Bone Regeneration Of Bone Morphogenetic Protein2/7Heterodimer On Peri-implant Bone Defect In Vivo

The osseous restoration of voluminous bone defect remains a challenge in oral maxillofacial surgery.several method such as gene, cell, and cytokine therapies has been taken to solve this problem. Homodimeric BMPs have been shown to induce bone formation in both animal experiments and human trials.However, the effective doses of BMP homodimers for current clinical use are extremely high, which results in not only a substantial economic burden to patients and healthcare system, but also a series of potential side-effects, such as the over stimulation of osteoclastic activity. One alternative approach to overcome this dilemma is to adopt more potent forms of BMPs. Heterodimeric forms of BMPs exhibited more effects than the respective homodimers in-vitro osteoblastogenesis or in-vivo bone regeneration. This study aims to delineate the osteoinductive effects of BMP2/7heterodimer in a peri-implant bone defect model of pigs in comparison with BMP2and BMP7homodimers. Part1:Animal modelObjectives:To build peri-implant bone defect model in minipigs' calvarias for compare the osteoinductive effects of the different rhBMPs.Materials and Methods:Round bone defects (4mm in depth and8mm in diameter) were created in18minipigs' calvarias. One dental titanium implant(3.1mm in diameter) was implanted in the centre of each defect with a4mm-fixture above the bottom of the defect. Collagen with or without different BMPs in a final concentration of30ng/mm3were filled in the bone defects. The bone defects and the implants were covered with a piece of Bio-Gide(?) membrane (40×50mm). Then the soft tissue was sutured layer by layer.Results:The area and thick of minipigs' calvarias were enough to support the defect and implant. All implant survived, have good retention. Collagen sponge and Bio-Gide membrane degrade slowly, few inflammations were observed.At each time point, each BMP group resulted in significantly higher new bone regeneration than control group. Six weeks after implant, there was no completely bone healing of rhBMP2,7and control group. Conclusion:The peri-implant bone defect model in minipigs'calvarias has clear operation field and easy to build. The consistency of defect was good and the interference factors were less. The research can be focused on the performance of the BMPs.Part2: The micro-structure of new bone guided by rhBMP heterodimerObjectives:The high effective doses of BMP homodimers prevent their clinical applications. BMP heterodimers were exhibited to be more potent than homodimers. Most of previous studies were based on the BMP heterodimers that were produced by the technology of combined BMP2and BMP7gene transfer, hitherto, as a promising cytokine therapy, the effects of purified recombinant human BMP heterodimers on in-vivo osteogenesis were merely reported. This study using a peri-implant bone defect model in minipigs to delineate the dynamic micro-architectures of bone induced by low-dose rhBMP2/7heterodimer in peri-implant bone defects compared to rhBMP2and rhBMP7homodimer by Micro-CT.Materials and Methods:The same bone defect animal model as part one was used. Four groups were set up (n=6animals per group per time point):1) collagen without BMPs;2) collagen with rhBMP2homodimer;3) collagen with rhBMP7homodimer and4) collagen with rhBMP2/7heterodimer. Also the uninjured bone was adopted as a positive control.2,3, and6weeks after implantation, samples and surrounding tissues were explanted, dehydrated and embedded in methyl methacrylate (MMA). The samples were scanned by Micro-CT to evaluate newly formed bone by measuring the following parameters: BV/TV, Tb.N, Tb.Th, Tb.Sp, Conn.D and SMI.Results:At each time point, BMP2/7heterodimer resulted in significantly higher relative bone volume, trabecular thickness, trabecular number and significantly lower trabecular separation, structure mode index than the homodimers. After6weeks, BMP2/7resulted in the equivalent trabecular thickness, trabecular number, trabecular separation and the nearest relative bone volume, connectivity density, structure mode index to those of the uninjured bone in comparison to the rhBMP2and rhBMP7.Conclusions:In30ng/mm3concentration, all BMPs has strong bone regeneration than control at each observed time point, and recombinant human BMP2/7heterodimer induced new bone formation in a significantly higher quality and quantity in comparison to BMP2and BMP7homodimers in peri-implant bone defects. Part3:BAP and BIC of new bone guided by rhBMP heterodimerObjectives:Because Micro-CT was an uninjured method, histological and histomorphometric analysis was taken to the same specimens as part1.Materials and Methods:Animal model and grouping as part2.The dehydrated and embedded in methyl methacrylate specimens were analysised of histological behavior, new bone area percentage(BAP) and bone implant contact(BIC)Results:Consistent with2and3weeks, after6weeks post-operation, rhBMP2/7heterodimer resulted in significantly higher BAP than the homodimers, the BAP of rhBMP2,7homodimers also significantly higher than the control group. At2,3weeks,the BIC of BMP2/7heterodimer and BMP2,7homodimers was significantly higher than the control. At2weeks, the BIC of BMP2/7heterodimer was significantly higher than BMP2,7homodimers. Conclusions:Consistent with the Micro-CT result, rhBMP2/7heterodimer induced new bone formation in a significantly higher quality and quantity in comparison to rhBMP2and rhBMP7homodimers in peri-implant bone defects at the same low dose. And it can promote bone implant contact at early stage.