Fluoride Fluoride is a mineral that occurs naturally in almost all foods and water supplies. The fluoride ion comes from the element fluorine. Fluorine, the 13th most abundant element in the earth's crust, is never encountered in its free state in nature. It exists only in combination with other elements as a fluoride compound. Fluoride is effective in preventing and reversing the early signs of tooth decay. Researchers have shown that there are several ways through which fluoride achieves its decay-preventive effects. It makes the tooth structure stronger, so teeth are more resistant to acid attacks. Acid is formed when the bacteria in plaque break down sugars and carbohydrates from the diet. Rep