W.D. Armstrong

Possible Relationship Between the Fluorine Content of Enamel and Resistance to Dental Caries

That the susceptibility and immunity of teeth to caries is to be accounted for, at least in part, by differences in composition is a hypothesis that has long been attractive. The evidence for the claims (7, 8) that such differences exist have failed of confirmation. We (3) found enamel and dentin fractions prepared from sound and carious teeth to possess compositions, with respect to the calcium, phosphorus, magnesium, and carbonate contents, which were not significantly different. LeFevre and Hodge (9) found whole tooth inorganic substance prepared from carious specimens to differ from that obtained from sound teeth only with respect to a slightly higher moisture content of carious tooth substance.2 Without regard to the data to be presented below, there is evidence that marked changes in some of the properties of enamel accompany changes in its fluorine content. The amount of fluorine in mottled enamel is relatively slight (4) in comparison to the total inorganic material; yet it produces, or is accompanied by, profound changes in the appearance and properties of the enamel. In this connection it is worthy of mention that it has not been demonstrated that mottling of enamel is due entirely to the effect of fluorine combined in the inorganic phase and is possible that the condition is produced, in part, by the operation of the fluoride ion on enzymes during the calcification of the enamel. The effect of fluorine added to the diet on the quality of the teeth of rats first observed by Schulz and Lamp (13) and independently by McCollum, Simmonds, Becker,

Stimulation of the Muscles of Mastication

From time to time investigations on the strength of the muscles of mastication have been conducted by various investigators during different periods and in different geographical centers. The earliest study on record, as far as we know, was made in 1681 by G. A. Borelli (1). He records a bite strength as high as 200 kilograms (Ca. 430 pounds). G. V. Black (2) reported in 1895 that he had tested the strength of bite of several thousand individuals and found an average of 175 pounds. L. H. Waugh (3) has now reported the strength of bite among Eskimos and has recorded up to 330 pounds bite pressure. In an experiment made at the University of Minnesota (4) among Minnesota athletes the average strength of bite was found to be 126 pounds pressure, which was the same as the average of the general student body at that time. From the figures available from these studies it is difficult to arrive at accurate statistical conclusions, but it seems that, with the increasing prevalence in dental caries, malocclusions, and gingival diseases, there has also been a decrease in the tone and strength of the muscles of mastication, an observation which is generally accepted. A. H. Thompson (5) in 1876 in a discussion on the dynamics of dental occlusion and the structural expenditure of

A Method for the Separation of Enamel, Dentin, and Cementum1

Routine analysis of enamel and dentin requires a simple method for the separation of these substances from each other and from cementum. Procedures commonly employed for the preparation of enamel, most of which utilize mechanical forces-grinding or desiccation, or combinations of these-usually give low yields, and the purity of the product is questionable. Rosebury, in connection with his study of the protein of enamel, indicated difficulties with available methods, and pointed out extreme precautions necessary to obtain a pure product.2 Our method takes advantage of the differences in the specific gravity of enamel and dentin. Finely pulverized whole-tooth is suspended in a liquid having a specific gravity intermediate between the two materials, causing the heavier enamel to sink and the lighter dentin (and cementum) to float on the surface. The specific gravity of dentin is 2.2-2.3; that of enamel, 2.7-2.8. In order to make the conditions optimal for the preparation of a pure-enamel fraction, even at the sacrifice of a small amount of this material in the dentin fraction, we employ a liquid having a density nearer that of enamel; namely, 2.53 at 250C.

A Condition Suggestive of Threshold Dental Fluorosis Observed in Tristan Da Cunha II. Fluorine Content of the Teeth

Armstrong and Brekhus (1, 2) have shown that a relatively high fluorine content is characteristic not only for fluorosed teeth but also for sound teeth (without clinical evidence of fluorosis) as compared with carious teeth. Since severe dental fluorosis is as undesirable as dental caries, it is of considerable interest to determine, firstly, the maximum fluorine content of the teeth compatible with their normal or nearly normal appearance, and, secondly, the optimal fluorine content, if such exists, necessary for preservation of sound teeth. Some information on these points may be derived from the fluorine determinations here reported. These analyses were made on a material of deciduous and permanent teeth collected by one of us (R. F. S.) during the recent Norwegian expedition to the South Atlantic island of Tristan Da Cunha (3), where a low incidence of dental caries was observed stimultaneously with a condition resembling threshold dental fluorosis (4).

