The document discusses investment materials used in dental prosthodontics, focusing on their composition, properties, and classifications such as gypsum, phosphate, and ethyl silicate bonded investments. It outlines the historical context and the requirements for ideal investment materials, including their thermal and hygroscopic expansions. The document also details the mixing and manipulation processes involved in preparing investment materials for dental applications.

1. Investment Materials
Dr. Neeraja M Menon
Dept of Prosthodontics
Coorg Institute Of Dental Sciences

2. CONTENTS
 Introduction
 History
 Definition
 Properties of an ideal investment material
 Composition
 Gypsum bonded investments
 Phosphate bonded investments
 Ethyl silicate bonded investments

3. ► Die stone investment combination.
► Hygroscopic thermal gold casting investments.
► Soldering investments.
► Investments for all- ceramic restorations.
► Investment of titanium & titanium based alloys.
► Review of literature.
► Summary & Conclusion.
► References.

4. Introduction
 An investment is a refractory material that is used to
form a mould around a wax pattern.
 Following the production of a wax pattern either by
direct or indirect method; the next stage in many
dental procedures involves the investment of the
pattern to form a mould.
 A sprue is attached to the pattern and the assembly is
located in a casting ring. Investment material is poured
around the wax pattern while still in a fluid state.
 When the investment sets hard, the wax and sprue
former are removed by burning out to leave a mould
which can be filled with an alloy or ceramic using a
casting technique.

5. History
Lost wax casting art was widely known in ancient times.
The Aztec gold smiths of Pre-Columbian Mexico used it to create
their elaborate jewellery.
 11th century – Theophilus first described the lost wax
technique.
 1558 – Benvenuto Cellini, used wax and clay for preparation of
castings.
 1884 – Aguilhon de saran – used 24K gold to form inlays.
 1897 – Philibrook described a method of casting metal fillings.
 1907 – Taggart devised a casting machine
Aztec Gold work

6. Definition
 An investment can be described as a ceramic material that is
suitable for forming a mold into which a metal or alloy is cast.
- Craig
 Refractory material used to form a mould casting for cast metals or
hot pressed ceramics.
- Anusavice.

7.  Dental casting investment dĕn΄tl kas΄tĭng ĭn-vĕst΄ment:
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

8. Requirements of an investment
materials
 Easy manipulation
 Should provide smooth surface to the casting
 Must not decompose at higher temperatures
 Sufficient strength
 Should break away readily from metal surface
 Porous to permit air and other gases in mould to escape
 Sufficient expansion
 Casting temperatures should not be critical
 Economical

9. Composition of investment material
Binder
Other chemicals
Refractory
material

10. Refractory material:
 This material is usually a form of silicon dioxide such as:-
Quartz Cristobalite.
Tridymite
Fused
quartz

11. Binder Material:
 Since the refractory materials alone do not form a coherent solid
mass, some kind of binder is needed.
 The common binders used for dental casting gold alloy is α -CaSO4
hemihydrate, Phosphate, ethyl silicate.

12. Other Chemicals:
 These are added in small quantities to modify various physical
properties.
 Sodium chloride.
 Boric acid.
 Potassium sulfate.
 Graphite.
 Copper powder.
 Magnesium Oxide.

13. Classification according to Binders
used
GYPSUM BONDED INVESTMENTS
PHOSPHATE BONDED INVESTMENTS
ETHYL- SILICATE BONDED INVESTMENTS

14. Gypsum bonded investments
 American Dental Association/American National Institute For
Standards specification no: 2 for casting investments used for gold
alloys.
Type 1: For casting inlays and crowns.
Type 2: For casting complete and partial removable
denture bases.
Type 3: For partial dentures with gold alloys

15. Composition:
 Binder:
25% to 45% - α -calcium sulfate hemihydrate.
 Refractory material:
65% to 75% - quartz or cristobalite.
 MODIFIERS :
2% to 3% - chemical modifiers.

16. Gypsum:
 25% to 45% of α-hemihydrate is present.
 α -hemihydrate acts as a binder to hold the ingredients together &
to provide rigidity.
 Used in casting gold alloys with melting ranges below 1000ºC.
Above 1000ºC greater shrinkage & frequent fractures takes place.

