dental casting alloys

1. BASE METALALLOYS

2. • General requirements of dental alloy
• Base metal alloys-Composition
• Physical Properties
Melting temperature
Density

3. • Mechanical Properties
Yield Strength
Tensile Strength
Elongation
Elastic modulus
Hardness
Fatigue
• Function of alloying elements
• Heat Treatment

4. • Cast Cobalt Chromium Alloys
• Cast Nickel Chromium Alloys
• Cast Titanium and Titanium Alloys
• Wrought Stainless Steel

5. • Wrought Cobalt- Chromium -Nickel
Alloys
• Wrought Nickel -Titanium Alloys
• Wrought Beta- Titanium Alloys
• Metallic Denture Base Alloys
• Etching of base metal alloys
• References

6. DENTALAPPLICATIONS
1.
( Vitalium &Nobilium).
Partial Denture Framework
Porcelain Metal Restorations
2.
(Ticonium).
Partial Denture Framework
Crowns & Bridges
Porcelain Metal Restorations.

7. 4.
Implants, Crowns, Bridges
Endodontic Instruments , Orthodontic Brackets
Preformed Crowns
3.
Crowns, Bridges, Partial Dentures, Implants.

8. 7.
Orthodontic Wires
Endodontic Files
Orthodontic Wires
Orthodontic Wires
Endodontic Files

9. •Should Not Produce Toxicological Or Allergic EffectS
•Provide Resistance To Corrosion And Physical
Changes When In Oral Fluids
•Thermal Conductivity ,Melting Temperatures,
Coefficient Of Thermal Expansion Should Be
Satisfactory.

10. •Use Should Be Feasible.
•Metals ,Alloys And Companion
Materials Should Be Abundant,
inexpensive And Readily Available.

11. PHYSICAL PROPERTIES
1.Melting Temperature – most of the base
metal alloys have at 1150-15000 c
•Though One Commonly Used Nickel
Chromium Alloy [Ticonium] Melts At
12750 C.
•Addition Of 1-2% Beryllium Lowers
Melting Temperature Of Ticonium By
About 100 0c.

12. 2. The Average Density Of Cast Base
Metal Alloys Is Between 7-8gms /Cm3
which is half the density of most dental
gold alloys.

13. MECHANICAL PROPERTIES
•Yield Strength:
•Gives an indication of when a permanent deformation of
a part such as clasp will occur.
•Base metal dental alloys have greater than 600Mpa to
Withstand Permanent Deformation When Used As Partial
Denture.
•Tensile Strength: Greater Than 800 Mpa
•Elongation: Indication Of Relative Brittleness And
Ductility.
The combined effect of elongation and tensile
strength is an indication of toughness of material.

14. • Increasing the nickel content with a
corresponding reduction in cobalt generally
increases the ductility and elongation.
• High values of elongation are obtained by
casting at the normal melting temperature .
• High elongation is achieved without sacrificing
strength and is the result of the precise and proper
combination of carbon, nitrogen, silicon,
manganese, and molybdenum content

15. •Elastic Modulus
• Higher Elastic Modulus ,More Rigid The
Structure.
• Elastic Modulus Of Base Metal Alloys Is
Approx Double The Modulus Of type IV
Cast Dental Gold Alloys

16. – ONE THIRD greater than gold alloys
Difference In Composition Of Cast Base Metal
Alloys Have Some Effect On Hardness.
Hardness Is An Indication- Finishing The
Structure & Its Resistance To ScratchingWhen
In Service.
Higher The Hardness ,Requires The Use Of
Special Polishing Equipment.

17. •Fatigue
Fatigue Resistance Of Alloys Is Important
When It Is Considered That These Alloys Are
Removed And Placed Daily .
Comparisons Of Cobalt ,Chromium, Titanium
And Gold Alloys Show That Cobalt
Chromium Alloys Possess Superior Fatigue
Resistance Indicated By Higher Number Of
Cycles Required To Fracture A Clasp.

18. • Any procedures that result in
increasing the porosity or carbide
content of the alloy will reduce
fatigue resistance.
• Also, soldered joints which often
contain inclusions or pores,
represent weak links in the fatigue
resistance of the prosthesis.

19. •Passivation
Elements In Some Base Metal Alloys Have
High Affinity For Oxygen,but The Oxide Film
Formed Can Serve A Protective Layer Against
Oxidation And Corrosion.
This Formation Of Protective Film By A
Reactive Substance Is Called Passsivation
Three Metals Are Known For Their Passivation
Potential.

20. •Aluminium
•Chromium
•Titanium
•The Most Corrosion Resistant
• Of These Titanium

21. FUNCTION OF ALLOYING ELEMENTS
Has A Passivating Effect
30% Of Chromium -Upper Limit For Attaining Maximum
Mechanical Properties. if the Cr content exceeds 30%, the
, which is undesirable from the viewpoint
of hot workability.
•Chromium- Content Is Directly Proportional
To Tarnish And Corrosion Resistance.
- Increases The Strength And Hardness Of
Alloys
- Decreases Strength And Hardness

22. -increases The Hardness Of Alloys
Carbon Content Increased By 0. 2% -Alloy
Becomes Too Hard And Brittle
If Decreased By 0.2% -Reduces The Yield And
Tensile Strength.
3-6% Increases The Strength.
- in Ni containing compd forms a
Compound of Nickel and Aluminium(Ni3Al).
1-2% Lowers The Fusion Range By 1000 C
Increases The Fluidity And
Castability.

