Degradation of optical and surface properties of resin-based composites with distinct nanoparticle sizes but equivalent surface area

Objective To determine the optical and surface properties of model resin-based composites made with distinct nanoparticle sizes but equalized surface area, among them, before and after ageing. Methods Model resin-based composites based on BisGMA/TEGDMA (50:50 mol%) were loaded with three different fumed silica filler content (7 nm/examethyldisilazane, 12 nm/octylsilane, and 16 nm/dimethylchlorosilane), but with equivalent surface area (BET method). The optical and surface properties of the disk-shaped specimens were measured in 24 h after photoactivation (baseline) and repeated after water storage (90 days at 37 °C), and after abrasion (20,000 cycles of brushing). CIELAB individual parameters, color difference (ΔE*_ab), translucency parameter (TP), gloss (G.U.) and roughness (Ra parameter) were measured. Data were statistically analyzed at α=0.05 significance level. Results CIE L* and TP were not affected by ageing in any group. CIE a* was increased and CIE b* decreased for the 12 nm and 16 nm groups and did not show any difference for the 7 nm group. After ageing, the lowest ΔE*_ab was observed for the 7 nm group. Gloss and roughness were statistically equivalent for all groups, before and after ageing. The water storage didn't show any significant difference while the abrasion decreased gloss and increased the roughness. Conclusion The optical properties of the tested materials were not dependent of the fillers’ surface area, while the surface properties were. Clinical significance Several factors influence the ageing resistance of the resin-based composites, including the surface area of the fillers and the amount and coupling treatment of them. The improvement of the material's physical stability could avoid the premature replacement of dental restorations.