Methods: Eight composite materials were examined: 1 micro-hybrid, 5 nano -hybrid and 2 flowable: (Bright Light® ; Vertise™ ; Nanoceram-Bright®; Tetric EvoCeram®; Grandio® SO; Ceram∙X™ duo; X-tra base; Venus® Diamond Flow). Disc specimens (6 x 2 mm) were prepared (N=9) for each material via manipulation and photopolymerisation according to manufacturers’ instructions. Specimens of each composite material were assigned as three groups (n=3) into solvents of increasing solubility parameter: distilled water, ethanol/water (75%) and MEK (methyl ethyl ketone). Materials were measured post-irradiation at 1 hour, then after storage at 37 ± 0.5 °C for 1day and 30 days. Vickers hardness was measured under a load of 300 g for 15 s at 23 ± 1°C. Data were analysed by three-way ANOVA, one-way ANOVA and Bonferroni post hoc tests (α = 0.05).
Results: There was a statically significant interaction between resin composites, conditions and aging times (p < 0.05). VHN ranged from (112.76) to (26.82) at baseline and (110.10) to (11.73) after solvent- aging. Grandio® SO had the highest VHN before and after aging followed by the self-adhering composite (Vertise™) and Nanoceram-Bright® (p < 0.05). Venus® Diamond Flow had the lowest VHN (p < 0.05). Moreover, VHN significantly decreased after conditioning in ethanol/water and MEK for all investigated materials (p < 0.05).
Conclusions: MEK caused the greatest softening (reduction in VHN) of these composites. A highly filled nano-hybrid composite had the highest VHN over time regardless of the storage conditions.