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PROCESSING
DENTURES
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FLASKING-1
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Purpose of flasking: To produce a mould of the
waxed-up denture for packingand processing of the acrylic
material.
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Preparation of dentures for
flasking 1-The teeth waxed
securely into
place. 2-The dentures
sealed to the casts
3-The castsseparated fromarticulator and
trimmed (tapered).
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Selection of flask
A big flask, allowing at least half an inch between the teeth and the
flask edge.
The rim of the cast should flush
with the bottom half of the flask.
The teeth are not too high inrelation to the top of the flask.
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Technique of Flasking
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Dental stone is the
best material for
flasking.
The lower flask is
filled with plaster
or dental stone, and
the model is placedin.
Excess plaster is
wiped away and
smoothed.
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A separating medium painted over theplaster
The top part is placed in position. Dental stone is placed over the teeth and
wax surfaces.
The top section is filled with plaster and
excess plaster is wiped away and the twosections closed together.
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WAX ELIMENATION - 2
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Wax elimination
The flask is placedin boiling water for
5 minutes. then
opened.
– Prolonged heating
will case molten
wax to penetrate theflasking plaster.
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Wax washing
Wax is washed by boiling
water
Care is taken to avoid loss of
teeth
Upper and lower flask
parts after wax washing
Wax washing
Upper flask with teeth
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Sharp edges of plaster removed
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PACKING OF ACRYLIC - 3
RESIN
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Separating medium application
Tin foil substitutesis applied by brush.
Examples of the
separating mediumare:
– water glass (sodium
silicate 60 per cent
in water)
– sodium alginate
solutions
– Vaseline.
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Mixing of acrylic resin
The hands washed,
mixing vessel cleaned.
The polymer tomonomer 3.5 to 1 by
volume. 6-8 c.c. of monomer is
placed in the mixingcontainer.
The polymer addedslowly, tapped andstirred.
The vessel covered.
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Packing of acrylic resin:
Packing done when: – The resin has reached dough
consistency-The plaster surfaces in the flask
are cold
– Separating medium is applied.
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The injection method - A
In this method a sprue arrangement with a suitable flask
is used.
Acrylic resin is constantly fed into
the mould during processing
through a plunger and spring tension system.
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Sprue placement
Sprue for upper denture Sprue for lower denture
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The
injection
system
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The open flask method - B
Excess resin is placedinto tooth section of flask
The flask is closedgradually under benchpress.
Then the flask isopened and excessresin is removed
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The open flask method The cast is painted with a separating
medium and the flask is closed The flask placed in flask press which is
firmly closed for 30 minutes before curing.
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Curing of acrylic resin- 4
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Curing of acrylic resinThe packed flask is heated in an oven
or water-bathThe temperature and time of heating
must be controlled.
If the material is under-cured thedenture have a high residual monomercontent. – a) Free monomer irritate the oral tissues.
– b) Residual monomer make the resinweaker.|
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.The rate of temperature rise mustbe gradual.
Monomer boils at 100.3 degree C.
Polymerization reaction is exothermic.
Thus if a large mass of unreactedmaterial is suddenly plunged intoboiling water, the temperature of theresin may rise above 100.3 degree C
So vaporizing the monomer occurs.
This causes gaseous porosity.
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Long curing cycle- A
A constant temperature At 74 C
For 8 hours or 9 hoursWith no terminal boil.
No degradation of resin properties
occurs.
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Short curing cycle- B
Heat at 740 c
For 1.5 hours
Boiling for an additional one hour.
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Rapid curing method -C
Rapid heating in boiling water for
20 minutes.
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Cooling
The flask is cooled slowly on thebench to room temperature
Slow cooling permits relief of stresses
to avoid distortion (warp) of the acrylic.
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DEFLASKING- 5
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Deflasking
1-The investing plaster isremoved in one block from the
flask. Investing plaster is cut down
from the cast.
Then the model is removed from
the denture.
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Deflasked denture; no porosity
or contaminations
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FINISHING AND-6
POLISHING
Fi i hi
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Finishing
The excess flush at the periphery
is removed with a large stone orbur.
The surfaces are shaped until it issmooth and cleans.
Particular care must be taken to
make the peripheries rounded The fitting surface small pimples
is removed with a small stone or
bur.
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Finishing
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Overheating during finishing cause
burn mark
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Polishing
Polish first with pumice
The final polish with:
A rag wheel, brush wheel and felt conewith pumice
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Finished and polished denture
with rounded border, festooning
and stippling
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Processing errors
of acrylic resins
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. Porosity1
Porous denture is
difficult to clean,
esthetically
objectionable
and weak
Large voids
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SHRINKAGE POROSITY - A
It appears as irregular voids throughout the
surface of the denture due to under packing.
Causes: • Lack of dough in the mold at the time of final closure.
• Lack of adequate pressure during polymerization.
• Packing the resin in a sticky rather than doughy stage..
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GASEOUS POROSITY - B
It appears as fine uniform bubbles
particularly in thick sections of the denture.
Cause:
• Thick denture bases heated too rapidly
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. Tooth movements 2
Causes: • The use of plaster instead of
stone in investing the trial denture.
• Incomplete closure of the flask.• Excessive and rapid pressure
during trial closure.
• Over packing of the mold withresin material before final closure.
D t b d t th3
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. Denture base and teeth 3
breakage during deflasking.
Causes:
• Knife blade hit teeth whenremoving stone cap.
• Hammer used to tap denture out
of the flask.
C i f li i b4
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. Crazing of acrylic resin base 4
or acrylic teeth:
Causes: • Stresses induced by the contraction
of the resin around the tooth by rapid
cooling.
• The use of solvents to remove waxfrom the mold before packing.
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. Bleaching of acrylic resin 5
Causes: •Undercured acrylic resin.
•Incorporation of the tinfoil substituteswith the acrylic resin.
C l t k i th i6
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. Color streaks in the resin6
material
Causes: Improper mixing of the monomer
and polymer.
• Contamination of the resin mix
with dirty hands or instrument.
• Adding resin material in layers
during packing.
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Metallic denture
base construction
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Palatal plate wax pattern
Spruing the wax pattern
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Spruing the wax pattern
Palatal plate sprue
Mandibular plate Sprue
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and casting Investing
The wax pattern is invested and
cast int chrome cobalt.
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Completed cast framework
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Record block on framework
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Mounting
and setting
up of teeth
Waxed up denture
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Waxed up denture
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Finished denture
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