aes

1. GOOD MORNING

2. DENTAL CASTING
ALLOYS

3. CONTENTS
• Introduction
• History
• Inter Atomic bonds
• Physical properties
• Metallic elements used in dental alloys
• Classification
• Gold casting alloys
• Heat treatment
• Metal ceramic alloys
• Base metal alloys
• References

4. INTRODUCTION
In dentistry, metals represent one of the three major classes of materials
used for the reconstruction of damaged or missing oral tissues.

5. Year Event
• 1907 Introduction of Lost-Wax Technique
• 1933 Replacement of Co-Cr for Gold in Removable Partial Dentures
• 1950 Development of Resin Veneers for Gold Alloys
• 1959 Introduction of the Porcelain Fused-to-Metal Technique
• 1968 Palladium-Based Alloys as Alternatives to Gold Alloy
• 1971 Nickel-Based Alloys as Alternatives to Gold Alloys
• 1980s Introduction of All-Ceramic Technologies
• 1999 Gold Alloys as Alternatives to Palladium-Based Alloys
HISTORY

6. INTERATOMIC BONDS
Primary bonds
Ref : Anusavice K.J.: Phillips Science Of Dental Materials, 10th Ed.
Secondary bonds
Ionic Covalent Metallic
H
2
1. Vander Waals forces
2. Polar compound
3. Nonpolar compound

7. COMBINATION OF PRIMARY BONDS
• Eg: calcium sulfate (CaSO4)
• Ionic bond between Ca2+ and [SO4]2−.
• Covalent bonds between S and O.

8. PHYSICAL
PROPERTIES

9. Stress
• Force per unit area within a structure
subjected to a force or pressure.
• s = Force/Area
• Units: lb/in2 = psi, or N/mm2 = Mpa
Strain
• Change in dimension per unit initial
dimension.
• e=dl/l
• Units: length/length
(inch/inch, or cm/cm)

10. Ductility
• It is the ability of a material to withstand permanent
deformation under a tensile load without rupture.
• A metal may be drawn readily into a wire and is
said to be ductile.
• Depends on tensile strength.
Malleability
• It is the ability of the material to withstand rupture
under compression, as in hammering or rolling into
a sheet.

11. HARDNESS
• Resistance of a material to plastic deformation, which is typically produced by and
indentation force.
• Barcol, Brinell, Rockwell, Shore, Vickers, and Knoop.

12. COEFFICIENT OF THERMAL EXPANSION
Change in length per unit of original length of a material when its
temperature is raised 1 ° K

13. TARNISH:
• Process by which a metal surface is dulled or discolored when a reaction with a sulfide,
oxide, chloride, or other chemical through formation of a thin oxidized film.
CORROSION:
• Corrosion is a process whereby deterioration of a metal is caused by reaction with its
environment.
• Chemical corrosion & Electro chemical corrosion

14. Corrosion
In this the metal reacts to form oxides,
sulphides in the absence of electrolytes
Chemical
Dry Corrosion
Electrochemical
Wet Corrosion
Galvanic corrosion Heterogeneous
Surface Composition
Stress
Corrosion
Crevice
Corrosion
Fatigue or
Cyclic loading

15. PROTECTION AGAINST CORROSION
i. Passivation (Chromium)
ii. Increase noble metal content
iii. Polishing restorations
iv. Avoid dissimilar metal restorations

16. METALLIC
ELEMENTS USED IN
DENTALALLOYS

17. • GOLD:
Pure gold is a soft, malleable, ductile and conductive metal.
CARAT & FINENESS (24k gold =100% gold or 1000 fineness)
• PLATINUM:
Platinum is a bluish white metal
It is tough, ductile, and malleable.
• PALLADIUM:
Hard, Malleable, ductile, Whitens the alloy, increase the resistance to tarnish
and corrosion.
Absorbs the gases during casting and reduces porosity.
Noble Metals

18. The ideal noble casting alloy should have
• Low melting range.
• Adequate strength, hardness, and elongation .
• A low tendency to corrode in the oral environment.
• Low cost.

