The Immediate-implantation Simulation Research For Restoration Of Bone Defects Around Implants

Immediate implantation is the method that the implant is put intothe tooth socket where the tooth was extracted just now,and it's anew technique developed recently. Compared with delayedimplantation, this technique can reduce operation frequency, shortenthe time waiting for restoration, recover chewing function, let theposition and direction of the implant accord with biomechanicsrequest. The most important thing is that it can prevent theabsorption and atrophy of alveolar bone caused by tooth extractionand maintain the height and width of alveolar crest effectively. Andso the technique of immediate implantation is very valuable forclinical practice. Sometimes the implant can't take up all the socketand leave the clearance between the implant and wall of socket whenimmediate implantation is committed. Some scholars considered thatthe bone-implant clearance will affect the osseointegration ofimplant, accordingly affect the success of implant. Because of that,the treatment for clearance became the controversy focus instomatology. Most scholars used bone graft and bioresorbablecollagen membrane to fill and cover the defect area. Such questionsas exposure of bioresorbable collagen membrane preventedossification, bone graft could be absorbed incompletely orcircumvoluted by fibre. Some scholars considered that thebone-implant clearance less than 1 mm need no treatment, it can berecovered in the osseointegration of implant and socket, thebone-implant clearance less than 2 mm also needn't use bone graft orbiomembrane, the bone regeneration is similar to the condition thatimplant contacted to bone tightly. The aim of this study is toinvestigate the ability of bone regeneration with different defects,and in which condition the bioresorbable collagen membrane shouldbe used in order to promote bone regeneration and relieve patient'spayment.Method: implants were installed in the femoral bone of ripedogs. On one side of bone walls near implants we respectively make3 mm horizontal width, 5 mm vertical depth and 0 mm,1mm,2mm,3 mm,4 mm horizontal depth(along the macroaxis of femoralbone) standard gradient bone defects. On one side we directly sutureby lamination, and on the other side we suture by lamination afterusing collogen membrane to cover on the defects. Three months afterthe operation we got specimens to analyze. By the way ofimageology, stereomicroscope, and tissue morphology method,ossification capability of different defects on dogs and the effect ofmedical collagen membrane on different bone defects were observed.Result: the soft X-ray indicated that the defects with horizontal depthbeing 1mm, 2mm, 3mm had been filled with new bones completely,implants combined with the bone closely;the new bone calcifiedwell, there was no obvious difference from the surrounding bone inbone density, and there was also no apparent boundary between them.It coincided with the tissue which had no defects on the whole. Thegroup that had been covered with membranes had no difference fromthe group which had not been covered with membranes. In the groupwith 4 mm defects had been filled with new bone, and the implantsintegrated with the bone closely. The density of the new bone is alittle lower than that of the surrounding bone. Trabecular bone wasmore but the arrangement was irregular. The bone density of themembrane group was higher than that of the no–membrane group.According to the stereomicroscope we can see that: in the groupswith 1mm, 2mm and 3mm defects, the defect areas had been filledcompletely with new bone. The new bone was extensively integratedwith the original bone, and they had the coincident colour and noobvious boundary. In the group with 4mm defects, the defect areawas filled with new bone. The implants intacted directly with thebone. The new bone tissues are mainly trabecular bone with biggerlacunes and irregular arrangement. The cortex of bone is thin, andhave no succession. The colour of it is deeper than the bone around.The membrane group which has coarser and more bone trabecula isbetter than no-membrane group.The results of histopathology: in the group with 1mm and 2mmdefects, the defect areas were filled with new bone completely, thenew bone was extensively integrated with the original bone, and theyhad no obvious boundary, but the huff's tubules were obvious. Andcompact osseous integration zone could be seen near marrow cavity(osseous interface). The group with 3mm defects, the defect area wasfilled with new bone completely, there were some round, ellipse orirregular lacunules in new bone, osteoblast were active on the edgeof lacunule. Huff's tubules were obvious,the new bone wasextensively integrated with the original bone, and they had noobvious boundary. Considerable new bone trabecula in thecancellous bone of defect area, regularly arranged, formed compactosseous interface, and the group that had been covered withmembranes had no difference from the group which had not beencovered with membranes. The group with 4mm defects, the defectarea was filled with new bone completely, the new bone seemed totrabeculum, and the arrangement was similar to that of thesurrounding bone. The cortex of bone was very thin, and had nosuccession. Osseous coherence formed on the surface of implant.The group that had been covered with membranes was better thanthe group which had not been covered with membranes. There hadbeen coarser and more bone trabecula with smaller lacunes.Conclusions: Implants were installed at the epiphysis of dogfemur, and different kinds models of bone defect could beestablished. Bone regeneration capacity was very well for verticaldefect around BLB implants with hydroxyapatite coat. If the defectwas less than 3mm, whether bioresorbable collagen membrane wasused or not, osseointegration was well in the implant-bone interface.Bioresorbable collagen membrane was not necessary within thedefect extension less than 3mm. If the level depth defect was morethan 4mm, regeneration capacity was not as well as the group with3mm defect whether the bioresorbable collagen membrane was usedor not. Suggest that if the level depth of bone defect is more than 4mm, bioresorbable collagen membrane should be used.