Enamel Ultrastructure Analysis After an In-office Bleaching

Objectives: To evaluate the effects of 35% hydrogen peroxide in-office-bleaching on enamel ultrastructure. Methods: A commercially available 35% hydrogen peroxide bleaching agent was applied simulating 4 clinical sessions of 8 min on quarter sectioned premolar teeth (n=8). All specimens were immersed on distilled water at 37°C. Micro tomography images of these sections were obtained (μ-CT 1072, SkyScan, Belgium) with an isotropic voxel size of 11.24 μm prior and post treatment. Two three-dimensional regions of interest (ROI) were selected, from outer enamel surface extending to 110.2 μm in depth towards dentin. CT-parameters of structure thickness (plate model)–St.Th (pl), structure separation (plate model)–St.Sp (pl) and fragmentation index–Fr.I were calculated for each (ROI). All data were then subjected to paired t-tests at a 95% confidence level. All specimens were covered with platinum for Scanning Electron Microscopy Analysis (SEM) and also for Field Emission Analysis (FEG) in high vacuum. The images were obtained from a secondary electron detector from a 10 mm working distance , high voltage of 10 kV and probe of 500 A with magnifications from 3.000 to 100.000. Results: There were no significant changes for – St.Th (pl), St.Sp (pl) when enamel before was analyzed before and after bleaching. However, this was noticed from the microscopic analysis that erosions suggesting demineralization areas occurred in the enamel prisms region, explaining the results found for the ROI 1 (outer enamel surface) before and after bleaching, which increased in Fr.I. Those areas were clearly seen from FEG images, especially with high magnification, in which a prismatic disorganization area could also be visualized. Conclusion: This in-vitro study shows that significant ultrastructural changing in enamel occurs when a 35% hydrogen peroxide in-office bleaching is applied. The enamel outer surface seems to be eroded by the peroxide along the edges of the prismatic structure, which suggests demineralization.