Influence of fluoride concentration and pH Value of 35% hydrogen peroxide on the hardness, roughness and morphology of bovine enamel.

AIM The aim of this in vitro study was to evaluate the effects of different sodium fuoride (NaF) concentrations and pH values on the Knoop hardness (KHN), surface roughness (SR), and morphology of bovine incisors bleached with 35% hydrogen peroxide (HP). MATERIALS AND METHODS Sixty-five bovine incisors were fragmented (5 mm(2) × 2 mm) and distributed in 5 groups: Control (unbleached), Low NaF/Acidic (35% HP + 1.3% NaF, pH 5.5), Low NaF/Neutral (35% HP + 1.3% NaF, pH 7.0), High NaF/ Acidic (35% HP + 2% NaF, pH 5.5), and High NaF/Neutral (35% HP + 2% NaF, pH 7.0). KHN analysis was performed with a microhardness tester under a load of 25 gf for 5 seconds. The average SR was obtained with a rugosimeter. KHN and SR were analyzed before and after treatments. For morphological analysis, specimens were dehydrated and gold-sputtered, and scanning electron micrographs were obtained and analyzed by 3 examiners with a double-blinded technique. KHN and SR results were analyzed by one-way ANOVA and Tukey's test (p < 0.05). RESULTS Only the Low NaF/Acidic and Low NaF/Neutral groups showed significant differences between the initial and final KHN values. All bleached groups presented significant differences between the initial and final SR values. Among the bleached groups, the least and most morphological changes were shown by the High NaF/Neutral and the Low NaF/Acidic group, respectively. CONCLUSION Treatment with 35% HP and 2% NaF at pH 7.0 promoted the least changes in morphology, hardness and roughness among the bleached groups. CLINICAL SIGNIFICANCE In-office bleaching with high-concentration HP and 2% NaF at neutral pH promoted the least changes in enamel hardness, SR, and morphology compared to other treatments.