Impact of laboratory treatment with coloring and fluorescent liquids on the optical properties of zirconia before and after accelerated aging.

STATEMENT OF PROBLEM: Laboratory procedures, such as dipping in coloring and fluorescent liquids, can be used to improve the optical properties of zirconia. However, information is lacking on the effect of these liquids.

PURPOSE: The purpose of this in vitro study was to evaluate the color differences and degree of fluorescence of zirconia (3Y-TZP) treated with coloring and fluorescent liquids before and after an accelerated aging protocol.

MATERIAL AND METHODS: Forty disk-shaped specimens of 3Y-TZP were fabricated by milling and separated according to the laboratory treatment performed: white zirconia (control group); zirconia treated with coloring liquid (A2 group); zirconia treated with fluorescent liquid (fluorescent group); and zirconia treated with both liquids (A2 fluorescent group). The L*a*b* coordinates before aging (T0 ) were obtained with a spectrophotometer, and the degree of fluorescence was measured. The disks were subjected to accelerated aging for 1 hour (T1 ) and 5 hours (T2 ). Measurements were made before and after each time interval. Color differences (ΔE00 ) were calculated using the CIEDE2000 formula and analyzed by 2-way ANOVA. Lightness (ΔL'), chroma (ΔC'), and hue differences (ΔH') were analyzed by multivariate ANOVA. Degrees of fluorescence were obtained as percentages and were analyzed by 2-way ANOVA. Multiple comparisons were performed by the Tukey HSD test (α=.05).

RESULTS: Color differences were observed when 3Y-TZP disks were treated with coloring (7.91 ΔE00 ), with fluorescent liquid (5.81 ΔE00 ), and with both liquids (5.52 ΔE00 ). Accelerated aging resulted in color differences in the T2 A2 group (6.74 ΔE00 ) and at both times evaluated in the fluorescent group (T1 =8.59 ΔE00 and T2 =8.47 ΔE00 ) (P<.001). In the A2 fluorescent group, the degree of fluorescence was not influenced significantly (P>.05). The use of fluorescent liquid influenced the degree of fluorescence in the fluorescent group (T0 =20%).

CONCLUSIONS: Significant differences in color, lightness, chroma, and hue were achieved in all tested groups before and after aging. The degree of fluorescence was statistically different only in the fluorescent group and was not influenced by accelerated aging.