Complete Denture Dent 482.01 and

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Custom Trays The Key to a Great Final
Impression
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Patient Visit 2
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Outline

• Over view of border molding making a final
  impression.
• Make custom trays on the preliminary cast.
• Outline the tray borders on the cast.
• Block out the undercuts.
• Apply the relief wax.
• Place shape the Triad resin material.
• Cure the resin.
• Adjust the tray.

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Border-Molding

• Definition Shaping of an impression material by
  the manipulation or action of tissues adjacent to
  the borders of an impression tray
• Objective
• To determine the contours, height and width of
  the borders of the complete denture

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Custom trays are constructed prior to the final
impression appointment.
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Why?

• Stock trays are universal. They are not made to
  fit a specific patients mouth.
• Stock trays are difficult, if not impossible, to
  adjust to fit a patients mouth.
• The most accurate impression is one that has an
  even thickness of impression material.
• Custom trays require a minimum amount of
  impression material.

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Requirements of a custom tray

• They must be rigid so as not to distort the
  impression.
• They must be able to be adjusted to fit the
  patients mouth.
• The tray handles must not interfere with the
  border molding process.
• The tray must allow for an even thickness of
  impression material.

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How to make a custom tray

• Draw the outline on the cast.
• Block out the undercuts.
• Place the wax spacer on the cast.
• Place the Triad on the cast.
• Mold the Triad into the proper shape.
• Cure the tray in a curing oven.
• Trim the tray.
• Cut back the wax.

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Draw the outline on the cast
Since alginate impressions in stock trays will
always leave the vestibular areas over-extended,
an outline is drawn 2 mm short of periphery in
the labial and buccal vestibular areas to
arbitrarily define the borders of the tray until
they are adjusted to fit the mouth. The line is
left long in the posterior palate and the
retromolar pad areas to allow the impressions to
capture the soft tissues in these areas.
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Block out the undercuts
Major undercuts on the preliminary cast are
blocked out with wax before the impression tray
is made. This is necessary so that the tray can
be inserted in the mouth without chafing the soft
tissue and be removed from the master cast once
the final impression is made and poured in yellow
stone.
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Place a wax spacer on the cast
A piece of wax is dipped in a hot water bath or
heated over a Bunsen burner to soften it
uniformly. One layer of warm baseplate wax is
pressed into place over the maxillary cast with
the thumb and finger pressure. It is trimmed
along the external borders of the land area by
pressing it against the sharp external edge of
the cast.
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Trim the wax to the outline
1 thickness of baseplate wax is cut back 2 mm
from the depth of the vestibule. The dark line
that was scribed on the cast should be visible
through the wax and provide an easy guide as to
where the cut needs to be made. It should be
easily visible after the wax is removed from the
cast.
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The same basic procedures described for the
making a maxillary tray also apply to the
mandibular tray. The wax is pressed into the
lingual area first and then the buccal and labial
areas, and cut by pressing the wax against the
outer border of the land area. The wax is trimmed
to the line marked on the cast at 2 mm from the
depth of the buccal and labial vestibules. The
wax is left long over the retromolar pad and
lingual flange areas, but does not extend onto
the land area.
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Trim the wax to the outline
The wax is left a little long in the posterior
palate and retromolar pad areas to allow the tray
to be constructed long in these areas and permit
recording the posterior palatal area where the
palatal seal will be formed and the retromolar
pad, which is the most stable support area of the
mandibuar ridge. The areas over all frenum
attachments are relieved to the 2mm distance to
allow for full movement of the lip.
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Place the Triad on the cast
One thickness of Triad tray material is placed
onto the wax. It is pressed into the lingual area
(mandibular) or palatal area (maxillary) first to
prevent air pockets from forming, then pressed
over the ridge and buccal areas. It is pinched
off at the edge of the land area and cut along
the edge of the lingual vestibule with a red
handled knife to remove this section.
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Place the Triad on the cast
The Triad is pressed into the internal border of
the land area with the thumbnail to form the
external border of the tray. This is done around
the entire border of the cast.
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Add a tray handle
A handle is molded onto the tray. It must
arise from the crest of the ridge in the anterior
of the tray and should be at a 45o angle to the
crest of the ridge. It must be just long enough
to accommodate the width of the thumb. This will
allow sufficient access for the border molding to
be accomplished in this area by allowing the lip
to be pulled along the surface without binding.
It also provides enough surface area for the tray
to be securely held while placing and removing it
during the impression procedures.
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Add a tray handle
The handle for the lower tray is made longer
and narrower than the one made for the upper
tray. This allows the tongue to move freely
around it and perfect the border molding in the
lingual area. Finger rests are placed on the
crest of the posterior ridges that are narrower
than the width of the tray to raise the finger
above the area that is being border-molded and to
prevent recording the width of the finger in the
final impression. Sufficient distance must be
provided between these and the handle for the
tongue to pass through.
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Cure the Triad in the curing oven
The tray is cured on the cast in a curing unit
for three minutes. It is removed from the cast
and placed in the curing unit with the waxed side
up for an additional two minutes. A quick look
will show where the Triad material extends beyond
the wax.
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The thumb is placed on the handle to determine
if there is sufficient thickness and length of
the handle to allow adequate grasp for the tray
to be placed and removed during the impression
procedure.
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Trim the tray
The wax is allowed to cool, then the tray
material is trimmed back to the level of the wax
spacer. A lathe will speed up the process and a
handpiece can be used to refine the cutback. A
laboratory diamond is especially made for this
task and will greatly reduce the time spent
adjusting the Triad.
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After the tray borders have been reduced and
the tray has been finished, it is placed back on
the cast to verify that it has been sufficiently
cut back 2 mm short of the vestibule to allow for
sufficient bulk of the border molding compound.
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Cut back the wax
An additional 2mm of wax is removed from the
inside of the tray to allow the border molding
material to overlap the edge of the tray and form
a U-shaped joint. This joint will be strong
enough to firmly retain the compound on the tray.
A few millimeters of wax is also removed from
the posterior palatal area to allow for the
palatal seal to be developed in the final
impression.
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This U-shaped joint will provide sufficient
strength to the compound so that it doesnt
fracture off during the border-molding or
impression phases.
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The tray is tried into the patients mouth and
the borders are reduced 2 mm short of the depth
of the vestibules and the frenuli attachments.
This is determined by pulling the lip outward and
having the patient raise the tongue. This
assures that there is sufficient room for the
border-molding,
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Custom trays are border-molded with dental
compound (also known as modeling plastic) prior
to making a final impression. This material
softens with heat and hardens at mouth
temperature, allowing several adjustments to
record the vestibular areas very accurately.
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The impression is then just a thin wash of
polysulfide impression material over the
compound-modified custom tray.
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The End