Combined effects of laser irradiation/solution fluoride ion on enamel demineralization.

Abstract

The effects of CO2 laser irradiation of dental enamel were evaluated in enamel demineralization experiments in partially saturated solutions (i.e., solutions containing both calcium and phosphate ions) with and without fluoride ions. Previous studies had shown that a continuous-wave CO2 laser at an energy density of around 130 J/cm2 may induce an increased acid resistance in human dental enamel as assessed by exposure to severe demineralization conditions (0.1 mol/L acetate buffer, pH 4.5 and ionic strength 0.5 mol/L). Enamel blocks were irradiated with a continuous-wave CO2 laser at a wavelength of 10.6 microns using energy densities of from 42.5 to 170.0 J/cm2. The blocks were then exposed to a partially saturated demineralizing solution with or without 0.2 ppm fluoride at a temperature of 30 degrees C for 24 hours. The demineralization was examined both qualitatively by light microscopy and quantitatively by microradiography. A comparison between the lased and the unlased portions of enamel showed increased acid-resistance with increasing laser energy density and, at the highest energy density of 170.0 J/cm2, there was little or no lesion development in the fluoride-free dissolution medium. The demineralization of enamel was reduced dramatically in the presence of 0.2 ppm fluoride for both lased and unlased enamel; there was only modest lesion development observed for unlased enamel and, at an energy density as low as 85.0 J/cm2, the surface of enamel was found to be completely protected. These findings are consistent with the mechanism that laser irradiation of dental enamel results in significant reduction of the effective solubility of enamel mineral and that there is a significant synergism between laser irradiation and solution fluoride with regard to this effect.