19. • Silver: Stronger and harder than gold and is malleable, ductile
and a the best conductor of heat and electricity.
• Copper: Malleable and ductile metal with high thermal and
electrical conductivity and a characteristic red color.
• Zinc: Blue-white metal with a tendency to tarnish in moist air.
In its pure form, it is a soft, brittle metal with low strength.
• Nickel: When used in small quantities in gold-based alloys,
nickel whitens the alloy and increases its strength and hardness.
• Tin: Combines with platinum and palladium to produce a
hardening effect, but also increases brittleness.
BASE METALS

20. CLASSIFICATION

21. ALLOY TYPES BY MECHANICAL PROPERTIES
ISO 1562 (2002) :
Type descriptor Yield
strength(
mpa)
%
elongation
Examples of applications
1 Low 80 18 Inlays
2 Medium 180 10 Inlays and onlays
3 Hard 270 5 Onlays, pontics, full crowns,
saddles.
4 Extra hard 360 3 Saddles, bars, clasps, crowns,
bridges, and partial denture
framwework

22. CLASSIFICATION OF METALLIC MATERIAL FOR
DENTAL APPLICATIONS- ISO 22674 (2006)*
Type YeildStrength
(mpa)
Elongation
(%)
Examples of applications
* 0 ----- ------ Single-tooth fixed restorations—e.g., small veneered one-
surface inlays, veneered Crowns
1 80 18 Single-tooth fixed restorations, veneered or nonveneered
one-surface inlays, veneered crowns
2 180 10 For single-tooth fixed restorations—e.g., crowns or inlays
without restriction on the number of surfaces
3 270 5 For multiple-unit fixed restorations—e.g., bridges
4 360 2 For appliances with thin cross sections that are subjected to
very high forces—e.g.,
removable partial dentures, clasps,
5 500 2 For thin removable partial dentures, parts with thin cross
sections, clasps.

23. ALLOY TYPE BY NOBILITY:
• Alloy Classification of the American Dental Association (1984)
Alloy type Total noble metal content
High noble metal Contains > 40 wt% Au and > 60 wt% of
the noble metal elements.
Noble metal Contains > 25 wt % of the noble metal
elements
Predominantly base metal Contains < 25 wt % of the noble metal
elements

24. Alloy Type By Principal Three Elements:
• Au-Pd-Ag,
• Pd-Ag-Sn,
• Ni-Cr-Be

25. DESIRABLE PROPERTIES OF DENTAL
CASTING ALLOYS
• Biocompatibility
• Ease of melting
• Ease of casting
• Ease of brazing (soldering)
• Ease of polishing
• Porcelain Bonding
• Little solidification shrinkage
• Minimal reactivity with the mold
material
• Good wear resistance
• High strength
• Excellent corrosion resistance

26. GOLD CASTING ALLOYS
ADA specification No. 5 classify dental gold casting alloys as:
1. High Gold Alloys
-Type I (Soft)
-Type II (Medium)
-Type III (Hard)
-Type IV(Extra hard)
2. Low Gold Alloys
3. White Gold Alloys

27.  Type I (Soft):- (83%)
• Weak, soft and highly ductile easily burnished.
• Designed for simple inlays such as used in class I, III & V cavities.
• Used only in areas of low occlusal stress
• At present, these are used very rarely.
 Type II (Medium):- (77%)
• These are harder and have good strength.
• Conventional inlay or onlay restorations
• Moderate stress, thick three quarter crowns, pontics and fullcrowns.
• They are less yellow in color due to less gold.
 Type III (Hard):- (75%)
• Age hardened and less burnish ability
• Inlays
• High stress and for crown and bridge
 Type IV (Extra Hard):- (56%)
• Very high stress, crowns and long span bridges.
• Lowest gold content, highest percentage of silver, copper, platinium and palladium.

28. RELATIONSHIP OF THE MECHANICAL PROPERTIES
TO VARIOUS TYPES OF ALLOY
Type Hardness Yield strength Tensile strength Ductility
I
increases increases increases decreases
II
III
1V

29. HEAT TREATMENT OF GOLD ALLOYS
Heat treatment of alloys is done in order to alter its mechanical properties.
Gold alloys can be heat treated if it contains sufficient amount of copper.
Only type III and type IV gold alloys can be heat-treated.
There are two types of heat treatment.
1. Softening Heat Treatment (Solution heat treatment)
2. Hardening Heat Treatment (Age hardening)

30. SOFTENING HEAT TREATMENT HARDENING HEAT TREATMENT
 Solution heat treatment
 Casting : 10 minutes at 700 °C
 Tensile strength, proportional limit, hardness
are reduced.
 Indicated: For appliances that are to be
grounded, shaped, or otherwise cold worked
in or outside the mouth.
 Age Hardening.
 Casting: 15 to 30 minutes at 200 °C and
450°C
 Increases strength, proportional limit, and
hardness, but decreases ductility.
 Indicated: Metallic partial dentures,
saddles, FPDs.

