James M. Hawkins

Background Botulinum toxin type A (BoNTA) injection into the masticatory muscles has been widely used to treat a number of painful and nonpainful conditions; however, no systematic reviews have been performed on the long‐term effect to the mandibular bone. Objective Our systematic review aimed to evaluate the impact of botulinum toxin injection into the masticatory muscles on mandibular bone based. Methods PubMed, Embase, Ovid, CINAHL and Web of Science were searched for human studies assessing mandibular bone after injection of BoNTA using computed tomography (CT) and cone beam CT (CBCT). Results Seven studies were eligible for review; five reported significant bony changes to one or more areas of the mandible. Most frequently affected were the condylar head, coronoid process and ramus. The most frequent changes were decreased bone volume, cortical thickness and cortical and trabecular density. Conclusions This is the first systematic review to examine an association between BoNTA injection into the masticatory muscles and mandibular bone quality. Data were analysed from a limited number of studies with a small sample size, and the quality of the included studies was very low. While the majority of available evidence suggests BoNTA injection results in bony change, further study is required to confirm a dose‐dependence effect and the impact of gender and age. High‐quality trials should utilise a combination of software analysis and radiologist review, with longer‐term follow‐up to monitor for persistence of bony effect and clinical significance.