All subgroups were subjected to an initial bleaching session, after which color and surface roughness were measured. The specimens were then stained by placing them in a coffee solution prepared by boiling 3.6 grams of coffee powder (Nescafe Classic, Nestle, Switzerland) in 300 ml of distilled water for 10 minutes, then filtering it. Immersion in the coffee solution was maintained for 48 hours at 37°C, after which the color of specimens was determined before subjecting them to a second bleaching session. Color assessment was performed using a colorimeter (Chroma Meter CR 300, Minolta Co. Ltd., Japan), which was calibrated before every session following the manufacturer’s instructions. The colorimeter displayed the different color parameters (L*, a* and b*) according to the CIELab color system, where L* describes the luminance reflectance, while a* and b* describe the red-green and yellow-blue color coordinates, respectively.