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.