dental CASTING PROCEDURE CASTING PROCEDURE.PPT

dental

1. 11
CASTING PROCEDURE CASTING PROCEDURE

2. 22
INTRODUCTIONINTRODUCTION
2020
ThTh
century generated many changes in the dental century generated many changes in the dental
prosthetic materialsprosthetic materials
Main factors that are driving new developments areMain factors that are driving new developments are
EconomyEconomy
PerformancePerformance
AestheticsAesthetics

3. 33
Taggart – 1907 – Demonstrated Taggart – 1907 – Demonstrated
Lost wax techniqueLost wax technique
casting : something that has been cast in a mold; an
object formed by the solidification of a fluid that has
been poured or injected into a mold.

4. 44
The objective-Providing a metallic duplication of The objective-Providing a metallic duplication of
missing tooth structuremissing tooth structure
All techniques are same except –All techniques are same except –
Sprue designSprue design
Type of investment &Type of investment &
Method of melting the alloyMethod of melting the alloy

5. 55
Die preparationDie preparation
Wax pattern – Type II( indirect)Wax pattern – Type II( indirect)
Sprue FormerSprue Former
Investing the wax patternInvesting the wax pattern
Wax Elimination( Burn out)Wax Elimination( Burn out)
Casting Casting
DevestingDevesting
Finishing and PolishingFinishing and Polishing
Steps in Casting ProceduresSteps in Casting Procedures

6. 66
sprue former : a wax, plastic, or metal pattern used to
form the channel or channels allowing molten metal to
flow into a mold to make a casting

7. 77
Sprue diameterSprue diameter – –
Thickest area of wax Thickest area of wax
patternpattern
Sprue positionSprue position – Based – Based
on shape & form of on shape & form of
wax patternwax pattern
Sprue attachmentSprue attachment – –
Generally flared for Generally flared for
high-density gold high-density gold
alloysalloys

8. 88
Sprue DirectionSprue Direction – Not – Not
attached at right angle to attached at right angle to
a broad flat surfacea broad flat surface
45% at proximal region45% at proximal region
Sprue lengthSprue length – Within – Within
6mm of trailing end of 6mm of trailing end of
casting ringcasting ring

9. 99
Casting ringCasting ring

10. 1010
Wax Elimination & Wax Elimination &
HeatingHeating
For gypsum bonded investment For gypsum bonded investment
500°C for hygroscopic technique.500°C for hygroscopic technique.
700°C for thermal expansion technique.700°C for thermal expansion technique.
Phosphate bondedPhosphate bonded
700°C to 1030°C.700°C to 1030°C.
Advisable to begin burn-out procedure when the Advisable to begin burn-out procedure when the
mould is still wet.mould is still wet.

11. 1111
Hygroscopic Low Heat Hygroscopic Low Heat
TechniqueTechnique
Obtains compensation expansion from 3 Obtains compensation expansion from 3
sources.sources.
37°C water bath expands wax pattern.37°C water bath expands wax pattern.
Warm water entering the investment mold from Warm water entering the investment mold from
top adds some hygroscopic expansion.top adds some hygroscopic expansion.
Thermal expansion at 500°C provides needed Thermal expansion at 500°C provides needed
thermal expansion.thermal expansion.

12. 1212
Advantages of Low Heat TechniqueAdvantages of Low Heat Technique
Less investment degradation.Less investment degradation.
Cooler surface for smoother castings.Cooler surface for smoother castings.
Convenience of placing molds directly in 500°C Convenience of placing molds directly in 500°C
furnace.furnace.
Care taken for sufficient burnout time.Care taken for sufficient burnout time.
The molds should remain in furnace for atleast 60 The molds should remain in furnace for atleast 60
min.min.
Back pressure porosity great hazard in low heat Back pressure porosity great hazard in low heat
technique.technique.

