Objectives:
This study presents data on the mineralization of the teeth in rats subjected to prolonged space flight. Although the pitfalls inherent in quantitative radiologic studies were kept in mind, there was an advantage in knowing the resorption in the spongy bone and the ambiguous result on dense bone in the same animals. Special efforts were made to standardize the regions of tooth structure measured, in the hope that masses of tissue in low experimental reactivity might not obscure more highly reactive sites.
Approach:
Heads were divided sagittally and x-rayed. Optical densities were measured on the films with a densitometer calibrated in American Standard Diffuse Density units. Limitations were principally: 1) that readings would be taken at some reasonable distance from the apex (region of tooth formation) to reach the mineralized band of structure and 2) that readings would not be over the tip of the tooth since the greatest part of the tooth was in fact closed in thin bone. While the density readings followed a logarithmic scale, the light transmission values were on an arithmetic percentage scale.
Results:
Although enamel values in the flight animals, both at recovery and 25 days postflight, seemed lower than controls, the difference was not significant. Other findings suggest a small amount of mineral loss may have occurred during the experimental period. Mineral repletion was not observed during the recovery period. The thin bone of the mandibular body was slightly reduced in both synchronous and flight rats, but rose to the level of vivarium controls after the recovery period. Changes of similar direction were found in the heavy bone underlying the molar teeth, suggesting that the stimulus of chewing was reduced in these groups, with restoration of a firmer diet during the recovery period increasing masticatory activity and improving bone structure.