Aim. Nanotechnology applied to fabrication of sub-micron filled composite resin is a fairly recent and promising innovation in dental restorative materials. The actual advantages that nano-sized fillers can provide to the surface smoothness and luster have not been supported yet by sufficient evidence. Effective polishing protocols presenting the fewest number of steps are demanded by clinicians in order to avoid waste of operative time. Polishing pastes have a better ability to reach irregular areas of restorations in comparison to semi-rigid rotating instruments. The aim of the present study was to assess the effectiveness of two simplified polishing systems with diamond abrasive pastes applied onto the surface of two nanohybrid composites. Materials and methods. Two nanohybrid resins were selected for the present experimentation, namely Filtek Supreme XT (3M ESPE) and Herculite XRV Ultra (Kerr). Thirty discs per material were fabricated by pouring the resin into silicon molds with a height of 2 mm and a diameter of 4 mm, covering it with a Mylar strip and applying 60 s light cure with a halogen lamp at 600 mW/cm2. For each material, the specimens were randomly allocated to a control unpolished group (n=10) and two experimental groups (n=10), which underwent finishing with 1200P sandpaper. The experimental groups were subjected to further polishing with either one-step (Unigloss paste) or two-step (Diamond Polish Mint, Ultradent) diamond polishing pastes. Three linear roughness measurements (Ra) were performed on the surface of each specimen. Statistical analysis was carried out by non-parametric tests. The surface of polished specimens was assessed by means of scanning electron microscopy. Results. Under all experimental conditions, the surface roughness of the tested resins never exceeded the threshold to inhibit bacterial adhesion (0.20 μm) and polished specimens exhibited surface smoothness that was similar to controls. The one-step system polished more efficiently the composite Herculite XRV Ultra than Filtek Supreme XT (p<0.05) and was more effective than the two-step system only when applied to Herculite XRV Ultra (p<0.001). No other significant differences were pointed out. Microphotographs showed mostly polished surfaces with sporadic isolated grooves left by the finishing procedure and not removed by the polishing pastes. Conclusions. Both one-step and two-step simplified protocols considered were effective for polishing the two nanohybrid composites being tested. Different association between material and polishing protocol can lead to slight but significant variation of performance.
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