Page 230 - My FlipBook

198 HISTORY OF DEXTAL SITRGEEY

lar, the average of four blocks being 4.37 per cent, in one case and 2.58 per
cent, in another case. If the gold was hammered the shortening was re-
duced to about one-half of one per cent., but if the hammered gold was
annealed the shortening was greater than of similar pieces cut from
the cast ingot. Tests were also made of fillings of similar size made by
a dozen ditferent operators, most of them making three or four,
and some by Dr. Black himself, about fifty in all. These showed
a very wide range in weight, or specific gravity, and in strength of
resistance to .stress. The specific gravity of cast gold is about 19."^, and of
hammered gold 19.3 to 19.35. The tested fillings (made in a steel matrix),
varied in specific gravity from a ma.ximum of 19.38 in one made with a
heavy mallet with the intention to obtain the maximum density, down to as
low as lit.?. The sliortening under a pressure of two hundred ])ouuds varied
from nothing, in those of extreme density, to as much as 3"2.37 per cent, under
one hundred and fifty i30und.s pressure. These fillings, made in the little steel
bo.xes by many different operators, indicated plainly enough that some men
are not in the habit of condensing gold fillings sufficiently to withstand the
force of mastication that may sometimes, perhaps often, come upon them.
The fillings also showed a wide difference in the closeness of adaptation to the
walls and margins and it was not always the case that the densest or hardest
fillings showed the best adaptation, though some of them did. Hardness de-
pends almost entirely on the amount of force used in malleting the gold, while
closeness of adaptation is chiefly a matter of skill and judgment. These fill-
ings, together with clinical obser^-ation of fillings seen in the mouth of
patients, seem to justify the opinion that too large a proportion of gold fillings
that look well when first made are either condensed so imperfectly as to
yield under force of mastication, or so imperfectly adapted to walls or margins
as to be sjwiled liy leakage, and many good operators believe that the dis-
credit of gold for filling teeth by considerable numbers of the dental profession
is caused by the very numero\is instances of the want of skill or knowledge
or patience in those who use it.
The publication of these papers may be fairly considered as opening the
way for a step in advance for operatiA'e dentistry. The work on amalgam
especiallv indicated what the chief trouble has been with amalgam fill-
ings for the past forty or fifty years, namely, shrinkage to such a degree
as to insure leakage sufficient to cause secondary decay in a few years in a vast
majoritv of cases. .\ small proportion of peo])le were so entirely immune to
caries that this did not happen and a small proportion of fillings were made