title: [Effects of hydrogen peroxide-containing bleaching on the growth of Streptococcus mutans biofilm on enamel disc surface].
abstract: OBJECTIVE
  To evaluate the effects of a commercial bleaching agent containing 35% (mass fraction) hydrogen peroxide on the growth of Streptococcus mutans biofilm on enamel disc surface.
  
  
  METHODS
  A total of 20 enamel disks were made from human extracted teeth and the enamel surfaces were kept intact. The discs were autocalved and randomly divided into two groups: bleaching group and control group. Each group contained 10 discs. For bleaching group, the enamel discs were whitened by commercial 35% hydrogen peroxide according to the instruction (Beyond(TM) Professional Dental Whitening Kit, Beyond Technology, TX,USA ); no treatment for control group. All the discs were kept in sterile human saliva for 3.5 hours, and then the mixture of brain heart infusion broth (BHI) medium and Streptococcus mutans were added. The discs and Streptococcus mutans were incubated together in BHI medium with 5% CO(2) (volume fraction), at 37 °C. After 3, 7, 14, 21 and 28 d's incubation, two discs of each group were taken out and the biofilms on the enamel surfaces were evaluated by using conventional bacteria counts and confocal laser scanning microscope (CLSM). The bacteria in the biofilm on one disc enamel surface were analyzed by plating on BHIS agar and the colony-forming units were counted. The biofilm on the other disc surface was stained using a two-colour fluorescent dye kit (Bacerial Viability Kit L-7012) for CLSM.
  
  
  RESULTS
  The vital bacteria counts of vital cells in the 3, 7, and 14 d's biofilms of the bleaching group were significantly fewer than those of the control group. Especially in the 3 days' biofilm on the whitened surface, the vital bacteria counts [(3 595 ± 2 903) μm(2) vs. (89 155 ± 65 963) μm(2),t = 8.71,P = 0.00] and proportion of vital bacteria [(26.0% ± 16.4%) vs.(92.2% ± 10.9%), t = 19.93, P = 0.00] were significantly fewer than those of the control. While, for the 21d's biofilm, the vital bacteria counts and the percentage of the vital cells of the bleaching group were more than those of the control group significantly [(66 262 ± 23 772) μm(2) vs. (51 184 ± 20 502) μm(2), t = 2.59, P = 0.012].
  
  
  CONCLUSIONS
  The hydrogen peroxide-containing bleaching agent may inhibit the growth of Streptococcus mutans biofilm for about 3 weeks; but after 3 weeks, it seems that the bleached surface will increase the growth of biofilm. Whether the whitening therapy will increase caries susceptibility of the bleached surface needs further research.
authors.affiliation: Department of Cariology and Endodontology, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Chun-yan
authors.initials: CY
authors.lastname: Zheng
authors.affiliation: Department of General Dentistry, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Pan
authors.affiliation: Department of Cariology and Endodontology, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Zu-hua
authors.initials: ZH
authors.lastname: Wang
authors.affiliation: Department of Cariology and Endodontology, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
mesh_terms: D018441:Biofilms / Q000187:drug effects*; D003743:Dental Enamel / Q000382:microbiology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry*; D013295:Streptococcus mutans / Q000187:drug effects*; D014073:Tooth Bleaching
chemical_list: D006861:Hydrogen Peroxide