Page 519 - Atlas of Histology with Functional Correlations

dentin is located at the periphery of the tooth. The latter, or secondary, dentin

lies along the pulp cavity, where it is formed throughout life by odontoblasts. In
the crown of a dried tooth at the dentinoenamel junction (2) are numerous
irregular, air-filled spaces that appear black in the section. In life, these
interglobular spaces (4, 10) are filled with incompletely calcified dentin
(interglobular dentin). Similar areas, but smaller and spaced closer together, are

present in the root, close to the dentinal–cementum junction, where they form the
granular layer (of Tomes) (12).

The dentin in the crown of the tooth is covered with a thicker layer of
enamel (1), composed of enamel rods or prisms held together by an

interprismatic cementing substance. The lines of Retzius (7) represent the
variations in the rate of enamel deposition. Light rays passing through a dried
section of the tooth are refracted by twists that occur in the enamel rods as they
course toward the surface; these are the light lines of Schreger (8). Poor

calcification of enamel rods during enamel formation can produce enamel tufts
(9) that extend from the dentinoenamel junction into the enamel (see Fig. 13.13).

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