The document discusses investment materials used for dental casting. It defines investment materials as ceramic materials used to form molds for casting metals or alloys. The history of investment materials is traced back to ancient Egypt, Persia and China. Key developments include the introduction of the lost wax technique in the early 20th century and the use of gypsum investments which provide compensation for metal shrinkage through thermal expansion and hygroscopic expansion. The ideal requirements, composition and types of modern investment materials are described, with a focus on gypsum-bonded investments which remain commonly used today.

1. INVESTMENT MATERIALS
SYED MANZOOR UL HAQ
Dept. Of Cons & Endo
RAMA DENTAL COLLEGE

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

3. 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

4. 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.
.

5. 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).

6. 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

7. HISTORY

8. 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.

9. • 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.

10. •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.

11. • 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

12. • 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.

13. • 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.
• HE NAMED THIS PHENOMENON AS HYGROSCOPIC
EXPANSION.

14. 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.

15. 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%.

16. 2. BINDER MATERIALS:
COMMON BINDER THAT FORMS A
COHERENT SOLID MASS IS:
• Α-CALCIUM SULFATE HEMI-HYDRATE
• PHOSPHATE
• ETHYL SILICATE
High temperature casting
Investment.

17. 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.

18. • TYPES OF INVESTMENT MATERIALS(O`BREIN
CLASSIFICATION)
GYPSUM BONDED HIGH
TEMPERATURE
PHOSPHATE
BONDED
SILICA
BONDED
INLAY DENTURE

19. 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

20. 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.

21. • 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

22. • 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

23. 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%.

24. HYGROSCOPIC SETTING
EXPANSION
• ACCORDING TO ADA SPECIFICATION NO. 2, THE MINIMUM
EXPANSION IN WATER IS 1.2% AND MAXIMUM EXPANSION IS
2.2%

27. 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.

28. 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.

29. 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

30. • 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.

31. • 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%

32. 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%

33. • 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.

34. 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

35. 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

36. • FINENESS
FINENESS MAY AFFECT THE SETTING TIME,
SURFACE ROUGHNESS
OF THE CASTING.
FINER SILICA MAY RESULTS IN HIGHER
HYGROSCOPIC EXPANSION
THAN A COARSER SILICA.

37. • 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.

38. • 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.

39. 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.

40. 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.

41. 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:

42. 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.

43. 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.

44. • AFTER THE
PATTERN HAS BEEN
COMPLETELY
COATED, THE RING
IS IMMEDIATELY
FILLED BY
VIBRATING THE
REMAINING
INVESTMENT OUT
OF THE BOWL.

45. • 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.

46. • 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

47. 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.

50. • 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.

52. 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
• WHICH MAY LEAD TO SURFACE DISCOLORATION
OF THE CASTING
• THIS REACTION OCCURS ABOVE 700 DEGREE
CELCIUS

53. 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

54. 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.

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

56. 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.

57. 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.

58. ETHYL SILICATE INVESTMENTS
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

59. • 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

60. - 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

61. - 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.

62. • 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.

63. 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.

64. • ETHYL SILICATE BONDED INVESTMENT:
USED PRINCIPALLY IN THE CASTING OF REMOVABLE
PARTIAL DENTURES WITH BASE METAL ALLOYS (COBALT-
BASED OR NICKEL BASED ALLOY)

65. RECENT ADVANCES :
INVESTMENT MATERIAL FOR TITANIUM
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.

66. 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

67. • 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.

68. • 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.

69. 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.

70. 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:

71. 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.

72. •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.

73. • THESE MATERIALS ARE ALSO PHOSPHATE BONDED AND
THEY GENERALLY CONTAIN FINE GRAINED REFRACTORY
FILLERS TO ALLOW ACCURATE REPRODUCTION OF DETAILS.

74. • 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

75. 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.

76. • 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.

77. • 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.
• E.C.CMBE NOTES ON DENTAL MATERIALS
6TH ED.
References

78. THANK YOU