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Paradoxical masseteric bulging after botulinum neurotoxin type A injection
  1. Shaiba Sandhu1,2 and
  2. Jeffry Shaefer1,3
  1. 1 Orofacial Pain, Harvard School of Dental Medicine, Boston, Massachusetts, USA
  2. 2 Oral Medicine Oncology Orofacial Pain, Workman School of Dental Medicine, High Point University, High Point, North Carolina, USA
  3. 3 Orofacial Pain, Massachusetts General Hospital, Boston, Massachusetts, USA
  1. Correspondence to Dr Shaiba Sandhu; ssandhu{at}


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.

  • Botulinum toxin
  • Dentistry and oral medicine
  • Mouth
  • Anatomic Variation
  • Musculoskeletal and joint disorders

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  • Contributors SS and JS: conception and design, and acquisition of the data; drafting the article or revising it critically for important intellectual content; final approval of the version to be published; agreement to be accountable for the article and to ensure that all questions regarding the accuracy or integrity of the article are investigated and resolved.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.