Effects Of Nerve Growth Factor On The Early Phase Of Osseointegration Around Immediate Implants In Periodontally Compromised Dogs

Background:The prevalence of periodontitis in China is about 70%-85%,which is the main cause of tooth loss in China.Dental implant repair is one of the important methods in the treatment of tooth loss.Immediate implant is defined as immediate implant placement in a fresh extraction socket.Compared with the traditional delayed implantation technique,the immediate implantation technique has been widely used in recent years due to its advantages such as short treatment time,less operation times and bone resorption.Good implant osseointegration is a prerequisite for the success of oral implantation in immediate implanting.However,the shape and bone mass of the alveolar socket after tooth extraction in patients with periodontitis and residual periodontal pathogens in the mouth may affect the initial stability and early implant osseointegration which can increase the risk of implant failure.Therefore,how to improve early osseointegration around immediate implants in patients with periodontitis after tooth extraction is the focus of current research.In recent years,it has been found that nerve growth factor can affect bone metabolism and reduce the release of inflammatory mediators and promote early osseointegration around implants.However,there are still few studies about the effects of nerve growth factor on early osseointegration around immediate implants to the periodontitis.Objectives:In this study,the nerve growth factor was applied to the periodontal dogs' immediate peri-implants in order to explore the effects of nerve growth factor on the early phase of osseointegration around immediate implants in periodontally compromised dogs and provide a reference for further clinical research.Methods:To establish periodontitis model,the necks of all mandibular premolars in four experimental healthy adult Beagle dogs were ligated with orthodontic ligation and silk and coated with Porphyromonas gingivalis and supplemented with high sugar sticky diet.The periodontal tissues of the dogs were observed and probed every week after modeling.The periodontitis models were completed at the fourth week.At the fifth week,the bilateral mandibular second and third premolars of all dogs were extracted and implanted immediately with a total of 16 implants.The left mandibular peri-implants subperiosteum were injected with nerve growth factor(1.0?g/d)as experimental group and the right were injected with equal dose of normal saline as control group for 2 weeks.At the end of the fourth week,two experimental dogs were randomly selected and sacrificed.At the end of the eighth week,the remaining two experimental dogs were sacrificed.The mandibles were removed from four experimental dogs.Each mandible was made into 1.0 × 1.0 × 1.5cm bone block containing one implant which was immersed in 10% formalin solution.The specimens were evaluated by means of general observation and X-ray observation,and then using the hard tissue slicer cut along the long axis of the implant and polished to a bone slice with a thickness ofabout 80?m.The bone slices were stained with toluidine blue for histological observation,and each of implant tissue slice image was analyzed by using the professional image processing software(Image-pro plus 6.0)and the implant bone contact ratio was calculated.Results:1.After 4 weeks of modeling,there were periodontitis clinical symptoms of gingival inflammation,probing bleeding,tooth loosening and serious absorption of alveolar ridge in the mandibular premolars of all dogs,which suggested the success of modeling.2.General observation: Two groups of experimental dogs surgical site healed well after the immediately implantation surgery.There were no emergence of postoperative complications.3.X-ray observation: 4 weeks after surgery,two groups both showed X-ray transmission area around the implant bone,and peri-implant bone density was significantly lower than normal bone tissues.8 weeks after operation,the X-ray transmission areas of two groups peri-implant bone tissues were smaller than that of the fouth week.The bone density was still lower than the normal bone tissues.Compared with the experimental group,the control group bone density decreased significantly.4.Tissue morphology observation: 4 weeks after operation,the control group showed that the implant and the bone tissue were partial combination and had more fibrous tissues,and it also showed osteoid formation and sparse trabecular bone;the experimental group showed relatively more binding sites between the implants and the bone tissues and fewer fibrous tissues,and it also showed continuous trabecular bone.8 weeks after operation,the bone tissues around the implants in the twogroups were more mature and dense than that of the fouth week.The control group showed that there were still some fibrous tissues.Although the bone tissues and implants binding sites were relatively more,the bone trabecula mineralization was not high;the experimental group showed a high degree of mineralization of trabecular bone in uniform and the new bone tissues were more and dense,and it also showed the bone tissues were more widely combined with the implants.5.Bone metrology analysis: The implant bone contact ratio was(41.06±3.31)% in the control group and(56.49±3.20)% in the experimental group at 4 weeks after operation.The implant bone contact ratio was(60.46±2.26)% in the control group and(77.45±2.33)% in the experimental group at 8 weeks after operation.The results showed that in the control group the osseointegration rate was significantly lower than that of the experimental group,and the difference between the two groups were statistically significant(P < 0.05).Conclusions:1.In this experiment,the necks of all mandibular premolars in Beagle dogs were ligated with orthodontic ligation and silk and coated with Porphyromonas gingivalis and supplemented with high sugar sticky diet to establish periodontitis models.This way can establish periodontitis model successfully.2.Early application of nerve growth factor in periodontitis can accelerate the formation and maturation of newborn bone around immediate implant and expand the implant bone binding range.It suggests that nerve growth factor can accelerate the formation of bone tissue and promote implant osseointegration.3.Nerve growth factor is applied to the immediate implantation of periodontitis after tooth extraction,which can improve the implant-bone contact rate and shorten the bone healing time.