title: Fracture toughness of water-aged resin composite restorative materials.
abstract: OBJECTIVE
  The purpose of this study was to assess the effects of aging experimental dimethacrylate resin composites in water at 37 degrees C for periods up to 6 wk by measuring the variations in fracture toughness (K(c)), elastic modulus (E), fracture energy (G(c)), and water sorption.
  
  
  METHODS
  Six experimental resins were formulated from dimethacrylate resins, and were filled to 86 wt% (ca. 70 vol%) with treated inorganic filler to form six experimental composites. The fracture toughness was determined using a double torsion technique, the elastic modulus was measured in flexure, and the fracture energy was calculated from the fracture toughness and elastic modulus.
  
  
  RESULTS
  As a result of aging in water, K(c) and the G(c) increased, and the elastic modulus decreased, but all values approached a plateau near 6 wk. Water sorption also occurred during this period, mainly during the first 2 wk.
  
  
  CONCLUSIONS
  Variations in the mechanical properties are interpreted as being due to plasticization of the resin matrix by water, which appears to lower the yield stress and increase in the size of the plastic zone ahead of the crack, thereby causing the observed increase in G(c) and K(c). After approximately 6 wk, no further changes in properties occurred.
authors.affiliation: University of Melbourne, School of Dental Science, Melbourne, Australia.
authors.forename: D J
authors.initials: DJ
authors.lastname: Indrani
authors.forename: W D
authors.initials: WD
authors.lastname: Cook
authors.forename: F
authors.initials: F
authors.lastname: Televantos
authors.forename: M J
authors.initials: MJ
authors.lastname: Tyas
authors.forename: J K
authors.initials: JK
authors.lastname: Harcourt
mesh_terms: D000042:Absorption; D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003793:Dental Restoration, Permanent / Q000379:methods; D003799:Dental Stress Analysis; D004548:Elasticity; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008956:Models, Chemical; D011092:Polyethylene Glycols / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D013314:Stress, Mechanical; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D014867:Water; C098758:tetraethyleneglycol dimethacrylate; C098757:1,12-dodecanediol dimethacrylate; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate