Placement of Restorative Materials
After the cavity preparation is completed, your
attention as the assistant is especially critical. You
must rapidly anticipate each step in the procedure to
have the necessary material ready at the proper time.
You must prepare and pass restorative materials, mix
them at the right time, and follow the manufacturer's
instructions. More instruments are needed to place the
restoration than to prepare the tooth; therefore, more
instrument transfers are necessary and occur more
rapidly than in cavity preparation. Once the restorative
materials have been placed in the oral cavity, the
dentist then begins to finish the restoration.
CAVITY LINERS AND BASES.Most
dentists use some type of cavity liner or base in almost
all cavity preparations. They are used primarily to
protect the pulp and to aid the pulp in recovering
from irritation resulting from cavity preparation.
Liners and bases are placed when the cavity
preparation is completed, just before insertion of the
Glass ionomer cements and dentin bonding agents
are used primarily to seal the dentin and protect the
pulp from bacterial invasion. Calcium hydroxide can
be used in extremely deep areas as an antibacterial
agent and/or as a pulp capping material.
Most bases are applied best when the assistant
wipes the instrument clean between each small
You will hold a gauze sponge in the
transfer zone and quickly wipe the end of the
instrument as the dentist moves toward the base mix. If
the dentist inadvertently gets the base on the enamel
walls of the cavity preparation, you will pass an
instrument for removal of the material.
Cavity varnish is a liner used to seal the dentinal
tubules to help prevent microleakage and is placed in a
cavity to receive amalgam alloy after any bases have
been placed. Cavity varnish is being used less and less
with amalgam restorations, and dentin bonding agents
are replacing cavity varnish as the liner of choice.
Cavity varnish has an organic solvent of ether or
chloroform that quickly evaporates, leaving the resin
as a thin film over the preparation. This varnish should
be slightly thicker than water. If it becomes very thick,
discard it. Cavity varnish is not used with composites
since the varnish retards the set of composites and
interferes with the bonding of composites.
A small cotton pellet held by cotton forceps is
dipped into the varnish just enough to wet the pellet.
The cavity varnish is applied to the pulpal area, walls
of the cavity preparation, and onto the edge of the
margins of the preparation. Any excess varnish can be
removed from the enamel with a fresh cotton pellet. A
second application of cavity varnish is placed over the
first to thoroughly coat the surfaces of the dentin and
fill any voids from bubbles created when the first
application dries. After liners and bases are placed into
the cavity preparation, the tooth may be restored with
materials, such as amalgam, composite resin, or glass
AMALGAM RESTORATIONS.Amalgam is
used as a restorative material on the surfaces of both
permanent and primary teeth. Amalgam also is
aesthetically acceptable for distal restorations of the
cuspid when the restoration is not readily visible.
Amalgam can also be used to prepare a sound base for a
tooth before the preparation of a full artificial crown.
This is commonly referred to as an amalgam buildup.
When multiple surfaces of the tooth are removed
during the cavity preparation, a matrix is required to
approximate the original wall and hold the restorative
material in proper form and position until it sets.
During the final stages of the cavity preparation, if not
sooner, you should acknowledge the need for the
matrix band and assemble it. While the liner and base
materials set, the dentist places the assembled matrix
band and retainer around the tooth, along with wedges
if needed. Figure 4-38 illustrates a properly contoured
and wedged matrix band.
While the dentist makes the final adjustments to
the matrix, you will need to ensure the precapsulated
amalgam is placed securely in the amalgamator and
ready to triturate (mix). The operation and
maintenance of the amalgamator is discussed in
chapter 11, Volume 1, under Dental Equipment. Wait
for a signal from the dentist to begin mixing the
Figure 4-38.Properly contoured and wedged matrix band.