Does external shading affect the optical properties and flexural strength of translucent monolithic zirconia?

Background To evaluate the impact of shading and aging on optical properties and flexural strength of translucent monolithic zirconia. Methods A total of 198 disc-shaped samples were produced with factory-made white zirconia (Zirconia White ZOLID-SHT), preshaded (Zirconia Light, Zirconia Medium ZOLID-SHT) translucent zirconia and lithium disilicate (IPS e.max HT A3) (n = 11) materials. For externally shading the samples were colored to the A3 color by dipping technique. A color evaluation and biaxial flexural strength test were performed. Statistical analyses were conducted using one-way and three-way ANOVA. Pairwise comparisons were conducted using Tukey HSD, and independent samples t-test were used to compare two groups. (p = 0.05) Results Aging and external shading significantly reduced the flexural strength of translucent monolithic zirconia samples (p < 0.001), with white zirconia samples exhibiting higher flexural strength than preshaded samples, regardless of external shading (p < 0.001). While external shading didn’t significantly affect color change, preshading significantly impacted color after aging (p = 0.002), and white zirconia experienced greater color change compared to lithium disilicate (p = 0.002). Aging also caused a significant decrease in translucency for both unshaded and externally shaded zirconia samples (p < 0.001 and p = 0.003, respectively), with more pronounced translucency changes in unshaded zirconia than in lithium disilicate (p = 0.026). Conclusions Aging and external shading negatively impact the flexural strength and translucency of translucent monolithic zirconia. Preshading significantly affects color stability after aging, while white zirconia experiences greater changes in both color and translucency compared to lithium disilicate.