Avoid asymmetric smile after masseter toxin injections

Key takeaways:

• Asymmetrical smile can occur after masseter botulinum toxin injections.
• Using a longer needle and injecting deep into the muscle can help avoid this complication.

CHICAGO — An asymmetric smile following masseter botulinum toxin injections can be avoided by adhering to a specific technique and keeping injections in the correct location of the muscle.

Botulinum toxin is often used off-label to treat both bruxism and masseter muscle prominence; however, toxin migration to the risorius or zygomaticus major muscle can cause an asymmetric smile effect, Derek Jones, MD, founder and director of Skin Care and Laser Physicians of Beverly Hills, described at the American Society for Dermatologic Surgery Annual Meeting.

In his presentation regarding pearls for cosmetic procedures, Jones outlined tips to avoiding this adverse event, starting with the use of a longer needle to fully reach the muscle.

“When treating the masseter, it’s important to inject deeply into the belly of the muscle,” he said. “Many of us use ultrafine insulin syringes to inject toxin; however, the needle is too short.”

He recommends a 30-gauge, 1-inch needle.

Additionally, he detailed the “safety zone” for masseter muscle injections. He draws four lines on the skin, the first from the tragus to the corner of the mouth, the second from the tragus to the mandibular angle, the third from the mandibular angle to the anterior border of the masseter and the fourth along the anterior border of the masseter.

“I draw these cutaneous landmarks for each treatment I perform, for every patient,” he said. “The safe zone is 1 cm away from each border.”

Dosage can also cause an asymmetric smile, with a dose-ranging trial finding larger doses associated with the adverse event.

“Use long needles, inject intramuscularly, inject in the safety zone and use the most conservative dose that is effective,” Jones said.