Casting Procedures; from intro to technique

1. DEPT. OF
CONSERVATIVE DENTISTRY
&
ENDODONTICS
9/26/2013 1

3. Presented By:- Dr Nishant Khurana
PG IInd Year
Guided By:- Dr M.P. Singh
9/26/2013 3

4.  INTRODUCTION
 CASTING
 INSTRUMENTS AND EQUIPMENTS
 STEPS IN METAL CASTING PROCEDURE
 STEP BY STEP CASTING PROCEDURE
 RECENT ADVANCES
 CONCLUSION
 BIBLIOGRAPHY

5. Casting:-An object,usually of metal,formed in
a mould

6.  Casting is a process in which molten material
is poured into a mould and allowed to harden
into the shape of the mould.
 Term “casting” is applied to the shape
produced as well as to the process by which
it is made.

7.  The lost wax technique has been used for
centuries but its use in dentistry was not
common until 1907,when W.H.TAGGART
introduced his technique with the casting
machine in Chicago-USA

8.  Casting ring
 Sprue former
 Crucible former
 Vacuum Investing unit
 High heat electric furnace
 Source of high heat i.e. flame
 Centrifugal casting machine
 Finishing and polishing instruments

9.  Dental waxes are originally polymers
consisting of hydrocarbons & their derivatives
(e.g. ether & alcohol) and are blends of natural
and synthetic waxes, natural resins, oils, foils,
and gums
 M. wt => 400-4000.
 Melting range of 50*C to 300*C, rather than
a single temperature,
because their components consists of a wide
distribution of molecular weight

10.  The American national standards institute /
American dental association(ANSI/ADA)
specification NO:4 waxes used for fabrication
of patterns for dental casting are divided into
two types
TYPE 1: medium wax used in direct
techniques;
TYPE 2: soft waxes used in indirect
techniques
.

11.  There are three basic requirements, as
follows:
1. The sprue must allow the molten wax to
escape from the mold
2. The sprue must enable the molten metal
to flow into the mold with as little
turbulence as possible.
3. The metal within it must remain molten
slightly longer than the alloy that has
filled the mold.

12.  The sprue can be wax, plastic, or metal
 Wax sprues are preferred for most castings
because they melt at the same rate as the
pattern and thus allow easy escape of the
molten wax.

13.  Solid plastic sprues soften at a higher
temperature than the wax pattern and
may block the escape of wax, resulting in
increased casting roughness.
 However, plastic sprues can be useful
when casting fixed partial dentures
(F.P.D) in one piece because their added
rigidity minimize distortion.
 Also, hollow plastic sprues are available
that permit the escape of wax

14.  METAL SPRUES
 If a metal sprue is used, it should be made
of non-rusting metal to avoid possible
contamination of the wax.
They are usually removed from the
investment at the same time as the crucible
former.

15. TECHNIQUES
A)Methods (1)direct spruing.
(2)Indirect spruing.
.

16. Wax patterns can be sprued in one of two
different methods.each method has it’s
advantages & disadvantages.

17. With the direct spruing the flow of the
molten metal is straight from the casting
crucible to pattern area in the ring.
This method requires less time
PROCEDURE:
A straight Sprue former is luted to the
thickest part of the wax pattern.

18.  One end is to the wax pattern & other end is
secured to the crucible former
 The sprue former can be modified by placing
a ball or round reservoir between the pattern
and the button

19.  Even with the ball reservoir, the spruingEven with the ball reservoir, the spruing
method is still direct.method is still direct.
 Direct spruing is used most frequently for
the single units.
 The draw back of this method is the
potential suck back porosity at the junction
of the restoration and the sprue.

20. With the indirect spruing,the molten metal
does not flow directly form the casting
crucible into the pattern area.
The casting alloy takes a circuitous root before
it reaches the pattern areas.