23. HEAT TREATMENT OF BASE METAL ALLOYS
•Reduces The Yield Strength And Elongation.
•Soldering Or Welding Must Be Performed At
The Lowest Possible Temperature with
shortest possible time of heating .
•Heat Treatment Of These Alloys At 10000 C Upto 1
Hour Did Not Change Their Mechanical
Properties.

24. COBALT CHROMIUM ALLOYS
• Edward Haynes Introduced Cr- Co Alloys
With Some Ni to the Automobile Industry
During Early 1900’s They Are Called
Haynes Stellites or Stellite Alloys Because
of Their Bright Shiny Starlike Appearance

25. COBALT-CHROMIUM AND NICKEL
CHROMIUM CASTING ALLOYS
•According To ADA Specifications No:14, The
Weight Of Chromium Should Be No Less
Than 20% And The Total Weight Of
Chromium, Cobalt And Nickel Should Be No
Less Than 85%.

26. COMPOSITION
- Cobalt, Chromium,
And Nickel (82%-92%)
•Minor Alloying Elements- Carbon,
Molybdenum ,beryllium ,tungsten And
Aluminum.

27. .

29. Upto 0.2 %,Is Most Critical .
•Small Amounts may Have Pronounced Effect
on Strength ,Hardness and Ductility.
Carbon Forms Carbides With Metallic
Constituents Which Is an Important Factor in
Strengthening the Alloy.
Excess Carbon Increases the Brittleness

31. PROPERTIES
• Density Is Half That of Gold Alloys,so They
Are Lighter in Weight (8-9 Gm/cm3)
• Elongation Depends on Composition,rate of
Cooling,fusion and Mould Temperature
Employed. Ductility is lower than that of
gold alloys. They may break if bent too many
times

32. • Modulus of Elasticity-They Are Twice As Stiff
As Gold Alloys . Thus Castings Are Made
Thinner ,Thereby Decreasing the Weight of
the R.P.D
• Hardness - These Alloys Are 50% Harder Than
Gold Alloys .Thus Cutting ,Grinding ,
finishing Is Difficult.

33. • Tarnish and Corrosion Resistance-
• Formation of Chromium Oxide Layer
on the Surface Prevents Tarnish and
Corrosion.
• Yield Strength- Is Indication of Amount
of Stress Is Necessary to Cause
Permanent Deformation . Higher
Than That of Gold Alloys 710 Mpa.

34. APPLICATIONS
• Denture Base
• Cast Removable Partial Denture
Framework
• Crowns And Bridges
• Bar Connectors

35. • Cobalt Chromium Alloys Are Ideal Materials for
Major Connectors , they Are Rigid and Strong in
Thin Section and Allows a Wide Variation in
Major Connectors.
• They Can Be Finished to High Polish.
• They Have Excellent Life Span.
• They Are Rather Difficult to Adjust at Chair Side

36. NICKEL - CHROMIUM ALLOYS
• Composition
• Nickel 61-81%
• Chromium 11-27%
• Molybdenum 2-9%
• Minor additions Beryllium,Aluminum, Iron,
Silicon, Copper, Manganese, Cobalt and
Tin.

37. PROPERTIES
• Cost- Cheapest of all casting alloys
• Density- ranges from 7.8-8.4gm/cm3 .
They have half the density of gold
alloys making them lighter.
• Castability-extremely technique sensitive

38. • Hardness and workability- ranges from
175-360 VKN.
These alloys are extremely difficult to work
with.
Their high hardness makes them very
difficult to cut,grind and polish

39. • Modulus of elasticity- Ranges From 150-210 Mpa.
Property Denotes Stiffness of Metal , Twice As
Stiff As Gold Alloys.
Practically Thinner, Lighter Castings Can Be
Made where other metals fail because of
flexing.

40. • Percent elongation- Ranges From 10- 28%
Gives Indication of Ductility of Alloys
Though They Are Ductile They Are Not
Easily Burnishable
• Tarnish and Corrosion Resistance-They Are
Highly Resistant to Tarnish and
Corrosion Resistance

41. This Is Due to a Property Called Passivation
PASSIVATION Is the Property by Which a Resistant
Oxide Layer Forms on the Surface of Chrome
Containing Alloys.
This Oxide Layer Protects the Alloys From
Oxidation
These Alloys Maintain Their Polish for Years.
Other Self Passivating Alloys Are Titanium and
Aluminum

42. • SOLDERING- Is Necessary to Join Bridge
Parts Long Span Bridges Are Often Cast
in 2 Parts to Improve Fit and
Accuracy
Base Metal Alloys Are Much More
Difficult to Solder

43. BIOLOGICAL CONSIDERATIONS
•Those Alloys That Contain Beryllium, Contain
1.6% -2% Of The Element.
Precaution Should Be Taken To Avoid
Exposure To Metallic Vapor ,Dust Or
Grindings Containing Beryllium
And Nickel.
•The Nickel Chromium Alloys Can Be Divided Into
Those Containing And Those Not Containing
Beryllium.

44. • Nickel May Produce Allergic Reactions in Some
Individuals.
• Incidence of Nickel Sensitivity Reported to Be 5-10
Times More in Females Than Males,with 5-8%
of Females Showing Sensitivity.
• It Is Also a Potential Carcinogen .Inhalation of
Beryllium Containing Dust,or Fumes Is the Main
Route.It Causes a Condition Called Beryllosis,
Characterized by Flu Like Symptoms, and
Granulomas of Lungs.

