What is the role of botulinum toxin (BTX) injections in the treatment of temporomandibular joint (TMJ) disorders (TMJDs)?

Updated: Jun 19, 2018
  • Author: Anthony H Wheeler, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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TMJDs are described as conditions that affect the temporomandibular joint (TMJ), masticatory muscles, and adjacent structures. Typical symptoms, in addition to jaw pain and TMJ dysfunction, include headache and facial pain. A BTX treatment-effect was evaluated in an open-label, prospective study of 46 patients who were predominately female and had symptomatic facial pain and TMJD due to myofascial and/or joint dysfunction for a median duration of 8 years. [155] Subjects received Botox® 50 U in each masseter and 25 U/5 sites in each temporalis muscle. Improvements in subjective and objective measures of pain and jaw function were demonstrated in most patients (87% and 96%, respectively). Investigators postulated that both peripheral neuromuscular and central neuromodulatory effects were responsible for BTX-induced pain relief.

A randomized, placebo-controlled study examining BTX-A treatment of chronic facial pain associated with masticatory hyperactivity showed a statistically significant improvement of pain in compared with placebo. [156] In contrast, Nixdorf and colleagues completed a double-blind, placebo-controlled crossover trial of BTX-A treatment of chronic moderate-to-severe orofacial pain of myogenic origin. [157] Using the same dosing paradigm as Freund and Schwartz, 25 U of BTX-A were placed into each temporalis muscle, and 50 U were injected into each masseter muscle. Crossover occurred at 16 weeks. The primary outcome variable used was the change in pain unpleasantness and intensity. No significant difference were demonstrated between placebo versus active treatment; however, only 15 patients entered the study, and only 10 patients completed it. These small participant numbers made statistical analysis difficult. Investigators postulated thatbothperipheralneuromuscularandcentralneuromodulatoryeffectswereresponsible for BTX-induced pain relief. [126]

The effect of BTX of prolonged experimental jaw clenching capable of producing pain and muscle fatigue in the human masseter muscle was evaluated. BTX was injected in 19 subjects, and isotonic saline was injected in 16 subjects. [158] Electromyographic activity at maximum voluntary contraction, pressure pain threshold before and after a 70% maximum voluntary contraction, clench sustained to pain tolerance, and the median frequency of the electromyographic power spectrum were measured.

After BTX injection, the BTX-treated group had a reduced maximum voluntary contraction lasting 3 mos and smaller decreases in pressure pain threshold from before to after the sustained clench. Also, the change in median frequency from before to after the sustained clench did not significantly differ during the postinjection sessions. However, postinjection, preclench median frequency was lower in the group injected with BTX. The authors interpret the reduced change in pressure pain threshold with BTX as a clinically modest but statistically significant analgesic effect on this model of acute muscle pain.

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