Preparation And Properties Of Bioactive Zirconia Dental Ceramic Materials

Since Br?nemark first proposed that high-purity titanium metals could be a new oral implant substitute for gold and other noble metals in 1960 s,titanium and its alloyhave become a reliable treatment option for the replacement of missing teeth caused by dental caries,periodontal disease and dental trauma.However,aesthetic problemsthat were caused by gingival recession and allergic reaction due to the release of toxic metal ions,will restrict the extensive application of titanium and its alloy.Yttria-stabilized tetragonal zirconia(Y-TZP)has a bright prospect for dental restorative materials due to its good biocompatibility,high mechanical properties and distinctive aesthetic effect,which is distinguished from titanium and its alloy.AlthoughY-TZPhas good mechanical properties and aesthetic effect,itis deficient in bioactivity.When bioinert Y-TZP is implanted in vivo,fibrous tissues that developed around the implants impede the osseointegration process between the implant and adjacent bone tissues,which will cause premature failure of the implant due to the weak combination and poor stability.Therefore,enhancing the bioactivity of Y-TZP is of great significance for developing oral implants.In this paper,bioactive glass(BG)was used as a modifier.The bioactive Y-TZP was prepared using an introduction of a thin glassy phase into the grain boundaries of Y-TZPin two different ways.One is the infiltration of BG sol precursors into the surface layers of zirconia ceramics,and another is zirconia powder particles coated by BG precursor sol.The microstructure,surface topographyand fracturemorphology of the modified Y-TZP were obtained using X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe micro analysis(EPMA)and Raman spectroscopy.The bulk density,relative density,bending strength and fracture toughness of the modified Y-TZP were also measured.In vitro biomineralization through simulated body fluid(SBF)immersion was used as anassessment for the bioactivity of modified Y-TZP.The cell adhesion,proliferation and differentiation of the materials were evaluated.The effects of the penetration time,the infiltration pressure and the cladding amount on the structures and properties of the material were also discussed.A thin glassy phase formed at the grain boundaries of the surface layer or the overall of Y-TZP after high temperature sintering when Y-TZP was infiltrated or cladded by BG sol.The results of the in vitro biomineralization test showed that induced calcium-phosphorus(Ca-P)layersdeposition capacity of the prepared Y-TZP was effectively promoted viagrain-boundary activation.In addition,the biomineralization abilities increased with the increase of BG infiltration time and BG cladding content.XRD and Raman confirmed that the deposited Ca-P layers were hydroxyapatite(HA).It followed that the bioactivity of Y-TZP was enhanced via grain-boundary activation.Cell experiments results revealed that the materials with BG sol permeation or claddinghad good biocompatibility,and the cell spreading,adhesion and differentiation were also promoted.The results of mechanical properties showed that the relative density,bending strength and fracture toughness of Y-TZP after BG infiltration and BG cladding decreased compared with those of the Y-TZP blank group.However,under appropriate conditions(the samples infiltrated with BG sol under-0.05 kPa and atmospheric pressure for 5 min;under-0.1 kPa for 1 mim and coated by 1% content of BG),the modified Y-TZP still retained good mechanical performance,which is satisfied the clinicallymechanical properties requirementsfor dental implants.