This document provides information on different types of casting investments used in dentistry, including their composition, properties, and applications. It discusses gypsum-bonded, phosphate-bonded, and ethyl silicate-bonded investments. Gypsum-bonded investments are the oldest and used for gold alloys. Phosphate-bonded investments are used for metal-ceramic restorations and base metal alloys due to their higher temperature resistance. Ethyl silicate-bonded investments were rarely used due to time-consuming processing and flammable byproducts. The document outlines the ideal requirements, composition, setting reactions, expansion properties, and limitations of the different investment materials.

1. 1

2. 2
CASTING
INVESTMENTS
FATEEMA PRIYAM FEROZ
1ST YEAR P.G

3. INTRODUCTION
IDEAL REQUIREMENTS
TYPES & COMPOSITION OF INVESTMENT MATERIALS
RECENT ADVANCES
CONCLUSION
DISCUSSION
SUMMARY
REFERENCES
3
CONTENTS

4. INTRODUCTION
4

5. Preparation of crown,bridge or other fixed prosthesis
Impression making and pouring of cast
Making of wax pattern
Attachment of sprue
Investing (investment materials)
Burnout
Casting
Divesting,finishing and polishing
5

6. 6

7. 7

8. 8

9. Easily manipulated.
Sufficient strength at room temperature.
Stability at higher temperature.
Sufficient expansion.
Porosity
Smoother surface.
Ease of divestment.
Inexpensive.
IDEAL REQUIREMENTS
9

10. 10
COMPOSITION
REFRACTORY
MATERIAL
BINDER
OTHER
MATERIALS
withstands higher temperature without degradation
sodium chloride
boric acid
magnesium
etc

11. Types of casting investments
Gypsum bonded investments
Phosphate bonded investments
Ethyl-Silicate bonded investments
11

12. Gypsum bonded investments are the oldest materials and are used for
casting conventional gold alloys.
The phosphate bonded investments are used for metal ceramic
restorations.
Silica bonded investments are principally used for the casting of base
metal alloy partial dentures
12

13. American Dental Association specification no: 2 for casting investments used
for gold alloys, lists 3 types of investments
Type I – for inlays and crowns utilizes thermal expansion of the mould.
Type II – for inlays and crowns utilizes hygroscopic setting expansion.
Type III – for gold partial denture utilizes thermal expansion
Gypsum bonded investments
13

14. Composition
Gypsum bonded investment is a mixture of 4 types of materials.
Refractory materials: usually a form of silica (quartz, crystobalite or tridymite)
Binder : alpha calcium sulphate hemihydrate is used. (25-45%)
• To react with water and on hydration binds the silica together.
• To impart sufficient strength to the mould and
• To contribute to the mould expansion by its setting expansion.
14

15. A reducing agent: such as powdered charcoal, reduces any oxide formed
on the metal.
Modifying chemicals : such as boric acid or sodium chloride to inhibit
shrinkage on heating
15

16. The alpha hemihydrate is usually used because of its
greater strength compared to the beta variety.
But this binder when heated to high temperatures for
complete dehydration, shrinks considerably and
frequently fractures
Gypsum
16
gold alloys below 1000℃

17. A thermal expansion curve of gypsum shows considerable
shrinkage from 200 to 400°C. A slight expansion then occurs
to approximately 700°C and then a tremendous contraction is
caused, probably due to decomposition, and sulphur gases like
sulphur dioxide are emitted which contaminates the casting.
17

18. Silica
• Silica (Silicon dioxide, SiO2) is the refractory material and it regulates
thermal expansion.
• Gypsum contracts during heating and silica eliminates this contraction and
changes it to an expansion.
• Silica exists in at least four allotropic forms: quartz, tridymite, cristobolite
and fused quartz.
• When quartz, tridymite or Cristobalite are heated, a change in crystalline
form occurs, called “inversion”, at a transition temperature characteristic of the
particular form of silica.
α form β forms
18

19. 19

20. Quartz inverts from a “low” form or alpha quartz to a “high” form
called beta quartz at 575°C,
Cristobalite inverts from 200 to 270°C from low or alpha cristobalite
to high or beta cristobalite.
The density decreases and volume increases as the alpha form
changes to the beta form and a rapid increase in linear expansion
occurs
20
ALL FORMS OF SILICA ARE PRESENT IN THEIR ALPHA FORM
IN THE INVESTMENT,AND DURING THE HEATING PROCESS THEY
ARE CONVERTED TO THEIR BETA FORM .THIS TRANSITION
INVOLVES AN EXPANSION OF THE MASS WHICH COMPENSATES
FOR THE CASTING SHRINKAGE.

