Study On The Production Process And Optical Properties Of Shaded Y-TZP Dental Ceramics

Yttria-stabilized tetragonal zirconia polycrystal（Y-TZP）have exceptionally highflexural strength because ofitsmartensite transformation under stress, in addition to itsexcellent biocompatibility.It has become an ideal ceramicmaterial for dentalrestorationscompared with other dental ceramics, because it’s very high strength andtoughness. Normally, the dental zirconia is white orivory color and its relativelytranslucent is not good, which make it difficult to match the color of natural teeth.Thewhite zirconia framework is not desirable in each case, and then applying opaquemaylose much translucence. If the shaded zirconia frameworkis adapted to the brightnessand chroma of the natural teeth, harmony color matching neighboring teeth would bearrived simpler and teeth would conserve more substance. Basically, two methods areused to shade dental zirconia materials.Firstly,pre-sintered porous zirconiaframework isinfiltrated with an aqueous solution.Secondly, zirconia materialis shaded during theproduction of the zirconia powder. The former may cause inhomogeneous color, andalso coloring liquid may not be used among different systems because of the differentmaking processand sintering procedure of material.The latter isbetter because the colormay be homogeneous and accurate. As core material, Y-TZP offers a advantage ofrelative translucence，which improves the esthetic appearance. The milled Y-TZPframework is veneered with dental porcelain forming bilayers，andthat the shadingdestination of the core ceramics should be reached is the key to reproduction of naturalteeth with dental ceramic material. The factors may include the translucence, lightnessand chroma of the core ceramics and also the translucency of the veneering porcelain.As an all-ceramic dental material,the shaded zirconia material is urgentlyneededin theclinical application, and it isone of the future developing trends for the dentalprosthodontics technologies. In this thesis, some intrinsic shaded dental zirconiasamples with chromatic value similar to Vita-3D Master shade guide were prepared byshading the zirconia ceramic with oxide powder. The preparation process,microstructure and optical properties of those samples were investigated. Results showas follows:1. Doing research of zirconia spray granulation slurry’s rheological characteristics.Using three factors and three levels of orthogonal experimental method. Getting ahigh solid content, low viscosity, good stability, a colorant dispersed zirconia slurryspray granulation.In this experiment, the influence of the nature of the Y-TZP slurrysolids content, PVA amount and length of time was studied.The slurry solidscontent of the analysis resulted have a significant effect on the rheology of theslurry, and PVA amount and length of milling were no significant effect on theaverage viscosity of Y-TZP and settling of the slurry.2. The spray granulation factors ofviscosity and sedimentation of the slurry could notbe ignored, because of the needs of large-scale industrial production. The solidcontent of the slurry was50wt%,and the amount of PVA was3wt%, according tothe results of orthogonal test, and production process validation tests. The mainpurpose of this experiment was to trial colored uniform and a certain translucencyof Y-TZP dental restorative materials. According to the production process ofindustrial production experience and verification, determined the length of time forthe milling24h. Preferably theexperimental analysis solution of slurryofspray-granulating was A3B3C3, i.e., solid content of50wt%; PVA added in anamount of3wt%; length of milling time was24h. Through process validation, thepowder particles were mostly spherical granulation that got the edge over the sleek,and no bubbles.3. Thedistribution of powder particlesofunshaded Y-TZP,0.15wt%Fe2O3coloredY-TZP and4wt%CeO2was substantially between40-120μm. While there was anarrow particle size distribution of powder particles,powder particles of60-90μmwere around more. Granulated powder particle size was not exactly the same, andthere was a certain size grading. Fe2O3as a coloring agent had some impact on thesize of the particles, but the effect was not obvious. 4. Fe2O3and CeO2as colorants had a little effect on flowability of the granulatedpowder, ball performance and density of the pre-sintered body.5. The colored sintered Y-TZP contained mainly tetragonal crystal phase ZrO2. Therewere not peaks of Fe2O3and CeO2in the XRD. The colored Y-TZP had uniformgrain size, and grain size of0.5-0.7μm. The colored Y-TZP fracture mode wastransgranular and intergranular fracture.6. Based on the previous study, the paper will prepare for Zirconia slurry, and use thespray granulation method to do zirconia granulation. Then using the VITAeasyshade color instrument to measure the color of Y-TZP. The study observed thatthe coloring process, which is added with Fe2O3could significantly reduce theoxidation zirconia ceramics (Y-TZP) lightness, brightness to75.27. While whenadded with CeO2,the coloring effect was not obvious.7. The visible light transmittance of shaded Y-TZP and unshaded Y-TZP had awavelength dependence in the region of visible light400-700nm. The transmissionrate was monotonic.The transmittance increaseswith increasing wavelength.Thetransmission curve of unshadedY-TZP was almost a straight line, and the visiblelight transmittance of unshaded Y-TZPwas higher than the shaded Y-TZP.8. There was significant differencebetween unshaded Y-TZP and Fe2O3groups（P＜0.05）;Compared with0.03wt%Fe2O3group,0.15wt%Fe2O3group has significantdifference （P＜0.05）. Aboutvisible light transmittance, unshaded Y-TZP＞0.03wt%Fe2O3Y-TZP＞0.15wt%Fe2O3Y-TZP.9. There was significant differencebetween unshaded Y-TZP and CeO2groups（P＜0.05）;Compared with1wt%CeO2group,4wt%CeO2group has significantdifference （P＜0.05）. Aboutvisible light transmittance, unshaded Y-TZP＞1wt%CeO2Y-TZP＞4wt%CeO2Y-TZP.