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

Abstract

ObjectiveTo investigate the surface micro-hardness (VHN) and fracture toughness (KIC) of resin-composites, with and without incorporated short fibers, after solvent storage. MethodsThree 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 2mm thick molds for 20s by a LED source of average irradiance 1.2W/cm2. Specimens (n=6/group) were stored dry for 1h and then in either water or 75% ethanol/water for 1h, 1 day and 30 days at 37±1°C. Vickers hardness was measured under a load of 300g for 15s. For fracture toughness (KIC) measurements, single-edge-notched specimens (n=6/group) were prepared: (32×6×3mm) 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). KIC 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 KIC between stored groups for each material. ResultsVHN decreased for all composites with storage time in both solvents, but more appreciably in 75% ethanol/water (an average of 20%). KIC ranged from 2.14 (everX Posterior) to 0.96 NovoPro Flow) MPa.m0.5. The longer storage period (7 days) had no significant effect on this property relative to 1 day storage. SignificanceReinforcement 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 KIC values, relative to 1 day storage.