21. With this method of spruing,the connector bar
is 6-gauge or 8-gauge round wax to which the
wax pattern sprues are attached on one side
and with two larger ingot sprue formers on
the other side.
Connecter bar
Wax pattern sprues
Ingot sprue formers

22.  Here the connector acts as a reservoir.
 Indirect Spruing offers advantages such
as greater predictability and reliability in
the casting plus enhanced control of
solidification shrinkage.

23.  The reservoir of spruing system should be
placed in the heat center of the ring.
 This should have the largest mass at any
part of the sprue system
HEAT CENTRE

24.  If the pattern is small, the sprue former
must be small, because attaching a large
sprue formers to thin, delicate pattern
could cause distortion.
 If the sprue diameters too small, this area
will solidify before the casting itself and
localized shrinkage porosity (suck –back”
porosity) may develop.

25.  2.5 mm (10 gauge) sprue is recommended
for molar and metal ceramic patterns.
 A smaller 2.0 mm (12 gauge) is adequate
for premolars & partial coverage
restoration including Inlays , Onlays and
Cast Post.
 The ideal area for theSPRUE POSITION (OR)
LOCATION is the point of greatest bulk in the
pattern to avoid distortion and to permit
complete flow of the alloy into the mold cavity.

26.  The sprue former should be directed away form any
thin or delicate part of the pattern, because the
molten metal may abrade or fracture investment in
this area and result in a casting failure.
 If it is sprued at a 45o
angle to the proximal area, a
satisfactory casting is obtained.

27.  This length is depends on the length of the
casting ring.
 Length should be adjusted so that the top of
the wax pattern is with in 6 mm of the open
end of the ring for gypsum bonded
investments.
 In the phosphate bonded investment it is
within 3-4 mm of the top of the investment.

28. Metal
Plastic

29.  Stainless steel rings
 Pyronel alloy metal rings.
Available in two shapes round and
oval and two diameters large & small.

30. PYRONEL ALLOY METAL RINGS (WHIP MIX
CORPORATION)
 Even after repeated heating they remain
precision fitting and stable in size.
They do not flake, corrode or peel away, thus
they have an unusually long life.

31.   These are used in ring less casting
system
 A ring less system that provides
maximum expansion of investment is
available commercially.

32. The system, called the power cast ring less
system consists of 3 sizes of rings and
formers with a release ring, preformed wax
sprues and investment powder, and a
special investment liquid.

33.  These rings are tapered to allow for
removal of the investment mold after the
material has set.
 This system is suited for casting of alloys that
require greater mold expansion than
traditional gold-based alloys

34.  The sprue is attached to a crucible former.
Usually made of rubber / wax which
constitutes the base of the casting ring
during investing.
 The exact shape of the crucible former
depends on the type of casting machine
used.

35.  With the use of solid metal rings or casting
flasks, provision must be made to permit
investment expansion.
 However, the most commonly used technique
to provide investment expansion is to line
the walls of the ring with a ring liner.

36.  Traditionally, asbestos was the material
of choice, but it can no longer be used
because its carcinogenic potential makes
it a biohazard
 2 types of non-asbestos ring liner material
have been produced.
1.An alluminosilicate ceramic liner
2.A cellulose (paper) liner

37. FUNCTIONs
a. Allows for mould expansion.
b. When the ring is transferred from the
furnace to the casting machines, it
reduces loss of heat, as it is a thermal
insulator.
c. Permits easy separation of the investment
from the ring after the casting is over.

38.  The dry liner is tacked in position with
sticky wax, and it is then used either dry or
wet.
 With a wet liner technique, the liner ring is
immersed in water for a time, and the excess
water is shaken away.
 Squeezing the liner should be avoided,
because this leads to variable amounts of
water removal and non-uniform expansion.

