Effect of pH on tooth discoloration from food colorant in vitro

The purpose of this study was to evaluate the effect of acidic, neutral and alkaline food colorant media (FCM) on tooth discoloration in vitro.

Treatment (n=24) and control (n=24) sterile, hydrated human molars were prepared in individual, impervious holders and their color measured (pretest) using a non-contact spectroradiometer system. Specimens were randomly assigned to and immersed in one of the three buffer solutions (pH 2, pH 7 or pH 12). Red food color (Red 40) was added to the treatment buffer solutions at 0.025%. Immersed specimens were incubated for 4h at 37°C. Color was also measured after immersion/incubation (posttest) and again after subsequent 2-min of polish using plain-pumice slurry with a slow-speed handpiece (post-polish). Differences in CIE a* (redness parameter) were analyzed by repeated measures ANOVA with Bonferroni-corrected t-tests for the pairwise comparisons of interest.

Tooth discoloration was measured as total stain (mean difference in a* between posttest minus pretest), extrinsic stain (mean difference in a* post-polish minus posttest) and intrinsic stain (mean difference in a* post-polish minus pretest). No significant change in color was observed between the control and treatment groups for neutral and alkaline FCM. However, acidic FCM caused reddish tooth discoloration posttest minus pretest, post-polish minus pretest and post-polish minus posttest compared to neutral and alkaline treatment and control groups.

The degree and type of tooth discoloration are influenced by both the low pH and food color rather than the dietary pigment alone.