Casting procedures in dentistry

Steps in casting
Wax pattern fabrication
Die
sprue
sprue former
Investing
burnout
crucibles
casting
casting machines
finishing & polishing

1. Good
Morning
1

2. 2

3. GUIDED BY :

Dr. AJAY SAXENA Dr. MANOJ CHANDAK
(Prof. & Guide) (H.O.D & Prof.)
Dr .Pradnya Nikhade Dr. N. U Manwar
(Prof.) (Prof.)

Dr. Anant Heda Dr. Anuja Ikhar

(Reader) (Reader)
Presented by Dr. Abhilasha dass

4. ContentsContents
Introduction
History
Preparation of a die
Wax Pattern fabrication
Sprue Former
Reservoir
Casting Ring liner
Investing
Burnout
Lost wax Technique
Crucibles
Casting
Casting machines
Cleaning of casting
Take home message
4

5. 5
Sr.no. Learning objective Domain Level Criteria
1 Steps in casting procedureCognitive Must know All
2 Preparation of a die Cognitive Must know All
3
Wax Pattern fabrication
Cognitive Must know All
4 Sprue former Cognitive Must know All
5 Casting Ring liner Cognitive Must know All
6 Investing Cognitive Must know All

6. 6
7 Burnout Cognitive Must know All
8 Lost wax Technique Cognitive Must know All
9 Crucibles cognitive Must know All
10 Casting machines cognitive Must know All
11 Finishing & polishing cognitive Must know All

7. Introduction :Introduction :
Casting is the process by which a wax pattern
of a restoration is converted to a replicate in a
dental alloy. The casting process is used to
make dental restorations such as inlays, onlays,
crowns, bridges and removable partial
dentures. 
In dentistry the resulting casting must be an
accurate reproduction of the wax pattern in
both surface details and overall dimension.
7

8. Reproducing the wax up in metal with
predictable results has always been a
challenge.
Small variation in investing or casting can
significantly effect the quality of the final
restoration.
Successful castings depend on attention
to detail and consistency of technique.
8

9. HistoryHistory
In approximately 500 BC, the Etruscans produced bridges made
of soldered gold bands. 
The most ancient dental prosthesis fabricated from gold wire was
found in Egypt and dated as far back as 2500 BC. 
Copper was cast in Mesopotamia about 3000 B.C. 
The oldest dental castings were gold inlays found in teeth from
the natives of Ecuador in about first Century AD. 
11th Century A.D
→
Theophilus Described lost wax technique,
→
which was a common practice in jewelry.
9

10. 10
•The renaissance craftsman and sculptor Benvenuto Cellini
(1500-1571) in his autobiography described his method of
casting in both gold and bronze by coating his finely detailed
wax model with a reinforced refractory shell.
•1558 → B. Cellini → attempted use of wax and clay for
preparation of castings.
18981898- Dr. Philbrook demonstrated the 1st cast gold inlay in the
Dental Society.
1903 Lentz cast occlusal surfaces to banded gold crowns by the
lost wax method of mould formation but apparently did not apply
his technique to the fabrication of cast inlays.

11. 19071907- Introduction of lost wax technique by W.H Taggart.
19101910 Van Horn introduced a different method of
compensation recommending that the wax pattern be
invested at a temperature equal to mouth temperature.  
1928 The low heat casting technique was finally abandoned
when Coleman published his research paper No.32 for the
United States National Bureau of Standards in which he
demonstrated the great shrinkage which occurred when
investment is cooled after heating. 
11

12. Weinstein in 19291929 found that adding boric acid to
customary investment mixtures prevented the shrinkage.
Sweeney, Paftenbarger  (1930-33) (1930-33) studied use of
cristobalite as a refractory in dental casting investment
and found that a cristobalite based investment (75%
cristobalite & 25% plaster) heated to temperatures
between 400ºC and 800ºC produced dimensionally
accurate castings.
19421942-Sonder- recognised thermal expansion of
investment was greatly inhibited by rigid metal casting
ring- advocated lining with soft asbestos.
12

13. 19341934- Classification of gold based casting
alloys.
Goldberg (1937) (1937) recommended the use of the 
wax with 0.1% Contraction for the direct
technique and the wax with 0.38%
contraction for the a  patterns made on a die
at room temperature in the indirect
technique.
 
