deals with different investment materials used in dentistry. their indications.

1. 1
Presented by
Dr Arunima Upendran
First year MDS

2. Introduction
2

3. 3
Investing : the process
of covering or
enveloping,wholly or in
part, an object such as
a denture, tooth, wax
form, crown, etc., with a
suitable investment
material before
processing,soldering,
or casting
GPT9

4. 4
Dental casting investment : a material consisting principally
of an allotrope of silica and a bonding agent; the bonding
substance may be gypsum (for use in lower casting
temperatures) or phosphates and silica (for use in higher
casting temperatures)
GPT9

5. 5
Acc to Craig ,
-An investment can be described as a ceramic
material that is suitable for forming a mold into
which a metal or alloy is cast.
-The operation of forming a mold is described as
investing.

6. History
6
 The Aztec gold-smiths of pre-Colombian Mexico used lost wax
process to create much of their elaborate jewellery.
 In the city of Benin,now a part of Nigeria, the brass smiths.
The brass cutters begin with a core of clay kneaded into a
mass. They shape the clay into the approximate size & shape
of the article to be made. These cores are then dried in sun for
several days. The brass smith creates a pattern for the casting
by covering one of these cores with beeswax. After finishing
the wax, it is covered in a thick coating of clay. The 1st layer is
applied as a very fine slip. Before the pattern is fully sealed in
the coating, a thin roll of wax is added to form a channel into
which the molten metal will be poured. The thicker layer of
clay is added for investing the form completely, creating a
mold.

7. 7
 .In 1538, molds for large statues were made which, if
one desired to make them of bronze, are first made
of wax by the ordinary procedure. In “ordinary
procedure”, the the original model was created in
wax. The image was then coated with the milky
slurry of plaster, building up successive layers untill
a strong shell enveloped the wax. Alternatively, the
image could be dipped or invested in a “bucketful” of
freshly mixed plaster which set up rock-hard in a
very short time. After melting the wax & casting
molten metal into the void, a perfect duplicate of the
original pattern was created.

8. 8
 Lost wax technique – william H Taggart - 1907
 He described a tech., formulated a wax pattern
compound of excellent properties, developed an
investment material & also invented an air pressure
casting machine.
 In a solid mold technique, a wax sprue was placed in
a steel casing & surrounded by a setting slurry.
Drawbacks were, extremely long pre-heat, size
limitations & poor dimensional tolerances

9. IDEAL REQUIREMENTS
9
1. Easily manipulated.
2. Sufficient strength at
room temperature
3. Stability at higher
temperatures
4. Sufficient expansion
5.Beneficial casting
temperatures
6. Porosity
7. Smooth surface
8. Ease of divestment
9. Inexpensive

10. Composition
10
 Refractory material
 Binder material
 Modifiers
 Other chemicals

11. 11
Refractory material
 It is usually a form of silicon dioxide, such as quartz,
tridymite, or cristobalite, or a mixture of these.
Binder material
 As the refractory material alone do not form a coherent
solid mass, some kind of binder is needed.
 Common binder used are: α-calcium sulfate
hemihydrate,Phosphate, ethyl silicate, and other similar
materials also serve as binder for high temperature casting
investments.

12. 12

13. 13
Modifiers
 Reducing agents - carbon / colloidal copper
 trace – boric acid & sodium chloride
 Colouring agents
 Oxalates

14. Classification
15
1.Based on processing temperature
High temperature casting investment –
 Phosphate bonded
 Silicate bonded
Low temperature casting investment
 Gypsum bonded

15. 16
2.Based on type of Binder Used
 Gypsum bonded investment
 Type I(thermal expansion )
 Type II(hygroscopic expansion )
 Type III(partial dentures with gold alloy)
 Phosphate bonded investments
 Ethyl silicate Bonded investments

16. 17
3.Based on type of refractory used
a.) Silica -
quartz
cristobalite
b.) Magnesium oxide
c.) Zirconia based investments

17. 18
 Gypsum bonded investments are the oldest materials and
are used for casting conventional gold alloys.
 The phosphate bonded investments - base metal alloys in
fixed partial prosthesis.
 Silica bonded investments are principally used for the
casting of base metal alloy partial dentures.

