Micro-Raman Spectroscopic Study on Laser-fluoride-enamel Interaction

Laser irradiation combined with topical fluoride application has been found exhibiting greater caries prevention than laser or fluoride treatment alone. Nevertheless, the underlying mechanism remained unclear. Objectives: To characterize the chemical and structural alteration on enamel surfaces after fluoride and/or Er:YAG laser treatment using micro-Raman spectroscopy. Methods: Six windows (1Χ1 mm) were created on the labial surface of each of four sound incisors, randomly allotted to one of the four groups with different treatment: laser (L), 72hr fluoride (72hF), 4 min fluoride-laser (FL), and 4 min fluoride (4mF). Samples were characterized by a micro-Raman microscope (514 nm) before and after treatment. A paired-samples t-test was used to evaluate the difference in peak-shift and bandwidth of each window before and after treatment. One-way ANOVA with a Scheffe test was used to compare the treatment effects between groups. Results: Indicating the incorporation of F ion into the enamel crystals, the band shift (v1, 960cm^-1) in the FL group (1.69±0.39 cm^-1), remains similar to that of the 72hF group (1.54±0.07 cm^-1), but is significantly greater than that of the L group (0.27±0.52 cm^-1) and the 4mF group (0.12±0.13 cm^-1). Related to atomic order, the decrease of bandwidth (FWHM) was significantly greater in the FL group (1.35±0.77 cm^-1) than those in the 72hF (0.61±0.30 cm^-1), the 4mF (0.24±0.62 cm^-1) and the L groups (-0.11±0.24 cm^-1). The paired-samples t-test revealed significant treatment effects for all groups, except no significant peak up-shift for the L and 4mF groups, and no significant bandwidth change for L group. Conclusions: The combined F-laser treatment may be more efficacious in caries prevention than the laser treatment and the 4-minute and 72-hr fluoride treatments, likely through the formation of FAP and increased crystallinity. This project was supported by MOE grant R222-000-012-113 and BMRC grant R222-000-015-30