Bone regeneration by recombinant human bone morphogenetic protein-2 in ratmandibular defects. An experimental model of defect filling

Background: Bone defects and irregularities are major problems for dental i mplant and periodontal therapies. Methods: We investigated whether the application of recombinant human bone morphogenetic protein-2 (rhBMP-2) induces bone formation in through-and-thr ough bone defects in the rat mandible. A round through-and-through bone def ect (5 mm in diameter) was created in the angle of the mandible on both sid es of the jaw using a steel round bur in each of 8 Long-Evans rats. In the experimental group, polylactic acid-polyglycolic acid copolymer/gelatin spo nge (PGS) containing rhBMP-2 (6 mu g/60 mu l) was inserted in the bone defe ct. In the control group, the same carrier without rhBMP-2 was applied in t he bone defect on the opposite side. Four weeks after application, the rats were sacrificed. Step serial sections stained with hematoxylin and eosin a t intervals of 200 mu m were prepared in a bucco-lingual direction. The siz e of the bone defects and new bone formation were evaluated histometrically . Results: In all cases in the experimental group, a large quantity of newly formed bone was observed. The bone defects were completely filled with new bone in 4 of 8 rats in the experimental group. In the control group, small amounts of new bone formation were observed along the border of the origina l mandibular bone. Histometrical analysis revealed that the amount of new b one was significantly larger in the rhBMP-2 treated sites than in the contr ol sites (P<0.0001; paired t-test). Conclusions: These results indicate that the rhBMP-2/PGS system induced eff ective bone regeneration on mandibular defects in rats. This procedure may be suitable as an experimental model for bone regeneration using various gr owth factors and effective for alveolar ridge augmentation followed by dent al implant surgery.