17.  All forms of gypsum shrink after dehydration between 200ºC to
400ºC .
 A slight expansion takes place between 400℃ and 700℃. And a
large contraction then occurs.
 The shrinkage on heating is due to the dehydration of the set
gypsum.
2CaSO4 · 2H2O → (CaSO4)2 H2O + 3H2O
(CaSO4)2 · H2O → 2CaSO4 + H2O

18.  Shrinkage is due to the transformation of calcium sulphate from the
hexagonal to the orthorhombic configuration.

19. Silica:
 55% to 75%.
 It acts as a refractory material during the heating of the investment
& regulates the thermal expansion.
 If the proper form of silica is used in the investment, the contraction
of gypsum during heating can be eliminated & changed to an
expansion.

20.  Silica exists in 4 allotropic forms:-
1) Quartz.
2) Cristobalite.
3) Tridymite.
4) Fused quartz.

21.  When quartz, cristobalite or tridymite is heated, a change in
crystalline form occurs at a transition temperature characteristic of
the particular form of silica.
Ex: When quartz is heated at 575℃
α-Quartz → β-quartz
 Cristobalite undergoes an anologous transition between 200ºC &
270ºC from α to β form.
 2 inversions of Tridymite occurs at 117ºC & 163ºC respectively.

22.  Density decreases as α form changes to β form, with a resulting
increase in volume exhibited by a rapid increase in linear expansion.
 On the basis of the type of silica employed, dental investments are
classified as:-
Quartz investment.
Cristobalite investment.

23. Effect of varying composition
Increasing the proportion of silica in the investment powder
Increases :
 manipulation time,
 initial setting time,
 setting expansion both in air & water
 thermal expansion
Decreases:
 compressive strength.
The rate of setting reaction is unchanged.

24.  The increase in manipulation & setting time occurs because the
particles of the refractory filler, interfere with the interlocking of the
growing gypsum crystals & making this less effective in developing
a solid structure.
 The compressive strength of the investment is reduced for the same
reason.

25. Modifiers
 a) Modifying Agents:-
• Regulates the setting expansion & setting time.
• They prevents most of the shrinkage of gypsum, when it is heated
above 300ºC.
• Eg. NaCl , Boric acid.

26. ► b) Reducing agents:-
They are used in some investments to provide a non- oxidizing
atmosphere in the mold when the gold alloy is cast.
Eg. Carbon, powdered graphite or powdered copper.

27. Setting time
► It can be measured by,
1. Loss of Gloss test for initial set.
2. Initial Gilmore test for initial set.
3. Gilmore Test For Final Setting Time.
4. Vicat test for setting time.

28.  According to ADA/ANSI specification no. 2 for dental inlay casting
investment, the setting time should not be less than 5 min. or more
than 25 min.
 Usually, the modern inlay investments set initially in 9 to 18 min.
 Sufficient time should be allowed for mixing & investing the pattern
before the investment sets.

29. Normal setting expansion
Definition:- The volumetric or linear increase in physical dimensions of
an investment caused by chemical reactions that occur during
hardening to form a rigid structure.
 Regardless of the type of gypsum product used, an expansion of
the mass can be detected during the change from hemihydrate to
dihydrate.

30.  A mixture of silica & gypsum hemihydrate results in setting
expansion greater than that of the gypsum product when it is used
alone.
 The ADA Specification no. 2 for Type 1 investment permits a
maximum setting expansion“in air”of only 0.6%. The setting
expansion of modern investments is 0.4%.
 The setting expansion of an investment with a comparatively high
gypsum content is more effective in enlarging the mold than with a
low gypsum content.

31. Factors affecting normal setting
expansion
 If the pattern has thin walls, the effective setting expansion is
somewhat greater, than for a pattern with thicker walls.
 The softer the wax, the greater is the effective setting expansion.
 If a wax other than the Type 2 inlay wax is used, the setting
expansion may cause a serious distortion of the pattern.
 The lower the W:P ratio for the investment, the greater is the
effective setting expansion.