13

14. •19451945- George D. Estes, introduced the vacuum investing
technique to prevent formation of air bubbles on the surface
of the wax.
•19491949- - Moore and Walt developed phosphate bonded
investment
•19501950-development of resin veneers for gold alloys
1959 –Asgar & Peyton stated that flaring should
occur at the sprue/ wax pattern junction.
 1959 - Strickland et al stated the importance of the
type, shape location & direction other than the size
of the sprue .
14

15. 1959 - Morrison and Warmick reported the findings of
ethyl silicate refractory material for dental use.
•19681968-Pd based alloys alternatives for gold
•19711971- Ni based alloys alternatives for gold
•1980’s1980’s-Introduction of all-ceramic technology
Moore (1993) (1993) discovered by the addition of chlorides to
investments he could obtain a thermal expansion of as
much as 1.1% from quartz based investment. 
15

16. Definition Definition
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)
“Casting is the process by which a wax pattern of
a prepared tooth is fabricated and converted to
its metallic replica”(Rosenteil)

16

17. Objectives of casting :Objectives of casting :

1) To heat the alloy as quickly as possible
to a completely molten condition.
2) To prevent oxidation by heating the
metal with a well adjusted torch .
3) To produce a casting with sharp details
by having adequate pressure to the well
melted metal to force into the mold.
17

18. STEPS IN MAKING A CAST STEPS IN MAKING A CAST
RESTORATIONRESTORATION
1. TOOTH PREPARATION /CAVITY
PREPARATION
2 . IMPRESSION
3. DIE PREPARATION
4. WAX PATTERN FABRICATION
5. SPRUING
6. INVESTING
7.BURNOUT
8.CASTING
9.CLEANING & POLISHING
18

19. Die Die
•Defined as the positive reproduction of the form of the prepared
tooth in any suitable substance in which inlays, crowns & other
restorations are made.
IDEAL REQUIREMENTS
•Accurate reproduction of the fine details
•Dimensional accuracy
•Good strength & hardness
•Ease of use
•Abrasion resistance
•Relatively inexpensive
19

20. PREPRATION OF MASTER DIE :PREPRATION OF MASTER DIE :
Commonly used die materials-
Type IV gypsum product - 0.1%
(setting expansion)
Type V gypsum product - 0.3% (setting
expansion)
Disadvantage- Susceptibility to abrasion

20

21. Means to increase abrasion
resistance of die :

-Silver plating
-Coating surface with die
hardener
- Adding die hardener to
gypsum
21

22. Die spacerDie spacer
Used to provide relief space for cement.
Applied within 0.5mm of the preparation finish line to provide relief
for the cement luting agent.

Example- resins (most commonly used)
- model paint
- colored nail polish
- thermoplastic polymers
dissolved in volatile solvents.

22

23. Diestone/investment combinationDiestone/investment combination
In this, die material and investment medium have a
comparable composition

Divestment – a commercially
available gypsum bonded material .
Divestment is mixed with colloidal silica and die is made
from this mix & wax pattern is constructed.
Advantage- It eliminate possibility of distortion
of wax pattern while removing it from die .
23

24. OTHER DIE MATERIALSOTHER DIE MATERIALS

Amalgam Amalgam
Acrylic resins (shrinkage 0.6%) Acrylic resins (shrinkage 0.6%)
Polyester resin Polyester resin
Epoxy resins (less shrinkage then Epoxy resins (less shrinkage then
acrylic resins0.1to0.2%) acrylic resins0.1to0.2%)
24

25. 25
ELECTROFORMED DIES :

