RADIOAUTOGRAPHIC STUDY OF MINERALIZATION OF GROWING TEETH WITH LABELED CALCIUM

¹ Department of Anatomy, McGill University, Montreal, Quebec

Radioautographic studies of the mineralization process of dentin have been carried out with the help of radioactive calcium. Newborn and 3-day-old rats were injected subcutaneously with this radioelement and later sacrificed at various time intervals up to 9 days. Histologic sections of their teeth were examined by the radioautographic technique.

Calcification of growing dentin occurred by accretion of layers of mineral salts in its inner region adjacent to predentin (which itself is free of calcium and phosphate). As more new dentin is formed, the site containing the maximum amount of labeled salts becomes further and further away from predentin, although it remains by and large in the same position with regard to the outer surface of dentin. Radioautographs of teeth of rats given two injections of Ca⁴⁵ clearly show the incremental or layered character of accretional deposition. The rate of this deposition has been established to be 18 microns per day.

In addition, interstitial calcification throughout dentin is held responsible for some of the diffuse reaction. This mode of mineralization is particularly important in young animals. (The diffusion of the autographic band observed at later intervals is attributed to local phenomena of dissolution and reprecipitation of the dentinal salts.)

The enamel showed a gradient of mineralization extending over the young and transitional enamel and corresponding to the progressive increase in mineral content over these areas.

Under the present experimental conditions, the fate of phosphorus and calcium in the teeth showed no apparent differences.

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