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GOLD AND TIN—TIX-GOLD. 365

can be used to advantage. These heavy golds—which are usually
rolled, not beaten—make a very dense filling, and, when great strength
and hardness are required, they are preferable to lighter grades.
AVhen a filling that is to be finished with heavy gold has been
brought to the point where the thick gold is to be added, the surface
should be as nearly level as possible, as it is difficult to adapt the heavy
gold to indentations and irregularities. The instruments used should
have the very finest serrations, if any at all. The gold can be put on
by hand or mallet pressure, or by burnishing with oval points having
very slight serrations, or with an ordinary burnisher. AVhcn done in
this way the burnisher is apt to become gold plated, and the instrument
will stick to and drag away the gold. AVhen this happens the gold
plating can be removed from the steel by rubbing on a piece of ink
eraser, or on flour-of-emery paper.
In using heavy gold great care is necessary that no portion of the
piece added be left uncondensed. Hard pressure must be applied to
every part of the gold, or it will flake oif and destroy the good appear-
ance, if not the utility, of the filling.

Gold and Tin.
Compound cavities are sometimes partially filled with tin and then
finished with gold.
At the present time it is a disputed question whether tin, if used as
above suggested, will not be dissolved out, after a time, by the action
upon it of the fluids of the mouth, leaving a cavity.
It can be used exactly as described for soft and cohesive golds, sub-
stituting the tin for the soft gold, or for a portion of it—for, as a rule,
much less tin would l)e used than soft gold.
If desired enough tin can be used to cover the cervical wall, followed
by sufficient soft gold to complete one-half or two-thirds of the filling,
the final finish being of cohesive gold.
The matrix wull be found of the same service as in the case of soft
and cohesive gold.
Tin-Gold.
The term " tin-gold " has been applied to the combination of tin and
gold when a sheet of tin and a sheet of gold have been laid one upon
the other, and rolled, folded, or crimped together, being then used in
the same manner as non-cohesive foil, depending on the " wedge " prin-
ciple for holding in the filling. Various authorities recommend differ-
ent proportions of the tin and gold to be used in this manner. All the
way from one-quarter of tin to three-quarters of gold, /. e. the propor-
tion of one-quarter of a sheet of tin and three-quarters of a sheet of