The color masking ability of a zirconia ceramic on the substrates with different values

Background. The color masking ability of a restoration plays a significant role in covering a discolored substructure; however,
this optical property of zirconia ceramics has not been clearly determined yet. The aim of this in vitro study was to
evaluate the color masking ability of a zirconia ceramic on substrates with different values.

Methods. Ten zirconia disk specimens,0.5 mm in thickness and 10 mm in diameter, were fabricated by a CAD/CAM system.
Four substrates with different values were prepared, including: white (control), light grey, dark grey, and black. The
disk specimens were placed over the substratesfor spectrophotometric measurements. A spectrophotometer measured the L*,
a*, and b* color attributes of the specimens. Additionally, ΔE values were calculated to determine the color differences between
each group and the control, and were then compared with the perceptional threshold of ΔE=2.6. Repeated-measures
ANOVA, Bonferroni, and one-sample t-test were used to analyze data. All the tests were carried out at 0.05 level of significance.

Results. The means and standard deviations of ΔE values for the three groups of light grey, dark grey and black were
9.94±2.11, 10.40±2.09, and 13.34±1.77 units, respectively. Significant differences were detected between the groups in the
ΔE values (P<0.0001).The ΔE values in all the groups were more than the predetermined perceptional threshold(ΔE>2.6)
(P<0.0001).

Conclusion. Within the limitations of this study, it was concluded that the tested zirconia ceramic did not exhibit sufficient
color masking ability to hide the grey and black substrates.