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120 DENTAL HISTOLOGY AND OPERATIVE DENTISTIIY.
illustrates the structure. It will be notit'cd tluit, in grinding, some of
the short twisted rods have broken out of the se(;tion.
Fig. 101 shows the tij) of" an incisor in labio-lingual section, and is of
interest in relation to the formation of nuirgins in step cavities in in-
cisors. The tip of this tooth has been worn off in use. The illustration
shows tliat the great inclination of the rods toward the axial plane in
the occlusal third of the incisors is such as to bring the wear almost at
right angles to the direction of the rods.

Dentin.

The structure of dentin is of comparatively little interest in the
present consideration, as its histological forms do not directly influence

Fig. 102.

Dentin at dento-enamel junction, showing tubules cut longitudinally: JV, dentinal tubules; D,
dentin matrix. (About 760 X.)

the cutting of the tissue in the excavation of cavities. Its histological
forms have, however, much to do with the penetration of caries and
with other considerations which are of importance to the intelligent
practice of operative dentistry.