Objectives: This in vitro study evaluated the effect of four over-the-counter tooth-whitening products on enamel microhardness.
Methods: Fifty enamel blocks were prepared from extracted human molar teeth. The enamel surfaces were polished up to 1200 grit fineness and the specimens randomly divided into five groups. Enamel blocks were exposed to: Rapid White (n=10); Absolute White (n=10); Speed White (n=10) and White Glo (n=10) whitening products, according to the manufacturers' instructions. As control, ten enamel blocks were kept in artificial saliva at 37 degrees C without any treatment. Microhardness values were obtained before exposure (baseline) and after 1, 7 and 14-day treatment periods using a digital hardness tester with a Vickers diamond indenter. Data were analysed using Wilcoxon Signed Rank Sum Test, one-way ANOVA and Tukey-Kramer Multiple Comparison Test (p<0.05).
Results: Both Rapid White and Absolute White reduced enamel microhardness. Speed White increased the microhardness of enamel, while White Glo and artificial saliva had no effect on hardness.
Conclusions: Over-the-counter tooth-whitening products might decrease enamel microhardness depending on the type of product.