13. 1313
Standardized hygroscopic technique was Standardized hygroscopic technique was
developed for alloys with high gold content; the developed for alloys with high gold content; the
newer noble alloy may require slightly more newer noble alloy may require slightly more
expansion. This added expansion may be expansion. This added expansion may be
obtained by making 1 or more of following obtained by making 1 or more of following
changes.changes.
1.1.Increasing water bath temperature to 40°C.Increasing water bath temperature to 40°C.
2.2.Using two layers of liners.Using two layers of liners.
3.3.Increasing burnout temperature to a range of Increasing burnout temperature to a range of
600°C to 650°C.600°C to 650°C.

14. 1414
High-Heat Expansion High-Heat Expansion
TechniqueTechnique
Depend almost entirely on high-heat burnout to Depend almost entirely on high-heat burnout to
obtain the required expansion, while at the same obtain the required expansion, while at the same
time eliminating the wax pattern.time eliminating the wax pattern.
Additional expansion:Additional expansion:
Slight heating of gypsum investments on setting. Slight heating of gypsum investments on setting.
Thus expanding the wax pattern.Thus expanding the wax pattern.
Water entering from wet liner adds a small Water entering from wet liner adds a small
amount of hygroscopic expansion to the normal amount of hygroscopic expansion to the normal
setting expansion.setting expansion.

15. 1515
Gypsum InvestmentsGypsum Investments
Fragile and require use of metal ring.Fragile and require use of metal ring.
Slowly heated to 600°C to 700°C in 60 mins. and held for 15 to Slowly heated to 600°C to 700°C in 60 mins. and held for 15 to
30 min. at the upper temperature.30 min. at the upper temperature.
Rate of heating:Rate of heating:
Smoothness.Smoothness.
Overall dimension of investment.Overall dimension of investment.
Too rapid heating.Too rapid heating.
Cracking of investment (outside layer expands >center Cracking of investment (outside layer expands >center
section).section).
Radial cracks interior to outward.Radial cracks interior to outward.
Casting with fins or spines.Casting with fins or spines.
Common with
cristobalite investment.

16. 1616
Investment decomposition and alloy contamination is related Investment decomposition and alloy contamination is related
to the chemical reaction between the residual carbon and to the chemical reaction between the residual carbon and
sulfate binder.sulfate binder.
Calcium sulfate does not decompose unless heated above Calcium sulfate does not decompose unless heated above
1000°C.1000°C.
Reduction of calcium sulfate by carbon takes place rapidly Reduction of calcium sulfate by carbon takes place rapidly
above 700°C.above 700°C.
CaSOCaSO
44 + 4C + 4C  CaS + 4CO CaS + 4CO
3CaSO3CaSO
44 + CaS + CaS  4CaO + 4SO 4CaO + 4SO
22
This reaction occurs when gypsum investment are heated This reaction occurs when gypsum investment are heated
above 700°C in presence of carbon. SO2 as a product of this above 700°C in presence of carbon. SO2 as a product of this
reaction contaminates gold castings and makes them reaction contaminates gold castings and makes them
extremely brittle.extremely brittle.

17. 1717
Sulfur gases are generated when investment is heated Sulfur gases are generated when investment is heated
above 700°C.above 700°C.
After casting temperature reached After casting temperature reached  Casting Casting
should be made immediately.should be made immediately.
Sulfur contamination.Sulfur contamination.
Rough surface on casting.Rough surface on casting.
Improved investment formulations.Improved investment formulations.
Gypsum investment with considerable amount of Gypsum investment with considerable amount of
cristobalite.cristobalite.

18. 1818
Few investments may be Few investments may be
directly placed into directly placed into
furnace at final burnout furnace at final burnout
temperaturetemperature
 held for 30 min. & cast.held for 30 min. & cast.

Factors affecting size and smoothness.Factors affecting size and smoothness.

Design of the furnace.Design of the furnace.

Proximity of the mold to the heating element.Proximity of the mold to the heating element.

Availability of air in the muffle.Availability of air in the muffle.

19. 1919
Phosphate InvestmentsPhosphate Investments
Obtain their expansion from following sources.Obtain their expansion from following sources.
Expansion of the wax pattern.Expansion of the wax pattern.
Setting expansion (because of liquid used).Setting expansion (because of liquid used).
 Thermal expansionThermal expansion
Phosphate investments much harder and stronger than Phosphate investments much harder and stronger than
gypsum investments.gypsum investments.
Burnout temperature range from 750°C to 1030°C. Burnout temperature range from 750°C to 1030°C.
315°C 315°C  rapid heating rapid heating  held at the upper held at the upper
temperatures for 30 temperatures for 30
mins.mins.

