treatment with fluorides ; the addition of fluorides to community drinking water as a measure to reduce the incidence of dental caries . Minute traces of fluoride are found in almost all food, but the quantity apparently is too small to meet the requirements of the body in building tooth enamel that resists cavities. Drinking water containing one part fluoride to one million parts of water does meet this need and has been found to reduce tooth decay in children by as much as 40 per cent. Since few natural water supplies contain the necessary amount of fluoride, it usually must be added if protection against tooth decay is desired. Statistics indicate that 20 per cent of the teenagers who drank fluoridated water from birth have teeth totally free of caries. The practice of fluoridating water is rated among the most cost-effective preventive programs in public health. There also is evidence that topically applied fluoride solutions help alleviate periodontal disease by removing bacteria from the site and rebuilding supporting bone tissue around the teeth. Dental professionals may apply fluoride solutions directly to a child's teeth, beginning at age 5 or 6 and repeating the treatment each year throughout life. This has been found to reduce caries by about 40 per cent. The dentist or other health care provider may prescribe chewable fluoride tablets if fluoride is not available in drinking water. However, use of these tablets must be carefully supervised, since an excess of fluoride causes dental fluorosis . Like most medicines, fluoride in large amounts is a poison. A dentifrice containing fluoride, or fluoride in gel form, may also prove effective. A dentist or dental hygienist should be consulted before any fluoride preparation is used.