title: Effect of a home bleaching agent on the fracture toughness of resin composites, using short rod design.
abstract: BACKGROUND
  Resin composites are brittle materials and their major shortcomings are manifested in their sensitivity to flaws and defects. Although various mechanical properties of resin composites have been described, few studies are available on assessing the effect of bleaching agents on resin composites using the short rod design.
  
  
  OBJECTIVE
  To place various resin composites into distilled water at 37°C for 21 days and determine the effect of immersion time in distilled water, with and without exposure to 10% carbamide peroxide by employing short rod design fracture toughness test.
  
  
  METHODS
  Specimens were prepared from three resin composites; Rok (SDI), Esthet (Dentsply), and Estelite (Tokuyama). For each material, a total of 24 disc-shaped specimens were prepared using a custom-made mould. Specimens were randomly divided into 3 groups of 8 and conditioned in 37°C distilled water for either 24 hours, or 21 days. 21 day specimens were tested both with and without applying bleaching agent; Polanight (SDI). Study group specimens were bleached for 21 days, 2 hours a day. The specimens were loaded using a universal testing machine with a crosshead speed of 0.5 mm per minute. The maximum load at specimen failure was recorded and the KIc (MPa. M (0.5)) was calculated.
  
  
  RESULTS
  Statistical analysis using two-way ANOVA showed a significant relationship between material and time (p< 0.05).Tukey's test showed that after 24 h of immersion in distilled water, Rok revealed the highest KIc followed by Esthet and Estelite. The bleaching agent significantly improved the fracture toughness values of Esthet while it decreased that of Estelite.
  
  
  CONCLUSIONS
  The fracture toughness of the resin composites was affected by the bleaching agent and distilled water. In comparison with Rok and Estelite, fracture toughness of Esthet was increased due to aging and application of bleaching agent.
authors.affiliation: Dept. of Dental Materials and Biomaterial Research Centre, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: R
authors.initials: R
authors.lastname: Bagheri
authors.affiliation: Student Research Committee, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: M
authors.initials: M
authors.lastname: Fani
authors.affiliation: Student Research Committee, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Ar
authors.initials: A
authors.lastname: Barfi Ghasrodashti
authors.affiliation: Student Research Committee, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: N
authors.initials: N
authors.lastname: Nouri Yadkouri
authors.affiliation: Student Research Committee, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Sm
authors.initials: S
authors.lastname: Mousavi
keywords: Bleaching agent; Fracture toughness; Resin composites