It represents different type of dental investment materials and its uses in clinical field

1. INVESTMENT MATERIALS FOR DENTAL
CASTING PROCEDURES
PRESENTED BY
DR. ALOK RANJAN SASMAL
FIRST YEAR PG
Dept. of Prosthodontics and Crown & Bridge

2. INTRODUCTION
CONTENTS-
DEFINITIONS
REQUIREMENTS OF INVESTMENT MATERIALS
MATERIAL SCIENCE
GYPSUM-BONDED INVESTMENT MATERIAL AND ITS PROPERTIES
PHOSPHATE-BONDED INVESTMENT MATERIALAND ITS PROPERTIES
SILICATE-BONDED INVESTMENTMATERIAL
IMPLICATION OF MATERIAL SCIENCE DURIING CASTING
OTHER INVESTMENT MATERIALS
SUMMARY
REFERENCES

3. DEFINITIONS
Investing: the process of covering or enveloping,
wholly or in part, an object such as denture, tooth,
wax form, crown, etc. with a suitable investment
material before processing, soldering or casting.
(GPT 8)
Dental casting investment: A material consisting
primarily 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).
(GPT 8)

4. 1. Must reproduce precisely the details form of the wax pattern
2. Must provide sufficient strength to withstand the heat of burnout and the
impact and the pressure of cast molten alloy
3. Must maintain the integrity at higher temperatures and should not
decompose to give off gases
4. Must expand sufficiently to compensate for the solidification shrinkage of
the alloy
5. Easily manipulated and setting time should be less
6. Should be inexpensive
7. Biological safety
Fundamentals of fixed prosthodontics,3rd
edi.Herbert T. Shillingburg

5.  Investment materials are basically composed of
1. A refractory material
2. A binder material
3. Additives .

6. REFRACTORY MATERIAL
SILICA (silicon dioxide) is used as refractory
material & to regulate the thermal expansion.
 It exists in four allotropic forms such as
Quartz
Tridymite
Cristobalite
Fused quartz
 Each form of silica exists in two phases.
 Low temperature phase or alpha phase
 High temperature phase or Beta phase
 On heating the change between the two phases is
rapid and readily reversible on cooling .this change is
known as inversion

7. IMPORTANCE OF INVERSION -
As form changes from Alpha to Beta
Density
volume
Increase in liner expansion(quartz-
0.45% ), which compensate shrinkage of
gypsum and casting shrinkage
Quartz- 5730C
Cristobalite- between 200 and 2700C
Tridymite- 1170C,1630c
Fused Qurtz- no inversion temperature
Inversion temperature
Quartz, cristobalite, or a combination of the two
forms may be used in a dental investment

9. BINDER
It binds the refractory materials together.
According to the binder used investment materials are of
three groups.
1. GYPSUM-BONDED INVESTMENTS
2. PHOSPHATE BONDED INVESTMENTS
3. SILICA BONDED INVESTMENTS

10. ADDITIVES
Used are
Reducing agents –provides a nonoxidizing
atomsphere in the mold cavity
 Modifying chemicals –regultes physical
properties like setting reaction, setting expansion
 Coloring matter

11. GYPSUM BONDED INVESTMENT
MATERIAL
 They are the mold materials used in the casting
of dental gold alloys with temperature below
7000C.
 Used for conventional casting of gold alloys
inlays, onlays, crowns and Fpd.

12. ADA SPECIFICATION-2; divided them further
into
 TYPE I- for casting inlays/crowns.
mode of expansion: Thermal
 TYPE II-for casting inlays/crowns
mode of expansion : Hygroscopic
 TYPE III-for partial dentures with gold alloys

13. Composition
Refractory
Crystalline polymorphs
of silica (quartz or
cristobalite)
 55-75%
Silica is added to provide
a refractory component
during the heating of the
investment and to
regulate the thermal
expansion.

