Figure 8-24.Compound knife with #25 blade.
Figure 8-27.Wax spatula, #7.
The plaster knife (fig. 8-25) is a heavy-duty knife
used to trim and chisel gypsum products and
impression compound. It has a large flat blade at one
end with a wide projection shaped Ii ke a screwdriver at
the other end. The handle is made of wood and is
riveted in place. You must keep its blade sharp.
Figure 8-28.Wax spatula, #31.
Preliminary impressions are a three-dimensional
record of a patient's dentition and anatomy of the
alveolar process. Almost all prosthodontic treatment
requires preliminary impressions be taken so that a
dental cast can be made and used by the dentist as a
diagnostic tool and to fabricate various prosthodontic
Spatulas are used in prosthodontics for handling
dental waxes and mixing impression materials. The
laboratory spatula shown in figure 8-26 is used to mix
the various impression materials. It has a 2-1/2 inch
flexible blade, which is about 1-inch wide with a
rounded end. The handle is usually made of wood or
The wax spatulas commonly used are the #7 (fig.
8-27) and the #31 (fig. 8-28). Both spatulas are used to
hold small bits of wax over a Bunsen burner flame that
delivers liquid wax.
Figure 8-25.Plaster knife.
Figure 8-26.Laboratory spatula.
The dentist may direct you, under supervision, to
take preliminary impressiom of the dental arches of a
patient. You will need the following materials:
Rope-style utility wax
Mixing bowl, spatula
Once you have all your materials standing by, take
a few minutes and explain to the patient what is
involved in the impression procedure. The key to
taking good impressions is to have the correct size
impression tray fit the arches, to mix the alginate,
position the tray correctly in the mouth, have the
patient relax and breathe through the nose, let the