Dwight E. Gardner

Solubility Rate and Natural Fluoride Content of Surface and Subsurface Enamel

THE surface enamel is more resistant to acid than is subsurface enamel, the rate of dissolution of phosphate from the surface being less than that from the subsurface enamel.1-3 With ordinary and polarized light microscopy, as well as with soft x-rays, it has also been shown that it is possible for demineralization of the subsurface enamel to occur without any apparent change in the enamel surface,4 5and when ground sections of teeth were exposed to EDTA the outer portion of enamel was the last to be demineralized.6 The reason for this difference between surface and subsurface enamel has not been established. That fluoride may play a role, at least at the level of 2 ppm in the water supply, is suggested by the work of Jenkins, Armstrong, and Speirs,2 who found that the solubility rate of surface enamel of teeth from areas with 2 ppm fluoride in the water supply was less than that from areas with 0.25 ppm, although there was no difference in the solubility rate of the bulk of the enamel. Since fluoride accumulates in the surface enamel, even in teeth from areas low in fluoride,7 it was considered that fluoride acquisition might generally be responsible for the decreased solubility rate of surface compared to subsurface enamel. Therefore, in the present study an attempt was made to correlate the solubility rate and fluoride concentration of successive layers of enamel from areas with different levels of fluoride in the drinking water.

Renal Clearance of Fluoride.

Summary Fluoride in dog plasma was completely ultrafilterable through visking membranes when tested using the centrifuge type apparatus. In dogs with a normal water load, the average normal renal fluoride clearance was 2.7 ml/min.; the fluoride : chloride clearance ratio, 19; and the fluoride : creatin-ine clearance ratio, 0.077. Fluoride clearance was more rapid than that of simultaneously measured sodium or chloride clearances or urine flow. During mannitol diuresis, fluoride was cleared at a rate higher than that of sodium, chloride, or phosphate. Fluoride clearance, although greater than urinary flow, varied directly with the flow under mannitol osmotic diuresis. Intravenous infusion of hy-pertonic NaNO3 or Na2SO4 solutions, creating a salt diuresis, did not affect fluoride excretion. Hypertonic NaCl infusion did increase the fluoride clearance. Although fluoride : creatinine clearance ratios were raised greatly by intravenous fluoride, the highest ratios were attained during fluoride infusion plus osmotic diuresis with hypertonic mannitol or NaCl. No evidence for a tubular secretion of fluoride was obtained.

Toxic effects of fluoride on the rat kidney. II. Chronic effects.

Abstract 1. 1. The 30-day LC50 of sodium fluoride administered in the drinking water was 205 ppm fluoride in the weanling rat. Death generally occurred between the third and fifth day after administration was begun. When levels of 150–250 ppm fluoride were administered in the water, 30–40% of the surviving rats showed a renal lesion consisting of dilatation of the tubules at the corticomedullary junction. 2. 2. Levels of 0, 1, 5, 10, 25, 50, and 100 ppm fluoride were administered in the drinking water to rats for 6 months. No growth depression was seen, even at 100 ppm, but mortality was slightly increased in males and females ingesting 50 ppm and males ingesting 100 ppm. The only pathologic changes were seen in the kidney and the bone. Two of the 12 rats receiving 100 ppm for 6 months showed a marked dilatation of the tubules in the corticomedullary region of the kidneys. The lesion was accompanied by a high water consumption and urine output. Radiographically, an increase in the deposition of trabecular bone was seen in the rats ingesting 100 ppm fluoride. A slight increase was also seen in the males ingesting 50 ppm fluoride. 3. 3. Balance studies showed that rats retained about 50% of the ingested fluoride after 3 months on fluoridated water. Seventy-five to 80% of the ingested fluoride was absorbed, and 65–70% of the absorbed fluoride was retained. After 6 months, the male rats retained 45% of the ingested fluoride, the females about 60%. Both males and females absorbed 80% of the ingested fluoride. The males retained 60% of the absorbed fluoride; the females, 80%. The percentage fluoride retained was independent of the fluoride level in the water. The increased age of the rats did not alter fluoride retention, except that the females retained a higher percentage of the ingested fluoride than the males after 6 months. 4. 4. The fluoride concentration in the femur ash of the rats ingesting fluoridated water for 3 months was directly proportional to the fluoride level in the water, even with a level of 100 ppm. After 6 months, the fluoride concentration was directly proportional to the fluoride level in the water at levels of 50 ppm and less. The rats ingesting 100 ppm fluoride in the water had a lower concentration than would be expected from this proportionality. 5. 5. The natural fluoride present in a stock animal ration such as Purina Fox Chow Meal was of limited availability. Only 10–15% of this fluoride was metabolized by the rat.

