Contrast Ratio of a Zirconia-Based Dental Ceramic

Methods: 24 rectangular zirconia specimens (ZENO®, WIELAND Dental and Technik GmbH & Co, Germany), with a dimension of 15x15 mm and four different thicknesses, i.e., 0.4, 0.6, 0.8, and 1.0 mm, were prepared in a laboratory. These core specimens were cut from a zirconia block and fired according to the manufacturer's recommendations. ZirLiner and dentin porcelain (IPS e. max Ceram, Ivoclar Vivadent AG, Liechtenstein, shade A3 Vita Lumin Vacuum) were applied and sintered on each core specimen. All specimens were finished to a final thickness of 1.5 ± 0.1 mm and glazed. Contrast ratios of each specimen (core and core+veneer) were measured three times using a spectrocolorimeter. The means contrast ratio before and after veneering of each group were calculated and statistical analyses of the data was performed using two-way ANOVA (a = 0.05).

Results: Contrast ratios or core opacity of zirconia specimens were significantly increased from 70.5 to 85.5% as their thicknesses were increased from 0.4 to 1 mm. (p<0.05) No significant difference was found between the contrast ratios of zirconia core specimens with thicknesses between 0.6 to 1.0 mm. After veneering to a final thickness of 1.5 mm, their contrast ratios were increased to 92 – 95 %. Specimens with a core thickness of 0.4 mm had the lowest contrast ratio either before or after veneering compared with other groups (p<0.05).

Conclusions: The opacity of zirconia core ceramic was affected by its thickness modification. An increase in opacity was observed when the thickness of zirconia core ceramic was increased. A significant increase in opacity was also observed after layering the zirconia core with veneering ceramic.