Effect of two multi-step polishing systems on surface characteristics of nanohybrid composite resins: Influence of reuse.

Background: Proper finishing and polishing are crucial for reducing surface roughness and eliminating the incompletely polymerized oxygen-inhibited layer. This study compared surface characteristics - specifically water contact angle, surface roughness, and morphology of three nanohybrid composite resins polished with two different multi-step polishing systems.

Material and methods: We evaluated Filtek Z250 (3M), Tetric N-Ceram (Ivoclar), and Spectra Smart (Dentsply), all in shade A2. Thirty-nine discs per resin (9 mm diameter × 2 mm thickness) were fabricated, stored in distilled water at 37°C for 24 hours, and pre-polished with silicon carbide paper (600, 1000, and 1200 grit). Final polishing employed two systems: the 3-step Astropol system (Ivoclar) and the 2-step ShapeGuard system (Diatech), with each system tested through six reuse cycles (three samples per resin per cycle). Surface analysis included water contact angle measurement, profilometry, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS).

Results: The Astropol system demonstrated significantly greater hydrophobicity (107.6° ± 10.9°) than ShapeGuard (99.1° ± 9.0°). Among the tested resins, Filtek Z250 polished with Astropol showed the lowest surface roughness (0.27 ± 0.11 µm), while Spectra Smart polished with ShapeGuard showed the highest (0.78 ± 0.20 µm). Polishing system reuse showed no significant effects on results. SEM revealed no noTable morphological changes, and EDS confirmed consistently high SiO2 content across all resins.

Conclusions: Both polishing system and resin composition significantly influence surface characteristics. Filtek Z250 performed optimally with both polishing systems. Further research should investigate the long-term effects of polishing system reuse. Key words:Nanohybrid resins, polishing systems, surface roughness, contact angle, SEM.