45. •Physiological Response May Range From Contact
Dermatitis To Severe Chemical Pneumonits.
•Safety Standard for Beryllium Dust Is 2 Ug/m3 of Air
in a Time Waited 8 Hour Day.
•Nickel Is Another Known Allergen.
•Safety Standard for Nickel Is 15 Ug/m3 of Air for a
40 Hour Week.
•To Minimize Exposure To Metallic Dust Containing
Nickel Or Beryllium Intraoral Finishing Should
Be Done With A High Speed Evacuation System.

46. • Titanium Was First Discovered in 1791by
Wilheim Gregor ,A Clergyman, Who
Found the Metal in Black Magnetic
Sand,in Cornwall,England and Was
Named As Titanium by Klaproth in 1794
After the Greek Mythological First Sons of
Earth- the Titans

47. Titanium Can Exist in Two Crystal Form
• Alpha Phase
• Beta Phase
• The Alpha Phase Has a Hexagonal Close Pack
Structure.The Alpha Phase Is Stable at All
Temperatures Upto 8820 C Which Is Beta
Transus Temperature .
• At This Temperature ,the Alpha Phase Gets
Transformed to Beta Phase

48. • The Beta Phase Is Stable From 8820C to
Melting Point of Titanium at 16700C
• This Phenomenon Can Be Used to Produce
Alloys Which at Room Temperature Can
Have Alpha, Beta or Alpha-beta
Structure,and Therefore Different
Mechanical and Chemical Properties.

49. • Pure Titanium Has Alpha Crystalline
Structure,hence It Is Mostly Used in
Chemical Industry,where the Excellent
Corrosion Resistance Is More Vital Than
Good Mechanical Qualities.
• The Need for Mechanical Qualities Are
More in Orthopedic Implants,dental
Prosthesis and Implants.

50. • In These Situations ,Titanium Is Combined With
Vanadium and Aluminium to Obtain the Most
Commercially Known Alloys,Ti 6 Al 4 V Which
Is Two Phase (Alpha +Beta) Alloy.
• The Addition of Alloying Elements Extend the
Stability Field of Different Phases .
• The Stability of Alpha Phase Can Be Extended by
Aluminium,carbon,oxygen and Nitrogen.

51. •The Alloying Elements Stabilizing the Beta Phase
Includes:Hydrogen,, Manganese, Chromium,
Molybdenum, Iron and Vanadium
•The Presence of Even Small Amounts of Interstitial
Elements Alter the Mechanical Properties,e.g.
Very Low Hydrogen Conc.(0.15%) Can Produce
Great Brittleness
•Small Quantities of Carbon, Nitrogen and Oxygen
Can Raise the Strength of Titanium and
Decrease Its Ductility.

52. COMMERCIALLY PURE TITANIUM
• Available In Four Grades According to Purity.
• According to American Society of Testing and
Material 67/89 Standard Specification,as
the Grades Increase From 1to 4 ,the Amount
of Contaminating Oxygen, Iron and Nitrogen
Increases.

53. TITANIUM PROCESSING
• Titanium Casting Is Highly Technique Sensitive Due
to Its Tendency to Interact With Atmospheric
Components
• The Intrinsic Properties of Titanium Make It a
Difficult Metal to Melt and Cast.
• A Heat Source Powerful Enough to Melt Titanium Is
Required
• The Molten Metal Should Be Isolated From Air and
the Crucible Should Not React With Molten
Titanium.

54. CASTING MACHINES
• In All These Machines ,the Main Characteristic
Feature ,Is That the Melting Occurs Inside an
Inert Gas Atmosphere Such As Argon Gas, So
That the Molten Titanium Does Not Absorb
Oxygen and Nitrogen Form Air.
• The Electric Arc or High Frequency Induction Is
Used to Reach the High Melting Point of
Titanium.

55. • A Centrifugal Method Is Used to Drive the Molten
Metal Into the Mold Cylinder.
• Copper Ceramic or Carbon Based Crucibles Have
Been Used to Contain the Molten Metal
• In the Casting System,by Gas Pressure,the
Equipment Consists of 2 Chambers ,an Upper
Melting Chamber,housing a Copper Crucible
and a Tungsten Electrode

56. • Lower Casting Chamber Connected to the First
One by a Mold Cylinder.
• Necessary Melting Power Is Generated by a
Electric Arc.
• After Placing the Titanium it is Melted Over the
Crucible.
• The Air in Both the Chambers Is Drained off by
Means of a Vacuum and Argon Gas Is Introduced in
the Melting Chamber.

57. • The Argon Gas Pressure Is Adjusted and Then The
Arc Generated Between the Titanium Load and
Tungsten Electrodes Heats Causing Titanium to
Melt.
• A Considerable Amount of Thermal Energy Is Kept
at the Center of Titanium Load for 60 Sec to
Compensate for Low Thermal Conductivity of
Titanium.

58. ALTERNATIVES TO CASTINGS
• Plasticization of Metallic Surface With a Thin Film of
Titanium,niobium and Ceramic.
• Second Option Is Forming of Superplastic.
• Third Option Is Titanium Processing by Milling and Spark
Erosion

59. •Density Is 4.5 G/cm3. Light weight metal
•Modulus Is 100 Gpa.,half the value of other BMA
PROPERTIES
•Melting point Is Quite High 16680C. Therefore
Special Equipment Is Required for Casting
Titanium.

60. • Tarnish and Corrosion Resistance- Has
Ability to Self Passivate
• Biocompatibility- Is Non Toxic and Has
Excellent Biocompatibility With Both
Hard and Soft Tissues.

61. OTHER APPLICATIONS OF CAST BASE
METALALLOYS
•In Surgical Repair Of Bone Fracture .
•Metallic Obturators And Implants.
•Cobalt Chromium Alloys Have Been Implanted
Directly Into Bone Structure For Long Periods
With Favorable Response Of The Tissue,
Probably Due To Low Solubility And Electro-
Galvanic Action Of The Alloy. The Product
Known As Surgical Vitalliun Is Used
Extensively For This Purpose .

