Effect of Er:YAG Laser Treatment on Enamel Diffusion

Dental caries, one of the most common diseases, is caused by dissolution of enamel hydroxyapatite crystals and diffusion of ions in the enamel. Several studies have demonstrated the preventive effect of lasers through strengthening enamel crystalline structure and/or sealing of the diffusion pathways. However, quantification of laser-induced change of diffusion in enamel remains a challenge with inconclusive published data. Objective: To quantify the effect of Er:YAG laser treatment on enamel diffusion coefficient (DC). Methods: Five caries free enamel sections (~200µm thick) were characterized morphologically by stereomicroscopy(SM), polarized light microscopy (PLM) and scanning electron microscopy (SEM) before and after laser treatment to provide site-specific guidance for “Fluorescence Recovery After Photobleaching”(FRAP). Sections were irradiated with Er:YAG laser 50mJ x 5's x 5Hz with water cooling and then incubated overnight in 200nM Fluorescein .To evaluate the laser effect, FRAP was performed at 10 different spots(20µm diameter) on both lased and normal enamel . Parameters involved were optimized by nonlinear least-square curve fitting using a 3-D FRAP model. Results: Morphologically, the lased area appeared as opaque (under SM), dark area interspersed with bluish patches (under PLM) and enamel structures intermingled with amorphous organic matrix (under SEM). The mean DC measured for normal enamel (2.65±0.09) x10^-7 cm²/s was consistent with the published data, which is significantly greater than (1.8±0.06) x10^-7 cm²/s of the lased enamel (p<0.05). Conclusions: FRAP combined with CLSM has been proven in this study to be a potential technique for investigating enamel diffusion quantitatively. Er:YAG laser treatment appears to be promising for caries prevention through retardation of diffusion in enamel. (This study was supported by BMRC Grant R-222-000-015-305)