Sequence of stannous and sodium fluoride solutions to prevent enamel erosion

Objectives: Investigate the timing of stannous (SnF₂) and sodium fluoride (NaF) application with and without salivary pellicle to prevent enamel erosion. Methods: Human buccal molar enamel samples (n =120, REC ref 12/LO/1836) were randomly assigned to three groups testing SnF₂ and NaF basic fluoride formulation and commercial mouthrinses with and without the presence of human saliva. Samples were randomly allocated to 2 subgroups: immersion in either fluoride for 1min either before or after citric acid immersion (0.3%, pH 3.2, 10min), and the cycle repeated 5 times. For human saliva group, samples were immersed in 80ml of natural saliva for 24h prior to the experiment. Analysis was done using non-contacting profilometry and microhardness change. Data were not normal and were log transformed. A linear model tested statistical differences between the groups. Results: SnF₂ application before erosion statistically reduced step height compared to application after erosion for all groups (solutions: 6.5μm (±1.2), 7.5μm (±0.8); p =0.01, mouthrinses: 3.2μm (±0.6), 4.2μm (±0.7); p 2 was applied before erosion and when NaF was applied after erosion (SnF₂: 156.6KHN (±32.8), 123KHN (±20.1); p =0.02. NaF: 119.5KHN (±33.5), 218KHN (±24.9), before, and after respectively). Conclusion: SnF₂ reduced step height formation overall when compared to NaF, but particularly when applied before citric acid immersion. In contrast, NaF reduced step height when applied after citric acid immersion, but only in the presence of saliva. Clinical significance: Stannous fluoride can be recommended over sodium fluoride to patients at risk of dental erosion and is optimally applied before erosion occurs. If sodium fluoride is to be used in the presence of saliva it is optimally applied after erosion has occurred.