Microhardness and color-change of dentin after exposure to whitening strips

OBJECTIVES: To assess microhardness and color changes of human dentin after exposure to over-the-counter hydrogen peroxide strips.

METHODS: Twenty-one caries-free human teeth were collected and crowns cut along the longitudinal axis to expose dentin surface. One half of each tooth was used for the study. Teeth were mounted into clear acrylic, then grinded up to 4,000 grit sand paper, to give a flat surface. Dentin microhardness was measured using an Akashi/LECO M-400-H1 Knoops Hardness Tester with a 200gr load at 15sec application. Microhardness was measured in three regions of the dentin close to the dentin enamel junction. Shades were also assessed using a Vita Shade Classic by one examiner. For each shade a numerical value was given. An over-the-counter hydrogen peroxide strip (Crest Whitestrips® Premium, Procter & Gamble, Cincinnati, OH) was applied over the dentin surface for 30min, twice a day, for 7 days, according to manufacturer instruction. In between treatments, specimens were immersed in filter sterilized pooled human fresh saliva to mimic physiological conditions. Microhardness and shades were reassessed after 14 applications of the strips. Mann-Whitney U-Test analysis was conducted at the significance level of a=0.05.

RESULTS: 63 measurements were taken before and after treatment for a total of 126 measurements. Microhardness in Knoops units was 48.10 (±10.86 SD) at baseline and 41.42 (±6.72 SD) post- treatment, indicating a statistically significant change (p=0.021). Mean shade values were 6.90 (±2.93 SD) at baseline and 1.61 (±2.43 SD) after treatment; post-treatment shade values showed to be statistically significantly lower (p<0.0001).

CONCLUSION: After exposure to over-the-counter whitening strips, there was a dentin shade improvement of 5 values. Post-treatment dentin surface microhardness decreased; however, its clinical significance needs further investigations.