39.  A ceramic liner not absorb water like
cellulose liner, its network of fibers can
retain water on the surface.
 The liner does not only afford greater
normal setting expansion in the
investment, but also the absorbed water
causes a semi hygroscopic expansion.
 The thickness of liner should be
approximately 1 mm

40.  The expansion of the investment is always
greater in the unrestricted longitudinal
direction than in to radical direction, that is,
toward to ring.
 Placing the liner short (3.25 mm) of the endsPlacing the liner short (3.25 mm) of the ends
of the ring tends to produce more uniformof the ring tends to produce more uniform
expansion; thus there is less chance forexpansion; thus there is less chance for
distortion of the wax pattern and the mold.distortion of the wax pattern and the mold.

41. In general, the investment materials contain.
1. Refractory material
2. Binder
3. Modifiers Quartz&Cristobalite Dental stone

42. 1. Gypsum bonded investmentsGypsum bonded investments
 They are used for casting gold alloys
 They can withstand temp up to 700o
C
2. Phosphate bonded investmentsPhosphate bonded investments
 They are used for casting cobalt chromium alloys
 They can with stand high temperatures
3. Silica bonded investmentsSilica bonded investments
Alternative to the phosphate bonded investments,
for high temperature casting used in the casting of
base metal alloy partial dentures.

43. Classification:- According A.D.A specification no.2 for casting
investments for dental gold alloys, there are 3 types.
Type – I
Are those employed for the casting of inlays or
crowns when the allow casting shrinkage
compensation is accomplished principally by
thermal expansion of the investment.
Type – II
compensation for alloy shrinkage is by the
hygroscopic expansion.
Type III
Investments are used in the construction of partial
denture with gold alloys.

44. Phosphate bonded investments have the
following approximate composition
according to ALLAN, ASGAR (1966) and
mabic (1973):
 Quartz, Cristobalite =>75 %to 90%
 Mono ammonium phosphate =>7 %to 10%
 Magnesium oxide =>3% to 5%

45.  Unspecified amounts of carbon are often
added to these powders, giving them a black
Color, to minimize oxidation of alloys cast
into them.
 Base metal alloy react with carbon at
temperature above 1500o
C, however, forming
Carbides that can embrittle these alloys;
carbon free (white) phosphate investments
are available for fabrication of copings and
frameworks.

46. Two techniques
1. Brush technique
2. Vacuum technique.

47. These are used for pouring impressions,
placing investment around wax patterns in
casting flasks (rings)
Two types
1.Offer variation in intensity
of vibratory action
2.Offer variation in vibration
frequency. The table of the unit is covered by a
rubber cushion, which moderates the
sharpness of the vibration and
facilitates cleaning

49.  The vacuum mixing of investments to
eliminate air bubbles from the mix is
essential to the production of fine dental
castings.
 It provides both vacuum source and power
spatulation in appropriate carriers or
vessels (bowls)
.

50.   The whip mix corporation manufactures a
combination mixing unit, which serves as a
vacuum pump, power mixer, and vibrator.
 Designed primarily for wall mounting

51.   The first attempts at wax elimination
and mold conditionings were gas-fired
appliances or other simple arrangements
typified by a casting flask (ring) resting upon
a wire mesh suspended over a Bunsen
burner.

52. Furnace with electric muffles were developed
that permitted adjustment of temperature for
high heat or low heat casting techniques and
timing devices were added later.

53.  With the development of high heat (silicate
and phosphate bonded) investments, the use
of multiple stage of burnout temperatures to
prevent mold cracking and damage became
necessary

54. 1. Allow the investment to set for the
recommended time (usually 1 hour) and then
remove the rubber crucible former
a. If a metal sprue is used, remove it as well
b. Any loose particles of investment should be
blown off with compressed air.

55.  2.Place the ring with the sprue facing down
in the furnace on a ribbed tray. The tray
allows the molten wax to flow out freely

56. 3.Bring the furnace to 200*C (400*F) and hold this
temperature for 30 minutes most of the wax is
eliminated by this time.
4.Increase the heat to the final burnout
temperature [generally 650*C (1200*F) or
480*C (900*F) follow the manufacturers
instruction] and hold for 45 min ; because the
heating rate affects the expansion.

