Application of Titanium Dioxide Nanotubes to Tooth Whitening

63 Introduction With a growing awareness of esthetics in clinical settings, an increasing number of patients are requesting orthodontics and tooth whitening. The demands for tooth whitening have also markedly increased. However, hydrogen peroxide (H2O2) is used at a high concentration (30-35%) in the office bleaching method, which raises concerns about hyperesthesia [1, 2] and its adverse effects on dental hard and periodontal tissues [3-7]. To minimize these adverse effects, titanium dioxide (TiO2), used in white pigments, cosmetics, paint, and food additives, has been applied to tooth whitening [8-10]. TiO2 is less expensive because it is abundant in nature, and is safe for the human body because it is chemically stable. TiO2, used as a photocatalyst, causes a strong redox reaction through holes and electrons generated by light absorption. TiO2 becomes super-hydrophilic when coated as a membrane. In the presence of water, multiple types of radicals are known to be generated by the redox power of a photocatalyst [11]. TiO2 absorbs light above band gap energy (approximately 3.1 eV), and electrons are excited to the conduction band. The excited electrons reduce oxygen, generating superoxide radicals, such as O2 •. The holes generated in the valence Application of Titanium Dioxide Nanotubes to Tooth Whitening