title: Effects on craniofacial growth and development of unilateral botulinum neurotoxin injection into the masseter muscle.
abstract: BACKGROUND
  The effects of botulinum neurotoxin type A (BoNT/A) on masseter muscles, when injected for cosmetic purposes (volumetric reduction) or treatment of excessive muscle activity (bruxism), have been investigated. However, the full anatomic effects of treatment are not known, particularly with respect to the mandible and relevant anthropometric measurements. The intent of this study was to use unilaterial BoNT/A injections to induce localized masseter atrophy and paresis and then to measure the effects of muscle influence on craniofacial growth and development.
  
  
  METHODS
  Growing male Wistar rats, 30 days old, were studied. The experimental group consisted of 8 rats. One side of the masseter muscle was injected with BoNT/A and the other side of the masseter muscle was injected with saline. The side with BoNT/A belonged to 1 group and the side with saline was the sham group. Three rats without injections was the control. After 45 days, the masseter muscles were dissected and weighed. Dry skulls were prepared, and anthropometric measurements determined.
  
  
  RESULTS
  One-way ANOVA showed that the animals maintained their weight in both groups; however, the muscles injected with BoNT/A were smaller than the sham or control muscles. Anthropometric measurements of the bony structures attached to the masseter muscle showed a significant treatment effect.
  
  
  CONCLUSIONS
  After localized masseter muscle atrophy induced by BoNT/A injection, alterations of craniofacial bone growth and development were seen. The results agree with the functional matrix theory that soft tissues regulate bone growth.
authors.affiliation: Graduate Institute of Dentistry, Department of Orthodontics, College of Oral Medicine, Taipei Medical University and Hospital, Taipei, Taiwan. cytsai@tmu.edu.tw
authors.forename: Chi-Yang
authors.initials: CY
authors.lastname: Tsai
authors.forename: Wan Chi
authors.initials: WC
authors.lastname: Chiu
authors.forename: Yi-Hsuan
authors.initials: YH
authors.lastname: Liao
authors.forename: Chih-Mong
authors.initials: CM
authors.lastname: Tsai
mesh_terms: D000818:Animals; D001284:Atrophy; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage / Q000494:pharmacology*; D002508:Cephalometry; D003393:Cranial Sutures / Q000473:pathology; D005147:Facial Bones / Q000187:drug effects / Q000254:growth & development* / Q000473:pathology; D007273:Injections, Intramuscular; D008297:Male; D008334:Mandible / Q000473:pathology; D008406:Masseter Muscle / Q000187:drug effects* / Q000473:pathology; D008437:Maxilla / Q000473:pathology; D008445:Maxillofacial Development / Q000187:drug effects*; D009465:Neuromuscular Agents / Q000008:administration & dosage / Q000494:pharmacology*; D009915:Orbit / Q000473:pathology; D009929:Organ Size; D010291:Paresis / Q000139:chemically induced / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar; D012886:Skull / Q000187:drug effects / Q000254:growth & development* / Q000473:pathology; D013701:Temporal Bone / Q000473:pathology; D015050:Zygoma / Q000473:pathology
chemical_list: D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A