Effect of bleaching agents and toothpastes on the enamel: An in situ study

Purpose: To evaluate in situ the effect of different types of toothpaste on enamel surface topography, microhardness and surface roughness (Ra) after bleaching with 7.5% hydrogen peroxide (H2O2). Methods: This was a single-center, triple-blind, randomized, two-period, crossover in situ study in 15 subjects with 60 bovine enamel blocks (9.0x9.0x3.0 mm) fixed to acrylic palatal devices which were divided into six groups (n=10): G1: control: placebo toothpaste (PT) and placebo bleaching (PB); G2: conventional toothpaste (CT) and PB; G3: whitening toothpaste (WT) and PB; G4: PT and H2O2; G5: CT and H2O2; and G6: WT and H2O2. After 14 days of whitening and brushing regime, the mineral volumetric loss of the enamel surface was evaluated according to qualitative scores, Ra was measured using 3D surface topography while Vickers microhardness (VH) (50g/10 seconds) comparing the test area with the control area and using scanning electron microscopy imaging. Results: G1 and G2 showed no visible volumetric loss of the enamel mineral content. G5 and G6 showed higher volumetric loss of the enamel surface compared to the other groups (P< 0.05). There was no difference between the groups in terms of VH (P= 0.596). For all groups, except for G1 (P= 0.197), VH decreased in the test area as compared to the control area (paired t-test; P< 0.05). G4 showed less surface roughness than the other groups, although it did not differ from G1. G3 showed higher surface roughness than G1, G4 and G5, but did not differ from G2 or G6 (P< 0.05). For G2, G3, G5 and G6, Ra increased in the test area when compared to the control area (P< 0.05). Bleaching gel and toothpaste affected the microhardness and roughness in the test area when compared to the control area. The change in enamel surface topography and roughness was related to the use of both conventional and bleaching toothpastes, independent of using bleaching gel.