Investigations on the Metabolism of Fluoride I. the Determination of Fluoride in Blood

THIS paper reports the analytic method used in the recently published investigation of the blood fluoride concentration of persons drinking water containing 1 ppm fluoride1 Studies of the biologic effects of fluorides have centered around a few important topies2-7; however a survey of blood fluoride concentrations reported for different methods8 showed erratic results, some as high as 460 ftg F per 100 ml. A brief investigation of various ashing procedures indicated that the principal source of the variability was to be found in this initial preparation of the sample. Using a variety of alkaline fluoride fixatives, 50 ml. samples of blood were made alkaline, evaporated to dryness, and ashed overnight either at 3500 or 5750 C. The fluoride was distilled from a perchloric acid solution of the ash and then determined in the distillate by a modification to be described later of the thorium-alizarin fluoride titration. Typical analytic data are shown in Table I; the recoveries are erratic and low. Because blood contains appreciable quantities of iron capable of forming volatile iron fluoride complexes or compounds, the importance of iron was established. Recovery studies were done as before, using an amount of iron as ferric chloride equivalent to the iron content of 50 ml. of blood, and sodium carbonate as fixative. Approximately 70 per cent of the added fluoride was lost, indicating that the low recoveries (Table I) could be attributed, at least in part, to volatile iron fluorides. These difficulties were obviated when the double distillation procedure of the Association of Official Agricultural Chemists9 was used. Distillation.-A general description of the reagents, apparatus, and procedure for the fluoride distillation as done in this laboratory has been given by Flagg.10 For the analysis of blood, a 50 ml. sample of oxalated whole blood is introduced directly into a 200 ml. distilling flask and the distillation carried out in the usual manner, using concentrated sulfuric acid rather than perchloric acid for the first distillation. A total of 140 ml. of distillate is collected. The distillate is evaporated to dryness in platinum, using calcium oxide. as a fixative, ashed 15 to 16 hours and redistilled as before, except that perchloric acid is used as an acidifying agent and 125 ml. of distillate are collected. Titration.-The salt-acid thorium method of Williamsil offers at least two improvements over the usual thorium-alizarin back titration9: (a) the use of a

Defluorination of fluoroacetate in the rat.

Abstract Rats given 5 ppm F as FAc (equivalent to 26 ppm of NaFac) in the drinking water for approximately four months deposited as much fluoride in the skeletal system as did rats receiving 5 ppm F as NaF in the water. Little evidence could be found for the presence of organically bound fluoride in bone after ingesting FAc, though an appreciable proportion of skeletal fluoride deposited when NaF was ingested was shown not to respond to the fluoride ion electrode. The daily urinary excretion of total fluoride after FAc was somewhat greater than after NaF; about two thirds of this fluoride responded to the electrode, whereas more than 90 percent of the total fluoride after NaF was ionic in nature. The data are interpreted as showing that the rat is capable of splitting the C-F bond in FAc and/or in its fluoride-containing metabolites, with subsequent skeletal storage and renal excretion of the released fluoride ion. The chronic administration of this low level of FAc caused an early but temporary retardation of growth. The Krebs cycle was interfered with, as evidenced by increased concentrations of citrate in the kidney and urine. At termination of the experiment, histological examination of the testes showed that the FAc had induced severe damage characterized by massive disorganization of the tubules, nearly total loss of functional cells, absence of sperm, and damage to the Sertoli cells.

Fluoride content of teeth from children who drank fluoridated milk.

In a fluid intake survey made during the Newburgh fluoridation study, it was found that the water consumption for a limited number of children was minimal, 60 to 420 ml per day (A.E. LIGHT: Arch Biochein 47:477-479, 1953). This range of intake has been confirmed by others (J.S. WALKER ET AL: Science 140:890891, 1963). The low intake of water and fluoride had been postulated earlier (A.E. LIGHT: Nutr Rev 10:159, 1952) and led to the addition of sodium fluoride solution to the milk consumed prenatally by the mother and postnatally by the children of one family, to insure a greater intake of fluoride in a more consistent manner. The deciduous teeth from one son and teeth from several other members of the family were analyzed for fluoride content. This data, presented previously (A.E. LIGHT ET AL: J Amner