## 4 Discussion
[53] compared the surface roughness of polymer-infiltrated ceramic materials (PICN) and CAD/CAM composite resins. They found that CAD/CAM composite resins had significantly lower roughness values than PICN materials. Likewise, [PERSON] et al. [54] examined the surface roughness of resin nanoceramic, hybrid ceramic, and leucite-reinforced ceramic and reported that hybrid ceramics, also called PICN, have higher roughness values. [PERSON] et al. [55] investigated the surface roughness of current CAD/CAM resin composites and found that the baseline roughness value of VE was the highest among other resin materials compared. Similar findings have been found in the current study. CS had the lowest mean R\({}_{\text{a}}\)0 value among the tested materials. However, there was no statistically significant differencebetween additively manufactured materials (FP and SC) and CS. [PERSON] et al. [36] evaluated the color stability and surface roughness of additively (composite resins; Saremco Crowntec and VarseoSmile Crown Plus) and subtractively (resin nanoceramic; Ceasmart) manufactured resins used for definitive restorations. They found that Cerasmart either had Ra results similar to or lower compared to those of additively manufactured composite resins. Cerasmart 270 is a prepolymerized resin composite CAD/CAM block that has been manufactured under high pressure and temperature [17; 56], and contains nanoceramic particles (silica and zirconia filler/cluster filler) embedded in a composite matrix, as is typical for resin composites. It can be assumed that the filler particles in CS are better connected to the resin matrix [17]. Structural stability and fluid consistency during printing and storage should be characteristics of 3D printed resins. Therefore, it is suggested that 3D printed composite resin materials used in the manufacture of permanent restorations, just like flowable dental composites, should contain fewer inorganic fillers than CAD/CAM composite blocks to maintain a stable liquid consistency. However, a low filler content also affects the mechanical properties of the composite material [57]. [PERSON] et al. [58] reported that the increase in the filler percentage may cause a decrease in the surface roughness. But, in the present study, although the 3D printed composite resins tested had lower filler content compared to CAD/CAM milled composites, the values of the surface roughness show that these composite resins have roughness similar to that of the resin nanoceramic CAD/CAM block and are better than the polymer-infiltrated ceramic and feldspathic ceramic (control) tested in the present study. Thermocycling, a popular artificial aging method, is utilized to simulate the thermal changes in the oral cavity during eating and drinking in in-vitro studies. When composite resins are subjected to water and thermal changes as a result of thermocycling, deterioration occurs in the organic matrix structure or at the matrix-filler interface [59]. Furthermore, thermocycling has a significant impact on the surface roughness of composite resins, according to [PERSON] et al. [29]. For this reason, thermocycling was chosen as the aging method to simulate oral environmental conditions in the current study. According to the results of the current study, although thermocycling slightly increased the mean R\({}_{\text{a}}\) values of the tested materials, this increase was not statistically significant. It is assumed that the color changes of the resin-based restorative materials will increase at a high rate due to the degradation of the polymer matrix, unreacted monomers of the polymerization agents after aging, and staining agents [60]. The present study's \(\Delta\)E\({}_{00}\) results show that SC had the highest mean \(\Delta\)E\({}_{00}\) values after the thermocycling and this mean \(\Delta\)E\({}_{00}\) value was above the clinically acceptable threshold value of 2.25.