Experimental Study On Onlay Grafting Of Autologous Cortical Bone Block To Reconstruct Bone Defect

Objective:Biomechanics-oriented implantation concept has been accepted by more and more implant doctors.However,lack of bone in implant areas caused by trauma,inflammation,tumors and other reasons,it will be difficult for this biomechanics oriented implant repair.Therefore,we usually need to use bone graft materials to restore the bone defect at the implant area.At present,we usually use bone materials include allograft,synthetic bone,xenograft and autogenous bone,each of which has its advantages and disadvantages.The regeneration process of allogenic bone is slower than that of autogenous bone,and the ability to combine with host bone is less than that of autogenous bone.Immune reaction can be produced after transplantation.Synthetic bone substitutes can promote bone healing without the risk of infectious diseases.However,these synthetic materials only have bone conductivity and do not have osteoinduction and osteogenesis.Autogenous bone has the properties of bone conduction,osteoinduction and osteogenesis,as well as biocompatibility and no rejection.It is considered as the gold standard of bone transplantation materials.However,the reconstruction process of autologous bone graft is difficult to predict,and the histological changes are not clear.In this study,the autologous massive cortical bone transplanted by Onlay was taken as the research object to observe the healing process of cortical bone graft,in order to provide basis and guidance for clinical application of autologous massive bone.Methods: The experiment included the following two parts.The first part is to establish a model of bone defect by removing the maxillary premolar on one side of the Beagle dog and transplanting autologous massive cortical bone on the buccal side of the mandibular body.The cellular activity and histological changes of autologous cortical bone after transplantation were studied,and the healing regularity of massive cortical bone after transplantation was discussed.The second part is to study the effect of massive cortical bone transplantation and simultaneous implantation on the osseointegration of implants by removing the premolar on the other side of the maxillary of Beagle dogs.Six beagle dogs were selected to remove bilateral maxillary premolars to create bone defect models.The left buccal autologous massive cortical bone of the mandibular body was implanted into the left maxillary defect area.The right buccal autologous massive cortical bone of the mandibular body was implanted into the right maxillary defect area and a Korean DIO implant was implanted simultaneously.The experimental dogs were sacrificed in batches three months and six months after operation to observe the implantation area.Soft tissue changes,bone resorption,and implant stability.The specimens were fixed in 10% neutral formalin solution and made non-decalcified hard tissue grinding sections and paraffin sections respectively.The bone resorption rate and lacuna vacancy rate were observed under optical microscope.The experimental data were analyzed by SPSS17.0 statistical software.The lacuna vacancy rate and bone resorption rate were compared by one-way ANOVA at each time point.Result:1.General observationAll the six dogs survived until the end of the experiment and were in good health.The boundary between the implanted cortical bone and the host bone was not obvious.The shape of the transplanted cortical bone became round and blunt.Bone absorption appeared at the edge and surface of the graft,and the edge of the graft became smooth.The absorption of cortical bone was more obvious at 6 months after operation than at3 months,and the shape of the graft area was irregular.The implant was stable and the sound of percussion was clear 3 months after the simultaneous implantation of cortical bone.At the same time,6 months after implantation,cortical bone graft loosened and fell off.The naked eye showed that most of the graft bone had been absorbed,and there were a lot ofgranulation tissue around the implant.2.Histological observationThree months after massive cortical bone transplantation,paraffin section HE staining showed that some osteocytes survived in the graft,new bone trabeculae connected the base bone of the recipient area with the graft bone,and new bone marrow cavity began to form.Osteoclasts accumulate around the bone graft to form bone resorption lacunae.The hard tissue abrasive stained with toluidine blue showed light blue bone-like junction graft and implant area,and the degree of new bone mineralization was low.The boundary line between the graft and the base bone is clearly visible.Six months after massive cortical bone transplantation,paraffin section HE staining showed that there were still some surviving bone cells in the transplanted bone.New bone formation and light staining of new bone were observed in the transplanted area,and arranged around the new vessels in an orderly manner.The number of new marrow cavity was more than 3 months after operation.A small number of osteoclasts were still involved in bone remodeling.Light blue bone-like substance was observed in hard tissue abrasive staining with toluidine blue,and the mineralization degree of bone trabecula was higher than that of 3 months after operation.The boundary line between the graft and the base bone was not obvious.There are large neonatal marrow cavities at the junction.Three months after concurrent implantation of cortical bone graft,toluidine blue staining showed that the implant and the base bone of the recipient area had osseointegration,and the cortical bone in the transplantation group was mainly fibrous,without osseointegration.The bone graft has a greater absorption and a small amount of light-stained osteoid formation.3.Histological measurement and analysisBone resorption and cell vacancy were measured at 3 and 6 months after cortical bone transplantation.The mean bone resorption rates at 3 and 6 months were 43.7%and 70.8%,respectively.The mean vacancy rates of bone grafts at 3 and 6 months were 60.2% and 39.1% respectively.Statistical analysis showed that there were significant differences between the two observation points(P < 0.05).Conclusion:1.After massive cortical bone transplantation,it can combine with the base bone of the recipient area,but the inner bone cells can only maintain partial viability,and the bone cortex of the peripheral area will absorb significantly.2.After the simultaneous implantation of cortical bone graft,the implant and the base bone of the recipient area formed bone bond,but did not form bone bond with the graft.3.Cortical bone graft absorbs more seriously after simultaneous implantation,and simultaneous implantation will affect the repair effect of bone transplantation.