title: Bone and cartilage changes in rabbit mandibular condyles after 1 injection of botulinum toxin.
abstract: BACKGROUND
  Temporary paralysis of the masseter muscle caused by botulinum toxin is a common treatment for temporomandibular disorders, bruxism, and muscle hypertrophy. Loss of masseter force is associated with decreased mandibular mineral density. Our objectives were (1) to establish whether bone loss at the mandibular condyle is regionally specific and (2) to ascertain whether the treatment affects the condylar cartilage.
  
  
  METHODS
  Young adult female rabbits received a unilateral masseter injection of botulinum neurotoxin serotype A (BoNT/A, n = 31), saline solution (n = 19), or no injection (n = 3) and were also injected with bromodeoxyuridine (BrdU), a replication marker. The rabbits were killed at 4 or 12 weeks after treatment. The condyles were processed for paraffin histology. Cortical thickness, cartilage thickness, and trabecular bone areal density were measured, and replicating cells were counted after BrdU reaction.
  
  
  RESULTS
  The BoNT/A rabbits exhibited a high frequency of defects in the condylar bone surface, occurring equally on the injected and uninjected sides. Bone loss was seen only on the side of the BoNT/A injection. Cortical as well as trabecular bone was severely affected. The midcondylar region lost the most bone. Recovery at 12 weeks was insignificant. Condylar cartilage thickness showed no treatment effect but did increase with time. The numbers of proliferating cells were similar in the treatment groups, but the BoNT/A animals showed more side asymmetry associated with the condylar defects.
  
  
  CONCLUSIONS
  Bone loss may be a risk factor for the use of botulinum toxin in jaw muscles.
authors.affiliation: Formerly, graduate student, Department of Orthodontics, School of Dentistry, University of Washington, Seattle, Wash; private practice, Burien and Kent, Wash.
authors.forename: Tori
authors.initials: T
authors.lastname: Matthys
authors.affiliation: Formerly, graduate student, Department of Oral Health Sciences, School of Dentistry, University of Washington, Seattle, Wash; National Hospital of Odonto-Stomagology, Ho Chi Minh City, Vietnam.
authors.forename: Hong An
authors.initials: HA
authors.lastname: Ho Dang
authors.affiliation: Senior lecturer, Department of Orthodontics, School of Dentistry, University of Washington, Seattle, Wash.
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Rafferty
authors.affiliation: Professor, Departments of Orthodontics and Oral Health Sciences, School of Dentistry, University of Washington, Seattle, Wash. Electronic address: herring@uw.edu.
authors.forename: Susan W
authors.initials: SW
authors.lastname: Herring
mesh_terms: D000818:Animals; D000963:Antimetabolites; D015519:Bone Density / Q000187:drug effects; D001862:Bone Resorption / Q000139:chemically induced / Q000473:pathology; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage / Q000494:pharmacology*; D001973:Bromodeoxyuridine; D002358:Cartilage, Articular / Q000187:drug effects* / Q000473:pathology; D002452:Cell Count; D049109:Cell Proliferation / Q000187:drug effects; D005146:Facial Asymmetry / Q000139:chemically induced / Q000473:pathology; D005260:Female; D007273:Injections, Intramuscular; D008335:Mandibular Condyle / Q000187:drug effects* / Q000473:pathology; D008336:Mandibular Diseases / Q000139:chemically induced / Q000473:pathology; D008406:Masseter Muscle / Q000187:drug effects; D009465:Neuromuscular Agents / Q000008:administration & dosage / Q000494:pharmacology*; D010010:Osteoclasts / Q000473:pathology; D011817:Rabbits; D013997:Time Factors
chemical_list: D000963:Antimetabolites; D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A; D001973:Bromodeoxyuridine