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FILLING WITH GOLD. 107

and are accustomed to using their teeth very vigorously in
chewing food, will bear much heavier blows of the mallet than
those who have weaker peridental membranes and habitually use
their teeth more delicately. All of this must be considered in
filling operations and the force used limited accordingly. A
point of no less importance is the requirements as to solidity
and strength of fillings for different persons. Persons
with strong peridental membranes who use their teeth vigor-
ously require the strongest possible fillings. Persons who have
weak peridental membranes and who habitually use their teeth
feebly will not require the same solidity and strength in the fill-
ings in order that they may stand. In either case, however,
the adaptation of the gold to the margins should be the same,
and in all cases a density that will be moisture-tight is absolutely
required.
Because a patient can bear heavy blows of the mallet
is no excuse for using a plugger of large impacting area,
for the reason that such persons require very dense
fillings.
For condensing the main portions of a cohesive gold filling
the impacting area of the plugger should never be more than one
square millimeter, and generally plugger points of one-half to
I'a millimeter area should be used. The area of a plugger point
is practically the square of its diameter. That is, a point one
millimeter in diameter has an area four times as great as one- half
millimeter in diameter. Five-tenths multiplied by five-tenths
gives twenty-five as the area, while ten-tenths multiplied by ten-
tenths gives one hundred, or four times as much. This being
true, a reduction of the size of the plugger point below one
millimeter increases the condensing power of the impact in pro-
portion to the square of the reduced area, and increasing the
size of the point above one millimeter diminishes the condensing
power of the impact in proportion to the square of the increased
area. Twenty-five pounds impact or pressure on a point one-
half a millimeter in diameter is equal in condensing power to
one hundred pounds upon a plugger point one millimeter in
diameter. Therefore, to make solid fillings small condensing
points must be used.
We must not, however, use points that are so small
that they will penetrate the gold and chop it instead of