The Effect of Liner Thickness on the Color of Y-TZP Based All-Ceramic Restorations

To evaluate the effect of various liner thickness on the color of Y-TZP based all-ceramic restorations. Forty disc specimens (10 mm diameter, 0.5 mm thick) were fabricated from IPS e.max ZirCAD core material. The specimens were randomly divided into four groups (n=10) according to layering with different ZL1 IPS e.max ZirLiner thicknesses as: 0.1 mm, 0.2 mm, 0.3 mm and one group had received no treatment as the control group. And 0.6 mm veneering porcelain was fired on the IPS e.max ZirCAD core material by traditional layering technique. Using a spectrophotometer to measure Color parameters L, a and b of the specimens after veneered. Delta E were calculated to compare color difference among the four groups. Intergroup differences of Delta E in different thicknesses were statistically significant at P<0.05. The Delta E between groups with different thickness were 2.03 +/- 0.07, 2.88 +/- 0.07, 3.54 +/- 0.07, 0.86 +/- 0.06, 1.47 +/- 0.06 and 0.67 +/- 0.06 respectively. Usually researchers apply Delta E=1.5 as the threshold for distinguishing two different colors by the human eye. Color difference Delta E between different groups with and without liner application was more than 1.5, which was in the perceptible range, but Delta E of liner application with the thickness of 0.1 mm, 0.2 mm and 0.3 mm were undistinguishable by human eye (Delta E<1.5). Thus liner application of the all ceramic system could significantly affected the final color of the all ceramic restorations and it ameliorated esthetics of Y-TZP all-ceramic restorations to good purpose. However, Changes in the thickness (0.1 similar to 0.3 mm) of liner application have no significant effect on the final shade of Y-TZP based all-ceramic restorations.