Effect of different coloring techniques and surface treatment methods on the surface roughness of monolithic zirconia

Abstract

Background: This study aimed to evaluate the effect of different coloring techniques and surface
treatment methods on the surface roughness of monolithic zirconia ceramic.
Materials and Methods: In this in vitro study seventy‑two disk‑shaped monolithic zirconia (2 mm × 10 mm) were
divided into three coloring techniques groups (white, internal staining, external staining) (n = 24).
Each group was subdivided into four surface treatment subgroups (n = 6), as unpolished, polished
with Shofu polishing kit, polished with dental direct polishing kit, and glazed. Profilometer was used
to measure the Ra (roughness average) and Rz (roughness height) surface roughness values (μm)
and scanning electron microscopy (SEM) for visual inspection of the surface morphology. The
surface roughness parameters were calculated and analyzed with two‑way ANOVA and Tukey’s
post hoc test (α = 0.05).
Results: The coloring technique, surface treatment method, and interaction of these two parameters
significantly affected the Ra and Rz parameters (P < 0.05). Concerning the surface treatment, the
Rz value was significantly higher in the unpolished subgroup, followed by the glazed and polished
subgroups. However, the two polishing systems were not significantly different. The internal staining
group had significantly higher Rz value than the other staining method, when the specimens were
glazed or polished with Shofu kit. SEM showed multiple scratches in unpolished samples which
were smoothened by glazing and specially by polishing.
Conclusion: Among all the studied surface treatment methods, the lowest surface roughness was
observed in highly polished monolithic zirconia, which was even less than the glazed one. The
internal staining method can create a rougher surface for some of the surface treatment methods.