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364 COMBINATION FILLINGS.

cohesion can be had between soft and cohesive gold. Tn large cavities^
after the first pieces of soft gold have been pnt in place and cohesive
gold worked in, the two kinds of gold can be uavxX interchangeably. A
piece of soft gold can be placed against a portion of the wall of the cav-
ity, followed by a [)iece of cohesive, which is first attached to the cohe-
sive portion of the filling and then nsed to force the piece of soft gold
to its place. Dexterity and tact in nsing these t^vo golds together can
only be obtained by experience, and carefully noting the characteristics
exhibited under manipulation.
In compound cavities soft gold })lays a most important part. Fill-
ings in these cavities fail, usually, at the cervical wall, and too much
care cannot be taken in making them at this place as nearly perfect a&
possible. For this purpose it is now generally conceded that soft gold
is much better than cohesive.
A suitable matrix will greatly facilitate the operation and assist in
obtaining the proper contour. The thorough packing of the gold will
also be much simplified if the cavity is so prepared that the walls form
no acute angles with the matrix, therefore attention to this point is
important.
A matrix having been properly adjusted—the one described under
" Amalgam and Gold " fillings is recommended—one-half or two-thirds
of the approximal portion of the cavity is filled with soft gold. For this
purpose soft cylinders, ropes, pellets, or mats can be used. Great care
must be taken in condensing the gold that it does not tilt under the
instrument. The pressure should force the matrix away from the tooth
enough to allow the gold to be condensed just a little over the edge of
the cavity, so that when the burnisher is applied there will be sufficient
gold to make a flush filling.
When all the soft gold has been put in that th(^ case will allow, the
cohesive gold should first be added in very small pieces in order to
facilitate the driving of it into the soft gold, so as to make a strong
union between the two. For this purpose very small cohesive cylin-
ders or No. 3 or No. 4 foil will generally be used, but sometimes No.
30 or No. 60 foil or some of the plastic or crystal gold can be used.
The filling can be finished with any cohesive gold, that kind being^
selected which the operator has found by experience he can best manipu-
late under the existing conditions. He will also remember, as the
work goes on, that a piece of soft gold laid against an exposed wall,,
and backed uj) with cohesive, as before described, will do much toward
securing a good filling.
(C) Soft, or Cohesive Gold, and Heavy Gold.—Fillings of soft
or cohesive gold, or a combination of the two, should sometimes be
finished with heavy gold. Nos. 30, 40, 60, and sometimes No. 120^