Page 153 - My FlipBook

differences in the structure of the teeth themselves ; there is ;
something else. Without knowledge of my work, apparently,
and I without knowledge of his. Dr. Williams published his
observations upon the enamel of the teeth of man and the
animals, in which he laid bare many facts relating to the
first beginnings of dental caries in the enamel. He found
always that the decayed area in its first beginning was over-
laid by gelatinous plaques which he could harden and grind
with the tooth. I had previously grown these gelatinous
plaques artificially and hardened them sufficiently to cut sec-
tions.
Now, in this we find that there are certain necessities
certain conditions controlling the placement of acids must
be brought about before caries of the enamel will begin, and
these conditions, briefly stated, are that micro-organisms
must be enabled to grow and attach themselves to the tooth
at some particular point, grow in this position and form a
gelatinous covering for themselves which will, in a manner,
exclude the saliva and confine the acids they form to that
particular point and allow them to act upon the enamel. In
other words, whenever micro-organisms have grown in a po-
sition in which the saliva or fluids of the mouth are freely
admitted to them, the acids they form are continually dissi-
pated in the saliva and lost, so far as their effect upon the
tooth is concerned. That is to say, the fluids of the mouth
never become so acid as to act upon the teeth ; if they did the
tooth would decay all over, not at particular points.
Now, in a careful examination, you will find, or have al-
ready found, that decay is confined to certain points of be-
ginning. The teeth do not decay all over. The greater
proportion of the tooth's surface is immune to decay. All of
that surface of tlie tooth that is exposed to the friction of
mastication is immune to decay, decay being confined to posi-
tions in which micro-organisms may grow comparatively un-
disturbed, as the pits, fissures, grooves, etc., that will hold
lodgments, and those parts of surfaces of the teeth that are
not kept clean by the friction of mastication. Then these
particular circumstances must occur before we may have
the beginnings of decay, no matter how susceptible the per-
son. Then differences in susceptibility come in to modify it.
Therefore, that which I said to you in a previous lecture
about the particular positions liable to decay just gingival of
T41