14. BINDER – Alpha hemi hydrate form of
gypsum(25-45%)
Strength of investment depends on amount
of binder present.

15. ADDITIVES - (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

16. Modifying chemicals: They regulate setting expansion and thermal
expansion and also prevent shrinkage of gypsum when heated
above 200ºC .
Ex– Boric acid
Soluble salts of alkali or alkaline earth metals

17. SETTING REACTION-same as
gypsum
Dissolution of calcium sulfate hemihydrate
Formation of saturated solution of calcium sulfate,
Aggregation of calcium sulfate dihydrate
Precipitation of dihydrate crystals
The crystallization of calcium sulfate dihydrate occurs while most of the
remaining hemihydrate particle dissolve
Theories to explain setting reaction
1.Colloidal theory
2.Hydration theory
3.Dissolution –precipitation theory
Among these dissolution-precipitation theory most
accepted

18. Properties
SETTING TIME
According to ANSI/ADA Specification No. 2 for dental
inlay casting investment, the setting time should not be
shorter than 5 min or longer than 25 min. Usually, the
modern inlay investments set initially in 9 to 18 min.
Should allow sufficient time for mixing and investing the
pattern.

19. SETTING EXPANSION
1. Normal setting expansion: the expansion takes place when
the material sets in air
2. Hygroscopic setting expansion: when setting occurs under
water.
3. Thermal expansion: when it is affected by heat
Purpose: to enlarge the mold to compensate for the casting
shrinkage of the gold alloy

20. Normal Setting Expansion
Liner dimensional change as the investment sets
Silica particles interfere with the intermeshing and
interlocking of crystals
resulting in outward thrust of crystals
Resulting in expansion
A mixture of silica and hemihydrate gypsum results
setting expansion greater than that of gypsum
product used alone

21. Normal Setting Expansion
ADA sp no 2 for type 1 investment permits a maximum setting
expansion in air of 0.6% setting expansion of modern
investments is 0.4%.It can be regulated by accelerators and
retarders .
Effective expansion in the mold depends on different factors
like wax pattern in the mold may expand due to heat of
reaction.
Soft wax- more NSE.
If wax softer than Type II inlay wax is used , it may cause
distortion of the pattern.

22. Hygroscopic setting expansion
Greater in magnitude than NSE.
The gypsum product is allowed to set in contact
with water for mold expansion.
Curve A-NSE;
Curve B-Hygroscopic expansion
Water is added 5 min after beginning of the mixing

23. The hygroscopic setting expansion may be 6 or more times greater
than the normal setting expansion of a dental investment
The increased amount of expansion is because the water helps the
outward growth of crystals
The investment should be immersed in water before the initial set is
complete.
ADA sp no 2 for such type 2 investments require minimum setting
expansion in water of 1.2% and maximum 2.2%.

24. Factors affecting expansion
Composition: more finer silica particles -more HSE.
 α hemihydrate greater HSE than β hemihydrate.
 W:P ratio-lower W:P RATIO-more HSE
 Spatulation: more mixing time- more HSE.
 Time of immersion: immerse in water before initial set
more expansion than immersion is delayed beyond the time
of initial set.
 Confinement: less opposing force from walls of casting
ring (wet cellulose), immersion in water bath at 37.7°C-
expansion of wax pattern-more HSE
 Added Water : HSE directly related to amount of water
added during the setting period until a maximum expansion
occurs.
 Shelf life: fresher investment-more HSE

25. Thermal setting expansion
The thermal expansion is directly related to the amount
and type of silica present.
Contraction of gypsum is balanced when quartz contain
increases to 75%.
Type 1 investments should have thermal expansion of not
less than1% and not greater than 1.6%.
Type 1I investments should have thermal expansion of
between 0% to 0.6% at 500°C.
Maximum thermal expansion should be attained at
temperature not higher than 700 degree centigrade

26. Factors affecting thermal
expansion
W/P ratio-more water less expansion
as thermal expansion related to the amount
of solids presents

27. When an investment is cooled from 700°C, it
contracts but less than its original dimension.
On reheating it expand thermally to the same
maximum reached before.
 PRECAUTION – Investment should not be heated
a second time because internal cracks
may develop.
SETTING CONTRACTION

28. COMPRESSIVE STRENGTH:
According to ADA sp no 2 the compressive strength should
not be less than 2.4MPa when tested 2 hr after setting to
withstand force of molten metal.
FINENESS: Surface roughness of the casting and
setting time depend upon the fineness of the material. Fine
silica- more hygroscopic expansion.

29. POROSITY: The material should be porous to allow
escape of air from mold space while casting. The common
method of venting the mold is through the pores of the
investment.
CLINICAL CONSIDERATION- Sprue length
should be adjusted so that the top of the wax pattern is
within 6 mm of the open end to allow sufficient interconnectivity
of the porous network, otherwise backpressure porosity will
develop.

30. STORAGE
Storage room with high relative humidity , the
setting time, setting expansion and
hygroscopic expansion altered casting
procedure adversely affected .
Due to different ingredients of investment
possesses different specific gravity ,they have
a tendency to separate as they settle
influence properties of material

31. Should be stored in airtight and moisture-proof
containers.
For an infrequent basis of use, it is advisable to
purchase prepackaged investment in relatively
small quantity.(also cost effective)
Quality of investment products depends on
Homogeneity of particulate components
Variations in weight of powder in packets
 So products with weight variations of 2% or less
between packets in a box represents excellent
quality control &variations of 5% implies serious
consequences in its properties.
PRECAUTION

32. Available products in market-
Gloriaa Special
SPOFA DENTAL

33. PHOSPHATE BONDED
INVESTMENT MATERIAL
Most palladium and base metal alloys used for partial
dentures and porcelain fused to metal restorations have
high melting temperatures. They should be cast
at a mold temperature higher than 700 ºc.
To withstand these high temperatures ,molds require
different types of binders such as phosphate
compounds.

34. They are used in construction of high melting temperature
dental alloys .
Soldering and porcelain veneering

35. Types
Type 1
For casting of inlays crowns and other restorations
especially for alloys like gold, platinum ,palladium cobalt
chromium and nickel chromium
Type 2
For casting of removable partial dentures

36. COMPOSITION
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.

37. Binder (<20%)
Magnesium oxide (acid) and a phosphate (base)
• Originally phosphoric acid was used but mono
ammonium phosphate has replaced it as it can be
incorporated in powder form

38. Modifiers :CARBON
Carbon is often added -clean casting.
Facilitates easy divesting of casting and mold.
Generally added when casting alloy is gold.
Not used with Ag-palladium alloys or base metal alloys as;
-palladium reacts with carbon at temperatures above
15040C
-carbon embrittles the alloys.
CLINICAL CONSIDERATION- So for base metal alloys and
palladium containing alloys carbon free phosphate bonded
investment should use. Also, a carbon crucible should not be
employed for melting the alloy.

39. 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 Metal Ceramic & newer gold
alloys.

40. SETTING REACTION
The chemical reaction that causes the investment to
set and harden is
NH4H2PO4 +MgO+5H2O→NH4MgPO4 +6H2O
 The product formed is the predominantly colloidal
multimolecular (NH4MgPO4·6H2O)n aggregate around
excess MgO and fillers.

41. Properties
1 Compressive strength
Type 1- 2.5 MPa
Type 2- 3 Mpa
 Thermal expansion
0.8% when 50:50 mixture of liquid and water

42. working & setting time
Temperature
Warmer the mix faster it sets
The setting reaction also liberate the heat and
accelerates rate of setting
Mixing time
increased mixing time and mixing efficiency
result in faster set.

