## 2 Materials and Methods
### Measurement of Color Parameters  
For the color stability and staining test, specimens of each material were randomly divided into two subgroups depending on the immersion solutions (coffee or distilled water) (\(n=10\)). The base color parameters of the specimens in both subgroups were measured using a spectrophotometer (VITA Easyshade V, VITA Zahnfabrik, KG, Germany) [38] according to the CIELAB system as L*, a*, b*. The color measurement of each specimen was performed three times, and the average L0*, a0*, and b0* values were recorded. The spectrophotometer's tip was set directly on the specimen surfaces. The white background [39] was used for color measurements by a single operator (Figure 5).  
After R\({}_{\text{a}}\)0 and L0*, a0*, b0* measurements, all test groups were subjected to the thermocycling procedure for 5000 cycles in a distilled water bath ranging from 5 \({}^{\circ}\)C to 55 \({}^{\circ}\)C. Each cycle lasted 60 s and involved the following steps: 20 s in a 5 \({}^{\circ}\)C bath, 10 s for transferring the samples to another bath, 20 s in a 55 \({}^{\circ}\)C bath, and 10 s for transferring the samples back to the 5 \({}^{\circ}\)C bath. After the thermocycling procedure, the specimens were rinsed and dried. Surface roughness and color parameters of material groups were remeasured as R\({}_{\text{a}}\)1 and L1*, a1*, b1* with the same measurement methods. The specimens of the staining groups were then stored in distilled water as a control or coffee solution  
Figure 4: Surface roughness measurement (R\({}_{\text{a}}\)) of the specimens with a 3D noncontact optical profilometer.  
for the staining procedure. The content of a 3 g coffee was dissolved in 300 mL of boiling distilled water (Nescafe Gold, Nestle, Istanbul, Turkey) [38]. The specimens were stored in containers with 300 mL of either distilled water or 300 mL of coffee solution for 7 days at 37 \({}^{\circ}\)C [40]. The solutions were refreshed daily during the test. The specimens were rinsed with water after the staining process and dried. The same protocol was utilized for color measurements of each specimen, and color parameter data were recorded as L2*, a2*, and b2*. The color changes (\(\Delta\)E\({}_{00}\)) of each specimen were calculated in relation to the baseline color parameter value and expressed as T1 (after 5000 thermocycling) and T2 (immersion in distilled water or coffee) using the CIEDE2000 (\(\Delta\)E\({}_{00}\)) formula [41].  
\[\Delta\)E\({}_{00}=\sqrt{\left(\frac{\Delta\mathrm{L}^{\prime}}{\mathrm{K}_{\mathrm{L}}S_{ \mathrm{L}}}\right)^{2}+\left(\frac{\Delta\mathrm{C}^{\prime}}{\mathrm{K}_{ \mathrm{C}}S_{\mathrm{C}}}\right)^{2}+\left(\frac{\Delta\mathrm{H}^{\prime}}{ \mathrm{K}_{\mathrm{H}}S_{\mathrm{H}}}\right)^{2}+\mathrm{R}_{T}\left(\frac{ \Delta\mathrm{C}^{\prime}}{\mathrm{K}_{\mathrm{C}}S_{\mathrm{C}}}\right) \left(\frac{\Delta\mathrm{H}^{\prime}}{\mathrm{K}_{\mathrm{H}}S_{\mathrm{H}}}\right)}\]  
For this study, the parametric factors of the \(\Delta\)E\({}_{00}\) were set to 1. Likewise, the threshold of clinical perceptibility was set at \(\Delta\)E\({}_{00}\)\(\leq\) 1.30, and the threshold of clinical acceptability was set at \(\Delta\)E\({}_{00}\)\(\leq\) 2.25 units [42].