Change of Distribution and Timing of Bite Force after Botulinum Toxin Type A Injection Evaluated by a Computerized Occlusion Analysis System

PURPOSE: The aim of this study was to determine the force distribution and pattern of mastication after injection of botulinum toxin type A (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. MATERIALS AND METHODS: 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 patients were examined using the T-Scan occlusion analysis system before and 4, 8, 12, and 24 weeks after BTX-A injection. RESULTS: 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. CONCLUSION: A decline in the difference in the clenching force between the left and right sides was found with increasing time up to 12 weeks following BTX-A injection.

A Proposal to Prevent the "Mephisto Sign" Side Effect of Botulinum Toxin Type A Injection in Chronic Migraine

Botulinum toxin type A (BoNT-A) has been reported as an effective treatment for chronic migraine. When BoNT-A is injected on the frontalis muscle for chronic migraine, an unexpected clinical side effect called the "Mephisto sign" may occur. The aim of this article is to propose a method to eliminate or prevent the Mephisto sign side effect. A 25-year-old female patient visited the hospital and was diagnosed with chronic migraine. A total of 155 U of BoNT-A was injected into 31 sites. 2-weeks later, and the patient developed the Mephisto sign. An additional 2-U dose was administered bilaterally to the lateral-most point of the frontalis muscles, and the eyebrow morphology returned to normal within 2-3 weeks. We propose that the development of the Mephisto sign may be prevented with an additional BoNT-A injection of 2-4 U bilaterally to the lateral most point of the frontalis muscles during the primary injection process.