Mastering the Masseter Muscle: Tailored Treatment of Masseter Hypertrophy

In the article “Classification of Masseter Hypertrophy for Tailored Botulinum Toxin Type A Treatment” (Plast Reconstr Surg. 2014;134:209e-218e), Xie et al systemically classified and compared degrees of masseter hypertrophy and then prospectively used this system to tailor treatment with botulinum toxin type A. The authors identified 5 different bulging types of a contracted masseter: minimal, mono, double, triple, and excessive. Ultrasound studies and cadaver dissections were used to identify the bulging type and showed that the masseter consists of 3 different muscle layers that exhibit different directions of muscle contraction. These muscle layers are innervated by separate nerve branches that originate from the nervus massetericus, the most prominent part of the masseter bulge corresponding to the distribution region of the nervus massetericus in the central lower one-third region. The authors concluded that an injection close to the nerve endings at this site of insertion would allow for a reduced injection dosage and limited dispersion. Therefore, they chose the most prominent point of the bulging masseter while clenching as the ideal initial injection point.

What’s the issue?

The off-label use of botulinum toxin type A for the treatment of masseter hypertrophy is becoming more popular. It has been used for aesthetic volume reduction of the masseter and lower-face recontouring. Masseter hypertrophy can cause a prominent mandibular angle resulting in a wide counter of the lower face, which can be a cause of aesthetic concern in women and men as well as individuals of many ethnicities, such as those of Asian descent. The reported doses of neurotoxin as well as injection points and techniques vary, making it difficult to translate into clinical practice. Xie et al have suggested a tailored approach to the treatment of masseter hypertrophy rather than injecting in a prototypical approach. The authors had the patient clench and palpated the masseter to classify it into 1 of 5 types. Then the main injection point was into the belly of the most prominent bulge. Further injection points (range, 1–3) were used depending on the type of masseter hypertrophy. The minimal dose of botulinum toxin type A used was 20 U with the highest amount being 40 U. The greatest effect in reduction of masseter hypertrophy occurred at 3 months. Adverse effects encountered were on par with prior reports and included unnatural smile, concavity below the zygomatic arch, and even paradoxical bulging. The overall complication rate was 9.1% (20/220), but it was 60% among patients who received higher doses. With this classification system and injection pattern described, the authors noted a reduction in injection dose and therefore complication rates as well as significantly reduced masseter volume and improved lower face contour (P<.01). When it comes to masseter injections and lower-face shaping, what is your method?

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