RESUMO
Masseter hypertrophy is a benign condition with variable causative factors, such as bruxism, temporomandibular disorders, malocclusion and others, but has an unclear etiology in the majority of cases. Surgical masseteric resection was the conventional method of treatment for the asymmetric swellings over the ramus and angle of the mandible on one or both sides, in addition to the generally unsuccessful treatments of occlusal adjustment, splint therapy, tranquilizers or others. An effective alternative was the local injection of very small doses of botulinum toxin type A into the masseter. The toxin binds permanently to the motor end plate preventing acetylcholine release causing pre-synaptic neuromuscular blockade, the muscle can be selectively weakened and local paralysis is followed by atrophy of the muscle. Four cases with their follow-up are reported. This technique provided a predictable and conservative method of treatment for this type of facial asymmetry