Short-term effects of rhBMP-2-enhanced bone augmentation beyond the skeletal envelope within a titanium cap in rabbit calvarium

Background: Recombinant human bone morphogenetic protein (rhBMP)-2 in a bioabsorbable collagen sponge (ACS) carrier supports significant bone formation. However, histomorphometric data on the augmentation of bone formation beyond the skeletal envelope are insufficient. Our objective was to evaluate the short-term effects of rhBMP-2 on bone augmentation beyond the skeletal envelope within a titanium cap in rabbit calvarium. Methods: Eighteen adult male Japanese white rabbits were used. ACS soak-loaded with rhBMP-2 (100, 500, or 1,000 mu g/ml) was placed at the calvarium; controls were packed with ACS alone. After 1 month, the animals were euthanized, and histologic sections were prepared. Newly generated tissue and mineralized bone areas were measured histomorphometrically and expressed as percentage ratios of the total submembranous space area. Results: At all concentrations, a statistically significant difference in the relative height and amount of newly generated tissue was observed between the experimental and control sites. There was a statistically significant difference in the relative amount of mineralized bone between the experimental and control sites in the 1,000-mu g/ml group, but no statistically significant differences were observed in the 100-mu g/ml and 500-mu g/ml groups. Conclusion: rhBMP-2/ACS has a short-term effect on bone augmentation beyond the skeletal envelope within a titanium cap in rabbit calvarium.