Restoration of occlusal function using osseointegrated implants in the canine mandible reconstructed by rhBMP-2

Bone morphogenetic proteins have been found to be one of the most promising osteoinductive substances and they are expected to be utilized clinically for the reconstruction of defective mandibles. However, newly formed bone induced by recombinant human bone morphogenetic protein-2 (rhBMP-2) has not yet been proven able to withstand the masticatory force applied by oral implants. In this study, we examined the qualitative changes in an rhBMP-2-induced mandible from the functional force of osseointegrated oral implants. Segmental (30 mm) bone defects were created in the mandibles of beagles. A poly D,L-lactic coglycolic acid-coated gelatin sponge impregnated with rhBMP-2 was grafted to the resected canine mandible. The new bone was formed 8 weeks after surgery and the Brånemark system fixtures were implanted into the reconstructed mandible. After another 8 weeks, the prosthesis was placed over the oral implants. The prosthesis was maintained in occlusion with the opposing natural dentition for 0, 4, 12, 24, or 48 weeks before the animal was euthanized. The quality of regenerated bone was then evaluated histologically and the osseointegration ratio between oral implants and the bonemeasured. During the first 4 weeks, the ratio remarkably increased from 48.9% to 64.5%. After 48 weeks, the ratio approached about 74.5%. The bone loaded for 48 weeks had undergone extensive remodeling and consolidation; its quality was better and maturer than that of bone that was not loaded. These results indicated that the newly formed bone induced by rhBMP-2 was able to withstand the masticatory force applied by oral implants and had become as functionally mature as a natural bone.