Enamel Repair And Dental Implant Modification By Amorphous Ceramics

BackgroundThe hard tissues in oral cavity such as enamel and bone are the supporting tissues possessed with chewing or other important physiological functions.At present,there are still certain gaps between the dental materials and the natural tissues in oral cavity.The direct in situ restoration methods of enamel include resin restoration and remineralization.But neither of them could diminish the differences in mechanical properties or the weak connection between different materials.Metal implants,especially titanium implants cannot match the mechanical properties of the bone,which can easily lead to stress shielding at the implantbone interface.Nowadays,amorphous material is one of the hotspots in material science.Compared with crystal materials with more stable properties,amorphous ceramics show obvious advantages in mechanics,electrochemistry and materials science.Recently,amorphous materials have been found in the enamel,bone and other structures of vertebrates.They are not only the precursors before mineralization,but also important components that can stably exist and regulate the properties of hard tissues in mature animals.ObjectiveDeveloping high-performance materials in physiological conditions to clinically repair stiff tissue for long lifespan remains a great challenge.This study is divided into two parts:1 In view of mechanical and antibacterial disadvantages caused by enamel defects,amorphous zirconia layer was uniformly formed on the surface of defective enamel.The effects on the mechanical and antibacterial properties were further investigated.2 The mechanical difference between the titanium implant and the jaw bone might lead to the stress shielding effect.A layer of artificial peri-implant ligament consisted of amorphous titanium oxide ceramic nanotubes and cross-linked chitosan was synthesized on the surface of the implant,which imitated the periodontal ligament around the tooth root.Experiments were prepared to explore its mechanical properties,mechanical attenuation capability and biological osteogenic potential,respectively.MethodsIn this study,we mainly discussed the mechanical and biological properties of the defective enamel and implant surface repaired by amorphous ceramics.1 After defective enamel was etched by phosphoric acid,amorphous zirconia was synthesized on the surface of defective enamel by a series of hydrothermal methods.A variety of electron microscopes were used to detect the morphology of enamel surface after restoration with amorphous zirconia.Nano-indentation technique was used to detect the mechanical properties of enamel before and after repairing.Human gingival fibroblasts and Streptococcus mutans were used to explore the distribution of cells and bacteria on different enamel surfaces to detect the biological influence.2 A layer of amorphous titanium oxide nanotubes was synthesized by anodizing method on the surface of pure titanium implants.Cross-linked chitosan was vacuously injected into the nanotubes and the structure finally called artificial peri-implant ligament.The morphology and mechanical behavior of peri-implant ligament were determined by tests like electron microscope,nano-indentation and finite element analysis.The biological osteogenic potential was manufactured by the behaviors induced after osteogenic culture of rat bone marrow mesenchymal stem cells and rat femur implant surgery were finished to justify the osseointegration capability of implants with peri-implant ligament.ResultsThe main results are as follows:1 By synthesizing a 400nm thickness amorphous zirconia ceramic layer on the defective enamel surface,the morphology and mechanical properties could be recovered to 82.5GPa(elastic modulus)and 5.2GPa(hardness).The connection to enamel was superior than the remineralization methods and kept stable.Besides,there were the least Streptococcus mutans existed on the repaired enamel,which can effectively protect the oral hard tissue from dental caries.2 The artificial peri-implant ligament possessed with the mechanical properties close to those of natural jaw bone,which were much lower than titanium.Besides,the ligament has mechanical attenuation potential.In addition,the structure and composition of peri-implant ligament is with good osteogenic properties,which activated FAK/MAPK and YAP nuclear translocation signal pathway and promotes local osteogenic differentiation.Conclusion1.Amorphous zirconia ceramics could recover the morphology and mechanical properties of acid etched enamel surface to the level of healthy enamel.The repaired layer connected closely to enamel and kept stable.Besides,the repaired enamel had excellent antibacterial adhesion ability which could effectively protect the hard tissue in oral cavity.2.By synthesizing a ligament structure around the implant with amorphous titania ceramic nanotube and cross-linked chitosan on the surface of pure titanium implant,the modified implant had the ability to reduce stress shielding.At the same time,the artificial peri-implant ligament could promote energy dissipation and osseointegration as well.The above amorphous ceramic materials could become a new repairing technology for hard tissue like enamel and periimplant modification technique with future clinical application potential.