18. 19
Type of alloy Casting shrinkage (%)
Type II gold alloy 1.56
Type III gold alloy 1.37
Type IV gold alloy 1.42
Ni cr alloy 2
Co cr alloy 2.3

19. Setting expansion of investment materials
20
 Normal s.e
 Hygroscopic s.e (low heat technique)
 Thermal s.e (high heat technique)

20. CALCIUM SULPHATE-BONDED
INVESTMENTS
21
 Casting metal inlays, onlays, crowns and bridges.
 Casting gold alloys.
 Withstand temp up to 700ºC.

21. 22
 Acc to ADA specification no-126 there are three types of
gypsum bonded investment materials:
 Type 1: thermal expansion type; for casting inlays and
crowns.
 Type 2 : hygroscopic expansion type; for casting inlays and
crowns
 Type 3 : for casting complete and partial dentures.

22. 23
 These materials are supplied as powders which are mixed
with water and are composed of a
 mixture of silica (SiO2) and calcium sulphate hemihydrate.
 Other minor components including graphite, or powdered
copper.

23. Composition
24
REFRACTORY
 Crystalline polymorphs of silica (quartz or cristobalite)-
65-75%
 Silica is added to provide a refractory component during
the heating of the investment and to regulate the thermal
expansion.
BINDER – Alpha hemi hydrate form of gypsum(25-45%)
 Strength of investment depends on amount of binder
present.

24. 25
MODIFIER - (4-7%)
 Used are
 Reducing agents
 Modifying chemicals
 Coloring matter
REDUCING AGENTS : they reduce any metal oxides
formed on the metal by providing a non oxidizing
atmosphere in the mold when the alloy enters mold.
 Ex– Copper

25. 26
MODIFYING CHEMICALS:
 regulate setting expansion & thermal expansion
 prevent shrinkage of gypsum when heated above
300ºc .
Ex– Boric acid,Soluble salts of alkali or alkaline earth
metals

26. 27
Gypsum
 α- hemihydrate form – as binder - provide rigidity.
 Heated to the temperatures required for complete
dehydration and sufficiently high to ensure complete
castings - it shrinks considerably & occasionally fractures.

27. 28

28. 29
 All forms shrink considerably after dehydration
between 200ºC and 400ºC.
 A slight expansion takes place between 400ºC and
700ºC.
 And a large contraction then occurs.

29. 30
 The shrinkage on heating is due to the dehydration
of the set gypsum in two stages.
2CaSO4 · 2H2O (CaSO4)2 H2O + 3H2O
(CaSO4)2 · H2O 2CaSO4 + H2O
 Shrinkage transformation of calcium sulphate
from the hexagonal orthorhombic
configuration.

30. 31
later shrinkage
decomposition and the
release of sulfur gases,
such as sulfur dioxide
contaminates the
castings with the sulfides
.

31. 32
 Thus it is imperative the gypsum products not be heated
above 700°C and these effects can be minimized by ‘heat
soaking’ the mould at 700°C for at least an hour to allow
the reactions to be completed before casting commences
 The gypsum products containing carbon should not be
heated above 650ºC

32. Silica (SiO2)
33
 refractory component -regulate the thermal
expansion.
 the wax pattern is eliminated from the mold by heat.
 During the heating, the investment is expected to
expand thermally to compensate partially or totally
for the casting shrinkage of the gold alloy.
 Gypsum shrinks considerably when it is heated,
regardless of whether it is set plaster or stone.

33. 34
 If the proper forms of silica are employed in the
investment, this contraction during heating can be
eliminated and changed to an expansion.
 Silica exists in at least four allotropic forms: quartz,
tridymite, cristobalite, and fused quartz.

34. 35
 When quartz, tridymite, or cristobalite is heated, a
change in crystalline form occurs at a transition
temperature characteristic of the particular form of
silica.
 For example, when quartz is heated, it inverts from a
"low" form, known as α-quartz, to a "high" form,
called β-quartz, at a temperature of 575o C (1067o
F).

35. 36
 In a similar manner, cristobalite undergoes an
analogous transition between 200o C (392o F) and
270o C (518o F) from "low" (α-cristobalite) to "high"
(β-cristobalite).
 Two inversions of tridymite occur at 117o C (243o F)
and 163o C (325o F), respectively.

