Change of distribution and timing of bite force after botulinum toxin type A injection evaluated by a computerized occlusion analysis system

Abstract

Often it has been observed that botulinum toxin type A has analgesic effects and reduces hyperactivity of injected muscle. However in our clinic, there are some patients who have unilateral chewing habits before botulinum toxin type A injection, but after injection, they indicate both masticatory force become similar. However, there were no study about this effect of botulinum toxin type A. So, we studied about relationship of botulinum toxin type A and distribution of masticatory force.The aim of this study was to determine the force distribution and pattern of mastication after injection of BTX-A into both masseter muscles. The hypothesis to be tested was that the difference between right and left balance of occlusal force diminishes over time following BTX-A injection.Fifteen patients were submitted to BTX-A injection therapy for subjective masseter hypertrophy. A total of 25 U of BTX-A (50 U in total) was injected into two points located 1 cm apart at the center of the lower one-third of both masseter muscles. All of the patients were examined using the T-Scan occlusion analysis system before and 4, 8, 12, and 24 weeks after BTX-A injection.A significant change in force balance was found between the right and left sides over time and the difference between the two sides decreased with the time post-injection, reaching a minimum at 12 weeks. Comparison of the force balance between the anterior and posterior occlusions revealed no significant difference at any of the time points. The occlusion and disclusion times (right and left sides) did not differ significantly with time since BTX-A injection.