Effects of Whitening Strips on the Enamel Microhardness

Objective: The purpose of this study was to determine how varying concentrations of hydrogen peroxide in whitening strips with and without fluoride rinses affect the microhardness of enamel in an environment mimicking real-life usage of whitening strips.

Method: Labial surfaces of twelve anterior human teeth were sanded, polished, and treated using six different methods: 1) Crest Classic 6% H₂O₂ Whitestrip for 30 minutes twice/day, 2) Crest Classic Whitestrip for 30 minutes twice/day plus 1 minute ACT fluoride rinse after each treatment, 3) Crest 3D 10% H₂O₂ Whitestrip for 30 minutes once/day, 4) Crest 3D Whitestrip for 30 minutes once/day plus 1 minute ACT fluoride rinse, 5) Crest Supreme 14% H₂O₂ Whitestrip for 30 minutes once/day, and 6) Crest Supreme Whitestrip for 30 minutes once/day plus 1 minute ACT fluoride rinse. Two teeth were used for each treatment and enamel microhardness of each sample was measured at baseline pre-treatments, after whitening treatments (for those without fluoride), after the fluoride rinse (for those with fluoride treatment), and 3 days post-treatment. Samples were placed in a 37^oC incubator to simulate the human oral cavity between treatments. 

Result: Varying concentrations of hydrogen peroxide agents result in decreases in enamel microhardness. Specimens treated with ACT fluoride rinse showed increases in microhardness.  Differences of microhardness observed immediately after treatment were significant between the Classic and 3D strips (p=0.01), as well as the Classic and Supreme strips (p=0.02). Differences of microhardness observed three days after treatment were only significant between the Classic and Supreme strips (p=0.008).

Conclusion: Whitening strips of all concentrations alone result in demineralization of enamel, while adding a fluoride rinse post treatment result in remineralization of enamel to levels comparable to baseline. 14% hydrogen peroxide agents demonstrate a significant greater loss of enamel microhardness as compared to the 6%.