Anticaries potential of products formed/retained on enamel by fluoride gels

Objective: Acidulated phosphate fluoride gel (APF-gel) forms more CaF₂-like products on enamel than neutral fluoride gel (NF-gel), but they may have the same anticaries effect because only part of fluoride products formed is retained after exposure to saliva. In this study, the anticaries potential of products formed and retained on enamel after fluoride gels application was evaluated using a highly-controlled in situ model.

Method: APF-gel (1.23% F, pH 3.5) or NF-gel (0.9% F) was applied on bovine enamel blocks. Untreated blocks were used as control. Half of the blocks were immersed in artificial saliva for 7 days to simulate the dissolution of CaF₂-like products that occurs in vivo. In a double-blind, crossover, short-term in situ design, 12 participating volunteers wore palatal appliances containing freshly-treated or exposed to saliva blocks, kept in contact with a S. mutans test plaque and acid challenged by a sucrose rinse. After 45 min, mineral loss was evaluated by change in blocks surface hardness and calcium and phosphate release to test plaque fluid.

Result: Although higher (p<0.05) alkali-soluble F (CaF₂-like) concentration (µg F/cm²) was formed on the APF-gel treated blocks (42.3±24.0) in comparison to the NF-gel (7.1±4.6), they did not differ in terms of F retained after exposure to saliva (1.7±0.7 and 1.4±0.7, respectively) (p>0.05), with significantly lower values in the control group (0.3±0.1) (p<0.05). CaF₂-like products formed and retained on enamel by both gels were able to reduce mineral loss when compared to the control (p<0.05). Although a higher effect of the freshly applied APF-gel was observed when compared to the NF-gel (p<0.05), no difference between them after exposure to saliva was seen (p>0.05).

Conclusion: The results suggest that the high concentration of CaF₂-like products formed on enamel immediately after application should not be used to estimate the anticaries potential of professionally-applied fluoride. FAPESP 2008/01727-3