Masticatory muscle hypertrophy (MMH) is a rare clinical phenomenon of uncertain etiology, characterized by a soft swelling near the angle of the jaw. This abnormal enlargement of the masseter muscle can alter the facial profile, leading to aesthetic concerns. Moreover, MMH may also have significant functional repercussions, including pain in the masseter region, often associated with temporomandibular disorders, fatigue, and discomfort during mastication. Non-conservative approaches offer an effective and minimally invasive solution by inducing localized muscle relaxation and reducing hypertrophy. Botulinum neurotoxin type A (BoNT/A) represents a therapeutic option for managing MMH, considering that injections can effectively reduce the masseter muscle volume, improving both facial aesthetics and related symptoms. Currently, the standard non-surgical management of MMH is BoNT/A injections, although consensus on the average dosage has not been definitely reached; on the other hand, there are data available in the literature about the injection technique of BoNT/A for lower face contouring. Therefore, the present comprehensive review aimed at exploring in detail the role of BoNT/A in the treatment of masseter muscle hypertrophy, describing its mechanism of action, the administration protocols, the clinical effects, and any side effects.

Dentistry Unit Department of Health Sciences University of Catanzaro Magna Graecia 88100 Catanzaro Italy

Department of Biomedical and Biotechnological Sciences University of Catania 95123 Catania Italy

Department of Medicine Surgery and Dentistry University of Salerno 84081 Baronissi Salerno Italy

Department of Rehabilitation and Sports Medicine 2nd Faculty of Medicine Charles University and University Hospital Motol 15006 Prague Czech Republic

Department of Rehabilitation Medicine 1st Faculty of Medicine Charles University and General University Hospital Prague 12800 Prague Czech Republic

Fondazione Policlinico Universitario Campus Bio Medico Via Alvaro del Portillo 200 00128 Roma Italy

Physical Medicine and Rehabilitation Department of Medical and Surgical Sciences University of Catanzaro Magna Graecia 88100 Catanzaro Italy

Physical Medicine and Rehabilitation Unit Department of Neurosciences ASST Carlo Poma 46100 Mantova Italy

Private Practice 10121 Turin Italy

Private Practice 90142 Palermo Italy

Rehabilitation Unit AOU Policlinico G Rodolico San Marco 95123 Catania Italy

Research Center on Musculoskeletal Health University of Catanzaro Magna Graecia 88100 Catanzaro Italy

Research Unit of Orthopaedic and Trauma Surgery Department of Medicine and Surgery Università Campus Bio Medico di Roma Via Alvaro del Portillo 21 00128 Roma Italy

Unità Spinale Unipolare Azienda Ospedaliera per le Emergenze Cannizzaro 98102 Catania Italy

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