title: Topography of the masseter muscle in relation to treatment with botulinum toxin type A.
abstract: 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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  The center of compartment VI is the safest and most efficient injection site for botulinum toxin type A into the masseter muscle.
authors.affiliation: Division in Anatomy and Developmental Biology, Department of Oral Biology, Yonsei University College of Dentistry, Seoul, Korea.
authors.forename: Kyung-Seok
authors.initials: KS
authors.lastname: Hu
authors.forename: Seong-Taek
authors.initials: ST
authors.lastname: Kim
authors.forename: Mi-Sun
authors.initials: MS
authors.lastname: Hur
authors.forename: Ju-Hyun
authors.initials: JH
authors.lastname: Park
authors.forename: Wu-Chul
authors.initials: WC
authors.lastname: Song
authors.forename: Ki-Seok
authors.initials: KS
authors.lastname: Koh
authors.forename: Hee-Jin
authors.initials: HJ
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage*; D002102:Cadaver; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular / Q000379:methods; D008297:Male; D008340:Mandibular Nerve / Q000033:anatomy & histology; D008406:Masseter Muscle / Q000033:anatomy & histology* / Q000098:blood supply / Q000294:innervation; D008875:Middle Aged; D009465:Neuromuscular Agents / Q000008:administration & dosage*; D010306:Parotid Gland / Q000033:anatomy & histology; D012449:Safety
chemical_list: D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A