Sodium fluoride (NaF) was the first fluoride compound to be used for topical application. The first clinical study was started by Bibby in 1941 using a 0.1% aqueous NaF solution. In 1942 Knutson applied a 2% aqueous NaF solution for 3 minutes, he suggested that the series of applications should be carried out at the age 3,7,11 and 13 years to coincide with the eruption of teeth and a caries reduction of 30%.

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2% NaF solution can be prepared by dissolving 20 gms of NaF powder in 1 litre of distilled water in a plastic bottle. Storing in glass containers results in the formation SiF2 thus reducing the availability of free active fluoride for anticaries action. 2% NaF is applied with the cotton application and is permitted to dry on the teeth for about 4 minutes, the patient is instructed to avoid eating, drinking or rinsing for 30 minutes so as to prolong the availability of fluoride ion to react with the tooth surface.

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When NaF is applied topically it reacts with hydroxyapatite crystals to form CaF2 which is the dominant product of the reaction, once a thick layer of CaF2 gets formed it interferes with the further diffusion of fluoride from the topical fluoride solution to react with hydroxyapatite called as choking effect.

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Advantages:

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• Relatively stable
• Taste is well accepted
• Non iritating
• Does not cause tooth discolouration
• Suitable for public health program