Scanning electron microscopic study of giant tubule content in bovine dentin.

Incisal segments of unerupted permanent incisors from 1/2-1 1/2-yr-old calves were fractured along an axiomesiodistal plane exposing the organic components within the giant tubule lumina situated in this plane. Along the lining wall of the pulpal vascularized giant tubule portion, large flattened cells and a few odontoblasts were situated in shallow depressions. Just incisal to the vascular loop numerous cells were seen, both along the giant tubule wall and enclosed within a loosely textured collagenous matrix. Further incisally, the number and size of the cells decreased, and they were embedded in a compact unmineralized collagenous matrix that completely filled out the giant tubule lumina. This matrix consisted of fibrils regularly arranged in separate bundles whose orientation was mainly longitudinal. The incisal origins of the giant tubules were filled with coarse fibrils being about three times thicker than those of the luminal matrix and those of the circumpulpal dentin proper.