Effect of different surface finishing and polishing procedures on the surface roughness and color stabitily of 3d-printed permanent crown materials

The aim of this in vitro study is to evaluate the effect of different surface finishing–polishing procedures and surface reduction protocols on the surface roughness and color stability of three different permanent crown materials (Bego VarseoSmile Triniq, Alias Dental Crown, Saremco Print Crowntec) fabricated using three-dimensional (3D) printing technology. The materials in shade A2 were designed in the form of disks with a diameter of 10 mm and a thickness of 2 mm. Specimens were fabricated using 3D printers in accordance with the manufacturers' instructions. All specimens were printed with a 50 μm layer thickness and a build angle of 90°. A total of 150 specimens were produced, 50 for each material. All specimens were wetpolished using 600-grit silicon carbide paper. Each material group was divided into five subgroups based on the surface treatments applied (n=10). The control group received only polishing with silicon carbide paper. Other groups included mechanical polishing, Optiglaze application, grinding after Optiglaze (simulating clinical adjustments) using a red-banded diamond bur, and repolishing following grinding. Surface roughness (Ra) values were measured using an optical profilometer (Zygo ZeGage, Zygo Corporation, Middlefield, CT, USA). Color measurements were performed using a spectrophotometer (EasyShade V, Vita Zahnfabrik, Germany). All specimens underwent 5.000 thermal cycles between 5°C and 55°C in baths. Subsequently, second color measurements were taken after immersion in a coffee solution at 37°C for 7 days. Color differences were calculated using the CIEDE2000 (ΔE00) formula. Normality of data distribution was assessed using the Kolmogorov- Smirnov test, and variance homogeneity using Levene's test. For statistical analysis, the Kruskal-Wallis H test was used for multiple group comparisons, followed by Mann-Whitney U test for pairwise comparisons. Spearman's correlation coefficient was used for correlation analysis. Statistically significant differences in Ra values were found among different surface treatment groups (p<0.05). All groups except the repolishing group showed statistically significant differences in Ra values among materials (p<0.05). Mechanical polishing, Optiglaze, and repolishing procedures achieved surface roughness values below the clinically acceptable threshold for plaque accumulation (<0.2 μm). The lowest Ra value was observed in the Bego-Optiglaze group. Statistically significant differences in color change (ΔE00) values were also found between surface treatment xiv groups (p<0.05). The lowest ΔE00 value was recorded in the Bego-Optiglaze group, while the highest was found in the Alias-Abrasion group. Among all groups, only the ΔE00 value of the Bego-Optiglaze group was below the clinically acceptable threshold. No correlation was found between surface roughness and color change. It was concluded that different finishing, polishing, and surface reduction procedures significantly affect the surface roughness and color stability of the tested materials. Optiglaze application showed performance comparable to or better than mechanical polishing. The similar or higher Ra values achieved with repolishing suggest that 3Dprinted hybrid materials can be mechanically polished after clinical cementation and intraoral adjustments. The finding that only the Bego-Optiglaze group exhibited ΔE00 values below the clinical acceptability threshold highlights the need for improvements in the long-term clinical performance of these materials. Keywords: Additive manufacturing, 3D printing, Optiglaze Color, mechanical polishing, surface roughness, color stability