Myers JA - "The Role of Some Nutritional Elements in the Health of the Teeth and their Supporting Structures" Annals of Dentistry XXII (2):35-47 (1958)"There is recent experimental proof of the association of thyroid and iodine in the prevention of dental caries. Joseph C. Muhler and William G. Shafer, Department of Chemistry and School of Dentistry, Indiana University, have produced convincing experimental evidence that the feeding of desiccated thyroid produces a marked reduction of dental caries in the rat. It is in fact as effective as the administration of sodium fluoride. They have also shown that there is an increase in the incidence of dental caries when the thyroid hormone level in the blood is lowered by blocking the thyroid with thiouracil. More striking is the fact that when the activity of the thyroid gland is diminished through the administration of thiouracil, the addition of fluoride to the drinking water has no effect on caries. This same amount of fluoride given to the animals with an active thyroid had produced previously a 20 per cent reduction in the caries rate. This work leaves no doubt that thyroid activity is related in some manner to the incidence of dental caries in the adult rat, and that whatever effect fluoride has, it is mediated through a normally active thyroid mechanism."
- Studies: Thyroid & Caries