Preparation And Performance Of Dental Opaque Fused To Co-Cr Alloy

In this research, a superfine leucite-reinforced dental material was prepared byhydrothermally-derived leucite precursor and basic frit. The leucite crystallizationmechanism and phase transition process were investigated. The effect of basic frit onthe crystallization temperature and phase transition process during the leucitecrystallization, as well as the microstructure of leucite crystal in dental porcelain wereanalyzed by X-ray diffractometer （XRD）, High-temperature X-ray diffractometer（HXRD）, DSC-TG analysis and Scanning Electron Microscopy （SEM）. To understandthe wetting and spreading behaviors, the interfacial reactions, and the bondingmechanism of porcelain fused on metal with TiO₂and MoO₃added to the dentalporcelain. The effect of dental porcelain added with SnO₂and CeO₂on color maskingability was investigated. Computer color matching of opaque porcelain was studied,and the opaque porcelain color database was established.A superfine leucite-reinforced dental material was prepared by heat-treating themixture of30wt%hydrothermally-derived leucite precursor and70wt%basic frit at750℃. The alkali and alkaline earth mental oxides in the basic frit can form liquidphases earlier, create cation vacancies, increase the chemical potential of the system,and thus effectively lower the crystallization temperature of leucite from1027℃to720℃. The cubic leucite was crystallization at720℃and the cubic leucite wouldtransform to tetragonal leucite in the cooling process. There exists a temperature rangefrom700℃to900℃in which leucite crystals are in the equilibrium of forming anddecomposition, when the temperature reached750℃, the content of leucite wasunchanged. The leucite average size in the dental porcelain prepared by the mixture oflow temperature frit and the material is about115nm, and the superfine leuciteparticles are homogeneously distributed in the matrix, which would improve thestrength and toughness of dental materials.In order to determine the leucite content in the dental material, quantitative XRDanalysis was used. The calibration curve was established by mixing various weight fraction of pure leucite into the basic frit. The leucite content in the dental material isabout30-34wt%.The high temperature wettability and bonding mechanism of porcelain to Co-Cralloy were investigated by TOMMI optical dimension measurement system, SEM andRaman spectra. The addition of TiO₂and MoO₃in the dental porcelain improved thewettability of the dental porcelain/Co-Cr alloy system, and obtained the formulationwas2wt%MoO₃,3wt%TiO₂,1wt%SnO₂and94wt%porcelain. The addition ofTiO₂can lower the high temperature viscosity of the dental porcelain and theexistence of MoO₃may promote the reaction between dental porcelain and the Co-Cralloy. The high temperature wetting of porcelain to Co-Cr alloy was reactive wetting,an intermediate layer with a new phase was formed, the main component of theintermediate layer was the oxide of chromium, and there existed diffusion andchemical reactions from porcelain to the intermediate layer. The intermediate layer ofthe porcelain added with TiO₂and MoO₃/Co-Cr alloy system is wider than theporcelain without TiO₂and MoO₃/Co-Cr alloy system. The bond strength of theporcelain modified with TiO₂and MoO₃was43±2MPa and that of the unmodifiedporcelain was38±3MPa. The bond strength of two samples is much higher than ISOstandard9693（the acceptable bond strength of metal ceramic restorations is25MPa）.The fracture occurred near the porcelain layer, and part of the porcelain wasembedded into the matrix of the Co-Cr alloy.The addition of SnO₂and CeO₂in dental porcelain can raise the color maskingability, when the adding amount was5wt%SnO₂,3wt%CeO₂, the opaque porcelain（thickness of opaque was0.2±0.02mm） can mask cobalt-chromium alloycompletely.The monochrome color samples of vanadium-zirconium yellow,zirconium-praseodymium yellow, chromium-aluminium-zincum red andzirconium-vanadium blue were prepared, and the opaque porcelain color database wasestablished. Computer color matching experiments of the opaque porcelain were performed accoding to the database. The chromatic aberration of opaque porcelainsprepared by this work and Vita A2、A3were1.17and1.12, respectively, which wereless than what the human eye can distinguish.