Appointment 1

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Appointment 1 Preliminary Impressions
Photo Provided by Dr. Tom Ward
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Preliminary Impression Objectives
Understand

• CD impression

• Tray selection

• Tray modification

• Border molding

• Impression material

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• Purpose
• Preliminary casts are used for diagnosis and
  construction of custom impression trays.
• Requirements
• The impression must capture all intraoral
  landmarks i.e. retromolar pads, retromylohyoid
  space, hamular notches, etc.
• The impression will be slightly overextended but
  must essentially capture the dimensional contours
  (3-D) of the vestibular borders of the limiting
  structures.

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• Characteristics of Alginate Impressions
• They do not require a custom tray.
• The impression material sets quickly.
• The impressions must be kept moist until they
  are poured.
• The borders (vestibules) are overextended.
• They must be poured within 30 minutes.
• They must be supported by the tray handle with
  the tissue surface facing up until the first pour
  sets if the two pour method is used.
• The heat of the thermal reaction must have
  dissipated before they are separated from the
  cast.

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Alginate Technique Uses a stock edentulous
tray which is border molded with periphery wax
and a standard alginate material (irreversible
hydrocolloid).

• Materials and instrument set-up
• Alginate
• Tray Adhesive
• Edentulous stock trays
• Rubber mixing bowl
• Round edge spatula
• Periphery wax
• Mouth mirror
• 2x2 gauze
• Mouthwash
• Water bath

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EVALUATING THE TRAY
Place the patients existing denture in an
edentulous tray to determine the appropriate size
tray to use for the impression. There should be
adequate clearance between the denture and the
tray to allow the tray to fully seat in the
patients mouth without impinging upon the tissue
surfaces when it is loaded.
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EVALUATE THE TRAY
Try the tray in the mouth.

• The tray should correspond to denture-bearing
  surfaces.
• Select a tray that is at least 3-4 mm larger than
  the residual ridge.
• The tray must fit the retromolar pad areas and
  the profile of ridge.
• Modify flange areas and palate for a more
  comfortable fit.

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The border-molded trays should be comfortable
and accurately represent the extensions of the
arch.
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Border Molding an Impression
Warm the periphery wax in a warm water bath. This
will soften it so that it easily molds to record
the vestibular extensions in the patients mouth.
Once the border-molding is complete, soak the
tray in cool water to set (harden) the wax.
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Border Molding an Impression
Insert the tray in the patients mouth.
(Note the use of a mirror to retract the lips.)
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Apply an alginate tray adhesive spray or paint a
thin layer of adhesive over the tissue surface of
tray .
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Mix the Alginate

• Use 70F water measured to the designated line
  on the vial.
• The mix will appear dry at first but do not add
  additional water. After several strokes the mix
  will become smooth and creamy. (It is recommended
  to use slightly less water to achieve a thicker
  mix when making the maxillary impression on a
  gagging patient.)
• Use a round edge spatula.
• Mix in a vigorous manner using sweeping strokes
  against the walls of the mixing bowl.

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Make the Lower Impression

• Hold the mandibular tray by the handle in one
  hand.
• Load the alginate from the back on one side of
  the tray and distribute it around the tray,
  pushing all air ahead of the mix.

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Make the Lower Impression

• Stand in front of and to one side of the
  patient.
• Place the tray in the mouth, using the fingers
  of both hands to spread the lips.
• Center the tray, making sure the handle comes
  straight out from the midline.
• Manipulate frena and lips (muscle trim) while
  gently holding down on the tray.

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Make the Lower Impression

• Have patient raise the tongue, push it out over
  the handle, then to the right and left. Do this
  several times while the alginate is setting.
• Dont let the patient place their tongue fully
  back into the mouth.

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A Suitable Impression
Finished Preliminary Mandibular Impression
Detailed and Free of Voids
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Make sure all vestibules are well-recorded by
the impression.
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Dont expect every impression to be as perfect
as this.
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Primary Impressions in Alginate

• Mandibular Impression Landmarks
• labial notch
• labial flange
• buccal notch
• buccal flange
• alveolar groove
• retromolar fossa

Alveolar groove
retromolar fossa
buccal flange
buccal notch
labial flange
labial notch
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Primary Impressions in Alginate
Mandibular Impression Landmarks
pterygomandibular notch
retromylohyoid eminence

• lingual flange

• premylohyoid eminence

lingual notch
lingual tubercular fossa
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Border Molding an Impression
Border mold the periphery wax to the intraoral
contours by massaging the lips and cheeks much
like you did with the mandibular tray.
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Border Molding an Impression
Carefully remove the tray to avoid distorting the
soft wax and place it in a bowl of chilled water
to harden the wax before loading the tray with
alginate.
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Make the Upper Impression

• Mix the powder and water to a thick, creamy
  consistency according to manufacturers
  directions.
• Use mechanical spatulation to minimize air
  incorporation into the mix.
• Load alginate into the tray so that the air is
  pushed ahead of the mix.
• Distribute and smooth material in tray using
  moist fingers.

