Detailed description of casting defects

1. Good morning

2. PRESENTOR- ZADENO KITHAN
PERCEPTOR – DR. SANA FATIMA
26.5.22
CASTING DEFECTS

3. CONTENTS
• INTRODUCTION
• HISTORY
• DEFINITIONS
• STEPS OF CASTING PROCEDURE
• CLASSIFICATION OF CASTING DEFECTS
-DISTORTION
-SURFACE ROUGHNESS AND IRREGULARITIES
-POROSITY
-INCOMPLETE OR MISSING DETAIL
• VARIABLES AND PRINCIPLES OF OPTIMAL SPRUE DESIGN
• CLINICAL RELEVANCE
• CONCLUSION
• REFERENCES

4. INTRODUCTION

5. HISTORY
2500 B.C-Egypt; Dental prosthesis made from gold wire found
1897-Philbrook described a method of casting metal into a mold
from a wax pattern for restoration of posterior tooth.
1907- William Taggart introduced “lost wax technique ’’
1908-Lane introduced mold expansion as a compensation technique
1910- Van horn discovered the value of wax expansion
 1930- Carl Scheu, discovered the phenomena known as
“Hygroscopic setting expansion”.

6. STEPS OF CASTING PROCEDURE
1.TOOTH
PREPARATION
6.RING LINER PLACEMENT
2.IMPRESSION
5. ATTACHMENT OF SPRUE
FORMER
3.DIE PREPARATION
7.ASSEMBLY OF CASTING
RING
9. BURN OUT OR WAX
ELIMINATION
4.WAX PATTERN
FABRICATION
10. CASTING
8.INVESTING
11. SAND BLASTING
AND RECOVERY
12. FINISHING AND
POLISHING

10. DEFINITIONS
CASTING
Casting is defined as something that has been cast in a mold, an object
formed by the solidification of a fluid that has been poured or injected into a
mold -GPT(7th edition):
Casting is the process by which a wax pattern of a prepared tooth is
fabricated and converted to its metallic replica - Rosenteil
CASTING DEFECTS
It is an unwanted irregularities that appear in the casting during metal casting
process.

11. DEFECTS IN CASTING
CLASSIFIED AS
DISTORTION
INCOMPLETE
OR MISSING
DETAIL
SURFACE
ROUGHNESS
AND
IRREGULARITI
ES
POROSITY

12. DISTORTION

13. DISTORTION
Most common cause of marked
distortion is related to a distortion of
the wax pattern.
Distortion of the wax
pattern occurs as the
investment hardens
around it
Removal from the oral
cavity during direct
technique owing to
thermal changes,
improper handling
during removal,
contraction on
cooling, relaxation of
stresses, distortion
during storage, etc
The setting and
hygroscopic
expansions of the
investment may
produce a
nonuniform
expansion of the
walls of the pattern.

14. Clinical relevance : Inaccuracy in the fit
of the margin may be due to distortion
during removal of the wax pattern from
the die.
DISTORTION INCREASE
As the thickness of the pattern
decrease
DISTORTION
DECREASE
Less setting expansion

15. PREVENTION
1.Use of hard wax for wax
pattern fabrication
2.Careful handling of the
pattern during removal along
the path of insertion taking
care not to disturb the margins
3. Softening the wax at uniform
temperature of 50°C.
-Adding wax in smaller
increments at a time
4. Immediate investment of the wax
pattern.
-The pattern must be stored in a
refrigerator for no more than 30
minutes

17. SURFACE ROUGHNESS,
IRREGULARITIES AND
DISCOLORATION

18. SURFACE ROUGHNESS, IRREGULARITIES AND DISCOLORATION
Surface roughness
Relatively finely 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.
SURFACE
DISCOLORATION
• Any deficiency in the
temperature or
heating time results
in incomplete
reaction and
formation of carbon
residue, which
contaminates the
alloy and results in
discoloration.
• Can also arise from
breakdown products
such as sulfur
compounds
contaminating the

19. CLINICAL RELEVANCE
Excessive roughness or
irregularities on the outer surface
of the casting necessitate
additional finishing and polishing
Irregularities on the cavity surface
prevent a proper seating of an
otherwise accurate casting

20. Material and methods: A master abutment of a
premolar mandibular tooth preparation with 4-
mm height and a 0.6-mm deep 120-degree
chamfer finish line with a 12-degree angle of
convergence was replicated in die stone and
scanned. Thirty-six cobalt-chromium alloy
copings were produced using 3 different
production techniques-laser-sintering, milling,
milled wax/lost wax.
Conclusions: Laser-sintered
Co-Cr crown copings showed
increased surface roughness and
better internal and marginal fit
than copings produced by
milling or milled wax/lost wax
technique.