36. 37
 The β-allotropic forms are stable only above the
transition temperature noted, and an inversion to
the lower α form occurs on cooling in each case.
 In powdered form, the inversions occur over a range
of temperature rather than instantaneously at a
specific temperature.
 The density decreases as the α form changes to the β
form, with a resulting increase in volume that is
exhibited by a rapid increase in the linear expansion.

37. 38
The density decreases when the alpha form changes to beta
form with a resulting increase in the new volume

38. 39
 Fused quartz is amorphous and glasslike in
character, and it exhibits no inversion at any
temperature below its fusion point.
 It has an extremely low linear coefficient of thermal
expansion and is of little use in dental investments.

39. 40
Thermal expansion of three forms of silica

40. 41
 Quartz, cristobalite, or a combination of the two
forms may be used in a dental investment.
 Both are now available in pure form.

41. 42
 Tridymite is no longer an expected impurity in
cristobalite.
 On the basis of the type of silica principally
employed, dental investments are often classified as
quartz or cristobalite investments.

42. Setting Time
43
 The setting time should not be shorter than 5 mins
or longer than 25 mins.
 Usually, the modern inlay investments set initially in
9 to 18 mins.

43. Normal setting expansion
44
 linear dimensional change as the investment sets
 Silica particles result in greater setting expansion HOW??
silica particles interfere with the intermeshing and
interlocking of crystals
resulting in outward thrust of crystals
resulting in expansion.

44. According to ADA sp no 2
45
FOR TYPE I investments:0.6%
 Value of setting expansion for modern investments is
0.4%,regulated by retarders and accelerators.
 Purpose :
To aid in enlarging the mold to compensate partially for the
casting shrinkage of gold.

45. Factors determining the effective setting
expansion
46
 Greater the gypsum content of the investment,
greater the exothermic heat transmitted to the wax
pattern and greater the mould expansion.
 Lower the W/P ratio for the investment, greater the
exothermic heat and greater the setting expansion.

46. 47
 Thinner the walls of the wax pattern, greater the
setting expasion of the investment.
 Softer the wax, greater the setting expansion. If a
wax softer than Type B inlay wax is used, the setting
expansion may cause a serious distortion of the
pattern.

47. 2)HYGROSCOPIC SETTING EXPANSION
48
 Expansion that occurs as the investment hardens while
immersed in water
 This is one of the methods for expanding the casting mold
to compensate for casting shrinkage.
 The hygroscopic setting expansion may be 6 or more times
greater than the normal setting expansion of a dental
investment

48. 49
 The water is drawn between the refractory particles by the
capillary action and thus causes the particles to separate
creating an expansion
 The investment should be immersed in water before the
initial set is complete.
 ADA sp no 2 : type 2 investments require minimum setting
expansion in water of 1.2% and maximum 2.2%.

49. 50
 In one, method known as the ‘water immersion’
technique, the investment mould is placed into
water.
 Another method is the ‘water added’ technique. Here
a measured volume of water is placed on the upper
surface of the investment material within the casting
ring.
 This produces a more readily controlled expansion.

50. FACTORS AFFECTING HYGROSCOPIC
SETTINGEXPANSION
51
1. Effect of composition
 The finer the particle size of the silica, the greater is
the hygroscopic expansion.
 Higher the silica content greater is the expansion.
 Alpha hemihydrate produces more expansion in the
presence of silica, than beta hemihydrate.

51. 52

52. 53
 The hygroscopic setting expansion of stone or plaster
alone is very slight.
 The investment should have at least 15% binder to
provide strength after hygroscopic setting expansion,
and to prevent drying shrinkage

53. 54
2. Effect of w/p ratio
 The higher the W/p ratio of the original investment
water mixture, the less is the hygroscopic setting
expansion- less binder/unit volume.

54. 55
3.Effect of temperature
 Higher the temperature of immersion water, less is
the surface tension and hence greater is the
expansion
4. Effect of time of immersion
 Immersion before the initial set causes greater
expansion.
5. Effect of spatulation
 The shorter the mixing time, more is the hygroscopic
expansion – delayed interlocking of crystals

55. 56 6. Effect of shelf life of the investment
 The older the investment, the less is the hygroscopic
expansion.
 The material should be stored in air tight containers and
should not be exposed to humidity.
 It is better to purchase small amounts of the investment at
a time.
7. Effect of confinement
 Both the normal and the hygroscopic setting expansions are
confined by opposing forces, such as the walls of the
container in which the investment is poured or the walls of
a wax pattern.

