Effect of Over-the-counter Tooth-whitening Products on Enamel Microhardness

Objectives: The purpose of this in vitro study was to evaluate the effect of three over-the-counter (OTC) tooth-whitening products on enamel microhardness. Methods: Forty enamel blocks were prepared from extracted human molar teeth. The enamel surfaces were polished up to 1200 grit fineness and the specimens were randomly divided into four groups. The enamel blocks were exposed to: Rapid White (Group 2, n=10); Absolute White (Group 3, n=10) and White Glo (Group 4, n=10) OTC whitening products according to the instructions of the manufacturers. Specimens were kept in artificial saliva at 37˚C between treatments. The control (Group 1, n=10) was enamel blocks kept in artificial saliva at 37˚C without any treatment. The microhardness values were obtained before exposure (baseline) and after a 14-day treatment period using a digital hardness tester with a Vicker's diamond indenter. Data were analysed by Wilcoxon Signed Rank Sum Test, one-way ANOVA and Tukey-Kramer Multiple Comparison Test significant at p<0.05. Results: All OTC whitening products tested in this study reduced enamel microhardness. However, only Group 2 (Rapid White) showed statistically significant reduction in enamel microhardness when compared to the baseline values (p<0.05). Group 2 also differed significantly from the control group and the other test groups (p<0.05). No significant differences were found between Groups 3 & 4. Conclusions: Over-the-counter tooth-whitening products tested in this study adversely affected enamel microhardness. Rapid White containing sodium chlorite showed the highest reduction in enamel microhardness as compared to the other products tested.