Page 143 - My FlipBook

ward. Having- penetrated the enamel the acid spreads within
the dentin and this shallower portion (referring to chart) may
have all of lime salts removed ; this deeper portion con-
siderable of "lime salts removed; in a still deeper por-
tion less and still less until we come to a line where it is
difficult to determine, perhaps, whether any lime salts have
been removed or not. Now, the decomposition of the basic
substance progresses in a similar way, being broken up little
by little progressively from without inward ; so that the for-
mation of a cavity follows slowly the solution of the lime
salts. It will often occur that the solution of lime salts
has progressed very much more rapidly than the decompo-
sition of the basic substance of the tooth, and in that case
we will find a very large amount of material that
is soft and leathery or spongy, may be easily cut with an
excavator, or a spoon excavator may be passed along the
margin of the softened area and the whole thing turned
out in a body, soft enough to cut through with a razor or
sharp knife. Occasionally w^e will see almost the entire
interior of the enamel cap, i. e., almost the entire dentin,
softened in this way, and yet the basic substance not broken
up ; a very slight cavity exists, and yet, when the softened
material is removed, almost the entire dentin of the crown
.of the tooth will be found to have been removed. This oc-
casionally happens ; it is the exception to the rule. The rule
is that the removal of the softened material, or the decom-
position of the basic substance, follow^s fairly closely the
removal of the lime salts.
In its beginnings dental caries has some very definite
peculiarities to wdiich I want to call your attention now and
will want to call your attention to them very frequently during
the progress of these lectures. It is a matter of the utmost
importance that we study these peculiarities of the begin-
nings of dental caries wath care that we may know them
well and combat them in our practice.
Caries never begins upon smooth, zvorn surfaees of the teeth.
That is a pretty strong expression, but it is correct. Now,
as very much the larger proportion of the surface of the
tooth is worn in the process of mastication, the larger pro-
portion of the surface of the tooth is immune to the begin-
nings of dental caries. Mind you, I speak of the begin-
nings of dental caries in the surface of the enamel, not of

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