31. The main function is to reinforce porcelain, thus increasing its
resistance to fracture.
Requirements:
1.They should be able to bond with porcelain.
2.Its coefficient of thermal expansion should be compatible with that of porcelain.
3.Its melting temperature should be higher than the porcelain firing temperature. It
should be able to resist creep or sag at these temperatures.
4.It should not stain or discolor porcelain.
METAL CERAMIC ALLOYS

32. The Gold-Platinum-Palladium (Au-Pt-Pd) System
Oldest metal ceramic alloy system.
Not used widely today because they are very expensive.
Composition:
Gold – 75% to 88%
Palladium – Upto 11%
Platinum – Upto 8%
Silver – 5%
Trace elements like Indium, Iron and Tin for porcelain bonding.
Advantages Disadvantages
1. Excellent castability 1. High cost
2. Excellent porcelain bonding 2. Poor sag resistance so not suited for
3. Easy to adjust and finish long span fixed partial dentures.
4. High nobility level 3. Low hardness (Greater wear)
5. Excellent corrosion and tarnish 4. High density (fewer casting per
resistance. ounce)
6. Biocompatible
7. Some are yellow in color
8. Not “Technique Sensitive”
9. Burnishable

33. GOLD-PALLADIUM-SILVER (AU-PD-AG) SYSTEM
High Silver Group
Composition:
• Gold – 39% to 53%
• Silver – 12% to 22%
• Palladium – 25% to 35%
• trace amount of oxidizable elements are
added for porcelain bonding.
Low Silver Group
Composition:
• Gold – 52% to 77%
• Silver- 5% to 12%
• Palladium – 10% to 33%
• Trace amounts of oxidizable elements for
porcelain bonding
Advantages:
• Less expensive than the Au-Pt-Pd alloys
• Improved sag resistance
• High noble metal content
• High malleability.
• Tarnish and corrosive resistant
Disadvantages:
• Silver creates potential for porcelain
discoloration (but less than high silver
group)
• High cost.
• High coefficient of thermal expanpotential
for porcelain sion.
• Less Tarnish and corrosion resistant.

34. Gold-Palladium (Au-Pd) System:
Developed in an attempt to overcome the major limitations like:
-Porcelain discoloration.
-Too high coefficient of thermal expansion & contraction.
Composition:
Gold – 44% to 55%
Gallium – 5%
Palladium – 35% to 45%
Indium & Tin – 8% to 12%
Indium, Gallium and Tin are the oxidizable elements responsible for porcelain bonding.
Advantages Disadvantages
1. Excellent castability 1. Not thermally compatible with high
expansion dental porcelain.
2. Good bond strength 2. High cost
3. Corrosion and tarnish resistance
4. Improved hardness
5. Improved strength ( sag resistance)
6. Lower density

35. Palladium-Silver (Pd-Ag) System
This was the first gold free system to be introduced in the United States (1974).
It was offered as an economical alternative to the more expensive alloy systems.
Composition: (available in two compo.)
1. Palladium – 55% to 60% Silver – 25% to 30%
Indium and Tin
2. Palladium – 50% to 55% Silver – 35% to 40%
Tin (Little or no Indium)

36. Advantages Disadvantages
1. Low Cost 1. Discoloration (yellow, brown or green) may
occur with some dental porcelains.
2. Low density 2. Some castibility problems reported (with
induction casting)
3. Good castibility (when torch 3. Pd and Ag prone to absorb gases.
casting) 4. Require regular purging of the porcelain
4. Good porcelain bonding, furnace.
5. Burnishability 5. May form internal oxides (yet porcelain
6. Low hardness bonding does not appear to be a problem)
7. Excellent sag resistance 6. Should not be cast in a carbon crucible.
8. Moderate nobility level 7. Non-carbon phosphate bonded investments
9. Good tarnish and corrosion recommended.
resistance. 8. High coefficient of thermal expansion.
10. Suitable for long-span fixed
partial dentures.

