Safer Tooth Whitening with Nanotitania

Teeth can become stained by foods, beverages, and some medications, and thus, tooth whitening is a popular dental procedure. However, the high levels of hydrogen peroxide in bleaching treatments used at dentist offices (30–40 %) can damage the tooth enamel and cause tooth sensitivity or gum irritation. Home bleaching products contain smaller concentrations of hydrogen peroxide (6–12 %), but they usually require longer-term treatment and do not work as well.

When a bleaching gel is applied to the teeth, hydrogen peroxide and reactive species such as hydroxyl radicals degrade pigments in the stains. The hydroxyl radical plays a major role in the bleaching process. Thus, the bleaching capacity of low-concentration hydrogen peroxide could be improved by boosting the generation of hydroxyl radicals.

Li Xie, Weidong Tian, Sichuan University, Chengdu, China, and colleagues have developed an efficient tooth-whitening strategy with improved safety that uses low-concentration hydrogen peroxide. The team used oxygen-deficient TiO₂ (TiO_2–_x) nanoparticles as a catalyst. These nanoparticles can convert hydrogen peroxide into hydroxyl radicals when exposed to near-infrared (NIR) light—a Fenton-like catalytic activity. Under NIR light and in the presence of hydrogen peroxide, the nanoparticles can bleach tooth samples stained with tea, the dye Orange II, or the dye rhodamine B almost completely within a few hours.

The researchers also prepared a gel from the nanoparticles, a carbomer (polyacrylic acid) gel, and 12 % hydrogen peroxide. The gel was applied to naturally stained tooth samples, which were then treated with NIR light for 1 h. The gel bleached teeth just as well as a commercially available tooth whitening gel containing 40 % hydrogen peroxide, with less damage to the enamel. The nanoparticle system is promising for tooth bleaching and could also be useful for other biomedical applications, e.g., in antibacterial materials.