56. 57
 This confinement can be avoided largely by placing
damp asbestos as a liner on the inner wall of the ring.
 The water in the asbestos also is utilized for
hygroscopic expansion.

57. 58
8. Amount of added water
 An increase in the amount of water added, increases
the hygroscopic setting expansion upto a certain
point, after which further addition of water does not
create any expansion.
 This degree of maximum expansion is called the
“critical point”.
 This critical point can be raised or lowered easily by
changing the manipulative conditions like W/P ratio,
time of spatulation, age of investment etc.

58. 59
 Particle size of silica
 Finer particles of silica produce greater hygroscopic
expansion.
 The hemihydrate particles have little effect on this
expansion.

59. 60
 Silica/binder ratio
 If this ratio increases, greater will be the hygroscopic
expansion and lesser the strength.
 This is because the added water can easily diffuse
through the silica particles.

60. Thermal Expansion
61
 Thermal expansion is directly related to the amount
and type of silica employed.
 The contraction of gypsum is entirely balanced when
the quartz content is about 75%.

61. 62
 Type I investments – thermal expansion of not less
than 1.0% nor greater than 1.6%.
 maximal thermal expansion be attained at a
temperature not greater than 700°C.
 Gold alloys -contaminated above this temperature.

62. Factors affecting thermal expansion
63
W/P ratio
water used for mixing – thermal expansion.
Effect of chemical modifiers-
 small amounts of chlorides of sodium, potassium or
lithium to the investment eliminates the contraction
and increases expansion.

63. 64
Type of refractory material-
 Quartz- 1.4% - 600ºc
 Cristoballite – 1.6% - 250ºc
 Tridymite 1% - 600ºc
Temperature
High temp- high exp

64. 65
Strength
 ADA specification no. 2 requires a minimum
compressive strength of 2.5 Mpa, 2 hours after
setting of the investment
 Modifiers aid in increasing the strength as more of
the binder can be used without much reduction in
thermal expansion.
 Use of alpha hemihydrate increases compressive
strength( than beta hemihydrates).

65. 66
Fineness
 Fineness of the investment affects the setting time
and surface roughness of the casting. Fine silica
particles increase the hygroscopic setting expansion
and gives smoothness to the casting.

66. 67
Porosity
 More gypsum crystals present in the set investment
– less is the porosity.
 Less the hemihydrate content – greater the amount
of gauging water – more is the porosity.
 Mixture of coarse and fine particles exhibits less
porosity than an investment composed of uniform
particle size.

67. 68
Storage
 Air tight & moisture proof containers.
 Purchase in smaller quantities.

68. 69
 Permissible min and max thermal exp of GBI
 0-0.5% at 500ºc
 1-1.6% at 700ºc

69. Phosphate bonded investment
material
70
 Base metal alloys & higher melting range gold alloys.

70. Composition
71
Refractory materials
(concentration of approximately 80%)silica in quartz ,
cristobalite or a mixture of two .
Purpose
 To provide high temperature thermal shock resistance
 To provide high thermal expansion.
Binder (<20%)
 Magnesium oxide (base) and a phosphate ion (acid)
 Originally phosphoric acid was used but mono ammonium
phosphate has replaced it as it can be incorporated in powder
form

71. 72
Modifiers :
 Carbon is often added -clean casting.
 Facilitates easy divesting of casting and mold.
 Generally added when casting alloy is gold.
 When silver palladium or base metal alloys are invested
with the investment containing carbon, it embrittles the
alloys even though the investment is heated to the
temperature that burn out the carbon.
 Palladium reacts with carbon even at above temp 1500°C, so
carbon free phosphate bonded invst used for higher temp

72. 73
It is available as two component systems
 1- It is a Powder which contains refractory materials
and binders and modifiers
 2- Aqueous solution stabilized with colloidal silica
Colloidal silica suspension facilitate greater expansion
of the investment which can compensate the greater
casting shrinkage of alloys used in MC & newer gold
alloys.
For BMA – 33% dilution of colloidal silica

73. 74
 Colloidal silica suspensions are available for use with
phosphate investments instead of water.
 These suspensions can freeze and become unusable
– so should be stored in frost free environment.
 Phosphate bonded investments are mixed with a
special liquid .
 The liquid is a form of silica sol in water, which gives
higher thermal expansion.

