Effect of the masseter muscle injection of botulinum toxin A on the mandibular bone growth of developmental rats.

[BACKGROUND] The objective of this study was to evaluate the influence of masticatory muscle injection of botulinum toxin type A (BTX-A) on the growth of the mandibular bone in vivo.

[METHODS] Eleven Sprague-Dawley rats were used, and BTX-A ( = 6) or saline ( = 5) was injected at 13 days of age. All injections were given to the right masseter muscle, and the BTX-A dose was 0.5 units. All of the rats were euthanized at 60 days of age. The skulls of the rats were separated and fixed with 10% formalin for micro-computed tomography (micro-CT) analysis.

[RESULTS] The anthropometric analysis found that the ramus heights and bigonial widths of the BTX-A-injected group were significantly smaller than those of the saline-injected group ( < 0.05), and the mandibular plane angle of the BTX-A-injected group was significantly greater than in the saline-injected group ( < 0.001). In the BTX-A-injected group, the ramus heights II and III and the mandibular plane angles I and II showed significant differences between the injected and non-injected sides ( < 0.05). The BTX-A-injected side of the mandible in the masseter group showed significantly lower mandibular bone growth compared with the non-injected side.

[CONCLUSION] BTX-A injection into the masseter muscle influences mandibular bone growth.