57.  When transferring the casting ring to the
casting machine, a quick visual check of the
sprue in shaded light is helpful to see
whether it is properly heated. It should be a
cherry red color.

58.  A vessel made of a refractory substance and
used for melting and calcining materials at
high temperature .

59. Generally 4 types of casting crucibles are
available: Clay, Ceramic, Quartz AndClay, Ceramic, Quartz And
Zirconia Alumina.Zirconia Alumina.

60.  Clay crucibles are appropriate for many of the
crown & bridge alloys, such as the high noble
and noble type.
 Ceramic crucibles can be used not only for high
noble crown & bridge alloys but also for the
higher fusing gold based metal ceramic alloys.

61. Crucibles made from alumina, quartz, or silica
Are recommended for high fusing alloys of
any type these are especially suited for alloys
that have a high melting temperature or those
that are sensitive to carbon contamination.

62. Casting machines provide the means for transferring the
molten alloy from the melting crucible to the mold.
Types-
1. Centrifugal casting machine
2. Air pressure machine- Hereus
3. Induction melting casting machine
4. Steam pressure machine- Solbrig machine
5.Spring wound electrical resistance-machine furnace-
casting machine

63. CENTRIFUGAL CASTING MACHINE:
May be spring driven or motor driven.
Advantage-
simplicity of design and operation.
both large and small castings can be cast on
same machine.

64. AIR PRESSURE MACHINE:
Gases like compressed air or gases like
carbon monoxide or nitrogen, can be used.
Used for making small castings.

65. INDUCTION MELTING CASTING MACHINE:
Metal is melted and forced by air pressure
into mould.
Used for casting base metal alloys.

66. Alloys can be melted by:
 Blow torch
 By electrical resistance
 Induction
BLOW TORCH:
 Fuel used is a combination of-
 Natural or artificial gas and air
 Oxygen and acetylene gas (for high fusion
aloys)

67. Element melting temp
Gold 1945 F
Copper 1981 F
Silver 1761 F
Platinum 3217 F
Palladium 2826 F
Indium 313 F
Zinc 787 F
Tin 449 F

68. Gallium 86 F
Iron 2797 F
Iridium 4449 F
Ruthenium 4530 F
Nickel 2647 F
Cobalt 2723 F
Rhenium 5755 F
Molybdenum 4730 F
Chromium 3470 F
Boron 3690 F
Manganese 2273 F

69.  Let first consider the gold crown and bridge
alloys.
 After the casting has solidifies, the ring is
removed and quenched in water as soon as the
button exhibits a dull-red glow.button exhibits a dull-red glow.

70. 1.The noble metal alloy is left in an annealed
condition for burnishing,polishing,and
similar procedures.
2.when the water contacts the investment, a
violent reaction ensures, resulting in a soft,
granular investment that is easily removed.

71.  After quenching, Gypsum bonded investment
quickly disintegrate.
 Phosphate bonded investment do not
disintegrate and must be forcibly removed from
the casting ring.

72. ** NOTE:-
Gold based ,palladium based , metal ceramic
alloys and base metal alloys are bench-cooled
to room temperature before the casting is
removed from the investment.

73. ** NOTE:-
Casting from these alloys are generally not
pickled.
Abrasive blasting devices (sand blaster) are
used for cleaning the surface of castings.

74.  Often the surface of casting appears dark
with oxides and tarnish such a surface film
can be removed by a processremoved by a process known as
pickling.

75.  The surface oxides from the casting are
removed by pickling in 50% hydrochloric acid.
 The disadvantage of HCL is the fumes from
acid are likely to corrode lab metal
furnishings and health hazard.

76.  So the process performed ultrasonically
while the prosthesis is sealed in a Teflon
container.
 The best method for pickling is to place
the casting in test tube and pour the acid
over it
 It may be necessary to heat the acid,but
boiling should be avoided.

