title: The topographic anatomy of the masseteric nerve: A cadaveric study with an emphasis on the effective zone of botulinum toxin A injections in masseter.
abstract: BACKGROUND
  Botulinum toxin injections are previously reported to be a noninvasive alternative method for treating masseteric hypertrophy. However, there is a debate on finding an ideal place for injection. The aim of this study is to document the anatomical landmarks for defining the motor nerve entry points (MNEPs) of the masseteric nerve in the masseter for effective botulinum toxin injections.
  
  
  METHODS
  Twelve sides from six adult fixed cadavers were used for this study. The MNEPs of the masseteric nerve were defined according to standard landmark lines including the orbitomeatal line (OML) and the line (VL), which intersects the mid-distance of the OML to the tip of the angle of the mandible.
  
  
  RESULTS
  All MNEPs were located 4.4 cm inferior to the OML. In addition, the average anterior distance of the MNEPs to the VL was 1.4 cm and the average posterior distance was 0.6 cm.
  
  
  CONCLUSIONS
  The ideal site of Botox injection into the masseter is a rectangular area: 5 cm inferior to the OML, 1 cm anterior and posterior to the VL, and just above the periosteum. Based on the data of our study, injections to the parotid gland and branches of the facial nerve such as the marginal mandibular and buccal can be avoided. The masseteric nerve can easily be found approximately 1.0-1.5 cm inferior to the zygomatic arch, 1 cm medial to the temporomandibular joint capsule, and 1 cm superior to mandibular notch, which makes its use for facial reanimations more efficient.
authors.affiliation: Department of Plastic and Reconstructive Surgery, Ankara University Faculty of Medicine, Ankara, Turkey.
authors.forename: B
authors.initials: B
authors.lastname: Kaya
authors.affiliation: Department of Anatomy, Ankara University Faculty of Medicine, Ankara, Turkey. Electronic address: napaydin@gmail.com.
authors.forename: N
authors.initials: N
authors.lastname: Apaydin
authors.affiliation: Department of Anatomical Sciences, St. George's University, St. George's, Grenada.
authors.forename: M
authors.initials: M
authors.lastname: Loukas
authors.affiliation: Pediatric Neurosurgery Children's Hospital, Birmingham, AL, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Tubbs
mesh_terms: D000368:Aged; D059925:Anatomic Landmarks / Q000033:anatomy & histology*; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage*; D002102:Cadaver; D005260:Female; D006801:Humans; D006984:Hypertrophy / Q000188:drug therapy*; D008297:Male; D008334:Mandible / Q000033:anatomy & histology; D008406:Masseter Muscle / Q000002:abnormalities* / Q000294:innervation*; D008875:Middle Aged; D009465:Neuromuscular Agents / Q000008:administration & dosage*; D013704:Temporomandibular Joint / Q000033:anatomy & histology; D015050:Zygoma / Q000033:anatomy & histology
chemical_list: D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A
keywords: Botulinum toxin; Facial reanimation; Masseter muscle; Masseteric hypertrophy; Masseteric nerve; Motor nerve entry point