| As a widely used restoration method, dental implant has many advantages including:satisfactory masticatory function; excellent aesthetics; optimal comfort; alveolar bone protection and avoiding abutment tooth injury. However, many patients cannot take those advantages by receiving implant therapy because of its strict indications, such as adequate bone mass and acceptable bone morphology. On this issue, dentists have endeavored to extend the application of implant, for instance, in improving implant survival rate of patients with osteoporosis or diabetes.Patients with severely absorbed alveolar bone usually suffer from severe bone defect because of lack of physiological stimulation followed by progressive bone absorption. In this situation, bone augmentation is an effective way. Several methods for alveolar bone vertical augmentation exist including bone grafting, autogenous dentin material transplantation, and distraction osteogenesis. However, bone grafting faces the donor site morbidity. Autogenous dentin material transplantation requires extractable healthy teeth as repairing materials thus its application is limited. Distraction osteogenesis requires a longer treat period and increases the discomfortableness and the risk of infection. Bone graft material is widely available and has good biocompatibility and osteoconductive, which promise a better result in bone repairing.unlike maxillary which can gain more bone height by maxillary sinus lifting, vertical bone augmentation in severely absorbed mandible is more difficult to achieve. The key issues are the following:(1)shaping and retention of repairing material;(2) The establishment and maintenance of the bone regeneration space;(3) Blood supply. The ideal GBR membrane should have favorable biosafety and bio-degradability; adaptive degradation rate and adequate mechanical property for establishment and maintenance of the bone regeneration space. Magnesium alloy, as biodegradable metal with both the mechanical property and the bio-degradability, is expected to be an optimal choice for GBR membrane. In this research we introduce magnesium alloy into to the GBR membranes combining with tissue engineered bone as the novel method in restoration. In addition, we add platelet-rich-plasma (PRP) as the osteogenetic factor which can promote angiogenesis in the prosthesis and therefore, resolve the blood supply problem both internally and externally.As the degradable metal, magnesium alloy’s physical property is close to cortical bone. Meanwhile the degradation products are alkaline MgCO3, Mg(OH)2and CaCO3. The alkaline environment is in contrast to the regular bacterial plaque environment and possibly provides the bacteriostatic factors. Intraoral bacteria can incite local inflammation or undermine the hard tissue by attachment, aggregation and proliferation. The main issue is the pathogens cause peri-implantitis. During the degradation process of magnesium alloy, the alkaline products will have effect on the pathogens. Some other issues including local biocompatibility and general influence of magnesium alloy. The second part of this research will focus on these issues and makes a tentative research on intraoral applications of magnesium alloy.The main properties of magnesium alloy are degradation and mechanical property. The degradation rate is directly related to the concentration of the degradation products and dosage evaluation. When introduce magnesium alloy to the GBR membranes, the dosage should maintain the integral structure in order to resist the external force during Osteogenesis period. Because of the favorable blood supply and complex biting force in oral maxillofacial area, the degradation rate in this environment may differ from that in long bones. During the degradation, the influence of changing mechanics parameters in the structural integrity under biting force will be discussed in the third part of this research. Part ⅠThe evaluation on osteogenetic effect of magnesium alloy membrane in severely absorbed mandibular alveolar boneObjective:to investigate the osteogenesis effects of magnesium alloy as GBR membrane combined tissue engineered bone in vertical augmentation of severely absorbed alveolar bone。Methord:1、Establish the severely absorbed canine alveolar bone defect animal model to simulate the clinical cases.2、To obtain the BMSCs through whole bone marrow culture. After differentiation and identification, culture and amplification, induced mineralization for10days, the BMSCs are cultured together with nHA/PLA graft to establish tissue engineered bone.3、Design the shape of AZ31B magnesium alloy GBR membrane based on alveolar defect morphology.4、To investigate the specific method of twice centrifugation to prepare PRP through adjust the centrifugal speed.5、Animal surgeries:experimental group:AZ31Bmagnesium alloy GBR membrane+PRP gel+tissue engineered bone; control group:titanium alloy GBR membrane+PRP gel+tissue engineered bone; blank group:tissue engineered bone+PRP.6、Fluorescence label the calcium deposition10days,20days and30days after the operation. Calculate