Fluoride is an essential mineral that protects teeth from decay and cavities. It can be obtained topically through toothpastes, mouth rinses, and fluoride treatments, and systemically through fluoridated water and dietary fluoride supplements. 

It was discovered by chance in the early 1900's by Frederick McKay that discovered that 90% of a Colorado town's population had brown staining on their teeth due to fluorosis, an imperfection in tooth enamel development. The staining was resistant to tooth decay, and the source was found to be the local water supply, rich in fluoride.

It has since been added to toothpaste, mouthwash, and water supplies.