62. WROUGHT BASE METALALLOYS
•Stainless Steel
•Cobalt Chromium Nickel
•Nickel -Titanium
•Beta- Titanium

63. STAINLESS STEEL
• This was first discovered by Brearely of
Sheffield, England in 1913.
• Stainless steel is an alloy of steel containing
minimum of 13% chromium.
• It is chromium which makes the steel
resistant to tarnish and corrosion.

64. FERRITIC (Alpha Form)
• Solid iron in which carbon is insoluble,because
of small space in between atoms.
• It has a Body centered cubic structure
• This condition remains from room
temperature to 9120C.

65. AUSTENITE(Gamma Form)
• Exists at Temperature Between 912-
1394 0C
As Face Centered Cubic Structure in
Which Carbon Is Soluble, Because
the Space Between the Atoms Is Larger
and So the Carbon Atoms Occupy
These Spaces to Form Interstitial Solid
Solution.

66. MARTENSITE
• If Such a Austenitic Steel at a Temperature
Above 9120 C Is Suddenly Cooled , It
Undergoes Transformation in Its
Structure to Form a Body Centered
Tetragonal Structure Called
Martensite.
• This Change Makes the Metal Hard,strong
but Brittle.

67. TEMPERING
• Such Hard Steel Can Be Heated To200-450 0 C
for Short Period and Cooled Rapidly to
Adjust the Precise Hardness and Strength
Required to Reduce Brittleness .
• This Process Is Known As Tempering

68. THUS ,THERE ARE THREE FORMS OF STAINLESS
STEEL
• Ferritic-Have BCC Space Structure.
• Austenitic- Have FCC Space Structure.
• Martensitic- Have Distorted BCC Tetragonal
Space Lattice Structure.
• 18-8 Stainless Steel Is a Special and Famous
Type of Austenitic ,and Called So Because It
Contains 18%chromium &Nickel

69. Sensitization
• It is the loss of corrosion resistance of 18-8
stainless steel due to removal of chromium
from it
• This happens when it is heated to temp
between 400- 9000 C, during soldering or
welding
• Therefore this condition is also called WELD
DECAY

70. Stabilization - Method To Minimize Sensitization.
Stabilizing Element - Titanium
MECHANICAL PROPERTIES:
•Tensile Strength-2100 Mpa
•Yield Strength - 1400 Mpa
•Hardness - 600 KHN

71. USES OF 18-8 STAINLESS STEEL
• In Prosthetics
For Partial Denture Clasps ,Bars
For Swaged Plates,implants.
• In Orthodontics
For Wires, Ribbons, Bands, Bows, Hooks,
Springs.

72. ADVANTAGES OF 18-8 STAINLESS STEEL
• Heat and Corrosion Resistance.
• More Ductile and Can Be Cold Worked.
• Can Be Easily Welded.
• Hardened by Cold Working.
• Can Be Stabilized Against Corrosion.

73. NICKEL- TITANIUM ALLOYS (NITINOL)
COMPOSITION:
Ni-54%,
Ti-44%,
Co-2%
•was introduced in 1972
•characterized by high
resiliency,limited
formability,thermal memory

74. Properties
• Shape Memory effect- it is the ability of the
alloy to retain and memorize a particular
shape given to it
• Mechanism of shape memory
• Structure of nitinol at room temperature is
BCC(austentic phase) when this is heated it
changes to HCP(martensitic phase)
• This change is responsible for shape memory
effect.

75. Superelasticity
• It is a large plastic deformation induced in a
alloy which generates constant stress when
the material undergoes transformational
change
• Mechanism-BCC changes to HCP due to
increase in stress.this gives the property of
superelasticity

76. WROUGHT Co-Cr- Ni ALLOYS (ELGILOY)
COMPOSITION:
CO-40% Mn-2%
Cr-20% C-0.15%
NI-15% Be-0.04%
Mo-7% Fe-15.8%
PHYSICAL PROPERTIES:
•Excellent Tarnish And Corrosion Resistance.

77. WROUGHT BETA -TITANIUM ALLOY
COMPOSITION: :
Ti-78%
Mo-11.55%
Zr-6%
Sn-4.5%
PROPERTIES: :
•Lower Elastic Modulus
•Lower Yield Strength
•Good Ductility
•Good Weldability

78. METALLIC DENTURE BASE MATERIALS
• Used In Clinical Situations Where a Single
Maxillary CD Opposes a Partial Component
of Natural Mandibular Teeth.
• Heavy Masticatory Load Directed in to a Thin
Palatal Resin Plate Which May Result
in Denture Fracture.

79. TECHNIQUE
• Relatively Thin Metal Base Is Cast to Contact
Denture Bearing Surface.
• Acrylic Resin Is Used to Retain the Denture Teeth
and Provide Buccal and Labial Flanges That
Enhances Esthetic Quality
• The Processed Resin Is Attached to Cast Metal
Base by a Retentive Meshwork.

80. • MATERIALS used
Cobalt chromium alloys
Nickel chromium alloys
Titanium alloys
• Cobalt and nickel containing alloys could be
potential allergens ,biological risks of metal
ions being released suggests use of titanium.

81. ADVANTAGES
• High Thermal Conductivity
• Decreased Bulk Across Palate
• Dimensional Stability,increased Fit
• Superior Bio-compatibility,in Case of Ti
• Stronger Denture Bases
• Does Not Break Easily ,Strength Is Many Times
More,hence Can Be Made Thinner.