77.  Important features, which have become
standard on most units offered.
1. A small, light, easily manipulated “pencil”,
which provides a precise continuous steam of
extremely fine abrasive blasting material on
demand and under control of the operator.

78. 2. An abrasive tight compartment within which the
blasting process can be confined.
The apparatus should provide a large viewing
window and a good internal light source for
visibility.
The blasting compartment should incorporateThe blasting compartment should incorporate
restricting cuffs to fit around the wrists.restricting cuffs to fit around the wrists.

79.  An adequate suction device to withdraw the
spent abrasive from the blasting
compartment

80.  After recovery of casting the casting is
held in a sandblasting machine to clean the
investment from its surface
SAND BLASTER & SAND
BLASTING MACHINE

81. Separating disc,heatless stone,green,pink,white
stones&rubber wheel.

85. 1. CAD-CAM PROCESS:
Computer -Aided Designing and
Computer -Aided Machining.
Process-
 involves imaging of prepared tooth.
 designing the restoration in size and shape with
the help of a computer.
 then machining (cutting) a ceramic or metal block
again by using a computer.

86. 2. COPY-MILLING PROCESS:
 First master die is made of a prepared tooth.
 Its 3-dimensions are recorded in a computer and enlarged.
 A block of metal is milled to form the surface of a crown.
 Another graphite die is made.
 Now both graphite die and milled metal block are placed in an
electroplating bath.
 After current is switched on, internal surface of the crown is
created in a metal block by copying the graphite die.

87. SIGNIFICANCE:
 Casting is a very important part of dentistry.
 A proper casting of a dental restoration i.e. inlay,
crown, bridge etc. can be of great use in giving
proper treatment and comfort to a patient.
A metal casting
eg. Gold alloy casting is-
 indestructible in saliva.
 perfect restoration can be produced.
 has maximum resistance to force of mastication.

88.  Thus we conclude that “casting is a complex
process involving number of steps and costly
equipment.”
A dental restoration having a perfect fit is
only possible when-
 the right technique is applied.
 one has good understanding of materials
used in casting.

89. DEFECTS IN CASTING:
 If proper procedure is not followed the casting may
have some defects.
The defective casting may –
 not fit.
 have poor esthetics.
 have poor mechanical properties.
Classification of Casting Defects:
(by COOMBE)
 Distortion
 Surface Roughness
 Porosity
 Incomplete Casting
 Contamination
 Black castings due to sulphur compounds.
TO
BE
CONTINUED
LATER…
.

90.  Fundamentals of fixed prosthodontics-
Herbert T. Shillingburg
 Dental laboratory procedures – FPD
kenneth D.Rudd , Robert M. Morrow
 PHILIPS’ Science of Dental Materials
Eleventh Edition Anusavice
 Essentials of Dental Materials
SH Soratur
 Basic Dental Materials
John J. Manappallil

91.  J Dent Res. 1988 Nov;67(11):1366-70
The effect of casting ring liners on the potential expansion of a
gypsum-bonded investment.
Earnshaw R.
 Effect of wet and dry cellulose ring liners on setting expansion
and compressive strength of a gypsum-bonded investment (J
Prosthet Dent 1996;76:519–23.)
 Dent Mater J. 1994 Dec;13(2):240-50.
Effects of rapid burnout type gypsum-bonded investment on
performance of castings. Part 1. Surface aspects and fit of
crowns.
Murakami S, Kozono Y, Asao T, Yokoyama Y, Sera M, Lu YS,
Uchida Y.
 Quintessence Int. 2007 May;38(5):e271-8.
Characteristics of commercial quick-heating phosphate-
bonded investments for the accelerated casting technique.
Yang CC, Yang HH, Ding SJ, Huang TH, Kao CT, Yan M
 Quintessence Int. 2007 Feb;38(2):e78-82.
Effect of sprue design on the castability and internal porosity
in pure titanium castings.