Tooth whitening treatments are based on the application of bleaching agents in the teeth surface. Although efficient at aesthetic level, these treatments may impair teeth health, due to their effect on enamel properties.
The main purpose of this work is to study the effect of pH on bleaching and enamel properties, namely surface morphology and hardness.
Teeth were disinfected and washed with toothpaste without any bleaching agent in its composition and stored in distilled and deionized water at 4º degrees. Then, they were polished with silicon carbide sandpapers (1000 and 4000), cut in four equal pieces and darkened by immersion in black tea solution for 48 hours. The colour of each part was determined using a spectrophotometer.
Teeth samples were bleached in 30% H2O2 solution with different pH values (2, 4 and 6) for several bleaching sessions until the same degree of whitening was reached. Each bleaching session consisted of 10 minutes of tooth immersion in solution with exposure to blue light each 2 minutes, for 30s, to activate the peroxide.
The enamel microhardness was measured before and after bleaching treatment and the topography was observed by scanning electron microscopy.
The results showed that the bleaching efficiency does not depend on the solution pH but the mechanical resistance is affected. Enamel microhardness decreases faster and tooth erosion rate is higher with low pH values. A significant decrease in enamel microhardness was found after bleaching with H2O2 solution at pH=2. A pH of 4 also induces demineralization but less than when bleached with H2O2 solution at pH 2. There were almost no differences before and after bleaching with H2O2 solution at pH=6.