21. Quartz and cristobalite are extensively used in investments. On the basis
of the type of silica principally employed, dental investments are often
classified as quartz or cristobalite investments
21

22. Modifying agents, colouring matter and reducing agents such as carbon
or powdered copper are also added.It provides a NON OXIDISING
atmosphere in the mould when gold alloy is cast.
Some modifiers such as boric acid and sodium chloride not only
regulate the setting expansion and setting time, but prevent most of the
shrinkage of gypsum when it is heated above 300°C.
22

23. Properties of gypsum bonded investment
SETTING TIME: According to ADA specification no. 2 for dental inlay
casting investment, the setting time should not be shorter than 5
min, nor longer than 25 min .
23
Modern inlay investments set initially in 9-18 minutes.

24. • After mixing with water and subsequent heating in furnace
• The investment undergoes series of expansion
SETTING EXPANSION
NORMAL HYGROSCOPIC THERMAL
24

25. NORMAL SETTING EXPANSION
Investment + water
Volumetric expansion
Occurs due to direct conversion of CaSo4
hemihydrate to dihydrate form
25
TYPE I INVESTMENT-0.6%

26. Factors determining the effective setting expansion
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.
Thinner the walls of the wax pattern, greater the setting expansion of the
investment.
Softer the wax, greater the setting expansion.
26

27. HYGROSCOPIC SETTING EXPANSION
According to ADA specification no. 2, the minimum
expansion in water is 1.2% and maximum expansion is
2.2%
27

28. J Dent Res 39:578,1960
28

29. FACTORS AFFECTING HYGROSCOPIC
EXPANSION
Silica content and particle size
More the silica content greater the hygroscopic reaction
Finer the particle size greater is the hygroscopic expansion
Effect of W:P ratio:
↑ed water powder ratio will cause ↓ed hygroscopic Expansion
29

30. Effect of spatulation:
↓ed mixing time ↓ed hygroscopic
setting expansion.
Shelf life of the investment:
Older the investment, lower the hygroscopic setting expansion.
30

31. Effect of time of immersion:
Increased amount of hygroscopic expansion takes place if the investment is
immersed before the initial set.(before the gloss of the investment is lost)
Effect of confinement:
Both the normal and the hygroscopic setting expansions are confined by
opposing forces-walls of the container,or walls of the wax pattern.
Confining effect is more pronounced on hygroscopic expansion as
compared to normal setting expansion
(diagram)
31

32. Effect of amount of added
water
It has been proved that the magnitude of the hygroscopic
expansion is in direct proportion to the amount of
water added during the setting period UNTIL A MAXIMUM
EXPANSION OCCURS.
32
CRITICAL POINT

33. THERMAL EXPANSION
Thermal expansion of gypsum bonded investment is directly
related to
1.Amount of silica present
2.Type of silica employed
When gypsum is heated initial contraction takes place
between 200-400°Celsius
To counterbalance that contraction quartz content is
increased to 75%
33

34. The investment containing cristobalite
expand earlier and to a greater extent
than those containing quartz
The desirable magnitude of thermal
Expansion depends upon its use
TYPE-I - 1-1.6%
TYPE-II - 0-0.6%
34

35. EFFECT OF WATER POWDER RATIO
Magnitude of thermal
expansion is related to the
amount of solids present.
Thus, if more water is used
in mixing the investment, the
lesser is the thermal expansion
achieved.
35

36. EFFECT OF CHEMICAL MODIFIERS
Small amounts of sodium, potassium or lithium chlorides
1.Eliminates contraction caused by gypsum.
2.Increases the rate of expansion.
Boric acid hardens the set investment. However,it apparently
disintegrates during heating and rough surface cast may
result.
Chlorides actually reduces gypsum shrinkage below 700°C.
36

