Characterization of Subsurface Enamel Diffusion Modulated by Er:YAG Laser

The laser-induced blocking of the enamel diffusion for caries prevention has been documented in several studies. Those experiments, however, did not quantify the diffusion in human enamel. Objective: to characterize quantitatively the diffusion coefficient (DC) of lased and normal enamel subsurface by employing the technique of “fluorescence recovery after photobleaching” (FRAP). Methods: Two windows (1X4 mm) were created on each of three non-carious molars, with one window randomly selected to receive an Er:YAG laser treatment (40mJ 3's 3Hz). Tooth sections (150µm±20) were cut longitudinally by microtome and characterized morphologically by polarized light microscopy (PLM). Seven defect-free sections were selected, covered on the cut surfaces with nail varnish, and immersed in the 20µM fluorescein for 8h. FRAP was performed in the lased and normal windows approximately 10µm beneath the natural surfaces. With the nonlinear curve fitting and a three dimensional model, the DC was obtained. Results: Qualitatively, there was no apparent difference between the lased and normal windows under PLM. The mean value of DC is 4.5±0.99 10^-7cm²/sec and 5.32±0.96 10^-7cm²/sec in the lased and normal windows, respectively. A paired-samples t test revealed a significantly lower DC of the lased windows compared with that of the normal windows (P=0.016). Conclusions: Er:YAG laser treatment may be effective in reducing subsurface enamel diffusion, as a potential mechanism for caries prevention. (This study was supported by BMRC Grant R222-1000-015-305)