Effects of a 445 nm diode laser and silver diamine fluoride in preventing enamel demineralisation and inhibiting cariogenic bacteria.

OBJECTIVE: To study the effects of a 445 nm diode laser (L) and silver diamine fluoride (F) on preventing enamel demineralisation and inhibiting cariogenic bacteria. METHODS: Thirty-three enamel slices were sectioned each into four blocks for four groups to receive L with F (LF), F, L and Water (W, control). Ten blocks from each group were used to evaluate demineralisation. Surface morphology, lesion depth and nanohardness of the blocks after pH-cycling were studied by scanning electron microscopy (SEM), nanohardness test, and micro-computed tomography, respectively. Twenty-three blocks per group were used for biofilm assessment. Morphology, viability, and growth kinetics of the Streptococcus mutans biofilm were assessed by SEM, confocal laser scanning microscopy, and the counting of colony-forming units (CFUs), respectively. RESULTS: SEM images of LF-treated enamel showed an intact surface compared with other groups. Nanohardness (GPa) for LF, F, L and W were 1.43+/-0.17, 1.01+/-0.11, 1.04+/-0.13 and 0.73+/-0.14, respectively (p < 0.001; LF>F, L>W). Their lesion depths (microm) were 46+/-8, 52+/-6, 88+/-13 and 111+/-9, respectively (p < 0.001; LF, F<L<W). SEM showed few bacteria for LF and F compared with other groups. Their dead-live ratio were 1.67+/-0.13, 1.60+/-0.15, 0.39+/-0.05 and 0.32+/-0.05, respectively (p < 0.001; LF, F>L>W). Log CFUs for LF, F, L and W were 4.2+/-0.3, 4.5+/-0.2, 7.9+/-0.3 and 9.4+/-0.2, respectively (p < 0.05; LF<F<L<W). Two-way ANOVA analysis revealed an interaction effect on nanohardness and Log CFUs between the laser irradiation and SDF treatment (p < 0.001). CONCLUSION: This study showed a superior caries preventive effect of a combined treatment of the diode laser and SDF. Because diode laser and SDF are affordable and readily available, clinicians can provide this treatment to their patients for caries prevention. CLINICAL SIGNIFICANCE STATEMENT: Diode lasers are handy, afforable and readily avaliable to clinicians. This study provides information of use of 445 nm diode laser for caries prevetion. The laser irradiation hopefully can be added before conventional topical SDF application.