ESR investigation of ROS generated by H₂O₂ bleaching with TiO₂ coated HAp

Abstract

It is well known that clinical bleaching can be achieved with a solution of 30% hydrogen peroxide (H₂O₂) or H₂O₂/titanium dioxide (TiO₂) combination. This study examined the hypothesis that TiO₂ coated with hydroxyapatite (HAp-TiO₂) can generate reactive oxygen species (ROS). ROS are generated via photocatalysis using electron spin resonance (ESR). The bleaching properties of HAp-TiO₂ in the presence of H₂O₂ can be measured using hematoporphyrin litmus paper and extracted teeth. We demonstrate that superoxides (O₂^•−) and hydroxyl radicals (HO^•) can be generated through excitation of anatase TiO₂, rutile TiO₂, anatase HAp-TiO₂, and rutile HAp-TiO₂ in the presence of H₂O₂. The combination of R HAp-TiO₂ with H₂O₂ produced the highest level of HO^• generation and the most marked bleaching effects of all the samples. The superior bleaching effects exhibited by R HAp-TiO₂ with H₂O₂ suggest that this combination may lead to novel methods for the clinical application of bleaching treatments.