Processing Dentures

8/4/2019 Processing Dentures

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PROCESSING

DENTURES



FLASKING-1



Purpose of flasking: To produce a mould of the

waxed-up denture for packingand processing of the acrylic

material.



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).



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.



Technique of Flasking



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.



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.



WAX ELIMENATION - 2



Wax elimination

The flask is placedin boiling water for

5 minutes. then

opened.

– Prolonged heating

will case molten

wax to penetrate theflasking plaster.



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



Sharp edges of plaster removed



PACKING OF ACRYLIC - 3

RESIN



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.



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.



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.



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.



Sprue placement

Sprue for upper denture Sprue for lower denture



The

injection

system



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



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.



Curing of acrylic resin- 4



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.|



.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.



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.



Short curing cycle- B

Heat at 740 c

For 1.5 hours

Boiling for an additional one hour.



Rapid curing method -C

Rapid heating in boiling water for

20 minutes.



Cooling

The flask is cooled slowly on thebench to room temperature

Slow cooling permits relief of stresses

to avoid distortion (warp) of the acrylic.



DEFLASKING- 5



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.



Deflasked denture; no porosity

or contaminations



FINISHING AND-6

POLISHING

Fi i hi



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.



Finishing



Overheating during finishing cause

burn mark



Polishing

Polish first with pumice

The final polish with:

A rag wheel, brush wheel and felt conewith pumice



Finished and polished denture

with rounded border, festooning

and stippling



Processing errors

of acrylic resins



. Porosity1

Porous denture is

difficult to clean,

esthetically

objectionable

and weak

Large voids



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..



GASEOUS POROSITY - B

It appears as fine uniform bubbles

particularly in thick sections of the denture.

Cause:

• Thick denture bases heated too rapidly



. 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



. 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



. 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.



. Bleaching of acrylic resin 5

Causes: •Undercured acrylic resin.

•Incorporation of the tinfoil substituteswith the acrylic resin.

C l t k i th i6



. 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.



Metallic denture

base construction



Palatal plate wax pattern

Spruing the wax pattern



Spruing the wax pattern

Palatal plate sprue

Mandibular plate Sprue



and casting Investing

The wax pattern is invested and

cast int chrome cobalt.



Completed cast framework



Record block on framework



Mounting

and setting

up of teeth

Waxed up denture



Waxed up denture



Finished denture

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Processing Dentures