20. 2020
2 stage heating:2 stage heating:
Placed directly in furnace at top temperature.Placed directly in furnace at top temperature.
Held for 20-30 min. then castHeld for 20-30 min. then cast
Elimination of metal ring and liner to save Elimination of metal ring and liner to save
more time.more time.
Metal ring replaced with plastic ring i.e. tapered.Metal ring replaced with plastic ring i.e. tapered.

21. 2121
Time allowable for castingTime allowable for casting
Investment contracts thermally as it cools.Investment contracts thermally as it cools.
When thermal expansion / high heat technique used.When thermal expansion / high heat technique used.
Investment loses heat after heated ring removed Investment loses heat after heated ring removed
from furnace and mold contracts.from furnace and mold contracts.
1 min. is allowable between the transfer of the ring 1 min. is allowable between the transfer of the ring
from the furnace to the casting machine.from the furnace to the casting machine.

22. 2222
BURN OUTBURN OUT

23. 2323
FURNACEFURNACE

24. 2424
Casting MachinesCasting Machines
Alloys are melted in one of the 4 following ways:Alloys are melted in one of the 4 following ways:
In a separate crucible by a torch flame, and cast In a separate crucible by a torch flame, and cast
centrifugally.centrifugally.
Electrically by a resistance heating or induction furnace. Electrically by a resistance heating or induction furnace.
Centrifugally by motor or spring action.Centrifugally by motor or spring action.
By induction heating. Centrifugally by motor or spring By induction heating. Centrifugally by motor or spring
action.action.
Vacuum arc melted. Cast by pressure in argon atmosphere. Vacuum arc melted. Cast by pressure in argon atmosphere.

Molten metal may be cast by air pressure, by vacuum, Molten metal may be cast by air pressure, by vacuum,
or both.or both.

25. 2525
Torch Melting of Noble Torch Melting of Noble
AlloyAlloy
Melted by placing on inner sidewall of crucible.Melted by placing on inner sidewall of crucible.
Fuel used - Natural or artificial gas and air.Fuel used - Natural or artificial gas and air.
- Oxygen air and acetylene.- Oxygen air and acetylene.
Non-luminous brush flame with different combustion zones Non-luminous brush flame with different combustion zones
should be obtained.should be obtained.
Mixing zoneMixing zone
Combustion zone.Combustion zone.
Reducing zone.Reducing zone.
Oxidizing zone.Oxidizing zone.
At proper casting temperature the molten alloy is At proper casting temperature the molten alloy is light orangelight orange
and tend to spin or follow the flame.and tend to spin or follow the flame.
Alloy should be approx. 38°C to 66°C above liquidus Alloy should be approx. 38°C to 66°C above liquidus
temperature.temperature.

26. 2626
The casting should be made when proper temperature The casting should be made when proper temperature
is reachedis reached
No more 30 secs should be allowed to elapse between No more 30 secs should be allowed to elapse between
the time the ring is removed from the oven and the the time the ring is removed from the oven and the
molten alloy is centrifuged into the the moldmolten alloy is centrifuged into the the mold
When the alloy is molten,slide the crucible against the When the alloy is molten,slide the crucible against the
ring,sprinkle flux over the metalring,sprinkle flux over the metal
Hold the casting arm so that the pin drops awayHold the casting arm so that the pin drops away
Release the arm and rotate till it comes to rest Release the arm and rotate till it comes to rest

27. 2727
Use of flux for gold alloyUse of flux for gold alloy
It is desirable to use flux for gold alloy toIt is desirable to use flux for gold alloy to
Minimize porosityMinimize porosity
To increase the fluidity of the metalTo increase the fluidity of the metal
Film of flux formed on surface of alloy prevents Film of flux formed on surface of alloy prevents
oxidationoxidation
Eg; 1.Powdered charcoalEg; 1.Powdered charcoal
2.Fused Borax powder ground with Boric acid 2.Fused Borax powder ground with Boric acid
powder powder

