Page 296 - My FlipBook

so well borne for that reason. Greater care is therefore
necessary in the use of force. Still there are not many of
these teeth that will not readily bear the full fifteen pounds
required in condensing the gold for an hour or more, if care-
fully applied from the beginning.
The rules for extension for prevention should he carried
out very cojupletely. The most common point of failure in
this is at the labio-gingival and linguo-gingival angles of
cavities. If cavities are not cut very wide at these points, or
so as to include all of the habitually unclean area, decay is
almost certain to recur within a few years. The reason is
that microbic plaques, which form upon the filling, overlap
the margin onto the tooth structure at these points and the
concentrated acid formed under them is applied directly along
the margin of the filling, the tooth structure is softened, the
acid begins to seep in, the enamel rods fall away, micro-or-
ganisms enter, decay is re-established and the filling is soon
undermined and lost. This is the history of thousands of
otherwise good fillings in the proximate cavities of incisors.
So common is this failure in practice that a surprisingly large
proportion of the dentist's work with these cavities is the re-
filling of those .from which the fillings have been lost, or have
recurrence of decay about their margins, in patients twenty,
thirty and sometimes forty years old. Many of these are, of
jcourse, fro'm other technical faults than the one mentioned,
especially in older patients. But this one, when permitted
'to pass in these young people, will wreck fillings otherwise
perfectly made.
Cavities of this class that have never been excavated
are presented to us by patients of all ages, but especially
by those from twenty to thirty and on toward forty years
old. From long and very careful observation I am of the
opinion that nearly all of these have actually begun to decay
before the patients were twenty years old, but on account
of the coming of comparative immunity their progress has
been slow or often their decay has been stopped by com-
plete immunity to again start and make a little progress in
periods of temporary returning susceptibility. These are by
far the easiest cavities of this class to treat successfully. In
many of them any kind of filling that will stay in the cavity
will be apparently successful because there is immunity to

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