Interodontoblastic collagen (von Korff fibers) and circumpulpal dentin formation: an ultrathin serial section study in the cat.

The collagenous fibers of von Korff pass from the dentin matrix between the odontoblasts into the dental pulp. Although collagen fibrils are known to be present between odontoblasts, the existence of von Korff fibers has remained controversial. This may be because their continuity between the dentin matrix and the pulp has not been demonstrated ultrastructurally. In this study we have examined the odontoblast layer in the middle to apical regions of perfusion-fixed permanent canine teeth of cats by using transmission electron microscopy. Ultrathin sections of demineralized specimens revealed frequent bundles of collagen fibrils 1) entering the odontoblast layer from the predentin, 2) present between odontoblast cell bodies, and 3) passing from between the odontoblasts into the pulp. The question of continuity of these bundles from the predentin, across the odontoblast layer into the pulp was examined in ultrathin serial sections. Unbroken continuity of a collagen bundle from the predentin between the odontoblasts into the pulp was established in a reconstruction of one series of 22 serial sections and was very strongly suggested by a number of other series in which the numbers of available sections restricted their full visibility. This investigation has shown, therefore, that classical von Korff fibers are present and that these fibers are present in fully erupted teeth with closed apices, i.e., at a time when secondary circumpulpal dentinogenesis is in progress. The findings call for a reexamination of the question of von Korff fibers during mantle dentinogenesis and primary circumpulpal dentinogenesis. Resolution of their existence at the earlier stages of dentinogenesis should be possible by using the ultrathin serial-sectioning technique.