Beta-Track Autoradiographic Study of Teeth with CA45 *

Variations of calcium45 taken up in vitro by the enamel and dentin of teeth have been reported recently. Dentin appears to adsorb more Ca45 than enamel, and carious dentin more than non-carious dentin. Underwood and Hodge'0 measured the Ca45 differences in solutions of powdered non-carious enamel and dentin. Minder and Gordonoff7 have published auto-radiographs with Ca45 of intact rat teeth, and Belanger' of dentin caries in a human tooth. Amprino and Camanni1 described experiments with dog and human teeth. In the present study, autoradiographs were used to locate and measure the Ca45 taken up in vitro by sections of intact and carious human teeth. METHOD The method used was that of "track" autoradiography"'55which differs from "contrast" autoradiography as follows: 1. Track autoradiography involves microscopic study of the linear sequence of silver grains rendered developable in an emulsion by the passage of a charged (ionizing) nuclear particle. Contrast autoradiography consists of observation of paths of great numbers of nuclear particles in an emulsion appearing in the developed image as a dense mass of silver grains. 2. Readily detected tracks can be obtained with use of specifically designed nuclear particle emulsions and low energy beta-emitters, such as Ca4 (maximum energy 0.25 Mev), or alpha-emitters. Contrast autoradiography is possible with any radioactive isotope and a variety of emulsions. 3. Due to the nature of beta-particle traversal through an emulsion-that is, its ionization increases as its speed is decreased-tracks are obtained which at the starting point are far apart and at the terminal end are close together. Thus, the origin of the particle may be determined. With contrast autoradiography this is not possible. 4. With use of Cae, microscopic study of the location of individual tracks may be correlated with very small morphological structure. Contrast autoradiographs are a record of a large accumulation of tracks and consequently are limited to relation with large morphological structure.