title: Properties of heat-treated composites after aging in water.
abstract: OBJECTIVE
  Post-cure heat treatments have been shown to increase the fracture toughness and elastic modulus of composites. The objective of this study was to determine if the increase remained after the composites were aged in water. METHODS. The fracture toughness (K(lc)), flexural modulus and flexural strength of four experimental and one commercial composite (Z-100, 3M Dental Products) were tested after 1, 7, 30, 60 and 180 d of aging in 37 degrees C water. The four experimental composites were made with a BisGMA/TEGDMA resin and were characterized as follows: Micro = 38 vol% silane-treated silica, Fine = 65 vol% silane-treated quartz of 1-2 micrometer average size, Hybrid = 65 vol% silane treated quartz of a mixture of 1-2 micrometer average and 8 micrometer average size, and Large = 65 vol% quartz of 8 micrometer average size (of which only 75% were silane-treated). All specimens were light-cured (normal-cured; Triad II - 80 s). One set of each composite was further heat-cured at 120 degrees C for 10 min (heat-cured). A third set of the Hybrid was heat-cured with simultaneous light exposure (Elipar, Espe) for the first 3 min.
  
  
  RESULTS
  By 30 d, normal-cured and heat-cured specimens showed significant (ANOVA/Tukey's test; p < or = 0.05) reductions in fracture toughness (avg. 16% and 22%, respectively), flexural modulus (avg. 11% and 11%, respectively) and flexural strength (avg. 25% and 29%, respectively). Further aging had little effect. The use of additional light-curing during heating did not affect the properties more than heat-curing alone.
  
  
  CONCLUSIONS
  The improvements in some of the properties of composites produced by heat-treating are of only short-term benefit, and are for the most part negated due to an alteration of the resin matrix as the composite equilibrates with water.
authors.affiliation: Oregon Health Sciences University, Portland, Oregon, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Ferracane
authors.forename: J K
authors.initials: JK
authors.lastname: Hopkin
authors.forename: J R
authors.initials: JR
authors.lastname: Condon
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D004356:Drug Storage; D004548:Elasticity; D006358:Hot Temperature; D008422:Materials Testing; D010316:Particle Size; D018583:Pliability; D011092:Polyethylene Glycols / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013997:Time Factors; D014867:Water / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D011109:Polymethacrylic Acids; C083568:Z100 composite resin; D014867:Water; C074741:Silux Plus; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D015040:Zirconium