Effects of Number of Firing Cycles on Color Stability and Surface Roughness in Two Different Zirconia-Based Ceramic Systems

Color matching between a zirconia-based ceramic restoration and a natural tooth is a common clinical challenge. This in-vitro study aimed to assess the effects of the number of firing cycles and zirconia core translucency on the color stability and surface roughness in two zirconia-based ceramic systems.

A total of 60 disk-shaped zirconia specimens (10×1 mm) were prepared in high and low translucencies (n=30 per group), veneered with 1mm ceramic layers, and subjected to 3, 5, and 7 firing cycles in three respective subgroups (n=10). Color stability (∆E) and surface roughness (Ra(µm)) parameters were measured after soaking the specimens in coffee solution and using a spectrophotometer and profilometer, respectively. Data were analyzed using two-way ANOVA and Tukey’s post hoc test (α=0.05).

The number of firing cycles affected the Ra value in both zirconia-based ceramic systems (P<0.001); however, it did not affect the color change (P=0.253). The surface became significantly smoother by increasing the number of firing cycles from 3 to 5 and from 3 to 7 (P<0.001). Zirconia core type significantly affected the color stability after soaking in coffee solution (P<0.001); however, it did not affect the surface roughness (P=0.189). High-translucency zirconia core sub-groups had a more stable color, compared to samples in low-translucency groups.

Multiple firings of veneering porcelain did not affect the color stability of the two zirconia-based ceramic systems; however, the color stability in the zirconia core system with low translucency was significantly lower than that in the high-translucency zirconia core system. The surface roughness in both zirconia core systems was reduced with increasing the number of firing cycles. However, zirconia core translucency had no effect on the surface roughness of restorations.