Effect of thyroxine and growth hormone on dentin production in maxillary incisors in the rat.

Dentin production and longitudinal growth of maxillary incisors in female rats, age 60--95 d, were determined by the tetracycline technique in hypophysectomized rats after administration of growth hormone and thyroxine during age 75--95 d. Hypophysectomy was performed at age 60 d. Administration of thyroxine resulted in a considerable increase in dentin apposition and longitudinal growth of the tooth. The same effect, but somewhat lower, was registered for growth hormone. Growth hormone and thyroxine administered simultaneously had an additive synergistic effect. Compared with the effect of hypophysectomy and of hormone administration on longitudinal bone growth and cortical bone remodleing the effect on dentin production and longitudinal growth of the maxillary incisors in the same rats is less pronounced and shows a different pattern in reaction, indicating differences in sensitivity for different cell systems and difference in endocrine control.