title: Hydrogen peroxide whitens teeth by oxidizing the organic structure.
abstract: OBJECTIVE
  The mechanism of tooth bleaching using peroxide oxidizers is not fully understood. It is unknown whether peroxide radicals make teeth whiter by deproteinizing, demineralizing, or oxidizing tooth tissues. This study was designed to define the mechanism of tooth bleaching and determine which of tooth enamel chemical components is/are affected by bleaching.
  
  
  METHODS
  Sixty sound teeth were collected from adult patients. The teeth were divided into 6 equal groups (n=10). Groups 1, 2, 3 and 4 were treated for 4 days with one of the following solutions: deproteinizing (NaOH) that removes organic content, demineralizing (EDTA) that decalcifies the mineral content, oxidizing (H(2)O(2)) and distilled water (control). Group 5 and 6 were pre-treated with either deproteinizing or demineralizing solutions before treating them with oxidizing solutions for 4 days. Changes in enamel elemental ratios, crystallinity index and tooth shade parameters of the treated teeth were examined by means of EDS, Raman spectroscopy and shade-spectrophotometry. The data obtained was analysed with Wilcoxon Signed-Ranks Test, and the statistical signiﬁcance was set at p<0.05.
  
  
  RESULTS
  Tooth deproteinization increased the lightness by 4.8 ± 2.7°, tooth demineralization resulted in 8.5 ± 5.6° decrease in the lightness and tooth oxidization induced 19.9 ± 6.5° increase in the lightness. Oxidization of the deproteinized teeth did not influence shade parameters, but oxidation of the demineralized teeth resulted in 10.7 ± 5.8° increase in the lightness.
  
  
  CONCLUSIONS
  Hydrogen peroxide does not induce significant changes in tooth enamel organic and inorganic relative contents, and it whitens teeth just by oxidizing their organic matrix. These findings are of great clinical significance since they explain the mechanism of tooth bleaching, and help understanding its limitations and disadvantages.
authors.affiliation: Faculty of Dentistry, McGill University, Montreal, QC H3A0C7, Canada.
authors.forename: Hazem
authors.initials: H
authors.lastname: Eimar
authors.forename: Ryan
authors.initials: R
authors.lastname: Siciliano
authors.forename: Mohamed-Nur
authors.initials: MN
authors.lastname: Abdallah
authors.forename: Samer Abi
authors.initials: SA
authors.lastname: Nader
authors.forename: Wala M
authors.initials: WM
authors.lastname: Amin
authors.forename: Pedro-Pablo
authors.initials: PP
authors.lastname: Martinez
authors.forename: Alicia
authors.initials: A
authors.lastname: Celemin
authors.forename: Marta
authors.initials: M
authors.lastname: Cerruti
authors.forename: Faleh
authors.initials: F
authors.lastname: Tamimi
mesh_terms: D000328:Adult; D001031:Apatites / Q000737:chemistry; D003116:Color; D003461:Crystallography; D003648:Decalcification Technique; D003743:Dental Enamel / Q000737:chemistry / Q000187:drug effects*; D004492:Edetic Acid / Q000494:pharmacology; D004577:Electron Probe Microanalysis; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008855:Microscopy, Electron, Scanning; D009930:Organic Chemicals / Q000737:chemistry; D055601:Organic Chemistry Phenomena / Q000187:drug effects; D016877:Oxidants / Q000494:pharmacology*; D010084:Oxidation-Reduction; D059748:Proteolysis; D012972:Sodium Hydroxide / Q000494:pharmacology; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D013997:Time Factors; D058205:Tooth Bleaching Agents / Q000494:pharmacology*
chemical_list: D001031:Apatites; D009930:Organic Chemicals; D016877:Oxidants; D058205:Tooth Bleaching Agents; D012972:Sodium Hydroxide; D004492:Edetic Acid; D006861:Hydrogen Peroxide