Construction Of Epitaxial Transition Film On Zirconia Ceramic Surface To Improve Bonding Quality

Because of the good biocompatibility,excellent esthetics,high flexural strength,and good toughness produced by the phase transformation toughening mechanism,yttria-stabilized tetragonal zirconia polycrystalline(Y-TZP)materials are receiving attention as dental materials.However,it is difficult to obtain stable bond properties,which affect the clinical prosthetic effect.How to improve the bond quality of zirconia ceramics is one of the challenges in the development of dental materials.The preferred adhesive for zirconia restorations is resin-based luting agent.The bonding mechanism mainly includes a chemical and micromechanical bonding force between the roughened and pretreated zirconia surface and the resin-based luting agent.Chemical bonding has been shown to play a decisive role in the bonding strength and durability of zirconia.However,there are many kinds of resin cements and the bonding effect to zirconia is different.Meanwhile,studies on the aging resistance of resin-based luting agents bonded with zirconia are lacking.Durable and stable bonding is an important factor to the long-term success of the prosthesis.The successful bonding depends on the chemical bonding between the ceramic and the resin cement and the micromechanical retention formed by the coarsening of the ceramic surface.The chemical bonding between ceramic and resin cement is mainly realized by silane coupling agent.The inorganic group at one end of silane coupling agent can condense with Si-OH group on the ceramic surface to form Si-O-Si;the organic group at the other end polymerizes with the organic group of composite resin.There are two main factors that make it difficult for zirconia ceramics to obtain ideal bonding: 1.The phase structure of zirconia is uniform and dense,which is not conducive to the formation of micromechanical retention;2.After densification and sintering,zirconia ceramics do not contain a glass phase(without a silicon component)and have a strong chemical stability.Silane coupling agents do not typically form chemical bonds with zirconia ceramics.Therefore,imparting silicon-containing components to the surface of zirconia ceramics is the key to improving the quality of the bonding.In addition,the other main reason for the failure of zirconia repair is secondary caries.When there is a crack between the prosthesis and the tooth tissue,the salivary membrane will enter into the fissure,and bacteria adhere to the salivary membrane and invade the whole fissure.When the nutrient and time are sufficient,the bacteria produce acid and multiply,and the tooth tissue demineralizes and secondary caries occur.Bacteria and plaque biofilm are essential factors for secondary caries.Therefore,improving the antibacterial properties of the restorative materials is the key to prevent secondary caries.The simplest way to endow the repair materials with antibacterial properties is to add widely recognized antibacterial agents,such as nano silver,chlorhexidine,Quaternary ammonium compounds(QACs),triclosan,chitosan,antibiotics,etc.QACs are a kind of broad-spectrum antibacterial agent of cationic surfactant.It has the advantages of excellent antibacterial performance,strong permeability and lasting biological effect.It is widely used in the antibacterial research of oral materials,such as pit and fissure sealant,resin adhesive,implant and denture base materials.Materials containing these antimicrobial agents exhibit a sustained antibacterial activity when in contact with bacteria and do not release active ingredients.In summary,the bonding strength and aging resistance of five resin adhesives were compared,and a relatively excellent adhesive was selected.Because the lattice parameters of silicate are similar to zirconia,zirconia can be used as nucleation center to induce crystal growth.Silicate transition layer is epitaxial grown on the surface of zirconia after densification and sintering,which can make up for the defect of silicon free zirconia surface and improve the bonding strength.The QACs antibacterial monomer was added to form chemical bond with KH570 hydrolysis system to endow the silicate transition layer with antibacterial properties and prevent the occurrence of secondary caries.In the special part of the restoration,such as the edge,play a sealing role to prevent the invasion of bacteria and prevent the occurrence of secondary caries.At the same time,the QACs antibacterial polymer was added to the selected adhesives to make the restoration system composed of zirconia prosthesis and adhesives have antibacterial properties,so as to prevent the occurrence of secondary caries more effectively.The polymerization conversion rate,surface wettability,micro tensile bond strength and aging resistance of five resin cement(Rely X Ultimate [RUL];Panavia F [PF];Clearfil SA Luing [CSA];Multilink Speed [MS];Rely X Unicem [RUN])were tested,and the bonding effect was comprehensively evaluated.The results have shown that the bond strength of resin cement was affected by many factors,such as DC and wettability.The Multilink Speed presented the highest ?TBS before and after 5000 cycles.The silicate transition layer was epitaxial grown on the surface of sintered zirconia by molecular epitaxy,and formed a stable chemical combination with zirconia.It was characterized by FTIR,FE-SEM,AFM,EDX,contact angle tester and step tester.After treated with KH570 hydrolysate,Multilink Speed was selected as the adhesive in Chapter two to evaluate the effect of silicate transition layer on the shear bond strength of zirconia to resin.Finally,MTT toxicity test was used to evaluate the cytotoxicity of silicate transition layer in vitro.The results shown that after silicate solution treatment,the silicates-based epitaxial transition film was successfully constructed on the surface of zirconia,and the surface morphology and composition of zirconia changed.The shear bond strength and aging resistance of zirconia-resin can be significantly improved by using silicate solution to constructed silicates-based epitaxial transition film on the surface of zirconia.Among them,3 wt%-5 wt% groups have higher bond strength and better aging resistance.Combined with the characterization parameters such as the thickness of the transition layer,3 wt% is recommended as the optimal concentration of silicate solution for the preparation of transition layer on zirconia surface.The epitaxial transition layer of silicate has good biocompatibility.In order to improve the antibacterial properties of zirconia ceramics and prevent secondary caries,in Chapter four,quaternary ammonium salt polymer(MHD-QAC)was synthesized by solution polymerization.Through the chemical combination of hydroxyl group and siloxane in KH570 hydrolysate,the epitaxial transition layer with antibacterial properties was prepared by introducing the silicate epitaxial transition layer selected in Chapter three.Then,according to the mass percentage,5 groups(0 wt%,1 wt%,3 wt%,5 wt%,7 wt%)of the antibacterial epitaxial transition layer were formed.The physical and chemical properties(FTIR,FE-SEM,EDX,static water contact angle,etc.),antibacterial properties,shear bond strength and in vitro cytotoxicity of the 5 groups of antibacterial epitaxial transition layer were evaluated.The results shown that uniform and dense antibacterial transition layer was prepared on the surface of zirconia.With the increase of MHD-QAC content,the N element content on the surface of the transition layer increased,and the static water contact angle decreased.1 wt%,3 wt%,5 wt%,7 wt% groups exhibited antibacterial effects and the antibacterial rates were over 90% and >99% for the 5 wt% and 7 wt% groups,respectively.The results of bond strength showed that the addition of 1 wt%-5 wt% MHD-QAC had no effect on the immediate shear bond strength,while the 7 wt% group decreased.After 5000 cycles,the shear bond strength of each group did not change significantly,and had good durability.All experimental groups had no significant cytotoxicity in vitro.In summary,the main contents of the three chapters present a progressive relationship.The resin adhesives with high bond strength were selected.The silicate epitaxial transition layer was prepared to make up for the defect of silicon free zirconia ceramics and improve the bond strength.Through the adjustment of the proportion of antibacterial polymer,it can give it strong antibacterial properties,effectively prevent the occurrence of secondary caries,improve the success rate of restoration,and lay a solid foundation for the clinical application of zirconia ceramic prosthesis.