Effect of shading on flexural strength of Cercon zirconia-based ceramics

Zirconia frameworks are generally shaded with colorant oxides before or after sintering in order to have more natural looking restorations. The aim of this in vitro study was to evaluate the effect of A3, B3 and D3 shading on biaxial flexural strength of Cercon zirconia ceramic system. A total of 40 Ceron ceramic discs were prepared in four groups of 10. The discs were placed in a sintering oven. The first three groups were shaded into A3, B3 and D3 using liquid coloring agents based on manufacturer’s instructions. The fourth group (the control group) was not shaded. The discs underwent biaxial flexural strength test in a universal testing machine after sintering. Five specimens from each group underwent EDDX (energy-dispersive x-ray analysis) for the evaluation of constituent elements. After evaluation of normal distribution of data, one-way ANOVA was applied; a post hoc Tukey test was used for two-by-two comparison of the groups (α = 0.05). Shading and its type resulted in significant differences in flexural strengths of the groups (p value < 0.03). Disks of B3 shade revealed the highest strength among the shaded disks, with no statistically significant differences from the control group (p value = 0.63). Only the discs with A3 shade exhibited significantly less flexural strengths in comparison to the unshaded discs (p value < 0.03). Shading can significantly decrease flexural strength of Ceron ceramics, which should be clinically considered when Ceron zirconia cores are used; however, further studies are necessary.