FLUORINE AND DENTAL CARIES 193 The reactions leading to carious attack can be represented as re- quiring all of the following con- tributing factors: / 1. Fermentable carbohydrate. 2. Acidogenic organism. 3. Plaque or static particle. 4. Susceptible tooth surface. Thus, if the chain of reactions were completely broken at any one point, caries could be prevented. It is practically impossible, of course, completely to avoid any one of the four contributing factors. There is, however, tenable evidence that caries can be reduced by at least four methods: 1. Reducing fermentable carbo- hydrate in diet. 2. Reducing the organisms in the mouth, •s by the use of germicidal agents or other agents inhibiting the fer- menting reaction. 3. Cleaning the teeth thoroughly to remove all food particles or plaques. 4. Increasing the resistance of the tooth surface to acid attack. Atkins (6), Dean (24), Jay (36, 37) and Miller (49) have reported that fluorine action is associated with low oral bacterial counts. Lipman (44) has stated that low concentrations of fluorine do inter- fere with fermentation of carbo- hydrate and Bibby (7) has found that fluorine in concentration of less than 1 ppm. reduces acid pro- duction by acidogenic bacteria. Atkins (6), Hodge (33) and McClure (47) have suggested that fluorine may decrease caries by interfering with the acidogenic process. In so far as fluorine may act within the mouth rather than by becoming an integral part of the tooth structure, its action could have little claim to specificity or natural physiological significance. Many other substances have been shown to influence caries by such action in the oral cavity, including penicillin, vitamin K, oxalate, am- monia, iodoacetic acid, and various germicides. The deposition of fluorine in tooth structure by the pre-eruptive consumption of fluoride-containing water can be accepted as fully established. Evidence that this is the important mechanism of fluoride caries prevention has been offered by Armstrong (4), Cox (18), Dean (23) and Irving (35). Of course, many workers who have claimed results from the post- eruptive topical application visual- ize the mechanism as absorption of fluorine by the tooth. The effect of fluorine in increasing the caries resistance of teeth appears to most workers to be accomplished by means of increasing the re- sistance of such enamel to attack by acids. Thus it has been reported that the enamel of fluorosed teeth is less acid soluble than that of normal teeth (33, 56). The treatment of ground enamel by topical application of fluoride

194 JOURNAL OF THE SOCIETY reduces its solubility in acids (8, 9, 14). Toxic EFFECTS OF FLUORINE USE There are many warnings in the literature that there are possible toxic or harmful results from the use of fluorine. An editorial in the 5tourhal of the A/merican Dental dssociation (27) stated in 1940 "Although it has been fairly well established that fluorine has a slightly retarding influence on the progress of dental caries . . . (the) deleterious influence . . . is too serious to be counterbalanced by questionable caries retarding in- fluence." On the 'other hand, Cox and Levin (19) in 1942 stated "We believe that when all of the facts are known, the toxic effects of fluorine will be far outweighed by the beneficial effects in the pre- vention of dental caries." These two contrary opinions can- not, today, be evaluated, since all of the facts are not yet known. It can be argued with considerable justification that public health con- trol of the fluorine in drinking water can achieve a desirable fluorine level by adding fluorine up to 1 ppm. or by removing excess fluorine to this level. The safety of this procedure. is not our' immediate concern, although Arnim (5), Box (12), and Dean (22) did report that even at the low 1 ppm. fluorine level there was some mild mottling. Phillips and Lamb (51) found that fluoride consumption by rats OF COSMETIC CHEMISTS produced pathologic changes in kidneys, testes, and thyroid. Wilson (60) reports that there appears to be a relationship, geo- graphically, between endemic fluorosis and endemic goitre. Morgareidge (50) found that fluorine interfered with the vitamin D healing of rat rickets. The systemic toxicity of fluorine has been reviewed by Machle and his associates (45, 46), who found some fluorine in the urine of people living in areas with fluorine-free water. They also report that fluorine ingested at low levels ap- pears to be completely excreted in urine and feces, while at higher levels there is retention. McClure (48) has reasoned that since fluorine is excreted, its toxicity may not be as great as would have been expected. R. R. Smith (54) reports that twice. the usual fatal dose of fluorine can be fed to guinea pigs if calcium carbonate or magnesium oxide are also administered. Smith reasons, therefore, that the inclusion of fluorine in a dentifrice may not be unsafe. The form in which fluorine is ingested, however, also influences its effects upon teeth. Greenwood (32) found that pups developed dental fiuorosis when fed sodium fluoride, while the same level of fluorine fed as bone meal did not produce fiuorosis. Lawrenz (43) reported that a high calcium content in the diet depressed the sensitivity to the deposit of fluorine in the teeth.