Radiopaque zones in the dentin beneath silicate fillings analyzed by electron microprobe

Seven teeth which showed radiopaque zones beneath silicate fillings were sectioned and studied by microradiography and electron microprobe analysis in order to elucidate which elements were responsible for the increased absorption of X-rays and whether the presence of carious lesions could be masked by foreign elements in the tissue. The Ca concentration was frequently found to be either slightly increased or reduced compared with radiographically unaltered dentin. Increased concentrations of F and Zn occurred in the radiopaque zones. The highest F concentrations (0.4--1%) were recorded in zones with an increased Ca content. The highest Zn concentrations (5--8%) were found in the three specimens having a reduced Ca content. The possible conditions responsible for the increased Ca, F and Zn concentrations are discussed. The results indicate that both Ca and Zn may contribute to the increased absorption of X-rays. The hypothesis that carious dentin may be obscured in intraoral radiographs by the presence of foreign elements in the tissue, was not substantiated.