Research On Color Regulation And Properties Of Dental Zirconia Ceramics Fabricated By Stereolithography

3 mol%yttria-stabilized tetragonal polycrystalline zirconia（3Y-TZP）ceramics have received widespread attention and become a very popular dental restorative material due to their excellent mechanical properties,chemical stability,good aesthetics,and biocompatibility.However,the zirconia ceramic materials currently on the market are mostly white,with a single color,which cannot meet the needs of all patients for color of dental restoration.To improve the aesthetics of zirconia ceramics and to meet the clinical requirements for tooth color matching,they need to be colored.Currently,dental restorations are usually fabricated by traditional techniques and CAD/CAM machining processes,which have the disadvantages of low manufacturing efficiency,low material utilization,long production cycle and difficulty in preparing parts with complex structures.Stereolithography（SLA）is used to build solid objects by layering ceramic materials,which has the advantages of high printing accuracy,fast molding speed,high material utilization,high molding freedom,and good surface quality of molded parts,which can effectively solve the problems of traditional ceramic molding technology.Based on the above background,this study combines the stereolithography（SLA）technology with the ceramic powder internal coloring method,using iron oxide（Fe₂O₃）as the colorant to prepare a new dental zirconia ceramic material with ideal mechanical properties and color characteristics to meet the requirements of dental clinical restoration.The main research contents of this paper are as follows:Firstly,the effects of dispersant type,content and solid loading of slurry on the rheological properties and viscosity of the slurry used in the SLA process were systematically investigated,and the stability of the slurry was verified.The results show that the 3Y-YZP ceramic slurry prepared by adding 2 wt%KOS110 has the best dispersion effect and stability with solid loading up to 58 vol%.Finally,six ceramic slurries with high solid loading,stability and suitable printing viscosity were prepared according to the Fe₂O₃doping in range of 0-0.14 wt%.Secondly,the relationship between exposure light intensity and curing depth in SLA process was established using the Beer-Lambert Law to obtaine the critical energy density of the slurry.Suitable printing parameters were determined:110 m W laser power and 3500 mm/s scanning speed with a forming layer thickness of 25μm.Based on thermogravimetric analysis,a suitable debinding procedure was developed,and the different stages and mechanisms of debinding were analyzed in detail.In this study,the debinding process was divided into four stages:initial debinding（20℃-250℃）,middle-stage debinding（250℃-450℃）,final-stage debinding（450℃-550℃）,and pre-sintering stage（550℃-1100℃）,and the sintering conditions were determined as atmospheric pressure air sintering.Meanwhile,the effects of different sintering temperatures（1400-1600℃）on bulk density,microstructure,phase composition,and mechanical properties of 3Y-TZP ceramics were investigated.The experimental results showed that 1500℃was the optimal sintering temperature for 3Y-TZP ceramics,and the highest bulk density and three-point flexural strength were obtained at this time.Finally,the effects of Fe₂O₃ content on the microstructure,mechanical properties and aesthetic characteristics of 3Y-TZP ceramics were investigated at a sintering temperature of1500℃.The results showed that Fe₂O₃ doping had little effect on the shrinkage and density of the ceramics,and the densities of the samples could all reach 99%.The average grain size and monoclinic phase of 3Y-TZP ceramics increased with the increase of Fe₂O₃ content.Although the three-point flexural strength,Vickers hardness and fracture toughness of the ceramics are slightly decreased by the Fe₂O₃ doping,they can still meet the requirements of the mechanical properties for dental restorations.In addition,the doping of Fe₂O₃ successfully modulated the color of 3Y-TZP ceramics prepared by SLA,decreasing the color index L^*of the ceramic material while increasing a^*and b^*at the same time.The values of chromaticity（L^*,a^*,b^*）basically falls within the range of the color of Chinese teeth,and the color of the colored material is uniform,which basically meets the requirements of dental restoration for color and has a certain degree of light transmission.