title: Morphologic and bony structural changes in the mandible after a unilateral injection of botulinum neurotoxin in adult rats.
abstract: OBJECTIVE
  Previous animal experiments showed how reduced masticatory function plays an important role in the craniofacial and mandibular regions in the growing period. However, articles focusing on the effects of reduced masticatory function in adult animals are quite scarce. The purpose of this study was to evaluate the effects of reduced masticatory muscle activity on the jaw bones of adult rats.
  
  
  METHODS
  Botulinum neurotoxin type A (BTX-A) was injected into the left masseter muscle to reduce masticatory muscle function, and sequential changes in the jaw bones were investigated. Ten male 60-day-old Sprague-Dawley rats with a mean body weight of about 300 g were used. The following procedures were performed on each sample: 25 U/mL (0.3 mL) of BTX-A was injected into the left masseter muscle, whereas the right masseter muscle received an equal amount of sterilized saline solution. Ninety days after the procedure, the rats were sacrificed, and the weights of the masseter muscles were recorded. Meanwhile, direct anthropometric measurements were taken, and the cortical thickness, trabecular thickness, and bone mineral content of the skull and mandible were measured. All measurements were evaluated with statistical software.
  
  
  RESULTS
  There were significant differences in all measurements on the BTX-A side compared with those on the control side. The differences included a decreased ramus height, increased gonial angle, and increased crown height of the posterior teeth on the injection side. Significant decreases in the muscle weight, bone mineral content, cortical thickness, and trabecular thickness were also seen on the paralyzed side compared with the non-injection side.
  
  
  CONCLUSIONS
  We found that reduced masticatory function in adult rats affected the weight of the masseter muscle and the bony structure and dentition.
authors.affiliation: Department of Orthodontics, Graduate Institute of Dentistry, 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: Rouh-Yi
authors.initials: RY
authors.lastname: Huang
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Lee
authors.forename: Wen-Tien
authors.initials: WT
authors.lastname: Hsiao
authors.forename: Liang-Yo
authors.initials: LY
authors.lastname: Yang
mesh_terms: D015502:Absorptiometry, Photon; D000818:Animals; D015519:Bone Density / Q000502:physiology; D019274:Botulinum Toxins, Type A / Q000009:adverse effects*; D002508:Cephalometry; D003724:Dental Arch / Q000473:pathology / Q000503:physiopathology; D007273:Injections, Intramuscular; D008297:Male; D008334:Mandible / Q000473:pathology* / Q000503:physiopathology; D008406:Masseter Muscle / Q000187:drug effects* / Q000503:physiopathology; D009498:Neurotoxins / Q000009:adverse effects*; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012886:Skull / Q000473:pathology / Q000503:physiopathology; D013997:Time Factors; D019228:Tooth Crown / Q000473:pathology
chemical_list: D009498:Neurotoxins; D019274:Botulinum Toxins, Type A