37. Thermal Contraction
When an investment is allowed to cool from 700°C, its contraction
curve follows the expansion curve, during 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.
37

38. STRENGTH
• The strength of the investment must be adequate to prevent fracture or
chipping of the mould during heating and casting the gold alloy.
• According to ADA specification no.2 the strength (basically compressive
strength) for the inlay investment should not be less than 2.4Mpa when
tested 2Hrs after setting.
• Strength basically depends upon
a) The amount and the type of gypsum binder present
b) Water powder ratio
c) Chemical modifiers
38

39. FINENESS
Fineness may affect the setting time, surface roughness
of the casting.
Finer silica may results in higher hygroscopic expansion
than a coarser silica.
39

40. POROSITY
Molten metal is forced into the mold
As molten metal enters into the mold air must be forced out.
Otherwise air will prevent the metal to completely fill the mold space, as back
pressure builds up.
During casting process
Common method of venting is through pores of the investment .
More the gypsum crystals present in the set investment, less is the porosity.
Particle size of investment:
More uniform the particle size, greater is the porosity
40

41. 41
Thus it is important that the extremity of a wax pattern is not
covered by more than approximately 6mm of investment
to allow sufficient interconnectivity of the porous network
which will permit gas within the mold cavity to escape
during filling of the mould with molten metal.

42. STORAGE
Investment should be stored in air tight and moisture proof containers.
During use, the container should be opened for as short a time as possible.
42

43. Manipulation
Before investing the wax pattern, it is washed with a non-foam detergent to
remove any oil or grease and to facilitate the wetting of the pattern by the
investment mix.
The casting ring is lined with wet asbestos strip. Investing the pattern may be
done under vacuum, to prevent trapping air on the surface of the pattern, or
painting investment material on to the pattern with a brush before gently
forcing it into the filled casting ring.
43

44. If the hygroscopic technique is employed, (Type II) the casting ring, with the
crucible former end down, is immediately immersed in a water bath at a
temperature of 37 to 38°C.
For the thermal expansion technique (Type I and III) the investment is
allowed to harden in the ring placed on the bench.
44

45. LIMITATIONS OF GYPSUM BONDED INVESTMENT
GBI (Gypsum bonded investment) decomposes above 1200 C by interaction of
silica with calcium sulphate to liberate sulphur trioxide gas.
Another reaction which may take place on heating gypsum bonded investment, is
that between calcium sulphate and carbon.
CaSO4+4C CaS+ 4CO
The carbon may be derived from the residue left after burnout of wax pattern
Further reaction can occur liberating sulphur dioxide.
3CaSO4+CaS 4CaO +4SO2
This reaction occurs above 700 degree celsius
45
Heat soaking??

46. PHOSPHATE BONDED INVESTMENTS
46

47. Introduction
Greater use of phosphate bonded investments.
The popularity of metal-ceramic and all ceramic
restorations,which require higher temperatures
Use of base metal alloys
Pure titanium and titanium alloys
47

48. 48

49. Types
According to ADA specification no: 42, phosphate-bonded investments are
classified into two types based on application
Type 1: For inlays, crowns and other fixed restoration
Type 2: For partial dentures and other removable restorations
49
Temperature range:750- 1080℃

50. Composition
Refractory material-combination of silica and quartz
80%-high temperature thermal shock resistance,high thermal expansion
Binder – 2 component
Magnesium oxide (basic) and a phosphate that is (acidic).
Originally phosphoric acid was used, but at present mono-ammonium phosphate .
Acid-base reaction
The powder is mixed with an aqueous colloidal silica suspension
50

51. Carbon is often added to the powder to produce clean castings and to facilitate
the divesting of the casting
It is suggested that carbon embrittles alloys like silver-palladium and base metal
alloys.
Thus if the casting temperature of a high palladium alloy exceeds this critical
point phosphate investment without carbon is used(above 1504℃)
MODIFIERS
51

52. Liquid
The liquid component consists of either water or colloidal silica (silica
sol/ special liquid).
It contributes to hygroscopic expansion and strength of the investment.
52

53. Setting reaction
53

54. Properties
Setting and thermal expansion
During the setting reaction a slight expansion occurs and this is more in
the colloidal silica-mixed materials than for water-mixed materials.
54

55. Thermal expansion is also greater for colloidal silica-mixed materials.
The combined setting and thermal expansion for phosphate investments is
around 2% if the special silica liquid is used
55
Both the setting expansion and the thermal expansion increase as the
concentration of the special liquid increases.
A decrease in expansion can be achieved by increasing the liquid/powder
ratio rather than by decreasing the concentration of the liquid

56.
Thermal shrinkage
This occurs due to decomposition of the binder, magnesium ammonium
phosphate, and is accompanied by the evolution of ammonia, which is
readily apparent by its odour.In gypsum????
56

57. Working and Setting time
Warmer the mix, faster the set.
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(2 mins or
less)
57

58. Surface quality of castings
Earlier inferior to GBI
But this has changed due to
Increasing special liquid/water ratio
Improvements in investment techniques
58

59. Evaluation of the thermal shrinkage of titanium and the
setting and thermal expansion of phosphate-bonded
investments
The thermal and setting expansion were measured for 3 phosphate bonded investments:
Rematitan Plus (RP) specific for titanium, Rema Exakt (RE), and Castorit Super C
(CA), using different special liquid concentrations (100%, 75%, and 50%). Setting
expansion was measured .
Titanium casting shrinkage was estimated as 1.55%. RP did not achieve this expansion.
RE achieved expansion of 1.55% only with a special liquid concentration of 100% at
594°C. CA with all special liquid concentrations attained this expansion (351°C to
572°C).
(J Prosthet Dent 2007;98:24-29)
59

60. Only RE and CA demonstrated sufficient expansion to compensate for
titanium casting shrinkage. All groups reached total expansion
equivalent to that of the control group at significantly lower
temperatures.
This study demonstrated that 2 of the less costly phosphate-bonded
investments evaluated were able to compensate for the casting
shrinkage of titanium at lower temperatures. Thus, marginal fit may be
achieved without diminishing the positive properties of titanium.
60

61. Effect Of Burnout Temperatures On Strength Of
Phosphate Bonded Investments
• Heat from the high-temperature casting metal has a material effect in
decreasing the strength of phosphate-bonded investments.
• Such heating increases the plastic behaviour of the investment and this,
together with the casting pressure, may result in a distorted mould and
thus inaccurate castings.
J Dent 1997,25:423-430
It had previously been found that the strength of phosphate-bonded
investments is temperature sensitive. However, while the effect of heat
from the cast metal is expected to have some effect on continued
reactions and melting, there is no published report dealing with this.
61

62. ETHYL SILICATE BONDED
INVESTMENTS
62

63. Used rarely now-a-days because
Involve time consuming procedure
Ethanol produced in liquid which is inflammable during processing.
Introduction
63
These are used for casting high fusing base metal partial denture
alloys.

64. Refractory material:Silica
Binder : The binder is a silica gel
It can be made in 2 ways
-Sodium silicate
-Ethyl silicate
Composition
64

65. 65
-pH is lowered by addition of an acid or an acid salt
-a bonding silicic acid gel is formed
-Accelerator:ammonium chloride
Sodium Silicate
Ethyl Silicate
-hydrolyzed in the presence of HCl acid,ethyl alcohol and water
-Sol is then mixed with quartz or cristobalite
-Finely powdered magnesium oxide is added.
-a coherent gel of polysilicic acid then forms,accompanied by a setting shrinkage.

66. The product formed is a colloidal solution of
silicic acid and ethyl alcohol.
Si(OC2H5)4 + 4H2O
Si(OH)4 + 4C2H5OH
66

67. 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.
Gelation
67

68. Drying
• Soft gel is dried to a temperature below 168OC.
• The gel loses alcohol and water to form a hard, concentrated gel of silica
particles tightly packed together
Green shrinkage
68

69. • This process is time consuming.
• Faster by addition of amines like piperidine to the solution of ethyl
silicate. Here hydrolysis and gelation occur simultaneously
69

70. Expansion
Thermal expansion:
• Considerably high as both refractory and binder are forms of silica.
• More refractory than PBI
• Can be heated between 1090oC to 1180oC
Properties
70

