Flexural fatigue behavior of resin composite dental restoratives

Objectives. The aim of this study was to evaluate the mechanical properties of resin composite dental restoratives under quasi-static and cyclic loading. Methods. Four-point-bending bars of 10 different resin composite materials were manufactured according to ISO standard and stored for two weeks in distilled water. The fracture strength (FS) was measured with the four-point-bending test in an universal testing machine. The flexural fatigue limits (FFL) for 105 cycles were determined under equivalent loading. All specimens were tested and fatigued in water at 37 °C. The data were analyzed using ANOVA, Weibull statistics of FS and the ‘staircase’ approach of FFL. Fractographic analysis was performed using SEM. Results. The initial flexural strength values for the resin composite materials varied from 55.4 MPa for Solitaire® up to 105.2 MPa for Filtek® Z250. The mean flexural fatigue limit for 105 cycles ranged between 37 and 67% of the initial strength. SEM analysis of the fractured surfaces suggests two kinds of failure mechanisms for initial and fatigue fracture. Significance. The fatigue behavior of resin composite materials does not correlate with initial strength values. Materials providing high initial strengths do not obviously reveal the best fatigue resistance. Flexural fatigue measurement of resin composite materials should be viewed as a useful tool to evaluate long term mechanical properties.