defects occur in casting with solution

1. PRESENTED BY
CHHAVI RANA
(DEPT OF PROSTHODONTICS)
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2. CASTING DEFECTS
 Error in the procedure often results in defective casting,
these defects are known as casting defects
Dental casting system aims to provide a metallic copy of
the wax pattern as accurate as possible.
Nevertheless, a wide range of variables may influence
the final result and predictable outcomes are hardly
achievable. While casting dental prostheses, problems
frequently observed are incomplete casting and
internal porosity
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3. Classification
According to philips
Distortion
Porosity
Incomplete or missing details
Surface roughness and irregularities-
1. Air bubbles
2. Water films
3. Rapid heating rates
4. Under heating
5. Liquid/powder ratio
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4. 1. Prolonged heating
2. Temperature of alloy
3. Casting pressure
4. Composition of investment
5. Foreign bodies
6. Impact of molten alloy
7. Pattern position
8. Carbon inclusion
Based on location
Internal
external
4
Anusavice, Kenneth J., et al. Phillips' science of dental materials.11th edition.

5. According to Rosensteil
 Roughness
 Nodules
 Fins
 Incompleteness
 Voids or porosity
 Marginal discrepancy
 Dimensional inaccuracies
5
Contemporary Fixed Prosthodontics STEPHEN F. ROSENSTIEL, 4th edition.

6. Distortion
 Distortion of the casting is probably related to distortion
of the wax pattern.
Causes:
 Can occur from the time of wax pattern preparation to the
time of investing due to stress relaxation.
 during the investment procedure Distortion of the
wax pattern can occur .
Minimized by:
 Application of minimum pressure
 Manipulation of wax at high temperature
 Investing pattern immediately
 If storage is necessary, store in refrigerator
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7. Hardening of the investment
Distortion of the wax
pattern
Setting and hygroscopic expansion of
investment produce non-uniform
expansion on the walls of the pattern
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8.  Distortion thickness of the wax pattern
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9. Surface Roughness and
Irregularities
Surface roughness
Defined as relatively fine spaced surface imperfections
whose height, width and direction establish the
predominant surface pattern.
Surface irregularities
Isolated imperfections such as nodules that are not
characteristic of the entire surface area
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10.  The surface roughness of the casting is greater than
the wax pattern from which it is made, because
- the particle size of the investment and
-its ability to reproduce the pattern in microscopic
detail
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11. A-AIR BUBBLE
 Small nodules on the casting are caused by air bubbles, that become
attached to the surface during or subsequent to the investing procedure.
Prevented By:
 Proper investment technique
 Vibration of mix or by vacuum mixing
 Application of wetting agent properly
and correctly – important that it be
applied in a thin layer.
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12. B-Water films:
Prevented By:
1.Use of wetting agent
2.Correct L/P ratio (Too high L/P ratio may
produce these irregularities)
Wax is repellent to water,
If Investment becomes
separated from the wax pattern
water film may form irregularly
over the surface.
Appears as minute ridges or
veins on the surface.
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13. C-Under heating
If the heating time is too short
Incomplete elimination of wax residues
Hot alloy come in contact with carbon residue
Voids or porosities may occur in casting from gas formed
 Occasionally casting is covered with TENACIOUS carbon
coating-impossible to remove by PICKLING
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14. D-Prolonged heating
High heat technique,
Decomposition or disintegration of the investment
Walls of the mold are roughened.
Product of decomposition are sulfur compounds, which contaminates the
casting,
Reason -surface of the casting does not respond to pickling sometimes.
 Prevented by- when thermal expansion technique is used, the mold
should be heated to the casting temperature & NEVER HIGHER.
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15. E-Liquid/Powder Ratio
 The amount of water and powder should be measure
accurately.
 Too little water- investment too thick & cannot be
applied to the wax pattern
 Too much water- reproduces rough casting.
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16. E-Casting pressure
 To high pressure – rough surface of the casting
 To low pressure – incomplete casting
 Average – 0.10 to 0.14 Mpa in an air pressure
machine
- 3 to 4 turns of the spring in centrifugal
casting machine is sufficient for small casting.
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17. F-Foreign bodies
Foreign body into mold surface roughness
 Any casting that shows sharp, well- defined deficiencies
indicates the presence of some foreign particles in the
mold. They may be:
- Pieces of the investment
- Bits of the carbon from the flux
- Sulfur components from – decomposition of the
gypsum investment and high sulfur content torch flame.
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18. G-Pattern position
Expansion of wax is higher
than that of investment
Causing breakdown or cracking
of investment
PREVENTION-3mm spacing
should be given
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PATTERN SHOULD NOT PLACED TO CLOSED
TOGETHER