74. 75
 Carbon is added to the powder to produce clean
casting and facilitate the divesting of the casting
from the mold.
 This addition is appropriate when casting alloy is
gold but not with base metal alloys.
 Carbon embrittles the alloy even though the
investment is heated to temp that burn out the
carbon.

75. 76
 The chemical reaction is as follows that causes the
investment to set and harden:
NH4H2PO4 + MgO + 5H2O NH4MgPO4 6H2O

76. 77

77. Working and Setting time
78
 markedly affected by temperature.
 Warmer the mix, faster the set.
 The reaction gives off heat, which further accelerates
the setting.
 Increased mixing time and mixing efficiency result in
a faster set; these two factors give smoothness and
accuracy to the casting.
 Mechanical mixing under vacuum is preferred.
 An increase in liquid/powder ratio increases the
working time.

78. Setting and thermal expansion
79
 As powder(gypsum) and liquid is mixed there is
slight expansion. This can be increased by using
colloidal silica solution instead of water.
 When phosphate bonded investment material is
mixed with liquid containing silica first there is early
thermal shrinkage.

79. 80
 This is associated with the decomposition of the
binder, magnesium ammonium phosphate and is
accompanied by evolution of ammonia.
 Shrinkage is masked because of the expansion of the
refractory filler, like cristobalite.

80. 81
 The combined setting and thermal expansion for
phosphate investments is around 2% if the special
silica liquid is used

81. 82
Universally applicable for precious metal alloys, non
precious metal alloys, pressed all-ceramic and pressover
ceramic
Properties:
Processing time approx. 3.30 min
Thermal expansion linear 0.8 % with 70 %
Compressive strength: approx. 11 N/mm²
Mixing ratio 100 g : 20 ml
Properties: indicated in partial denture
Processing time 4-5 min
Thermal expansion linear 0.8-0.9 %
Total expansion linear 1.7-2.2 %
Compressive strength 4.2-5.1 N/mm²
Mixing ratio 100 g : 25 ml.
Properties:
Mixing liquid: BegoSol (Anti-freeze optimization up to -10 °C)
Processing time at 20 °C: approx. 3 min.
Total expansion: approx. 2.3 %
Shelf life in unopened bag: 2 years
Bellavest SH
BegoSol K

82. 83
Not for metal casting. Used for
pressed ceramic
Adenta-vest
phosphate-bonded investment - the partial denture
Technique
The adequate expansion can be adjusted for
every type of alloy by changing the concentration
of the apropriate Adentatec Liquid.
GC Stellavest
•suitability for use with non-precious
dental alloys.

83. 84
Hinrivest® G
Mixing liquid distilled water
Powder : liquid 100 g powder : 26 – 30 ml
distilled water
Recommended liquid factor 100 g powder :
28 ml distilled water
Mixing under vacuum 30 sec.
Working time approx. 5 min.
Initial setting time approx. 14 min.
Final setting time 30 - 45 min.
Max. preheating temperature 700 °C
Setting expansion ca. 0,6 %
Linear thermal expansion approx. 1.0 %

84. ETHYL SILICATE BONDED
INVESTMENTS
85
 Less popular -more complicated - time consuming
procedures.
 Construction of high fusing base metal partial
denture alloys.
 Refractory material – silica ; mgo is added to ↓ph of
silica gel
 Binder is silica gel that reverts to silica on heating.

85. 86
 Several methods are used to produce silica or silicic
acid gel binders.
 When a pH of sodium silicate is lowered by the
addition of an acid or an acid salt such as
monoammonium phosphate, a bonding silicic acid
gel forms. The addition of Magnesium oxide will
strengthen the gel.
 An aqueous solution of colloidal silica can be made
to gel by the addition of an accelerator, such as
ammonium chloride

86. 87
 A colloidal silicic acid is first formed by hydrolyzing
ethyl silicate in the presence of hydrochloric acid,
ethyl alcohol and water, as follows:
Si(OC2H5) + 4H2O Si (OH)4 + 4C2H5OH
 Because a polymerized form of ethyl silicate is
actually used, a colloidal sol of polysilicic acids is
formed instead of the simpler silicic acid shown in
the above reaction.