82. DISADVANTAGES
• Greater Technical Costs,expensive
• Difficulty in Relining and Rebasing
• Increased Weight
• Repair Is Difficult
• Color Is Unaesthetic

83. ETCHING OF BASE METAL ALLOYS
• When First Introduced ,Micromechanical
Retention of Etched Metal Resin Retainers
Was Obtained by Electrolytically Etching the
Base Metal Alloys
• More Recently Chemical Etchants Have Been
Marketed
• Technique-the Surfaces of the Restoration That
Are to Be Bonded to Etched Enamel Are
Treated With Acid Gels or Liquids for
Short Periods of Time

84. REFERENCES:
•Craig R.G., Restorative Dental Materials,
11th Edition, 2002, India.
•Anusavice, Science of Dental Materials, 10th
Edition, 1998, India
•Micheal McCcracken: Dental implant
Materials: commercially pure titanium
and titanium alloys,Jprosthod
1999;8:40-43

85. THANK YOU

88. INVESTMENT MATERIALS
Presented by:
Dr.Atul Bhandari

89. TOPICS
1. INTRODUCTION
2. DEFINITIONS
3. HISTORICAL BACKGROUND
4. IDEAL REQUIREMENTS
5. COMPOSITION OF INVESTMENT MATERIALS
6. TYPES OF INVESTMENT MATERIALS
7. RECENT ADVANCES
a)brazing investment
b)investment materials for titanium
c)all ceramic investments

90. Prepration of crown,bridge or other fixed prosthesis
Impression making and pouring of cast
Making of waxpattern
Attachment of sprue
Investing (investment materials)
Burnout
Flow of molten metal

91. INVESTMENT MATERIALS
DEFINITION
1. Investment material(craig): It can be
described as a ceramic material that is
suitable for forming a mold into which
a metal or alloy is cast.
2. Investing(craig): The operation of
forming the mold is described as
investing.
.

92. 3.Investing(GPT-8) The process of covering or
enveloping, wholly or in parts; an object such as a
denture, tooth, wax form, crown etc. with a suitable
investment material before processing, soldering or
casting
4.Investment(dentalcastinginvestment)(GPT-8):
Material consisting principally of an allotrope of
silica and a bonding agent. The bonding substance
may be gypsum (for use in lower casting
temperature) or phosphates and silica (for use in
higher casting temperature).

93. 5. Refractory:(GPT-8) Difficult to fuse or corrode,
capable of enduring high temperature
without significant degradation.
6. Refractory investment (GPT-8): An investment
material that can withstand high
temperature used in soldering or casting

94. HISTORY
• In ancient Egypt, Persia, or China, conceived the idea
of making a wax replica of the item to be cast,
surrounding this replica with a ceramic material
allowing the material to harden into a solid mass, and
then making and burning out the wax to provide a
mould having an intricate and accurate cavity.
• After preparation of the mould, the metal melted and
poured in to the cavity.

95. • The hoax of golden tooth started in 16th century
AD but Theophelus in 11th century described
metalworking and devotes considerable space to the
work of goldsmiths. The casting practice was so
clearly described by Theophelus that it is possible to
follow it in practice as well as in principle.
• Well beaten clay was used to cover the wax
carefully so that all the details of the wax were filled.
Afterwards, these moulds were placed near warm
coals, so that when the moulds become warm, it was
possible to pour out the wax.

96. •After the clay mould was baked and
still hot, metal was poured in through
the funnel. When the mould and
casting became cold, the clay mould
was removed and a replica of the wax
model remained.
•In 1907, W.H. Taggart
introduced the lost wax
technique that is now a
common practice in
dentistry.

97. • Dr. J.G. Jane of Pennsylvania Dental School became
convinced that casting made by the Taggart method
was definitely undersized and conceived the idea of
casting in to an enlarged mould.
• He was the first one to attempt the use of a
compensated mould

98. • In 1909, he described a method, which consisted of
using an investment containing very high percentage of
silica and plaster of Paris 25%.
• He believed this investment could give a high thermal
expansion.
• In his paper, he tells of casting in to a mould heated to
cherry red (approximately 1200 F).
• The thermal expansion of the silica would thus
increases the dimension of the mould and theoretically
it may compensate for the shrinkage of gold.

99. • Dr. Carl. H. Shair (Ohio 1932) in studying the
physical properties of gypsum products,
found most of them showed a greatly
increased setting expansion when allowed
to set while immersed in or in contact with
free water.
• Apathy named this phenomenon as
hygroscopic expansion.

100. IDEAL REQUIREMENTS
• Easily manipulated.
• Sufficient strength at room temperature.
• Stability at higher temperature.
• Sufficient expansion.
• Beneficial casting temperature.
• Porous
• Smoother surface.
• Inexpensive.
• Ease of divestment.

101. Investment contains 3 distinct materials:
1. Refractory material : it’s usually a form of silicon dioxide, such as
1) Quartz,
2) Tridymite or Cristobalite.
MECHANISM
when the refractory is heated, it undergoes a change in crystalline form.
α-cristobalite ↔ β-cristobalite (high temperature)
α-quartz ↔ β-quartz
This change is accompanied by volumetric expansion.
COMPOSITION
• Refractory is responsible for thermal expansion of the investment.
• To provide resistance to deformation at elevated temperatures.
• Total amount of refractory in the investment is 55-75%.

102. 2. BINDER MATERIALS:
Common binder that forms a coherent solid mass
is:
• α-calcium sulfate hemi-hydrate
• Phosphate
• Ethyl silicate High temperature casting
Investment.