19. H-Impact of metal alloy
Cause:
 The direct impact of molten alloy on the weak portion of the
mold surface, may fracture or abrade the mold surface
regardless of its bulk.
This can lead to improper seating of the casting.
Prevented by:
 Proper spruing by directing the molten alloy at an <90o to
investment surface.
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20. Carbon inclusions
 Carbon from- carbon crucible,
- carbon containing investment,
- improperly adjusted torch–
Can be absorbed by the alloys during casting results in formation
of carbides or visible carbon inclusion.
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21. Porosity
The presence of voids or pores within a structure.gpt 9
This can be internal/external.
Surface roughness
Internal porosity not only weaken the casting-lead to 2o
caries by accumulation of plague
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22. Porosity
Classified as follows:
I. Solidification defects
A. localized shrinkage porosity
B. Micro porosity
II. Trapped gases
A. pin hole porosity
B. gas inclusion porosity
C. sub surface porosity
III. Residual air
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23. I. Solidification defects
 A. localized shrinkage porosity-
 By premature termination of the molten metal during
solidification.
 Linear contraction of noble metal alloy changing from
liquid to solid is at least 1.25%
 Molten metal through sprue compensates this
shrinkage
 Metal in sprue freezes incomplete casting.
localized shrinkage void
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24.  Porosity in the pontic is caused by- retain heat because of its
bulk and located in the center of the rings.
 Prevented-adding one or more gauge sprues(18gauge)
To area which is far from the main sprue. & extending laterally
within 5mm of edge of ring.
Localized shrinkage –occur near the sprue casting
junction
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25. Suck back porosity
 Interior of the crown near the area of the sprue create
a hot spot on the mold wall
Hot spot
Created by hot metal impinging from sprue channel on a
point on mold wall.
Causes local region to freeze last
Result SUCK BACK POROSITY
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26.  SUCK BACK POROSITY-occurs at inciso axial line angle
 Metal at this surface creates higher localized mold
temperature k/A HOT SPOT.
 This area retain the localized molten metal for lone after the
casting have solidified
 Eliminated by- flaring the point of sprue attachment
 Lowering the casting temprature by 300
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27. Microporosity
 Occurs from solidification shrinkage.
 This is not detectable unless the casting is sectioned
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28. Pin hole and Gas inclusion
porosity
 Related to the gas entrapment.
 Characterized by spherical contour.
 On solidification the absorbed gases are expelled &
pinhole porosity result.
 Eg- copper & silver dissolves oxygen
platinum & palladium dissolves hydrogen
 Also be caused by gas occluded from a poorly adjusted torch
flame or use of oxidizing zone rather than reducing zone.
 Casting is usually black, do not clean easily on pickling
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29. Sub surface porosity
 Caused by simultaneous nucleation of solid grains and
gas bubbles at the first moment that the alloy freezes
at mold walls
 Prevented by controlling the rate at which the molten
metal enters the mold.
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30. Back pressure porosity
 Some times referred to as entrapped-air porosity.
Causes
 Inability of the air in the mold to escape through the pores in
the investment
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31. Prevented by:
Proper burnout
Sufficiently high casting pressure
Investment of adequate porosity
Adequate L/P ratio
Adequate mold and casting temperature.
Thickness of investment between tip of pattern and
end of ring is not greater than 6mm.
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32. INCOMPLETE CASTINGS: -
 Partially complete casting or perhaps no casting at all
 Two factors –that inhibit the ingress of the liquefied
metal are insufficient venting of the mold and high
viscosity of the fused metal.
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33. Insufficient Venting
 Due to the back pressure exerted by the air in the mold.
 Molten alloy does not fill the mold before if solidifies
 Overcome back pressure
 Continuous pressure is applied for 4sec
 The mold is filled and the metal is solidified in 1 second
or less, yet it is quite soft during the early stages point.
These appear as rounded incomplete margins.
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34. According to Rosensteil
• Excess surfactants
• Improper water powder
ratio
• Excessive burnout
temperature
Rough casting
• Air trapped during
investing procedure
• Inadequate vacuum
during investing
• Lack of surfactants
Nodules
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35. 35
• Excessive vibration
Nodules on
occlusal
surface
• Wax pattern too thin
• Cool mold
• Inadequate metal
Incomplete
casting