87. 88
 The formation of poly silicic acid constitutes the 1st
stage of the setting reaction, called
“hydrolysis”.
 Stage 2 is called “gelation”. Here the sol is
mixed with quartz or cristobalite to which is added a
small amount of finely powdered MgO to render the
mixture alkaline. A coherent gel of polysilicic acid
then forms accompanied by a slight ‘setting
shrinkage’.

88. 89
Stage 3 is called “drying”.
 Here the soft gel is dried to a temperature below
168°C. During drying, the gel loses alcohol and water
to form a hard, concentrated gel of silica particles
tightly packed together.
 A considerable volumetric contraction accompanies
the drying. Which reduces the size of the mould. This
contraction is known as “green shrinkage” and it
occurs in addition to the setting shrinkage.

89. 90
 A faster method to obtain silica gel is by the addition
of amines such as piperidine to the solution of ethyl
silicate. Here hydrolysis and gelation occurs
simultaneously. But an unacceptable shrinkage may
occur, mainly in the stage of hydrolysis.

90. 91
 Stock solutions of hydrolysed ethyl silicate binder
may be prepared and stored in dark bottles.
 The solution gels slowly on standing and its viscosity
may increase noticeably after 3-4 weeks when it has
to be discarded.

91. 92
 Silica-bonded investments being more refractory
than phosphate-bonded investments, can tolerate
higher burn-out or mould-casting temperatures.
 Temperatures between 1090 and 1190°C are
employed when the higher fusing chromium
containing alloys are cast.

92. 93
Steps in making metal inlays, onlays crowns and
bridges
 case selection
 tooth preparation
 gingival retraction
 making impression
 die preparation

93. 94
 Wax pattern preparation
 Investment of wax pattern
 Burnout procedure
 Casting
 finishing and polishing
 Cementation
 Recall.

94. Hand investment
95

95. 96

96. Vaccum investment
97

97. 98

98. SOLDERING INVESTMENT
99
 ANSI/ADA Specification No. 93 (IS0 11244) for
dental brazing investments defines two types of
investment:
 Type 1: Gypsum-bonded dental brazing investments
 Type 2: Phosphate-bonded dental brazing
investments

99. 100
 Soldering investment differ from casting investment
by
lower setting and thermal expansion
most often ingredients do not have as fine particle as
casting investment
USES
 TYPE 1- for soldering of low melting alloys
 TYPE 2 - for soldering of high melting alloys

100. DIVESTMENT
101
 Die stone and investment combination.
 These mixed with colloidal silica liquid
 The die is made from this mix and the wax pattern is
then constructed on it.
 The whole complex is then invested in a mixture of
divestment and water
 This combination used to compensate distortion of
wax pattern of long span bridges or RPD frameworks
during removal from die.
 Special GBI or PBI investment materials are used.

101. NEWER INVESTMENTS FOR CASTING
TITANIUM BASED ALLOYS
102
In 1993 a study was done by Togoxa T.& Maixazaki T
& Tamaki X. on the selection of investment for
improving fits of Ti castings & they said that the
castings of Ti should not be done with conventional
PBI or SBI, because, Ti is highly reactive with oxygen
& is capable of reducing some of the oxides
commonly found in these investments. Ti can also
dissolve residual oxygen, nitrogen & carbon from the
investment. These elements can harden & embrittle
Ti in the solid state

102. OBJECTIVE FOR A TITANIUM
INVESTMENT
103
 To reduce breakdown of the investment
 To reduce contamination of the titanium –
refractory materials that are less easily reduced by
titanium should be used

103. PHOSPHATE BONDED TITANIUM
INVESTMENT
104
 To achieve expansion without the use of reactive
powders
 PBI that contains both magnesia & alumina as
refractories was developed
 large expansion by the reaction of alumina &
magnesia- at 1150ºC - 1200ºC

104. ETHYL- SILICATE BONDED INVESTMENT
105
 Reactions of ethyl silicate bonded investments with
the liquid Ti has been reported to be somewhat less
than that of PBI.
 due to the use of highly refractory oxides in the
powder.
 But these investments require more complex
procedure for their use.

