatment [4]. Contradictory results support the multifaceted nature of TMD. Since pain is the main symptom of TMD, most studies have concentrated on the pain-alleviating effect of BoNT-A, and clinical studies applying objective measurable parameters, such as electromyography (EMG), are missing [5]. Accordingly, there is an urgent need for controlled studies that assess subjective complaints and compare these with objective physical findings and provide a long-term follow-up (4-6 months). The TMD treatment response evaluation method presented in this case, including EMG and bite force measurements, provides a good tool for proper evaluation of treatment outcomes, taking into account the variable etiology and manifestation of TMD.