Acquired Acid Resistance of Enamel and Dentin by CO 2 Laser Irradiation with Sodium Fluoride Solution

Abstract

Objective: 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. Background Data: 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. Materials and Methods: 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°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). Results: 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. Conclusion: 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.