Abstract:
Objective: To compare the effects of 25% and 35% hydrogen peroxide in-office bleaching systems on surface roughness and streptococcal biofilm formation on human enamel. Materials and Methods: Human anterior teeth and premolars were cut into 3x3x2 mm3. Enamel specimens (n=162) were randomly divided into 3 groups (n=54 each): control, bleached with 25% hydrogen peroxide (Zoom2™, Discus Dental, Culver City, CA, USA), and bleached with 35% hydrogen peroxide (Beyond™, Beijing, China). The surface roughness was measured by a profilometer before and after treatments. The specimens were then placed randomly into 3 subgroups (n=18 each) and incubated with trypticase soy broth control, Streptococcus mutans, or Streptococcus sanguinis, for 24 hours. Biofilm formation was quantified by crystal violet assay. The biofilm structure was also visualized by scanning electron microscopy (n=3 each). Data were analyzed by Kruskal-Wallis and Man-Whitney U tests with Bonferroni corrections with significance level at p<0.05. Results: Both bleaching systems significantly reduced enamel surface roughness comparing to control (p<0.001). Remarkably, Streptococcus sanguinis biofilm on enamel bleached with 35% hydrogen peroxide was significantly higher than other groups (p<0.001). In contrast, no difference in Streptococcus mutans biofilm was observed. Conclusion: Both 25% and 35% hydrogen peroxide caused similar degrees of reduction in enamel surface roughness, but 35% hydrogen peroxide markedly promoted Streptococcus sanguinis biofilm formation.
