Color And Fluorescent Tuning Of 3Y-TZP Based Dental Ceramics

Zirconia ceramics are the most ideal materials for all-ceramic dental restorations due to their excellent mechanical property and optimal biocompatibility. Especially the clinical applications of full zirconium teeth can overcome the disadvantage of large amount of abutment teeth preparation, which makes them gradually become the mainstream of denture material. With the improvement of patient demand for the aesthetic effect of restoration, the simulation of teeth optical performance such as color and fluorescence became more and more been taken seriously. However, the coloring of dental zirconia ceramics had shortcomings of single coloring method and poor color reproduction. Moreover, the fluorescence studies were relatively few. Therefore, on the one hand, this study used different methods to improve the dyeing of zirconia ceramics, on the other hand also by europium doping method to realize the natural tooth fluorescent simulation:Pr-colored 3Y-TZP ceramics were prepared via the mechanical activation of ZrOCl2·8H2O, YCl3·6H2O and Pr Cl3·7H2O and NaOH in a planetary ball mill. The best preparation procedure was found that the first step is calcination of the milled precursor and then is the removing of NaCl by washing. Therefore, Pr-doped 3Y-TZP nanoparticles with an average particle size less than 10 nm can be obtained by 30-min milling of reagents and subsequent 120-min heat treatment at 500 °C. 3Y-TZP ceramic discs with a range of yellow shades in color range of natural teeth have been obtained by sinterring 3Y-TZP nanopowders doped with different contents of Pr. Among them, the ceramic disc with dopping 0.09 mol% Pr shows a drastic increase of b* value as well as a slight decrease of L* value and a* value.Using 3Y-TZP as starting materials, Fe(NO3)3 as coloring agent and PEG 2000 as dispersant, five different colors of 3Y-TZP with different amounts of Fe2O3 were prepared by heterogeneous precipitation method. The result showed that heterogeneous precipitation method could produce a uniform colored zirconia blocks. Adding Fe2O3 could increase the b* value of sintered body significantly, but had little influence on the L* and a* value. SEM observation on the cross section of the colored 3Y-TZP showed a relatively dense polycrystal structure, and the fracture models was mainly transgranular fracture. The XRD spectra showed that only tetragonal phase(t-ZrO2) was detected. The heterogeneous precipitation method could be a novel route for the fabrication of coloring uniform and superior performance dental 3Y-TZP ceramics by adding different amounts of Fe2O3.Five color gradients of zirconia porcelain pieces were prepared By solution immerse staining method using propyl alcohol and deionized water solutions containing different concentrations of Fe3+ colorant and Nonylphenolethoxylate(NP-8) surfactant. It was found that the obtained zirconia ceramic pieces after high temperature sintering show more even color due to the adding of surfactant NP–8 in iron staining solution, the color difference value < 2, which reachs the clinically acceptable level. The SEM observation on the cross section of the colored 3Y-TZP showed a relatively dense polycrystal structure, and the fracture models was mainly transgranular fracture. The XRD spectra showed that only tetragonal phase(t-ZrO2) was detected.Eu-doped 3Y-TZP ceramics were prepared by powder mixing and immersion method followed by calcination at high temperature under different atmosphere. The surface microstructure, phase constitution and fluorescence spectrum were analyzed by X-ray diffraction(XRD), scanning electron microscope(SEM), fluorescence spectrometer. The results showed that Eu-doped 3Y-TZP ceramics with blue fluorescence emission similar to natural tooth have been prepared after calcination under reducing atmosphere using above two methods. The excitation spectrum excited by 470 nm shows a broad band absorption peak at 370 nm, which corresponds to 4fâ†'5d transition of Eu2+. The emission spectrum excited by 365 nm shows a characteristic blue broad band with peak at around 470 nm, which corresponds to 4f65d1 â†' 4f7(8S7/2) transition of Eu2+. The sintered Eu2+ doped 3Y-TZP ceramics are density with uniform grain size about 450 nm, and their main crystal phase is tetragonal phase. They can emit blue fluorescence similar to natural teeth under the excitation of near ultraviolet in natural light, proving the realization of natural teeth blue fluorescence simulation. However, Eu-doped 3Y-TZP ceramic prepared by calcining under air atmosphere presents a red fluorescence with characteristic emission bands at 604 nm(5D0â†'7F2) and 595nm(5D0â†'7F1) of Eu3+ under excitation of 395 nm radiation.L-929 cells were cultured in vitro with the leaching solutions of above Fe, Pr and Eu doped 3Y-TZP ceramics for 3 days to evaluate the cytotoxicity of colorized zirconia by microscope observation and MTT method. At the same time, fresh blood of rabbit was mixed with leaching solutions to determine their hemolysis ratios. The results showed that during 3 days culturing, L-929 cells grows well with normal morphology. The toxicity ratings of 0 ~ 1 grade, indicating that Fe, Pr, Eu doped 3Y-TZP ceramics has no cytotoxicity. The observed hemolysis rate is between 0.031 ~ 0.072%, meaning that they have security foundation of clinical application.