The Effect of Thermocycling and Bleaching on the Color Stability and Lightness of Monolithic CAD-CAM Dental Ceramics.

Purpose: The purpose of this in vitro study was to evaluate the effect of coffee thermocycling and carbamide peroxide bleaching on the color stability and lightness of monolithic CAD-CAM ceramics, including zirconia, lithium disilicate (LDS), polymer infiltrated ceramic network (PICN), pre-sintered zirconium-reinforced lithium silicate (PS-ZLS), and PS ZLS with additional sintering (PS-ZLS+AS).

Materials and methods: A total of 50 rectangular plate-shaped specimens with A2 shade in 1 mm thickness were investigated (n=10). Each specimen underwent coffee thermocycling for a total of 20 000 cycles and a 20% carbamide peroxide bleaching for 14 days The color changes were calculated using the ΔE00 formula between 3 steps: initially, after thermocycling, and after bleaching steps. A one-way ANOVA, followed by relevant post hoc tests, was used to analyze ΔE00, while a two-way repeated measures ANOVA, followed by Bonferroni-adjusted multiple comparisons for pairwise analyses of lightness, was performed (α = .05).

Results: Zirconia and LDS demonstrated the highest stability in color and lightness. In contrast, PS-ZLS and PS-ZLS+AS exhibited significantly greater color changes and lightness reduction during thermocycling, with PS ZLS showing more pronounced alterations than PS-ZLS+AS (P<.001). Bleaching effectively restored the altered color and lost lightness from thermocycling, resulting in less than 1 color change and significantly higher post-bleaching lightness for PICN, PS-ZLS and PS-ZLS+AS.

Conclusion: The PS-ZLS groups exhibited the lowest color stability and the greatest lightness reduction during coffee thermocycling. However, additional sintering effectively stabilized the optical properties of PS-ZLS. Bleaching successfully restored the lost lightness and the clinically acceptable original color.