Influence of Sintering and Coloring on Surface Roughness of Monolithic-zirconia

Objectives: The aim of this in-vitro study was to evaluate the effect of the various sintering conditions and dipping time in the coloring liquid on the surface roughness of the translucent monolithic zirconia.
Methods: Seventy-five disc-shaped specimens (12 mm diameter, 1.5 mm thickness) were cut from presintered non-colored monolithic zirconia blocks (InCoris TZI, Sirona GmbH, Germany). The specimens were randomly divided into three groups according to the sintering conditions (n=25): Classic sintering (1510°C for 120 minutes), speed sintering (1540°C for 30 minutes) and super-speed sintering (1580°C for 10 minutes). Each group was then divided into five subgroups according to coloring time by dipping method in a coloring liquid: control (no-coloring), 3 minutes, 5 minutes, 7 minutes and 9 minutes (n=5). After the coloring process, the specimens were sintered in three different conditions (classic, speed, and super-speed). The average surface roughnesses (Ra) were measured by a contact-profilometer. Data were analyzed by two-way ANOVA and Tukey HSD tests (α=0.05).
Results: Mean Ra of the control groups (0.197 ± 0.048 for classic sintering; 0.224 ± 0.035 for speed sintering; 0.207 ± 0.026 for super-speed sintering) showed the lowest Ra values in all groups. However, there was no statistically significant interaction between sintering conditions and dipping time for mean Ra of the groups (P=.887). There was also no statistical difference found among the groups for sintering conditions (P=.980) irrespective of dipping time. And dipping time did not have a statistically significant effect on mean Ra of the groups regardless of sintering conditions (P=.609).
Conclusions: Different sintering conditions and dipping time did not alter the surface properties of the translucent monolithic zirconia. Therefore, clinicians could select any of the appropriate sintering parameters and coloring liquid application time for their clinical requirements without changing the surface roughness of the monolithic zirconia.