The masseters: Hypertrophy, bruxism, and facial shaping with botulinum toxin


Summary and key features

  • The masseter is a powerful muscle of mastication with both aesthetic and functional significance.

  • Masseteric hypertrophy may be associated with bruxism and facial pain syndromes.

  • Botulinum toxin may be used to reduce masseter muscle bulk to nonsurgically shape the lower face.

  • Botulinum toxin may be used to decrease masseter muscle clenching power, potentially alleviating parafunctional grinding and clenching.

  • Knowledge of anatomy and precise injection technique significantly reduces the risk of complications and allows for a tailored treatment approach for each patient.

Introduction

Masseter muscle hypertrophy is the enlargement of one or both masseter muscles. Masseter hypertrophy is most commonly observed between the ages of 20 and 40 years, without gender predilection. It may be apparent as lower facial asymmetry, prominent mandibular angles associated with masculinization, or lower facial heaviness associated with aging, as the resultant lower facial shape is the opposite of the ideal “inverted triangle” of youthful proportions. Although many cases are benign and asymptomatic, masseter hypertrophy has also been associated with pain, bruxism, and functional impairment. Patients are motivated to seek treatment for cosmetic concerns, symptomatic relief, or both.

Successful treatment of masseter muscle hypertrophy with botulinum toxin type A was first described in 1994 by Moore and Wood and by Smyth. Over three decades, the body of literature describing the symptomatic and aesthetic benefits of botulinum toxin has grown, with numerous case reports and clinical studies demonstrating both safety and efficacy of this therapy. However, to date, there are no marketing authorizations for botulinum toxin treatment in the masseter.

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