The action of pouring or injecting a flow-able material into a refractory mold.The object formed is also referred to as “a casting”.

1. Casting Procedures And Defects
Dr. Ibadat Jamil
Assistant professor
Dep. Of Prothodontics

2. • According to (GPT-9) the action of pouring or
injecting a flow-able material into a refractory
mold.
• •The object formed is also referred to as “a
casting”.

3. Steps in Making a Cast Restoration
•Tooth preparation
•Impression
•Die preparation
•Wax pattern fabrication
•Attachment of sprue former
•Ring liner placement
•Assembly of casting ring
•Investing
•Burn out or wax elimination
•Casting
•Sand blasting and recovery
•Finishing and polishing

4. Tooth Preparation
•The tooth is prepared by the dentist to receive
a cast restorations.

5. Impression
• An accurate impression of the tooth is made
usually with elastomers .

6. Die Preparation
• A die is prepared from die stone or a suitable die
material
• A die spacer is coated or painted over the die
which provides space for the luting cement.

7. Wax pattern fabrication
•A pattern of final restoration is made with type
II Inlay wax or other casting waxes with all
precautions to avoid distortion.
•A die lubricant is applied before making the
pattern to help separate the wax pattern from
the die.

8. Attachment of sprueformer
• A sprue former is made of wax, plastic or
metal.
• A reservoir is attached to the sprue or the
attachment of the sprue to the wax pattern is
flared.
• The length of the sprue is adjusted so that the
wax pattern is approximately 1/4” from the
other end of the ring.

9. FUNCTIONS OF SPRUE FORMER:-
• To form a mount for the wax pattern.
• To create a channel for the elimination of wax
during burnout.
• Forms a channel for entry of molten allloy
during casting.
• Provides a reservoir of molten metal which
compensates for alloy shrinkage during
solidification.

10. For preventing cavities
and porosities, due to
the thermal
contraction
Lost-head
(reservoire)
Sprue

11. Ring liner placement
• A ring liner is placed inside of the casting ring.
• Non asbestos ring liners like fibrous ceramic
aluminous silicate, cellulose or combination
of both can be used.

12. FUNCTIONS OF RING LINER:-
• Allows for mold expansion(cushion effect)
• Permit easy removal of the investment after
casting.
• It acts as a thermal insulator.

13. Investing
• Apply wetting on the wax pattern to reduce
air bubbles.
• Seat the casting ring into the crucible former
taking care it is located near the center of the
ring.
• Mix the investment and vibrate.
• The ring is reseated on the crucible former
and placed on the vibrator and gradually filled
with the remaining investment.
• It is allowed to set for 1 hour.

14. Investing the wax pattern-
Vacuum mixing

16. Investing the wax pattern

17. Burn out or wax elimination
Purpose of burnout is:
• To eliminate the wax from the mold
• To expand the mold (mold expansion)

18. Two stage burnout and expansion
technique
• Ring is placed in a burnout furnace and heated
to 400c in 20 minutes.
• Maintain it for 30 minutes.
• Over the next 30 minutes, temperature is
raised to 700c and maintained further for 30
minutes.

19. Single stage burnout and expansion(Rapid
technique)
• Followed only if patterns & sprues are wax.
• Place molds directly into preheated oven at
700-850c.
• Hold for 30-40 minutes and cast.

20. Casting
Various Casting machines are used like:-
•Based on method of casting
1.Centrifugal force type
2.Air pressure type
•Based on heating system employed
1.Torch melted
2.Induction melted
3.Arc melted

21. • Alloy is melted with a suitable heat source.
• When the alloy is molten it has a mirror-like
appearance and shifts like a ball of mercury.
• Hot casting ring is shifted from burnout
furnace to the casting machine.
• Arm is released and allowed to rotate which
creates a centrifugal force which forces the
liquid metal into the mold cavity.
PROCEDURE

22. Gold alloys placed in the crucible
Shiny ball like appearance of gold alloy

23. • The arm is allowed to rotate till it comes to
rest.
• The ring is allowed to cool for 10 minutes till
the glow of the metal disappears.
• We do Quenching for gold alloys. The ring is
then immersed in water which leaves the cast
metal in an annealed or softened condition.
• Metal ceramic and base metal alloys are not
quenched.

24. Releasing the lock Casting takes place
Quench ring in cold water

25. Sandblasting and Recovery
• Investment is removed and the casting is
recovered.
• A pneumatic chisel is used to remove the
investment.
• Sandblasting is a process by which particles of
an abrasive is projected at high velocity using
compressed air in a continuous stream.
• Casting is held in a sandblasting machine to
clean the remaining investment from its
surface.

