| BACKGROUND:Peri-implantitis is a chronic progressive marginal inflammation surround thedental implants. It leads to functional failure of the implants. After implant dentureserves weight loading, peri-implantitis may occur and bone resorption surround theimplants may happen under pathological stimuli, such as overexertion, poor oralhygiene, lesions of adjacent teeth. Without appropriate control, the peri-implantitisand bone resorption would cause implant denture failure ultimately. In order toincrease the success rate of dental implants, prophylaxis and treatment ofperi-implantitis have attracted much attention for clinical researches. So far, thetreatment method and skill for peri-implantitis are far away from satisfaction.Along with the increase of people's living and life quality, the traditionalremovable denture and fixed denture with grinding natural teeth inevitably could notmeet the satisfaction of the patients. Implant denture has been accepted by more andmore patients with a lot of advantages such as good stability, comfortableness, goodfunction, and without grinding natural teeth. As more implant dentures are appliedclinically, new problem occurs. The complication of dental implants, peri-implantitishappens frequently. The bone loss caused by peri-implantitis is the main reason forimplant denture failure. To re-construct the bone defects in peri-implantitis is the key for long-term function of the implant denture.GBR technique is generally accepted as an effective bone reconstruction method.Investigation with re-entry and histology observation has shown that new boneformation vertically and horizontally in non-inflammatory bone defects surroundingimplants treated with GBR. GBR has become a routine treatment technique fornon-inflammatory bone defects surrounding implants.Recent years there have been some experimental reports on applying GBR totreat bone-loss in peri-implantitis, and gaining bone-rebuilding. However theseexperimental animal models about bone-defeats in peri-implantitis were allestablished within short time using silk-ligature induced, the pollution of implantsurfaces is not as severe as in peri-implantitis. In peri-implantitis, the dental implantsurfaces are exposed to pathological environment for long time. The mechanical andchemical treatment techniques used for root surface preparation in periodontitistreatment during flap surgery were applied to treat implant surfaces in bone-defects ofperi-implantitis combined with GBR, bone-reconstruction was obtained. In thesestudies, only one surface treatment method was used to compare the effects ofdifferent GBR methods, eg. autogenous bone, Bio-Oss, autogenous bone +collagen,Bio-Oss+collagen. There was not obvious difference found. Due to the differencebetween natural dental roots and dental implants, the effects of the surface treatmentsshould be different, but without appropriate study so far. There is no study about thebone reconstruction and osteogenesis efficacy in different surface treatment inperi-implantitis. The present study is to establish bone-defect animal model inperi-implantitis, to apply different surface treatments combined with GBR to selectthe best surface treatment technique on osteogenesis efficacy. It is going to establishscientific basis for GBR study in clinical peri-implantitis bone defects, and to provideappropriate methods for long-term function of implant denture.OBJECTIVES:The present study is to establish bone-defect animal model in peri-implantitis, to apply different surface treatments combined with GBR to select the best surfacetreatment technique on osteogenesis efficacy. It is going to establish scientific basisfor GBR study in clinical peri-implantitis bone defects, and to provide appropriatemethods for long-term function of implant denture.METHODS:Part 1, To establish animal model of implant osseointegration.The lower mandible premolar teeth of 4 adult Beagle dogs were pulled out,dental implants were inserted immediately. The wounds were open for healing. Theosseointegration was formed in 3 months and healing abutments were connected.Part 2, To establish animal model of experimental peri-implantitis bone-defects.The silk thread was ligatured subgingivally around implant abutments. Theligature was removed in 1-2 months after peri-implantitis developed. With plaquecontrol, the dental implants were exposed over 6 months in experimental animal oralcavity.Part 3 To apply different techniques to prepare implant surface with bone-defects.Selection: The pocket depth surrounding implant was probed, over 3-5mm bonedefects were selected and divided randomly into 2 groups:CDIC (MTS surface, 12 implants)Blank group: machanical treatment +antibiotics treatment.Experiment group 1: machanical treatment +antibiotics treatment +Bio-OssExperiment group 2: machanical treatment +antibiotics treatment +OAMBAM (HA surface, 12 implants)Blank group: machanical treatment +antibiotics treatment.Experiment group 1: machanical treatment +antibiotics treatment +Bio-OssExperiment group 2: machanical treatment +antibiotics treatment +OAM.Part 4 To obtain inferior maxilla samples with implants.In 5 months after implant surface treatment, bone-reconstruction was obtained indefects areas. The animals were sacrificed and inferior maxilla samples with implants were taken. The slices along with implant long axis were cut and then were handlyground to thickness of 30—50μm. The slices crossing the central part of implants andbone defects were selected for dyeing by methyl blue and mounting by gum.Part 5 The histological changes and osteoanagenesis of microspecimen with implantwere observed and analyzed by medical image analysis system.The histological changes and osteoanagenesis were observed by light microscopewith different enlargement sizes.Each specimen was examined on 3 slices. The circumference of the implant in thebone, the distance of the newly formed bone on the implant were measured, thechanges of the areas of newly formed bone on the implant were calculated.RESULTS:1. General state of health4 dogs all survived, The soft tissue wounds healed well. The all 24 implants andthe biomembranes were maintained well till the end of the experiment. There was noinfection. During the re-entry, the newly formed bone tissue was observed to fill thedefects around the implants, to be whitish and tenacious.2. X-ray observations:The bone contact levels at mesial, distal, buccal and lingual sides were measured.There was no statistics difference between each group (P＞0.05) before therapy, thebone resorption level surrounding implants in all groups approached 40％. Aftertreatment, there was no difference between two groups of different interfaces on thebone formation, but the bone formation differed significantly between the differenttreatment sub-groups. In both groups of MTS and HA, the bone formation in theanimals treated with Bio-Oss or OAM was better than Blank. These results indictedthat Bio-Oss and OAM can promote bone formation in peri-implantitis bone defects.3. The histomorphology examinations:Under the light microscope, there is abundant new bone formation aroundimplant shoulder in the experiment groups, Bio-Oss or BMP was substituted by newly formed woven bone and lamellar bone. Haversian system was formed withdirect contact to the implant. The new bone formation in blank grounps is much less,the fibrous connective tissue between implant and bone can be observed, and bigbone defects exist. Through bone histomorphology quantitative assay, it indicatedthat ther was no significant difference between two groups of different interfaces onthe bone contact percentage, but the bone contact percentage differed significantlybetween the different treatment sub-groups. In both groups of MTS and HA, the bonecontact percentages in the animals treated with Bio-Oss or OAM were better thancontrols.CONCLUSIONS:1. Adopting GBR treat peri-implantitis with different surface smear layer, boneformation and production bone mass are alike, and their ratio of bone contact are alsoalike.2 Adopting GBR combine of biomembrane and Bio-Oss/OAM shows advantage fornew bone formation in the treatment of peri-implantitis bone defects.3. The implant surface decontamination can be obtained using pure Ti worktip, mildoutput power, and irrigating repeatedly with 50％citric acid and 0.9％saline, whichprovide a favorable environment for bone re-osseointegration.
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