103. 3. Other chemicals/ chemical modifiers
• To regulate the investment regarding:
Setting time
Setting expansion
For eg. Boric acid helps in eliminating the contraction around the binder;
also helps in strengthening the investment.
• Small amounts of Na and K fluoride also help to control the
contraction around the gypsum binder.
• Graphite particles- added to prevent oxidation of gold casting by
creating a reducing atmosphere in the heated mold chamber. Pure
copper is also used for the same purpose.

104. • TYPES OF INVESTMENT MATERIALS(BREIN CLASSIFICATION)
GYPSUM BONDED HIGH TEMPERATURE
PHOSPHATE
BONDED
SILICA
BONDEDINLAY DENTURE

105. GYPSUM BONDED INVESTMENTS
COMPOSITION
2.Binder:gypsum (alpha hemi hydrate)
1. Refractory material: silica (SiO2)
.
Modifier : boric acid
sodium chloride
sometimes balancing agents
also to control the setting time
and setting expansion

106. GYPSUM BONDED INVESTMENT
THREE TYPES USES COMPENSATION FOR
SHRINKAGE
1.TYPE-l Principally thermal
expansion
2.TYPE-II Employed for casting
Inlays and crowns
Major mode of
Compensation is
Hygroscopic exp.
3.TYPE-III
Employed for casting
inlays and onlays.
Used for construction of
Partial dentures.

107. • 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 .
Properties of gypsum bonded investment

108. • SETTING EXPANSION
After mixing with water and subsequent heating in furnace
The investment undergoes series of expansion
Normal setting
expansion
Hygroscopic setting
expansion
Thermal
expansion

109. NORMAL SETTING EXPANSION
• Investment + water
Volumetric expansion
Occurs due to direct conversion of CaSo4 hemihydrate to dihydrate
form
POSSIBLE EXPLANATION:
Silica particles probably interferes with the intermeshing and
interlocking of the crystals as they form; thus the thrust of the crystal
is outward during growth and they increase expansion.
According to ADA specification no.2 total amount of setting
expansion is 0.6%.

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

112. FACTORS AFFECTINg hygroscopic
EXPANSION
1. Effect of composition:
a) Hygroscopic expansion α silica content of the
investment
Finer the particle size greater is the
hygroscopic exp.
2. Effect of W:P ratio:
↑ed water powder ratio will ↓ed the
hygroscopic
Exp.

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

114. 5. Effect of time of immersion:
Increased amount of hygroscopic expansion
takes place if the investment immersed before
the initial set.
6. Effect of confinement:•Confinement effect is produced by both the walls of the
container in which the investment is placed and the walls
of the wax pattern.
•Confining effect is more pronounced on hygroscopic exp-
sion as compared to normal setting expansion

115. • 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 MAXI-
-MUM EXPANSION
OCCURS.
The phenomena is purely physical. The water is drawn between
the particles by capillary action and thus causes the particles to
separate, creating an expansion.

116. • TERM HYGROSCOPIC IS A MISNOMER
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°c
To counterbalance that contraction quartz content
Is increased to 75%

117. 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%

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

119. EFFECT OF CHEMICAL MODIFIERS
• Small amounts of sodium, potassium or
lithium chlorides
1.Eliminates contraction caused by gypsum.
2.Increases expansion without the presence
of an excessive amount of silica.
•Boric acid also hardens the set investment. However,
It apparently disintegrates during heating and rough
surface cast may result.
•Chlorides actually reduces gypsum shrinkage below 700°C

120. 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

121. • FINENESS
fineness may affect the setting time, surface
roughness
of the casting.
finer silica may results in higher hygroscopic
expansion
than a coarser silica.

122. • POROSITY:
during casting process
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.
•Common method of venting is through pores of the investment .
•More the gypsum crystals present in the set investment, less is the
porosity.

123. • Particle size of investment:
More uniform the particle size, greater is the porosity.
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.

124. GYPSUM BONDED INVESTMENT
MANIPULATION:
• Mixing is similar to dental stone
• Use of correct W:P ratio is important to ensure
correct strength, setting time and expansion.

125. Before investing a wax pattern, it should
be washed with a non-foam detergent to
remove any oil or grease and to facilitate
wetting of the pattern by the investment
mix.

126. a)Facilitate mold expansion as
rigid casting ring will not
allow this.
b)Contributes hygroscopic
expansion
Casting ring is lined by
asbestos or cellulose ring
liner that helps:

127. Coat the entire pattern with investment, pushing
the material ahead of the brush from a single
point. Gently vibrate through out the application
of investment, being especially careful to coat
the internal surface and the margin of the
pattern.

128. A finger positioned under the
Crucible former on the table of the
vibrator
minimizes the risk of excessive
vibration and possible breaking of
the pattern from the sprue.

129. • After the pattern has
been completely
coated, the ring is
immediately filled by
vibrating the remaining
investment out of the
bowl.

130. • When the investment reaches the level of the
pattern, tilt the ring several times to cover and
uncover the pattern, thereby minimizing the possible
entrapment of air. Investing must be performed
quickly within the working time of the investment. If
the investment begins to set too soon, rinse it off
quickly with cold water.

131. • After the ring is filled to the rim, allow the
investment to set.
• If the hygroscopic technique is used, the ring is
placed in a 37C (100F) water bath for 1 hour

132. VACUUM TECHNIQUE (ROSENSTAIL)
• First, hand spatulate the mix
• With the crucible former and pattern in place
attach the ring to the mixing bowl
• Attach the vacuum hose and mix according to the
manufacturer’s recommendations
• Invert the bowl and fill the ring under vibration
• Remove the vacuum hose before shutting of the
mixer
• Remove the filled ring and crucible former from
the bowl
• Immediately clean the bowl and mixing blade
under running water.

