Evaluation of human enamel permeability exposed to bleaching agents

Aim: To evaluate the human enamel permeability after different external bleaching techniques.Methods: The coronal portions of 20 maxillary human incisors were covered with an acidresistant varnish, except the labial surface, to prevent dye penetration of silver nitrate. Thespecimens were divided randomly into four groups (n=5) according to the bleaching treatments:Group 1 (G1) - without bleaching agent (control group), Group 2 (G2) - 35% hydrogen peroxide(HP) – one session of three 10-min applications, Group 3 (G3) - 35% HP – 2 sessions of three10-min applications, and Group 4 (G4) - 6% HP – 14 days (1h/day). G1 was exposed to artificialsaliva only and in the other groups the bleaching agents were applied following the manufacturers’recommendations. After bleaching, teeth were immersed in a 50% silver nitrate solution for 2 hand photodeveloped for 16 h. Then, three longitudinal slices of each tooth were photographedby an optical microscope (100x). The degree of dye penetration was analyzed in the middle thirdof the dental crowns using a 0 to 4 score system (0= no dye penetration, 1= less than half theenamel thickness, 2= half of the enamel thickness, 3= full extent of enamel without reaching thedentin, and 4= tracer agent reaching dentin). The data were analyzed statistically by the Kruskal-Wallis and Dunn tests (α=0.05). Results: The median (1st/3rd interquartiles) ranges were: G1:0(0/0), G2: 2(2/3), G3: 3(3/3) and G4: 3(3/3). G2, G3 and G4 showed significantly higher dyepenetration compared with G1 (p=0.0017). Conclusions: The use of bleaching agents increaseddental enamel permeability, regardless of the bleaching technique.