Molecular sieve behaviour of normal and carious human dental enamel

In an attempt to understand the basis for the histological appearances of the dark zone of enamel caries a detailed study of it was made by polarized light in various media. It is shown to contain a system of minute spaces constituting a molecular sieve. As a result of this system, liquids with small molecules, such as water and methanol, may penetrate the dark zone freely, whereas the degree of penetration of liquids with larger molecular depends upon the size of the molecule. Such features are shown to varying degrees in both normal enamel and the translucent zone of the carious lesion. The spaces in the body of the lesion are sufficiently large to allow the inclusion of almost all liquids. Extensions of such studies on the three zones of the carious lesion and normal enamel allowed the percentage volume and approximate size of the spaces present in these areas to be assessed. On this basis the histological appearances of normal and carious enamel as seen in ground sections viewed by ordinary and polarized light in various media may be explained.