105. CEMENTED TITANIUM INVESTMENT
106
 magnesia bonded by an aluminous cement(CaO-Al2O3)
& 5% zirconium powder by weight.
 aluminous cement -binder for the magnesia refractory &
it sets by mixing with water.
 Oxidation of the zirconium powder to zirconia during the
burnout process provides irreversible expansion to
compensate for the shrinkage of the casting during
cooling from the solidification temp.
 The zirconia formed is highly stable & it does not
contaminate Ti.
 Ti castings from this investment had smooth surface, free
of contamination from the mold reaction

106. RINGLESS CASTING SYSTEM
107
 To provide maxi. Expansion of investment, a ringless
system is available commercially. The system called
“powder cast ringless system,”
 consists of 3 sizes of rings & formers, preformed wax
sprues & shapes, investment powder, & a special
investment liquid.
 The tapered plastic rings allows for the removal of
the investment mold after the material has set.
 This system is suited for the castings of alloys that
require greater mold expansion than traditional gold
based alloys

107. INVESTMENT FOR ALL-CERAMIC
RESTORATIONS
109
 2 types of investment materials have been developed
recently for producing all- ceramic restorations:
 Type 1 – Used for the cast glass technique composed
of phosphate bonded refractories.
 Type 2 – Refractory die type of material, used for
all- ceramic veneers, inlays & crowns.
 Refractory dies are made by pouring the investment
into impressions. When the investment is set, the die
is removed & is heated to remove gases that may be
detrimental to the ceramic (degassing) A refractory
die spacer may be added to the surface

108. 110
 Then, the porcelain or other ceramic powders are
added to the die surface & fired. These materials
must accurately reproduce the impression, remain
undamaged during the porcelain firing & have a
thermal expansion compatible with that of ceramic,
otherwise the ceramic could crack during cooling.
These materials are also phosphate bonded & they
generally contain fine grained refractory fillers to
allow accurate reproduction of detail

109. Review of literature
111
 Asgars, D.B. Mahler & F.A. Peyton, Dental J. 5:173
(1955)
 investigated a hygroscopic technique for inlay casting
using controlled water additions. A technique &
equipment for this particular technique was described by
them. They concluded that:- - The av. Deviation of
expansion values resulting from controlled water
additions was significantly less(0.1%) than that for
complete immersion(0.3%). - The hygroscopic expansion
for an av. mix was higher than for a thinner mix & the
expansion reduced with the no. of spatulation turns
within limits. - The expansion for a new investment was
significantly higher than for an aged one

110. 112
 Junzo Takahashi, Masayuki Okazaki,1999,
conducted a study with the purpose of measuring the
internal setting expansion of PBI & assessed the
effect that different pattern materials may have on
internal setting expansion. They concluded that
vertical setting expansion was higher than the
horizontal setting expansion & regardless of the type
of pattern material, a PBI caused non uniform
setting expansion, especially in horizontal direction,
which lead to the distortion of the pattern
 Jpd Volume 81, Issue 4, Pages 375-498 (April 1999)

111. 113
 C.L. Chew, M.F. Land, 1999, conducted a study with the
purpose of evaluating & comparing the compressive
strength characteristics of phosphate bonded v/s gypsum
bonded investments. They also investigated if these
values changed as a function of time & temp. It was
concluded that at elevated temp., all materials
approximated peak strength 2hrs after initial
mixing.There was no significant difference in their
strengths at room temp. However, the PBI exhibited
significantly increased compressive strength as a
function of time & temp
 J Dent. 1999 May;27(4):297-302.

112. Conclusion
114
 Of the three main types of casting investment
materials, the phosphate bonded products are
becoming most widely used. Silica bonded materials
are rarely used now a days due to the fact that they
are less convenient to use than the other products &
that the ethanol produced in the liquid can
spontaneously ignite or explode at elevated
temperatures. The investment which is best able to
retain its integrity at the casting temp. & able to
provide the necessary compensation for casting
shrinkage is chosen.

113. reference
115
 PHILLIPS”Science of Dental material, 11th edition
 Restorative Dental materials, Robert G. Craig.11th
edition
 Fundamentals of fixed prosthodontics,3rd
edi.Herbert T. Shillingburg
 Contemporary fixed prosthodontics , 4th edition
Rosensteil
 S. mahalekshmi , materials used in dentistry

114. 116