32. Hygroscopic setting expansion
 If the setting process is allowed to occur under water(slurry), the
setting expansion may be more than double in magnitude because
of the additional crystal growth permitted.
 ADA Specification no. 2 for Type 1 investments requires a minimum
setting expansion in water of 1.2% & maximum expansion
permitted is 2.2%.

33. Purpose:-
 To expand the casting mold to
compensate for the casting shrinkage of
the gold alloy
 The HSE differs from the NSE in that, it
occurs when gypsum is allowed to set
under or in contact with water & that it is
greater in magnitude than NSE.

34. Factors controlling the hygroscopic
expansion
 Effect of Composition
- Finer silica particle size, greater expansion
- α hemihydrate, in presence of silica, produces
greater expansion when expansion is unrestricted.
► Effect of Water/Powder Ratio
- Higher ratio, less expansion.
► Effect of Spatulation
- Reduced mixing time, decreased expansion.

35.  Effect of Time of Immersion
- More expansion observed if immersion
takes place before the initial set.
► Shelf Life
- Older investment, lower expansion.

36.  Effect of Added Water
- Magnitude of the hygroscopic expansion
is in direct proportion to the amount of
water added during the setting period until a
maximum expansion occurs.
- The term ‘hygroscopic’ is a misnomer as
although the added water may be drawn
into the setting material by capillary action,
the effect is not related to hygroscopy

37. Thermal expansion
Definition:- It is the increase in dimension of a set investment due to
temperature increase during burnout.
► The expansion of a gypsum bonded investment is directly related to
the amount of silica present & to the type of silica employed.

38.  A considerable amount of quartz is necessary to counterbalance the
contraction of the gypsum during heating. Even when the quartz
content of the investment is increased to 60% with the balance
being hemihydrate binder, the initial contraction of the gypsum is
not eliminated.
 The contraction of the gypsum is entirely balanced when the quartz
content of the investment is increased to 75%.

39.  The thermal expansion of quartz investment are influenced by:-
- The particle size of the quartz.
- Type of gypsum binder
- W:P ratio
Since greater expansion occurs during the inversion of the crystobalite,
the normal contraction of the gypsum during heating is easily
eliminated.

40.  According to ADA/ANSI Specification no. 2 for
• Type 1 investment which rely on the thermal expansion for
compensation, the thermal expansion must not be <1% nor
>1.6%.
• Type 2 investment which rely on hygroscopic expansion for
compensation of the contraction of the gold alloy, the thermal
expansion be between 0% & 0.6% at 500ºC

41. Thermal Contraction
 When an investment is allowed to cool from
700°C, its contraction curve follows the expansion
curve.
 Due to inversion of the beta quartz to its stable
form at room temperature , it shrinks to less than
its original dimension because of the shrinkage of
the gypsum when first heated.
 In practice, the investment should not be heated
a second time, since internal cracks may develop
which affect the quality of the casting.
Curve 1 is first heating
Curve 2 is cooling
Curve 3 is re heating

42. Factors affecting thermal expansion
1) W:P ratio:-
• The magnitude of thermal expansion is
related to the amount of solids present.
↑W:P ratio → ↓ thermal expansion.

43. 2) Effect of Chemical Modifiers –
• A disadvantage of an investment is the weakening effect of silica.
• The addition of small amount of Na, K or Lithium chloride to the
investment eliminates the contraction caused by the gypsum &
increases the expansion.
• Boric acid hardens the set investment but, it disintegrates during
the heating of the investment & a roughened surface of the casting
may result.

44.  3) Strength
• Increases rapidly as the material hardens after initial setting time.
The free water content of the set product affects its strength.
• The strength of an investment must be adequate to prevent fracture
or chipping of the mold during heating & casting of the gold alloy
and is measured in terms of its compressive strength.

45.  The compressive strength is increased according to
• Type & amount of gypsum binder present
• Use of chemical modifiers.
According to ADA Specification no. 2, the compressive strength for the
inlay investment should not be less than 2.4 MPa when tested 2hrs
after setting.

46. Other gypsum investment
considerations
 Fineness:- Finer the investment, the smaller are the surface
irregularities on the casting.
 Porosity:- More gypsum crystals present in the set investment, less
porosity. More uniform the particle size, greater is its porosity.
 Storage:- The investment should be stored in airtight & moisture
proof containers.