21. CAUSES / RELATED FACTORS
AIR BUBBLES
Small nodules on a casting are caused by air bubbles
that become attached to the pattern during or
subsequent to the investing procedure.
PREVENTED
BY
1. Use the vacuum investing technique
2. A wetting agent

22. WATER FILMS
This type of surface irregularity appears as minute
ridges or veins on the surface.
If the pattern is slightly moved, jarred, or vibrated
after investing, or if the painting procedure does not
result in an intimate contact of the investment with the
pattern,
Appearanc
e
Cause
Prevention Use of a wetting agent
Too high an L/P ratio

23. FOREIGN BODIES
A rough crucible former with investment clinging
to it may roughen the investment on its removal
so that bits of investment are carried into the
mold with the molten alloy
Cause
Sharp, well-defined deficiencies of castings
Appearanc
e
Pieces of
investment and
bits of carbon
from a flux.
Bright-appearing concavities Flux being
carried into the
mold with the
metal.
Contamination results not only in surface roughness
but also in incomplete areas or surface void

25. RAPID HEATING RATES
Appears as - Fins or spines on the
casting
Cause
Flaking of the investment when the
water or steam pours into the mold.
such a surge of steam or water may
carry some of the salts used as
modifiers into the mold, and these
salts are left as deposits on the walls
after the water evaporates

26. Prevention
The mold should be heated
gradually; at least 60 min should
elapse during the heating of the
investment-filled ring from room
temperature to 700˚ C
The greater the bulk of the
investment, the more slowly it
should be heated

27. PROLONGED HEATING
Causes disintegration of the gypsum-bonded
investment
The products of decomposition are sulfur
compounds that may contaminate the alloy to the
extent that the surface texture is affected.
When the thermal expansion technique is
employed, the mold should be heated to
the casting temperature—never higher—
and the casting should be made
immediately
Prevention

29. UNDER HEATING
Incomplete elimination of wax residues may
occur if the heating time is too short or if
insufficient air is available in the furnace
Voids or porosity may occur in the casting from
the gases formed when the hot alloy comes in
contact with the carbon residues

30. LIQUID/POWDER RATIO
The higher the L/P ratio, the rougher the
casting.
If too little water is used, the investment
may be unmanageably thick and cannot be
properly applied to the pattern

32. TEMPERATURE OF THE ALLOY
The surface of the investment is likely to be
attacked.
Prevention
Use of gas-air torch
Special care should be observed that the color
emitted by the molten gold alloy is no lighter than
a light orange

33. CASTING PRESSURE
A gauge pressure of 0.10 to 0.14 MPa in an air
pressure casting machine or three to four turns
of the spring in an average type of centrifugal
casting machine is sufficient for small
castings.
Prevention
Too high a pressure during casting
can produce a rough surface.

35. COMPOSITION OF THE
INVESTMENT
The ratio of the binder to the quartz
influences the surface texture of the
casting.
A coarse silica causes a surface
roughness.

36. IMPACT OF MOLTEN ALLOY
Proper spruing so as to prevent the
direct impact of the molten metal at an
angle of 90 degrees to the investment
surface.
Appearance
Raised area on the casting, often too
slight to be noticed yet sufficiently large
to prevent complete seating of the
casting.
Prevention

37. The expansion of wax is much greater than that of the investment, causing
breakdown or cracking of the investment if the spacing between patterns is less
than 3 mm.
 If several patterns are invested in the same ring, they
should not be placed too close together
 Positioning too many patterns in the same plane in the
mold should be avoided.
PATTERN POSITION
Prevention

38. Carbon, as from a crucible, an improperly adjusted torch,
or a carbon-containing investment, can be absorbed by the
alloy during casting
CARBON INCLUSIONS
Visible carbon inclusions

39. ENDOGENOUS
• Degassing and
desulfurization products
• Supersaturated precipitated
components
The Influence Of Inclusion In Casting
POSITIVE
oxides and sulfides increase the hardness of
the material and increase the wear
resistance.
EXOGENOUS
• mostly oxides
• Non-metallic inclusions generated
by the interaction with the furnace
lining
NEGATIVE
• The larger the inclusions, the lower the
fatigue limit of the material.
• source of cracks in part fracture.
• Sharp-angled inclusions cause stress
concentration
INFLUENCE

40. The aim of this study was to assess the surface roughness of 2 base
metal alloys, submitted to different casting techniques, to
determine the influence of surface roughness on loss of mass after
polishing compared to commercially pure titanium castings.
Base metal alloys submitted to vacuum casting showed
decreased surface roughness, similar to that of titanium,
compared to base metal alloys submitted to acetylene-oxygen
flame casting. There were no significant differences in loss of
mass after polishing for all tested specimens.