These dies have high strength, hardness &
excellent abrasion resistance.
First step – Treating the surface of impression
material so that it conducts electricity. This process
is referred as METALLIZING.
PROCESS : A thin layer of metal, such as silver
powder, is deposited on the surface of impression
material.
Example : Bronzing powder
aqueous suspensions of silver powder
powdered graphite

26. ARRANGEMENT IN ELECTROPLATING BATHARRANGEMENT IN ELECTROPLATING BATH
~~Impression- act as cathodeImpression- act as cathode
Electroplating bath solution- silver cyanide or Electroplating bath solution- silver cyanide or
silver nitrate solution silver nitrate solution
(better details) (better details)
~ ~Silver plate- act as anodeSilver plate- act as anode
Electric current of 5-10 mA/cm² square of cathode is Electric current of 5-10 mA/cm² square of cathode is
passed for 10 hour. passed for 10 hour.
The impression that contains the electroformed die The impression that contains the electroformed die
surface is then filled with dental stone. When the surface is then filled with dental stone. When the
stone hardens, it is mechanically locked to the stone hardens, it is mechanically locked to the
rough interior of the electroformed metal shell. rough interior of the electroformed metal shell.



26

27. Wax pattern fabricationWax pattern fabrication
27
- It is contouring of wax
pattern into desired shape and
form.
- All aspects of final
restoration are incorporated
into the wax pattern
- Shortest time should elapse
between the time the pattern is
removed from the die & the
time
it is invested.

28. Wax Technique Wax Technique
28
A) DIRECT
Wax pattern is made
directly inside the
mouth, as in inlay
case.
Type-1 medium wax.
Exceptionally
demanding procedure.
B) INDIRECT
Wax pattern is made on
the
die.

Type -2 soft wax.
More commonly used
technique.

29. Sprue & Sprue formerSprue & Sprue former
29

30. Sprue Sprue
Part of casting that acts as a channel for the
molten metal to flow into the mold cavity after
the wax has been eliminated.
PURPOSE:
To form a mount for the wax pattern & fix the
pattern in space so a mold can be made.
To create a channel for elimination of wax
during burn out.
To form channel for ingress of molten alloy .
To compensate for alloy shrinkage during
solidification.
30

31. Wax pattern attached to the crucible formerWax pattern attached to the crucible former
with a sprue ready for investing. A ring liner is with a sprue ready for investing. A ring liner is
in place. in place.
31

32. Spruing of wax pattern :Spruing of wax pattern :
32

33. FUNCTION:
Facilitate flow of molten metal from crucible
to mold.
Store additional metal & prevent shrinkage
porosity.
May be used as handle to remove wax
pattern.
33

34. 34
Types of Sprue

35. 35

36. 36

37. SprueSprue
DIAMETER
LOCATION
LENGTH
ATTACHMENT
DIRECTION
37

38. SPRUING TECHNIQUE SPRUING TECHNIQUE
DIRECT : sprue former provides direct connection
between pattern area & the sprue base/crucible
former area.
A basic weakness of direct Spruing is the potential for
suck-back porosity at the junction of restoration and the
Sprue.
INDIRECT: connector/ reservior bar is positioned
between pattern & the crucible former.
Indirect Spruing offers advantages such as greater
reliability & predictability in casting plus enhanced control
of solidification shrinkage .The Connector bar is often
referred to as a “reservoir .
38

39. Sprue formerSprue former
The sprue is attached to a crucible
former, usually
made of rubber, which constitutes the
base of the
casting ring during investing.
May be metal , plastic or rubber
The exact shape of the crucible former
depends on the type of casting machine
used.
With most modern machines, the crucible
former is tall to allow use of a short sprue
and allow the pattern to be positioned
near the end of the casting ring.
also referred to as a sprue former
39

40.  Crucible formers/ Sprue formers are
basically of 2 types---
a)Steep-sided cone: used with metal
when casted using centrifugal casting
force.
b) Shallow cone: used to cast metal
using stream/air pressure
40

41. RESERVOIRRESERVOIR
Piece of wax attached to the sprue about 1mm away
from the pattern ,as a enlarged round mass or a
connector bar between the wax pattern sprue former.
41

