Use of a novel 9.3-mum carbon dioxide laser and silver diamine fluoride: Prevention of enamel demineralisation and inhibition of cariogenic bacteria.

OBJECTIVE: To investigate the effects of a 9.3-mum carbon dioxide (CO(2)) laser and silver diamine fluoride (SDF) on the prevention of enamel demineralisation and inhibition of cariogenic bacteria. METHODS: Enamel blocks were applied with Laser (Group-1), SDF (Group-2), Laser + SDF (Group-3) and no treatment (Group-4), and then subjected to an 8-day pH-cycling for cariogenic challenge. Lesion depth and cross-sectional micro-hardness were assessed. Surface morphological and chemical changes were studied using scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). For the antibacterial activity, treated enamel blocks were incubated with Streptococcus mutans. The biofilm morphology, kinetics and viability were assessed by SEM, colony-forming units (CFUs) and confocal laser scanning microscope (CLSM), respectively. RESULTS: Lesion depths (mum) for Group-1 to Group-4 were 88 +/- 21, 26 +/- 11, 13 +/- 9 and 115 +/- 25, respectively (p < 0.001; Group-2 and Group-3 < Group-1 < Group-4). Group-3 had a significantly higher cross-sectional micro-hardness than the other three groups. EDS determined that Group-4 had the lowest calcium-to-phosphorus molar ratio among the groups (p < 0.001). SEM images showed apparent bacteria accumulation on enamel surfaces in Group-4, but not in other groups. Log CFUs for Group-1 to Group-4 were 6.2 +/- 0.6, 2.9 +/- 0.8, 2.2 +/- 1.1 and 7.3 +/- 0.3, respectively (p < 0.001; Group-2 and Group-3 < Group-1 < Group-4). CLSM images revealed that live bacteria dominated in Group-4, but not in other groups. SIGNIFICANCE: The irradiation with a 9.3-mum CO(2) laser alone can prevent the demineralisation of enamel and reduce the adhesion of cariogenic bacteria. Moreover, adding SDF can significantly increase the preventive effect and antibacterial ability.