## 4 Discussion
This could be explained by OG's ability to infiltrate the surface, which reduces the restoration's surface permeability, fills in nanopores, and reduces leakage into the restoration surface [40]. [PERSON] et al. [21] investigated the relationship between the surface texture obtained by different polishing procedures and the resultant stainability of IPS ceramic discs after 12 days of immersion in a coffee. They found that glazing resulted in the smoothest and the most stable surface. The polishability is not the sole determinant of color change, but the composition of the different materials, as well as the variations in polymer-to-filler ratio, have a significant impact on polishability and, hence, the color change. The LU and CS exhibited the highest color change, which can be attributed to both resin nanoceramic clusters and the presence of Bis-GMA, hydrophobic UDMA, and hydrophilic TEGDMA in their composition [41]. On the other hand, CU and LU are polymer-infiltrated ceramic networks that are created by first producing the ceramic network and then crosslinking the polymer with the existing ceramic network by capillary action [9]. The heat treatment to form a dense polymer network [9] could possibly explain the least color change in VE and CU materials. The BFS test is among the common methods for determining fracture strength and predicting the forces a material can withstand [24]. The current study's findings indicate a substantial variation in the BFS of the investigated materials following different surface finish protocols (\(p<0.001\)). The second null hypothesis that the studied CAD/CAM materials do not significantly differ in BFS after various surface finishing protocols was rejected. The OG protocol resulted in the highest BFS. There is no study that the authors are aware of that evaluates the effect of OG surface finish on the resin-modified ceramic's flexural strength. However, [PERSON] et al. [42] in their study assessed the effect of surface sealing on polymer-based provisional materials. They found that surface sealing improves the mechanical properties, including the flexural strength of the tested materials. On the contrary, [PERSON] et al. [43] demonstrated that surface sealing does not affect the flexural strength of polymer-based provisional materials. Their contradicting conclusions about using the same glaze (Palaseal glaze) can be attributed to the different brands of the materials tested. The OG (154.75 \(\pm\) 3.05 MPa) and MP+PP (153.33 \(\pm\) 2.78 MPa) demonstrated the highest BFS values, and there was an insignificant difference between the two protocols among the tested resin-modified ceramics, except for VE (\(p>0.005\)). Earlier studies have demonstrated an inverse association between BFS and Ra, which implies that a smoother surface has a higher BFS [44; 45; 46]. [PERSON] et al. [27] explained the effect of polishing paste in reducing Ra and stated its ability to round the profile, making the surface more uniform and smoother. The composition of the polished material has an impact on polishability and, accordingly, the BFS. This fact can partially explain why VE demonstrated a significant difference (\(p<0.005\)). VE has the lowest percentage of polymer (14% of its composition) compared to the other tested materials (20-30% of their composition) [41], and manual polishing using polishing paste may not smoothen the higher percentage of incorporated fillers. When compared to OG and MP+PP, the MP resulted in a lower BFS and a higher color difference. Based on these findings, it is apparent that the MP protocol is not effective at smoothening the surface compared to other protocols. Because of the heterogeneity in the composition of the resin ceramics, using MP without subsequent polishing paste might be insufficient. This is particularly evident in the CU material, as there is no statistically significant difference between MP and control (\(p>0.005\)).