## 4 Discussion
After brushing, all groups showed a significant reduction in \(\Delta\)E values (E-max = 2.51 \(\pm\) 0.64, Lisi = 1.74 \(\pm\) 0.76, and Celtra = 2.61 \(\pm\) 0.52). However, all the reported \(\Delta\)E values after brushing were above the PT and below the AT. Again, a significant reduction in color change was reported in the Lisi group (\(p\) < 0.05). According to the results of this study, all the tested crowns constructed from repressed lithium disilicate ceramics were vulnerable to staining when immersed into coffee solution. This finding is consistent with previous studies investigating the stainability ofc ceramic restorative materials [18; 21; 29]. Fortunately, the clinically acceptable color of the stained ceramics was recovered after manual routine brushing with a toothbrush and cavity fighter toothpaste, which may be considered additional evidence supporting the reuse of previously pressed lithium disilicate ceramic ingots. The overall color of ceramic restorations is affected by many factors, such as the shade and thickness of the ceramic, the cement shade and thickness, and the processing technique [33]. In this study, the prepared typodont tooth was duplicated with 3D printing to produce 72 identical abutment teeth [34]. The same virtual wax pattern design and cement space parameters were used in all specimens. These measures were followed to standardize the specimens and cement thickness. Translucent cement shade was used for all groups to standardize its effect on the color measurements [35]. The color of dental restorations can be evaluated using spectrophotometers, colorimeters, or digital cameras [36]. A spectrophotometer was selected for our study because it measures the wavelength reflected or transmitted by one object at a time, without being affected by subjective interferences [37]. In addition, the irregular surface of human teeth makes the color measurement of human teeth very difficult, because the reproducibility of the measurement itself is poor [38]; however, with the aid of the compare tool available in the Spectro Shade Micro portable dental spectrophotometer, the color of an equal area of the labial surface of teeth crowns can be compared, as well as the measurements reproduced before and after different treatments of the surface [39]. A recently published in vivo study [40] used a putty index for each patient to ensure the repeatability of measurements. However, the device (VITA Easy shade) used for measurement in that study only measured the color change in a small, rounded area of the teeth labial surfaces, unlike the Spectro Shade Micro device used in our study, which could measure the color change of the whole labial surface of the tooth [12]. The color stability of dental ceramics can be investigated using a variety of aging methods. Extrinsic factors, including exposure to the environment, are considered in most methods. In our study, we chose to use coffee, as it is among the most commonly consumed beverages [37; 41]. The incubation period was selected based on the following association: 3 Cs per day correspond to an exposure of 1 min per cup, which equals 1095 min or 18 h each year [18]. It has been reported that coffee preparation and concentration have an impact on the level of color shift [36]. As a result, the study's solutions were created with daily use in mind [42]. This study was conducted outside the oral cavity. In vitro studies have the advantage of simulating long-term intraoral service in a short amount of time as compared to clinical research. As a result, the color stainability can be evaluated by submerging the samples in a variety of beverages for a short period of time rather than waiting for the material to degrade over an extended period of time [43]. When evaluating the color of in vitro samples, an especially critical issue is to standardize illumination and background. The Spectro Shade Micro device used in this study has its own light source; thus, it can be used under any light source.