Effects of the hydroxyl radical and hydrogen peroxide on tooth bleaching.

The mechanisms of bleaching of discolored coronal teeth using hydrogen peroxide (H2O2) were investigated. In a scanning-electron-microscopy study, the intertubular dentin and peritubular dentin were dissolved by high concentrations of H2O2, which is used for bleaching. The X-ray diffraction study showed that hydroxyapatite was not influenced by H2O2. In an electron-spin-resonance study, more hydroxyl radical (* OH) was detected as the H2O2 concentration was increased. When amino acids that are core components of dentin proteins, such as proline and alanine, were added to H2O2, the generation of * OH decreased, but there was no change when glycine was added. A nuclear-magnetic-resonance study showed that proline was degraded completely by H2O2, the structure of alanine changed slightly, and glycine was not affected by H2O2. It is suggested that H2O2 and * OH do not influence the inorganic tissue of dentin but attack the organic component of dentin. These facts suggest that * OH has the main role in tooth bleaching with H2O2.