Hardness and fracture toughness of resin-composite materials with and without fibers

Objective: To investigate the surface micro-hardness (VHN)and fracture toughness (K_IC)of resin-composites, with and without incorporated short fibers, after solvent storage. Methods: Three resin-composites incorporating fibers, additional to particle reinforcement, were examined: everX™, NovoPro Fill™ and NovoPro Flow™. Four composites were used as controls, with only particle reinforcement: Filtek bulk Fill™, Filtek bulk one™, Filtek XTE™, and Filtek Flow XTE™. For hardness measurement, materials were cured in 2 mm thick molds for 20 s by a LED source of average irradiance 1.2 W/cm². Specimens (n = 6/group)were stored dry for 1 h and then in either water or 75% ethanol/water for 1 h, 1 day and 30 days at 37 ± 1 °C. Vickers hardness was measured under a load of 300 g for 15 s. For fracture toughness (K_IC)measurements, single-edge-notched specimens (n = 6/group)were prepared: (32 × 6 × 3 mm)for 3-point bending and stored for 1 and 7 days in water at 37 °C. Fractured surfaces of fiber-reinforced composite were examined by scanning electron microscopy (SEM). VHN data were analyzed using three-way ANOVA, one-way ANOVA and the Tukey post hoc test (p ≤ 0.05). K_IC data were analyzed by two-way ANOVA and one-way ANOVA and the Tukey post hoc test (p ≤ 0.05). An independent t-test was used to detect differences (α = 0.05)in K_IC between stored groups for each material. Results: VHN decreased for all composites with storage time in both solvents, but more appreciably in 75% ethanol/water (an average of 20%). K_IC ranged from 2.14 (everX Posterior)to 0.96 NovoPro Flow)MPa. m^0.5. The longer storage period (7 days)had no significant effect on this property relative to 1 day storage. Significance: Reinforcement with short fibers, and possibly matrix compositional differences, significantly enhanced the fracture toughness of EVX. However, for nano-fiber containing composites, there were no evident beneficial effects upon either their fracture toughness or hardness compared to a range of control composites. Water storage for 7 days of all these resin-composites produced no significant change in their K_IC values, relative to 1 day storage.