this PowerPoint is concerning with the different types and causes of defects that happened during the casting of dental alloys and how to avoid this fault.

1. Casting Failures &
Defects in Dentistry
By
Dr. ahmed gaml

2. Casting Defects
• Casting defects are broadly classified as :
1. No Casting
2. Casting defects by Addition
3. Casting defects by Loss (Incomplete Casting)
4. Porosity
5. Discolored casting that resists pickling
6. Oversized or Undersized restorations
7. Distorted restorations

3. No Casting
Occurs due to :
1. Obstruction at the entrance of the mold due to :
a) Presence of fractured investment fragment
b) Presence of metallic sprue former
2. Use of flat crucible former may result in improper entry of molten alloy into the
mold cavity.

4. 3. Premature solidification of the alloy due to :
a) Use of Thick sprue (when alloy is melted within the ring)
b) Inadequate casting pressure
c) Cold ring
d) Incomplete heating of alloy
4. Escape of alloy from the opposite side of the ring due to the fracture of the
investment bridge. This can happen due to a thin investment bridge or high casting
pressure.

5. Casting defects by Addition
1. Fins or Wings – It’s a wing like formation on the
cast restoration due to the crack formed in the
investment adjacent to the wax pattern . Molten
alloy fills these cracks to form the Fins. Can be
caused to use of weak or old investment, rapid
heating or dropping of the investment ring.

6. 2. Bubbles or Nodules – Small globular
structures formed on the cast restoration, due
to entrapment of air around the wax pattern,
during investing. If nodules are formed away from
the crown margins , they are removed. If they are
formed on the margins, the casting has to be
remade.

7. 3. Rough surface of the casting – Caused due to :
– Rough surface of the pattern / investment.
• – Overheating of Alloy / Investment.
• – Investing before the drying of the wetting agent
4.Water films (Veins) – Caused due to the
separation of the investment from the wax
pattern.

8. Casting defects by Loss (Incomplete Casting)
• Occurs mainly at the margins or on the thin areas of the casting, due to:
1. Inadequate heating of the alloy
2. Incomplete wax elimination
3. Excessive cooling of the mold
4. Insufficient casting force
5. Inadequate amount of alloy
6. Accessory sprues not used or not enough

9. Porosity Types :
1.Back pressure porosity
2.Gas inclusion porosity
3.Suck back porosity
4.Micro porosity
5.Shrink spot porosity
6.Surface porosity
7.Sub Surface porosity

10. 1. Back pressure porosity
Cause : Inability of the air in the mold to escape through the pores of the
investment.
Prevention :
a. Locating the wax pattern towards the end of the casting ring (6-8 mm)
b. Using a more porous investment material
c. Using the proper water powder ratio
d. Adequate burnout
e. Adequate mold and casting temperatures
f. Adequate casting pressure
g. Casting with Vacuum technique

12. 2. Gas Inclusion Porosity
Cause : Inability of the gas in the mold to escape through the pores of the
investment.
The gas comes from :
a. Blowpipe torch flame ( If reducing zone not used)
b. Gases released by the investment material
c. Absorption of oxygen by the molten alloy
Prevention : (same as back pressure porosity)
Using the reducing zone of the flame to melt the alloy.

14. 3. Suck Back Porosity
Porosity resulting from solidification shrinkage.
Cause: Occurs if the metal in the sprue solidifies before the metal in the mold.
Prevention :
1. Avoiding too narrow or too long sprues.
2. Proper sprue attachment to the wax pattern
3. Adequate and uniform heating of the mold

16. 4. Micro Porosity
• Micro porosities formed in the restoration which are visible only under a magnifier. They
make the restoration weak and can be easily corroded.
• Cause: Can be caused due to unequal solidification of the alloy.
• Prevention :
1. Adequate and uniform heating of the mold
2. Adequate and uniform melting of the alloy.

18. 5. Shrink Spot porosity
• Cause: Porosity created at the connecting point of the cast restoration and the sprue, due
to their solidification at the same time. Hence, compensation for the shrinkage is done
from the connecting area.
• Prevention:
1. Avoiding too narrow or too long sprues.
2. Proper sprue attachment to the wax pattern

21. 6. Surface Porosity
• Gives a rough surface appearance.
• Cause:
• – Rough surface of the pattern / investment
• – Overheating of Alloy / Investment.
• – Investing before the drying of the wetting agent.

22. 7. Sub-Surface porosity
• Porosities present within the structure of the restoration.
• Cause :
• – Casting the metal in cold mold.
• – Unequal solidification within the restoration.

23. Discolored casting that resists pickling
• Cause : Release of sulfur by gypsum bonded investment, due to overheating, forms
compounds with the gold alloy, which resist pickling.
• The restoration has to be repeated again.

24. Oversized or Undersized restoration
• Cause : Over expansion of the investment or over shrinkage of the cast restoration
• The restoration has to be repeated again.

25. Distorted restoration
• Cause : Incorrect techniques used in all or
any of the steps, beginning from impression
making until the casting and the finishing
procedure.

28. Thank you