Study On Coloring Methods And Properties Of Dental Y-TZP Ceramic

With the improvement of people’s living standard, dental implants have been asked to meet progressive requirements. Y-TZP (yttria-stabilized tetragonal zirconia polycrystalline) ceramic used as dental implant has been widespread concerned by academic and industry for three decades. Chromaticity of a dental implant is our first priority as well as translucency. However there is a certain gap between Y-TZP ceramic and natural tooth. Y-TZP/porcelain bilayered structure can achieve a suitable color easily. Meanwhile poor performances on translucency and mechanical property are brought about in this conventional coloring method. Therefore the self-colored Y-TZP all-ceramic crown has been standing in the spotlight. At present, there are few reports about effects of coloring methods on the properties of Y-TZP ceramic.In the present paper, ZrO2(3Y) nanopowder was prepared by chemical precipitation process. We studied the influences of different coloring methods on physical and chemical properties of Y-TZP such as mechanical properties, translucency and chromaticity. The coloring methods (with colorants of Fe2O3 and CeO2) included in situ doping coprecipitation, mechanical mixing of ZrO2(3Y) nanopowder with colorants, immersion of ZrO2(3Y) in coloring liquid and immersion of Y-TZP in coloring liquid. The results showed that:(1) The dispersion of precursor suspensions was best when the addition of PEG-6000 reached 1.4 wt% with powder grain sizes of 15 nm after heat treatment. With the elevating of temperature, the content of monoclinic phase in ZrO2(3Y) nanopowders increased gradually. Crystal transition temperature of amorphous ZrO2(3 Y) decreased with the increase of CeO2 resulting in the increase of content of monoclinic phase.(2) Volume density of unsintered Y-TZP increased first and then decreased with the increase of dry pressure in dry pressing and cold isostatic pressing moulding process. Machinability rating increased first and then decreased with the increase of presintering temperature. Trace of monoclinic phase formed in Y-TZP due to excessive sintering temperature or holding time. Increase of sintering temperature or holding time contributed to higher light transmittance and poorer mechanical performance. The sintering condition was identifies as 1470 ℃/2 h.(3) Y-TZP colored through in situ doping precipitation had excellent performances in hardness, fracture toughness and flexure strength. However, these properties were relatively poor in the method of mechanical mixing of ZrO2(3Y) nanopowder with colorants due to the limitation of homogeneity. Y-TZP colored with Fe2O3 showed decreasing hardness resulted from the hydrolysis Fe3+ which might lead to inhomogeneity. Immersion of Y-TZP in coloring liquid significantly reduced the flexure strength of Y-TZP.(4) Light transmittance of Y-TZP in the range of low wavelength decreased due to the doping of Fe2O3 and CeO2. The method, mechanical mixing of ZrO2(3Y) nanopowder with colourants, had greatest influence on light transmittance and this might be related to the inhomogeneity of colourants and decrease of density(caused by poor formability). Samples prepared by in situ doping coprecipitation had the highest light transmittance; for the Y-TZP doped with Fe2O3, chromaticity index L* incresed while a* and b* decreased; for the Y-TZP doped with CeO2, b* increased while a* and L* scarecely changed. Chromatic aberration of Fe2O3 doped Y-TZP was highest prepared by method of immersion of unsintered Y-TZP and this might caused by high content of Fe2O3 in the Y-TZP surface resulting from little permeation of Fe3+.