| Background and Objective:In recent years,patients with dentition defects and deletions have gradually increased in number because of trauma,inflammation,and other causes.The implant denture repair technique based on mimicking the natural root has become the first choice approach for more and more patients.One of the key to success in implant is that there is sufficient bone mass around the implant,but the loss of dentition is often accompanied by over-absorption of alveolar bone,resulting in insufficient bone around the alveolar ridge around the implant,which in turn leads to the failure of implant denture.The emergence of guided bone regeneration(GBR)has greatly improved this challenge.The core concept behind GBR is restricting soft-tissue growth into space for bone formation by using artificial barrier membranes with substantial biocompatibility.Therefore,the role of the shielding membrane is crucial in GBR,but whether it is degradable or non-degradable barrier film,there are some drawbacks.Nondegradable membranes possess good mechanical stability.These membranes can adequately maintain space and do not affect the tissue regeneration process.However,at the same time of barrier soft tissue,it also blocks the soft tissue from supplying blood to the tissue below the membrane.Prolonged placement may result in wound dehiscence,which increases infection risk.In clinical practice,nondegradable membranes are usually removed at the second time.By contrast,degradable membranes do not require secondary removal and are more conducive to cell proliferation.But the mechanical properties are poorer and the degradation time is uncontrollable in these membranes than in the nondegradable counterparts.Some scholars believe that nondegradable membranes can be more effectively to maintain the bone height and width in GBR surgery than do degradable membranes.New bone formation may terminate soft-tissue growth,and the barrier membrane placed for an excessive duration causes bone formation delay.However,the specific time point for nondegradable-shielding-membrane removal is not yet clear.At present,the commonly used nondegradable-shielding-membrane is mainly polytetrafluoroethylene(PTFE).However,the optional barrier time for PTFE membrane is controversial,and the role of PTFE in promoting cell proliferation is not ideal.In contrast,the titanium membrane not only meets the requirements as a barrier membrane,can separate the soft tissue growth,but also isolates the growth of soft tissue and maintains the space for bone formation.The titanium membrane also has the effect of promoting the adhesion of osteoblasts.And the characteristics of smooth surface and the low porosity can also reduce bacterial adhesion.In clinical applications,titanium membranes are usually removed after 3 to 6 months,and their effective barrier time is obscure.In addition,since the different bone defect repair materials have different ability to promote osteogenesis,the optimal barrier time for the titanium membrane is also different.At present,the clinical application of osteogenic materials can be divided into two types: autologous sources and non-autologous sources.The autologous source osteogenic material is represented by platelet-rich fibrin(PRF),which is obtained by venous centrifugation.It has the advantages of low cost,simple preparation method and remarkable osteogenic effect.Its natural scaffold materials and abundant growth factors have been favored by many clinical scholars.Non-autologous sources of bone-forming materials currently mainly use artificial bone grafts in clinics,and bio-ceramic materials represented by hydroxyapatite occupy an important position.Hydroxyapatite and β-tricalcium constitute a different ratio,resulting in different bone properties.Studies have shown that the ratio of hydroxyapatite and β-tricalcium phosphate is 6: 4,can better promote the formation of new bone.In this experiment,we used titanium membrane as a barrier membrane,PRF,Osteoid hydroxyapatite,and their mixture as bone defect repair materials,to explore the best barrier time of titanium membrane in GBR application.Methods:1.Thirty six adult healthy white rabbits were randomly divided into two groups as follows: experimental group A(n = 18)and control group B(n = 18).Each group was randomly divided into six subgroups(A1–A6 and B1–B6,n = 3).Different subgroups represent different time points.One-stage operation of 36 rabbits performed a unified operation,four skull defects with a diameter of 6mm were created in each rabbit.Three of the defects were filled with PRF,osteoid hydroxyapatite and their mixture,the last defect was left as blank.The defect was covered with a 2cm × 2cm titanium membrane.The edges of the titanium membrane were trimmed and then fixed with four titanium pins.After 1 week,the titanium membranes in group A1 were removed,while the titanium membranes in group B1 were not removed.After the second surgery,the rabbits in A1 and B1 groups were fed for 2 weeks and finally sacrificed together.In the same manner,until the 6th week after surgery,the titanium membranes in group A6 were removed,while the titanium membranes in group B6 were not removed,then the rabbits in A6 and B6 groups were continued to fed for 2 weeks and finally sacrificed together.2.Volume and density of new bone formation by microcomputed tomography(micro-CT).Histology(HE,Masson trichrome staining)to assess new bone formation area,bone tissue maturity.Immunohistochemistry was used to detect osteocalcin expression to assess osteoblast activity.Results: 1.The results of imaging showed that in the blank group before 4 weeks,the volume of new bone formation in the control group was significantly higher than that in the experimental group.In PRF group,the volume of new bone formation in the control group was significantly higher than that in the experimental group before 2 weeks.At 3 weeks and 4 weeks,there was no difference between the experimental group and the control group,but by the time of 5 and 6 weeks,there was a statistical difference appeared again between the experimental group and the control group,and the experimental group was superior to the control group.2.The percentage of new bone formation to the area of bone defect was calculated by HE staining.The results showed that there was no difference between the control group and the experimental group in PRF group at 3 weeks,and no difference was found in the blank group at 5 weeks,which was consistent with the imaging results.There was no difference of new bone formation area between OHA group and mixed group at the beginning of the experiment.All experimental groups and control groups were re-emerged statistical differences at 6 weeks,and experimental group was better than the control group.3.The results of Masson staining showed that the bone tissue in experimental group and control group became more mature with the increase of time.Initially,the control group had more new blood vessels and more active osteoblasts around new bone.4.Immunohistochemistry results showed that the control group showed strong positive results at 1 week,the number of osteoblasts was more than that of the experimental group,and the control group in PRF group was more obvious,then the positive degree gradually weakened.In the OHA group and the mixed group,the experimental group was weakly positive in the early stage,while the control group showed moderate or even strong positive results.The positive results in experimental group gradually increased with the passage of time.At 6 weeks,weak positive results were expressed in each group.4.Conclusion:The experimental results show that the presence of barrier membrane can effectively shield the soft tissue,and remove the barrier membrane in the right time is conducive to guide bone regeneration.Different bone defect filling materials showed different osteogenic potential.The optimal removal time of titanium membrane in PRF group is 3 weeks.The best removal time of titanium membrane in mixed group is 4 weeks,while that in OHA group and blank group,the best removal time is 5 weeks. |
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