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GOLD AS A FILLING-MATERIAL. 65

which I think many failures depend. I like to have all three kinds
of cohesive gold in the office. A cavity may be filled with either,
and in There
exclusively, many smaller cavities it is wise to do this.
are many other cases where the employment of two and sometimes
of three kinds of gold is expedient.
Of the plastic golds, I have had the most experience with Watts' s
This is a form of gold much and much
crystal. praised by many,
condemned by others. Its strongest advocates undoubtedly use it
too frequently, and place too much dependence upon it, while those
who condemn it utterly are simply ignorant of its virtues. They have
probably endeavored to use it as they do other plastics, forgetting
that it is a metal. Its chief virtues are : first, its great cohesiveness,
no gold having more, if any has as much ; second, the small amount
of force necessary for condensing it ; and third, the fact that it will
remain where it is placed, having no tendency to ball up, and roll
about in a cavity.
Its first advantage, cohesiveness, makes it especially useful in many
instances, of which I will enumerate a few. It has occurred to many
that while inserting a large filling, leakage has made some portion of
the surface of the non-cohesive. The effort to add
partly-made filling
another pellet of foil is vain. If the surface be touched with alcohol
and then dried with hot air, crystal gold will adhere, provided it is
used in small pieces. I have even removed the dam, where a large
a^ a
gold filling was but half finished, and continued the operation
subsequent sitting, the gold meanwhile having been protected by
gutta-percha, though of course this did not keep it dry. Such a pro-
cedure should not be adopted unless the remainder of the cavity still
presents a retentive shape. Thus the adhesion of the crystal gold
in such cases.
becomes more a matter of convenience than of necessity
Where a filling becomes wet before completion, it being in an exposed
as the corner of a central incisor, if it be dried with alcohol
position,
and hot air, as before advised, and then a clean rose bur be used to
freshen the whole surface of the metal, crystal gold may be made to
unite firmly with it, and the filling may then be safely completed.
If, while filling, a bit of the edge of a cavity crumbles away by acci-
dent, or when finishing it is seen that there is a slight imperfection
along the border, crystal gold is invaluable. The tiniest burs may be
used to cut a groove or pit, and this may be more perfectly filled with
crystal gold than any other, because of its cohesiveness, and more
particularly because it can be torn into smaller bits without losing its
pliability.
A third use is where a portion of a cavity which is very inaccessible
the use of the mouth-mirror. Such a place might occur
requires
where, in an approximal cavity in an incisor, the palatal depredation
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