28. 2828
CENTRIFUGAL CASTING CENTRIFUGAL CASTING
MACHINEMACHINE

29. 2929

30. 3030

31. 3131
Torch melting centrifugal casting Torch melting centrifugal casting
machinemachine
Casting machine spring Casting machine spring
wound from 3 to 4 turnswound from 3 to 4 turns
Alloy is melted by a torch flame Alloy is melted by a torch flame
in a glazed ceramic crucible in a glazed ceramic crucible
attached to the broken arm of attached to the broken arm of
casting machine.casting machine.
Broken arm feature Broken arm feature
accelerates the initial accelerates the initial
rotational speed of the rotational speed of the
crucible and casting ring.crucible and casting ring.
Torch flame is generated from a Torch flame is generated from a
gas mixture of propane and air.gas mixture of propane and air.
Machine is released and spring Machine is released and spring
triggers the rotation motion.triggers the rotation motion.
As the metal fills the mold, a As the metal fills the mold, a
hydrostatic pressure gradient hydrostatic pressure gradient
develops along the length of the develops along the length of the
casting.casting.

32. 3232
The pressure gradient from the tip of the The pressure gradient from the tip of the
casting to the bottom surface is quite, sharp casting to the bottom surface is quite, sharp
and parabolic in form, reaching zero at the and parabolic in form, reaching zero at the
button surface.button surface.
Pressure gradient before solidification reaches Pressure gradient before solidification reaches
0.21 to 0.28MPa (30 to 40 psi) at the tip of 0.21 to 0.28MPa (30 to 40 psi) at the tip of
casting.casting.
Greatest rate of heat transfer to the mold is at Greatest rate of heat transfer to the mold is at
the high pressure end of the gradient (tip of the the high pressure end of the gradient (tip of the
casting).casting).

33. 3333
SPRING-WOUND CASTING SPRING-WOUND CASTING
MACHINE WITH ELECTRIC MACHINE WITH ELECTRIC
RESISTANCE FURNACE RESISTANCE FURNACE

34. 3434
Electrical Resistance-Heated Electrical Resistance-Heated
Casting MachineCasting Machine
Current is passed through a resistance heating conductor, and Current is passed through a resistance heating conductor, and
automatic melting of the alloy occurs in a graphite or ceramic automatic melting of the alloy occurs in a graphite or ceramic
crucible.crucible.
Advantages:Advantages:
For metal ceramic prosthesis.For metal ceramic prosthesis.
Base metals in trace amounts that tend to oxidize on Base metals in trace amounts that tend to oxidize on
overheating.overheating.
Crucible located flush against casting ring. Crucible located flush against casting ring.
Carbon crucibles should not be used in melting of:Carbon crucibles should not be used in melting of:
High PdHigh Pd
Pd-AgPd-Ag
Ni-CrNi-Cr
Co-CrCo-Cr

35. 3535
INDUCTION MELTING CASTING INDUCTION MELTING CASTING
MACHINESMACHINES
WATER COOLED
INDUCTON COIL
VERTICAL
CRUCIBLE
POSITOINED
WITHIN INDUCTION
COIL

36. 3636

37. 3737
Induction Melting MachineInduction Melting Machine
Alloy is melted by induction field that develops within Alloy is melted by induction field that develops within
a crucible surrounded by water cooled metal tubing.a crucible surrounded by water cooled metal tubing.
The electrical induction furnace is a transformer in The electrical induction furnace is a transformer in
which an alternating current flows through the primary which an alternating current flows through the primary
winding coil and generates a variable magnetic field in winding coil and generates a variable magnetic field in
the location of the alloy to be melted in crucible.the location of the alloy to be melted in crucible.
Once the alloy reaches casting temperature in Once the alloy reaches casting temperature in
air/vacuum it is forced into mold by centrifugal force air/vacuum it is forced into mold by centrifugal force
by air pressure, or by vacuum. by air pressure, or by vacuum.
More commonly used for melting base metal alloys.More commonly used for melting base metal alloys.