135. • Mold is heated through 150-200°C:
this dries off the excess water and burns off
the wax. The mold is then slowly heated
above the temperature of inversion, usually
700°C, and held at this temperature for 30
min, for complete burn out.

137. LIMITATIONS OF GYPSUM BONDED INVESTMENT• GBI (Gypsum bonded investment) decomposes above
1200 C by interaction of silica with calcium sulphate to
liberate sulpher 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 celcius

138. PHOSPHATE BONDED INVESTMENTS
POWDER:
REFRACTORY MATERIALS:
Silica in the form of cristobalite, quartz or
mixture of both, in concentration of
approx. 80%
BINDER:
•A chemical reaction between MgO and
a phosphate provides the binder system
•Excess, un-reacted ammonium hydrogen
phosphate is available to react with silica
and other excess metal oxide ions, to
form complex silico-phosphates that
provides fired strength.
Modifiers
•Carbon

139. Liquid:
Water or special liquid:
• special liquid, which is a form of silica
solution in water.
• freeze stable products are also available as
colloidal silica liquid suspension.

140. SETTING AND THERMAL EXPANSION
Setting and thermal expansion is more while
using silica sol as liquid, as compared to
water.

141. WORKING AND SETTING TIME
• Unlike gypsum investments, phosphate investments are markedly affected
by temperature.
• Warmer the mix, the faster it sets.
• Increased mixing time and mixing efficiency result in a faster set and greater
rise in temperature.
• An increase in water powder ratio will increase the working time.

142. ADVANTAGES OF PHOSPHATE BONDED
INVESTMENTS:
• Rapid setting rate
• Useful for lower burn out temperature, because much of the expansion is
achieved as a result of setting reaction, rather than temperature increase.
• High green strength
• High fired strength, which results in less mold cracking and fewer fins on
casting.
DISADVANTAGES:
• Investment powder will react with moisture, imposing limitations on the
shelf life of open container.
• High tendency for reaction with non precious alloys, producing oxides that
are difficult to remove from the castings.
• Lower permeability, which yields a tendency to produce short castings via
gas entrapment.

143. ETHYL SILICATE INVESETMENTS
Available as powder liquid system.
• In this investment, the binder is a silica gel
that results to silica(cristobalite) on heating.
• Various methods to produce silica or silicic
acid gel are:
1.when the ph of sodium silicate is lowered by the addition of acid
or an acid salt, a bonding silicic acid gel forms.
2. An aqueous solution of colloidal silica can also be converted to a
gel by the addition of an accelerator such as ammonium chloride.
Powder
- refractory particles of silica.
- MgO
Liquid
-supplied in three
component system, two
component system or as
one pre-mixed liquid

144. • Another system for binder formation is based on ethyl silicate.
- a colloidal silicic acid is first formed by hydrolysing ethyl silicate in
the presence of HCl, ethyl alcohol and water.
Si(OC2H5)4 + 4H2O Si(OH)4 + 4C2H5OH
- because a polymerized form of ethyl silicate is actually used, a
colloidal sol of poly silicic acid forms instead of simpler silicic acid.
- the sol is then mixed with quartz or cristobalite to which a small
amount of finely powdered MgO is added to make the mixture
alkaline.
- a coherent gel of polysilicic acid then forms, accompanied by a
setting shrinkage.
- this soft gel is dried at a temperature< 168°C.
- during drying process, the gel loses alcohol and water, which
causes a volumetric contraction( reducing the size of the mold);
this is called green shrinkage.

145. - this gelation process is slow and time consuming.
ALTERNATIVE METHOD:
- certain types of amines (piperadine) can be added to the solution of ethyl
silicate, so that hydrolysis and gelation occur simultaneously.

146. • ADVANTAGES:
PRIMARY ADVANTAGE:
1. High refractory nature.
2. Small dimensional changes on setting.
3. High degree of thermal expansion can be attained.
ADDITIONAL BENEFITS:
1. High permeability.
2. Very fine surface details can be achieved.
DISADVANTAGES:
1. Limited shelf life of liquid.
2. Must wait for a substantial period of time, prior to using the freshly mixed liquid.
3. Potential of cracking during burn out owing to high thermal expansion.
4. More care must be exercised in handling and burn out, because flammable
alcohol is given off.

147. GYPSUM BONDED INVESTMENT
THREE TYPES USES COMPENSATION FOR
SHRINKAGE
1.TYPE-l Principally thermal
expansion
2.TYPE-II Employed for casting
Inlays and crowns
Major mode of
Compensation is
Hygroscopic exp.
3.TYPE-III
Employed for casting
inlays and onlays.
Used for construction of
Partial dentures.

148. USES OF VARIOUS INVESTMENT
MATERIALS
Gypsum bonded investment:
It is used for conventional casting of gold alloy
inlays,onlays crowns,and fixed partial dentures.
Phosphate bonded investment:
It is designed primarily for alloys used to produce
copings or framework for metal ceramic
prosthesis.
It can also be used for pressable ceramics.

149. • Ethyl silicate bonded investment:
used principally in the casting of removable partial
dentures with base metal alloys (cobalt-based or
nickel based alloy)

150. • Setting time:
• Usually,the modern inlay investments set initially in 9
to 18 min.
• Setting expansion:
• According to O.BRIEN the total expansion at 700˚c is
about 1.6-2.2%.

