Effects of two in-office bleaching agents with different pH values on enamel surface structure and color: An in situ vs. in vitro study

Objectives: To investigate in situ and in vitro effects of acidic and neutral in-office bleaching agents on human enamel in terms of chemical structure and tooth color. Methods: Ninety enamel slabs were obtained from premolars. Then specimens were randomly distributed into six groups (n = 15) and the human saliva (HS) in volunteers' oral cavities was used to simulate in situ condition: group Beyond + distilled water (DW); group Opalescence Boost (O-Boost) + DW; group control + DW; group Beyond + HS; group O-Boost + HS and group control + HS. Twice in-office bleaching treatments were performed with a one-week interval and the total bleaching time was 90 min. ATR-IR spectroscopy, Raman spectroscopy and color measurement were performed before the bleaching treatment and after one week post-treatment, respectively. Then ATR-IR and Raman spectroscopies were analysed and the carbonate: mineral (C:M) ratio, Raman absolute intensity (RAI), Raman relative intensity (RRI) and laser-induced fluorescence intensity (FI) were calculated for evaluation. Results: C:M ratio and percentage RRI showed significantly decrease in group Beyond + DW (p < 0.001, p < 0.001) while little variation was observed in the other groups (p > 0.05, p > 0.05). Percentage FI and Delta E revealed statistical difference in all bleached groups (p < 0.001, p < 0.001) while no statistical difference in control groups (p > 0.05, p > 0.05). Conclusion: Acidic and neutral in-office bleaching agents had the same whitening efficiency in situ and in vitro. Acidic agents could induce demineralisation of human enamel in vitro and the presence of natural human saliva could minimise this adverse effect. (C) 2012 Elsevier Ltd. All rights reserved.