Purpose. This study aimed to investigate the effect of the coloring technique on the surface hardness of monolithic zirconia blocks.
Materials and Methods. Monolithic zirconia blocks were milled from monolithic zirconia blanks by using a CAD/CAM system, then, using a water-cooled diamond blade, thirty pre-sintered disk-shaped specimens (2 mm 10 mm) were made from monolithic zirconia blocks. Ten disks were cut from precolored blocks (A2) and twenty from pure white zirconia blocks (A2). The samples were divided into three main groups (n=10) based on the coloring procedure used: Group (WZ) white zirconia, Group (ISZ) internal staining group (pre-colored zirconia block, A2), and Group (ESZ) external staining group, where white zirconia discs were dipped in coloring liquid (A2). Following the instructions from the manufacturer, the coloring liquid was applied. The acrylic resin was used to mount each specimen from the three groups in the center of the polypropylene holders. Each group tested for the surface microhardness test (𝑛=5). Data were analyzed using a one-way ANOVA test to compare the means of three groups with the Bonferroni post-hoc test. SEM photomicrographs were taken at ×500 and ×5000 magnification and observed under a (Quanta 250; FEG) to evaluate the surface morphology and visual inspection.
Results. The results showed the highest Vickers hardness number in the group (ISZ), where zirconia samples were pre-colored (A2).
Conclusion. Coloring techniques affect the surface hardness of monolithic zirconia blocks—the highest Vickers hardness number in precolored zirconia samples.