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Masseter Muscle Hypertrophy (MMH) is a well-known clinical benign condition that is not gender-specific and it can be monolateral or bilateral. Botulinum Toxin type A (BoNTA) injection has been widely described for MMH treatment and non-surgical facial slimming. BoNTA masseter injections have high efficacy and safety profile, but the risks of side effects remain. Muscular bulging during mastication is a complication due to the superficial overcompensation of masseteric fibers in response to neurotoxic weakening of the deep masseter. We present a biphasic-injection technique for BoNTA administration, based following anatomical concept and developed in order to prevent paradoxical bulging. A total of 98 treatments from 2015 to 2020 were performed with this technique. No remarkable complications occurred in our study. No cases of loss of full smile, difficulty in mouth opening, dizziness, headache, neurapraxia, and xerostomia were reported. A case of asymmetric smiling was self-resolved within a week. No patient claimed transient muscle weakness as distressing. No cases of paradoxical bulging were observed. Extensive knowledge of muscular anatomy and appropriate injection technique are key factors in achieving the desired result and avoiding complications. We feel that sharing this tip could be helpful for all the physicians involved in MMH treatment with BoNTA. [ABSTRACT FROM AUTHOR]

Background: Botulinum toxin type A (BTA) injection is a widely‐used procedure to correct cosmetic problems caused by muscular hyperactivity. "Cobblestone chin" refers to the appearance of remarkable chin creases caused by mentalis contraction. Aims: The aim of this case report is to raise the awareness of paradoxical bulging after BTA injection in mentalis. Patient/Methods: A 26‐year‐old female asked for cosmetic correction of the "cobblestone chin". BTA injection was performed routinely to the mentalis muscle. However, on the second day after injection, an unusual paradoxical bulging at chin was presented. Results: We speculated that the imbalanced relaxation of mentalis caused by improper injection and uneven diffusion of BTA is responsible for the bulging. After a supplementary injection of BTA in the remaining hyperactive muscle fibers based on the ultrasound examination, the bulging was relieved and chin contour improved significantly. Conclusion: Injection of BTA in mentalis should cover the whole thickness of the muscle to prevent imbalanced paralysis and paradoxical chin bulging, especially in severe mentalis hyperactivity cases. [ABSTRACT FROM AUTHOR]

Masseter Muscle Hypertrophy (MMH) is a well-known clinical benign condition that is not gender-specific and it can be monolateral or bilateral. Botulinum Toxin type A (BoNTA) injection has been widely described for MMH treatment and non-surgical facial slimming. BoNTA masseter injections have high efficacy and safety profile, but the risks of side effects remain. Muscular bulging during mastication is a complication due to the superficial overcompensation of masseteric fibers in response to neurotoxic weakening of the deep masseter. We present a biphasic-injection technique for BoNTA administration, based following anatomical concept and developed in order to prevent paradoxical bulging. A total of 98 treatments from 2015 to 2020 were performed with this technique. No remarkable complications occurred in our study. No cases of loss of full smile, difficulty in mouth opening, dizziness, headache, neurapraxia, and xerostomia were reported. A case of asymmetric smiling was self-resolved within a week. No patient claimed transient muscle weakness as distressing. No cases of paradoxical bulging were observed. Extensive knowledge of muscular anatomy and appropriate injection technique are key factors in achieving the desired result and avoiding complications. We feel that sharing this tip could be helpful for all the physicians involved in MMH treatment with BoNTA.

Competing Interests: None.