الفهرس 
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Abstract
Since polishing of resin composites is a crucial step for the longevity and final esthetic outcome of restorations. This study was conducted to evaluate the effect of one-step, two-step and multi-step polishing systems on the surface roughness average (Ra) of nanofilled and suprananofilled resin composite materials.
A total of 56 resin composite discs were prepared (divided into 2 main groups of 28 discs each according to the tested composite material, where group FK (Filtek™ Z350 XT Universal Restorative - 3M ESPE Dental Products), and group OM (Omnichroma - Tokuyama Dental) using split Teflon mold and cured against Mylar celluloid strip. Except for control group, samples were manually ground with wet 600-grit silicon carbide paper for 30 seconds, and then subdivided into 3 groups (n = 7) in each main group, where group ES (Enamel Plus Shiny polishing pastes - Micerium), group SS (Super-Snap X-treme aluminium oxide discs - Shofu INC), and group OG (OneGloss® - Shofu INC) polishing systems. Each polishing protocol was done according to the instructions of their corresponding manufacturers, in the same direction at a very slow rotational speed of 3000 rpm, using a kitchen scale to maintain each stroke pressure approximately 30-40 gm (approximately 0.3 newton). Scanning electron microscope (SEM) was used to scan all samples, and the images were subjected to Gwyddion 2.56, (An SPM data visualization and analysis tool) supported by the Czech Metrology Institute, 2020) to attain surface roughness average (Ra) data, which were statistically analysed by two-way ANOVA followed by Tukey’s post hoc test. Representative samples from each group were randomly selected to qualitatively evaluate the surface of the resin composite samples.
The type of resin composite and the polishing system as well as the type of resin composite and polishing system interaction were found to have a statistically significant effect on the surface roughness average (Ra) of the tested groups. The suprananofill groups as well as the one-step polisher groups had the least statistically significant Ra values (p<0.001). Whereas the multi-step polisher groups had the highest statistically significant Ra values followed by the two-step polisher, then the control groups (p<0.001).
Under the limitations of this study, the following conclusions could be suggested:
1. No polishing system can reach surface roughness average (Ra) above the clinically accepted threshold. However, the one-step polishing system produces the smoothest surface, even smoother than matrix-set surface.
2. Polishing pastes not preceded by a pre-polishing step produces the roughest surface.
3. The type of resin composite significantly affects the surface roughness, the suprananofill resin composite can obtain a smoother surface than the nanofill resin composite.