HORMONAL CONTROL OF TOOTH ERUPTION

III. THE RESPONSE OF THE INCISORS OF HYPOPHYSECTOMIZED RATS TO GROWTH HORMONE, THYROXIN, OR THE COMBINATION OF BOTH

¹ Division of Dental Medicine, College of Dentistry, the Institute of Experimental Biology, and the George Williams Hooper Foundation for Medical Research, University of California, San Francisco and Berkeley, Calif.

Replacement therapy in hypophysectomized rats served to identify the individual hormones controlling their odontogenic defects. It had the same qualitative effect shortly after the operation as well as after long postoperative intervals.

1. Growth hormone resulted in an increase in size without hastening the eruption rate. The latter remained in the young as well as old groups identical with the untreated hypophysectomized controls. Histologically, a "rejuvenation" of the connective tissues, without activation of amelogenesis, was observed. Administration of growth hormone to intact animals had similar effects.

2. Thyroxin treatment increased the tooth dimensions and accelerated the eruption rate 36 per cent in the young group and 46 per cent in the old group. Amelogenesis showed an improved pattern, and the vascularization of the tissues was restored.

3. The combination of both hormones showed optimal effects on eruption rate, and growth was characterized histologically by an amazing restoration of the completely atrophied enamel organ.

These observations thus lead to the conclusion that tooth eruption is presided over by the synergism of two hormones: The pituitary growth hormone, which stimulates the basic process of growth, and the thyroid hormone, which controls differentiation or maturation.