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FILLING TEETH 39

form of gold for producing accurate adaptation and
great density. Pellets or cylinders in the cohesive
or semi-cohesive state should be loosely rolled. The
best cylinders for cohesive or semi-cohesive work
are those purchased ready-made. As a rule they
are made of very thin gold, and the smaller sizes,
by reason of their delicacy, should be particularly
applicable against cavity walls when hand pressure
— probably owing to the ex-
used.
Cylinders
is
tremely thin foil of which they are made—are not
so reliable as foil, inasmuch as their quality seems
to vary. There is very rarely any trouble with foil
in this respect, but it is not uncommon to find one
bottle of cylinders work perfectly, and the next one
prove most unsatisfactory when the gold is annealed.
Heavy foil, such as No. 30 or No. 60, is principally
useful for surfacing fillings, although some operators
use the No. 30 heavy foil in strips of single thick-
ness for filling large cavities. In using heavy tape,
such as single strips of heavy foil or the lighter foil
folded into a heavy tape, it is usually necessary to
pack each layer flat, by attaching one end to the
gold already in place, and then carefully folding the
strip backwards and forwards on itself, layer by
layer, taking care to weld each layer absolutely flat
to the already condensed gold. If thin tape, such
as four folds of No. 4 foil (producing No. 16), is