Does fluoride gel/foam application time affect enamel demineralization?

The American Dental Association Council on Scientific Affairs recommends a four-minute application of professionally applied topical fluoride, based on clinical evidence for caries reduction. However, some product manufacturers imply that a one-minute application is sufficient. The purpose of this laboratory study was to ascertain if a one-minute application of acidulated phosphate fluoride (APF) is equivalent to a four-minute application for reduction of enamel demineralization. We measured baseline hardness of polished bovine enamel before treatment with APF gel or foam for one or four minutes (N = 10). A control group received no fluoride treatment. The teeth were then immersed in pooled human saliva for 30 minutes, rinsed, and subjected to lactic acid gel to simulate the initial stage of dental caries. After three hours, the hardness was measured and the difference in hardness was determined as an indication of demineralization. We found that enamel hardness was significantly reduced after exposure to lactic acid gel. The reduction was significantly less in all APF-treatment groups compared to the control. However, there was no significant difference between a tooth exposed to APF gel or foam for 1 minute or for 4 minutes (ANOVA/Student-Newman-Keuls, significance level 0.05). In conclusion, APF gel and foam reduced enamel demineralization regardless of a one- or four-minute application time.