| BackgroundThe development of biomaterials and surgical techniques have contributed to promote the application of dental implantation, which has become one of the important methods for the restoration of partially and totally edentulous patients. An important factor to ensure the long-term success of dental implants is a sufficient volume of the bone at recipient areas. However, alveolar bone always defects as a result from teeth extraction, trauma, or inflammation and so on. Various bone augmentation techniques have been suggested to repair the inadequate bone volume of the residual ridge. At present, the main approaches in clinical practice include bone condensing and bone splitting, guided bone regeneration (GBR), distraction osteogenesis (DO), bone grafting, maxillary sinus floor lifting. Onlay bone grafting is one of the important bone augmentation technology, which fixes the bone substitutes on the surface of the alveolar bone to increase width and (or) height of the maxilla and mandible, which can increase bone quantity significantly, and carry a lower rate of complications.Onlay bone grafts were applied to oral implantology field in the early 1990s to recover the volume of the bone defect sites, which guaranteed the success rate of dental implants. Currently, bone substitute materials mainly include autografts, allografts, xenografts and artificial synthetic bone grafts. These different materials can solve the problems in bone defects, but have their own advantages and disadvantages respectively. Autografts are considered the"golden standard"for bone graft in terms of their osteoconductive, osteoinductive and osteogenic, but it has some weak points such as limited sources, needing to open the second operative area, great traumatic, so their clinical appliance is limitted. Allografts exist immunological rejection and the dangers of spread infectious diseases. Most synthetic bone grafts are nonbiological materials, and lack of osteoconductive activity, absorbed degradation obstacles the osteogenesis. Bone substitutes are divided into granular materials and block by their shapes. Granular bone graft materials have some weaknesses such as difficult plastotype, easily shifting to spread, maintaining alveolar ridge forms unsatisfactoryly, poor mechanical stability, osteonecrosis and wound easily occurs as result from granular moving, thus, their clinical applications are limited.Osteoinduction active material (OAM) is a new kind of bone graft materials which is prepared by antigen-extracted bovine cancellous bone as a carrier combined with bone morphogenetic protein (BMP). It has excellent biocompatibility and good osteoinductive and osteoconductive capability. The three-dimensional network structure of bovine cancellous bone is considered as a scaffold which plays a role of conductive ability, which is both much efficient in releasing BMP and effectively guiding bone regeneration, also it has good biodegradability and the rate in step with bone formation, can not affect bone plasticity. In bone nonunions, bone defect, and fracture etc have achieved satisfactory clinical effects. However, there are not any reports about the use of massive OAM as an onlay bone graft material in mandibles.ObjectiveThe purpose of this study is to investigate the feasibility of block OAM as an onlay bone graft in rabbit mandibles, to evaluate its bone regenerative capability and the ability of bone volume maintaining, to discuss the bone formation mechanism in bone grafting.MethodsNine healthy Japanese white rabbits were used for the study with an average weight of about 2.5-3.0 kg and regardless of sex. They were randomly divided into 3 groups and 3 animals in each group, based on the time they were to be euthanized at 4, 8 and 12 weeks after bone grafting. The mandibles of each rabbit were divided into experimental groups and control groups at random. Experimental groups: OAM block + titanium screw + collagen membrane; Control groups: autologous tibia+ titanium screw + collagen membrane. Under general anesthesia, the skin, subcutaneous tissue and muscles were incised along the border of the submandibular region to expose the buccal of mandibular body and make surface roughness. OAM, and autologous tibia were implanted as onlay grafts in each side of mandibles at random, the graft materials in the form of a 5mm×5mm×2 mm cube, covered with collagen membrane, and fixed with titanium screws. The rabbits were respectively sacrificed at 4 weeks, 8 weeks, 12 weeks after bone grafting, and the specimens were collected for X-ray and histopathology analysis. Then, we evaluated the healing of grafts-host interface through the observation, new bone formation and maintaining in the bone height.ResultsAll wounds were healed well after operation, and no postoperative infections and immunological rejection were observed in bone graft area and donor site. Except for one moved limp, others could leap without any pathologic fracture or limitation. Experimental samples, the extend of combination between OAM and host bone interface increased with the time, the stability of bone graft materials decreased ,without any moved in 12 weeks, while in the experimental group, absorption of OAM reduced slightly, in Control group, autogeneous bone absorbed and lost severely.X-ray showed that there was a radiopaque shadowgraph in the OAM-host bone interface of experimental groups at 12 weeks, callus formation, and density were the same with the host bone density. At 8 weeks, the control group had no obvious boundaries between them, but absorbing seriously.Histological observation showed that at 8 weeks after surgery, in the experimental group , a few of host bone grew into OAM , new bone connected with both, osteoblasts were rich, and there were plenty of angiogenesis, the biodegradation occurred and obviously degrade lacunae could be seen. In the Control group, grafting materials absorbed severely. At 12 weeks, in experimental group, there was good osseointegration between the OAM and host bone interface, which were thicker and more mature than at 8 weeks. New bone grew into the hole of OAM, which had lots of osteocytes in lacuna. OAM absorption was more severe than at 8 weeks, degraded into fragment, the cavity could observed after degradation .In the Control group, absorbed obviously and the remaining host bone with the new bone together, could not be distinguished.ConclusionIn this experiment, we used the massive OAM as an onlay bone graft material in rabbit mandibles for the first time, and disscused the osteogenetic mechanism after transplantation. We drew the following conclusions:1. OAM block is connected with the host bone in the term of osseointegration in experimental study.2. OAM has biodegradability, and can maintain better bone volumes of augmentation than control groups.3. OAM has excellent biocompatibility, osteoconductive and osteoinductive osteogenesis ability, could be considered as a good substitute of autologous bone.In conclusion, the OAM has excellent biocompatibility and osteoconductive and osteoinductive ability, which can be used as a kind of autogenous substitute materials in onlay bone grafting. |
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