## 4 Discussion  
Resin-modified ceramics are considered a viable substitute for glass ceramics which perform clinically satisfactorily for prosthodontic management in areas with moderate chewing loads. Despite having similar mechanical qualities to conventional CAD-CAM ceramics, resin-modified ceramics are deemed aesthetically pleasing [36]. This study aimed to determine the influence of various surface finish protocols on the color change and BFS of resin-modified ceramics. According to the current study's findings, the investigated resin-modified ceramic materials and surface finish protocols significantly affected the color difference (\(p<0.05\)). Therefore, the stated first null hypothesis had to be rejected. As it is one of the most consumed drinks worldwide and is more chromogenic than other beverages, coffee was used as a staining agent in this study. Furthermore, coffee's pH, which ranges from 4.9 to 5.2, will expedite the discoloration process. Discoloration brought by coffee has been related to ingredients, including tannin and chlorogenic acid [35]. Color is influenced by surface finishing techniques and roughness, as previously described [21]. A human observer can detect a color change that is perceptible as a color difference. A 50% of spectators can detect a color difference if the perceptibility threshold (PT) is set at 50%. Similarly, a 50% acceptance threshold (AT) refers to a color change that 50% of spectators deem acceptable [37]. Accordingly, the reference values of the PT and AT are \(\Delta\)E \(\leq\) 1.2 and \(\Delta\)E = 2.7, respectively. Any \(\Delta\)E \(>\) 2.7 is considered clinically unacceptable [37]. In the current study, none of the surface-finished discs demonstrated \(\Delta\)E values below the PT; however, the values were within the AT limit (\(\Delta\)E = 2.7). The color changes in the control specimens of nanoceramics (LU and CS) were above the AT limit. The color change in the specimens after surface finishing with MP was 1.96 \(\pm\) 0.43, and after using polishing paste MP+PP, it was reduced to 1.85 \(\pm\) 0.35. The two values were statistically insignificant, and the color change was above the PT but well below the AT. This outcome demonstrates  
Figure 7: SEM images of fractured surface of representative CU specimen following BFS test: (**A1**) control specimen showing the origin (asterisk) of the fracture. Multiple crack planes and voids are also shown; (**A2**) higher magnification showing compression curl, delamination defects, and hackle region (solid white arrow); (**B1,B2**) MP specimen showing similar fracture features displayed in the control group in addition to distinctive multiple fracture planes and arrest lines (solid black arrow); (**C1**) OG specimen shows the crack origin; (**C2**) higher magnification shows multiple fracture plane, voids, and hackle regions; (**D1**) MP+PP specimen showing origin of the crack as well crack arrest lines (solid black arrow); (**D2**) multiple crack planes, compression curl, and hackle region are shown. that both surface finishing was comparable in terms of color changes in the materials. In a previous study, [PERSON] et al. [38] studied the influence of various polishing techniques on the Ra and \(\Delta\)E of CS, LU, and VE. They found that the diamond paste polishing alone produced an acceptable Ra and \(\Delta\)E, while the two-stage diamond-impregnated polishers resulted in increased color change, and hence they were deemed unsuitable for the tested materials. The current study findings confirm that glazing (OG) makes the surface more stain resistant. The influence of OG, a light-polymerizing clear resin covering on ceramics, has received little attention in the literature. One study explored the \(\Delta\)E of 3D-printed interim restorations following surface finishing with aluminum oxide polishers and OG [39]. After six months of immersion in different staining solutions, they discovered that OG caused the least color change [39].