Page 152 - My FlipBook

lation of the acid into the substance of the enamel. Where ;
we find this percolation to a considerable depth we find that
the cementing substance between the rods is dissolved, leav-
ing the rods. This I have tried to illustrate here (indicating),
this showing the enamel rod, and in these conditions we often
get good views of that ball formation, the rod appearing as
if it was made up of one ball stuck to another, making long
rods of balls laid together. In this way the dissolution pro-
ceeds little by little from without inward, until the whole
thickness of the enamel is broken up. Now, there are cases
occurring in which the effect is very superficial, in which you
can scrape away the superficial effect of an acid and repolish
the surface and gain a new surface .that seems very perfect.
This you will often be able to notice in decays upon the labial
surface of upper incisors, where they are broad and a decay
has begun in the central portion of the area. In these you
may find this whitish streak following fairly close to the free
margin of the gum to the mesial and to the distal, and in this
position particularly you will be able to scrape away the
superficial effect of the acid, repolish, and gain a new enamel
surface that seems very perfect. It is well enough for you to
do this as an observation, because you will learn the appear-
ances produced by the beginnings of decay in so doing, but
when you have done this cut out and include in the area of
the cavity as far as this effect has been noticed, or a little
farther, before you make a filling.
Dr. Williams of London has recently thrown much light
upon this subject by his wonderful work in the preparation
of specimens. I will show you, later, photographs from his
specimens. He has become able to harden the gelatinous
plaques under which caries begins, retain the micro-organ-
isms and the partially broken up enamel and make sections
of this with all of the parts in position. So that we have be-
come able to study these processes more intimately than be-
fore. You will find Dr. Williams' description of these in the
Cosmos of 1897, running through a number of months, and I
advise you to read them with care.
I have been pointing out for some years that, while caries
is intrinsically the action of an acid, there was something
more, something lying behind, that controls that action.
Caries is not caused simply by acid conditions of the saliva
there is something else. Also, that caries is not caused by
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