It is the process of investing the cast with its waxed denture in a flask to make a two sectional mold used to form the acrylic resin denture base. It is a metal case or tube uses the dental stone to invest the cast and trial wax denture to create the mold within it, or can defined as a sectional metal case in which a sectional mold is made of artificial stone for the purpose of compressing and processing dentures or other resinous restorations. Lower half: Drag (bottom), which contains the cast. Upper half: Cope (ring), which captures the teeth of the denture. The cover: Cap (lid) The master cast with the waxed trial denture is invested in the lower half of the flask with gypsum investment material. Then the upper half of the flask is put in place and gypsum is poured to the occlusal surfaces of the teeth. The top portion of the flask is poured with another layer of plaster or stone and the cover is placed on the flask. It is a complicated procedure required special flask and equipment. In this technique the wax pattern is sprued and the material is injected into the mold. This process allows injection of further material during processing to compensate for the polymerization shrinkage Sealing the upper and lower trial denture all over the border until the margin of the cast while the casts still on the articulator. Soak the casts and the mounting plaster in water a few minutes to separate the casts from the mounting plaster, save the plaster mounting as it will be used to reposition the casts on the articulator after the dentures have been processed.Make sure that there is enough space between the incisal and occlusal surfaces of the teeth and the top of the upper ring about 3-6 mm, if there is no space then the cast base must be reduced in thickness. Adapt a layer of tinfoil to the base of the casts, slightly overlapping the edges to insure clean removal from the investment, apply separating medium to the casts and flask. Waxed denture painted with surface tension reducing agent to decrease likelihood of bubbles formation. Use the mixture of the plaster or stone and placed in the bottom of the flask Center the cast in the lower half of the flask. The cast is pushed down to place until its rim is nearly level with the top edge of the bottom of the flask. Note that the posterior portion of the cast is level with the edge of the flask. Remove any undercuts in the stone. Undercuts will prevent the separation of the upper ring from the lower portion of the flask The stone is smoothed and leveled between the edge of the cast and the rim of the flask, and then allows the stone to set. After the final setting of stone has occurred, it will be coated with separating medium. Position the ring of the flask. Mixing of stone is done, pouring of the mixture to flow and reach all surfaces of teeth without any air bubbles by putting the flask on the vibrator. The investment material must reach the incisal edge and the occlusal surfaces of the teeth.

1. Processing of Complete Denture
By
Mark Samir
Undersupervision
DR. Reham Tharwat

2. Steps of processing of
complete denture

3. (
1
)
FLASKING PROCEDURE
The procedure of investing the cast
with the waxed denture ina flask
to create a sectional mould for the
acrylic resin denture foundation is
known as flasking. It is sometimes
referred to as investing.

4. Flask
:
It’s a metal tube used in investing procedures, in which a
mold is made of artificial stone or plaster of Paris for the
purpose of Processing denture or other resinous
restorations.
Components of
flask:
(1) the upper half
(2) the lower half
(3) the cover(lid)

5. FLASKING(INVESTING)PROCEDURE
(1)Flask must close fully accurately
without resistance. If it failsto do this,
distortion or excess increase in vertical
dimensions may occur
(2)The Innersurface of the flask is
coated with Vaseline, while the base of
the cast is painted with separating
medium(cold mold seal)

6. (3) Thin mixture of plaster of Paris poured inthe base
of the flask, place the model, teeth should be vertical.
(4)All the parts of the model should be
covered with POP and all the wax and teeth
must be uncovered.
(5) POPshould be covered by thin layer of
Vaseline
after its setting

7. (6) Amixture of gypsum should be
prepared, then put the mid part in its place
and pour the gypsum without covering
occlusal surfaces.
(7) After setting this layer
, cover it with
Vaseline or cold mold seal
(8) Another layer of gypsumshould be
filled in the flask, it shouldcover it, put the
flask under mild pressure and then wait for
complete setting

