Effect of Hypophysectomy on the Incisor of the Rat.

Abstract

The gross and microscopic anatomy and the rate of eruption of the incisors were studied in 2 groups of rats:

A. Completely hypophysectomized. 16 animals. Age at operation: 34 to 64 days. Age at death: 145 to 459 days. B. Littermate controls. Some were unoperated but most were unsuccessfully subjected to operation. Normal oestrous cycles and normal rate of growth. 9 animals.

Significant alterations were observed only in group A. The incisors of these animals were about two-thirds the size of those of the other groups as judged by planimeter readings of radiographs. In a few of the rats that lived longest after the operation there were seen definite waves on the exposed labial contour of the upper incisors. The rate of eruption was retarded about 7 days after the operation. This retardation was progressive until there was cessation of eruption.

The radiographs of the teeth showed no changes in the size or structure of the molars but indicated very clearly striking disturbances in the form and structure of the rapidly-growing incisors, especially the upper incisors. There were 2 areas to be distinguished in the radiographs and the histologic sections: an anterior zone which comprised about eight or nine tenths of the tooth, and a basal zone which contained the base of the pulp and was the seat of activity of Hertwig's sheath. The tooth substance was practically solid in the anterior zone. The labial contour in the anterior zone was not an arc of a circle but was interrupted by several waves. In the basal zone the labial contour was distorted and presented multiple narrow and deep foldings.

The histologic studies served to confirm and amplify the gross findings. The enamel-epithelium was lacking in the anterior zone and markedly reduced in the basal zone.