title: Effects of two 10% peroxide carbamide bleaching agents on dentin microhardness at different time intervals.
abstract: OBJECTIVE
  The purpose of this in vitro study was to evaluate the microhardness of human dentin exposed to two 10% carbamide peroxide agents at different bleaching times.
  
  
  METHODS
  Opalescence 10% and Rembrandt 10% were tested. A placebo agent was used as a control group. The bleaching and placebo agents were applied to the surface of human dentin fragments for 8 hours and then stored in individual receptacles with artificial saliva for the remaining 16 hours each day. Microhardness testing was performed at baseline, after 8 hours, 7, 14, 21, 28, 35, and 42 days of treatment, and 7 and 14 days posttreatment.
  
  
  RESULTS
  Analysis of Variance and the Tukey test revealed significant differences in microhardness values for dentin treated with the agents within each time interval. There was a decrease in the microhardness values of dentin for both bleaching agents after 8 hours of treatment. Fourteen days after the completion of treatment, the microhardness values for dentinal surfaces treated with either Opalescence or Rembrandt reached the baseline values; the dentinal surfaces treated with a placebo exhibited an increase in microhardness values posttreatment.
  
  
  CONCLUSIONS
  Ten percent carbamide peroxide bleaching agents decreased dentinal microhardness over time, but after 14 days in artificial saliva storage at the completion of treatment, the baseline microhardness values were recovered.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry of Piracicaba, University of Campinas (UNICAMP), Piracicaba, Brazil.
authors.forename: Patrícia Moreira
authors.initials: PM
authors.lastname: de Freitas
authors.forename: Roberta Tarkany
authors.initials: RT
authors.lastname: Basting
authors.forename: Júnior Antonio Luiz
authors.initials: JA
authors.lastname: Rodrigues
authors.forename: Mônica Campos
authors.initials: MC
authors.lastname: Serra
mesh_terms: D000704:Analysis of Variance; D000077463:Carbamide Peroxide; D003804:Dentin / Q000187:drug effects*; D004338:Drug Combinations; D006244:Hardness; D006801:Humans; D016877:Oxidants / Q000008:administration & dosage / Q000494:pharmacology*; D010545:Peroxides / Q000008:administration & dosage / Q000494:pharmacology*; D010919:Placebos; D011145:Polyvinyls / Q000494:pharmacology; D012464:Saliva, Artificial / Q000494:pharmacology; D013223:Statistics as Topic; D013997:Time Factors; D014073:Tooth Bleaching; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D010919:Placebos; D011145:Polyvinyls; C112939:Rembrandt Lighten; D012464:Saliva, Artificial; D000077463:Carbamide Peroxide; D014508:Urea