Purpose: To evaluate the effects of botulinum toxin-A in the treatment of patients who have myofascial pain with or without functional disc displacement.
Patients and methods: Twenty-four participants were randomly assigned to the study by using Research Diagnostic Criteria for Temporomandibular Disorders. All patients were informed about botulinum toxin-A, and were required to give informed consent. Before the injections, patients were asked to fill out a Biobehavioral Questionnaire to evaluate their pain and psychological status, and afterward, electromyography of the right and left masseter and anterior temporal muscles was recorded. Saline was injected into the masseter and anterior temporal muscles in the placebo group, and botulinum toxin-A was used in the study group. On days 14 and 28, patients were asked to fill out a Biobehavioral Questionnaire again, and electromyography of the right and left masseter and anterior temporal muscles was recorded again.
Results: The study group showed improvement in pain and psychological status. Although a decrease in the action potentials of the masseter muscles on day 14 was followed by an increase on day 28, the reduction of pain scores and improvement in psychological status continued on day 28.
Conclusions: The injection of botulinum toxin-A decreases the muscle action potential in 14 days. The patients also show improvement in pain and psychological status.