Recently the news have been flashing headlines about Fluoride levels in water. Many of our patients have asked us the question of whether fluoride is beneficial when ingested. It's important to understand that ingested fluoride may help only developing teeth in children. For teeth that have erupted in the mouth, fluoride is only effective as a topical agent: It takes a delivery medium such as tooth paste or gel to allow the fluoride to form a matrix with the calcium on the tooth enamel. That matrix helps resist tooth decay.
Here is the article from the California Dental Association regarding the recent guidelines for optimal fluoride level in drinking water.