The effect of multiple botulinum toxin a injections on masticatory muscles in postmenopausal rats on bone loss and muscle atrophy

Objective: The aim of our study was to evaluate the changes in the bone tissue and muscles including the mandibular condyle, coronoid and ramus region by the application of multiple botulinum toxin to the masseter and temporal muscles in rats with osteoporosis induced by ovariectomy. Method: A total of 40 female Wistar rats were used in our study. The subjects were randomly divided into 4 groups, each containing 10 rats. Three of the groups were determined as the experimental group (Group-1, Group-2, Group-3), and one of them was determined as the control group (Group-4). All groups underwent ovariectomy procedure under general anesthesia. 8 weeks after ovariectomy, botulinum toxin A was administered to the rats in Group-1 once, twice to the rats in Group-2, and three times to the rats in Group-3, while no injection was given to the rats in Group-4. Two weeks were waited between multiple injections in Group-2 and Group-3. The rats in group 4 were euthanized with intravenous high-dose thiopental sodium 8 weeks after ovariectomy and 4 weeks after the last injection of botulinum toxin-A to the rats in the study groups. Bilateral muscle and bone samples were evaluated histologically and histomorphometrically to examine the degree of atrophy and effects on bone tissue. Results: Right masseter and temporal mean muscle weights and mean atrophy degrees were significantly different in all paired group analyzes except Group 1-Group 2 and Group 2-Group 3. (p<0.05) In comparisons within the group (right-left), all results were significant except for the temporal muscle weight level in the control group and Group-1. All results were significant except for the atrophy levels in the control group in within-group comparisons. Masseter muscle was more affected than temporal muscle by the number of injections in terms of both muscle weight and degree of atrophy. Changes in bone tissue were not statistically significant. Conclusion: Based on the information obtained from this study, it can be said that the level of atrophy and weight loss caused by BTX-A injections increase in proportion to the number of injections. However, further experimental and clinical studies are needed to better understand the effects of BTX-A injections in bone. Key words: bruxism, botulinum toxin, experimental,postmenopausal osteoporosis