Binding of dyes to hydroxyapatite treated with cetylpyridinium chloride or cetrimonium bromide.

The effect of cetylpyridinium chloride (CPC) and cetrimonium bromide (CTAB) on the adsorption of some acidic food dyes to hydroxyapatite was studied. The dyes investigated were brilliant blue (FD&C Blue No. 1), tartrazine (FD&C Yellow No. 5), sunset yellow (FD&C Yellow No. 6) and amaranth (FD&C Red No. 2). The apatite had adsorbed 9.2 mumol CPC per g dry weight. The adsorbed CPC was in equilibrium with a free concentration of 20 microgram/ml (58 micrometer). The adsorption of CPC and CTAB to the apatite was followed by an increased ability of the crystals to bind the dyes. The dyes were very firmly adsorbed and were not released during a series of washings. Untreated apatite showed only a minor affinity for the dyes. The adsorbed dyes were easily washed out. CPC and CTAB showed the smae specific ability to increase the binding capacity of the apatite. The results are discussed and related to the formation of stains on the teeth in persons using quaternary ammonium compounds for mouthrinsing. A mechanism explaining the production of stains is proposed.