Objectives: 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.
Conclusion: 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.
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