Chemical Composition of Enamel and Dentin. II. Fluorine Content

It is generally agreed that fluorine is a constant component of enamel and dentin and that of all structures in the body, the teeth probably contain the largest amount of this element. In spite of efforts extending over the last 130 years no agreement has been reached as to the actual amount of fluorine in enamel and dentin. McClure (9) reviewed the literature of the period 1803-1933 and found the reported fluorine content of enamel, dentin and whole teeth to vary from zero to 1.4 per cent. Jacob and Reynolds (7), whose work was not reviewed by McClure, found whole teeth to contain 1.8 to 3.5 per cent fluorine. Of the older reports most credence has been placed in the results of Gautier and Clausmann (6) who found the fluorine content of enamel to vary between 0.118 and 0.172 per cent. It was McClures opinion that the creditable literature indicated the presence of 0.1 to 0.2 per cent fluorine in enamel. The analyses made since McClures review have indicated a lower fluorine content of teeth and teeth structures than had been found by the older investigators. The recent improvements in fluorine analytical methods have resulted in a downward trend of the determined amounts of fluorine in biological materials. Klemet (8) found enamel and dentin to possess an identical fluorine content, namely 0.05 per cent. Bowes and Murry (3) reported enamel to contain 0.02 per cent fluorine. They (4) later found mildly mottled teeth to contain 0.035 per cent fluorine in the enamel and 0.07 per cent in the dentin.

RADIOTRACER STUDIES OF HARD TISSUES

One of the first of the important discoveries made with artificial radiotracers, soon after radiophosphorus became available, was the demonstration of the unexpectedly large and rapid incorporation of this radioisotope in calcified tissues. These results, and those of subsequent studies with radioisotopes, have shown that the skeleton and the teeth are not static structures but are dynamic tissues in which the elements are constantly turned over and renewed. The revolution in our concept of the physiology of the calcified tissues which was made necessary by the work with radioisotopes is well described by an extract from an address given by Professor August Krogh, on Sept. 10, 1936, a t the Harvard Tercentenary Celebration.‘ In this address, Professor Krogh referred briefly to the early work of Hevesy with radiophosphorus, then just beginning to be published: 5 8 and said: “To my mind the most interesting result is the extensive exchange taking place in bones and teeth. It is, of course, well known that the organism is able to draw upon the skeletal system as a reserve of inorganic salts but, even remembering this, I have never before been able to look upon the atoms deposited in practically insoluble salts and at a considerable distance from blood vessels, in the dentine for instance, as being in constant interchange with the atoms of the salts in tissue fluids and blood. This is, however, what the experiments clearly indicate.” The extent and the rapidity of skeletal mineral turnover, demonstrated with radioisotopes, are such as to indicate clearly that the inorganic ions of calcified tissues are intimately associated with all other aspects of the transport and metabolism of these ions. An example of a research which is frequently cited to indicate the high order of rate of turnover of skeletal phosphorus is the work reported by Hevesy, Levi, and Rebbe.6 These workers maintained a constant specific activity of plasma inorganic phosphorus of rabbits over a period of several weeks by spacing of repeated intravenous injections of radiophosphorus as inorganic phosphate. The specific activity of the bone phosphorus as a percentage of the specific activity of the plasma inorganic phosphorus gave the results in T A B m 1, which denote the fractions of the phosphorus in the bones which were renewed in 50 days. For example, about one fourth of the phosphorus of the femur and tibia epiphyses was replaced in 50 days. Smaller fractions of the phosphorus of long bone diaphyses were replaced but, even in this case, the quantity of phosphorus involved is considerable. The rate of turnover of skeletal calcium and sodium can be estimated in the living animal without the necessity of maintaining the plasma specific activity constant by following the rate and degree of dilution in the blood of intravenously injected radioisotopes of these ions. This procedure is applicable only to those inorganic ions which are located solely or mainly in bone mineral and

