Effect of coloring liquids on color of zirconia frameworks and bond strength of zirconia/veneering ceramic

Abstract

Statement of problem: Zirconia substructures must be colored to fabricate esthetic restorations. However, the coloring procedure may affect the color match and bond strength of the veneering ceramic to the zirconia.

Purpose: The purpose of this in vitro study was to evaluate the bond strength of veneering ceramic to zirconia after dipping in coloring liquid for different durations and to compare the color of dipped blocks with precolored blocks.

Material and methods: Sixty-four cube-shaped specimens were fabricated from uncolored zirconia blocks by using computer-aided design and computer-aided manufacturing and divided into 4 groups (n=16). The G30 group was subjected to coloring liquids for 30 seconds, G60 for 60 seconds, and G120 for 120 seconds. After the coloring procedures, the color of the specimens was evaluated by using a spectrophotometer. Precolored zirconia (PCZ) was used as the control. Once the color measurements were completed, the same specimens were prepared for the bond strength test, with 2 groups as the control: PCZ and the uncolored control group (control bond-strength [CBS]). Veneering ceramic was applied to the zirconia specimens and sintered. The shear bond test was conducted using universal testing equipment with a crosshead speed of 1 mm/min. Statistical analysis was carried out by using 1-way ANOVA followed by the Tukey HSD test (α=.05). A Weibull analysis was performed, and the Weibull modulus was calculated for each group.

Results: The mean E value for the PCZ group (77.34 ±0.22) was statistically significantly different from that of all groups (PCZ-G30; P=.018, PCZ-G60; P= <.001, PCZ-G120; P<.001). The mean E value for G60 group was significantly different from mean E values of the G30 and G120 groups (G60-G30; P<.001, G60-G120; P<.001). The PCZ group had the highest mean shear bond strength value (31.5 ±7.67 MPa) and was significantly different from the mean bond strength values of the G120 and CBS groups (PCZ-G120; P=.008, PCZ-CBS; P<.001). The CBS had the lowest mean bond strength value (16.62 ±7.11 MPa) and was statistically significantly lower than that of the G60 group (CBS-G60; P=.001). The Weibull modulus was 64.78 for the PCZ group and 0.1 for the G120 group.

Conclusions: Immersing zirconia in coloring liquid altered the color and negatively affected the bond strength between the veneering ceramic and zirconia.