Page 206 - My FlipBook

to make repairs by filling. Absorption would occur and fill-
ings would be loosened and thrown out, the same as such'
things are loosened and thrown out from the bone.
This much to bring your thought to the fact that we are
working on a special class of tissue ; the pathological condi-
tions are different from the pathological conditions we find in
other parts of the body. Or, in other words, the tissues of
the teeth once laid down are laid down once for all, they are
not changed afterward by physiological processes.
Now, for this kind of repair to be successful it must be
very minutely done. It has been said that it is not necessary
that a filling be water tight to exclude micro-organisms, and
since we have learned that micro-organisms stand in a direct
causative relation to decay, some persons seem to have the
thought that if we exclude micro-organisms we necessarily
prevent recurrence of decay. Now, gentlemen, do not allow
yourselves to harbor that thought for a moment. It is neces-
sary, in conditions of susceptibility to dental caries, that filU
ings be absolutely water tight. I want you to get a concep-
tion of what that means. Perhaps you have obtained a pretty
clear conception of the size of micro-organisms. A couple
of thousand of them can be laid in a straight row across the
head of a pin and not fall off, and vet they are large enough so
that by the use of the microscoi;e and microscopic methods
we can see them, handle them, count them and measure their
size. We cannot see the molecules of water ; they are so infi-
nitely smaller than micro-organisms that we gain no concep-
tion of the size we can't see them, count them, measure them ;
;
we have no means of getting at the size of a molecule of water,
or a molecule of acid, or a molecule of alcohol. They are in-
finitely small. Yet we must make our fillings so perfect that
a molecule of water will not go in between the walls of our
cavity and our filling material, that a molecule of acid will
not go in, because if micro-organisms happen to lie on the
margins of our filling and form their acid, the point is to pre-
vent that acid seeping in by the side of our filling, not sim-
ply to prevent micro-organisms from going in; if the. acid
p-oes in it will soon make room bv the solution of the lime
salts for the micro-organisms to go in. Now you will see
from this again why we should lay our enamel margins in
regions least susceptible to decay; but, do as we may, the

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