the osteoporosis rate under the laser scanning confocal microscope7、Harvest after4,8and12weeks and evaluate the osteogenesis effects through Radiological and histological observationResult: 1、We successfully establish the severely absorbed canine alveolar bone defect animal model. The morphology and physiological status approximate clinical situations.2、The BMSCs are obtained after induced mineralization to manifact the tissue engineered bone.3、The shape of AZ31B magnesium alloy GBR membrane is coincidence with that of the bone defect. When the distance from the centre of screw to the centre of the membrane is2.4mm, the resistance reached the maximum, which can maintain the whole structure under500N’s biting force.4、To centrifugate14ml whole blood in speed of2200r/min. To decant the supernatant. The remaining liquid is conducted to the second centrifugation. The concentration of PRP received is810×109/L,(6times of that of original whole blood),which meet the criterion of5-8times.5、In early stage, the osteogenesis rate in magnesium alloy group is significantly higher than other two groups. No statistical difference founded between the positive control and the blank group.6、No statistical difference in bone density or Trabecular bone volume is founded between titanium alloy group and the magnesium alloy group. Although the osteogenesis is more active around the magnesium alloy, but the volume of new formed bone is less than that in titanium alloy group and exhibit highly irregular charistic because of the gas generated during magnesium degradation.Part2the effect of the application of AZ31B magnesium alloy on the oral environment and evaluation of its biological safetyObjective:To investigate the effect of the application of AZ31B magnesium alloy on local environment and the safety throughout the body. Methods:1、Test and analysis the PH value of saliva with short range PH paper both before implantation and harvest procedure.2.To collect the supragingival and subgingival dental plaque of the first mandible molar in canine. Extract the genomic DNA, measure the DNA concentration, estimate the amounts of bacteria. To evaluate the impact of magnesium alloy on the amount of bacteria3、Draw venous blood4ml both before implantation and harvest procedure. Evaluate the changes in blood biochemical indexes.4、Observe the Healing characteristics of soft tissues after implantation. The soft tissues adhered to magnesium alloy are observed by using tissue sectioning under microscope.5、The tissues of heart, liver, spleen, lung and kidney are also observed using tissue sectioning (HE staining) under microscope.Result:1、The PH value of saliva with short range PH paper has a slightly change before and after implantation. However the difference is not statistically significant.2、The result of Q-PCR shows that the amounts in all sorts of bacteria are lower after the procedure. The differences were all statistically significant, especially Pg and Fn, the amount of which reduced more than100times.3、No statistical difference in blood biochemical indexes was founded before and after the procedure, and both are within the normal range.4、Mucous failed to heal in4cases7days after the procedure because of infection and presents local swelling. All other tissues healed well without inflammatory reaction. Normal cell arrangement is observed in both epithelial layer and固有层under microscope without inflammatory reaction.5、No damage, lesion or other abnormal founded in heart, liver, spleen, lung and kidney according to the results of tissue sectioning Part Ⅲ Effect of AZ31B magnesium alloy intraoral degradation on its mechanical propertyObjective:To investigate the intraoral degradation rate of the AZ31B magnesium alloy and analyze the effect of degradation level on its mechanical property.Methods:1、To weigh the AZ31B magnesium alloy GBR membrane and the screws with the electronic balance.2、The methods of preparation, implantation and harvest see part Ⅰ. The magnesium alloy materials harvested are weighed after cleaning and air-drying and analyzed compared with the blank control group.3、To observe the surface degradation morphology of the AZ31B magnesium alloy material and to describe the detail of its intraoral degradation.4、To conduct the energy spectrum analysis on the surface of AZ31B magnesium alloy and to investigate the effects of intraoral degradation on the surface substances.5、To manufacture the mould with denture acrylic for AZ31B magnesium alloy material fixation and to measure the maximum loading force.Result:1、The degradation process of AZ31B magnesium alloy are proved to be lamellar and exfoliative.2、The degradation rate of AZ31B magnesium alloy are1.42%in4weeks,4.27%in8weeks,11.37%in12weeks postoperatively3、The surfacing substances of the magnesium alloy are significantly changed, especially the amount of Calcium phosphorus and kalium4、The mechanism property of magnesium alloy descends during degradation, yet the maximum biting force can still be withstand12weeks after implantation. |
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