Effect of partially stabilized zirconia thickness on the translucency and microhardness of resin cement

Statement of problem: Partially stabilized zirconia has been introduced as a more translucent iteration. However, knowledge of the effect of the thickness of partially stabilized zirconia on the microhardness of resin cement is sparse. Purpose: The purpose of this in vitro study was to evaluate the effect of thickness and material type on the translucency of partially stabilized zirconia and the microhardness of the resin cement polymerized beneath. Material and methods: Specimens were prepared from 2 translucent zirconias with different yttrium content (Ceramil Zolid HT+ [HT] and Ceramil Zolid FX [SHT]) and a lithium disilicate glass-ceramic (e.max CAD [EX]) of different thicknesses (0.5, 1, 1.5, and 2 mm) (n=10). Color coordinates were recorded by using a spectrophotometer, and the relative translucency parameter (RTP) was calculated by using the CIEDE2000 formula. The microhardness of the resin cement polymerized under ceramic specimens was measured. Two-way analysis of variance, the Tukey honestly significant difference, and independent samples t tests were used to analyze the data (α=.05). Results: Material type (P<.001), thickness (P<.001), and their interaction significantly affected the RTP (P=.001) and hardness values (P<.001). Regardless of the thickness, EX had the highest RTP (P≤.027), and the resin cements polymerized under EX showed the highest microhardness (P≤.002). However, the difference between HT and SHT for RTP (P≥.082) and resin cement hardness (P≥.984) was not significant. Specimens of 0.5 mm resulted in higher RTP (P≤.001) and resin cement hardness (P≤.006) than the 1.5- and 2-mm specimens of each ceramic. Conclusions: Increasing material thickness reduced the translucency of the partially stabilized zirconia and the hardness of the resin cements polymerized beneath.