Page 102 - My FlipBook

98 THE TECHNICAL PROCEDURES IN FILLING TEETH.

is not SO perfect as that of gold, though apparently so easy
- when used in a very plastic state as to be very deceptive. Much
careful study and experience are required to work it well. Its
resistance to attrition is good, but its capability of resistance to
the force of mastication is less than that of gold.
Much of the difficulty attending the use of amalgam arises
from a lack of an understanding of its qualities. It is a metallic
compound in which each element entering into its composition
exerts its special influence upon the qualities of the product; and
these qualities are varied with every little change in its composi-
tion. These changes of qualities and the laws controlling them
are as yet understood by but few makers of amalgam alloys, and
are not generally understood by the dental profession. For
these reasons dentists are in constant danger of using amalgam
alloys with which good fillings can not be made because of
shrinkage or expansion of the material after being made into
fillings.
In secondary qualities its color is bad, so bad indeed that it
should never be used in the anterior teeth on this account. Its
conductivity of thermal changes is nearly equal to that of gold.
Its working qualities render it much more convenient than gold
in very large and difficult cavities. It can be placed much
quicker, less expenditure of force is required, and much less
time, but ordinarily perfection of adaptation is less certain.
Forms of Gold.

Gold is prepared in the form of foil for filling teeth. This
foil is prepared in various thicknesses, which are rated on the
basis of the number of grains in the sheet four inches square.
If a sheet of this size contains two grains it is called No. 2; if
three grains. No. 3; if four grains. No. 4, and so on up to what
is known as the heavy foils, such as Nos. 30, 60, 120, etc.
Gold is also prepared for use in filling teeth in the crystalline
form. These crystals are put up in various kinds of masses,
with about as many names as there are makers, and in these
forms possesses certain desirable qualities, especially convenience
of manipulation. In any of these forms, however, it is much
less readily kept in good working condition than foil, and for
this reason is not so certain in its working properties. It often
fails to weld perfectly, and especially it is often unreliable in