Structural changes after whitening: bioactive materials benefits-in situ study

Objectives: Investigate in situ the influence of bioactive materials on bleached enamel and dentin using Knoop hardness test (KHN), field emission microscope (FEG) and quantification of mineral content by light-induced fluorescence (QLF).
Methods: 20 extracted human molars were selected, 10 were used for the KHN and FEG evaluation. 4 specimens having enamel and dentin were obtained from each tooth and randomly divided into 3 experimental groups and one control (n=10), initial hardness values were measured. For the QLF test, specimens were obtained from the other 10 teeth, which were sectioned into 3 fragments of superficial enamel (n=10). Fragments were evaluated by QLF. All specimens were mounted on intraoral devices, used by 10 volunteers (24 hours/day, during 14 days). On each device 3 different treatments were applied: 1. Opal, Opalescence PF-15% carbamide peroxide (CP) (Ultradent); 2. NWACP, NiteWhite ACP-16% CP (Philips); 3. Opal+Bio (Biosilicate®, Vitrovita) mixed. At the end of the experimental period KHN, FEG and QLF final analysis were performed.
Results: Statistical analysis showed that Opal group presented statistically significant reduction on the enamel and dentin hardness values. For groups NWACP and Opal+Bio no demineralization was observed. Hardness values are in line with results obtained in FEG analysis of enamel and dentin, where for groups NWACP and Opal+Bio no change in the dental structure was observed, while for Opal group was observed demineralization of enamel and dentin. QLF analysis showed no sensitivity to detect statistically significant differences between groups, nor between initial and final stages in each group.
Conclusions: QLF test was not sensitive enough to show changes in the bleached teeth. When analyzing hardness and morphology of the dental structure, Opal group presented demineralization of bleached enamel and dentin. However, the mixture of a bleaching gel with a bioactive agent, groups NWACP and Opal+Bio, showed a positive influence, preventing tooth demineralization.