angement in the tooth means interruption of circulation, and young
teeth will be most affected.

"Thermal effect depends on heat-conducting power [gold is nearly four
times as good a conductor of heat as tin] and also on specific heat, so
the more the latter approaches that of the tooth the less it is liable
to produce sudden changes [thus favoring tin]. Specific heat manifests
itself by the speed of changes, while the heat-conducting power
influences the intensity [then the intensity of heat in a gold filling
would be three or four times as much as in a tin filling]. In speed gold
produces this change in one-tenth of a minute" [tin in one-fifth,--that
is, gold absorbs heat and expands about twice as fast as tin].

In 1838 Dr. J. D. White introduced sharp-wedge-shaped instruments for
filling teeth, and he claims to have been the first to use them; they
pack laterally as well as downward, and present as small a surface to
the filling as possible, so that the greatest effect may be produced
upon a given surface with a given power. Rolls of either tin or gold are
made by cutting any desirable portion from a sheet of No. 4 foil; cut
this portion once transversely, place on a napkin or piece of chamois,
then with a spatula fold a very narrow portion of the edge once upon
itself; then with the spatula resting on the thickened edge draw the
spatula away from it with gentle pressure, and the foil will follow in a
roll.

[Illustration: FIG. 9.]

The old method of using rolls, ropes, and tapes or strips is the same,
but we will describe one method of using tapes. (See Fig. 9.) A _strip_
is a single thickness of foil in ribbon form; a strip folded lengthwise
once, twice, or more forms a _tape_ of two, four, or more thicknesses of
foil. The tin foil should be cut into strips and folded into tapes
proportioned in width and thickness to the size of the cavity. One end
of the tape is carried to the bottom of the cavity and then forced
against the side opposite the point where we intend to finish; now
remove the wedge-shaped plugger and catch the tape outside of the
cavity, and fold another portion against that already introduced,
letting all the folds extend from the bottom to a little beyond the
margin. Proceed in this manner, with care and sufficient force, until
the cavity is full, using for the last folds a small instrument.
Condense the surface with a large plugger, then go over it carefully
with a small instrument, and if an