Relationship between Thyroid Function and Resistance to Dental Caries

¹ Emory University School of Dentistry, Atlanta, Georgia

Five experiments were conducted using littermate groups of albino rats to investigate the relationship between thyroid function and resistance to dental caries.

In the first experiment, 20 groups of rats were fed (1) a control diet, (2) the same diet to which had been added propyl thiouracil, and (3) the same diet plus desiccated thyroid. The dental caries experience of the animals was increased by propyl thiouracil and decreased by desiccated thyroid.

The second experiment was conducted in a similar manner, except that the animals were sialoadenectomized at weaning. No difference in caries experience was observed in the three groups of animals in this experiment.

In the third experiment a comparison was made in the caries experience of 20 pairs of intact and thyro-parathyroidectomized animals. The removal of the thyro-parathyroid apparatus resulted in an increase in the incidence and extent of caries. Determinations were made on the pH on the teeth of these animals before and after eating. The pH readings in all instances were slightly lower in the test than in the control rats. These differences, though slight, were statistically significant.

The fourth experiment was conducted on twenty groups of animals to compare the effects of ingestion of desiccated thyroid in the food and by stomach tube. The administration of desiccated thyroid by either route reduced the caries experience.

In the fifth experiment 20 groups of animals were given (1) control diet plus water to drink, (2) control diet plus 20 ppm I₂ in the diet, and (3) control diet plus 20 ppm I₂ in the drinking water. The caries experience was identical in all three groups. The results of these experiments support the idea expressed by other investigators that the thyroid-dental caries relationship is mediated by the salivary glands. Elucidation of the mechanisms involved must await further experimentation.