title: Effect of prolonged direct and indirect peroxide bleaching on fracture toughness of human dentin.
abstract: BACKGROUND
  The effects of prolonged exposure to peroxide bleaching agents on dentin structural integrity are uncertain.
  
  
  OBJECTIVE
  To evaluate the effect of in vitro prolonged tooth bleaching on the fracture toughness (K(1C)) of human dentin.
  
  
  METHODS
  Dentin from recently extracted molar teeth was directly or indirectly treated to simulate a prolonged at-home (10% carbamide peroxide or 3% hydrogen peroxide, 6 hours/day, 5 days/week for 8 weeks) or in-office (30% hydrogen peroxide, 1 hour/week for 8 weeks) bleaching regimen (N=8/group). Placebo gel and distilled water acted as control materials. Compact tension test specimens (approximately 4.60 x 4.50 x 1.60 mm) were prepared from coronal dentin and tensile loading was applied at a rate of 10 mm/min 24 hours after the last bleaching session. Results were analyzed using analysis of variance and Tukey's test (p < 0.05). For direct bleach application, the treatment materials were applied onto dentin that was already prepared as compact tension specimens. For indirect bleach application, bleach was applied to the enamel of intact teeth prior to specimen preparation.
  
  
  RESULTS
  There was a significant decrease in dentin K(1C) after 8 weeks of direct bleach treatment (p < 0.05). There were no significant differences between the bleach and control groups after 8 weeks of indirect bleach treatment (p=0.19).
  
  
  CONCLUSIONS
  The in vitro fracture resistance of dentin was reduced after the prolonged use of bleach products that were applied directly to dentin.
  
  
  CONCLUSIONS
  Caution should be considered when using bleach for prolonged treatment times in clinical cases where there is dentin exposure such as occlusal attrition or gingival recession.
authors: Faculty of Dentistry, University of Toronto, Toronto, Canada. laura.tam@utoronto.ca
authors: Laura E
authors: LE
authors: Tam
authors: Vicki Y
authors: VY
authors: Kuo
authors: Amin
authors: A
authors: Noroozi
mesh_terms: D000704:Analysis of Variance; D000077463:Carbamide Peroxide; D003742:Dental Devices, Home Care; D003799:Dental Stress Analysis / Q000379:methods*; D003804:Dentin / Q000187:drug effects*; D004338:Drug Combinations; D006801:Humans; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000009:adverse effects; D008855:Microscopy, Electron, Scanning; D008963:Molar; D016877:Oxidants / Q000008:administration & dosage / Q000009:adverse effects; D010545:Peroxides / Q000008:administration & dosage / Q000009:adverse effects; D013718:Tensile Strength; D014073:Tooth Bleaching / Q000009:adverse effects* / Q000379:methods; D014082:Tooth Fractures / Q000209:etiology; D014508:Urea / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives
chemical_list: D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide