b. Varieties of Matrices. Composite resin restorations require some kind of
matrix to hold, shape, and protect them against stain and moisture contamination. Metal
matrices, if used in conjunction with resin restorations, would stain the resin. Celluloid,
which is issued in roll form, is normally the matrix of choice for proximal restorations. The
celluloid matrix strip is approximately three-eighths of an inch wide and is cut to the
desired length. Another celluloid-type matrix that is used with resin restorations is the
cervical matrix. It is cylindrical or tabular in shape and is generally used on the facial and
lingual surfaces of anterior teeth. This matrix offers the same protection against
contamination as do the celluloid strips. Crown forms are also made of celluloid and are
shaped to match the morphology of the tooth. They come in numbered sets that vary in
size, depending on the size and shape of the tooth involved. These crowns may also be
used to prepare a temporary crown, to contain a sedative filling, or as a matrix for other
types of restoration. If necessary, these crown forms may be modified and cut to fit the
tooth being worked on. In order to hold many of these matrices in place and help them
conform to an irregularly shaped tooth, a small wedge of wood is commonly used. Thus,
always include a selection of wooden wedges in any setup.
c. Mixing Composite Resins. Composite resins have largely replaced unfilled
acrylic resins because they last longer and have more desirable properties. They usually
have a calcium hydroxide base. They are also very simple to mix and use. Most of these
restorative kits contain the mixing instructions and mixing materials. If a crown form is not
used to place the material, a plastic-coated plugger may be used. In using any of the
composites, it is always wise to follow the manufacturer's instructions. Failure to do so
may result in a faulty restoration.
d. Completing the Restoration. If resin is the restorative material, the matrix will
be removed and then the restoration will be smoothed and polished. Initially, the dental
officer may want to trim the resin restoration with a surgical scalpel. Therefore, a scalpel
handle and a surgical knife blade should be included in the setup. For the remaining
finishing to be done, different finishing materials may be used depending on the nature of
the restoration. Proximal resin restorations are finished with abrasive strips known as
cuttlefish strips. They vary in width from one-sixteenth to three-sixteenths of an inch and
are six inches in length. These are available in three grits--fine, medium, and coarse.
Cervical resin restorations are usually finished by using sandpaper disks mounted on a
snap-head type mandrel. The disk mounted on a mandrel is used in conjunction with the
handpieces. The snap-head mandrel is readily identified by its pyramid-shaped head
over which the disc with a brass fitting will snap into place.
e. Alternative Finishing. A restoration of one of the composite resins may be
initially trimmed with a surgical knife and surgical knife blade. Other finishing may be
done with some type of finishing bur or with a diamond cone or abrasive wheel that is
used in conjunction with handpieces. White and green stones may also be used for this
procedure. After using the stones, cuttlefish strips and fine sandpaper disks might be
employed as a final finishing measure.