title: Surface microhardness of enamel after different home bleaching procedures.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the influence of different home bleaching procedures on surface microhardness of human enamel.
  
  
  METHODS
  Among eight groups 192 incisors were distributed. The facial surface of each incisor was polished and baseline hardness of enamel (m0; Knoop) was assessed with a load of 1N for 30s. Subsequently, the enamel was treated for 14 days with the bleaching agent: groups 1, 2 and 4 Viva Style Paint on, 8% carbamide peroxide (CP) 1x20min, 2x20min and 2x5min; group 3 Colgate Simply White, 5.9% hydrogen peroxide (HP), 2x30min; group 5 Viva Style 10% CP 1x1h; group 6 Blend-a-med White Strips, 5.9% HP 2x30min; group 7 Odol-med3 Beauty-Kur, sodium chlorite 2x10min; group 8 control, running water 1x1h. Hardness was reassessed after the last bleaching treatment (m1) and after 6 weeks storage in artificial saliva (m2).
  
  
  RESULTS
  Changes in microhardness were as follows (m0-m1): (1) -2.3 (+/-20.3); (2) -8.9 (+/-27.2); (3) 63.4 (+/-56.3); (4) 9.6 (+/-30.1); (5) 12.8 (+/-62.6); (6) 92.2 (+/-50.2); (7) 158.4 (+/-59.7); (8) 10.6 (+/-38.5). Statistical analysis showed that hardness values were significantly (p< or =0.0005; Wilcoxon test) reduced in groups 3, 6, and 7 (m1) and in group 7 (m2).
  
  
  CONCLUSIONS
  Both type of bleaching agent and concentration have a significant influence on the microhardness of enamel. The most critical bleaching agent seems to be the one containing sodium chlorite in combination with citric acid.
authors.affiliation: Department of Operative Dentistry and Periodontology, University School of Dental Medicine, Campus Benjamin Franklin, Charité-Universitätsmedizin Berlin, Berlin, Germany. catharina.zantner@charite.de
authors.forename: Catharina
authors.initials: C
authors.lastname: Zantner
authors.forename: Nils
authors.initials: N
authors.lastname: Beheim-Schwarzbach
authors.forename: Konrad
authors.initials: K
authors.lastname: Neumann
authors.forename: Andrej M
authors.initials: AM
authors.lastname: Kielbassa
mesh_terms: D000077463:Carbamide Peroxide; D002712:Chlorides / Q000008:administration & dosage / Q000627:therapeutic use; D019343:Citric Acid / Q000008:administration & dosage / Q000627:therapeutic use; D045424:Complex Mixtures / Q000008:administration & dosage / Q000627:therapeutic use; D003743:Dental Enamel / Q000187:drug effects* / Q000473:pathology; D004338:Drug Combinations; D005782:Gels; D006244:Hardness; D006801:Humans; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000627:therapeutic use; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D016877:Oxidants / Q000008:administration & dosage / Q000627:therapeutic use*; D010545:Peroxides / Q000008:administration & dosage / Q000627:therapeutic use; D012464:Saliva, Artificial / Q000008:administration & dosage; D013314:Stress, Mechanical; D014073:Tooth Bleaching / Q000379:methods*; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000627:therapeutic use; D014867:Water / Q000008:administration & dosage
chemical_list: D002712:Chlorides; C475021:Colgate Simply White Clear Whitening Gel; D045424:Complex Mixtures; D004338:Drug Combinations; D005782:Gels; D016877:Oxidants; D010545:Peroxides; D012464:Saliva, Artificial; C500417:Vivastyle; D014867:Water; D019343:Citric Acid; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide; C001599:chlorite