Preparation And Experimental Study Of Dental Implants Made By Additive Manufacturing Combined With Subtractive Processing

The conventional manufacturing process of oral titanium implant is to use titanium bar as raw material to obtain titanium implant with certain shape and size by mechanical reduction processing.The three-dimensional printing technology can directly realize the near-net forming of titanium implants through the forming principle of discrete stacking,with few technological steps,high material utilization,and can be customized for patients with special bone mass.It is not limited by the fixed shape and limited size choice of commercial titanium implants.In addition,three-dimensional printing can establish a porous structure for the surface of the implant,and the bone tissue can grow into it,which can enhance the osseointegration,and its existence can also reduce the stiffness of the surface of the titanium implant.make the elastic modulus of the implant surface closer to the jaw tissue.Three-dimensional printing belongs to the manufacturing process of near-net forming,but for some key parts of the titanium implant,such as the abutment connection structure inside the implant,it can not be formed directly by using three-dimensional printing technology.This is because the 3D printing technology has inherent spheroidization and "step" phenomenon,which leads to the high surface roughness of the molded parts,which can not meet the requirements of close assembly between the two-stage implant and the abutment.The metal reduction processing technology can obtain higher surface quality,and now it has been used as a common supplementary process to improve the precision and reduce the surface roughness of three-dimensional printing parts.The process of combining increasing material manufacturing with reducing material manufacturing,taking into account the advantages of both,has become a development direction of metal parts manufacturing industry.At present,some foreign implant manufacturers have used this combination process to produce two-stage titanium implants,which have been successfully listed on the market,but due to the core patent issues,the detailed technological process and other information are less public.there is no effective guidance for the development of domestic three-dimensional printing titanium implants.Therefore,this topic is based on independent research and development,to explore the feasibility of forming two-stage titanium implants by the combination of increased and reduced materials,and to provide a basis for further clinical application through the study of mechanical and biological properties.Finally,an one-year clinical trial was conducted to evaluate the short-term clinical effect of three-dimensional printed two-stage titanium implants in supporting the restoration of missing single crowns of mandibular posterior teeth,so as to provide reference for the development of domestic three-dimensional printed titanium implants.Objective:1.To explore the feasibility of using selective laser melting technology to form the main body of the implant,combined with subsequent material reduction processing to prepare the gingival part of the implant and the connecting structure of the abutment,in order to realize the close cooperation between the implant and the abutment.Meet the requirements of clinical application.2.The mechanical properties and biological properties of three-dimensional printed titanium implants were evaluated comprehensively through mechanical properties tests,in vitro cell experiments and animal in vivo implantation experiments,so as to provide scientific basis for clinical application.3.A prospective clinical trial was conducted to evaluate the short-term effect of the two-stage short implant made by the above process in the restoration of mandibular posterior teeth supported by single crown implant.Methods and contents:1.To explore a two-stage titanium implant processing technology based on the combination of increased and subtracted materials.The standard test parts for accuracy inspection are prepared,and the forming accuracy of selective laser melting parts is measured by micrometer.The plasticity of three-dimensional printing titanium implant is improved by heat treatment to meet the requirements of comprehensive mechanical properties of implant materials.The standard tensile specimens were made,and the tensile properties of 3D printed titanium alloy tensile test bars after heat treatment were tested.According to the requirements of the industry standard,the dynamic fatigue performance of the molded implant was tested to evaluate whether its fatigue resistance can meet the clinical application.2.The biocompatibility and osteogenic differentiation ability of selective laser melting titanium alloy implants were evaluated by means of cytotoxicity and osteogenic differentiation in vitro.Through the in vivo implantation experiment,with the traditional sandblasted acid etched surface implant as the control group,the osseointegration property of selective laser melting implant was evaluated.3.A clinical trial was conducted on the basis of preclinical study.The special clinical scene of insufficient bone height in the mandibular posterior region was selected.The twosegment short titanium implant(the length of the intraosseous segment was 6mm)was used as the treatment factor to evaluate the short-term(one-year)clinical effect of the implant.The main outcome index: the change of marginal bone level of the implant one year after implantation.Results:1.The two-stage implant is successfully prepared by the combination of added and subtracted materials,and the connection effect of cold welding sample can be achieved between the implant and the abutment.From the microstructure photos of scanning electron microscope,it can be seen that the titanium alloy implant formed by SLM technology has uniform structure,no pores,cracks and other defects,and has a natural micro-rough surface,which reproduces the thread structure designed by CAD,and the pore structure is distributed between the dense lamellar structures.The printing accuracy of each test sample is within the allowable tolerance(< 0.08mm),which proves that the print has qualified dimensional accuracy.After heat treatment,the mechanical properties such as tensile strength,postfracture elongation and fatigue limit of all samples can meet the standards specified in GB/T13810-2017 titanium and titanium alloy processing materials for surgical implants"and "dynamic fatigue test of YY/T0512-2018 intraosseous dental implants".2.The results of in vitro cytotoxicity test-extract test showed that the absorbance values of the experimental group and the blank control group increased gradually after 1,3 and 5days of culture,and there was no significant difference between the two groups(P > 0.05).It was suggested that the addition of SLM titanium alloy extract had no effect on the proliferation of MG-63 cells.According to the grade 5 toxicity standard,the cytotoxicity was 0,which confirmed that the titanium alloy molded by SLM had good biocompatibility.Can be used for in vivo implantation.The results of alizarin red staining showed that there was no significant difference in osteogenic mineralization between bone marrow mesenchymal stem cells on SLM titanium tablets and the control group.The animal experiment in vivo showed that there was no significant difference in bone volume fraction,bone binding rate and spin-out torque between the SLM implant and the control group(sandblasting acid etched surface implant).3.The results of clinical trials showed that among 45 subjects,a total of 45 implants were implanted.There was no significant difference in the marginal bone level between the implant six months and one year after implant implantation and the baseline(implant implantation).The probing depth around the implant and the width of the attached gingiva also had no significant change,and the soft tissue around the implant was healthy and stable.Conclusion:This study confirmed the feasibility of the process of making two-stage titanium implants with increased and subtracted materials,and the implant was closely connected with the abutment.The dimensional accuracy of the implant is consistent with that of the original design,and the mechanical properties such as tensile properties and fatigue strength meet the requirements of national and industry standards,and the implant has good biocompatibility and the ability to induce osteogenic differentiation.the bone bonding property is similar to that of sandblasted acid etched surface implant,which confirms the feasibility of clinical application of the implant.At the same time,the three-dimensional printing short implant developed by this study has a high short-term survival rate and stable marginal bone level.In a word,this study plays an important role in promoting the development of domestic three-dimensional printing two-stage titanium implants.