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The Effect of Different Polishing Systems on the Surface Roughness and Color Changes of Monolithic Zirconia Crowns: A
Purpose:
To evaluate the surface roughness and color stability of three-dimensionally (3D) printed zirconia crowns after treatment with three different chairside polishing systems, in comparison with conventionally milled zirconia.
Materials And Methods:
One hundred twenty maxillary incisor monolithic zirconia crowns were fabricated using subtractive (milled, n=60) and additive manufacturing (3D-printed, n=60). Specimens were further divided into as-received, unpolished, and polished subgroups. Polishing was performed using three systems: Zolid Sinter-State (Amann Girrbach), OptraGloss (Ivoclar Vivadent), and Meisinger Zirconia Polishing Kit (Meisinger) (n=20/subgroup). Surface roughness (Ra) was measured using a noncontact 3D optical profilometer. Specimens were then immersed in coffee solution for 30 days (simulating ≈2.5 years of clinical exposure), and color differences (ΔE₀₀) were calculated using the CIEDE2000 formula. Surface morphology was examined using scanning electron microscopy. Data were analyzed using two-way ANOVA and post-hoc Bonferroni tests (α=0.05).
Results:
Polishing significantly reduced surface roughness in both milled and 3D-printed zirconia (p<0.001). As-received milled zirconia exhibited higher Ra (0.69±0.12 µm) than printed zirconia (0.60±0.14 µm) (p<0.001). After polishing, no significant difference was observed between manufacturing techniques (p=0.095, p>0.05). For milled zirconia, all polishing kits performed similarly (p>0.05); for printed zirconia, Amann Girrbach produced lower Ra (0.03±0.016 µm) than Meisinger (0.04±0.01 µm) and OptraGloss (0.04±0.008 µm) (p<0.001). Coffee staining caused significant color change in all specimens (p=0.001), with no significant difference between milled and printed zirconia across polishing subgroups (p>0.05). All polished surfaces achieved Ra values below the clinically accepted threshold of 0.2 µm.
Conclusions:
3D-printed zirconia represents a clinically reliable alternative to milled zirconia, as initial surface roughness differences are eliminated after standardized polishing. All polishing systems achieved clinically acceptable smoothness. Both materials exhibited comparable staining susceptibility, suggesting discoloration depends more on material composition than on surface finishing.
