By the Lewis definition, an acid is an electron pair acceptor. In the presence of light &/or electrical induction, valence electrons from a wetted titanium dioxide (TiO2) semiconductor will donate electron pairs to neutralize organic acids. Whereas a tooth surface is negatively charged, plaque has a net positive charge, and in part, ionic attraction contributes to the adherence of plaque to the tooth surface. Donating electrons to the plaque will alter polarity and diminish the ionic attraction between the plaque and the tooth surface (iontophoretic effect).