47. Technical specifications
Mixing ratio (powder:
distilled water):
100 g :32-40 ml
Total expansion (in %
linear) :
1.3% - 1.6%

48. Expansion control
 The expansion of the compound can be controlled by varying the
amount of liquid added to compensate the contraction of the
casting alloy.
 The less water used, the greater the total expansion of the
investment compound.
Distilled water Setting
(average)
Thermal
expansion
(average)
Total expansion
32 ml 0.4% 1.2% 1.6%
40 ml 0.1% 1.2% 1.3%

49. Manipulation
 Mix the investment compound by hand for approximately
30 seconds with a spatula, allow to stand under a vacuum
for approx. 30 seconds. Then mix under vacuum for 60
seconds with a mixing and evacuation unit.
 After mixing, place the mixing bowl on a vibrator (approx.
30 seconds) and allow the investment compound to flow
together. Then let the compound to flow into the mould,
shaking gently and ensuring that no bubbles form. After
the mould has been filled, switch off the vibrator.
 Allow the mould to set for 45-60 minutes, depending on
the size. If the mould is preheated too soon the
investment compound can crack.

50.  During wax elimination, place the mould in the oven in such a way
that the wax can run out of the mould easily, otherwise wax residue
will be absorbed by the investment compound capillaries and will
carbonize damaging the cast object.
 The mould which have dried overnight should be wetted slightly
before casting rings are placed in furnace.
 Devesting- Allow the casting ring to dry slowly in the air at room
temperature after casting and removing the investment compound
under running water with a plier.

51. PHOSPHATE BONDED INVESTMENTS
 The rapid growth of the use of metal ceramic restorations, cast
removable partial dentures and higher melting alloys resulted in an
increased use of phosphate bonded investment materials.
1) Type I - For crowns, inlays & other fixed restorations
2) Type II - For partial denture & other cast removable restorations
- Make soldering fixtures.

52. Composition
Consists of :-
1) Filler - Silica, in the form of Cristobalite, Quartz, or a mixture of the
two and in a concentration of 80%.
- Provides high temperature and a high thermal
expansion.
2) Binder - The binder consists of magnesium oxide and a
phosphate.

53. 3) Colloidal Silica Liquid Suspensions:-
- The colloidal silica suspensions are used with the phosphate
investments in place of water to compensate for the greater
contraction of the high fusing alloys during solidification, as it
increases the setting expansion of the investment.
- For base metal alloys, a 33% dilution of the colloidal silica is required.

54. 4) Carbon:-
- Often added to the powder to produce clean castings to facilitate the
divesting of the casting from the mold.
- Appropriate if the casting alloy is gold.
- Evidence indicates that palladium react with carbon at temperature
above 1504°C. Thus, if the temperature exceeds this temperature
during casting, a carbon free investment should be used.*
*Dental Materials and Their Selection - 3rd Ed. (2002) by William J. O'Brien

55. Setting reaction
 Magnesium ammonium phosphate formed is polymeric. An excess
of magnesia is usually present, and some of it is never fully reacted.
- So, colloidal multimolecular aggregate around excess MgO and
fillers is formed.
 On heating, the binder of the set investment undergoes thermal
reactions.
NH4H2PO4 + MgO + 5H2O → NH4MgPO4 6H2O

56.  NH4. H2PO4 + MgO + 5H2O → Mg.NH4.PO4.6H2O
↓ Room Temperature
Mg.NH4. PO4. 6H20
↓ Dehydration on heating at 160℃
NH4. MGPO4. H2O
↓ At 300℃ - 650 ℃ , NH3 is released
Mg2. P2O7 + 2NH3 + 13H20
↓ 1040℃
Mg3(P2O4)2 Crystalline form

57. Setting & thermal expansions
 Instead of shrinkage , the reaction entails slight
expansion which increases by using colloidal silica
solution instead of water.
 The early thermal shrinkage of phosphate
investments is associated with the decomposition
of the binder magnesium ammonium phosphate,
and is accompanied by evolution of ammonia.
 Some of the shrinkage is masked because of the
expansion of the refractory filler especially in
cristobalite.

