Proliferation of masseter myocytes after distraction osteogenesis of the porcine mandible.
OBJECTIVE
Long-term success of distraction osteogenesis depends on the ability of the surrounding soft tissues to tolerate distraction forces and to adapt to the resulting increase in skeletal length and volume. The hypothesis tested in this study was that mandibular elongation by distraction induces myocyte proliferation.


METHODS
Unilateral mandibular angle osteotomies were performed in 16 Yucatan minipigs. The hemimandibles were lengthened using semiburied distraction devices (Synthes Maxillofacial, Paoli, PA) with 0-day latency, 1, 2, or 4 mm/d distraction rates, and a neutral fixation period of twice the gap size in days. In 2 additional animals, the dissection and osteotomies were performed, and distraction devices were placed without activation (sham control). At the end of neutral fixation, tissues were taken from masseter muscle overlying the osteotomy and the equivalent region on the unoperated side (contralateral control). Proliferation of myocytes was estimated using immunohistochemical localization with antibodies against proliferating cell nuclear antigen (PCNA).


RESULTS
Muscle overlying the distracted mandible showed 6-fold more PCNA-positive myocytes (16.8% +/- 11.3%) than the contralateral control side (2.8% +/- 1.1%, P < .0001). In the 2 sham-control animals, there was a low index of PCNA-positive myocytes on both the osteotomy (2%, 5%) and the contralateral sides (1%, 2%).


CONCLUSIONS
The results of this study suggest that distraction of the porcine mandible by the protocol described induces myocyte proliferation in the masseter muscle. A proliferative response may contribute to improved long-term stability of mandibular expansion by distraction osteogenesis.
Skeletal Biology Research Center and Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, Harvard School of Dental Medicine, Boston 02129, USA.
F J
FJ
Castaño
M J
MJ
Troulis
J
J
Glowacki
L B
LB
Kaban
K E
KE
Yates
D000818:Animals; D002455:Cell Division; D002467:Cell Nucleus / Q000648:ultrastructure; D002508:Cephalometry; D005260:Female; D007150:Immunohistochemistry; D016268:Internal Fixators; D008334:Mandible / Q000473:pathology / Q000601:surgery*; D008406:Masseter Muscle / Q000473:pathology*; D019857:Osteogenesis, Distraction / Q000295:instrumentation / Q000379:methods; D010027:Osteotomy; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D015203:Reproducibility of Results; D018709:Statistics, Nonparametric; D013552:Swine; D013556:Swine, Miniature
D018809:Proliferating Cell Nuclear Antigen