## 4 Discussion  
The current study evaluated the color stability and surface roughness of additively and subtractively manufactured permanent composite-based restorative materials and compared them to those of a feldspathic glass-ceramic after thermocycling. In addition, the stainability of these materials was examined after immersion in coffee/distilled water. Based on the current study's data, both null hypotheses of the study were rejected. Since the type of material significantly affected the color stability and surface roughness of tested restorative materials after thermocycling. In addition, the type of tested CAD/CAM material had a statistically significant effect on the stainability of materials after storage in coffee or distilled water. Currently, CAD/CAM composite-based milled and glass ceramic restorative materials are frequently used in the construction of indirect restorations such as inlay, onlay, veneer, and crown [44]. However, the popularity of 3D printed tooth-colored restorations among clinicians has recently increased [45]. It may be considered that 3D printed materials can be replaced by CAD/CAM milled materials due to their advantages. They can be an alternative to feldspathic ceramics, which are preferred due to their aesthetic properties but are fragile. Despite the increase in variety and frequency of use of 3D printed materials, the lack of literature on properties such as surface roughness and color stability required for the longevity of the material has been the reason for the present study. Therefore, this present study aimed to investigate the surface roughness and color stability of 3D printed permanent resin and CAD/CAM milled composite-based materials and compare them to those of a feldspathic glass-ceramic. The feldspathic ceramic VM, which has been on the market for several years, was chosen as the control group due to its excellent aesthetic superiority and the required stable properties for indirect restorative materials [46; 47]. The R\({}_{\text{a}}\) value, which is the roughness average, is the universally accepted and commonly used roughness parameter. Recent studies have specified R\({}_{\text{a}}\) = 0.2 \(\upmu\)m as the threshold value of surface roughness for bacterial retention and plaque accumulation [42]. In this study, the mean R\({}_{\text{a}}\)0 values of tested materials ranged between 0.037 \(\pm\) 0.008 \(\upmu\)m and 0.174 \(\pm\) 0.043 \(\upmu\)m and the mean R\({}_{\text{a}}\)1 values of the same materials ranged between 0.038 \(\pm\) 0.007 \(\upmu\)m and 0.201 \(\pm\) 0.041 \(\upmu\)m. The mean R\({}_{\text{a}}\)0 and R\({}_{\text{a}}\)1 values of each material tested were equal to or below the plaque accumulation threshold. However, none of the groups' mean surface roughness values reached the clinically unacceptable level of 10 \(\upmu\)m [48]. A statistical difference was found in the comparison of both the R\({}_{\text{a}}\)0 and R\({}_{\text{a}}\)1 values of the tested materials. While the VE group had significantly the highest mean R\({}_{\text{a}}\)0 and R\({}_{\text{a}}\)1 values, no statistical difference existed among SC, FP, and CS. Furthermore, SC, FP, and CS had lower mean R\({}_{\text{a}}\) values than the VE. The difference in microstructural compositions of the composite-based materials tested could explain these results. CAD/CAM composite-based resins have been introduced in different compositions and with various percentages of the polymeric matrix and inorganic filler components depending on the type of material, such as polymer-infiltrated ceramics and resin composite blocks [49; 50]. Vita Enamic has two interconnected networks made of ceramic and polymer [51]. Despite the high filler content percentage of Vita Enamic, infiltration of the sintered porous ceramic matrix with low-viscosity resin presents a challenging interfacial adhesion problem. The higher surface roughness of VE compared to other resin composite materials could be due to the adhesion between the ceramic structure and the resin [52]. [PERSON] et al.