COMBINED EFFECTS OF LASER IRRADIATION SOLUTION FLUORIDE-ION ON ENAMELDEMINERALIZATION/

The effects of CO2 laser irradiation of dental enamel were evaluated i n enamel demineralization experiments in partially saturated solutions (i,e,, solutions containing both calcium and phosphate ions) with and without fluoride ions. Summary Background Data: Previous studies had shown that a continuous-wave CO2 laser at an energy density of around 130 J/cm(2) may induce an increased acid resistance in human dental en amel as assessed by exposure to severe demineralization conditions (0. 1 mol/L acetate buffer, pH 4.5 and ionic strength 0.5 mol/L), Methods: Enamel blocks were irradiated with a continuous-wave CO2 laser at a w avelength of 10.6 mu m using energy densities of from 42.5 to 170.0 J/ cm2. The blocks were then exposed to a partially saturated demineraliz ing solution with or without 0.2 ppm fluoride at a temperature of 30 d egrees C for 24 hours, The demineralization was examined both qualitat ively by light microscopy and quantitatively by microradiography. Resu lts: 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/cm(2), there was little or no lesion development in the fluoride-free dissolution medium. The demineralization of enamel was reduced dramatically in the presence o f 0.2 ppm fluoride for both lased and unlased enamel; there was only m odest lesion development observed for unlased enamel and, at an energy density as low as 85.0 J/cm(2), the surface of enamel was found to be completely protected. Conclusions: These findings are consistent with the mechanism that laser irradiation of dental enamel results in sign ificant reduction of the effective solubility of enamel mineral and th at there is a significant synergism between laser irradiation and solu tion fluoride with regard to this effect.