Optical Microscopic, Microradiographic and Scanning Electron Microscopic Observations of Some Dens Invaginatus

The simple or branched invaginations of dens invaginatus were histologically observed by using 6 ground sections (2 molars and 4 incisors). In all the teeth, the invaginations have hypoplastic enamel showing a variable thickness and an irregular outline. The relatively thick enamel irregularly arranged the Retzius lines and prismless structures were present in the innermost layers besides the surface layers. In 4 teeth, enamel-free areas were partially found on the dentin surfaces, and afibrillar cementum occasionally covered the enamel-free areas as well as the enamel surfaces. The dentin of a molar tooth had giant tubules between the dichotomously branched invaginations and other giant tubules opened into the invagination floor. Some dentinal tubules in the terminal regions had abnormal structures similar to the Tomes' granules adjacent to the invaginations of the 2 molar teeth. In all the incisor teeth, a seam line of dentin fusion or a slit line succeeding to the dental pulp cavity was present in the dentin under the linguogingival ridge. Thus, the gross formation of dens invaginatus also causes the invagination to form locally abnormal structures, especially in the enamel regions; although some findings have been previously reported.