The Effect of Whitening Oral Rinses on Enamel Microhardness

Objective: The purpose of this study was to determine the effect of three over-the-counter whitening oral rinses on human enamel micro-hardness. Method: Three dental enamel fragments of about 4x4mm were sectioned from each crown of fifteen extracted teeth; embedded in a ring-mould, sanded down up to 1200 grit fineness and randomly divided into three groups. The one group was exposed to Colgate Plax Whitening Blancheur (CPW) for 1 minute twice a day, the 2^nd group to White Glo 2 in 1 (WG) for 30s twice a day and the 3^rd group to Plus White (PW) for 30s twice a day, respectively, according to the manufacturer’s instructions. In between the samples were stored in artificial saliva. Surface micro-hardness of all three groups was measured before exposure and again after 14 days using a digital Vicker’s diamond indenter. The pH levels of the oral rinses were also determined with a pH combination glass electrode. Result: The pH values were found to be 3.74, 3.59 and 5.0 for Colgate Plax Whitening Blancheur, White Glo 2 in 1 and Plus White, respectively. Micro-hardness values were respectively: CPW (before 318, after 14 days 301); WG (before 308, after 14 days 295) and PW (before 301, after 14 days 311). The Wilcoxon Signed Rank Sum Test showed no statistical significant differences (on a 5% basis) between baseline values and the values obtained after a 14 day treatment period. However, a lowering in the median enamel hardness values were found. Conclusion: According to the micro-hardness values no significant enamel damage was found, probably due to the short exposure periods to the three different products in addition to re-mineralisation in the artificial saliva solution.