151. What happens with gypsum at higher
temperature?

152. RECENT ADVANCES :
Investment material for Titanium(JPD MAR2007, DENT MAT2006)
TITANIUM :
Most frequently used in dentistry, due to various advantages.
1. Low density.
2. Low modulus.
3. Excellent biocompatability
4. Good corrosion resistance.
5. High tensile strength.
6. Potential to be coated with porous surfaces that facilitates tissue integration.
7. In patients who are allergic to base metal alloys.
• Pure Ti metal is reactive and reacts to certain elements in the investment
material, notably with silicate or phosphate bonded investment.
• This produces a hard, brittle surface layer on the casting.
• To avoid this, CaO, MgO and ZrO are included as refactories.
• Also, it helps in reducing the surface roughness produced by the conventional
investment materials.

153. Three types of investment materials were tried:
• Sio2 based investment-80% (sio2)
• Al2o3 based investment-80% (al2o3)
• Mgo based investment-80% (mgo)
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.
This layer consists of 3 layers;
1. OXIDE LAYER
2. ALLOY LAYER REACTION LAYER
3. HARDENING LAYER made of molten titanium

154. • 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.

155. • 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.

156. PROPERTIES:
• Little is known about the properties of these investments.
• Magnesia investments have about the same green strength as phosphate
investments.
• In the fired state, they are twice strong in compression compared to
phosphate bonded investments.
• 80% thermal expansion is achieved at 800°C.

157. 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.
• Soldering investments are designed to have low
setting and thermal expansion so that the
assembled parts don’t shift in position during the
setting and heating of the investment.
• Soldering investments are often made of
ingredients that don’t have as fine a particle size
as the casting investment because the smoothness
of the mass is less important.
• 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.

158. INVESTMENT FOR ALL-CERAMIC
RESTORATIONS:
• Two types of investment materials have been
developed recently for producing all-ceramic
restorations.
• 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 refractories.
• 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.
• Refractory dies are made by pouring the investment
into the impression.

159. •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.

160. • These materials are also phosphate bonded and they generally contain
fine grained refractory fillers to allow accurate reproduction of details.

161. REVIEW OF LITERATURE

162. • V.P.DELGADO AND F.A.PEYTON in 1953
conducted studies on hygroscopic setting expansion of
a dental casting investment and concluded that
1. The use of mechanical spatulation or hand spatulation
does not affect the amount of HSE when water bath at
mouth temperature is used.
2. Mechanical spatulation gives higher expansion values for
thick mixes than hand spatulation,when water bath at
room temperatureis used.
3. Under similar conditions, higher expansion values are
obtained when water bath is at room temperature rather
than at mouth temperature

163. 4. The addition of borax to the investment mix decreases
the
amount of expansion appreciably depending on the
conc.
5. Increased mechanical spatulation increases the
amount of
HSE.

164. • ALTON M.LACY et al conducted studies on incidence of
bubbles on samples cast in a phostate bonded
investment and concluded that
1. dilution of special liquid has no effect on the incidence of
bubble formation for mixes of higher L/P ratio.
2. higher L/P ratio favor reduction of the incidence of
bubbles for any mixing time and mode.
3. Debubblizer is effective in reducing the incidence of
bubbles adhering to the pattern surface.
4. machine mixing under vacuum is more effective than
hand mixing under the same condition in reducing the
no. of bubbles.

165. • DAVID B.MAHLER AND A.BRUCE (1963)
investigated the influence of various factors on the effective setting expansion
of casting investment and concluded that:
1. ESE is not the same as linear trough expansion.Expansion of the investment
away from the wax pattern is relatively small,whereas expansion of the
investment surrounded by the wax pattern is relatively large.
2.The vertical position of the wax pattern in the ring is one of the most
significant factors influencing the ESE.and within the practical limits imposed
by venting and investment strength,the position of the pattern should be
carefully considered.
3.Greased and dry asbestos liners tend to decrease ESE,while loose and
double asbestos liners tend to increase it.
4. Use of softer wax results in greater ESE.

166. REFRENCES
1. DELGADO V.P. PYTOM F.A. - The hygroscopic Setting
Expansion of dental casting Investment. J. Prosthet.
Dent 1953; 3-423.
2. ASGAR. K - Further Investigation into the nature of
hygroscopic expansion of dental Casting
Investment. J. Prosthet. Dent 1958: 8;678.
3. DAVID B.M., BRUCEADY - Influence of factors on
setting expansion J.Prosthet.Dent 1963; 13:365

167. 4. LACY. M. A and MORA. A. incidence of bubbles on
sample cast in phosphate bonded investment. J.
Prosthet. Dent 1985; 44, 367-369.
5. RUSSELL R.WANG,GERHARD E.WELSCH
AND MARIO CASTRO-CEDENO interfacial reactions of
cast titanium with mold materials.Int J. of Prost
1998;11,33-43.
6. PEDRO CESAR GARCIA et al the effect of mould temp.
on castibility of CPTi and Ti-6Al-4V castings into
phosphate bonded investment materials.Dent
Mater2006;22,1098-1102.

168. • YU GUILIN et al The effects of different types of
investments on the alpha-case layer of titanium
castings.J. of pros dent.
march 2007;97,157-164.

169. • Stephen F. Rosenstiel. Contemporary fixed
prosthodontics III Ed. 1995.
• Kenneth J. Anusavice. Phillips Science of Dental
materials. 11 th Ed. 2003.
• Robert G.Craig and John M.Powers Restorative Dental
Materials 11th Ed.
• John f. McCabe and Angus W.G.Walls
8th Ed.
• E.C.Cmbe Notes on Dental Materials 6th Ed.