42. Importance :Importance :
42

43. SURFACE TREATMENT OF SURFACE TREATMENT OF
COMPLETED WAX PATTERNCOMPLETED WAX PATTERN

Before the wax pattern is invested, it
should be cleaned of any debris, grease,
oils and separating medium.
43

44. 44

45. Preparatory steps for investingPreparatory steps for investing
•Secure wax pattern,
•Cleaning the wax pattern of debris, grease or oil
by surfactants-
a)Pattern cleanser
b)Dil. synthetic detergent sol.
c)Debbublizer
45

46. Debubblizer :Debubblizer :
Citric acid
Sodium 2-phenylpropane-2-sulfonate
Propane-1,2-diol - also known as
propylene glycol
46

47. Casting ring & linerCasting ring & liner
The casting ring serves as a container for
the investment while it sets & restricts
setting expansion of the mold.
47
Metal casting
ring
Sprue base or
Crucible former
Ring liner

48. Casting RingCasting Ring
They are available as-
1) Shapes - Round
- Oval
2) Complete rings
I) - Rigid
- Metal (stainless steel)

- Plastic
II) Flexible - Rubber
3) Split rings
I) metal
II) plastic
48

49. Casting Ring Considerations :Casting Ring Considerations :
1)The internal diameter of casting ring
should be 5-10mm greater than the widest
measurement of the pattern and about 6
mm higher.
2)For single crown/inlay - small rings as
used. Diameter - 32 mm
3)For large fixed partial denture –
63mm round/oval shaped casting ring are
used
49

50. CASTING RING
LINERS
ASBESTOS
LINERS
NON ASBESTOS
LINERS
CELLULOSE PAPER
AL-SILICATE CERAMIC
50
Asbestos:- carcinogenic potential makes it a biohazard.
Functions of a liner
Affords greater normal expansion in the
investment
The absorbed water causes a semi hygroscopic
expansion
Thickness – not less than 1mm

51. Liner techniqueLiner technique
A)DRY LINER TECHNIQUE - tacked in
position with sticky wax.
B)WET LINER TECHNIQUE - lining ring is
immersed in water & excess water is shaken
off.
The liner is cut to fit the inside diameter of
the casting ring with no overlap and 3mm
short of the top and bottom of the ring , this
serves to lock the investment within the ring
& equalize expansion.
51

52. 52

53. RINGLESS CASTING TECHNIQUE RINGLESS CASTING TECHNIQUE
With the use of higher-strength, phosphate-
bonded
investments, the ringless technique has become
quite popular.
The method uses a paper or plastic casting ring
and is designed to allow unrestricted expansion.
53

54. 54
Crucible formers and cone-shaped plastic rings for a
ringless casting system.
The crucible former and plastic ring are removed
before wax elimination, leaving the invested wax
pattern.
 The systems are designed to achieve expansion that
is unrestricted by a metal ring.

55. Investing Investing
Process by which the sprued wax pattern is
embedded in a material called an investment.
OR
 A ceramic material that is suitable for forming a
mould into which a metal or alloy is cast.
The operation of forming a mold is known as
INVESTING

55

56. 56

57. While the wax pattern is air drying,
the appropriate amount of distilled
water (Gypsum Bonded
investments), colloidal silica special
liquid (Phosphate Bonded
investments) is dispensed.
Powder should be weighed before
mixing it with liquid.
The liquid is added to clean dry
mixing bowl, and the powder is
gradually added to the liquid using
care and caution to minimize air
entrapment.
57

58. Paint off techniquePaint off technique
Wet investment material
is gently painted over a
complex wax pattern by
the use of sable hair brush,
covering it completely .
58

59. Poured into the ring thinly
from a height (20-30)cm at
a slight angle from
bottom to the top of a ring
59

60. 60

61. 61
Allow the investment to set
(45 – 60) min before
burnout procedure
commences
Place invested pattern in a Place invested pattern in a
humidator if burnout process is humidator if burnout process is
delayed.delayed.

62. METHODS OF INVESTING :
A) HAND INVESTING
B) VACCUM INVESTING
Advantages of vacuum investing
•The amount of Porosity in the investment is
reduced
•The texture of cast surface is smoother with
better detail reproduction
•The tensile strength is greatly increased
62

63. Brush technique of investingBrush technique of investing
63

64. Vaccum InvestingVaccum Investing
64

65. 65
•When the investment has set,
the "skin" at the top of the ring
is trimmed off.
•The rubber crucible former is
removed, and any loose particles
of investment are blown off.
•The ring is then placed in the furnace
for the recommended burnout schedule

66. BURN OUTBURN OUT
•Elimination of the wax
pattern from the mold of set
investment is referred to as a
burnout.
•Ring may be placed on a
raised object within the oven
to completely eliminate the
wax & form a cavity into
which the molten metal is
cast.
•Oven is preheated to approx.
400 degree C for 20 mins.
•Temperature raised slowly to
700 degree C for 30 mins.
66

67. a) For gypsum investment.
500 degree c - hygroscopic expansion
tech.
700 degree c - thermal expansion
tech.
b)For phosphate investment 700 - 1030
degree c
c)Ethyl silicate bonded investment- 1090
degree c
67

68. The ring should be maintained long
enough at the maximum temperature
(“heat soak”) to minimize a sudden drop
in temperature upon removal from the
oven.
Such a drop could result in an incomplete
casting because of excessively rapid
solidification of the alloy as it enters the
mold.
68

69. If materials used during the casting process didn't
shrink or expand, the size of the final cast
restoration would be the same as the original wax
pattern. The management of dimensional changes is
complex, but can be summarized by the equation:
wax shrinkage + metal shrinkage = wax
expansion + setting expansion +
hygroscopic expansion + thermal expansion
.
69

70. CastingCasting
Casting of an alloy into the mold space
uses 2 basic requirements:
A) Heat source – to melt the alloy
B) Casting force – to force molten alloy
into mold
70

71. Casting force > surface tension of alloy
+ resistance offered by gas in the
mold
This can be done by use of following
different type of force-
Vacuum force
Air or Gas Pressure
Centrifugal force
71

72. Melting temp of pure gold –1063⁰c
Melting temp of gold alloy-924-960⁰c
Melting temp of base metal alloy-1155-1304⁰c
72

73. A)Heat Source: Different types of materials
and method are used as heat source to melt
alloy. Two basic modes are by using
1)Torch flame–
Gas air
Gas oxygen
Air acetylene
Oxygen acetylene.
hydrogen oxygen generator
2)Electricity
73

74. METHODS OF MELTING ALLOYMETHODS OF MELTING ALLOY
A)TORCH
MELTING
-For low
temperature
metals
-Mixture of
natural/artificial
gas, oxygen/tank
gas –oxyacetylene
Less faster than
electric heating but
more faster than
resistance heating.


B) ELECTRIC MELTING
-For higher temperature
metals.
electric resistance
melting, induction
melting.
 melts alloy faster,& can
be easily over heated
74

75. 75
Two type of torch tips:
1.Multi-orifice
2.Single-orifice
Zones of the blow torch flame:
Zone 1 - colorless zone /Non combustion zone
Zone 2 – Combustion zone
Zone 3 – Reducing zone
Zone 4 - oxidizing zone

76. Melting methodsMelting methods
Gas air torch: -Gas-air torch is used to
melt conventional noble metal alloys
(used for inlays, crown and bridge) whose
melting points less than 1000c
⁰
76

77. Gas oxy torch:Gas oxy torch:
Used to melt metal
ceramic alloys of higher temperature
up to 1200⁰c
The tip of torch is available as
single orifice/multiorifice. The
oxygen pressure is adjusted to10-
15 psi.
The flame is directed onto metal
with the nozzle of the torch about
1.5 cm away from the metal.
Complete fluid should be obtained
within 30 second at which point
the metal is poured into the
mould.
77

