title: Monomer release from nanofilled and microhybrid dental composites after bleaching.
abstract: OBJECTIVE
  The aim of this study was to assess the effect of bleaching on elution of monomers from nanofilled and microhybrid composites.
  
  
  METHODS
  80 samples (5mm diameter and 3mm thickness) of each composite were prepared. After curing, half of them were randomly polished. Each group was divided into 8 subgroups and immersed in water or 10%, 20% and 30% H2O2 for 3 or 8 hours. Eluted Bis-GMA (Bis-phenol A Glycidyl Dimethacrylate), TEGDMA (Triethyleneglycol Dimethacrylate), UDMA (Urethane Dimethacrylate) and BisEMA (Bis-phenol A ethoxylate Dimethacrylate) were quantified by high performance liquid chromatography and the results were analyzed by univariate ANOVA and t-test (P<0.05).
  
  
  RESULTS
  Bleach significantly increased the overall release of monomers (P<0.001); TEGDMA was released more than Bis-GMA (P<0.001). Supreme released more TEGDMA compared to Z250 (P<0.001). Bleaching increased the release of this monomer (P<0.001). Increasing both the concentration of H2O2, and the immersion time, increased the release of TEGDMA (P<0.001). Polishing had no effect on release of this monomer (P=0.952). Supreme released more Bis-GMA than Z250 (P=0.000). The more concentrated H2O2 caused more elution of Bis-GMA (P= 0.003); while the effect of immersion time was not significant (P=0.824). Polishing increased the release of Bis-GMA (P=0.001). Neither the type of composite nor Bleaching had any effect on release of UDMA (P=0.972) and (P=0.811) respectively. Immersion duration increased the release of UDMA (P=0.002), as well as polishing (P=0.024).
  
  
  CONCLUSIONS
  Bleaching increased the release of monomers. Nanofilled composites released more monomer than the microfilled.
authors.affiliation: Associate Professor, Dental Research Center Dentistry Research Institute, Department of Operative Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Masumeh Hasani
authors.initials: MH
authors.lastname: Tabatabaee
authors.affiliation: Assistant Professor, Department of Operative Dentistry, School of Dentistry Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Sakineh
authors.initials: S
authors.lastname: Arami
authors.affiliation: Associate Professor, Dental Research Center Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Ghavam
authors.affiliation: Dentist.
authors.forename: Asieh
authors.initials: A
authors.lastname: Rezaii
keywords: Bleaching; Chromatography; Dental composites; Monomer elution