43. Surface Quality of cast metal
In the past, detail reproduction and surface smoothness of a
metal-ceramic gold alloy restoration cast in a phosphate bonded
investment were considered inferior to those characteristic
of a conventional gold alloy that had been cast in a
gypsum-bonded investment.
Due to improvement in technique and in composition of material Phosphate
bonded investments now approach the surface quality or fineness of the
gypsum investments,

44. Advantages
1.They have high fired strength. This make them
handle without breaking before they are placed in a
furnace for the wax burn out process and strong
enough to withstand the impact and the pressure of
centrifugally cast molten alloy
2.They also provide high setting and thermal
expansion enough to compensate cast metal
prosthesis or porcelain veneers during cooling
3. They can withstand temp more than 700°C

45. Disadvantage
When used with alloys having casting temperature greater
than 10300C results in mold breakdown & rougher
surfaces on casting.
Although high strength of these investments is an
advantage during casting, but can make divesting a difficult
and tedious task.
Less porous than gypsum bonded investment .
CLINICAL CONSIDERATION-For proper venting of
investment, wax pattern should be within 3 to 4 mm from
the top of the investment .
 The permeability low casting pressure should
be greater than that of gypsum investment

46. Bellavest SH
Properties:
Processing time approx. 3.30 min
Thermal expansion linear 0.8 % with 70 % BegoSol K
Compressive strength: approx. 11 N/mm²
Mixing ratio 100 g : 20 ml
Properties:
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
indications in the partial denture
Universally applicable for precious metal alloys, non
precious metal alloys, pressed all-ceramic and press-
over ceramic.
(SH-Shock heat)

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

48. SILIKAN( P) &SILISAN (L) SPOFA
SANIVEST INVESTMENT MATERIAL
for precious and non-precious metal applications
WiroFast( Phosphate bonded investment material)
Partial denture investment material suitable for shock
heating

49. 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 %Hinrivest® G
(ERNST HINRICHS)

50. SOME IMPLICATION OF MATERIAL
SCIENCE DURIING CASTING
Investing procedure-(common for both gypsum and
phosphate investment)
Mixing by-1.Hand mixing 2.vacuum mixing.
In vacuum mixing-removes air bubbles,texture
somewhat smoother and better details reproduction.
• Excessive vibration should be avoided as-
. causes solids in the investment to settle and may
lead to free water accumulation adjacent to wax pattern
Surface roughness
.May dislodge small pattern Produce a miscast

51. Wax elimination and Heating-
After investment set, approximately-1hr,it is ready for burnout
BURNOUT TEMPERATURE-
Gypsum investment-5000C for hygroscopic technique
7000C for thermal expansion technique
Phosphate bonded investment- range from 7500C to
10300C depending of the type of alloy
The temperature setting is more critical with
gypsum-bonded investments than for the phosphate type
because the gypsum investments are more prone to investment
decomposition. As temperature rises above 7000C ,calcium
sulfate reduce as following reaction-
CaSO4 + 4C CaS + 4CO
3CaSO4 + CaS 4CaO+ 4SO2

52. Carbon produce from the wax burnout.
The sulfur dioxide as a product of this reaction contaminates
gold castings.
Heating in burnout furnace
For gypsum bonded investment- The molds are usually placed in a
furnace at room temperature, slowly heated to 650 °C to 700 °C in 60
minutes, and held for
15 to 30 minutes at the upper temperature.
For phosphate bonded investment- The heating rate is usually slow
to 315 °C and is quite rapid thereafter, reaching completion after a
hold at the upper temperature for 30
minutes.
.

53. RAPID HEATING IN BURNOUT FURNACE-
Generate steam Causes flaking or spalling of the mold walls
Outside layer of the investment expands more than central
Tensile stress develop in the middle
Crack from interior outwards in the form of radial cracks
Casting fins or spines

54. ETHYL SILICATE BONDED
INVESTMENTS
Though losing popularity because of the more
complicated and time consuming procedures,
still used in the construction of high fusing
base metal partial denture alloy.

