Proliferation of masseter myocytes after distraction osteogenesis of the porcine mandible

Purpose: Long-term success of distraction osteogenesis depends on the abili ty of the surrounding soft tissues to tolerate distraction forces and to ad apt to the resulting increase in skeletal length and volume. The hypothesis tested in this study was that mandibular elongation by distraction induces myocyte proliferation. Materials and Methods: Unilateral mandibular angle osteotomies were perform ed in 16 Yucatan minipigs. The hemimandibles were lengthened using semiburi ed distraction devices (Synthes Maxillofacial, Paoli, PA) with 0-day latenc y, 1, 2, or 4 mm/d distraction rates, and a neutral fixation period of twic e the gap size in days. In 2 additional animals, the dissection anti osteot omies were performed, and distraction devices were placed without activatio n (sham control). At the end of neutral fixation, tissues were taken from m asseter muscle overlying the osteotomy and the equivalent region on the uno perated side (contralateral control). Proliferation of myocytes was estimat ed using immunol histochemical localization with antibodies against prolife rating cell nuclear antigen (PCNA). Results: Muscle overlying the distracted mandible showed 6-fold more PCNA-p ositive 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 inde x of PCNA-positive myocytes on both the osteotomy (2%, 5%) and the contrala teral sides (1%, 2%). Conclusions: The results of this study suggest that distraction of the porc ine 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. (C) 200 1 American Association of Oral and Maxillofacial Surgeons.