Review – Is there an effect on bruxism from botulinum toxin injections?

Background

Botulinum neurotoxin type A (BTA) injection in muscle tissue renders motor nerve filaments unexcitable. The effect gradually wears off and normal neural signalling occurs within 12 weeks. Generally bruxism is not a disorder, but a risk factor for among other extensive tooth wear and implant failures. The bite force is mainly generated by the three jaw closing muscles, masseter, temporalis and medial pterygoid muscles, where the masseter muscle contributes to 43% of the strength.

Aim/Hypothesis

The aim of this review was to evaluate the scientific evidence present today, whether BTA injection influence bruxism, be that less episodes of clenching or less bite force, and if the effect is long-lasting.

Material and Methods

A PICOS question was formed as follow- Population included study groups treated for headache, bruxism, myofascial pain or masseter hypertrophy. Intervention was treatment by botulinum toxin injections of masseter muscles. Control would be pre-injection values and or placebo injections. Outcome would be difference in EMG activity or change in bite force and study design would be RCT, prospective or retrospective studies. To identify relevant articles following databases were used+ PubMed, Web of Science, SCOPUS, Ovid and EBSCO. A manual search were performed for sources from review articles. Case reports, unilateral treatment, botulinum toxin of not type A, patients treated due to systemic diseases or afflictions, or patients treated due to an initial trauma leading to bruxism, and studies scoring less than 3 on the Jadad scale were all excluded.

Results

Initial search results yielded 331 articles. 327 articles were excluded, leaving 4 articles included. In 3 of 4 articles both masseter and temporalis muscles were injected with BTA, in 1 article only the masseter muscle was injected. 1 study measured EMG in awake state. When relaxing the jaw a significant drop in activity was prevalent at day 14 but not day 28. When clenching significant drop was prevalent in the masseter at day 14 but not temporalis at any point. 2 studies measured EMG activity at sleep. One article with one measuring point (4–8 weeks) did not record a significant drop of activity, whereas the other study recorded significant drops at all measuring points, ending at week 12.1 study measured maximal voluntary bite force where there was a significant drop in bite force at all points ending at 6 months, but no significant difference to the control at 6 months, but at 3 months and prior.

Conclusion and Clinical Implications

The available research is inconclusive and does not show enough evidence that bruxism can be treated with BTA injections. However, promising results have been shown in individual studies and further research in this area is needed.