Fluor-A-Day Tablets Fluoride is used to help prevent tooth decay. It is thought to work by strengthening the mineral composition of the tooth enamel, which makes the teeth more resistant to attack by acid in the mouth. Fluoride is most effective when taken in childhood, when teeth are developing. Fluoride deficiency increases the risk of tooth decay. Fluor-a-day tablets provide fluoride & help strengthen tooth enamel, which helps to protect against tooth decay.