Optimal Er:YAG laser energy for preventing enamel demineralization

Objectives: The purpose of this study was to identify the optimal laser energy range of Er:YAG laser irradiation for laser-induced caries prevention (LICP). Methods: Twenty-one human non-carious molars were selected. The teeth were covered with nail varnish, except two 4 mm×1 mm windows on both the buccal and lingual surfaces. The windows were randomly assigned to groups A, B, C and D, receiving no irradiation, 100, 200 and 300 mJ irradiation, respectively. The pulse width 10 pps (pulse per second) with a 1.0 mm spot size was used. After the laser treatment, each tooth was cut into two halves longitudinally. Then a two-day pH-cycling was performed, with an 18-hour demineralization followed by a 6-hour remineralization. Sections of 120±20 μm in thickness were obtained from each window. Lesion depth was measured using polarized light microscope coupled with an image analysis software. One-way ANOVA and post-hoc Tukey tests were used for evaluation of treatment effects. Results: The laser treatments of 100 and 200 mJ have demonstrated significant protection of enamel demineralization ( p=0.01 and 0.001, respectively), but not the treatment with 300 mJ ( p=0.106). A smaller lesion depth was observed for the 200 mJ group (97.1 μm) than that of the 100 mJ group (105.6 μm). Compared with the control, a lesion reduction of 32.78 and 26.93% for the 200 mJ group and the 100 mJ group were obtained, respectively. Conclusion: Caries prevention may be achieved by using Er:YAG laser treatment if the optimal range of laser parameters for LICP can be employed.