38. 3838
Direct Current Arc Melting MachineDirect Current Arc Melting Machine
Direct current arc is produced between two Direct current arc is produced between two
electrodes- the alloy and water cooled tungsten electrodes- the alloy and water cooled tungsten
electrode.electrode.
The temperature between the arc exceeds 4000°C.The temperature between the arc exceeds 4000°C.
Has high risk of overheating.Has high risk of overheating.

39. 3939
Vacuum or Pressure Assisted Casting Vacuum or Pressure Assisted Casting
MachineMachine
Molten alloy is heated to casting temperature drawn Molten alloy is heated to casting temperature drawn
into the evacuated mold by gravity or vacuum and into the evacuated mold by gravity or vacuum and
subjected to additional pressure to force the alloy subjected to additional pressure to force the alloy
into the mold. into the mold.
Used for titanium and titanium alloys. Under Used for titanium and titanium alloys. Under
vacuum arc heated-argon pressure casting machine.vacuum arc heated-argon pressure casting machine.

40. 4040
Vacuum-or Pressure-Assisted Vacuum-or Pressure-Assisted
Casting MachineCasting Machine

41. 4141
Casting CruciblesCasting Crucibles
Clay.Clay.
Carbon.Carbon.
Quartz.Quartz.
Zirconia-alumina.Zirconia-alumina.

42. 4242
Cleaning the casting Cleaning the casting
Quenching: ring is removed and quenched in water Quenching: ring is removed and quenched in water
as soon as the button exhibits a dull red glowas soon as the button exhibits a dull red glow
Purpose of quenching Purpose of quenching
•All the intermediate phases are changed to a disorderly All the intermediate phases are changed to a disorderly
state and ductility is increasedstate and ductility is increased
•Soft granular investment that is easily removed Soft granular investment that is easily removed

43. 4343
SAND BLASTINGSAND BLASTING

44. 4444
Sand blastingSand blasting
Casting is held in an sand blasting machine to Casting is held in an sand blasting machine to
clean the investment from the surface. The clean the investment from the surface. The
blasting materials used are:blasting materials used are:
Sand shellsSand shells
Recycled aluminium oxide with pressure of 100psiRecycled aluminium oxide with pressure of 100psi
GarnetGarnet

45. 4545
PicklingPickling
Removal of oxide residues of carbon by heating the discoloured Removal of oxide residues of carbon by heating the discoloured
casting in an acidcasting in an acid
Advantages of HCl:Advantages of HCl:
Aids in removal of residual investment as well as oxide Aids in removal of residual investment as well as oxide
coatingcoating
Disadvantages:Disadvantages:
Likely to corrode laboratory metal furnishingsLikely to corrode laboratory metal furnishings
Fumes are health hazardFumes are health hazard
Method of cleaning Method of cleaning
Place the casting in test tube or dish and pour acid over it Place the casting in test tube or dish and pour acid over it
Other methods: Heating the casting and then dropping into the Other methods: Heating the casting and then dropping into the
pickling solutionpickling solution

46. 4646
CASTING DEFECTSCASTING DEFECTS
Any impressions or irregularities that result in Any impressions or irregularities that result in
unsuccessful casting which interfere with the fit of the unsuccessful casting which interfere with the fit of the
final restoration-basically classified into 4 categoriesfinal restoration-basically classified into 4 categories
DISTORTION DISTORTION
SURFACE ROUGHNESS AND SURFACE ROUGHNESS AND
IRREGULARITIESIRREGULARITIES
POROSITY POROSITY
INCOMPLETE OR MISSING DETAILINCOMPLETE OR MISSING DETAIL

47. 4747
SURFACE IRREGULARITIESSURFACE IRREGULARITIES
Air bubblesAir bubbles
Water filmsWater films
Rapid heating,under heating and prolonged heatingRapid heating,under heating and prolonged heating
Liquid/powder ratioLiquid/powder ratio
Temperature of alloyTemperature of alloy
Casting pressure (gauge pressure of 0.10-0.14MPa)Casting pressure (gauge pressure of 0.10-0.14MPa)
Composition of investmentComposition of investment
Foreign bodiesForeign bodies
Impact of molten alloyImpact of molten alloy
 Pattern positionPattern position
Carbon inclusons (from crucibles, torch flame and carbon containing Carbon inclusons (from crucibles, torch flame and carbon containing
investment)investment)