An Evaluation of the Role of Vitamins and Minerals in the Control of Caries

It has been possible to produce clear evidence that certain -vitamins and minerals are required for the formation of teeth of normal structure. It has been very difficult, however, to demonstrate that mature teeth require these nutrients in amounts greater than are needed to prevent gross and obvious signs of deficiency in other tissues. My first task will be to review the evidence in support of these statements. I shall, thereby, indicate why it appears that a mineral or vitamin deficiency must be present during the period of tooth formation if the tooth is to be affected in a manner which could lower its susceptibility to decay. As a sort of after-piece to the first topic, I shall attempt to present a summary of the somewhat controversial evidence which has been produced to show that single mineral or vitamin deficiencies are important causal factors in dental caries. The effects of inadequate diets on developing teeth cannot always be stated in quantitative terms. Our best device, at present, for indicating the importance of the effects produced by nutritional deficiencies on teeth is to compare these effects with those produced on another tissue, such as bone. When such comparisons are made, we shall see that in many circumstances, developing teeth appear to be less liable to alteration by metabolic abnormalities than is forming bone. We shall also see that mature teeth, in so far as any objective criteria are concerned, appear to be almost, if not entirely, removed from the direct influence of nutrition.

The Effect of a Low Calcium and Vitamin D Free Diet on the Skeleton and Teeth of Adult Rats1

Several investigations have shown that the histological structure and the chemical composition of the continually growing incisor tooth of the rat may be altered by deficient diets (1, 2, 4, 6, 7, 13). Toverud (14) investigated the influence of a calcium low diet and pregnancy on the calcification of bone and teeth of rats. The ash content of the femur diaphysis was greatly decreased, while that of the incisors and molars was 3.5 per cent and 2.0 per cent, respectively, below the average for the normal control rats. Schour (12) has concluded, from a review of his work and that of others, that the mineral phase of mature teeth of limited growth is not susceptible of alteration. However, it does not appear that the effect of a low calcium and vitamin D free diet on the composition of the bones and of the enamel and dentin of the separately examined incisor and molar teeth of adult rats has been studied.

H. Trendley Dean Memorial Award for Research in Epidemiology and Dental Caries

I am pleased to join the company of Francis Arnold, Roy Blayney, and John Knutson who earlier received the H. Trendley Dean Memorial Award. It may be that I am near the last of the Dean Awardees who knew this remarkable, interesting, and warmhearted man. Accordingly, I thought it appropriate for me to relate to the Association something of Doctor Deans personality and of his work. Doctor Dean served as a captain in the Army Dental Corps with a field artillery unit in World War I and, as a result, he became imbued with the ideals and traditions of the old Army. His devotion to duty, his unquestioning patriotism and his unhesitating acceptance of responsibility were a natural part of his character. Nevertheless, these attributes were, I am convinced, enhanced and formalized by his continued military associations. Doctor Dean was first commissioned in the Public Health Service in 1921. Ten years later he was assigned to duty in dental research. I think it probable that Doctor Deans first paper, published in June. 1930, while he was a clinician at the Staten Island Marine Hospital, caused Surgeon General Cumming to recognize his talents in investigation. The validity of the Surgeon Generals judgment was amply confirmed over the 22-year period in which Doctor Dean developed dental research in the Public Health Service from near nothing into that which we now know as the entire enterprise of the National Institute of Dental Research. Doctor Dean early gave his attention to the epidemiology of mottled enamel. The second paper of his career, published in February, 1933, was on this subject. His further observations showed conclusively the beneficial role of water-borne fluoride in reducing the susceptibility of teeth to decay. His utilization of these extensive experiments of Nature has furnished the most cogent and convincing support for the programs of controlled water fluoridation now practiced in 3,147 communities in the United States. Experiments were carried out with rats which showed the role of the skeleton in controlling and regulating plasma fluoride concentration and the nearly equal participation of the mineral of various bones in removing fluoride from body fluids.

The Stability of Aqueous Solutions of Sodium Fluoride

IlI conelulsive de(lnionstiratioln of the effectiveness of topical fluoride ap1plicatioln iii reduction of caries has raised the question of the stability of the sodium flutoride solutions use(l, particularly with regard to changes in 1)11. The l)unl)ose ot this investigation was to determine the action of light, dark, and atmospheric agocnclies, and of common. types of glass cootainens OI a 2 enr CEnt sodium fluoride solution over a period of six months.