Does Speed Sintering of Hight Translucency Zirconia Impact it's Color ?

Objectives: The main objective was to assess the colour difference between traditionally sintered and high-speed sintered monolayer zirconia at different thicknesses with different underlying tooth colours.
Methods: 14 discs of 3Y-TZP (yttria-stabilized tetragonal zirconia polycrystal) in HT12 (hight translucency) shade (Katana, Kuraray) where milled and polished at 0.6, 0.7, 0.8, 0.9, 1, 1.5 and 2 mm thickness. The discs were sintered either with a regular program (7 hours) or with a high-speed sintering program (21 minutes). Nine discs of different shades were fabricated at 2mm thickness as replica of the underlying teeth (UT) using standardized natural die resins (Natural Die, Ivoclar-Vivadent). Each zirconia disc was placed over the UT, using an interposed neutral try-in paste (Variolink Esthetic, Ivoclar) to simulate the cement interface.
CIE coordinates were measured 5 times for all combinations using a spectrophotometer (EasyShadeV,VITA).
The difference in color ( ΔE₀₀ ) was assessed for the two types of sintering, with and without UT. A two-way ANOVA test ( α=0.05 ) was performed to evaluate the impact of sintering and ceramic thickness, followed by multiple pairwise comparisons.
Results: For both ceramics, without UT, lightness and hue decreased with thickness, while chroma increased. High-speed sintered 3Y-TZP had higher hue (p<0.05), yet lower chroma (p<0.05), for most thicknesses, compared to traditionally sintered 3Y-TZP.
ΔE₀₀ between the two types of ceramics, without UT, was acceptable ( ΔE₀₀<2.7, perceptibility threshold, PT) for most thicknesses. For discs of 0.7 and 0.8 mm, the color difference was imperceptible (ΔE₀₀<1, perceptibility threshold, PT).
When combined to the underlying teeth, ΔE₀₀ between traditionally sintered 3Y-TZP and high-speed sintered 3Y-TZP, was acceptable for most thicknesses, for all UT.
Conclusions: Speed sintered high translucency zirconia might replace the standard sintered zirconia without a significant esthetic compromise. The clinician should carefully select the biomaterial thickness, according to the tooth color.