41. Purpose: This study evaluated the marginal fit and surface roughness of complete crowns made with a
conventional and an accelerated casting technique.
Materials and methods: A conventional technique (as recommended by the manufacturer) was compared
with an accelerated technique that used 13- to 17-minute bench set and 15-minute wax elimination cycle in a
815 degrees C (1500 degrees F) preheated furnace.
Results: For the marginal discrepancy and surface roughness, crowns fabricated with the accelerated casting
technique were not significantly (P > 0.05) different from those fabricated with the conventional technique.

43. POROSITY

44. POROSITY
within the interior region of a
casting and on the external
surface
External porosity
• Also a factor in
surface roughness
• Generally a
manifestation of
internal porosity.
Internal porosity
• weaken the casting
location

45. CLINICAL RELEVANCE
Internal porosity weaken the casting, and if it extends to the surface,
it may be a cause for discoloration
If severe, it can cause plaque accumulation at the tooth-restoration
interface, and secondary caries may result.

46. CLASSIFICATION
Solidification
defects
Residual air Trapped
gases
Localized shrinkage
porosity
Pinhole porosity
Microporosity
Gas inclusions
Subsurface
porosity
Back pressure
porosity

48. Premature termination of the flow of molten metal during
solidification
LOCALIZED SHRINKAGE
POROSITY
Cause
Freezing of sprue before feeding is completed to the casting
proper
Most
common
location
Near the sprue-casting junction

49. Prevention
Continual feeding of
molten metal through
the sprue
Adequate diameter of
the sprue
Appearance

50. Attaching one or more small-gauge sprues (e.g., 18-gauge) at the
surface most distant from the main sprue attachment and extending
the sprue(s) laterally within 5 mm of the edge of the ring
Ability of the pontic to retain heat because of its bulk and because it was located in
the heat center of the ring
Cause
Prevention
Localized shrinkage porosity in pontic of three-unit bridge

51. SUCK-BACK POROSITY
Cause
When a hot spot has been
created by the hot metal
impinging from the sprue
channel on a point of the
mold wall, it causes the
local region to freeze last
and results in suck-back
porosity
Most
common
location
Occlusoaxial line angle or
incisoaxial line angle that
is not well rounded.

52. Prevention
It can be eliminated by flaring the point of sprue attachment
and reducing the mold-melt temperature differential, that is,
lowering the casting temperature by about 30˚ C.

53. MICROPOROSITY
Cause
Rapid solidification if the mold or casting
temperature is too low
Appearance
small, irregular
voids
Generally present in fine-grain alloy castings
when the solidification is too rapid for the
microvoids to segregate to the liquid pool.

54. The present study was designed to analyse the average depth of the microporosity of a nickel-
chromium (Ni-Cr) system alloy (Verabond II). The metal surface was subject to one of the following
surface treatment: (i) Electrolytic etching in nitric acid 0.5 N at a current density of 250 mA cm(-2); (ii)
chemical etching with CG-Etch etchant; and (iii) Sandblasting with alumina particles 50 microm
The depth of porosity was measured through photomicrographs (500x) with a profilometer
• The greatest and identical depth of microporosity was observed following electrolytic etching and
chemical etching
• The least and identical depth of microporosity was observed with chemical etching and sandblasting
with alumina particles 50 micron

55. Cause
Inability of the air in the mold to
escape through the pores in the
investment or by the pressure
gradient that displaces the air
pocket toward the end of the
investment via the molten sprue
and button.
The entrapment is frequently found in
a “pocket” at the cavity surface of a
crown or mesio-occlusaldistal casting
BACK PRESSURE /
ENTRAPPED AIR
POROSITY
location

56. Appearance
Large concave depressions
prevention
Proper burnout, an adequate mold and casting
temperature, a sufficiently high casting pressure,
and proper L/P ratio

