To reduce the risk of tooth decay or cavities, toothpaste and mouthwash that contains fluoride must be used. Fluoride is a compound that is added to most tap water supplies, toothpaste, and mouth rinses to reduce decay and cavities. Fluoride becomes incorporate into our teeth as they develop and makes them more resistant to decay. After our teeth are formed, fluoride can reverse the progress of early cavities, and sometimes prevent the need for corrective dental treatment.