title: Fracture toughness and cyclic fatigue resistance of resin composites with different filler size distributions.
abstract: OBJECTIVE
  To verify the influence of filler size distributions on fracture toughness (KIc), 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 d50 of 0.5; 0.9; 1.2; 1.9 μm KIc 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 d50 vs. KIc and statistical difference was found only between C0.5 (1.24±0.10 MPa m0.5) and C1.9 (1.41±0.17 MPa m0.5). There were no statistical differences among IFS means, which ranged from 155.4±18.8 MPa (C0.9) to 170.7±23.1 MPa (C1.2). C0.5 (93.0±18.6a MPa) showed the highest and C0.9 the lowest CFR (82.5±8.0c MPa). There was no correlation between CFR with d50 values or with KIc 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.
  
  
  CONCLUSIONS
  Resin composites showed different failure mechanisms for quasi-static and fatigue loading. For KIc 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.
authors.affiliation: School of Dentistry, Positivo University, Curitiba, Brazil. Electronic address: bpo@up.com.br.
authors.forename: Bárbara P
authors.initials: BP
authors.lastname: Ornaghi
authors.affiliation: Department of Chemistry, Santa Catarina State University and FGM Produtos Odontológicos, Joinville, Brazil.
authors.forename: Marcia M
authors.initials: MM
authors.lastname: Meier
authors.affiliation: Laboratory for Biomaterials Research, Dental Clinic 1, Operative Dentistry and Periodontology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Lohbauer
authors.affiliation: Department of Biomaterials and Oral Biology, School of Dentistry, University of São Paulo, São Paulo, Brazil.
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Braga
mesh_terms: D000180:Acrylic Resins; D003188:Composite Resins; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011140:Polyurethanes
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D011140:Polyurethanes
keywords: Cyclic fatigue; Fractography; Fracture strength; Fracture toughness; Resin composites