Calcification of Teeth I. Composition in Relation to Blood and Diet* by Albert E. Sobel

These investigations were undertaken to test the hypothesis, of the authors, that there is a relationship between the inorganic composition of teeth and the fluid from which the tooth salts precipitate and that the composition of this jluid in turn is related to the blood serum. If this hypothesis is valid, it should be possible to vary the composition of teeth (during the period of active lime salt deposition), since the composition of blood serum can be regulated by the diet (l-6). The mineral phase is regarded as essentially the same in teeth and bone (7, 8). The variations in the composition of bone are well known (9) and were shown to be related to that of blood (5, 6). Hitherto no such relationships have been shown for teeth. In fact, some recent investigations, indicate that t,he inorganic composition of enamel is constant (10). There is, however, evidence that teeth are tissues in equilibrium with body fluids, Barnum and Armstrong (11) fed P32 to cats and found that it was present in both enamel and dentin after an interval. They then postulated that dentin phosphate may be in equilibrium with blood phosphate and that enamel phosphate may be in equilibrium with dentin phosphate. Greenberg (12) administered Ca* to rachitic rats and found that in the absence of vitamin D the uptake of the isotope in the femurs was greater than in the molars but less than in the incisors. In the presence of vitamin D, the uptake was greatest in the femur, less in the incisors, and least in the molars. Vitamin D had a minor influence on teeth but a major influence on bone. Armstrong and Barnum (13) fed Ca46 and P32 to albino rats and measured the amounts found in the teeth. They found that the turnover of the isotopes in the incisor dentin was two-thirds and in the incisor enamel about one-third of that in the femur. The molar dentin was about onesixth that of the femur and the molar enamel was from 1.5 to 3 per cent of the femur. These studies with isotopes indicate that the continually growing incisors may undergo changes almost as rapidly as bone and thus were considered suitable for our experiments. It is worth pointing out that the hypothesis