title: In situ effect of 10% carbamide peroxide on microhardness of human enamel: function of time.
abstract: OBJECTIVE
  This study evaluated the effect of two home bleaching regimens (1 h/day versus 7 h/day for a total of 21 days) on the microhardness of superficial enamel treated with 10% carbamide peroxide gel.
  
  
  METHODS
  Rectangular enamel specimens (2.5 x 2.5 x 1 mm) were obtained from human third molars and mounted on the palatal aspect of removable orthodontic retainers. Nine enamel specimens were mounted in each of 10 retainers, used by 10 volunteers during the active phase of the study. Modified 0.089 cm thick bleaching trays were fabricated for each participant. Each bleaching tray fit a participant's arch and the retainer containing the enamel specimens. Enamel specimens were treated with a 10% carbamide peroxide bleaching gel (Nite White Excel 2Z, Discus Dental, Culver City, CA, USA) for either 1 h/day (n = 30) or 7 h/day (n = 30), both for 21 days. Three enamel specimens in each retainer were never treated and served as controls. The retainers were worn by the participants whether or not they underwent bleaching. This simulated the natural action of the saliva/oral fluids on the enamel specimens. Enamel specimens were subjected to pre- and post-treatment microhardness measurements. Post-treatment Knoop hardness numbers were compared with baseline values and analyzed statistically.
  
  
  RESULTS
  Bleaching treatment resulted in a nonsignificant reduction in microhardness values when compared with values of the control nontreated specimens (1.7% and 2.5% reduction in hardness for 1 h/day and 7 h/day, respectively). There was no difference in microhardness between the different treatment regimens.
  
  
  CONCLUSIONS
  Home bleaching with 10% carbamide peroxide for up to 7 h/day for 21 days does not significantly affect enamel microhardness.
  
  
  CONCLUSIONS
  Bleaching with 10% carbamide peroxide for 1 h/day or 7 h/day for a total of 21 days is safe for human enamel.
authors.affiliation: Department of Operative Dentistry, Federal University of Santa Catarina, Florianópolis, San Catarina, Brazil.
authors.forename: Edson M Júnior
authors.initials: EM
authors.lastname: Araujo
authors.forename: Luiz N
authors.initials: LN
authors.lastname: Baratieri
authors.forename: Luiz Clóvis C
authors.initials: LC
authors.lastname: Vieira
authors.forename: André V
authors.initials: AV
authors.lastname: Ritter
mesh_terms: D000293:Adolescent; D000328:Adult; D000077463:Carbamide Peroxide; D003742:Dental Devices, Home Care; D003743:Dental Enamel / Q000187:drug effects*; D004338:Drug Combinations; D005260:Female; D006244:Hardness / Q000187:drug effects*; D006801:Humans; D008297:Male; D009968:Orthodontic Appliances, Removable; D016877:Oxidants / Q000008:administration & dosage / Q000494:pharmacology*; D010545:Peroxides / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors; D014073:Tooth Bleaching / Q000295:instrumentation / Q000379:methods; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology*
chemical_list: D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D000077463:Carbamide Peroxide; D014508:Urea