THE ACTION OF SODIUM FLUORIDE ON THE DENTIN AND PREDENTIN OF THE INCISOR TEETH OF RATS CONSUMING DIETS CONTAINING CALCIUM AND PHOSPHORUS IN VARIOUS RATIOS

¹ Department of Physiology, Medical School, University of Cape Town, Union of South Africa

1. This paper records the studies of the early action of fluorine on the incisor teeth of rats consuming diets of normal, high and low Ca:P ratio (diets 1, 2 and 3 respectively).

2. A hypercalcified line was first seen 18 hours after NaF injection in the distal predentin of the incisors of rats on diet 1. Measurements showed that the first part of this stripe was formed in predentin which was being laid down at the time of the injection. The stripe moved outwards with the incremental growth of the dentin and was preceded by a hypocalcified layer and the calciotraumatic line of Schour, Chandler and Tweedy. These latter 2 zones were formed in predentin laid down up to 16 hours before the NaF injection. In addition, a fine calcified line was found at and after 18 hours in the extreme proximal predentin. This line was also formed at the time of the injection.

3. The wide predentin of animals on diet 2 showed no calcification changes after NaF injection. The dentin had a hypercalcified stripe when the animals were allowed to live long enough for the matrix forming at the time of the injection to become calcified.

4. The proximal labial predentin of animals on diet 3 showed a fine calcified line 12 hours after the injection of NaF. This moved outwards with the incremental growth of the predentin and later a similar line was seen in the proximal lingual predentin and finally in the intermediate predentin on both sides. Measurements showed this line to be present in predentin forming at the time of the injection. The animals on this diet were very liable to tetany after NaF injection.

5. The above results are discussed with relation to the action of fluorine on the teeth and to some problems of dentin calcification. It is concluded that fluorine acts primarily by altering the composition of the blood and that the calcification changes produced thereby are variants of the normal process.