Zur frage der organischen matrix in Bezug auf Dentin, Zement (und Knochen)

Abstract

Texture diagrams are often obtained when applying micro-beam electron diffraction techniques to ultra thin sections of undecalcified dentine. Morphological studies show that the crystallites which appear light in the electron microscope have often a parallel arrangement over small areas. Most are attached to dark segmented strands which the author considers to be fragments of collagen fibres for collagen fibres are not only surrounded by apatite crystals but are also penetrated by them. Collagen fibres and the crystallites attached to or growing between them are preferentially orientated in dentine only over small areas. Therefore it seemed reasonable to investigate the problem of the close connexion between collagen and apatite by examining cement and bone, which exhibit a more clearly defined preferential orientation over wider areas. Ultra thin sections of cement and bone often show that crystallites of similar size with a regular periodic spacing grow within the fibres. They simulate the known cross striations of intact collagen fibres. These electron microscopical observations and the small angle X-ray investigations of Engstrom and his co-workers on fish-bones indicates the influence of the 640 Å macromolecular structure on the manner of nucleation and the length of the crystallites. Furthermore Glimcher has shown by his in vitro mineralization experiments that only the collagen of the 640 Å period can act as a nucleus for apatite. The first nuclei of apatite appear evenly spaced and are related to the “bands” of collagen; it has still to be determined whether they are formed preferentially on the “bands” or “interbands”. This pattern of collagen and apatite for dentine disappears under the influence of caries. As the basic structural elements are dissolved, the orientation is lost.