37. HIGH PALLADIUM SYSTEM
Several types of high palladium systems were originally introduced (Tuccillo, 1987).
More popular composition groups contained cobalt and copper.
Composition
PALLADIUM-COBALT ALLOY:
Palladium – 78% to 88% Cobalt – 4% to 10%
(Some high palladium-cobalt alloys may contain 2% gold)
Trace amounts of oxidizable elements (such as gallium and indium) are added for porcelain
bonding.
PALLADIUM-COPPER ALLOYS:
Palladium – 70% to 80% Copper – 9% to 15%
Gold – 1% to 2% Platinum – 1%

38. Advantages Disadvantages
1. Good castability 1. Produces dark, thick oxides
2. Lower cost (than gold based alloys) 2. May discolor (gray) some dental
3. Low density means more castings porcelains.
Per ounce 3. Must visually evaluate oxide color to
4. Tarnish and corrosion resistance determine if proper adherent oxide was
5. Compatible with many dental formed.
Porcelains. 4. Should not be cast in carbon crucibles
6. Some are available in one unit ingots. (electric casting machines)
5. Prone to gaseous absorption.
6. Subject to thermal creep.
7. May not be suitable for long span fixed
partial denture prosthesis.
8. Little information on long term clinical
success.
9. Difficult to polish
10. Resoldering is a problem

39. BASE METALALLOYS

40. BASE METALALLOYS
-Nickel based
-Cobalt based
Alloys in both systems contain chromium as the second largest constituent.
A classification of base metal casting alloys
Base metal
Casting alloy
Removable
Partial denture
Co-Cr
Co-Cr-Ni
Ni-Cr
Co-Cr-Mo
Surgical
Implant
Ni-Cr
Co-Cr (Class-III)
Fixed
Partial denture
Be. Cont.(Class-II)
No Be. (Class-I)

42. Nickel-chromium (Ni-Cr)
System

43. NICKEL-CHROMIUM BERYLLIUM FREE ALLOYS
Composition:
Nickel – 62% to 77% Chromium – 11% to 22%
Boron , iron, molybdenum, Niobium or columbium and tantalum (trace elements).
Advantages Disadvantages
1. Do not contain beryllium 1. Cannot use with Nickel sensitive patients.
2. Low cost 2. Cannot be etched. (Cr doesn’t dissolve
in acid)
3. Low density means more casting 3. May not cast as well as Ni-Cr-Be alloys
per ounce 4. Produces more oxide than Ni-Cr-Be
alloys.

44. NICKEL-CHROMIUM-BERYLLIUM ALLOY
Composition:
Nickel – 62% to 82% Chromium – 11% to 20%
Beryllium – 2.0%
Numerous minor alloying elements include aluminum, carbon, gallium, iron,
manganese, molybdenum, silicon, titanium and /or vanadium are present.
Advantages Disadvantages
1. Low cost 1. Cannot use with nickel sensitive patients
2. Low density, permits more 2. Beryllium exposure may be potentially
casting per ounce. harmful to technicians and patients.
3. High sag resistance 3. Proper melting and casting is a learned skill.
4. Can produce thin casting 4. Bond failure more common in the oxide layer.
5. Poor thermal conductor 5. High hardness (May wear opposing teeth)
6. Can be etched to increase 6. Difficult to solder
retention 7. Difficult to cut through cemented castings

45. DISADVANTAGES OF NICKEL-CHROMIUM ALLOYS:
Nickel may produce allergic reactions in some
individuals (contact dermatitis). It is also a potential
carcinogen.
Beryllium which is present in many base metal alloys
is a potentially toxic substance. Inhalation of beryllium
containing dust or fumes is the main route of exposure. It
causes a condition know as ‘berylliosis’. It is characterized
by flu-like symptoms and granulomas of the lungs.
Adequate precautions must be taken while working
with base metal alloys. Fumes from melting and dust from
grinding beryllium-containing alloys should be avoided. The
work area should be well ventilated.

