Topography of the masseter muscle in relation to treatment with botulinum toxin type A

OBJECTIVE: The objective of this study was to provide the safest and most efficient site for injection of botulinum toxin type A into the masseter muscle. STUDY DESIGN: This study was performed on 40 hemifaces from cadavers. The surface of the masseter was compartmentalized into areas I to VIII. Areas I, III, V, and VII were assigned to represent the upper 4 compartments from the posterior aspect of each muscle, and areas II, IV, VI, and VIII were assigned to represent the lower 4 compartments. RESULTS: The parotid gland usually covered compartments I and II, and the marginal mandibular branch of the facial nerve was located a mean of 7.4 mm above the inferior mandibular margin. The parotid duct was usually located above the reference line connecting the tragus and the cheilion. CONCLUSION: The center of compartment VI is the safest and most efficient injection site for botulinum toxin type A into the masseter muscle.ope