Fluoride does not act synergistically with iron on enamel demineralization

Iron ion (Fe+2) has been shown to reduce enamel demineralization, but its use can cause tooth staining. Objectives: This study investigated if the addition of fluoride (F) in the reaction medium could act synergistically with Fe+2 to inhibit the dissolution of bovine powdered enamel, thus allowing the use of lower Fe+2 doses. Methods: Forty mg of enamel powder (particles between 75-106 µm) were subjected to 0.4 mL of 10 mmol/L acetic acid with increasing concentrations of Fe+2 (0-120 mmol/L), associated or not with fluoride (0-4 ppm) for 30 s. Each experiment was repeated 6 times. The amount of enamel dissolved was assessed by measuring the phosphate released, using the Fiske-Subarrow method. Data were tested using 2-way ANOVA and Bonferroni's post hoc test (p<0.05). Results: The amount of phosphate released into the acetic acid decreased with increasing Fe+2 concentrations. Fe+2 at 1.25, 2.5, 5.0, 10, 15 and 30 mmol/L significantly reduced the dissolution of enamel powder in 18, 18, 23, 35, 35 and 55%, respectively, in comparison to control (no Fe+2). Fe+2 concentrations higher than 30 mmol/L did not have a better effect. In the presence of F, the effect of iron on the inhibition of enamel dissolution was reduced. Conclusion: Our data suggest that F does not act synergistically with Fe+2 on the inhibition of enamel demineralization. Supported by FAPESP (06/04605-0)