Peter J. Brekhus

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,

A Study of the Pattern and Combinations of Congenitally Missing Teeth in Man

According to the established dental formula, man has 32 teeth in his permanent set. It is frequently observed that many persons fail to develop 1 or more of their third molars, thereby causing the formula to lie between 28 and 32. A small percentage of persons also fails to develop even that allotted number. A tooth that has failed to develop is considered to be congenitally missing. The congenital deficiency in teeth cannot always be considered a detrimental anomaly provided there is no associated glandular defect which is more harmful in its reaction. Actually, the deficiency may represent a prediction of mans future dental formula. However, the deficiency is a disturbing factor for some persons, particularly if the absence of the teeth mars the facial features. Some affected persons are extremely conscious of their anomalies, especially if the anterior teeth are involved. Several theories have been offered to explain the congenital absence of teeth. One finds rather frequently in the literature the suggestion that the dental anomaly is associated with congenital syphilis. Although congenital syphilis can and does cause anomalies of the teeth, many persons who lack teeth or have abnormally shaped teeth are not syphilitic, and syphilitic stigmata and dental anomalies should be considered as separate entities. Congenitally missing teeth are considered by some investigators to be the expression of an evolutionary trend. A reduced dentition would thus be related to the attempt by nature to fit the shortening of the arches. In support of the theory, Schultz (11) cited the high frequencies with which the third molars in the posterior part of the arches and the upper second incisors and lower first incisors in the anterior portion are missing. However, he did not consider the second premolars which are also missing very frequently and yet do not have a like anatomical relationship to the ends of the arches. Those investigators who suggest that the theory of disuse may satisfactorily explain the congeniital absence of teeth in modern man will also find it difficult to explain the absence of second premolars. It is hard to establish a relationship wlth function or disuse which can explain why the first premolar, the second molar, or possibly the first

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.

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.

Study of Congenitally Missing Second Premolars and Space Factors in the Arches

The theory that human dentition is passing through a transitional stage leading to a decrease in the number of teeth is supported by most odontologists. Recently, Dahlberg (2) discussed this tendency and referred to the general trend toward a reduction in size, form, and number of teeth in human beings. The causal factors associated with this deficiency in the dental arches is difficult to identify. Several theories which have been presented, such as those by Montagu (3), Schultz (5), and others, seem to fit special cases but do not account for the congenital absence of teeth located in the premolar region of the arches. Mere chance alone does not explain the failure of some types of teeth to develop. In an earlier publication (1), the authors called attention to a definite pattern or regularity with which certain teeth failed to develop in 184 persons. They reported that the teeth most frequently congenitally missing were the upper second incisors, second premolars, and third molars. Any other tooth may on occasion be congenitally absent, but except for the lower first incisors the frequency is very low. Since that report, 232 new cases of congenitally missing teeth have been collected and studied. In tabulating the new data we find that the pattern of the congenital absence of teeth remains the same. The upper second incisors, second premolars, and third molars which are most often absent have also been found to be the most variable in pattern and size (6). It seems justifiable, therefore, to assume that some factor or factors control the variation in the development of these tooth buds. The authors of this report have suggested in a previous publication (1) that arch size and congenital absence of teeth seem to be separate entities. This contention is also borne out by our study of missing second premolars which is reported in the present paper. All interpretations are based upon examinations of the patients with a study of dental models made from impressions of the arches and complete oral radiographs of those persons.