A text-book of dental histology and embryology, including laboratory directions . ion withacids and alkalies the intertubular * material assumes afibrous appearance, as if bundles of white connective-tissuefibers had been fused together. There is apparently nodefinite arrangement of these fibers and there is no indica-tion of the arrangement of the substance in layers. The Sheaths of Newman.—There has been much discussionas to the character of these structures, which were firstdiscovered in 1863 by Newman. Some investigators havedenied their existence entirely, explaining the appearance 170 TH
A text-book of dental histology and embryology, including laboratory directions . ion withacids and alkalies the intertubular * material assumes afibrous appearance, as if bundles of white connective-tissuefibers had been fused together. There is apparently nodefinite arrangement of these fibers and there is no indica-tion of the arrangement of the substance in layers. The Sheaths of Newman.—There has been much discussionas to the character of these structures, which were firstdiscovered in 1863 by Newman. Some investigators havedenied their existence entirely, explaining the appearance 170 THE DENTINE in some other way. These structures are in no sense asheath surrounding the dentinal fibril and lying in thedentinal tubule, but are that portion of the matrix whichforms the immediate wall of the tubule. That this materialdiffers from that which occupies the rest of the space betweenthe tubules is certain, and is shown by the examination ofground sections, the action of stains upon ground sections,and the action of the matrix when boiled with strong acids Fig. 132. Dentine showing tubules in cross-section: Dt, dentinal tubules; D, dentine matrix:S, shadow of sheaths of Neumann. (About 1150 x) and alkalies. In Fig. 132, a photograph of a ground section,there is evidently a difference in the refracting index of theportion of the matrix immediately surrounding the the sheaths of Newman are composed of amaterial similar to that forming elastic connective-tissuefibers, and known as elastin. This substance is very resistantto the action of acids and alkalies. After the remainderof the intertubular material has been destroyed by boiling DIRECTION OF TUBULES IN CROWN PORTION 171 with strong acid, the sheaths remain like hollow elasticfibers, having the appearance of pipestems, which resistlong continued action of the boiling acid. Some authorshave suggested that the great elasticity of the dentine waslargely due to the presence of this substance. The Den
Size: 1893px × 1320px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectteeth, bookyear1912
