d. Placement of a Metal Matrix Band.
(1) Proper placement of amalgam requires condensation by applying strong
pressure to the surface of the amalgam with amalgam pluggers. In cavities involving
more than one tooth surface, it is usually necessary to surround the tooth with a matrix
band to help confine the restorative material to the cavity preparation during
condensation. The matrix band also helps determine proper contours and the location
and form of proximal contacts in the restored tooth. A number of types of matrix retainers
are available. Many are designed to be used with matrix bands premade in assorted
sizes and configurations. Matrix bands may also be tailored individually from matrix band
material and tied or otherwise held in place on the tooth. When the matrix is in place on
the tooth, a wedge or wedges are often used to hold the band tightly against the neck of
the tooth on proximal surfaces involved in the cavity preparation (see figure 2-30). The
wedge keeps the amalgam from squeezing out under the matrix band and into the
interproximal space or spaces. Some dental officers use red or green stick impression
compound to add further support and rigidity to the matrix.
Figure 2-30. Wooden wedge.
(2) The assistant, with the dental officer, will prepare materials designed to
replace the missing walls of a cavity preparation and to shape or protect the restoration.
Placing a matrix for an amalgam restoration will allow the dental officer to insert the
restorative material without exceeding the limits of the normal tooth structure. The most
common type is the Tofflemire matrix retainer and band. This comes in two parts--a small
stainless steel band that encircles the tooth and the instrument that holds the band in
place (called the Tofflemire retainer). Note that the number 1 Universal band is doubled
over when it is placed in the retainer. In assembling and placing the matrix, there are
three essential rules to follow. First, the small opening of the band must point toward the
cervical portion or root of the tooth. Secondly, the slotted side of the retainer always
points toward the root of the tooth to facilitate the removal of the retainer after the
restorative material has partially set or crystallized. Finally, the retainer is usually
positioned on the facial side of the tooth being worked on (in the vestibule).