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152 THE TREATMENT OF TEETH

is made of gold is as easy of access, and can
consequently be as accurately filled as an ordinary
occlusal cavity. The gold top, or masticating sur-
face, does away with the curled- up edges and
chipping of margins that might take place if the
filling were made wholly of amalgam, and the best
properties of both materials are thus utilised. In
inaking these fillings the gold may be packed
directly on to the amalgam as soon as the latter is
inserted ; a matrix is generally used in order to pre-
vent the amalgam from being forced out of the
cavity or broken by the force used in inserting the
gold. It is also a convenience, if not a necessity,
to use a gold that will adhere to the unset amal-
gam ; several makes of crystal gold will do this, and
whichever is selected is generally used until it ceases
to become amalgamated, and a suflEicient layer of
gold is built up ; then the filling is completed with
crystal gold, or foil, as preferred. The filling may
also be started at the end of the occlusal step, or
occlusal undercut, remote from the amalgam, and
then gradually worked to, and over, the amalgam.
It is possible, by proceeding in this way, and
directing the force principally at right angles to
the long axis of the tooth, to dispense with the
matrix. The most convenient and generally satis-
factory method is to build up the amalgam to the