The aim of this study was to evaluate, in vitro, the microhardness of human enamel after office bleaching with hydrogen peroxide 35% with and without calcium.
Method:
This study was approved by research ettics committee of Universidade de São Paulo. 24 human teeth were sliced until enamel fragments ± 5x5mm were obtained. Specimens were embedded in acrylic resin and subjected to wear with decreasing grain silicon carbide discs of # 400, # 600, # 1200 and # 4000 in periods of 20, 30, 60 and 70 seconds respectively. Polishment with felt disc and diamond paste (1 µm) and ultrasonic clean for 15 minutes were performed. Specimens were divided into 2 groups (n = 12) according the bleaching agent used: G1 - hydrogen peroxide 35% without calcium (35% Whiteness HP – FGM, Joinville, SC, Brazil); G2 - hydrogen peroxide 35% with calcium (Whiteness HP Blue calcium 35% - FGM, Joinville, SC, Brazil). Knoop microhardness was determined using 100 kgf loads for 15 seconds at 3 different times: baseline, immediately after bleaching and seven days after whitening. Data were submitted to ANOVA with a significance level of 5%.
Result: Microhardness average values was G1 = 319, 200, 256 and G2 = 329, 236, 267, considering each period evaluated. These results were not statistically different from each other
Conclusion:
Calcium incorporated in hydrogen peroxide 35% bleaching agent did not improve enamel microhardeness after whitening, compared with hydrogen peroxide 35% without calcium.