title: Effect of cyclic loading and environmental aging on the fracture toughness of dental resin composite.
abstract: OBJECTIVE
  The main purpose of this study was (1) to investigate the effects of cyclic loading and environmental aging on three dental resin composites with different filler compositions: a fiber filler, a hybrid filler, and a microfill; and (2) to predict fracture in dental resin composite under mixed-mode loading conditions.
  
  
  METHODS
  Diametral disk specimens 25 mm in diameter and 2 mm in thickness were used in this study. Two methods were used for generating initial cracks in the specimen. The first method involved machining a 3-mm notch in the center of the disk specimens, and then the notch tips were sharpened with a 0.2-mm-diameter jeweler's saw blade. In the second method for obtaining sharper crack tips, a three-way wedge was forced into a 3.175-mm hole drilled in the center of the specimen, resulting in sharp cracks emanating from the notch tips. CYCLIC TESTS: The specimens were aged for 4 months in air, water, artificial saliva, and a 50/50 (by volume) mixture of ethanol and water at room temperature in sealed polyethylene containers. Both unaged and aged specimens (5 specimens for each variable) were subjected to cyclic loading at a frequency of 5 Hz with sinusoidal loads cycling for 1, 1000, and 100,000 cycles at a load level approximately 60% of the fracture load for noncycled specimens. Following load cycling, the specimens were tested in compression in a displacement-controlled loading mode at a loading rate of 1.27 mm/min.
  
  
  RESULTS
  Test results show that aging in a 50/50 alcohol-water mixture lowered the fracture toughness of dental resin composite, which was further reduced by cyclic loading. MIXED-MODE TESTS: The maximum tensile stress (MTS) criterion was used to predict fracture in dental resin composite under mixed-mode loading conditions. The loads at failure were used as input into a finite element model. After obtaining the stress field in the specimens by the finite element method, the mixed-mode stress intensity factors were calculated using an interaction energy integral method.
  
  
  RESULTS
  Good agreement was obtained between the fracture envelope predicted by the MTS criterion and the experimental fracture toughness data. Hence, it can be concluded that it is only necessary to characterize the mode I fracture toughness to fully characterize the mixed-mode behavior of the dental resin composites that were considered in the present study.
authors.affiliation: Mechanical, Materials and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, Illinois, USA.
authors.forename: Viswanath
authors.initials: V
authors.lastname: Ravindranath
authors.forename: Michael
authors.initials: M
authors.lastname: Gosz
authors.forename: Eduardo
authors.initials: E
authors.lastname: De Santiago
authors.forename: James L
authors.initials: JL
authors.lastname: Drummond
authors.forename: Sheldon
authors.initials: S
authors.lastname: Mostovoy
mesh_terms: D003188:Composite Resins; D003738:Dental Cements; D003799:Dental Stress Analysis; D006244:Hardness; D008954:Models, Biological; D013997:Time Factors; D014082:Tooth Fractures / Q000628:therapy
chemical_list: D003188:Composite Resins; D003738:Dental Cements