Page 140 - My FlipBook

124 THE TREATMENT OF TEETH
of mercury in order to obtain the best results. The
proportion of mercury has Httle effect on shrinkage
or expansion, but either too much or too httle
mercury will produce a weak amalgam that
crushes at far less stress than one that has
been properly mixed (Dr. Black).
The method of packing amalgams into a cavity
*ls of importance. Because it is a plastic material,
it is generally supposed that its perfect adaptation to
cavity walls is a simple proceeding. A few experi-
ments made out of the mouth will show that this is
not so easy as it seems, and the general method of
rubbing it against the walls with ball-ended bur-
nishers ' is productive of uncertain results. Dr.
Flagg says that after each piece is placed in
position, it should be crushed by a round-end or
flat-end plugger, and then tapped with light blows
from an appropriate instrument, until it is placed
in accurate apposition to the walls of the cavity.
The use of a mallet is " not only unnecessary, but
really objectionable. It is not needful that the
blows should bo in any degree forcible, but, on the
contrary, it is better that they should be such as
would more properly come under the signification
of ' taps.' The consistency of the amalgam should
be such as will permit of perfect adaptation of filling
to cavity wall, by tapping with light blows." " This