A microradiographic and electron microscopic study of tertiary dentin in human deciduous teeth

Abstract

This study deals with the structure of the inorganic phase of tertiary dentin, and is limited to dentin formation caused by mild or moderate stimuli, e.g., attrition or initial or shallow carious lesions. Ground sections were prepared from 20 human deciduous teeth extracted mainly because of orthodontic treatment, and contact microradiographs were produced. Based on visual inspection of the ground sections in reflected and transmitted light and microradiographic findings, small areas were dissected out and processed for electron microscopy. In the tertiary dentin formed in the pulp horns the number of tubules was reduced, while in that on the side walls of the pulp there was often no marked reduction in the number of tubules. Several tubules could be followed from the physiological (primary and secondary) dentin into the tertiary dentin, and a change in the direction of the tubules was often noted. Interglobular dentin was frequently observed, and in some teeth incremental lines with alternating high and low mineral content were seen, indicating that tertiary dentin, like other mineralized tissues, is subject to biological rhythms during formation. When studied in the electron microscope, tubules with varying size and distribution as well as occluded tubules with a high mineral content were seen. The tubules often had an irregular circumference with projections of mineralized tissue protruding into the lumen. Highly mineralized peritubular dentin was rarely observed. The present results show that orthodentin is formed when dentin in primary human teeth is exposed to mild or moderate stimuli.