Online Encyclopedia


Online Encyclopedia
Originally appearing in Volume V26, Page 501 of the 1911 Encyclopedia Britannica.
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HISTOLOGY. If a section he made vertically through a tooth all the exposed part or crown is seen to be covered with enamel, which, microscopically, is composed of a number of fine hexagonal prisms arranged at right angles to the surface of the tooth, and formed chiefly of Bone Cement or Alveolar periosteum crustapetrosa or root-membrane From Ambrose Birmingham, in Cunningham's Text-Book of Anatomy. its various parts, and its structure. calcium phosphate with small amounts of calcium carbonate, magnesium phosphate and calcium fluoride, but containing practically no organic matter. The enamel rests on the " dentine," of which hard yet elastic substance by far the greater part of the tooth is composed. It is made of the same salts as the enamel, but contains in addition a good deal of organic matter and forms a structureless mass through which the fine " dentinal tubes " run from the pulp cavity to the periphery. Surrounded by the dentine is the " pulp cavity," which is filled by the tooth pulp, a highly vascular and nervous mass of branched connective tissue cells, which, in a young tooth, has a layer of epithelial cells, the " odontoblasts, " lying close against the wall of the cavity and forming new dentine. Slender processes (" Tomes's fibrils ") project from these cells into the dentinal tubes, and are probably sensory. A nerve and artery enter the apex of the root of the tooth, but it is not understood how the nerve ends. Surrounding the dentine where it is not covered by enamel is the " cement " or " crusta petrosa," a thin layer of bone which is only separated from the bony socket by the alveolar periosteum.
End of Article: HISTOLOGY
HISTIAEUS (d. 494 B.c.)
HISTOLOGY (Gr. Ler6c, web, tissue, properly the web...

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