36. • Increase w/p ratio
• Pattern too near to investment
• Premature heating(wet mold)
• Too rapid heating
Fins
• Incomplete wax elemination
Incomplete casting
with shiny,round
defect
• Improper w/p ratio
• Improper mixing time
• Improper burnout
temperature
Inadequate or
excessive
expansion
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37. • Wax pattern distortion
• Uneven expansion
Marginal
discrepancy
• Suck-back-improper pattern
positin & norrow,long sprue
• Inclusion-particle of
investment & dislodge
during casting
porosity
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38. Casting made simple using modified sprue
design: An in vitro study
 Indian Journal of Dental Research, Vol. 25, No. 3, May-June, 2014, pp. 340-345
 Abstract
 Background: Success in dental casting restorations for fixed partial dentures (FPDs) depends on the
castability. Castability is described as the ability of an alloy to faithfully reproduce sharp detail and fine
margins of a wax pattern. The goal of a prosthodontist is to provide the patient with restorations that fit
precisely. Regardless of the alloy used for casting, the casting technique should yield a casted alloy,
which should possess sufficient mass, surface hardness and minimal porosity after casting. Materials
and Methods: Twenty patterns for casting were made from three-dimensional printed resin pattern
simulating a 3 unit FPD and casted using modified sprue technique. Later test samples were cemented
sequentially on stainless steel model using pressure indicating paste and evaluated for vertical marginal
gap in eight predetermined reference areas. Marginal gap were measured in microns using Video
Measuring System (VMS2010F-CIP Corporation, Korea). A portion of the axial wall of the cast
abutments depicting premolar and molar were sectioned and embedded in acrylic resin and tested for
micro hardness using Reichert Polyvar 2 Met Microhardness tester (Reichert, Austria) and porosity
using Quantimet Image Analyzer (Quantimet Corporation London, England). Results: The results
obtained for marginal gap, micro hardness, and porosity of all test samples were tabulated,
descriptive statistics were calculated and the values were found to be within the clinically acceptable
range. Conclusion: The new sprue technique can be an alternative and convenient
method for casting which would minimize metal wasting and less time consuming.
However, further studies with same technique on various parameters are to be conducted for its broad
acceptance
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39. CONCLUSION
 An unsuccessful casting result in considerable trouble and
loss of time, in almost all instances, defects in castings can
be avoided by strict observance of procedures governed by
certain fundamental rules and principles.
 Seldom is a defect in a casting attributable to other factors
than the carelessness or ignorance of the operator. With
present techniques, casting failures should be the
exception, not the rule
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41. REFRENCES
 K. J. Anusavice, Phillips Science of Dental
Materials, 11th edition
 Rosensteil, Contemporary fixed rosthodontics
 Shillinburg, fundamentals of fixed prosthodontics
 Indian Journal of Dental Research, Vol. 25, No. 3,
May-June, 2014, pp. 340-345
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