Fabrication And Biological Evaluation Of RAI Based On High Precision SLM Technology

The main purpose of dental treatment is to enhance and maintain the patient’s health.In the past,fixed dentures or removable dentures were usually used to repair the missing teeth.However,with the development of implant technology,dental implant has become the best substitute to repair the missing teeth at present.Among various dental implant techniques,immediate implantation is believed to shorten treatment time,reduce the number of operations,maintain soft tissue volume,and preserve the surrounding bone volume as much as possible.During the operation,the operator can use the tooth extraction socket to guide the direction of implant placement.Increasingly,it is also replacing delayed implantation in some cases.However,due to the mismatch between the morphology of traditional implants and tooth extraction fossus,the initial stability of implants in immediate implantation is not good,and bone graft meterials are often needed to be filled,which has high technical sensitivity,relatively obvious postoperative reaction and prolonged recovery time.This study is based on the selective laser melting（SLM）technology after improving the accuracy to manufacture the root analysis implant（RAI）which can be used for immediate implantation.The shape of RAI is matching he extraction socket to increase the initial stability of the implant,so as to improve the problems caused by the mismatch between the shape of the implant and the alveolar socket in the traditional immediate implant.Generally,the surface roughness of RAIs printed with SLM is much larger than that produced by traditional acid-etched sand blasting,and the roughness is varies greatly in different areas.In this study,the forming process of RAIs as firstly optimized to obtain the maximum 99.73%relative density of titanium materials.By controlling the line energy density（LED）and offset,the roughness of different regions on the same RAI surface was uniformly controlled at Sa≈13μm in combination with gradient molding.The standard titanium plates（3D-Ti group）were printed by the optimized parameters,compared with smooth titanium plate（group S-Ti）and acid corrosion sandblasting titanium plate group（SLA-Ti）on microstructure,composition elements,surface roughness and hydrophilicity as well as protein adsorption ability.And human Bone marrow mesenchymal stem cells（h-BMSCs）were cultured on the surface of titanium sheets in each group.The adhesion ability,cytoskeleton arrangement,cell spreading,cell proliferation ability and osteogenic differentiation ability of h-BMSCs in each group were compared.It had been found that the surface of 3D printed titanium sheet is hydrophilic,with good biocompatibility and roughness,which can promote cell proliferation and osteogenic differentiation.Then,the mandibles of Beagle dogs were scanned by cone beam computed tomography（CBCT）,and three-dimensional models of the abutment and root of the target teeth were obtained by reverse technique.Finally,the abutment and root of the target teeth were printed by SLM technique.Compared with conventional implants,this bone level RAIs had achieved a survival rate of over 90%in vivo experiments in Beagles.Micro-CT and hard tissue biopsy results at 3^th and 6^th month suggested that compared with conventional threaded columnar implants,the implantation of RAIs did not damage important anatomical structures around the alveolar fossa,and that the new bone formed on the surface was more continuous and had a greater area of attachment to the old bone.BIC and BV/TV of implants at 3^th and 6^th month were not significantly different between the two groups.Finally,in this study,zirconia crowns were repaired in the upper part of RAIs of three Beagles,which restored the chewing ability to a certain extent.To sum up,in order to improve the problems caused by the mismatch between the implant and the alveolar socket in the traditional immediate implantation,this study improved the printing accuracy of SLM technology and produced personalized bone-level root analogue implants with high density and small roughness surface.The results suggested that RAIs had good biocompatibility,and they had the ability to promote osteogenic differentiation of BMSCs and form stable osteogenesis in Beagles’jaw.Finally,the connection structure between the abutment and the root was designed,and the crowns were restored on the RAI in the Beagles’mouth,which restored some chewing function.Therefore,this kind of personalized root analogue implant based on high precision selective laser melting technology has a certain clinical application prospect.