Adsorption/desorption of amine fluorides to hydroxyapatite

This study concerned the adsorption and desorption of commercial amine fluoride (AmF) preparations to hydroxyapatite (HA). The influence of pH, ionic strength, temperature, saliva and albumin, the latter as a gingival crevicular fluid analogue, on adsorption/desorption was investigated. AmF levels were determined using a surfactant electrode. AmFs 297 and 335 were found to bind immediately and irreversibly to HA in water over a range of pH values, ionic strengths and temperatures, the amounts increasing with concentration. More monovalent AmF 335 was adsorbed than divalent AmF 297. Any AmF desorbed by water from HA was at the lowest end of the minimum inhibitory concentration for oral bacteria. AmF 297 was desorbed by CaCl2, and to a lesser extent by H+, OH−, NH4+, La3+, EDTA, Triton X100 and ethanol, whereas AmF 335 was only slightly desorbed by ethanol. Preadsorption of proteins on HA had little effect on subsequent adsorption or desorption of either AmF. It is postulated that both AmF 297 and AmF 335 are inactivated by an excess of proteins in the surrounding medium, supra- or subgingivally, and not by such proteins preventing or altering the mode or rate of adsorption, or interfering with antibacterial activity, when the AmFs contact a protein-coated tooth surface.