title: Serial histologic and immunohistochemical changes in anterior digastric myocytes in response to distraction osteogenesis.
abstract: OBJECTIVE
  To document histologic and immunohistochemical changes in the anterior digastric muscle during distraction osteogenesis (DO).
  
  
  METHODS
  Nineteen Yucatan minipigs with mixed dentition were used for these experiments. Group A (n = 16) underwent unilateral mandibular distraction at a rate of 1 mm/day (no latency) for 12 days. Animals were killed at mid-DO (n = 5), end-DO (n = 5), mid-fixation (n = 4), and end-fixation (n = 2). Group B (n = 2) underwent acute 12-mm advancement, and group C (n = 1) dissection and osteotomy. Animals from groups B and C were killed at the end-DO time point. Digastric muscles from treatment and contralateral sides of all animals were harvested and embedded in paraffin. Specimens were stained with hematoxylin/eosin or immunohistochemically for proliferating cell nuclear antigen (PCNA; total cell proliferation), paired Box-7 gene protein (Pax7; satellite cells), or myogenic differentiation 1 protein (MyoD; differentiating myoblasts). Descriptive and bivariate statistics were computed to compare groups (P ≤ .05 statistically significant).
  
  
  RESULTS
  All animals survived the operation and observation period; there were no device failures. Two animals (1 at mid-DO, 1 at mid-fixation) were eliminated from the study because of postoperative infection. There was minimal digastric inflammation, fibrosis, and muscle fiber size variability during active DO. Immunohistochemical analysis showed statistically significant increases in PCNA (cellular proliferation), Pax7 (satellite cells), and MyoD (differentiating myoblasts) positive nuclei in digastrics at mid-DO and end-DO.
  
  
  CONCLUSIONS
  Results of this study indicate that there are minimal pathologic changes but significant increases in PCNA, Pax7, and MyoD positive nuclei during active distraction. This supports the hypothesis that the digastric muscle response to DO consists of proliferation and hypertrophy.
authors.affiliation: Department of Pediatric Oral and Maxillofacial Surgery, Harvard School of Dental Medicine, Boston, MA, USA.
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Lawler
authors.forename: Gentry M
authors.initials: GM
authors.lastname: Hansen
authors.forename: W Bradford
authors.initials: WB
authors.lastname: Williams
authors.forename: Srinivas M
authors.initials: SM
authors.lastname: Susarla
authors.forename: William C
authors.initials: WC
authors.lastname: Faquin
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Troulis
authors.forename: Leonard B
authors.initials: LB
authors.lastname: Kaban
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D049109:Cell Proliferation; D004210:Dissection / Q000379:methods; D005260:Female; D006984:Hypertrophy; D007150:Immunohistochemistry; D008334:Mandible / Q000601:surgery; D018485:Muscle Fibers, Skeletal / Q000166:cytology*; D017570:MyoD Protein / Q000032:analysis; D032448:Myoblasts, Skeletal / Q000166:cytology; D009334:Neck Muscles / Q000166:cytology*; D019857:Osteogenesis, Distraction / Q000295:instrumentation / Q000379:methods*; D010027:Osteotomy / Q000379:methods; D051763:PAX7 Transcription Factor / Q000032:analysis; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D011897:Random Allocation; D032496:Satellite Cells, Skeletal Muscle / Q000166:cytology; D013552:Swine; D013556:Swine, Miniature; D013997:Time Factors
chemical_list: D017570:MyoD Protein; D051763:PAX7 Transcription Factor; D018809:Proliferating Cell Nuclear Antigen