HISTOMORPHOMETRIC AND MOLECULAR BIOLOGIC COMPARISON OF BIOACTIVE GLASS GRANULES AND AUTOGENOUS BONE-GRAFTS IN AUGMENTATION OF BONE DEFECT HEALING

The applicability of bioactive glass (BG) granules as a substitute for bone grafts was tested by comparing the histologic, histomorphometric , and molecular biologic healing patterns to those of bone autografts and ungrafted bone defects in a rat model. The cellular response in de fects filled with BG granules was characterized by continuous overexpr ession of type III collagen. Osteogenic mesenchymal cells, prior to th eir differentiation to osteoblasts, organized as a dense periosteumlik e layer on the surface of the BG granules. By day 14 new bone formatio n was more extensive in autografted defects than in BG filled defects (p = 0.039). No cartilage-specific type II collagen mRNA was detectabl e, confirming the uniformity of intramembranous bone formation. The di fference in the initiation of new bone formation was further confirmed by the mRNA analyses of the de novo production of TGF-beta 1 and type I collagen. Autografted defects demonstrated the highest levels of TG F-beta 1 and type I collagen mRNAs during the first 2 weeks of healing , whereas BG-filled defects showed biphasic expression patterns of the same genes. Spontaneous new bone formation in ungrafted bone defects was also characterized by biphasic expression of type I collagen gene. Osteonectin mRNA declined gradually over time in autografted and BG f illed defects, whereas unfilled defects showed a gradual increase of o steonectin mRNA during healing. By 8 weeks, about 70% of the BG surfac e showed evidence of direct new bone contact. Energy-dispersing Xray a nalyses confirmed the presence of silica-rich and CaP-rich zones at th e bonding interface. In conclusion, the osteoconductive surface of bio active glass granules efficiently bonds to ongrowing new bone but the material does not reach the capacity of autogenous bone graft in promo tion of osteogenesis. (C) 1997 John Wiley & Sons, Inc.