Longevity of Enamel Fluoride Reservoirs Formed after Fluoride Application: An in situ Study

Introduction: Professional fluorides form reaction products on tooth substrates, which once dissolved, interfere with the caries process. However, the persistence of these reservoirs before the need of a new application is unknown. We investigated in situ the effect of various cariogenic challenges and exposure to fluoride toothpaste on the retention of enamel fluoride reservoirs. Methods: In a blind, 4-period crossover study, 12 participants wore palatal devices containing human enamel slabs previously treated with one application of acidulated phosphate fluoride gel. No biofilm or biofilm accumulation and exposure to 20% sucrose 0, 2, or 8 times/day were tested. Participants used non-fluoridated or fluoridated toothpastes (1,100 mg F/kg) throughout the experimental periods. Slabs were collected after 2, 7, or 14 days to assess remaining alkali-soluble fluoride reservoir concentrations. Results: The loss of the enamel fluoride reservoirs was accelerated either in the absence of biofilm or under biofilms exposed to sucrose 8 times/day (p < 0.05). The loss of these reservoirs was reduced by fluoride toothpaste use (p < 0.05). Conclusion: The results support a personalized recommendation of the frequency of professional fluoride application based on patients’ caries activity since the cariogenic challenge and exposure to fluoride influence the retention of fluoride reservoirs formed on enamel by professional fluoride application.