Influence of enamel surface pretreatments on its microhardness throughout bleaching

Objectives: The aim of this in vitro study was to assess the changes on enamel microhardness when exposing it to fluoride, CPP-ACP or Nd: YAG laser associated with fluoride 24 h before the whitening treatment. Methods: Forty bovine enamel blocks had their surfaces planned and polished and were randomly divided into four experimental groups (n=10): G1 – control (no surface treatment), G2 – fluoride, G3 - CPP-ACP and G4 - Nd: YAG laser + fluoride. After 24 h, the samples were bleached with 35% hydrogen peroxide. Knoop Microhardness tests were performed on specimens' surface before (baseline) and after surface treatment, and after bleaching procedures (immediately and 7 days). The average microhardness (5 indentations) at each time interval was considered for statistical analysis. ANOVA and Tukey tests were performed (α=5%). Results: Results have shown statistical significant differences between the experimental groups immediately after the whitening treatment (G1 – 206.20±13.14, G2 – 248.80±30.33, G3 – 245.90±25.66, G4 – 241.80±22.68). Enamel microhardness values were recovered for all experimental groups after 7-days storage in artificial saliva, expect for the control group. Conclusion: It was concluded that enamel surface treatments 24 hours before whitening procedures were able to prevent significant mineral loss immediately after.