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FORMA TION OF CA }~ITY B ORDJ-1RS. 2 1

corner as far as the dotted line a, and place a contour rilling. The
argument is, that the tendency toward cleavage in both enamel and
dentine is so great that this corner must be lost sooner or later, so that
it is best to fill at once as directed.
This again I think a grave error. Many deductions have been
made as to the of enamel and dentine which are
cleavage misleading,
because the experiments have been conducted upon dried teeth, out
of the mouth. Using the chisel upon these, the investigator finds
that very little force need be exerted, either to separate parts of
enamel along the line of the enamel-rods, or to cleave off slabs of
enamel from the dentine. In of this latter
underlying consequence
fact one gentleman has advised that where the border of decay
approaches nearly the gingiva, the narrow remainder of enamel should
be chipped away and the gingival edge of the gold allowed to rest
against che cementum. It seems to me that this is going to a great
and hazardous extreme in following a theory.
The truth is that we do not have to deal with dried teeth in our
at all we must it as
practice. Therefore if we consider cleavage study
FIG. 38. FIG. 39.

d

we have to contend with it. We are called upon to fill two classes of
teeth, those having living pulps, and those which are partly devital-
ized because of the loss of that organ. A wholly dead tooth, one in
which both pulp and pericementum have died, should invariably be
extracted.
In as to the form to be to such a as we are
deciding given cavity
discussing, it becomes important to determine whether the pulp is
alive or dead, and if dead, whether it has been freshly devitalized, or,
died from disease, the tooth-substance has been permeated by
having
putrescent matter.
Supposing that the pulp be alive and the tooth in a state of health,
I consider that it would be malpractice to remove the natural corner,
rather than
and my advice is based upon the result of practice upon
theories, which, though apparently logical, often prove unpractical.
The cavity borders should be curved as gracefully as possible with-
out making further encroachment upon the tooth-substance, and the