58.  Phosphate investments when mixed with H2O have shrinkage in
essentially the same temperature range, as gypsum bonded
investments at 200-400C (400-750F).
 This contraction is practically eliminated when a colloidal silica
solution replaces the water, expansion of a phosphate bonded
investment is decreased by increasing the liquid to powder ratio.
 The early thermal shrinkage in phosphate investments is due to the
decomposition of the binder magnesium ammonium phosphate
and is accompanied by evolution of ammonia’s which is readily
apparent by its odour.

59. Working & setting time
 Phosphate investments are affected by temperature as warmer the
mix, faster it sets.
 The setting reaction itself gives off heat, and this further accelerates
the rate of setting.
 Increase in mixing time and mixing efficiency results in faster set &
a greater rise in temperature.
 Increase in w:p ratio, increases the working time

60. Miscellaneous properties
 Increasing the special liquid to water ratio used for the mix
markedly enhances casting surfaces smoothness but can lead to
oversized extra coronal castings.

61. Technical Data
Mixing ratio (Water:powder) 100g :22 ml-23 ml
Total linear expansion 1.2% - 2.4%
Mixingtime (under vacuum) 60sec
Compressive strength (depending on
concentration of the mixing liquid)
4MPA- 8MPa

62. Advantages
 They have high strength which makes them easy to handle without
breaking before burnout & strong enough afterwards to withstand
the impact & pressure of centrifugally cast molten alloy.
 Provide setting & thermal expansion high enough to compensate
for the thermal contraction of cast metal prosthesis or porcelain
veneers during cooling.
 Have the ability to withstand the burnout process with temperature
that reach 900ºC.

63. Disadvantages
 When used with higher melting alloys i.e. those with casting temp. ≥
1375ºC, these investments results in mold breakdown & rougher
surface on castings.
 The high strength of these investments can make removal of the
casting from the investment difficult.

64. REVIEW OF LITERATURE
The Effect of Investment Materials on the Color of Feldspathic Ceramics
Cubas et al, European Journal of Dentistry, October 2015, Vol.5
The aim of this study was to evaluate the influence of investment type
on the color of feldspathic ceramics. Ceramic specimens were
constructed using four investments (i.e., Vitadurvest, Duravest, Duceralay
Superfit, and Fortune) to observe their effect on the color of five
commercially available ceramics (i.e., Super Porcelain EX-3, Vision
Esthetic, Vintage Halo, IPS Classic, and Vitadur Alpha). The color analysis
of the ceramics was performed with a colorimeter.

65. RESULT:
Two investments (Duravest and Fortune) produced alterations in color
parameters with three of the five ceramics tested. Hence the
investment materials produced alterations on the ceramic color
parameters.

66. MARGINAL GAP OF CROWNS MADE WITH A PHOSPHATE-BONDED
INVESTMENT AND ACCELERATED CASTING METHOD
Shilling RE et al, J Prosthet Dent 2011;81:129-34.
This study measured the marginal gap and determined the clinical
acceptability of single castings invested in a phosphate-bonded
investment with the use of conventional and accelerated methods. 44
individual stone casts were poured from impressions made from a
master die. Conventional and accelerated methods of investing and
casting were followed. 22 casts were used in each of the 2 groups.
Each casting and its respective stone die were examined with a
microscope at 4 predetermined sites. Marginal gap were documented
for each.

67. RESULT:
A phosphate-bonded investment (Ceramigold) selected for an
accelerated casting technique produced single castings within 30
minutes with marginal gaps comparable to those found that used
conventional methods.

68. Devesting :-
After casting, let the casting ring cool down to room
temperature and devest. For this purpose the
investment material mold must be soaked for
approx. 15 min and carefully split open at several
points using plaster pliers.
When this method is employed, the dental casting
can be easily removed from the investing
compound, and formation of dust is prevented.
Final residues of investing compound in the crowns
can be picked out or carefully blasted out with
aluminum oxide, granularity 100 µm to 150 µm.

