Acquired Acid Resistance of Enamel and Dentin by CO2Laser Irradiation with Sodium Fluoride Solution

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Abstract
The purpose of this study was to investigate the caries-preventive effect of CO2 laser irradiation with or without sodium fluoride (NaF) solution at human dental enamel and dentin in vitro. The capability of caries prevention with CO2 laser irradiation has been reported in many previous studies, but few studies have been performed with regard to the combined effect of fluoride and laser. Forty extracted human incisor teeth were used for the enamel study, and 40 molar teeth were used for the dentin study. Samples were then divided into four categories: control (no treatment); CO2 laser irradiation only; NaF treatment only; and NaF treatment followed by CO2 laser irradiation. Each sample was immersed in 2 mL of lactic acid (0.1 M, pH 4.8) solution for 24 h at 37 degrees C in 100% humidity. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry. The samples were also observed by stereoscopy and scanning electron microscopy (SEM). The lowest mean Ca2+ ppm was recorded at the enamel or dentin samples treated with NaF and laser. Statistical analysis of the data was considered significant (p < 0.01). SEM observation showed that surfaces were changed to melted, smooth, and mirror-like appearances when CO2 laser irradiation was applied with NaF solution. It can be concluded that CO2 laser irradiation with NaF solution has more caries-preventive effect than CO2 laser irradiation only at the enamel and dentin surfaces.