Development of in vitro tooth staining model and usage of catalysts to elevate the effectiveness of tooth bleaching

Objectives: Whole blood or tea was frequently used to stain the teeth for measuring the effectiveness of different bleaching materials. However, the components of blood or tea cannot be quantitatively determined and variability might exist among different brands of tea. The purpose of this study was to develop a reproducible in vitro tooth-staining model to simulate the intrinsic discoloration of teeth and evaluate the ability of two catalysts to enhance the bleaching activity of H₂O₂. Methods: Rhodamine B, Orange II, Fe(III) phthalocyanine, and tea were used to stain the tooth specimens for 4-72 h and subsequently bleached by H₂O₂ for 4-72 h. The process was photographed using a digital stereoscopic microscope and a digital camera. The image was transformed to get L^*, a^*, b^* values of CIE Lab system with image processing software. The catalytic ability of light irradiation plus addition of Fe/Sodium-Y or Mn/Sodium-Y for specimens stained by Orange II was evaluated in test tubes and in extracted tooth model. Results: The color of specimens stained by Rhodamine B could not be sufficiently recovered after bleaching by H₂O₂. In addition, the reaction of Fe(III) phthalocyanine with H₂O₂ in test tubes was too fast to be monitored. Light activation plus use of Fe/Sodium-Y or Mn/Sodium-Y could significantly accelerate the bleaching efficiency of H₂O₂. Significance: Orange II was the most appropriate dye for tooth staining among the dyes used in this study. Addition of Fe/Sodium-Y or Mn/Sodium-Y plus light irradiation could elevate the bleaching efficacy of H₂O₂ for those specimens stained by Orange II.