Research studies continue to show that fluoride uptake in enamel is time-dependent due to a diffusion-controlled process and that it should be left on the teeth for the full four minutes with the gel tray method. Although the most update of fluoride is in the first minute, research continues to support the full 4 minutes providing the best topical benefit when using the tray method. The ADA states “there are considerable data on caries reduction for professionally applied topical fluoride gel treatments of four minutes or more. In contrast there is laboratory, but no clinical equivalency data on the effectiveness of 1-minute fluoride gel applications.” Upon examining current information on this topic, dental professionals need to determine if professional topical fluoride applications are appropriate for all their patients, based on caries risk factors. The American Dental Association’s current fluoride evidence-based guidelines indicate a 2.26% sodium fluoride varnish be applied at least every 3-6 months for children younger than 6 years of age at an elevated risk for caries. For children 6-18 years of age who are at risk for caries, the ADA recommends 2.26% sodium fluoride varnish every 3-6 months or 1.23% APF gel for 4 minutes at least every 3-6 months. However, with acidulated fluoride gel at only 12,300 ppm and sodium fluoride varnish at 22,600 ppm fluoride, it would appear sodium fluoride varnish would be more beneficial. However, we also know that fluoride’s efficacy is enhanced with an acidic environment. See the current ADA Clinical Recommendations for Use of Professionally-Applied or Prescription-Strength, Home-use Topical Fluoride Agents for Caries Prevention in Patients at Elevated Risk of Developing Caries on the ADA website.