Effect of fluoride therapy before or after bleaching on enamel permeability

Bleaching may cause decrease in Calcium, Phosphate and Fluoride content of enamel. However, the topical use of fluoride can help reabsorb those minerals. The aim of this study was to determine the effect of fluoride therapy before and after bleaching on enamel dye penetration. Sixty extracted carries-free human premolars were selected. All teeth surfaces were covered by nail varnish, except a square about 6 mm² on the buccal surfaces for exposure to fluoride and bleaching agent. The teeth were randomly divided into 5 groups (n=12) and then stored in artificial saliva at 37ºC for 7 days. Each group was processed as below: Group1: Specimens with no treatment were immersed in 50% silver nitrate solution. Group2: Specimens were bleached by 45% carbamide peroxide for 30 minutes twice a day for 5 days. Group3: the sodium fluoride varnish was used on specimens for 5 minutes. Group4: After bleaching like group2, specimens were stored in artificial saliva. Fluoride therapy was performed next like group3. Group5: All processes were conducted like group4 after fluoride therapy. All specimens were cut bucco-lingually along the longitudinal axis and stored in developer solution for 6 hours. Stereotactic microscope images were captured by digital camera for dye penetration assessment. Data was analyzed using SPSS (11.5) software and ANOVA and Kruskal Wallis tests. Data showed that bleaching can significantly (P=0.001) increase dye penetration. However, fluoride treatment can significantly decrease dye penetration (P=0.001). Fluoride therapy is highly recommended after bleaching process.