71. POROSITY
• The material is so closely packed that they are virtually porosity
free- danger of back pressure.
• Overcome by making vents
COMPRESSIVE STRENGTH
• Is around 1.5 MPa
71

72. High refractory nature.
Produce good surface finish
High thermal expansion
Very fine surface details
Advantages
72

73. Disadvantages
Limited shelf life of liquid.
Must wait for a substantial period of time, prior to using the freshly
mixed liquid.
Potential of cracking during burn out owing to high thermal
expansion.
More care must be exercised in handling and burn out, because
flammable alcohol is given off.
73

74. Effects of setting under air pressure on the number of surface pores
and irregularities of dental investment materials
• Three dental investments, 1 gypsum-bonded investment and 2 phosphate-
bonded investments, were investigated. They were vacuum mixed according
to the manufacturers’ recommendations, then poured into a ringless casting
system.
• The prepared specimens were divided into 2 groups: 1 bench setting and the
other placed in a pressure pot at 172 kPa. After 45 minutes of setting, the
rings were removed and the investments were cut at a right angle to the long
axis with a diamond disk.
Specimens set under positive pressure in a pressure chamber presented fewer
surface bubbles than specimens set under atmospheric pressure. Positive
pressure is effective and, therefore, is recommended for both gypsum-bonded
and phosphate-bonded investment material
Journal of Prosthetic Dentistry 2014
74

75. RECENT ADVANCES
75

76. INVESTMENT MATERIAL FOR TITANIUM
76
Excellent biocompatability
Good corrosion resistance.
High tensile strength.
Potential to be coated with porous surfaces that facilitates tissue
integration.
In patients who are allergic to base metal alloys.

77. A variety of investment formulations for the casting of titanium alloys
have been developed.
Many kinds of refractories such as silica (SiO2), alumina (Al2O3),
magnesia MgO) and zirconia (ZrO2)have been used
Composition
77

78. Three types of investment materials were tried:
• Sio2 based investment-80% (SiO2)
• Al2o3 based investment-80% (Al2O3)
• MgO based investment-80% (MgO)
78
• According to thermodynamic calculations,Mgo doesn’t react with
titanium.
• After reaction of investment with titanium,a contamination zone known as
alpha-α layer that forms onto the casting.

79. 79
This layer consists of 3 layers;
OXIDE LAYER
ALLOY LAYER REACTION LAYER
HARDENING LAYER made of molten titanium
The surface microhardness of titanium castings depends on the
phase composition of the reaction layer
The oxide layer may not consist of pure oxide and is a composite
of oxide and titanium namely CERMET.
CERMET(ceramic+metal)-is a composite material composed of
ceramic and metallic materials.
More ceramic content in the composite, the higher is the
hardness.

80. 80
Sio2 based investment materials produced the thickest reaction
layer(50-500 µm) consisting of Si , P,O and titanium.
Mg based investment material produce the thinnest reaction layer and
thus Mg based investment material may be the best choice.

81. Effect of different investments and mold temperatures on
titanium mechanical properties
The aim of the present study was to evaluate commercially pure titanium
(CP Ti) casting quality when a specific to titanium and a conventional
phosphate bonded investments were used under different mold
temperatures.For this, the evaluated parameters were surface roughness,
bending strength, Vickers microhardness, casting quality by radiographies
and microstructure of CP Ti.
Journal of Prosthodontics Research 56 (2012)
81

82. 82
Casting porosities found in the specimens cast using conventional
investments(CAS)and lower mold temperatures would limit their use,
even mechanical properties were similar than in specimens cast using
specific to titanium investment (REM) at temperatures recommended by
the manufacturer.
Qualitative analysis of radiographs showed that specimens which were
cast using CAS-RT presented more casting porosities while the specimens
which were cast with REM-430 did not present any casting porosity.

