Page 63 - My FlipBook

THE ENAMEL. 59

while operating at the chair. In preparing cavities one is han-
dHng the enamel all the time, and by noting the direction of the
cleavage and remembering that this cleavage follows the length
of the enamel rods, may be continuously studying their direction
in ditTerent positions upon any and all of the teeth. This study,
when pursued for some time, enables an operator to so place his
instruments as to split ofif the enamel easily in opening cavities,
which is of immense advantage in this work, as he will do it
easier and quicker. The operations will also be greatly improved
because of more perfect preparation of the enamel margins. He
will come to know very perfectly the direction of the rods, and
the proper inclination of the enamel wall in all positions.
One soon learns to feel for the direction of the enamel
rods with his cutting instruments and to take advantage of the
cleavage in cutting the enamel, and then readily feels this in
the formation of the enamel wall and its cavo-surface angle, and
knows when his enamel margin is firm and strong. Carry on
the study at the chair and become a rapid and strong operator.
The shaving up of the enamel in forming the enamel wall
should be looked to with great care. Those points at which the
enamel rods are more or less broken apart will generally appear
a little whitish, and in pushing a sharp edge lighdy along them
the loosened rods are easily dislodged in what appears as a fine
powder. By continuing this shaving motion the enamel wall
will become clear, and have a firm, vitreous appearance.
This condition of the enamel wall should always be obtained in
finishing the preparation of the cavity.
In the study of the enamel in sections and on the screen, it
has been seen that the lines of the grooves are weak lines on
account of the imperfect fusion of the enamel plates in coming
together during development. This is true even in those grooves
that are most perfecdy closed. But in very many cases they are
imperfectly closed, so that along these lines the enamel has no
strength.
It should, therefore, be the rule that, when in the prepara-
tion of a cavity the marginal lines must approach near
a groove, cut to the groove or past it.
This rule should be regarded as applying in all positions upon
the teeth if the cavity margin is parallel, or very nearly parallel,
with the groove. For instance, I will mention that in preparing