| Objective: This study was designed to reveal the mechanism of expression and effect of Bone Morphogenetic Protein2(BMP-2) and basic fibroblast growth factor (bFGF) which result in successful osteogenesis, and to provided evidence for further application of bone growth factors to shorten the long period of distraction osteogenesis(DO), reconstruct bone defect and facilitate bone healing. Methods: Twenty-eight adult dogs were randomly divided into DO group (n=12) ,acute lengthening group(n=12) and normal group(n=4). All the dogs in DO group were underwent bilateral mandibular osteotomy between the first and second molars, and two custom-made distraction devices was fixed in the both two osteotomy regions of each dog. After a lantency period of 7 days post-operation, the distraction devices had been activated at a rate of 1mm per day ,four dogs were respectively sacrificed at days 6 of distraction period, weeks 2,8 of the consolidation after distraction for 10 days. All the dogs in acutely lengthened groups were underwent bilateral mandibular osteotomy as the DO group, both side of the mandible were acutely lengthed 10mm and were fixed by titanium plates, four dogs were respectively sacrificed at the same time of DO group, Callus of distraction gaps , lengthing gaps and the same regions of normal mandible were harvested. The change of histology was observed by HE staining micrograph examination. The spatial and temporal expression patterns of BMP-2 and bFGF were studied using immunohistochemistry. The X-ray examination was taken respectively at The first day, 2, 4, and 8 weeks after completion of distraction.Results: X-ray examination In DO group, The density of new bone was enhanced gradually from both side of osteotomy to the center of distraction gap, and appeared nearly the normal after 8 weeks of consolidation;In acute lengthening group, the rate of ossification appeared slower than DO group and the quantity of new formed bone seemed lesser, at last the center of lengthening gap still appeared low density. HE staining micrograph examination In DO group ,the active intramembranous ossification was seen at the osteotomized bone edges in 6 days of distraction, after 2 weeks of consolidation, the activity of intramembranous ossification was continued represented, accompanied with a few endochondral ossification; after 8 weeks of consolidation, the distraction gaps were nearly completely ossified. In the acutely lengthening group, active intramembranous ossification existed along the osteotomized bone edges in early stage too, but the major mode of new bone formation appeared change to be endochondral ossification after 2 weeks , fibril connective tissue and endochondral tissue were filled in the center area after 8 weeks. Immunohistochemistry In DO group and acutely lengthening group, during the distraction period, the strongly positive stain of BMP-2 and bFGF were both found in the osteoblasts around the newly formed trabecular bone and the bone formation front, mesenchymal cells and fibroblasts from the periosteum and distraction gap and the fibrous collagen. There was no statistic difference between the stain grays of two groups; after 2 weeks of consolidation, the positive stain of BMP-2 and bFGF were found in osteoblasts, cartilaginous tissue and fibrous connective tissue in the distraction gap of DO group, while the positive stain of BMP-2 and bFGF in acutely lengthening group were remarkably weakened. There were statistic difference between the stain grays of two groups (P<0.05); after 8 weeks of consolidation, the stain intensity of BMP-2 and bFGF in the two group were both markedly decreased, only faint positive stain was found in few rudimental cartilaginous tissue, fibroblasts, newly formed bone matrix and osteoblasts around it ,there was no statistic difference between the stain grays of two group(p>0.05). Conclusion: The major mode of new born formation in distraction osteogenesis is intramenbranous ossification, and result in bone union; the major mode of new bone form...
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