A topical gel form of fluoride application. Acidulated phosphate fluoride gel (APF) is an aqueous solution derived from sodium fluoride acidulated with a mixture of sodium phosphate and phosphoric acid, which yields an effective fluoride ion concentration of 0.02%, and is used as a preventive measure to reduce caries. It is professionally administered by brushing on the teeth or placing in a tray which fits over the tooth arch. It is not normally given to children under the age of 6 years because of the risk of ingestion.
Richards D. Topical fluoride guidance. Evid Based Dent 2006;7(3):62–4.