Complete Denture Dent 482.01 and

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Boxing and Pouring a Final Impression
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Boxing

• Definition Enclosing an impression to produce a
  base, to preserve the vestibular contours of the
  final impression, and to create a land area to
  protect the cast
• Techniques
• Wax
• Alginate
• Play-Doh or clay
• Plaster/Pumice

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The putty or clay method may seem neater, but
it does not support the impression like a
plaster/pumice matrix will, so the stone fill may
force out the sides when poured with vibration,
therefore students are discouraged from using it
here. The same thing goes for using wax by
itself or alginate, since they both lack the
support that the plaster/pumice mixture affords.
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Pumice
H2O
Plaster
The method we will use in the clinic is the 11
plaster/pumice mixture. Students must become
knowledgeable and proficient with this method
while here. Equal parts of plaster and pumice are
mixed together dry, then enough water is added
for the mix to become smooth and creamy.
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Boxing and Pouring an Impression
Place a band of sticky wax around the entire
periphery of the impression. Then affix
sufficient rope wax to the sticky wax
approximately 2-3 mm below the border of the
impression to serve as a guide to position the
plaster/pumice mix or putty the correct height on
the impression.
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Boxing and Pouring an Impression
After the plaster/pumice mix is placed, the wax
can be smoothed with a hot 7 wax spatula before
trimming the base to the desired size.
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Boxing and Pouring an Impression
Trim the plaster/pumice mix on the model
trimmer. The acrylic handle will be trimmed down
also, allowing an even reduction of the base.
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Boxing and Pouring an Impression
These bases were poured in 11 (50/50)
plaster/pumice mixture prior to the boxing
procedure. These bases were trimmed to about 4mm
from the border to establish the land area.
Notice the tray handle is trimmed off to be flush
with this dimension.
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Boxing and Pouring an Impression
When a defect exists in the base, just patch
the hole with plaster/pumice and move on.
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Boxing and Pouring an Impression
The same is true for the wax spacer. Just add
wax where needed and smooth it up.
11
Better yet, add wax to the lingual area. It is
an effective separating medium and it will be
easier to separate the cast from the
plaster/pumice support base.
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Use the Hanau torch to flame the wax and a hot
instrument to make it very smooth. Your poured
cast will only be as smooth as the form of the
mould it is poured into. A little work on the wax
now when you have access saves al lot of
difficult finishing of the stone cast when access
is limited.
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Boxing and Pouring an Impression
If the wax at the joint does not overlap
sufficiently, take a piece of boxing wax and
press it against the area of the joint and fold
it over the edge of the box, then lute it in
place with a hot instrument. There must be a
tight seal at this junction if the stone is to be
contained.
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Seal the wax of the land area to the box
containing the plaster/pumice bases with sticky
wax to make them ready to pour in yellow dental
stone. The land area should be about 4mm wide and
about 3 mm down from the border to allow for
trimming. The wax rim should extend at least 15
mm above the impression to allow sufficient
thickness for the base of the cast.
15
Lubricate the plaster/pumice bases with
VaselineR, Model Release AgentR, or other
separating medium so that the poured cast will
separate from the plaster/pumice matrix.
16
Vibrate the stone mixture on the vibrator at
medium vibration, flexing the bowl and bouncing
it up and down to eliminate bubbles. Better yet,
use a vacuum spatulator to mix the stone and
bubbles will be minimized.
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Pour the mixed stone into the boxed impression.
Turn it on its side and move it around under
vibration to spread the stone on the surface of
the impression. This will minimize any bubble
formation.
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Pour the boxed impression, let it set for at
least 30 minutes or until the heat of the setting
disappears, whichever comes first, before
attempting to separate the cast from the
impression.
19
Peel the boxing wax border from the poured
impression when the set stone has cooled.
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Immerse the entire cast and plaster/pumice
matrix in a container of hot water to soften the
compound of the impression and the utility wax
used to define the land area. The water should
be about 140o F, the same heat as the tempering
bath used during the border-molding procedure.
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Use a sharp knife to pry the plaster pumice
matrix loose from the cast. The impression may
not come off easily, so the impression and cast
will need to be re-immersed in the hot water bath
for a few more minutes.
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Continue to remove the plaster/pumice matrix
until it is all off the cast and impression. If
the cast has cooled down, immerse the impression
and cast in the hot water bath for a few more
minutes.
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After the cast is separated from the
impression, it is trimmed on the model trimmer so
that the base is about 13 mm thick and 4 mm of
land area is left.
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Finish the land area of the master cast by
reducing its height to 2 mm from the depth of the
vestibule all around the border, then trim the
cast on the model trimmer set to cut at a 90o
angle so that the land area is 4 mm in width.
The red-handled compound knife or a scalpel
should not be used for this. Use a sharp knife
with a stiff blade which will not break.
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The base of the cast should be about 10-15 mm
thick. A thinner cast may break in processing or
be significantly weakened by the remount index
cut into the base of the cast. A thicker cast may
not fit in the processing flask and have to be
thinned, thereby removing the remount index and
eliminating the possibility of doing an accurate
laboratory remount.
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Master Casts for Complete Dentures

• The master cast is an accurate replica of the
  residual ridge areas, and other parts of the
  dental arch upon which a complete denture
  prosthesis can be fabricated. This cast must be
  protected by blocking out all undercuts before
  making the baseplate.

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The end
Photo by Dr. Tom Ward