Ultrastructure of the predentinal-dentinal border zone of human teeth exposed to basic chromium (III) sulfate. A method for contrasting of collagen fibrils.
An electron microscopic investigation was undertaken to study a method for contrasting predentine collagen fibrils by their cross-striations after exposure of tissue to chromium solution for various periods. After 1 day of treatment, the cross-striations of collagen fibrils in predentine were clearly visible. The contrast of the cross-striations increased with longer periods of exposure to chromium. This method makes it possible to study the orientation of crystallites as well as collagen fibrils.
A new technique for decalcifying thin ground specimens of adult human enamel.
Abstract A new decalcification technique is described for the recovery of the organic matrix from thin ground specimens of adult human enamel. An aqueous solution of chromium sulphate which has both fixing and decalcifying properties is used. The results are compared with those obtained when an adjacent part of the same ground specimen was decalcified with the hydrochloric acid solution of Brain (1962). Dependent on slight differences in pH of the chromium solutions, two different appearances of the recovered matrix are obtained: above pH $ 3.2 a structural matrix which is positively birefringent at refractive index 1.55, whereas below this pH a matrix which is homogeneous and non-birefringent and almost similar to the matrix obtained after hydrochloric acid decalcification. The two types of matrices are discussed and the one favoured on morphological grounds, the chromium sulphate structural matrix, is related to present concepts of the structure of the native enamel matrix.
X-ray diffraction studies of the insoluble protein in mature human enamel.
Abstract Tooth enamel protein was generally believed to be a keratin, but recent investigations on its amino acid content suggested some affinity with collagen. Up to now X-ray diffraction patterns of tooth enamel protein showing its nature could not be obtained because of the high content of inorganic matter in enamel and the fragility of the protein network after complete removal of the hydroxy-apatite. A special method of decalcification, however, made it possible to obtain X-ray diffraction fibre diagrams of the insoluble tooth enamel protein, showing that it does not belong to the collagen group of proteins. Rather does it belong to the keratin group, but it is definitely not in the completely extended form of the β-keratins. On the other hand it seems to be in a slightly more stretched form than the epithelial α-keratins, so that we prefer to call it δ-keratin, the structure of which and its connexion to the apatite crystal structure is the subject of further investigations. The correspondence between the repeat distances in tooth enamel protein and the main lattice translations of the apatite structure is striking.