The Effect of Fluoride on the Permeability of Bleached Teeth Enamel and dentine permeability increases after dental bleaching. Objective: This in-vitro study tested the hypothesis that fluoride-based products reduce the permeability of bleached teeth to dye penetration. Methods: Forty surgically extracted caries-free human third molars were bleached for 30 days using 10% carbamide peroxide for 8 h/day. The teeth were place in artificial saliva for the remaining 16 h/day. The bleached teeth were numbered and sliced mesio-distally resulting in two sets of 40 tooth-halves. The 40 specimens from the buccal side were divided into two groups of 20 specimens and treated for seven days as follows: neutral fluoride gel was applied for 10 min (Group 1A), and brushing fluoride toothpaste for 2 min (Group 1B). Specimens in Groups 1A, 1B, and the 40 specimens from the lingual side (Groups 2A and 2B) that served as controls were sealed using nail polishing except for a 8-mm² window and placed in methylene blue dye for 48 h. All specimens were sliced longitudinally through the middle of the window. An optical microscope was used to examine the amount of dye penetration that was quantified from no penetration (score 1) to full tooth wall penetration (score 4). Results were statistically analyzed using Student t-test. Results: Groups 1A and 2A showed no statistically significant difference (p=0.804). Although Group 1A had more specimens with no dye penetration than Group 2A, it was not statistically significant (p=0.14). Groups 1B and 2B also showed no statistical differences overall (p=0.527) and by score 1 (p=0.50). Conclusion: Treating bleaching teeth with either neutral fluoride gel or fluoride toothpaste did not show a significant reduction in dye penetration.

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