57. Appearance
 Spherical in contour
 Gas inclusion porosities are usually
much larger than pinhole porosity
PIN HOLE POROSITY GAS INCLUSION POROSITY
Entrapment of gas during solidification

58. Cause Many metals dissolve or occlude gases while they are molten. On
solidification, the absorbed gases are expelled and pinhole porosity
results.
Larger spherical porosities- Gas occluded from a poorly adjusted torch flame, or by
use of the mixing or oxidizing zones of the flame rather than the reducing zone
Prevention Can be minimized by premelting the gold alloy on a graphite crucible or
a graphite block, and by correctly adjusting and positioning the torch
flame during melting

59. Appearance
Can be diminished by controlling the rate at which the molten metal enters the mold.
SUB SURFACE POROSITY
Simultaneous nucleation of solid grains and gas bubbles at the first moment that the
alloy freezes at the mold walls.
Cause
Prevention

60. INCOMPLETE CASTING

61. INCOMPLETE CASTING
• Incomplete elimination of
wax residues from the
mold.
The molten alloy has been prevented, from completely filling the mold.
FACTORS
CAUSE
• Insufficient venting of the
mold
• Discrepancy in
temperatures between the
casting ring/mold and the
molten alloy
• small diameter of sprue

64. If insufficient casting pressure is
used, the back pressure cannot
be overcome. Furthermore, the
pressure should be applied for at
least 4 sec
Directly related to the back pressure exerted by the air in the mold.
PREVENTION
Insufficient venting of the mold
If the air cannot be vented quickly, the molten alloy does not fill the mold before it solidifies.

65. If too many products of combustion remain in the mold, the pores in the investment may
become filled so that the air cannot be vented completely
Incomplete elimination of wax
residues from the mold.
If moisture or particles of wax remain, the contact of the molten alloy with these foreign
substances produces an explosion that may produce sufficient back pressure to prevent the
mold from being filled.

66. Results in molten metal solidifying in the sprue area before completely filling the mold
cavity
SMALL DIAMETER OF SPRUE
Should always be at the bulkiest portion of the wax pattern directed at 45° angulation to the
surface.
ATTACHMENT OF SPRUE

67. Improper L/P ratio, mixing time, and improper burnout temperature
OTHER CASTING DEFECTS
UNDERSIZED AND
OVERSIZED CASTING
Cause
Prevention Adherence to the proper protocol of selection of materials and
techniques will ensure a proper fit of the casting without any defect

68. VARIABLES AND PRINCIPLES OF OPTIMAL SPRUE DESIGN
The purpose of a sprue former, or sprue pin, is to provide a
channel through which molten alloy can reach the mold in an
invested ring after the wax has been eliminated

70. Sprue Diameter
• same size as the thickest
area of the wax pattern
• If it is too small, this area
will solidify before the
casting itself and localized
shrinkage porosity (“suck-
back” porosity) may
develop
Sprue Position
At the greatest bulk in the
pattern to avoid distorting
thin areas of wax during
attachment to the pattern and
to permit the complete flow
of the alloy into the mold
cavity

71. Sprue Attachment
Flaring of the sprue former facilitating the
entry of the fluid alloy into the pattern area
with the largest cross-sectional areas
Sprue Direction
• Directed away from any thin or
delicate parts of the pattern
because the molten metal
may abrade or fracture
investment
• Not be attached at a right
angle to a broad flat surface
as it may leads to turbulence
within the mold cavity and
causes severe porosity
Sprue Length
1)Gypsum-bonded investments
-Top of the wax pattern is within 6 mm of the
open end of the ring
2)phosphate-bonded investments
within 3 to 4 mm of the top of the investment

72. CONCLUSION

73. REFERENCES
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• Contemporary fixed prosthodontics – Rosenstiel
• Craig,s Textbook of Restorative Dental Materials -11th edition
• Textbook of Operative Dentistry Vimal Sikri 4th Edition

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metal alloys: a comparative study with titanium. J Prosthet Dent. 2004
Sep;92(3):274-7.
• Konstantoulakis E, Nakajima H, Woody RD, Miller AW. Marginal fit and surface
roughness of crowns made with an accelerated casting technique. J Prosthet Dent.
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75. • Chan D, Guillory V, Blackman R, Chung KH. The effects of sprue
design on the roughness and porosity of titanium castings. J Prosthet
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76. Thank you