title: Dentin microhardness during and after whitening treatments.
abstract: OBJECTIVE
  This in vitro study aimed to evaluate the effect of bleaching agents on dentin microhardness during and after bleaching.
  
  
  METHODS
  Specimens were randomly assigned to seven groups (n = 15): Nite White Excel 2 Z [NW] 10% and 22%; Rembrandt [REM] 10% and 22%; Opalescence [OPA] 10% and 20%; and a placebo agent. The 42-day whitening treatment consisted of daily application of the agents to the dentin surfaces for 8 hours, followed by immersion in artificial saliva for 16 hours. After the bleaching treatment, specimens were kept immersed in artificial saliva for 14 days. Microhardness was measured at baseline, 8 hours, and 7, 14, 21, 28, 35, and 42 days of bleaching and during the posttreatment period (7 and 14 days).
  
  
  RESULTS
  The analysis of variance for split-plot showed a significant effect on the interaction between bleaching agent and time. Tukey's test and regression analyses revealed that during the bleaching period, the agents NW 10%, NW 22%, and OPA 20%, which did not differ from each other, did not alter dentin microhardness, showing constant microhardness values. There were no differences among REM 10%, REM 22%, and OPA 10%, which showed significant reductions in microhardness after day 14 compared to other agents. After bleaching procedures, there was an increase in dentin microhardness for all groups.
  
  
  CONCLUSIONS
  Throughout the bleaching treatment, depending on the agent applied, dentin showed a transitory decrease in microhardness values. In the posttreatment period, artificial saliva presented a remineralizing effect on the bleached surfaces.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry of Piracicaba, State University of Campinas (UNICAMP), Piracicaba, Brazil.
authors.forename: Patricia Moreira
authors.initials: PM
authors.lastname: de Freitas
authors.forename: Cecilia Pedroso
authors.initials: CP
authors.lastname: Turssi
authors.forename: Anderson Takeo
authors.initials: AT
authors.lastname: Hara
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 / Q000627:therapeutic use*; D010545:Peroxides / Q000627:therapeutic use; D010919:Placebos; D011145:Polyvinyls / Q000627:therapeutic use; D012044:Regression Analysis; D012464:Saliva, Artificial / Q000627:therapeutic use; D013997:Time Factors; D014073:Tooth Bleaching / Q000379:methods*; D014089:Tooth Remineralization; D014508:Urea / Q000031:analogs & derivatives* / Q000627:therapeutic use
chemical_list: D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D010919:Placebos; D011145:Polyvinyls; C112939:Rembrandt Lighten; D012464:Saliva, Artificial; D000077463:Carbamide Peroxide; D014508:Urea