The effect of bleaching agents on mineralised tooth tissues and metallic biomaterials

In recent years, bleaching has become very popular as an effective method of whitening teeth. Although bleaching is considered a conservative technique for improving aesthetics, it has the potential to cause adverse changes to dental tissues and biomaterials. The aim of this research was to assess the effect of varying concentrations of bleaching agents on (i) tooth demineralisation and microhardness, and (ii) metal ion release from dental amalgams and casting alloys. Freshly extracted bovine incisor teeth were investigated before and after bleaching with hydrogen peroxide (10% - 30% w/v). The results showed a significant decrease in mineral content of both enamel and dentine following bleaching. The enamel also exhibited an associated reduction in microhardness when bleached. Tests were carried out on amalgam discs bleached with hydrogen peroxide (0-30% w/v). Data showed a significant increase in Hg, Cu, Ag and Sn ion release with increasing hydrogen peroxide concentrations. Similar tests were carried out on two typical dental casting alloys, Ni-Cr and Pd-Cu-Ga. The data again indicated an increase in ion release with increasing hydrogen peroxide concentrations. The elevated ion release from dental amalgams, casting alloys and mineralised tooth tissues suggested that caution should be exercised when applying bleaching agents. Moreover, there is a case for not applying hydrogen peroxide at relatively high concentrations. The data reported here reinforces the view that bleaching agents may have deleterious effects, especially if bleaching agents are applied at high concentrations and/or long periods.