This study aims to evaluate the AEP thickness after treatment with a fluoride plus stannous dentifrice and mouthrinse, and the amounts of KOH-soluble fluoride on enamel after treatment with these products in the presence and absence of the AEP. For this, a 3-phase, single bind, cross over in situ trial, involving 12 volunteers. The experimental groups will be the following: B+R- toothbrushing with F+Sn dentifrice, followed by rinse with F+Sn solution; R+B- rinse with F+Sn solution, followed by toothbrushing with F+Sn dentifrice and C: Control (toothbrushing with artificial saliva). The voluntaries will use two mandibular devices containing 6 specimens each one. The devices containing the specimens will be firstly immersed in 20ml of the 0.3% citric acid (pH=2.6) solution extra-orally, for 5min. One device will be placed into the mouth and remain there for 1h, to allow the formation of the AEP. The other device will be kept under humid environment (without pellicle). After, two specimens will be removed from each of the devices. The remaining specimens from both devices will be then exposed intra-orally to 10ml of the mouthrinse for 30s or will be brushed for 5s with the dentifrice and the suspension will kept in the mouth until a total of 2 min, depending on the study phase. After, two more specimens will be removed from each device. In the sequence, the volunteer that performed the rinse will brush and vice-versa. The final two specimens from each side will then be removed. The control group will only hold 4 specimens at each side and will be brush with saliva only and there would be no rinse. Pellicle thickness will be measured by confocal laser scanning microscopy (CLSM) and the fluoride content in the solution will be measured with a fluoride selective electrode. If normality and homoscedasticity assumptions were satisfied, data will be analyzed by two ANOVA repeated measures and Tukey tests. The level of significance will be 5%.
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