## 4 Discussion  
Several systems for F&P of resin composites are currently available, and some data are available in the literature. They are quite different in terms of methods (disc, point, wheels, paste, resin), steps (1 to 4), use (in office/chairside, laboratory), and required equipment (micromotor, lab motor, clinical curing light, laboratory curing light in oxygen or nitrogen environment), whereas the effects of these F&P systems on the roughness and  
Figure 3: SEM observations (400\(\times\)) of the eight systems tested. OS (1), HL (2), and SW (3) showed roundish depressions. SD (4) showed linear depressions. Lp (5) and Ln (6) also showed linear depressions, but they were smaller than SD and less visible in Lp than in Ln. OG (7) showed scratches partially filled by the resin. NG (8) showed a quite homogeneous surface with depressions or scratches almost not visible. gloss of direct and indirect resin composites such as conventional hybrid, nano-hybrid, and bulk fill composites have been investigated [26; 27; 28; 29; 30; 31; 32; 33]. So far, few investigations have been performed researching the effects of F&P procedures on 3 DP resin composite materials for permanent use. F&P procedures are of utmost importance for these materials, as the 3 DP layering process can lead to rough surfaces. In the present study, the effects of different F&P systems on the roughness and gloss of one 3 DP resin composite material for permanent restorations have been investigated, selecting eight different procedures with different workflows. The data obtained in the present study suggest rejection of the null hypotheses as the performed F&P procedures significantly influenced the surface roughness and gloss of 3 DP resin composites. Roughness and gloss are important surface properties of dental restorative materials. Roughness is linked to surface unevenness, and it is generally measured in terms of roughness average (Ra), which has been defined as the \"mean arithmetical value of all the absolute distances of the profile inside of the measuring length\" [34]. Gloss is conversely an optical property measured in gloss units (GU) correlated with specular reflection from a surface, and it is responsible for shiny or mirror-like appearance [35; 36]. Gloss is influenced by the reflection of light from a surface, but for composite resins, it is also influenced by the refractive indices of the resin matrix and filler [37] and by filler size and filler-matrix similarity, observing that the lower the filler-matrix homogeneity, the lower the light reflectivity [38]. An inverse linear relationship between roughness and gloss has been reported in previous studies [39; 40; 31], and this is corroborated by the present one. Since the goal of an F&P procedure is to provide a surface that matches its range enamel, the final roughness of the composite restorative material should be ideally similar to enamel roughness (0.45 \(\upmu\)m/0.64 \(\upmu\)m) [41]. In the present study, the roughness measured ranged from 0.25 \(\upmu\)m to 0.83 \(\upmu\)m. Therefore, not all the F&P systems were able to provide enamel-like results. Statistically significant differences emerged among the various systems tested. In particular, HL showed the highest Ra, even if no statistically significant differences were found with SS. It should be noted that all the manual 1- or 2-step systems showed the worst results, with only OS not statistically significantly different from a laboratory system used without polishing paste. The use of the polishing paste showed a tendency to improve the polishability both for Ra and SEM observation, but this tendency was not statistically significant. No statistically significant differences in roughness emerged among SD, GL, LP, and LN. SD, a direct 4-step system, showed statistically significantly better results than all the other direct systems, OS, SW, and HL.