78. Oxy acetylene torch Oxy acetylene torch ::
The actual production of flame can be done by
adjusting the pressure and flow of individual gases .
commonly advised pressure for acetylene nozzle
is 3.5 N/cm2 and oxygen nozzle 7-10 N/cm2
 one part of acetylene + 2 and half part of oxygen
The best results are obtained when flame is used
with a distance of 10cm between the face of blow
torch nozzle and the base of crucible.
If distance is reduced to –
- 7.5 mm -slight porosity
- 5 mm -increased porosity due to occluded H2
gas
78

79. CRUCIBLESCRUCIBLES : :
The Melting of alloy requires a crucible to act
as a platform on which the heat can be
applied to the metal.
79
Clay
Quartz Carbon

80. 1. Clay - High noble & noble metal types
2. Carbon - High noble crown and bridge
alloys also for higher fusing gold-based
metal ceramic alloys.
3. Quartz - Higher fusing, gold based metal ceramic
alloy & palladium alloys.
4. Zirconia – alumina -High fusing alloys of any type :
specially for alloys that have a high melting
temperature or are sensitive to carbon contamination.
(Alloys like High Pd,Pd - Ag ,Ni based or Co based
are included in this category)

80

81. 81
• The crucibles used with noble metal alloys should
not be used for melting base metal alloy
•Crucible should be discarded if it contains large
amount of oxides and contaminants from previous
metals
•Sufficient mass of alloy must be present to sustain
adequate casting pressure---
6gm is typically adequate for premolar and anterior
casting
10gm is adequate for molar casting

82. Casting machinesCasting machines
Air pressure casting machine.
Torch melting /Centrifugal casting
machine.
Electrical resistance–heated casting
machine.
Induction melting casting machine.
Vacuum or pressure assisted casting
machine.
Direct-current arc melting machine.

83. Air Pressure casting machineAir Pressure casting machine
Alloy is melted in the hollow left by the crucible
former by torch flame and then air pressure is
applied through a piston.
Carbon dioxide, carbon monoxide or nitrogen
gas can be used.
Pressure of 10-15 psi is usually applied.

84. Vaccum casting machineVaccum casting machine
Vaccum is applied through the base beneath the casting
ring and the molten alloy can be drawn into the mold by
NEGATIVE PRESSURE. In this case, the material is
sucked upwards into the mold by a vacuum pump. The
mold in an inverted position from the usual casting
process, is lowered into the flask with the molten metal.

85. CENTRIFUGAL CASTING MACHINECENTRIFUGAL CASTING MACHINE
85
This machine makes use of centrifugal force to thrust the liquid
metal into the mold.
Centrifugal casting is a method of casting parts having axial
symmetry. The method involves pouring molten metal into a
cylindrical mold spinning about its
axis of symmetry. The mold is kept rotating till the metal has
solidified.
Mold material like steels, Cast irons, Graphite may be used.

86. Centrifugal casting is carried out as
follows:
•The mold wall is coated by a refractory
ceramic coating
•Starting rotation of the mold at a
predetermined speed.
•Pouring a molten metal directly into the
mold
•The mold is stopped after the casting has
solidified.
•Extraction of the casting from the mold.
86

87. Direct current arc melting machineDirect current arc melting machine
The alloy is vacuum
melted & cast by
pressure in an argon
atmosphere.
Direct current arc is
produced between 2
electrodes
Alloy & water cooled
tungsten electrode.
The temperature within
the arc exceeds 4000
˚c, the alloy melts
very quickly.
Disadvantage- alloy can
become overheated.
87

88. ELECTRICAL RESISTANCE HEATED CASTING ELECTRICAL RESISTANCE HEATED CASTING
MACHINEMACHINE
--There is automatic melting of metal in graphite There is automatic melting of metal in graphite
crucible .crucible .
-This is advantageous for-This is advantageous for
metal-ceramicmetal-ceramic
restoration in which restoration in which
trace amount of basetrace amount of base
metals are prevented from metals are prevented from
oxidation from torch flameoxidation from torch flame
from overheating.from overheating.
88

