The Radiopaque Surface Layer of Enamel and Caries

Abstract

In 1934 Thewlis (1) made radiographic study of ground sections of human teeth and described what he regarded as hypercalcified outer layer. Hollander and Saper (2) considered this apparent radiopaque surface layer of the enamel as an artifact. In 1937 Thewlis (3) described microphotometer experiments indicating that the surface layer of the enamel is in fact hypercalcified. He found that there is a steady increase in calcification from the amelodentinal junction outwards and the outer enamel layer is in many cases markedly hypercalcified. Hollander and Saper (2) also noted that the radiopaque white line usually persisted on the surface of enamel over an area of decalcification corresponding to an early caries lesion. They concluded that this is also an artifact. Following this view the writer attached no significance to this line in grenz-ray studies of incipient caries lesions (4, 5, 6, 7). If the line is not an artifact, however, its significance needs investigation. Pincus pointed out the paradox of decalcification occurring in enamel under an apparently intact outer layer. He suggested that the radiographic effect is due to bacterial invasion of the organic matrix of enamel rather than to acid attack (8). To check up on the nature of the white line which persists on the surface of incipient caries lesions, the writer sent several grenz-ray negatives to Thewlis in England. He replied as follows: