title: Flexural strength and modulus properties of carbamide peroxide-treated bovine dentin.
abstract: BACKGROUND
  The effects of carbamide peroxide bleach on tooth structure are uncertain.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the effects of direct or indirect carbamide peroxide application on dentin flexural strength and modulus in vitro.
  
  
  METHODS
  Dentin bars were machined from bovine incisors and treated with 10% carbamide peroxide for 6 h/d for 14 days. Four groups were created, with eight bars in each group: group 1-direct bleach application only; group 2-indirect bleach application only; group 3-direct bleach application followed by a 2-week storage in artificial saliva; group 4-direct bleach application followed by a 2-week storage in artificial saliva and daily topical fluoride treatments. The specimens' flexural strength and modulus were tested after 24 hours, and the results were compared with water controls using independent t-tests (p < .05).
  
  
  RESULTS
  Flexural strength results (in megapascals) for bleached versus control dentin (1=205+/-26 vs 215+/-14, 2=257+/-25 vs 261+/-14, 3=180+/-22 vs 193+/-36, 4=157+/-18 vs 184+/-11) were significantly lower in group 4 (p=.005). Modulus results (in gigapascals) for bleached versus control dentin (1=10.7+/-1.4 vs 12.2+/-0.6, 2=14.2+/-1.7 vs 14.4+/-1.6, 3=10.0+/-2.0 vs 10.9+/-1.3, 4=9.0+/-1.2 vs 11.1+/-1.0) were significantly lower in groups 1 and 4 (p=.013 and p=.003, respectively). There were no significant differences in strength and modulus results between the bleached and control dentin in groups 2 and 3. A direct application of carbamide peroxide to bovine dentin significantly decreased some dentin mechanical properties in vitro. An indirect application of carbamide peroxide to dentin did not significantly decrease dentin strength and stiffness.
  
  
  CONCLUSIONS
  This in vitro study suggests that a bleaching treatment, when applied to the enamel of intact teeth, does not significantly affect the mechanical properties of the underlying dentin. However, when applied directly to dentin in clinical situations such as root exposure or occlusal attrition, the bleaching treatment may result in altered mechanical properties of dentin. The clinical consequences of this observation are, however, unknown.
authors.affiliation: Restorative Dentistry, Faculty of Dentistry, University of Toronto, ON, Canada. laura.tam@utoronto.ca
authors.forename: Laura Eva
authors.initials: LE
authors.lastname: Tam
authors.forename: Ryan
authors.initials: R
authors.lastname: Abdool
authors.forename: Wafa
authors.initials: W
authors.lastname: El-Badrawy
mesh_terms: D000818:Animals; D000077463:Carbamide Peroxide; D002327:Cariostatic Agents / Q000494:pharmacology; D002417:Cattle; D003804:Dentin / Q000187:drug effects*; D004338:Drug Combinations; D004548:Elasticity; D005460:Fluorides, Topical / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology*; D010545:Peroxides / Q000494:pharmacology*; D018583:Pliability; D012464:Saliva, Artificial / Q000494:pharmacology; D012969:Sodium Fluoride / Q000494:pharmacology; D013314:Stress, Mechanical; D013997:Time Factors; D014073:Tooth Bleaching; D014089:Tooth Remineralization; D014508:Urea / Q000031:analogs & derivatives* / Q000494:pharmacology; D014867:Water
chemical_list: D002327:Cariostatic Agents; D004338:Drug Combinations; D005460:Fluorides, Topical; D016877:Oxidants; D010545:Peroxides; D012464:Saliva, Artificial; D014867:Water; D000077463:Carbamide Peroxide; D014508:Urea; D012969:Sodium Fluoride