Paradoxical masseteric bulging after botulinum neurotoxin type A injection
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Updated: Jun 26, 2025

Single-stage Dynamic Reanimation of the Smile in Irreversible Facial Paralysis by Free Functional Muscle Transfer
Published on: March 1, 2015
Shaiba Sandhu1,2, Jeffry Shaefer3,4
1Orofacial Pain, Harvard School of Dental Medicine, Boston, Massachusetts, USA ssandhu@highpoint.edu.
Abstract:
Paradoxical masseteric bulging refers to an unexpected occurrence of masseter muscle bulging or protrusion following the administration of botulinum toxin injections, contrary to the anticipated muscle weakening effect. It may occur secondary to toxin failing to diffuse through the entire masseter muscle due to the presence of an inferior tendon structure within the superficial masseter that divides it into a superficial and deep belly. We report a clinical case of paradoxical masseteric bulging in a female in her late 40s who developed this adverse effect within a week of her masseter botulinum neurotoxin type A injections. We also describe the masseter two-site injection technique for the management of this complication.
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