An in vitro study on the influence of viscosity and frequency of application of fluoride/tin solutions on the progression of erosion of bovine enamel

Objective: To evaluate the influence of the viscosity and frequency of application of solutions containing fluoride (F) and stannous chloride (SnCl2) on enamel erosion prevention. Design: Bovine enamel specimens were randomly distributed into 12 groups (n = 10), according to the following study factors: solution (C: deionized water; F: 500 ppm F- ; F + Sn: 500 ppm F- + 800 ppm Sn2+); viscosity (low and high); and frequency of application (once and twice a day). Specimens were submitted to an erosive cycling model, consisting of 5 min immersion in 0.3% citric acid, followed by 60 min exposure to a mineral solution. This procedure was repeated 4 x /day, for 5 days. Treatment with the experimental solutions was performed for 2 min, 1 x /day or 2 x /day. Enamel surface loss (SL) was determined by optical profilometry. Data were analyzed by 3-way ANOVA and Tukey tests (alpha = 0.05). Results: There were significant differences between the levels of the factor solution (p < .001), viscosity (p < .001) and in the interaction between solution and viscosity (p = .01). Regarding solution, the mean SL standard deviation for the groups was F + Sn (4.90 +/- 1.12) < F (7.89 +/- 1.19) < C (14.20 +/- 1.69). High viscosity solutions demonstrated less SL than low viscosity; however, only when applied once a day (p < .001). Applying the solutions twice a day yielded lower SL than once a day, but only for the low viscosity solutions (p = .003). Conclusions: Under the conditions of this short-term in vitro experiment, it could be concluded that increasing the viscosity of the oral rinse solutions reduced enamel loss by erosion; however, this effect was small and only observed when the solutions were applied once a day.