Scanning electron microscopic observations of microcanals and continuous zones of interglobular dentin in human...

Scanning electron microscopic (SEM) observation of the coronal dentin of deciduous incisors revealed microcanals and continuous zones of interglobular dentin (CID) in the labio-lingual central portion of dentin beneath the incisal edge. The microcanals, which were clearly larger than dentinal tubules, extended from the incisal edge to the vicinity of the pulp cavity. They were located essentially in the labio-lingual central portion of the dentin and were arranged linearly in the mesio-distal direction. Inside the microcanals, collagen fiber bundles were arranged almost in parallel with the canal long axis: spherical bodies 1.0-2.5 microns in size made up of assemblies of regular parallelpipedal crystals and granulated crystals were also seen. In some instances, bacteria had invaded incisal dentin that had been exposed by attrition. The CID were made up of interglobular dentin aligned with the long axis of the tooth. As was true in the case of the microcanals, several zones were arranged irregularly in the mesio-distal direction, generally in the labio-lingual central portion of the coronal dentin. The CID were confined to about half the width of the incisal edge dentin on the incisal edge side and did not appear in the vicinity of the pulp cavity. Within the interglobular dentin itself, which was surrounded by calcospherites, were longitudinal collagen fibers connected with dentinal tubule walls inside calcified dentin and collagen bundles forming a network with those fibers. Spherical bodies 1.0-1.5 microns in size were observed attached to the surfaces of the bundles or distributed among these fibers. In some instances, the microcanals penetrated the CID.