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

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.

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.

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.

The center of compartment VI is the safest and most efficient injection site for botulinum toxin type A into the masseter muscle.