Effect of Estrogen, Thyroxin, and Their Combination on Dental Caries and Salivary Glands in Ovariectomized and Intact Female Rats

¹ Department of Physiology, School of Dentistry, University of Pittsburgh, Pittsburgh, Pennsylvania

Ovariectomized and intact weanling female rats were maintained, ad libitum, on a cariogenic diet and were supplied with distilled water; they were given subcutaneous injections of estradiol benzoate, thyroxin, or their combination two or three times a week for 17 or 12 weeks, respectively. The number and score of dental caries were examined. Histologic studies were made on submandibular, parotid, thyroid, and adrenal glands, and plasma PBI levels were analyzed.

It was found that estradiol and thyroxin treatments caused, respectively, an increase and a decrease in dental caries activity in comparison with the controls. Thyroxin given simultaneously with estradiol caused decreased thyroid epithelial height and increased plasma PBI level, but did not prevent the increase in dental caries activity that ordinarily occurred in estradiol-treated rats. Estradiol and thyroxin given alone to the intact rats caused, respectively, a significant decrease and increase in the mean absolute submandibular and parotid weight.

The mean diameter of the submandibular granular tubules was decreased in estradiol-treated rats, but it was increased in thyroxin- or estradiol-thyroxin-treated rats in comparison with that of the controls. The mean numbers of the submandibular granular tubules per square area were significantly decreased in thyroxin- or estradiol-thyroxin-treated rats, however.

Thyroxin still appeared to be effective in stimulating or maintaining the normal salivary glandular development in the presence of excessive estrogen, but did not prevent the increase in dental caries activity in estrogen-treated rats. No significant difference in mean plasma PBI levels of control and estrogen-treated rats was observed.

It was suggested that the cariogenic effect of estrogen is not entirely mediated via the decreased thyroid function and the altered histologic structure of the submandibular glands. Estrogen may effect a change in the chemical compositions and physical properties of the teeth and possibly of the saliva, or estrogen may effect some other unknown changes in the oral environment to facilitate dental caries formation.

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