48. 4949
BLACK COATED NOBLE METAL ALLOY BLACK COATED NOBLE METAL ALLOY
(sulfur contamination or oxidation)(sulfur contamination or oxidation)

49. 5050
POROSITYPOROSITY
SOLIDIFICATION DEFECTSSOLIDIFICATION DEFECTS
• LOCALISED SHRINKAGE POROSITYLOCALISED SHRINKAGE POROSITY
• MICROPOROSITYMICROPOROSITY
TRAPPED GASESTRAPPED GASES
• PINHOLE POROSITYPINHOLE POROSITY
• GAS INCLUSIONS GAS INCLUSIONS
• SUBSURFACE POROSITYSUBSURFACE POROSITY
RESIDUAL AIRRESIDUAL AIR

50. 5151
LOCALISED SHRINKAGE LOCALISED SHRINKAGE
POROSITYPOROSITY
Premature termination of flow of Premature termination of flow of
molten metalmolten metal
Sprue freezes before feeding is Sprue freezes before feeding is
complete to casting propercomplete to casting proper
Retain heat because of bulk and Retain heat because of bulk and
heat center of ring heat center of ring
Small chill set spruesSmall chill set sprues

51. 5252
MICROPOROSITYMICROPOROSITY
OCCURS BY SOLIDIFICATION SHRINKAGE IN OCCURS BY SOLIDIFICATION SHRINKAGE IN
FINE GRAIN CASTINGSFINE GRAIN CASTINGS
OCCUR FROM RAPID SOLIDIFICATION IF OCCUR FROM RAPID SOLIDIFICATION IF
MOLD /CASTING TEMPERATURE IS TOO LOWMOLD /CASTING TEMPERATURE IS TOO LOW

52. 5353
SUCK BACK POROSITY SUCK BACK POROSITY
Occlusoaxial/incisoaxial Occlusoaxial/incisoaxial
line angleline angle
Hotspot Hotspot
Flaring the point of sprue Flaring the point of sprue
attachmentattachment
Lowering casting Lowering casting
temperature by 30 temperature by 30
degreesdegrees

53. 5454
PINHOLE POROSITY AND PINHOLE POROSITY AND
GAS INCLUSIONS GAS INCLUSIONS
ENTRAPMENT OF AIR DURING ENTRAPMENT OF AIR DURING
SOLIDIFICATIONSOLIDIFICATION
SPHERICAL CONTOURSPHERICAL CONTOUR
LARGE SPHERICAL POROSITIES CAUSED BY LARGE SPHERICAL POROSITIES CAUSED BY
GAS OCCLUDED BY A POORLY ADJUSTED GAS OCCLUDED BY A POORLY ADJUSTED
TORCH FLAMETORCH FLAME

54. 5555
SUB SURFACE POROSITYSUB SURFACE POROSITY
SIMULTANEOUS NUCLEATION OF SOLID SIMULTANEOUS NUCLEATION OF SOLID
GRAINS AND GAS BUBBLES AT THE FIRST GRAINS AND GAS BUBBLES AT THE FIRST
MOMENT THAT THE ALLOY FREEZES AT THE MOMENT THAT THE ALLOY FREEZES AT THE
MOLD WALLSMOLD WALLS
RATE OF MOLTEN METAL THAT ENTERS THE RATE OF MOLTEN METAL THAT ENTERS THE
MOLDMOLD

55. 5656
BACK PRESSURE POROSITY BACK PRESSURE POROSITY
Large concave depressionsLarge concave depressions
Inability of air in mold to Inability of air in mold to
escape through the pores in escape through the pores in
the investment the investment
Proper burnout,adequate Proper burnout,adequate
mold and casting mold and casting
temperature,high casting temperature,high casting
pressure,proper l/p ratio pressure,proper l/p ratio

56. 5757
INCOMPLETE CASTING INCOMPLETE CASTING
MOLTEN ALLOY PREVENTED FROM MOLTEN ALLOY PREVENTED FROM
COMPLETELY FILLING MOLDCOMPLETELY FILLING MOLD
Insufficient venting and high viscosityInsufficient venting and high viscosity
Incomplete elimination of wax residuesIncomplete elimination of wax residues
Shiny margins caused by CO left by residual waxShiny margins caused by CO left by residual wax
Temperature of alloy should be raised so that its Temperature of alloy should be raised so that its
viscosity and surface tension are lowered.viscosity and surface tension are lowered.