69. ETHYL SILICATE-BONDED INVESTMENT
 These are used for high fusing base metal alloys.
 Losing popularity - complicated and time consuming procedures
involved.
 Consists of powder & liquid.
- Powder contains refractory particles of silica & glass along
with calcined MgO & some other oxides in minor amount.
- 2 Liquids are ethyl silicate & acidified solution of denatured
ethyl alcohol. - Binder is a silica gel that reverts to silica
(crystobalite) on heating.

70.  COMPOSITION:
1) REFRACTORY MATERIAL : Silica
2) BINDER:
BINDER BASED ON SODIUM SILICATE:
An aqueous solution of sodium silicate is acidified by the addition of
HCl acid to form a bonding silicic acid gel. However such investments
are not generally used.

71. An aqueous suspension of colloidal silica can also be converted to a
gel by the addition of an accelerator, such as AMMONIUM CHLORIDE.
BINDER BASED ON ETHYL SILICATE:
A colloidal silicic acid is first formed by hydrolyzing ethyl silicate in the
presence of hydrochloric acid, ethyl alcohol and water. The solution is
then mixed with quartz or cristoballite, to which is added small amount
of MgO. Thus polysilicic acid gel is formed within one hour after
mixing.

72. Advantages
 The investments have the ability to cast high temp. cobalt-
chromium & nickel- chromium alloys with good surface finish, low
distortion & high thermal expansion.
 They are less dense than Phosphate bonded investments & thin
sections with fine details can be reproduced.
 The low strength makes removal of casting from investment easier
than with Phosphate bonded investments.

73. Disadvantages
 Added processing attention & extra precaution needed in handling
the low strength fired molds.
 The low strength & high thermal expansion requires a more precise
burnout process & firing schedule to avoid cracking.

74. Die stone investment combination
 In this the die material & the investing medium have a comparable
composition.
 A commercial Gypsum Bonded material called “Divestment” is
mixed with colloidal silica liquid.
 The setting expansion of the material is 0.9% & thermal expansion
is 0.6%, when heated to 677ºC.
 Not recommended for high fusing alloys, as used for metal ceramic
restorations.

75. Hygroscopic thermal gold casting
investment
 Designed for use with either hygroscopic or thermal type of casting
technique.
 Thermal expansion of this investment takes place in the range 482ºC &
649ºC .
 This expansion is high enough to use the investment with the thermal
casting technique without water immersion. But when it is immersed in a
water bath, then the investment expands hygroscopically.
 With the hygroscopic technique the investment only needs to be heated to
482ºC to provide appropriate expansion.

76. Soldering/brazing investments
 When soldering the clasps on a RPD, the parts must be surrounded
with a suitable investment material before the heating operation.
 The assembled parts are temporarily held together with sticky wax
until they are surrounded with the investment material, after which
the wax is softened & removed.
 The portion to be soldered is left exposed & free from investment
to permit wax removal & effective heating before it is joined with
solder.

77.  Types of brazing investments are:-
- Type 1 - Gypsum bonded.
- Type 2 - Phosphate bonded.
 The investment for soldering is similar to casting investment.
 They are designed to have lower setting & thermal expansions than
casting investments, a feature that is desirable so that the
assembled parts do not shift in position during the setting &
heating of the investment.

78. Investments for all-ceramic
restorations
Type I – Used for the cast glass technique composed of
phosphate bonded refractories.
Type II – Refractory die type of material, used for all-
ceramic veneers, inlays & crowns.
 Refractory dies are made by pouring the investment into
impressions. When 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.

79.  Then, the porcelain or other ceramic powders are added to the die
surface & fired.
 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 phosphate bonded & they generally contain
fine grained refractory fillers to allow accurate reproduction of
detail.

80. Investment of titanium & titanium
based alloys
 Ti is highly reactive with oxygen & is capable of reducing some of
the oxides commonly found in phosphate and silica bonded
investments.
 Ti can also dissolve residual oxygen, nitrogen & carbon from the
investment.
 These elements can harden & embrittle Ti in the solid state.
 Hence, modification in the existing refractory formulation & binder
are required.

