A rabbit experimental mandibular defect was reconstructed with rhBMP-2 and atelocollagen gel, and examined using μCT (R_mCT, Rigaku mechatronics, Tokyo) in vivo and histological techniques. Using eight rabbits, we made an experimental mandibular defect and filled it with 1% atelocollagen gel including rhBMP-2 10μg (Astellas Pharma Inc.). In μCT observation, the density was slightly elevated at the bone marrow side at day 5, and the phenomenon gradually expanded during the course of this experiment. Histologically, mesenchymal cell proliferation and immature bone formation occurred at one week, and mature bone gradually increased and filled in at four weeks. The histological data suggests that atelocollagen gel is effective as carrier of rhBMP-2. The μCT observation is extremely useful for follow-up of such reconstruction of animal bone defect model.

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The ability of osteoblasts to form bone greatly diminishes with aging, which may be due to the rise of oxygen-derived free radical formation. However, changes that occur in the mineral crystallinity of bone nodules formed by osteoblasts under conditions of oxidative stress have not been sufficiently clarified. The aim of this study was to elucidate the effects of oxidative stress on osteogenesis. We investigated bone nodule formation in an osteoblast-like cell line, MC3T3-E1, using von Kossa staining and micro-X-ray diffraction (micro-XRD). For the micro-XRD examinations, the bone nodules were analyzed after removal from the culture plate and placed on a slide glass or a silver membrane filter. We found that nodule formation was lower on day 30 following treatment with H₂O₂ and mineral crystallinity in H₂O₂-treated cells was also lower than in the controls. These results suggest that osteoblasts damaged by oxygen free radicals produced during the aging process show a decline in their bone nodule formation ability.

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Mouse mandibular angle development started as a coagulation of mesemchymal cells on the 15^th fetal day. On the 16^th fetal day, cells of the central portion of the cell coagulation showed metachromasia to toluidine blue, and type 2 collagen positive chondrocytes were immunohistochemically detected. After the 17^th fetal day, cartilaginous osteogenesis occurred with invasion of capillaries. At the same stage, membranous (perichondral) ossification occurred in the periphery of the chondrocyte mass. These proliferating chondrocytes showed positive reactions to type 2 collagen, type 1 collagen and osteopontin. These results suggest that the characteristics of mandibular angular cartilage are slightly different from those of normal physiological articular cartilage.

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