Biological Response to Recombinant Human Bone Morphogenetic Protein-2 on Bone-Implant Osseointegration in Ovariectomized Experimental Design.

Objective: The aim of this study is to investigate the effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) on bone-implant osteointegration in osteoporotic rats. Materials and Methods: Thirty-six female Wistar rats were randomly divided into 3 groups: sham-operation (SHAM), ovariectomized (OVX), and ovariectomized with rhBMP-2 (OVX thorn rhBMP-2). The bone density of right tibia was observed with x-ray and the serum alkaline phosphatase (ALP) activity was measured preovariectomy and postovariectomy using an ALP-kit. In OVX thorn rhBMP-2 group, rhBMP-2 was embedded in the peri-implant area, while SHAM and OVX groups did not contain rhBMP-2. Four and eight weeks after implantation, the rats were killed and the right tibia with implants was taken by x-ray. Histologic changes were investigated by hematoxylin and eosin staining, scanning electron microscope (SEM), and energy dispersive spectrometer examinations. Results: The serum ALP level was significantly higher in ovariectomized rats compared with that before ovariectomy (P<0.05), while no difference was found in SHAM rats. At 12 weeks after ovariectomy, radiographic and histologic findings showed significant osteoporotic changes in proximal tibial metaphyses of OVX rats, including reduced cortical bone density and enlargement of bone marrow cavity compared with SHAM ones. The results of implantation verified new bone formation around implants in OVX thorn rhBMP-2 and SHAM groups, indicating favorable bone healing and osseointegration. No bone resorption was found in OVX thorn rhBMP-2 group, while some soft tissue was observed in bone-implant interface in SHAM group. In OVX group, there was no effective bone-implant osseointegration and mature bone formed around implants, and some implants were even lost due to chronic inflammation. The percentage of calcium and phosphorous atoms was significantly higher and the percentage of sulfur element was significantly lower in peri-implant area in OVX thorn rhBMP-2 and SHAM groups than that in OVX group. Conclusion: rhBMP-2 could enhance the osseous healing and restore bone-implant osseointegration in osteoporotic rats.