8. Wax Elimination

9. The flask is placed in boiling water for 4 to 6 minutes. Then
it is removed from the water and opened. Then the Wax is
washed away with boiling water. After the stone of the flask
is dry, the inner side of the mold and the cast are Painted
with a separating medium. The separating medium must
not come in contact with the teeth because wax residue on
the teeth is contaminant and causes adhesion failure with
the denture resin

10. PACKING AND CURING

11. ACRYLIC PACKING PROCEDURE:
1. Isolate the gypsum of the flasking by using one of these systems of isolation:
 Physical separator or isolator: tin foil.
 Chemical isolator: solution of alginate (cold mold seal). It reacts with
the calcium of the gypsum to form a film of insoluble calcium alginate.
2. Use the brush, move it in one direction to spread the cold mold seal.

12. STAGES OF ACRYLIC MIXING:
1. A sandy stage: where a fluid mass occurs due
to the settling of the polymer into the monomer.
2. A stringy or fibrous stage: where the monomer
starts to attack the polymer. In this stage the mix
is tacky, sticky and adheres to the sides of the
mixing jar.

13. 3
.
Smooth dough like stage: where the monomer
diffuses into the polymer
.
4. Rubber like stage: further penetration of the
monomer into the polymer. In this stage the acrylic
resin cannot be packed or molded being too stiff.
Stiff stage: hard

14. 5. Packing of acrylic
It is the procedure of application of acrylic
resin into the mold and pressing the flask by using
sufficient pressure to compensate for the contraction
of the acrylic after polymerization to
prevent shrinkage and porosity.
Put acrylic in the mold, press in a clamp, do curing
immediately

15. Note:
Too early– (Stage II) – acrylic resin has too low viscosity to densely fill the mold. Results
in porosity in the final prosthesis.
Too late– (Stage IV) – inability to close the flask, loss of detail and increase in vertical
dimension of occlusion in final prosthesis, as well as, movement and/or fracture of
teeth.

16. • Acrylic placed into mold cavity and covered with cellophane for trial pack
 Flask pressed until excess acrylic squeezes out around edges.

17.  Acrylic flash to be trimmed away, small amount of acrylic to be added where needed.
Take note of the wrinkles from cellophane.
 The mold is full when the acrylic is pressed smooth and dense. A small amount will be
added at wrinkles.

18. • Close the upper and lower parts of the flask together.

19. CURING OF ACRYLIC
:
The packed mold is heated (cured) in an oven or in water bath. Temperature and time should be
controlled
.

Two water bath heating techniques may be used
:
)a
Heating the flask in a special bath of water, beginning from the room
temperature until reaching 72°C for 16 hours
.
)b
Heating the flask in an ordinary water bath beginning from the room
temperature until reaching 72°C, lasting for 2 hours, then the temperature is raised
to boiling for another 1 hour
.

This technique takes shorter time but there is a likelihood to be distorted
during de-flasking. Also, the free monomer is more
.

.

20. COOLING OF THE FLASK / BENCH COOLING:
After curing, the flask is to be cooled slowly on the bench in its water bath.
The slow cooling will permit the relief of the internal stresses caused by the difference in
contraction between the acrylic and the mold material.

21. DEFLASKING

22. DEFLASKING
:
It is the procedure of opening the flask after
curing of acrylic resin. It should be done
carefully to prevent the breakage of the
denture.
It includes the following steps:
1. Remove the flask from the clamp.
2. Remove the upper and lower lids.

23. 3 Separate the 2 parts of the flask with
attention using the plaster knife.
4 Liberate the denture with its model,
then try to remove the model carefully. If
there is undercut, split the model into 2 or
3 parts to remove them easily.

24. Finishing and Polishing

25. FINISHING :
 Each denture is hand
finished using special burs
to remove any excess
acrylic around the edges
and palatal area .The
articulation is adjusted if
necessary.

26. Polishing:
• Finally the denture is polished
and smoothed with
polishing paste to create
a natural looking luster.

27. - A tooth brush can be used to remove the
remaining plaster and pumice.
After polishing, the denture should be
thoroughly washed in soap water.

28. Thank You