Effect of fabrication techniques on the optical properties of zirconia-based systems

Statement of problem. How the optical properties of zirconia restorations are affected by their differing processing techniques is unclear. Purpose. The purpose of this in vitro study was to evaluate the effects of 5 different fabrication techniques on the optical properties of zirconia-based systems, including the color difference between the corresponding shades (Delta E*(ab), Delta E-00), translucency parameter, opalescence parameter, and fluorescence (Delta E*(ab)-FL). Material and methods. Sixty zirconia disks (IPS e.max ZirCAD) were prepared (0.5 +/- 0.01mm thick) and veneered by using different techniques (n=15): Group L e layering with fluorapatite ceramic; Group P e pressing with fluorapatite ceramic; Group CB e veneered with pressing followed by layering technique; Group CO e digitally veneered with lithium disilicate glass-ceramic; and Group FZ e prepared from monolithic zirconia (inCoris TZI) (n=15). All the specimens were set to 1.5 +/- 0.02 mm in thickness. Color measurements were made with a spectrophotometer. Data were statistically analyzed with 1-way ANOVA and the Tukey honestly significant difference, Kruskal-Wallis, Bonferroni (alpha=.05), Pearson, and Spearman correlation tests (alpha=.01). Results. Significant differences were found among the groups for all the optical parameters (P<.05). All the groups showed color differences higher than the perceptibility and acceptability thresholds for Delta E*(ab) and Delta E-00, except the P and FZ groups that showed values lower than the acceptability threshold (Delta E*(ab)<2.7). Translucency parameter, opalescence parameter, and Delta E*(ab)-FL values ranged between 5.77 and 9.95, between 4.72 and 7.07, and between 1.93 and 3.14, respectively. Strong positive correlations were found between Delta E*(ab) and Delta E-00, as well as between translucency parameter and opalescence parameter (P<.001). Conclusions. The optical properties of the zirconia-based systems were significantly affected by the fabrication techniques even when the same nominal shade was used. Therefore, the color reproduction, translucence, opalescence, and fluorescence of the selected materials should be considered for acceptable color matching.