Complications of botulinum toxin injection for masseter hypertrophy: Incidence rate from 2036 treatments and summary of causes and preventions.

[BACKGROUND] Masseter hypertrophy is a common, prominent feature in many Asian patients, and correction procedures are often requested for esthetic reasons. Toxin masseter injections have a high efficacy and safety profile, but the risks of a variety of side effects or complications remain.

[OBJECTIVES] The categorization of various complications was based on etiology, with a presentation of the author's own incidence rates for consideration and comparison.

[METHODS] Six hundred and eighty patients received a total of 2036 sessions of toxin injection for masseter hypertrophy from 2011 to 2016, and complications or complaints were recorded through follow-up on a by-treatment basis. Complications were grouped together based on etiology and discussed.

[RESULTS] Of 2036 sessions, temporary mastication force decrease was reported after 611 (30%), bruising after 51 (2.5%), headaches after 12 (0.58%), smile limitation after 3 (0.15%), paradoxical bulging after 10 (0.49%), sunken cheeks (subzygomatic volume loss) after 9 (0.44%), and sagging after 4 (0.20%).

[CONCLUSIONS] Masseter injections remain very safe. To further decrease the incidence rate, injections should only be inside the recommended safety zone, a quadrilateral within the muscle that avoids most important local structures. Keeping injections inside the safe zone, and ideally in 3-4 different locations at least 1 cm from any border, is crucial for the prevention of complications.