## 4 Discussion
In agreement with these findings, our study demonstrated that all ceramic materials tested--both lithium disilicate and monolithic zirconia--achieved clinically acceptable surface roughness values after glazing and after grinding followed by mechanical polishing. These results support the effectiveness of mechanical polishing as a chairside alternative to glazing for restoring surface quality. Surface gloss is one of the desirable properties for restorative materials to mimic the appearance of enamel [81]. The American Dental Association considers a gloss of 40 to 60 GU to be appropriate for dental restorations [40]. [PERSON] and [PERSON] reported that a poorly finished restoration is generally considered to be below 60 GU, while an acceptable finish is between 60 and 70 GU, and a finish above 80 GU is considered excellent [82]. A gloss value of more than 70 GU means that the human eye cannot distinguish between high and very high gloss [83]. In other words, a material that reaches 70 GU does not appear to be brighter than a material that reaches 90 GU. In contrast to roughness, a clinically accepted threshold for gloss in terms of GU has not yet been established. Nevertheless, some data are available for enamel surface gloss. When the visual luster of different composites was compared to and approximated natural enamel, the gloss of the latter ranged from 40 to 47 GU. In this study, after mechanical polishing, glazing, and repolishing processes, gloss values higher than 80 GU with an excellent finish were obtained in all materials [83]. [PERSON] et al. [72] conducted a study to evaluate the effects of different polishing systems on the surface roughness and gloss of conventional zirconia. Glazed specimens were used as the control group and were mechanically polished after being ground with a fine-grit diamond bur. The polishing process led to gloss values that were clinically acceptable and either comparable to or better than the glazed control specimens [72; 84; 85]. [PERSON] investigated the impact of various surface finishing techniques on the surface roughness and gloss of different ceramic materials. The gloss values obtained in the glaze and mechanical polishing after grinding groups were within the clinically acceptable values for EC ceramic, as we found in our study [86]. The gloss values achieved by glazing, mechanical polishing, and repolishing for all the ceramic groups in our study were within acceptable intraoral limits, indicating that these procedures can be successfully applied in dental restorations for achieving clinically satisfactory outcomes. In a separate study [87], evaluating the gloss retention and surface roughness of contemporary aesthetic CAD-CAM dental restorative materials, the average gloss value of monolithic translucent zirconia was found to be higher than that of IPS e.max CAD (EC) following polishing. This difference was attributed to zirconia's high refractive index and whiteness, which enhance light reflection [87]. In a similar study, [PERSON] et al. [88] reported that the gloss values of polished monolithic zirconia ceramics were higher than those of the lithium disilicate ceramic groups [88]. In line with previous research, our study also showed that the gloss attained through mechanical polishing for monolithic zirconia was significantly higher than that achieved by EC. The different responses of lithium disilicate and zirconia ceramics to surface treatments can be attributed to their distinct microstructures and compositions. Lithium disilicate ceramics (e.g., EC, LS) contain a glassy matrix and are less hard, allowing polishing to create smoother, glossier surfaces [3]. In contrast, zirconia (e.g., KAT) is a fully crystalline, harder material with no glassy phase, making it more resistant to polishing and requiring specialized protocols to achieve similar gloss. These intrinsic differences explain the variation in surface outcomes after identical treatments [47]. [PERSON] et al.