Electrostatic Interaction between Fluoridated Hydroxyapatite and Bacterium

Abstract

The attachment of bacteria to a dental enamel surface is affected by various interactions consisting of long range and short range forces. In this study we studied the theoretical attachment due to electrostatic (Vel) and van der Walls (V_A) interactions, long range forces, between fluoridated hydroxyapatite and bacterium. Hydroxyapatite (HAp) was treated with NaF, APF and SnF_2. Zeta potentials of HAp and bacterium, a dominant parameter in the Vel, was measured in 0.03M phosphate buffer at different pHs. In the Vel calculation Hogg-Healy's theory, of dissymmetrical double layer interactions was applied. Hamaker (van der Walls) constants for the VA were taken from the literature. We obtained a maximum (Vmax) and minimum (Vmin) in the total interaction potential energy as a function of distance between fluoridated HAp and bacterium. In general Vmax tended to slightly decrease for APF and faintly increase for SnF_2 in comparison with untreated HAp. These effects in the degree of Vmax depended on bacterial species. We concluded that the fluoridation of HAp has effect on the surface potential energy, only for bacterium that have a high zeta potential, but the potential energy is markedly influenced by a bacterial surface feature which comes from surface charges.