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Make the Upper Impression

• Stand behind the patient (11 oclock position).
• Place tray in the mouth with one hand holding the
  tray handle while using the fingers of both hands
  to spread the lips.
• Rotate the tray into position, making sure the
  handle comes straight out from the midline and
  that it is located evenly over the ridge.

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Make the Upper Impression

• Seat the anterior portion first so that the air
  is forced out the back as the tray is seated.
• Remove any excess that is forced to the back with
  a mouth mirror.
• Gently border mold the impression.

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Make the Upper Impression

• Have the patient lean forward to minimize
  gagging.
• Have the patient raise the napkin to catch any
  drooling.
• Have patient raise their legs to tense the
  stomach muscles.
• Hold the tray firmly in place for the entire time.

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Remove the Upper Impression

• Grasp the handle of the tray firmly, raise the
  cheek on one side to break the seal, and remove
  the impression in one quick, but guarded motion.

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FINISHED PRELIMINARY IMPRESSION
Detailed and free of voids
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Primary Impressions in Alginate
Maxillary Impression Landmarks

• labial flange

• labial notch

• alveolar groove

• buccal notch

• median palatal groove

• buccal flange

• coronoid contour

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Primary Impressions in Alginate
Maxillary Impression Landmarks

• incisive fossa

rugae

• tubercular fossa

• Pterygo-maxillary seal

• fovea palatinae

• posterior palatal seal area

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Completed Preliminary Impressions
-Should have no major pressure spots or
voids -Should capture all peripheral extensions
Note the capture of the retromolar pad and the
peripheral extensions.
This impression captures all of the anatomical
landmarks i.e. hamular notch, posterior palatal
seal, etc. However note the pressure spot over
incisal papilla.
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• Pour the impression
• Disinfect the impression properly before pouring.
• Mix water and powder according to manufacturers
  instructions.
• Use a vacuum mixer to ensure dense mix.
• Thoroughly rinse the impression before pouring.
• Start the pour by placing the mix in the center
  of the palate on the maxillary or the distal on
  one side in the mandibular.

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• Tilt the impression on the vibrator until the
  stone has covered the entire tissue surface.
• Allow the stone to run out of the impression.
  This will leave a thin layer of stone over the
  entire tissue surface and allow any bubbles to
  flow out of the impression.
• Vibrate more stone into the impression from the
  same point as established by the first pour.

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Note The stone should cover the peripheral
borders of the impression.

• Add several small mounds of stone to the poured
  impression. This will provide retention form for
  the second pour.
• Place the poured impression in a drying rack or
  a groove in the bench so that it is supported by
  the tray handle while the stone sets.
• Allow the stone to dry for 30 minutes.

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• Allow the setting stone to cool so the stone is
  sufficiently hard to make the base.
• Place the impression in a bowl of cold water
  while you mix the second batch of stone.
• Make a patty of stone on a flat plastic plate.
• Vibrate a small layer of stone on the set stone
  of the poured impression.
• Invert the impression and set it gently on the
  patty.
• Shape the base with a mixing spatula.
• Remove the set stone cast from the impression
  after 30 minutes setting time.

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An accurate preliminary cast records all
anatomic landmarks that should be covered by a
denture and permits fabrication of properly
extended custom trays that will expedite border
molding and facilitate a quality final
impression.
The cast should be 13 mm thick in the palate
palate.
The retromolar pad and hamular notch areas should
be well-recorded.
All land areas should be 3-4 mm wide all the way
around the cast.
The tongue area of the lower cast should be flat
and 13 mm thick.
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This cast shows some deficiencies from those
aspects previously mentioned that need to be
specific sizes to be usable. If a denture does
not extend back over the retromolar pad area, a
significant amount of support will be lost and
ridge resorption will be hastened. Land area
protects the borders of the impression and the
cast.
This area should show more of the retromolar pad.
This area should be 3-4 mm wide all the way
around the cast.
This area should be flat.
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Land Area
Land area is any part on the face of the cast
that was not captured in the impression. Since
the land area is not recorded by the impression,
it is therefore not a landmark. It will serve to
protect the areas recorded by the impression and
represented in the cast. It should not limit
visual or working access to the vestibular area
of the cast.
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The End