cast duplication

1. Duplication

2. DUPLICATION STEPS
1- Melt the duplicating material according to
manufacture’s instructions. One part
hydrocolloid to three parts water
2- Soak the master cast in water for 15 minute.
3- Select the proper size of duplicating flasks.
There should be at least ½ inch clearance
4- Place a strip of clay or utility wax around the
rim of the base to form a seal

3. DUPLICATION STEPS
5- Remove the cast from the water and lightly
blow off excess water
6- Secure the cast to the base with clay or utility
wax
7- Place the body of the flask onto the base
8- Position the pouring reservoir
9- Flow melted colloid through the pouring
reservoir. The temperature of the colloid should
be between 136-140F

4. DUPLICATION STEPS
10- When the duplicating material reaches the
level of the two vent holes, plug them with wax
or clay and continue pouring until at least 2/3 of
the pouring reservoir is full. (The vent holes
initially prevent air from being trapped).
11- Set the flask in a pan of circulating tap water,
Setting time is 30 minutes for a small flask and
45 minutes for a large flask.

5. 12- Remove the base of the flask. Retrieve the master
cast by prying with two plaster knives where the clay
or wax was placed for stability.
13- Inspect the mold for defects. If none are noted, it
should be poured immediately; otherwise, it will
dehydrate and distort
14- Mix refractory material according to the
manufacture’s instructions. Ticonium: 29cc distilled
water to 100 grams powder; 30 sec mechanical
spatulation or 60 sec. Manual spatulation

6. DUPLICATION STEPS
15- Place a small amount of investment on the
teeth and the along the ridges; then vibrate to
displace all trapped air.
16- After the investment cast has hardened (60
minutes) remove the mold from the flask and
break the hydrocolloid away from the cast

7. REFRACTORY CAST PREPARATION
The refractory cast should not be handled
unnecessarily before it is dried. Do not rinse the
refractory cast, since this may result in etching
of the surface of the cast.

8. REFRACTORY CAST PREPARATION
1- When necessary, trim the cast with- a dry
stone (1/4 inch from proposed patterns and
blow off grindings with compressed air).
2- Dry the cast in an oven for ½ to 1 hour at 180-
200F.
3- Melt beeswax in a pan until it reaches 280 -
300F (Thermostatically controlled pots are
desirable to prevent overheating).

9. REFRACTORY CAST PREPARATION
4- Immerse the cast in the beeswax. Remove the
cast 15 seconds after the beeswax begins to
foam
5- Place the cast on a piece of absorbent paper.
After a few seconds move to a different position
so that a pool of wax will not accumulate in any
area of the cast.
6- When the cast has cooled, it is ready for
waxing the pattern

10. Waxing-Up
The waxing of a framework can be done free
hand or by using preformed plastic patterns. The
free hand method requires more skill and is
more time consuming, because the pattern is
formed from bulk wax strips.

12. Waxing-Up
Even when patterns are used, free hand waxing
is still necessary to: (1) form rests, (2) seal the
pattern to the refractory cast, (3) connect the
various parts, and (4) create the proper contour
The finished wax-up should be accurate,
smooth, and properly contoured to minimize
finishing of the casting

13. .1
1.Carefully trace the design on the refractory cast
2. Select the pattern and paint the underside with
glue.
3. Always seal and reinforce the mesh where it joins
the connector.
4.A butt joint external finish line is formed at the
junction of the major connector and denture base
retentive network.
5. Connect and seal the parts of the pattern

14. Spruing
A sprue is a channel which allows molten metal
to flow from the crucible to the mold cavity
during the casting procedure

15. the following characteristics are recommended:
1. All sprues should leave from a common point.
2. The sprue should be attached to bulky areas and
should be as thick as the pattern so that the molten
metal will not solidify before reaching the pattern
area.
3. The point of attachment should be rounded to
prevent the investment from breaking off during
casting.
4. The sprue design should not require molten metal
to pass from a thin to a bulky section.

16. Methods of spruing:
1) Multiple spruing, this is subdivided into top
spruing and inverted spruing.
2) Single spruing (horizontal sprue).

17. Top Spruing
.1
1. A main or a central sprue is made
2. from the central sprue auxiliary sprues run to each
corner of the wax pattern, The auxiliary sprues are
made of 10 gauge wax.
3. Usually four auxiliary sprues will be sufficient, but
more may be added depending on the requirements
of the case.
4. Auxiliary sprues should join the main sprue, half an
inch above the highest potion of the wax pattern

18. Top Sprue

19. Inverted Spruing
.1
1. the base of the investment model should
have a hole in its center
2. A cone-shaped metal sprue is placed into the
hole
3. Auxiliary sprues are then placed between the
main sprue and the thick sections of the wax
pattern
4. The bottom end of the central sprue is then
attached to a crucible former

21. Single Spruing
It has a limited application. It should be used
only when a partial denture pattern is designed
so that all parts lead to a single sprue. In order
to use a single sprue, part of the refractory cast
must be removed to provide a straight entrance
for the molten metal

22. Investing the sprued pattern
The outer investment surrounding the cast and
pattern confined within a metal ring.

23. Purposes of the investment
1- It provides the strength necessary to hold the
forces exerted by entering stream of molten metal
until solidification of the metal occurs.
2- It provides a smooth surface for the mold cavity
so that the final casting will require as little finishing
as possible.
3- It provides an avenue of escape for most of the
gas entrapped in the mold cavity by entering a
stream of molten metal.
4- Together with other factors it provides necessary
compensation for contraction of the metal from the
molten to the solid state

24. Types of investment used
The investment for casting gold is plaster- bound
silicate material. Total expansion offset the
contraction of gold which varies from 1% to 1.7%.
The investment for chromium cobalt alloys which
have high melting temperature is quartz powder
heat by ethyl silicate or sodium silicate binder. This
is to offset casting shrinkage of the order of 2.3%
(through thermal expansion of the mold).

25. Step by step procedures of investing
1- Just before mixing the investment, line the ring
with one layer of sheet asbestos. The asbestos
should be 6 millimeters (1/4 inch) shorter than the
ring at the crucible end. The asbestos permits some
hot gases to escape through the asbestos layer
2- If the investment cast has not been dipped in
bees’ wax (which prevents it from absorbing water
from the painting investment) it must be soaked in
water at room temperature before painting for four
minutes. This is to ensure a good bond between
the old investment and the new one.

26. 3- Paint the pattern with a wetting agent
(debubbilizer) just prior to applying the
investment to reduce surface tension of wax so
that the outer investment readily covers and
adheres to the pattern. Mix the investment
powder with water using two millimeters more
than are used to make the investment cast.
Mechanical spatulation under vacuum gives best
results. The entire pattern should be covered
with about 6 mm (1/4 inch) investment

27. 4- After 10 minutes (initial set of painting
investment before application of the ring, dip
the assembly in water to wet the outer layer of
painting investment
5- Allow the investment to set for one hour, and
then remove the crucible former which will
leave the investment concave or funnel shaped

28. Procedures of
investing