HORMONAL CONTROL OF TOOTH ERUPTION

II. THE EFFECTS OF HYPOPHYSECTOMY ON THE UPPER RAT INCISOR FOLLOWING PROGRESSIVELY LONGER INTERVALS

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.

The growth and eruption of the upper incisors of intact and hypophysectomized female rats of the Long-Evans strain has been studied metrically and histologically.

1. In intact rats a rapid increase in the radius of curvature was terminated at 120 days of age to be followed by a slow but steady gain until old age. The weekly eruption rate averaged 2.53 mm., and showed periodic variation and a decreasing gradient with increasing age.

2. Hypophysectomy effected an immediate drop of the eruption rate to one-half of the normal average; in ten weeks it was progressively reduced 76 per cent.

Stunting of dental growth was noticed two weeks after operation so that the size of the incisor of 500-day-old operated animals never exceeded that of 40-to 50-day-old normal controls.

Apical folding occurred in 60 per cent of the operated animals 160 days after operation. It showed a uniform histopathologic sequence: (1) dysgenesis of inner enamel epithelium with enamel aplasia, (2) disturbed calcification of mantle dentin, (3) agenesis of odontoblasts. Possibly under the influence of masticatory stresses, the little-consolidated apical structures became folded and gave rise to displacement of the odontogenic epithelium. Its pathogenesis seems to be involved in the panglandular syndrome of hypophysectomy.

3. In the old hypophysectomized rats, the unfolded incisors were comparatively larger and maintained a minimal eruption rate (0.55 mm.) in contrast to the folded ones which were smaller and had practically ceased erupting. This shows that eruption involves a basic process of growth.

The generally more drastic effects of hypophysectomy, in comparison to thyroidectomy, point to the action of a specific pituitary factor in addition to thyrotropin, which is to be identified with substitution therapy.