Effects of Cold-Light Bleaching on Enamel Surface and Adhesion of Streptococcus mutans

Tooth bleaching is becoming increasingly popular among patients with tooth staining, but the safety of bleaching agents on tooth structure has been questioned. Primarily thriving on the biofilm formation on enamel surface, Streptococcus mutans has been recognized as a major cariogenic bacterial species. The present study is aimed at investigating how cold-light bleaching would change enamel roughness and adhesion of Streptococcus mutans. Human premolars were divided into 72 enamel slices and allocated into 3 groups: (1) control, (2) cold-light bleaching with 35% hydrogen peroxide (Beyond^™), and (3) 35% hydrogen peroxide (Beyond^™) alone. Biofilms of Streptococcus mutans were cultivated on enamel slices in 5% CO₂ (v/v) at 37°C for 1 day or 3 days. Enamel surfaces and biofilms were observed using scanning electron microscope (SEM). Atomic force microscopy (AFM) was applied to quantify the roughness of enamel surface, and the amounts of biofilms were measured by optical density of scattered biofilm and confocal laser scanning microscopy (CLSM). Cold-light bleaching significantly increased (p < 0.05) surface roughness of enamel compared to controls, but significantly inhibited (p < 0.05) adhesion of Streptococcus mutans on enamel in the bacterial cultures of both 1 day and 3 days. In conclusion, cold-light bleaching could roughen enamel surface but inhibit Streptococcus mutans adhesion at the preliminary stage after the bleaching treatment.