Page 67 - My FlipBook

cavity it is then turned over the margins by wiping the metal toward the
margins with a pledget of cotton and by pressing toward the walls of the
cavity. After removing the goldbeater's skin or china silk the matrix
is again inserted into the cavity and is then filled with paraffin and wax,
which is forced gently toward the walls of the cavity with large burnish-
ers. If the matrix is for an approximal cavity a strip of rubber dam is
then placed over it with the wax in position and used as a means of
swaging the foil to the margins (Fig. 71). After this the matrix
is removed and the wax absorbed from it by placing a roll of cotton over
the wax and heating it to its melting point. The cotton absorbs the molten
wax and leaves a clean matrix.
When matrices are constructed of gold, platinous gold or platinum
foil 1/2000 of an inch or heavier, most of the burnishing should be done
directly on the metal with proper burnishers (Figs. 66 to 69). A piece
of foil large enough to be held between the thumb and forefinger without
interfering with the burnishing is placed over the cavity (Fig. 72). It
is pressed into the cavity with a pledget of cotton ; then with a large ball
burnisher the metal is gently and gradually forced into the cavity, when
smaller burnishers are used to gradually conform the foil to the seat.
A strip of heavy rubber dam is then placed over the matrix, which is
filled with tightly rolled cotton, and with direct pressure, the foil is
turned over the margins of the cavity and the adjacent surfaces of the
tootb, to prevent wrinkling of the matrix at the margins (Fig. 71). The
matrix is now withdrawn from the cavity and the surplus metal is
trimmed so that its edges will rest uniformly on a flat surface. It is now
replaced and held firmly against the walls of the tooth with the thumb
and forefinger and reburnished with a series of ball burnishers begin-
ning with the largest, then continuing with smaller ones until the matrix
conforms to all walls of the cavity and its margins (Fig. 73). The mar-
gins of the matrix are now burnished with the special marginal burnisher
(Figs. 68 and 74) until the foil is closely conformed to the cavity mar-
gins. If the cavity extend to or beneath the gum the foil may be made
to overlap and conform to the gingival margin by the use of a pair of
special gingival marginal burnishers (Figs. 69 and 75). The matrix
should now be annealed, then placed into the cavity and filled with gum
camphor or hard wax. If gum camphor is used, a piece of gum that
will fill the cavity is placed into the matrix and is used as a means of
swaging it to the walls and margins of the cavity with the assistance of
blade burnishers. A piece of heavy tape is then placed over the camphor
and pulled directly toward the margins of the cavity (Fig. 76). This
swages the metal under direct and uniform pressure and forces the matri.x

63