title: Effect of different bleaching techniques on enamel surface microhardness.
abstract: Conservative techniques for treatment of discolored human enamel include in-office bleaching with heat-activated 35% hydrogen peroxide, Nightguard vital bleaching with 10% carbamide peroxide, and enamel microabrasion with 18% hydrochloric acid.
  
  
  OBJECTIVE
  In this study, these bleaching techniques were performed on 30 extracted teeth to evaluate their effects on microhardness of enamel surfaces.
  
  
  METHODS
  The enamel surface microhardness measurements were performed 0, 24, 48, and 72 hours and 1 week after treatment. Paired t tests were performed in the statistical analyses.
  
  
  RESULTS
  No changes were found on specimens treated with carbamide peroxide. There was a significant decrease in the surface microhardness of enamel after 0 and 24 hours when the specimens were treated with 18% hydrochloric acid (softening 85.7 and rehardening 99.4) or with 35% hydrogen peroxide (softening 85.7). However, after 72 hours, significant rehardening was observed in these groups (P <.001).
  
  
  CONCLUSIONS
  According to the results, except Nightguard vital bleaching, all other techniques softened the enamel surface.
authors.affiliation: Dental Faculty, Department of Conservative Dentistry, Istanbul University, Istanbul, Turkey. ulukapi@istanbul.edu.tr <ulukapi@istanbul.edu.tr>
authors.forename: Hasmet
authors.initials: H
authors.lastname: Ulukapi
mesh_terms: D000077463:Carbamide Peroxide; D003743:Dental Enamel / Q000187:drug effects*; D004338:Drug Combinations; D019243:Enamel Microabrasion / Q000009:adverse effects; D006244:Hardness / Q000187:drug effects; D006801:Humans; D006851:Hydrochloric Acid / Q000009:adverse effects; D006861:Hydrogen Peroxide / Q000009:adverse effects; D016877:Oxidants / Q000009:adverse effects; D010545:Peroxides / Q000009:adverse effects; D013499:Surface Properties / Q000187:drug effects; D013997:Time Factors; D014073:Tooth Bleaching / Q000009:adverse effects*; D014508:Urea / Q000009:adverse effects / Q000031:analogs & derivatives
chemical_list: D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide; D006851:Hydrochloric Acid