title: Effect of bleaching on tooth discolouration from food colourant in vitro.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the effect of bleaching on tooth discolouration from neutral food colourant media (NFCM).
  
  
  METHODS
  Freshly extracted human molar teeth (n = 32) were divided into four groups (n = 8): non-bleached treatment-NBT, non-bleached control-NBC, bleached treatment-BT and bleached control-BC. Bleached teeth specimens were subjected to 20% carbamide peroxide bleaching agent for 10h. Colour measurements (pre-test) were done using a non-contact spectroradiometer. The teeth specimens were immersed in a neutral buffer solution. NBT and BT groups had 0.025% red food colour (Red 40) added to the buffer solution. The immersed specimens were incubated for 4h at 37°C. Colour was again measured after immersion/incubation (post-test) and after subsequent polishing using plain-pumice slurry (post-polish). Differences in CIE a* (redness parameter) were analysed by repeated measures ANOVA with Bonferroni-corrected t-tests for the pairwise comparisons of interest.
  
  
  RESULTS
  Tooth discolouration was measured as total stain (mean difference in a* between post-test minus pre-test), extrinsic stain (mean difference in a* post-polish minus post-test) and intrinsic stain (mean difference in a* post-polish minus pre-test) A statistically significant difference in the mean Δa* was observed (P = 0.009) between staining treatment for bleached and non-bleached teeth. Also, a statistically significant difference (P < 0.001) was noted between control and treatment groups of bleached teeth that were subjected to staining.
  
  
  CONCLUSIONS
  Bleaching resulted in total and extrinsic tooth discolouration by the NFCM.
  
  
  CONCLUSIONS
  It might be beneficial to avoid highly pigmented foods immediately following bleaching in order to optimize the effects of tooth whitening.
authors.affiliation: Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry, 305 West 12th Avenue, Columbus, OH 43210-1267, USA. azer.1@osu.edu
authors.forename: Shereen S
authors.initials: SS
authors.lastname: Azer
authors.forename: Anne L
authors.initials: AL
authors.lastname: Hague
authors.forename: William M
authors.initials: WM
authors.lastname: Johnston
mesh_terms: D000704:Analysis of Variance; D000077463:Carbamide Peroxide; D005505:Food Coloring Agents / Q000009:adverse effects*; D006801:Humans; D008964:Molar, Third; D010545:Peroxides / Q000627:therapeutic use; D011874:Radiometry; D018709:Statistics, Nonparametric; D014073:Tooth Bleaching / Q000009:adverse effects*; D058205:Tooth Bleaching Agents / Q000627:therapeutic use; D014075:Tooth Discoloration / Q000209:etiology* / Q000628:therapy*; D014508:Urea / Q000031:analogs & derivatives / Q000627:therapeutic use
chemical_list: D005505:Food Coloring Agents; D010545:Peroxides; D058205:Tooth Bleaching Agents; D000077463:Carbamide Peroxide; D014508:Urea