83. BRAZING INVESTMENTS:
• When brazing the parts of a restoration such as clasps on an R.P.D, the parts must
be surrounded with a suitable ceramic or investment material, before the
heating operation.
• ANSI/ ADA sp. No.93 for dental brazing investments defines two types of
investments:
- Type 1:- gypsum bonded dental brazing investment.
- Type 2:- phosphate bonded dental brazing investment.
83

84. Low setting and thermal expansion so that the assembled parts don’t
shift in position during the setting and heating of the investment.
Don’t have as fine a particle size as the casting investment because
the smoothness of the mass is less important.
PROPERTIES
84

85. Two types.
The first type is used for Cast Glass Technique: this investment is
provided by the manufacturers of the glass casting equipments, and is
composed of phosphate bonded refractory.
The second type of investment for making all- ceramic restoration is
the refractory die type of material, which is used for all-ceramic
veneers, inlays and crowns.
INVESTMENTS FOR ALL-CERAMIC RESTORATIONS
85

86. Refractory dies are made by pouring the investment into the impression.
When the investment is set, the die is removed and is heated to remove gases
that may be detrimental to the ceramic.
A refractory die spacer may be added to the surface.
Next, porcelain or other ceramic powders are added to the die surface and fired.
These materials must accurately reproduce the impression remaining undamaged
during the porcelain firing, and have a thermal expansion compatible with that
of ceramic.
Procedure
86

87. • Forty disk-shaped wax patterns were prepared and divided into 4 groups. A phosphate-
bonded, carbon-free investment was used for the investment procedures.
• Twenty specimens were invested using a vacuum mixer, while the remainder were
invested using a vacuum mixer and investor.
• The specimens in both broad categories were divided evenly to set in 2 different
conditions of pressure.
• Half were left to set under atmospheric pressure for 1 hour, while the rest were placed
in a compression chamber under a pressure of 3 bars for 24 minutes, then allowed to
bench set for another 36 minutes.
Within the limitations of this study, the results suggest that specimens set under
atmospheric pressure are much more likely to present surface irregularities than
specimens set under positive pressure. The use of pressure can help produce castings with
fewer surface irregularities.
The effect of different investment techniques on the surface
roughness and irregularities of gold palladium alloy castings
Journal of Prosthetic Dentistry 2008
87

88. VIDEO
88

89. DISCUSSION
89

90. Summary
90
Casting investments form an important part in the construction of indirect
permanent restorations
Based on the material to be fabricated, different types of investments are
used
Gypsum bonded are the conventional material used
Phosphate bonded-most commonly used nowadays

91. 1. Anusavice: “Phillips Science of dental materials”; 11th edition. St.Louis,
Elsevier, 2010.
2. Anusavice K J, Shen, Rawls, Philip’s science of dental materials, 12th
edition,Elsevier, 2013.
3. William J O’Brien, Dental materials and their selection, 4th edition,
Quintessence
4. John. M.Powers, Ronald L, Sakaguchi: Craig’s restorative dental
materials ; 12th edition, Elsevier, 2007
91
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93. 93
Kenzo , Ji-Young Bae,Porosity of dental gypsum-bonded investments in setting and
heating process,.Dental Materials Journal 2012; 31(1): 120–124
Abhayjit Bedi,The effect of different investment techniques on the surface roughness
and irregularities of gold palladium alloy castings.J Prosthet Dent 2008;99:282-286
Anelise R. Ferreira ,Evaluation of the thermal shrinkage of titanium and the setting
and thermal expansion of phosphate-bonded investments.J Prosthet Dent
2007;98:24-29
W H Luk,Effect of burnout temperatures on strength of phosphate-bonded
investments .Journal of Dentistry, Vol. 25,423-430
Ana Paula Macedo ,Effect of different investments and mold temperatures on
titanium mechanical properties .Journal of Prosthodontic Research 56 (2012)
JOURNAL REFERENCES

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Erica F. morey, Richard Earnshaw.The effect of potential investment expansion and hot
strength on the fit of full-crown castings made with gypsum- bonded investment. Dent
Mater 1995;11(5-6): 317-321.
D. Low, T. Mori,”Titanium full crown casting: thermal expansion of investments and
crown accuracy”. Dent Mater 1999;15:185–190
Chun-Cheng Hung, Guey-Lin Hou, Chi-Cheng Tsai. “Pure titanium casting into
zirconia-modified magnesia-based investment molds”. Dent Mater 2004;20:
846–851
. Edme Lodovici, Josete Barbosa Cruz Meira. “Expansion of high flow mixtures
of gypsum-bonded investments in contact with absorbent liners”. Dent Mater
2005; 21:573–579.

95. 95