55. Composition
Refractory material – Silica
Binder –Silica gel that reverts to silica
(cristobalite) on heating.
Modifier –
Magnesium oxide (strengthen the gel)
Ammonium chloride - accelerator

56. Binder
 Lowering the pH of sodium silicate by addition
of an acid or an acid salt.
Converting colloidal silica to gel by adding
ammonium chloride
Ethyl silicate: colloidal silicic acid is formed by
hydrolyzing ethyl silicate in presence of Hcl, ethyl alcohol
& water.
Si(OC2H5)+4H2O Si(OH)4+4C2H5OH
Methods used to produce the Binder

57.  It is then mixed with quartz or cristobalite
and magnesium oxide ( alkaline). Coherent
gel of polysilicic acid formed(accompanied
by a setting shrinkage) ,dried at temp
168°C, loses alcohol & water to form
concentrated hard gel . Volumeric
contraction during drying is known as
green shrinkage.
 As the gelation process is slow and time
consuming , amines are added to ethyl
silicate- hydrolysis and gelation occurs
simultaneously.

58. It is supplied as a powder and liquid
Powder consists of refractory particles of silica
and glasses along with the magnesium oxide and
some other refractory oxides in minor amounts
Liquid contains stabilized alcohol solution of silica
gel

59. Manipulation
The powder is added to hydrolyzed ethyl silicate liquid,
mixed quickly and vibrated into a mold , that has an
extra collar to increase the height.
The mold is placed on a vibrator that has a tamping
action
This allows the heavier particles to settle while the
excess liquid and some of the finer particles rise to the
top .

60. In about 30 minutes the accelerator in the powder
hardens the settled part, and the excess is poured off
(to avoid crack formation).
The liquid powder ratio in settled part is greatly
reduced and the setting shrinkage is reduced to 0.1%

61. Can be used for higher temp castings (
1090°C-1180°C) and compactible with higher
fusing alloys.
Care should be taken while handling and
burnout as inflammable alcohol is given off.

62. Disadvantage
Non porous material.
Complicated manipulation
Cannot be used for titanium and its alloys as silica can
oxidize titanium or its alloys easily.

63. Other investment materials
Soldering investment
Divestment materials
Investment material for titanium alloys
 Investments for all ceramic restoration

64. Soldering investment
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

65. 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

66. DIVESTMENT
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.

67. Newer investments for casting
titanium based alloys
Problems with conventional investment materials-
0 Molten titanium is highly reactive with the oxygen and
is capable of reducing some of the oxides commonly
found in the investment.
0 Titanium can also dissolve residual oxygen, nitrogen,
and carbon from the investments.
0 These elements can also embrittle titanium in the
solid state.

68. Objective for a titanium
investment
0 To reduce breakdown of the investment
0 To reduce contamination of the titanium – refractory
materials that are less easily reduced by titanium
should be used

69. INVESTMENTS USED FOR CASTING
TITANIUM ALLOY
Silica based investment
Magnesia based investment
Zirconia based investment
Alumina based investment
Resin based calcia investment

70. SUMMARY
Due to increase in the use of the higher melting alloys
,the use of phosphate bonded investment materials
increases.
Gypsum bonded investment cannot withstand
temperature higher than 7000C and it can be used only
with conventional gold alloys.
The complex procedures limited the use of silicate
bonded investments.
Due to highly reactive of titanium with the oxygen in the
mold cavity , newer investment materials are
developed.

71. • Gypsum bonded
investment
(700OC)
• Mold for gold casting alloys
Phosphate bonded
investment
(700-1030oC)
 Silica bonded
investments
(1090-11800C)
Mold for base metal
and gold casting
alloys, cast ceramic
and glasses
 Mold for base
metal casting alloys

72. References-
PHILLIPS”Science of Dental material, 11th edition
Restorative Dental materials, Robert G. Craig.11th edition
Fundamentals of fixed prosthodontics,3rd edi.Herbert T. Shillingburg