FLUORINE AND DENTAL CARIES* B.y T. H. /Issociate Director of Research, Lever Brothers Co., Cambridge, Mass. O•E Or T•E most fertile fields of dental research has been the study of the role played by fluorine in dental health. No brief summary can pretend to cover the field exhaustively. FLUORINE IN TOOTH ENAMEI. The presence of fluorine in human tooth enamel was reported as early as 1805 by Gay-Lussac and Ber- thoiler (31). Crichton-Browne (20) in 1892 thought "it well worthy of consideration whether the reintro- duction into our diet... of a supply of fluorine in some suitable natural form... might not do something to fortify the teeth .... " Such early references were, per- haps, prophetic, but cannot be credited as originating the current scientific consideration. The current knowledge of the action of fluorine stems from a study of mottled tooth enamel, a disfiguring dental defect. Recognition of fluorine as the agent in production of mottling of enamel sprang, in 1931, from the * Presented at the May 13, 1947, Meeting, New York City. work of Churchill (17) and of Smith, Lantz, and Smith (52). Later studies proved that mottled enamel is endemic in nature, and directly related to the concentration of fluorine in the drinking water consumed by children during tooth- formation years. Dean (22) has shown that fluorine at 1 ppm. in the drinking water produces mottled enamel of the mildest form in about 10 per cent of children, while 4 ppm. produces more definite mot- tling in 90 per cent of cases. Black and McKay (11) had re- ported, as early as 1916, that the incidence of caries was less in mottled teeth than in normal teeth. Cox (18) was apparently the first, specifically, to suggest (in 1937) a beneficial role for fluorine in pre- venting caries. Within limits, there appears to be a distinct relationship between fluorosis and caries, and in areas of edemic fluorosis there is an inverse relationship, caries de- creasing as fluorosis increases. This evidence is supported by reports 'that the fluorine content of sound teeth is higher than that of carious teeth (3). 100

FLUORINE AND DENTAL CARIES 191 Some contrary opinions have been expressed. Bunting in 1928 reported (13) his finding that the frequency of caries was the same although the extent and activity of caries was less in fluoride areas. Applebaum in 1936 reported (2) that he found a lack of correlation between the severity of mottling and the number of carious areas. M. C. Smith (53) warned that the favorable results might be misleading. Smith reported that in St. David, Ariz., where the drinking water contained from 1.6 to 4.0 ppm. of fluorine, children of 12-14 years did show a definite rec•uction in caries but that residents aged 2141 showed excessive caries. Weaver (58) also stated that fluorine had a postponing action, but did not prevent caries, the delay not exceeding five years. FLUORIDE ADDED TO DIET In sp{te of the few contrary op{n{ons, and in spite of poss{b]e dangers which will be discussed later, there have been numerous proposals to add fluoride inten- tionally to the diet (usually to the drinking water) in order to reduce caries. Tests are at present be{ng con- ducted in Evanston, IiL, Grand Rapids, Mich., and Newburgh, N. Y., in which fluorine is being pur- posely added in low concentration to the drinking water of these test towns, while neighboring control towns are continuing to use fluoride- free water. The results of these tests, over a sufficiently long period, should be convincing. Such results presumably cannot be entirely conclusive, however, until continued for the entire life span of the generation born after the experiments started. The earlier studies, both on animals and on humans, indicated that the caries-inhibiting and fluorosis-producing action of fluoride-containing drinking water were both found when the water was consumed during the tooth formative age (1). It was naturally assumed that the tooth enamel contained fluorine, which, as a result, and de- pending upon the amount of fluorine laid down in the enamel, showed an increased caries resistance and fluo- rosis or mottling. ' Continued observation has indi- cated that the consumption of fluorine-containing water may still have a caries inhibiting effect on fully erupted teeth (25, 39). Since it is unlikely that ingested fluorine can be deposited by meta- bolic processes in the enamel of erupted teeth, these observations have suggested that fluorine may find its way directly from drinking water into the tooth structure. Volker, in 1939, showed (56) that tooth enamel would pick up fluoride on contact with fluoride solution. TOPICAL APPLICATION OF FLUORIDE SOLUTIONS There have been numerous re- ports of the use of fluoride solutions by topical application, recognized by a recent editorial in the yournal