Effect of bleaching on tooth discolouration from food colourant in vitro.

OBJECTIVES: 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.

CLINICAL SIGNIFICANCE: It might be beneficial to avoid highly pigmented foods immediately following bleaching in order to optimize the effects of tooth whitening.