89. Metal is melted by induction field that develops with in Metal is melted by induction field that develops with in
the crucible surrounded by water cooled metal tubing.the crucible surrounded by water cooled metal tubing.
Molten metal is forced in to mold by air pressure or Molten metal is forced in to mold by air pressure or
both. both.
89
INDUCTION CASTING
MACHINE

90. Vacuum Vacuum
or pressure- assisted or pressure- assisted
casting machinecasting machine
Titanium & its alloys require
vacuum arc heating argon
pressure casting machines.
The melting point of
commercially pure titanium is
1671˚c.
In such high temperature ,
either a graphite or water
cooled copper crucible is
used.
To prevent absorption of
gases in its molten state,
titanium is cast in the
protective atmosphere of
argon or in vacuum.
90

91. DIVESTINGDIVESTING
“It refers to removal of casting from
the investment mold “
91

92. Recovery of a casting from phosphate-bonded investment.Recovery of a casting from phosphate-bonded investment.
A, Trimming is done from the bottom end of the ring. A, Trimming is done from the bottom end of the ring.
B, Investment is being pushed out of the casting ring.B, Investment is being pushed out of the casting ring.
C, The mold is broken open. C, The mold is broken open.
D, Investment is removed from the casting. D, Investment is removed from the casting.
Care must be taken to avoid damaging the marginCare must be taken to avoid damaging the margin
92

93. 93

94. Sandblasting :Sandblasting :
The casting is held in a sandblasting
machine to clean the remaining
investment from its surface.
94

95. Cleaning the castingCleaning the casting
•After the casting has solidified the ring is
removed and quenched in water. This
leaves the cast metal in annealed
condition resulting in a porous, soft,
granular investment that is easily
removed .(Gold alloys)
•Often the surface of casting appears dark
with oxides and tarnish, such a film can be
removed by process called pickling.
95

96. Pickling Pickling
Heating a discolored casting in an acid.
Mask the dark/tarnished appearance of adherent oxide.
Solution used-
 1.(50%) dil HCL,
 2. (50%) dil Sulphuric acid,
Others –ultrasonic device.
96

97. Disadvantages of hydrochloric acid :
It is a health hazard
Fumes from the acid are likely to corrode the clinic and
laboratory metal furniture
Dilute hydrochloric acid should not be used unless
necessary neutralizing solutions are immediately at hand
It causes irreversible tissue injury.
Ultrasonic pickling can be carried out while the
prostheses is sealed in a Teflon container
Best method of pickling- the casting is placed in a test
tube and acid is poured
97

98. After cleaning of casting :After cleaning of casting :
98

99. Trimming & polishing :Trimming & polishing :
The casting is trimmed , shaped and smoothen
with suitable burs or stones.
The sprue is sectioned off with a cutting disc.
White stone ,rubber wheels, rubber disks, and
fine grit are included in the finishing and polishing
agents
99

100. Inspection & finishing of castingInspection & finishing of casting
A)Inner surface ( which will be in contact with the
prepared surface of the tooth)should be carefully
examined under higher magnification & illumination for
any discrepancy.
B)Tiny air bubbles in the investment create very minute
nodules on the inner surface, which interfere with the
fitting of the casting.
100

101. C) Improper coating of inner surface of a narrow wax
pattern with investment material may result in
entrapment of large volume of air.
This will result in large nodule over the metal blocking the
whole inner surface.
101

102. Referenes Referenes
Craig’s – 13
th
edition
Phillip’s SCIENCE OF DENTAL MATERIALS:
ANUSAVICE – 10th edition &11
th
edition
Contemporary fixed prosthodontics –
Rosenstiel & Fujimoto 4
th
edition
Materials used in dentistry- S. Mahalaxmi 1
st

edition
Vimal sikri- Operative dentistry 3
rd
edition
102

103. 103
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