The effect of different surface finishing procedures and resin cement shades on the optical properties of monolithic zirconia

Aim: The aim of this in vitro thesis study was to evaluate the effects of different surface finishing procedures (glaze, polish, and polish+glaze) and two resin cement shades (Universal [A2] and Translucent [TR]) on the color stability of monolithic zirconia materials with different translucency levels. Materials and Methods: A total of 120 disc-shaped specimens (15 mm × 1.2 mm) were fabricated from two monolithic zirconia materials with different translucency levels (4Y-TZP [ST]; 5Y-TZP [XT]) and sintered at 1450 °C according to the manufacturer's instructions. Following sintering, the samples were subjected to three different surface treatments: glazing, mechanical polishing, or polishing after glazing. Initial color measurements were performed using a dental spectrophotometer, and recorded based on the CIE Lab* system. Resin cement samples in Universal and Translucent shades were prepared at 0.2 mm thickness using standardized molds. Second color measurements were taken by placing cement discs under the untreated surface of the zirconia specimens. Glycerin was applied between the zirconia and cement discs to ensure optical contact. Color differences (ΔE₀₀) were calculated using the CIEDE2000 formula. Data were analyzed with Minitab v14 and Jamovi v2.3.28 software. Statistical evaluations were performed using three-way ANOVA and Tukey tests considering the factors of material type, surface treatment, and cement shade (p<0.05). Results: Mean color difference values (ΔE₀₀) showed statistically significant differences based on zirconia material type (p=0.011), surface treatment (p=0.006), and resin cement shade (p=0.001). The polish+glaze group exhibited significantly higher ΔE₀₀ values (1.60±0.27) compared to the other surface treatment groups. ST blocks had higher mean values (1.56±0.30) than XT blocks (1.44±0.25). The TR cement group exhibited greater color differences (1.58±0.33) compared to the A2 group (1.42±0.21). A statistically significant interaction was found between block type and surface treatment (p=0.002), while the other two-way and three-way interactions were not significant (p>0.05). Conclusions: This study demonstrates that esthetic outcomes in monolithic zirconia restorations are influenced not only by material selection but also by surface treatment and resin cement shade. The increase in ΔE values observed in the polishing+glazing group suggests that this combination may require cautious application in esthetically critical zones. Except for the ST*Polish*TR group, all values were above the perceptibility threshold but within the clinically acceptable range (0.8 < ΔE < 1.8). ST blocks exhibited more color change than XT blocks, and TR cement led to greater differences than A2. Thus, proper evaluation of both material and cement shade prior to clinical use is recommended to optimize esthetic results. Key Words: monolithic zirconia, resin cement, surface finishing, color