RADIOAUTOGRAPHIC VISUALIZATION OF THE FORMATION AND FATE OF THE ORGANIC MATRIX OF DENTIN

¹ Department of Anatomy, McGill University, Montreal, Quebec

Sodium bicarbonate labeled with C¹⁴ was administered to newborn and 3-day-old albino rats, whereupon these animals were sacrificed at intervals of from four hours to fifteen days after injection. Radioautographs of their teeth were prepared after decalcification.

The radiocarbon of bicarbonate is incorporated into the organic matrix of the dentinal organ. At the earliest time intervals studied, the labeled matrix lies in the predentinal area. But at later intervals, the reactive zone is farther and farther and farther away from the odontoblasts as new, nonlabeled predentinal matrix is laid down. In the process, the labeled matrix of predentin becomes dentin matrix proper.

Counts of the individual silver grains constituting the radioautographic image of the matrix show no decrease in its intensity during the fifteen-day period studied. Thus, the labeled matrix and, by inference the whole matrix of dentin, is a very stable substance (in contrast to C¹⁴-labeled substances formed in other organs).

The formation of dentin may be considered to occur in three steps: (1) the formation of a matrix framework, presumably a collagen, which first appears as predentin at the apices of the odontoblasts (this collagenous material is presumably the substance which is traced by means of C¹⁴); (2) the addition of large amounts of carbohydrate material to the framework of the matrix, changing it from predentin to dentin; and (3) the appearance of calcium phosphate crystals in the matrix of dentin.

Because of their simultaneous appearance at the predentinodentinal junction, it is suggested that the crystals may be bound to the collagen matrix of dentin by means of the carbohydrate material.