Botulinum toxin type A injection into the masticatory muscles and its effects on mandibular bone resorption and density. A systematic review.

[OBJECTIVE] This systematic review aims to summarize and synthesize the evidence that investigates the secondary effects of the application of botulinum toxin (BT) into the masticatory muscles and its effects on bone density.

[MATERIALS AND METHODS] Database searches were conducted until March 19th, 2024. The quality of the studies was assessed by the Cochrane tool risk of bias for the randomized controlled trials and the ROBINS-I tool for non-randomized studies. The Cochrane Grading of Recommendations Assessment Development and Evaluation (GRADE) was used to evaluate the confidence in the overall evidence.

[RESULTS] Five studies looking at the effects of botulinum toxin on bone density and resorption when applied to masticatory muscles were found. No significant changes were observed in most of the studies when looking at the effects of botulinum toxin on mandibular condyle volume, density, mandibular angle thickness, and coronoid process volume. The only finding that was statistically and clinically relevant was the difference between patients who received a double application of BT when compared with patients who received a single application (SMD: -0.99 [95%CI: -1.94,-0.05]) on the volume of the mandibular angle.

[CONCLUSIONS] There is no clear pattern on whether the application of botulinum toxin is associated with bone resorption or not. Although some studies show statistical significance of the findings, the magnitude of the changes in bone density and their clinical significance are not completely clear.

[CLINICAL RELEVANCE] To understand the effectiveness of the use of botulinum toxin into the masticatory muscles and its possible secondary adverse effects on the density of the mandible.