Influence of Bleaching-agents pH on Changes in Enamel Surface Roughness

Objectives: To evaluate the influence of the pH of different bleaching agents on the changes in the surface roughness of human enamel.
Methods: 40 human premolars were collected according to ethical considerations. The samples were randomly divided into five groups. The pH of each substance was determined using a pH-meter. A qualitative assessment of surface micro-structural changes was made by scanning electron microscopy (SEM), the quantification of mineral content by Energy Dispersive X-ray Spectrometry (EDS) and the measurement of surface roughness by Atomic Force Microscopy (AFM) in intact enamel and after the application of different bleaching agents: Group 1 (Control without treatment), Group 2 (Opalescence Boost 38%), Group 3 (Pola Office Plus 37.5%), Group 4 (Whiteness HP Maxx 35%), Group 5 (Pola Office Bulk 35%). The data were analyzed with a one-way ANOVA test, p <0.05.
Results: The pH of the bleaching agents was found in a range of 4.38 and 6.33. All the bleaching agents caused changes in the surface roughness with respect to the roughness of the enamel prior to the bleaching agent application. No statistically significant differences were found in the surface roughness between the test groups with respect to the pH values evaluated. A correlation of the pH with the surface roughness of the enamel was found within each test group. The analysis by SEM revealed alterations in the enamel surface morphology characterized by an increase in pores and erosion areas, related to loss of enamel mineral content.
Conclusions: The application of hydrogen peroxide in high concentrations and acidic pH, generates changes in the enamel surface roughness, which can be related to an alteration of the mineral content by decreasing the percentage of calcium and phosphate. Oxygen-free radicals released during the catalysis process of the bleaching agent reaction play an important role in the micro-structural changes of the dental enamel.