c. Preparing and Placement of Cement Base.
(1) General. It is common practice to insert a low thermal conducting cement
material as a base in deep portions of cavities underlying metallic restorations to insulate
the pulp against thermal and electrical shock and pressures induced during placement of
the restorations. Zinc phosphate cement is the material most used for this purpose.
(2) Assisting procedures. When the dental officer is finishing the cavity
preparation, he will direct the dental specialist to prepare the base. The dental specialist
manipulates the material in accordance with the manufacturer's directions and the
general techniques discussed in a previous subcourse. A thick mix is normally used for
this purpose. When the dental specialist has completed the mix to the desired
consistency, it is presented to the dental officer. Usually, the mix is scraped from the
spatula onto the center of one edge of the glass slab. Some dental officers may want the
glass slab placed on the bracket table while others may want it held by the specialist
while the dental officer takes the amount of material required. Some excess powder
should remain for the dental officer's use in placing the base. Upon completion of the
placement of the base, the dental specialist should remove the slab and spatula from the
operative area. If zinc phosphate is used as a base, a glass slab (which should have a
"Z" or "ZP" etched on the side) with a matched set of zinc phosphate powder and liquid is
used. There are several other base materials that may be used; most of these will be
mixed on paper or parchment mixing pads. You will also need a stainless steel spatula in
mixing all of the base materials. To carry and pack the cement into the preparation
requires the use of one of several cement pluggers available to the dental officer. One of
the more commonly used pluggers is the Ladmore plugger number 3, which has teardrop
shaped working ends on both ends of the instrument. The Woodson pluggers number 1,
number 2, and number 3 may also be used. Both nibs of the Woodson number 1 are flat,
one in the same plane of the shank and the other at a slight angle to the shank. The
Woodson number 2 has a cylinder-shaped plugger on one end and a paddle-shaped nib
on the other. A Woodson number 3 has nibs similar to the Woodson number 2 except
that the cylinder-shaped nib is larger. Many dental officers will prefer to use a much
smaller base instrument called the "Dycal instrument." This instrument is furnished by
certain manufacturers with their base materials. It is much shorter and smaller than the
others previously discussed and has a beaded end to the nib.
MD0503
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