Effect Of Different Thickness Of High Translucent Zirconia Ceramics On The Final Color

Objective:The purpose of this experiment is to evaluate the effect of the thickness of the high translucent zirconia ceramic on the final color,and to obtain the minimum thickness of the high translucent zirconia ceramic within the range of color differences acceptable to the human eye,and to provide a reference for the preparation of anterior teeth for clinical practice.Material and methods:In this experiment,three types of high translucent zirconia blocks commonly used in clinical practice were selected:Upcera TT（Upcera,China）,Cercon HT（Dentsply Germany）,and Lava aesthetic translucent porcelain blocks（3M USA）.The blocks were precolored to A2 shade.The zirconia blocks were cut into disks with thickness of 0.7mm、0.9mm、1.1mm and diameter by CAD/CAM.and then sintered according to the manufacturer’s requirements.A 10mm*10mm*10mm cylindrical substrate was made by A4 shade composite resin.The A2 shade test pieces were put on the A4 shade cylindrical substate,and then were measured by Shade Eye NCC computer colorimeter to obtain the CIEL*a*b*value of each test piece.The colorimetric environment was performed in a dark room.The A2 shade CIEL*a*b*values in the VITA classical A1-D4shade guide was used as standard reference.TheΔE*value was calculated according to the formulaΔE*=（ΔL²+Δa²+Δb²）^1/2,and The effect of thickness and brand onΔE*was analyzed by ANOVA,and the comparison betweenΔE*and threshold 3.3 was by single-sample t test.Results:1.Lava Esthetic high translucent zirconia porcelain blocks with a thickness of0.7mm,0.9mm,and 1.1mm averageΔE*values are 3.82,3.17,and 2.42,respectively.The averageΔE*values of the Upcera TT high translucent zirconia porcelain blocks at thicknesses of 0.7mm,0.9mm,and 1.1mm are 4.07,3.2,and 2.58,respectively.Cercon HT high translucent zirconia porcelain blocks with a thickness of 0.7mm,0.9mm,and 1.1mm averageΔE*values are 10.04,10.04,9.97,respectively.2.SPSS25.0 statistical software was used for data analysis:（1）Color difference caused by the Cercon HT group in any range of thickness of the anterior teeth preparation can not be accepted by the human eye;（2）When using high translucent zirconia blocks of different thickness,the resulting△E*value decreases with increasing thickness（P<0.05）;（3）Lava Esthetic group and Upcera TT group:（1）different brands have no significant effect on△E*（P>0.05）,there is no interaction between brand and thickness（P>0.05）;（2）Performing a single-sample t-test on the calculated△E*value and threshold△E*=3.3 to find that when the thickness is 0.7mm,the△E*value is higher than 3.3 and the difference is statistically significant（P<0.05）;when the thickness is 0.9mm,the△E*value and the threshold 3.3 there are no significant difference（P>0.05）;when the thickness was 1.1mm,the△E*value are significantly lower than threshold 3.3（P<0.05）.Conclusion:1.The thickness of the high translucent zirconia restoration material has an impact on the final color.2.Cercon HT high translucent zirconia ceramic is not suitable for aesthetic restoration of anterior teeth as a monolithic restoration.3.In order to obtain the color difference acceptable to the human eye,the minimum thickness of the high translucent zirconia ceramic for aesthetic restoration of anterior teeth is 1.1mm.