Mineralization of the Growing Tooth as Shown by Radio-Phosphorus Autographs. ∗

Abstract

The deposition of radio-phosphorus in growing molar teeth was examined in young hamsters with the help of the autographic technic. An injection of carrier-free radio-phosphorus (P³²) was given at the age of 4 days, that is, soon after the appearance of dentin and enamel in the germs of the first and second molars. The animals were sacrificed 1 hour, 6 hours, 1 day, 2 days or 4 days later. The jaws were fixed in a neutral formalin-alcohol mixture, embedded in celloidin without decalcification- sectioned as usual, autographed by coating the sections with photographic emulsion according to the “inverted method”(1), and stained with basic fuchsin. Dentin and enamel, but not soft tissues, showed autographic reactions. These were attributed to the presence of radio-phosphorus in a form sufficiently insoluble to be retained in the sections during the histological procedure. Presumably, the radio-phosphorus had become part of the complex phosphate salt making up the crystalline structures of the tooth (apatite).

At 1 and 6 hours after injection, the autographic reactions were of 2 kinds: diffuse reactions extending throughout dentin and enamel, and localized reactions restricted to definite parts of these structures. The presence of diffuse reactions was in itself proof that the circulating phosphate must have been able to enter dentin and enamel. Immature enamel is known to be permeable to dyes and other solutions( 2 ), and dentin to radio-sodium( 3 ) and radio-iodine( 4 ). These findings indicate that the “extra-cellular” spaces extend throughout these structures and provide the pathway for the diffusion of the circulating phosphate. Presumably, the radio-phosphorus responsible for the diffuse reactions was deposited by a process of “exchange” between the labeled phosphate circulating in the extracellular spaces and the surface phosphate groups of the crystals making up dentin and enamel( 5 ).