57. 5858
ROUNDED INCOMPLETE ROUNDED INCOMPLETE
MARGNS MARGNS

58. 5959
INCOMPLETE CASTINGINCOMPLETE CASTING

59. 6060
Review of LiteratureReview of Literature
Cooney JP and Caputo AA: Cooney JP and Caputo AA:
JPD 1981,Vol46,page no 414-419JPD 1981,Vol46,page no 414-419
Marginal fit of the complete cast crowns made in Marginal fit of the complete cast crowns made in
phosphate bonded investment is superior, surface phosphate bonded investment is superior, surface
roughness was less in the gypsum bonded investment.roughness was less in the gypsum bonded investment.
Finger W, and Ohsawa M :Finger W, and Ohsawa M :
JPD1984,Vol 52 page no. 800-803JPD1984,Vol 52 page no. 800-803
By minimyzing distortion of the wax pattern, the By minimyzing distortion of the wax pattern, the
refractory die-investing procedure can produce refractory die-investing procedure can produce
consistently accurate cast gold restoration.consistently accurate cast gold restoration.

60. 6161
 Santos JF,and Ballester RY:Santos JF,and Ballester RY:
Dent Mater 1987 Vol 3 page no.165-167Dent Mater 1987 Vol 3 page no.165-167
Delayed hygroscopic expansion occurs when the Delayed hygroscopic expansion occurs when the
investment is immersed in water after setting. investment is immersed in water after setting.
Increased time of immersion and an increase in the Increased time of immersion and an increase in the
special liquid concentration increased the hygroscopic special liquid concentration increased the hygroscopic
setting expansion.setting expansion.
 Verrett RG, and Duke ES:Verrett RG, and Duke ES:
JPD 1989 VOL 61 Page no. 418-424.JPD 1989 VOL 61 Page no. 418-424.
Effect of sprue attachment, flared and straight sprues Effect of sprue attachment, flared and straight sprues
optimized castability and minimized porosity.optimized castability and minimized porosity.

61. 6262
ConclusionConclusion
The accuracy of the fit of a cast restoration is The accuracy of the fit of a cast restoration is
essential for its longevityessential for its longevity
This allows for less plaque accumulation at the This allows for less plaque accumulation at the
marginal areamarginal area
It also provides better mechanical properties It also provides better mechanical properties
like stability and resistance, less microleakage like stability and resistance, less microleakage
and good estheticsand good esthetics

62. 6363
ReferencesReferences
Phillips’science of dental materials – Kenneth Phillips’science of dental materials – Kenneth
J.Anusavice,11J.Anusavice,11
thth
Edition. Edition.
Contemporary Fixed Prosthodontics – Stephen F. Contemporary Fixed Prosthodontics – Stephen F.
Rosenstiel, Martin F. Land, Junhei Fujimoto,4Rosenstiel, Martin F. Land, Junhei Fujimoto,4
thth
Edition. Edition.
Dental laboratory procedures – Fixed partial dentures - Dental laboratory procedures – Fixed partial dentures -
John E. Rhoads,Kenneth D. Rudd, Robert M. Murrow, John E. Rhoads,Kenneth D. Rudd, Robert M. Murrow,
Volume Two,Second Edition. Volume Two,Second Edition.
Dental laboratory procedures – Removable partial Dental laboratory procedures – Removable partial
dentures - Kenneth D. Rudd, Robert M. Murrow John dentures - Kenneth D. Rudd, Robert M. Murrow John
E. Rhoads, Volume Three, Second Edition.E. Rhoads, Volume Three, Second Edition.

63. 6464