Selvig, KA. An Ultrastructural Study of Human Cementum Formation. ACTA Odont. Scand. 22:105, 1964.

Aim

Molar teeth of young and adult mice were selected as specimen material in order to examine an attachment apparatus comparable to that of human teeth.

Methods

• The teeth with surrounding periodontal tissues were dissected out from 18-, 24-, and 78-day old albino mice.
• Thin sections were examined in the electron microscopy.

Results

• In the he earliest stage of the development of cementum and periodontal membrane, a zone of rather densely packed collagen fibrils was found adjacent to a thin layer of root dentin. These fibrils did not exhibit any preferred orientation. In the periodontal membrane, on the other hand, bundles of parallel fibrils were seen.
• The formation of cementum started by a simultaneous deposition of amorphous ground substance and of mineral crystals in close approximation to the root dentin. The cementum surface had an irregular outline, with protruding points corresponding to the points of insertion of each fibril or bundle of fibrils.
• In the underlying dentin, the matrix fibrils generally were oriented parallel to the long axis of the root, and often formed broad bands.
• A more advanced stage in the development of the attachment apparatus could be observed in the middle and cervical root portions of the same teeth. A greater amount of cementum was found in these areas than in the apical region, and thick bundles of collagen fibrils could now be traced from the cementum surface to the collagen fibers of the periodontal membrane.
• Following eruption of the molars into the oral cavity, a change in orientation of the periodontal fibers became evident; they now were arranged more or less at right angles to the cementum surface.
• In the 78-day old animals, there was a marked increase in thickness of the cementum and 2 layers could now be identified. The inner layer, which was 1 to 3 microns in width, was characterized by an irregular arrangement of the matrix fibrils. In the outer layer the collagen fibrils formed thick bundles which were oriented more or less at right angles to the surface. The thickness of the cementum on molars of the 78 day old mice varied considerably in different areas , the thinnest layer being in the order of 5 microns. In sections which were cut parallel to the root surface most fibrils of the periodontal membrane were seen in cross section.

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