Surface tension and contact angle on enamel of surfactant solutions for caries diagnosis with dyes

We measured the surface tension of solutions of five surfactants in water, ethanol, and a 50% water/ethanol mixture at 25 degrees C, as well as the contact angle of these solutions on ground and polished bovine enamel in vitro and on intact pellicle-covered human enamel in vivo. All surfactants lowered the surface tension of water. In ethanol, no reduction of the surface tension was achieved by any of the five surfactants. In the water/ethanol mixture, only Fluorad lowered the surface tension from 29.2 to 19.7 mJ.m-2 at 25 degrees C. On bovine dental enamel, all surfactant solutions showed a significantly lower contact angle than did distilled water. On pellicle-covered human enamel, Rewoteric in distilled water showed no significantly lower contact angle than did pure distilled water, but all other solutions did. Both in vitro and in vivo, ethanol spread instantaneously over the enamel surface. Based on these measurements, we concluded that several surfactants may be used to spread aqueous dye solutions. In a 50% mixture of water and ethanol and in pure ethanol, no surfactant is necessary for enhanced spreading of the solution, but surfactants may be considered for adhesive properties.