28. Pickling
• Surface oxides like black castings from the
casting are removed by pickling in 50%
hydrochloric acid.
• HCL is heated not boiled with the casting in it.

29. Finishing and Polishing
• Sprue is sectioned off with a cutting disc.
• Casting is trimmed, shaped & smoothed with
suitable burs & stones
• Minimum polishing is required if all the
procedures are followed meticulously.

30. DEFECTS IN CASTING
• A casting defect is an irregularity in the metal
casting process that is undesired.
• Errors in the procedure often results in defective
castings.
• Defects in casting can be classified under four
headings:-
1)Distortion
2)Surface roughness and irregularities
3)Porosity
4)Incomplete or missing detail
5) Contaminated casting

31. Distortion
• Probably related to distortion of wax pattern.
• Can be minimized or prevented by proper
manipulation of the wax and handling of the
pattern.
• Distortion increases as the thickness of the
pattern increases.
• Lower is the setting expansion of the investment,
less lower its distortion.
• If storage is necessary, store in refrigerator.

32. Surface roughness and irregularities
• Surface roughness is defined as finely spaced
surface imperfections whose height, width
and direction establishes the predominant
surface pattern.
• Surface irrregularities are isolated
imperfections such as nodules.
• Excessive irregularities on outer surface
necessitate additional finishing and polishing
whereas irregularities on cavity surface
prevent proper seating.

33. • Small nodules on
casting are caused by
air bubbles that
become attached to
the pattern during or
subsequent to the
investing procedure.
• The best method to
avoid air bubbles is to
use vacuum investing
technique.
Reasons are- 1- AIR VOIDS

34. 2- Water films
•If the investment
becomes separated
from the wax pattern,
a water film may form
irregularly over the
surface as wax is
repellent to water.
•Too high L/P ratio also
produce this.
•A wetting agent may
prevent the film
formation.

35. 3- Liquid/powder ratio
•Higher the L/P ratio, rougher the casting.
•Ratio of quartz and the binder influence the
surface texture of casting.
•Coarse silica produces coarse casting.

36. Porosity
•It occur both on interior region of casting and
external surface.
EFFECTS:-
• Weaken the casting
• Discoloration
• If severe, can cause plaque accumulation at
the tooth-restoration interface.

37. Classification of porosity
SOLIDIFICATION DEFECTS
•Localized shrinkage porosity
•Microporosity
•Suck-back porosity
TRAPPED GASES
•Pinhole porosity
•Gas inclusions
•Subsurface porosity
•Backpressure porosity

38. Localized shrinkage porosity
•Large irregular voids found near the sprue-
casting junction.
•It occurs when the cooling sequence is
incorrect and sprue freezes before the rest of
the casting, so no more molten metal can be
supplied from the sprue.

39. Can be avoided by:-
• Using sprue of correct thickness
• Attach sprue to thickest portion of wax
pattern.
• Flaring the sprue at the point of attachment or
placing reservoir close to the wax pattern.

40. Microporosity
•These are fine irregular voids within the
casting.
•It is seen when the casting cools too rapidly.
•Rapid solidification occurs when the mold or
casting temperature is too low.

41. Suck back porosity
•This is an external void seen in the inside of a
crown opposite the sprue.
•A hot spot is created by the hot metal
impinging on the mold wall near the sprue
which causes this region to freeze last.
•Since the sprue has already solidified, no more
molten material is available and the resulting
shrinkage results in suck back porosity.
•Avoided by reducing the temperature
difference between mold and the molten
alloy.

43. Pin hole porosity
• Many metals dissolve gases when molten.
• Upon solidification the dissolved gases are
expelled causing many tiny voids.

44. Gas inclusion porosities
•They are spherical voids but are larger than pin
hole type.
•They are due to gases carried in or trapped by
the molten metal.

45. Back pressure porosity
• This is caused by inadequate venting of the
mold. Air is trapped in the mold and is unable
to escape.
• When the molten metal enters the mold the
air inside is pushed out through the porous
investment at the bottom.
• If the bulk of the investment is too great, the
escape of air becomes difficult causing
increased pressure in the mold.

46. • The metal is then solidify before the mold’s
completely filled resulting in a porous casting
with rounded short margins.

47. Avoided by:-
•Using adequate casting force
•Use investment of adequate porosity.
•Place pattern not more than 6 to 8 mm away
from the end of the ring.
•Providing vents in large castings.

48. Incomplete casting
Incomplete casting may result from-
• Insufficient alloy or alloy not sufficiently
molten.
• Alloy not able to enter thinner areas of mold.
• Mold is not heated to proper temperature.
• Premature solidification of alloy.
• Sprue blocked with foreign bodies.
• Low casting pressure.

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