46. COBALT CHROMIUM ALLOYS
High strength.
Excellent corrosion resistance especially at high temperatures.
Also known as ‘satellite’ because they maintained their shiny, star-like appearance under
different conditions.
They have bright lustrous, hard, strong and non-tarnishing qualities.
APPLICATIONS:
1. Denture base
2. Cast removable partial denture framework.
3. Surgical implants.
4. Car spark plugs and turbine blades.
COMPOSITION:
Cobalt - 55 to 65%
Chromium - 23 to 30%
Nickel - 0 to 20%
Tungsten, Manganese, Silicon and Platinum in traces.
According to A.D.A specification No. 14 a minimum of 85% by weight of chromium,
cobalt, and nickel is required. Thus the gold base corrosion resistant alloys are excluded.
Molybdenum - 0 to 7%
Iron - 0 to 5%
Carbon - upto 0.4%

47. Summary of base metal alloy properties
Property Ni-Cr without
Be
Ni-Cr with Be Co-Cr
Strength (MPa) 255-550 480-830 415-550
Ultimate tensile
strength (MPa)
550-900 760-1380 550-900
% elongation 5-35 3-25 1-12
Modulus of
elasticity (MPa)
13.8-20.7 x 104 17.2-20.7 x 104 17.2-22.5x104
Vickers
hardness
175-350 300-350 300-500
Casting
temperature
(°C)
1430-1570 1370-1480 1430-1590

48. TITANIUM ALLOYS
• Uses:- Metal and metal-ceramic prostheses, Implants, and RPD frameworks.
• Titanium derives its corrosion protection from a thin passivating oxide film
approximately 10 nm thick, forms spontaneously with surrounding oxygen.
• It requires a special casting machine with arc-melting capability and an
argon atmosphere along with a casting investment consisting of oxides, such
as MgO.
• The high melting temperature of titanium alloys makes them highly resistant
to sag deformation when used as metal frameworks at porcelain sintering
temperatures.

49. Properties of titanium
-Resistance to electrochemical degradation
-Relatively light weight
-Low density (4.5 g/cm3)
-Low modulus (100 GPa)
-High strength (yield strength = 170-480 MPa; ultimate strength = 240-550 MPa)
-Passivity
-Low coefficient of thermal expansion (8.5 x 10–6/°C)
-Melting & boiling point of 1668°C & 3260°C

50. Commercially Pure Titanium (CP Ti):
Alpha phase structure at room temperature
Converts to beta phase structure at 883°C which is stronger but brittle.

51. TITANIUM ALLOYS
Alloying elements are added to stabilize alpha or the beta phase by changing
beta transformation temperature
e.g. in Ti-6Al-4V, Aluminum is an alpha stabilizer whereas Vanadium as well as
Copper and Palladium are beta stabilizer.
Alpha titanium is weldable but difficult to work with at room temperature.
Beta titanium is malleable at room temperature and is used in orthodontics, but
is difficult to weld.
Pure titanium is used to cast crowns, partial denture, and complete denture.

52. Properties of Two α-β Titanium Alloys for Dental Prostheses
Alloy Elastic modulus
(gpa)
Yield strength(mpa) Hardness
(VHN)
Elongation(%)
Ti-6Al-4V 117 860 320 10-15
Ti-6Al-7Nb 105 795 330 10

53. CAST TITANIUM
• Precision casting can be obtained from it.
• High melting point (1668°C) and Chemical reactivity.
• Special melting procedures, cooling cycles, mold materials, and casting
equipments are required to prevent metal contamination, because it readily reacts
with hydrogen, oxygen and nitrogen at temperatures greater than 600°C.
• Casting is done in a vacuum or inert gas atmosphere.
• The investment materials such as phosphate bonded silica and phosphate
investment material are used.
• It has been shown that magnesium based investment cause internal porosity in
casting.

54. Low density, difficult to cast in centrifugal casting machine.
Advanced casting machine combining centrifugal, vacuum, pressure and gravity casting
with electric arc melting technology have been developed.
Difficulties in casting Titanium :
-High melting point
-High reactivity
-Low casting efficiency
-Inadequate expansion of investment
-Casting porosity
-Difficulty in finishing
-Difficulty in welding
-Requires expensive equipments

55. REFERENCES
1. Anusavice K.J.: Phillips Science Of Dental Materials, 10th Ed. W.B.
Saunders Co.:111-555,1996.
2. Craig G.R., O'Brien W.J., Powers J.M.: Dental materials- properties and
manipulation. 4th ed., C.V. Mosby Co.: 114-272, 1987.
3. Richard Von Noort: Introduction To Dental Materials, Second Edition.
4. Sturdevant’s Art and Science Of Oprative Dentistry, 5 th edition. Mosby.
5. Marzouk M.A, Operative Dentistry