The Evanston Dental Caries Study has been a carefully controlled, 15-year fluoridation program. The basis of the study was to determine the effectiveness of controlled fluoridation as a dental caries preventive measure and to study some of the physiologic effects that might result from the addition of one part per million of fluoride to the drinking water.' The fluoride was added as sodium fluoride, and the fluoride concentration was determined spectrophotometrically on daily samples.2 6 The range of fluoride concentration maintained was 1.00 ± 0.1 ppm F-. EXPERIMENTAL METHODSIn the course of our study, samples of various biologic fluids and soft and hard tissues were analyzed for fluoride content. The results obtained were then studied in conjunction with the time of exposure to 1.00 ± 0.1 ppm F-from 0 to 15 years. Most of the studies were done on iliac-crest specimens obtained from autopsies at a local hospital. Specimens under consideration were not restricted to age, race, sex, or any pathologic malfunctions. The analytical method used, utilized a steam distillation similar to that of Willard and Winter2 and a macro-spectrophotometric determinations At the beginning of the study, a colorimetric thorium nitrate titration method was used.6 The results of the two methods were shown to be in good agreement. Iliac specimens for analysis were scraped clean, all fat extracted with acetone for 48 hours, air-dried for at least 72 hours, ground to pass through 60-mesh sieve, weighed, and ashed with low fluoride calcium oxide fixative at 5750 C., with the temperature being brought up gradually and kept at 5750 C. for 1 hour. The samples were then distilled from perchloric acid, and the fluoride was determined spectrophotometrically.5 RESULTS AND DISCUSSIONPrevious studies on fluoride deposition in skeletal tissue have indicated that several factors influence the level of fluoride in bone. A number of workers7-13 have reported that there is a definite increase of fluoride deposition in bone with an increase in age. Zipkin, McClure, Leone, and Lee7 compare two rather extreme cases of fluoride deposition in human bone, where the individuals were in the same age group but one was exposed to 0.2 ppm F-for 24 years, and the other to 8.0 ppm F-for 34 years. Their study indicates that prolonged ingestion of drinking water containing 8.00 ppm Faccounts for a high deposition of fluoride in bone. A comparison of available data and

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