Tooth whitening, oxidation or reduction? Study of physicochemical alterations in bovine enamel using Synchrotron based Micro-FTIR

Abstract

ObjectivesTooth whitening demand formulations have not evolved significantly over years being hydrogen peroxide (HP) or carbamide peroxide (CP) the main active agents used. These oxidizing compounds need high concentrations and long application times to achieve the desired whitening results, leading to painful secondary effects. A novel treatment based on a reducing agent, sodium metabisulphite (MBS) encapsulated in liposomes, demonstrated significant whitening results in just 3 minutes. The aim is to provide information about the chemical interactions of the encapsulated MBS with the enamel structure compared with CP’s and to study their penetration in the hydroxyapatite (HAP). MethodsChemical imaging is performed by synchrotron-based micro Fourier transformed infrared spectroscopy (SR-µFTIR). Continuous Stiffness Measurements (CSM) were used to determine the depth reached by the treatments in order to delimitate the area of study. ResultsPrincipal component analysis (PCA) showed that the main differences between treatments were found in the intensity of the ν3 PO3-4 peak related with tooth demineralization produced by the acidic nature of MBS; these changes were observed in deeper regions of the enamel when MBS was encapsulated. SignificanceThe obtained results indicated that CP and MBS promote different changes in the HAP mineral, and that liposomes favour the diffusion of MBS into the enamel. It is the first time that synchrotron light is used to map chemically the bovine incisor’s enamel, and to determine the effect of a whitening treatment in terms of chemical HAP modifications, and the extent in deep of these effects.