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BEVELING ENAMEL MARGINS 137
that material. The enamel is an extremely brittle substance,
owing to its chemical composition (being composed largely
of inorganic salts) and its histological structure. Micro-
scopically, it consists of numerous layers of hexagonal shaped
rods, united together with cementing substance. Each
individual rod is composed of prisms placed end to end, each
of these also united (much more firmly than the rods) with
cement substance. Mechanically, the material resembles a
Fig. 169.—Diagram showing the Fig. 170.—Radiation of the enamel rods on
direction of the enamel rods on a bi- a molar. Mesial view. (Diagrammatic.)
cuspid. Mesial view.
brick wall, the prisms representing the individual bricks and
the rods representing a single layer of them, the layers being
superimposed one upon the other. The difference, though,
between the enamel and the brick wall is that in the wall the
various layers run parallel to the surface on which they are
placed, while in the enamel they run perpendicular to the
dentin, radiating around in various directions, depending on
the surface from which they are viewed, one end of the rod
lying on the dentin, the other being at the surface.
that material. The enamel is an extremely brittle substance,
owing to its chemical composition (being composed largely
of inorganic salts) and its histological structure. Micro-
scopically, it consists of numerous layers of hexagonal shaped
rods, united together with cementing substance. Each
individual rod is composed of prisms placed end to end, each
of these also united (much more firmly than the rods) with
cement substance. Mechanically, the material resembles a
Fig. 169.—Diagram showing the Fig. 170.—Radiation of the enamel rods on
direction of the enamel rods on a bi- a molar. Mesial view. (Diagrammatic.)
cuspid. Mesial view.
brick wall, the prisms representing the individual bricks and
the rods representing a single layer of them, the layers being
superimposed one upon the other. The difference, though,
between the enamel and the brick wall is that in the wall the
various layers run parallel to the surface on which they are
placed, while in the enamel they run perpendicular to the
dentin, radiating around in various directions, depending on
the surface from which they are viewed, one end of the rod
lying on the dentin, the other being at the surface.
