The Influence of Coloring Liquids on the Substrate Masking Ability and Adhesive Properties of Different Zirconia
Rafaela Oliveira Pilecco1, Gabriel Bauken2, Pablo Machado Soares2
1Department of Conservative Dentistry, Faculty of Dentistry, Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil.
Objective:
The aim of this study was to assess the colorimetric characteristics and substrate masking ability of zirconia specimens with coloring liquids applied at the intaglio surface; the zirconia bond strength to a resin-based luting agent and topographic characteristics were also assessed.
Materials And Methods:
Zirconia materials tested were: 5Y-PSZ (Prettau Anterior), 4Y-PSZ (IPS e.max ZirCAD MT), and 3Y-TZP (IPS e.max ZirCAD MO) veneered with lithium disilicate (IPS e.max CAD LT). Disc-shaped specimens (8 mm of diameter, shade A2, n = 10) with 1.5 and 2.0 mm of thicknesses were produced for the colorimetric assessments. For the experimental groups, coloring liquids White and White Plus were applied at intaglio surface of zirconia specimens before sintering. Data for lightness (L*), chroma (C*), hue angle (ho), translucency parameter (TP00), and whiteness index for Dentistry (WID) were recorded; color differences (ΔE00) of specimens over discolored substrates C3, C4, coppery and silvery metals in comparison with a reference (A2) were calculated. Additional specimens (n = 10) were produced to assess the microshear bond strength (μSBS) of a resin-based luting agent to the zirconia intaglio surface with and without coloring liquid. The outcomes were obtained after 24 h water storage and after 10,000 thermal cycles (5°C-55°C). Analyses of variance (two-way for L*, C*, and ho and three-way for TP00, WID, ∆E00, and μSBS) and Tukey post hoc test (α = 0.05) were applied. Topographic images were also obtained via scanning electron microscopy (SEM).
Results:
The use of coloring liquids (especially White Plus) and thicker zirconia specimens provided, in general, reductions in TP00, ΔE00 and hue angle, and an increase in lightness and chroma (p < 0.001). WID increased in 5Y-PSZ and decreased in 4Y-PSZ with the use of coloring liquids in specimens of 1.5 mm (p < 0.001). The μSBS of groups was in the range from 20 to 25 MPa, in which only specimens of 5Y-PSZ with coloring liquids showed statistically lower MPa values in comparison with the control group after aging (p > 0.05). In the SEM analysis, zirconia specimens with coloring liquids did not show relevant differences in topographic characteristics in comparison with controls.
Conclusion:
The application of coloring liquids at zirconia intaglio surface has significantly improved its substrate masking ability without detrimental effects on the bond strength to a resin-based luting agent and topographic characteristics.
Clinical Significance:
The use of coloring liquids at zirconia intaglio surface before sintering is an effective technique to enhance the masking ability of restorations confectioned over discolored substrates.
