Color Stability of Pressed Lithium-Disilicate Ceramics Under Repeated Firings Evaluated by Different Methods

To determine and compare color differences of pressed lithium-disilicate ceramic specimens after repeated firing cycles. Another objective was to determine and evaluate the correlation of CIEDE2000 values analyzed using X-Rite Color i5 spectrophotometer, VITA EasyShade Advance 4.0, and Adobe Photoshop.

Tile specimens (n = 36) with 8 × 10 × 1.5 mm dimensions were prepared using lithium-disilicate monochromatic ingots (IPS e.max Press MT, Ivoclar) and lithium-disilicate multichromatic ingots (IPS e.max Multi Press, Ivoclar). Specimens were exposed to seven repeated firing cycles. Color analysis was performed after the first, second, third, fifth, and seventh firing cycles. CIE L*a*b* values were measured with Color i5 spectrophotometer, EasyShade, and Photoshop. CIE DE*2000 (ΔE*00) was calculated to estimate color differences.

Linear regression and multiple comparison analysis (Tukey HSD test) showed a statistically significant (P < .001) color difference ΔE*00 after multiple firing cycles. Statistically significant differences (P < .05) were also noted in different shade groups and between different instruments used for shade evaluation. Moreover, significant differences (P < .05) were found in interactive effects between different shades tested using different instruments, different shades tested after multiple firing cycles, and different instruments after multiple firing cycles.

Lithium-disilicate material shows significant color differences after repeated firing cycles tested with three color analysis instruments. However, those differences are considered clinically acceptable. Measuring instruments used to evaluate CIE L*a*b* color values showed significant differences in color values analysis. Nevertheless, those differences are within the human perceptible tolerance threshold.