Fracture toughness and cyclic fatigue resistance of resin composites with different filler size distributions

Objectives. To verify the influence of filler size distributions on fracture toughness (K-Ic), initial fracture strength (IFS) and cyclic fatigue resistance (CFR) of experimental resin composites. Methods. Four composites were prepared with same inorganic content (78 wt%), in which 67 wt% was constituted by glass particles with d(50) of 0.5; 0.9; 1.2; 1.9 mu m K-Ic of the composites was determined by the single-edge notched beam (SENB) method. To evaluate the IFS and the CFR a biaxial bending test configuration was used. The CFR was determined under cyclic loading for 10(5) cycles using the 'staircase' approach. The fracture surfaces of IFS and CFR specimens were analyzed under scanning electron microscope (SEM). Results. There was a positive linear correlation between d(50) vs. K-Ic and statistical difference was found only between C0.5 (1.24 +/- 0.10 MPa m(0.5)) and C1.9 (1.41 +/- 0.17 MPa m(0.5)). There were no statistical differences among IFS means, which ranged from 155.4 +/- 1 18.8 MPa (C0.9) to 170.7 +/- 1 23.1 MPa (C1.2). C0.5 (93.0 +/- 18.6(a) MPa) showed the highest and C0.9 the lowest CFR (82.5 +/- 8.0(c) MPa). There was no correlation between CFR with d(50) values or with K-Ic means. SEM images showed the morphology with brittle fracture patterns for the surfaces of IFS specimens and a more smooth fracture surface for CFR specimens. Significance. Resin composites showed different failure mechanisms for quasi-static and fatigue loading. For K-Ic and IFS, composites with larger filler size distributions showed better results due to crack deflection; while under cyclic loading, viscous behavior was predominant and composites with smaller particles showed higher fatigue resistance. (C) 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.