81.  COMPOSITION:-
These investments can be classified as:-
1) Phosphate bonded
2) Ethyl silicate bonded
3) Cemented
► REFRACTORIES:-
- Silica(SiO2)
- Alumina(Al2O3)
- MgO
- Zirconia(ZrO2)

82.  PHOSPHATE BONDED TITANIUM INVESTMENT:-
- To achieve expansion without the use of reactive powders, a PBI that
contains both magnesia & alumina as refractories was developed.
- This investment can achieve large expansion by the reaction of
alumina & magnesia, when it is burned out at 1150ºC - 1200ºC .
 ETHYL- SILICATE BONDED INVESTMENT:-
- Reactions with the liquid Ti has been reported to be somewhat less
than that of Phosphate bonded investments due to the use of highly
refractory oxides in the powder.

83.  CEMENTED TITANIUM INVESTMENT:-
- This investment use magnesia bonded by an aluminous cement & contains
5% zirconium powder by weight.
- The aluminous cement serves as 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 temperature.
- The zirconia formed is highly stable & it does not contaminate Ti. Ti
castings from this investment have smooth surface which are free of
contamination.

84. Recently a new investment material for titanium casting has been
developed, which contains calcia (CaO2) as refractory and cold-cure
acrylic resin (PMMA) as binder, known as “RESIN-BONDED CALCIA
INVESTMENT”.

85. CALCIA BONDED INVESTMENT
 This is a the recently developed investment for casting titanium
inlays, crowns and bridges.
REFRACTORY - Zirconia
BINDER - Calcia
 PROPERTIES:
1. Total thermal and setting expansion found was 1.5 to 2.5%
2. The maximum thermal expansion was found at 900 to 1200°C

86. CERAMIC OR SILICA FREE
INVESTMENT
• Casting of ceramic crowns using castable glasses is done in refractory moulds.
• Castable moldable ceramic are hot pressed into ceramic mould by pressure
where no compensation expansion is needed
• Special GBI of low thermal expansion are used, made from pure gypsum and
Calcium sulphate hemihydrate
• Same investment additives as GBI to prevent their contraction or deterioration
on heating.

87. Effect of Investment Type and Mold Temperature on Casting Accuracy
and Titanium-Ceramic Bond
Leal MB et al, Brazilian Dental Journal (2013) 24(1): 40-46
This study evaluated the casting accuracy of crown margins and
ceramic shear bondstrength (SBS) of pure titanium injected into
molds made using phosphate-bonded investment(P) and magnesium
oxide-bonded(U) investment types at 400,550 and 700°C mold
temperatures. 60 crown (30-degree beveled finish line) and 60
(5mm diameter x 8 mm high) patterns were divided into 6 groups
(n=10) and casted. Crown margins were recorded in impression
material, the degree of marginal rounding was measured and margin
length deficiencies (μm) were calculated. Titanium-ceramic specimens
were prepared using Triceram ceramic (2 mm high) and SBS was

88.  Result
The results of the study suggest that there were no significant
differences for titanium-ceramic SBS for any of the combinations of
investments and mold temperatures. Nevertheless, marginal accuracy
of crowns cast with CPTitanium was significantly affected by
investment type and mold temperature.

89. Conclusion
 As Prosthodontists, our aim is to make a restoration as accurate as
possible. Hence knowledge about various materials and techniques
used in casting dental restoration is important.
 Investment materials are to be selected based on the type of
restoration, the type of metal or alloy to be casted etc and also the
technique used for casting and investing a wax pattern is a very
important procedure as it will determine the seating accuracy of the

90. References
1. Phillips science of dental materials - Kenneth J.Anusavice, 11th
edition
2. Introduction to dental materials - Richard van noort,1st edition
3. Applied dental materials - John F, Mc.Cabe, 8th edition
4. Dental materials and their selection - Willian J .O’Brien, 2nd edition
5. Restorative dental materials - Robert .G.Craig, 11th edition

91. 6. Contemporary fixed prosthodontics – Rosenstiel, 3rd edition
7. Fundamentals of fixed prosthodontics – Shillingburg, 4th edition
8. Dental laboratory procedures - Rudd & Morrow, 2nd edition
9. Operative dentistry-modern theory & practice, M.A.Marzouk
10. Internet sources