Base metal alloys

*

1. “BASE METAL ALLOYS”
Presented by :
Apurva Deshmukh.
Guided By:
1. Dr. Trupti Dahane
2. Dr. Parag Bhoyar

2. Contents:
Introduction
Definitions
General requirements for all metal alloys.
Classification.
Dental Application of Base metal alloys.
Different base metal alloys.
Table of comparison between different base metal
alloys.
Summary.
References.

3. Metals represents one of the three major
classes in dental prosthetic materials, other
being polymers and ceramics.
Major factors that were driving new
developments in prosthetic materials in the
twentieth century were economy, material
performance and aesthetics.
Introduction:

4. For casting dental restorations and for the fabrication
of wire and other structures, it was necessary to
combine various metals to produce alloys with
adequate properties.
As a result, the wide varieties of metal alloy that we
use today consist of :
1.Noble metals alloys.
2.Base metals alloys; and
3.Dental amalgams.

5. Cobalt chromium alloys were first
discovered by Sir.Elwood Haynesin
1907by fusing cobalt and chromium in
presence of other elements in minor
quantities. He then called them Stellite.
But it was not until 1930's that these
alloys got their attention.
Sir.Elwood.P.Haynes

6. One of the primary reasons
were the escalating cost of gold
throughout the 20
th
century.
Developed in the early 1970s,
most of the base metal alloys
were based on nickel and
chromium.

7. Grain:A microscopic single crystal in the
microstructure of a metallic material.
It can be altered by heating.
When the metal is heated
and rapidly quenched, small grains are formed.
When they are allowed to cool slowly, grain size is
large.
More fine the grain structure, better the metal's
properties.
Definitions:

8. Definitions:
Noble Metals: Metals which are highly resistant to
oxidation and dissolution in inorganic acids.
Gold + Platinum group metals.
( Platinum group consists of Platinum, palladium,
rhodium, ruthenium, iridium and osmium ).
Base Metals: A metal that readily oxidizes or dissolves
to release ions when exposed to air or moisture. Eg-
Nickel, Iron, Cobalt, Copper, Lead, Tin, Zinc, etc.

9. Alloy: A crystalline substance with metallic properties that is
composed of two or more chemical elements, at least one of
which is metal.
Methods of alloying:
1.Melting: It is a process where molten base metal (main)
and other alloying elements are mixed thoroughly and the
mixture is allowed to cool and solidify.This is a common
method.
2.Sintering/Powder metallurgy: Metals are powdered, mixed
and pressed to the desired shape and then heated (but not
melted) till the powder unites to form a solid mass.

10. General Requirements of casting
alloys
The alloys that we intend to use must possess
certain minimal fundamental characteristics such
as:
Biocompatible.
Resistant to tarnish and corrosion.
Non-allergic.
Ease of melting and casting.
Ease of finishing and polishing.
Minimal reactivity with the mold material.

11. Less solidification shrinkage.
High strength.
Wear resistant.
Porcelain bonding.
Economical.

12. A)In1984,ADAproposedasimpleclassificationof
dentalcastingalloysbycomposition:
ALLOY TYPE
TOTAL NOBLE METAL
CONTENT
HIGH NOBLE METAL
(HN)
Noble Metal Content* ≥ 60%
+ and gold ≥ 40%.
NOBLE METAL
(N)
≥25% Noble metal content*
PREDOMINANTLY BASE METAL
(PB)
<25% Noble metal content*
*Noble metal :Gold(Au) + Platinum(Pt), Palladium(Pd), Rhodium(Rh),
Osmium(Os), Ruthenium(Rh), Iridium(Ir).
Classification

13. B) The ADA Council has revised the classification
system for alloys.
(Which was published in March 2003 in Journal of the
American Dental Association)
Revised ADA Classification for Prosthodontic Alloys.
Classification Requirements
High Nobel Alloys Noble Metal Content ≥ 60% (gold+
platinum group*) and gold ≥ 40%
Titanium and Titanium alloys. Titanium ≥ 85%
Nobel Alloys Noble Metal Content ≥ 25% (gold
+ platinum group*)
Predominantly Base metal alloysNoble Metal Content < 25% (gold
+ platinum group*)
*Platinum group:Platinum(Pt), Palladium(Pd), Rhodium(Rh),
Osmium(Os), Ruthenium(Rh), Iridium(Ir).

14. C) Mechanical Property Requirement for Dental Casting Alloys acc
to ANSI/ADA Specification No. 5.
ADA
Type
Description Clinical use Yield Strength (MPa)
I Soft Restorations subjected to low stress:
some inlays
<140
II Medium Restorations subjected to moderate
stress: inlays and onlays
140-200
III Hard Restorations subjected to high
stress: crowns, thick-veneer crowns,
short-span fixed dental prostheses
200-340
IV Extra hard Restorations subjected to very high
stress: thin-veneer crowns, long-
span fixed dental prostheses,
removable dental prostheses
>340

15. Dental applications of Base metal
alloys :

16. Alloy type All-metal Metal-ceramic
Removable partial
dentures
Base Metal Pure Ti Pure Ti Pure Ti
Ti-Al-V Ti-Al-V Ti-Al-V
Ni-Cr-Be Ni-Cr-Be Ni-Cr-Be
Ni-Cr Ni-Cr Ni-Cr
Co-Cr Co-Cr Co-Cr
Co-Cr-W Co-Cr-W Co-Cr-W
Classification of alloys for All-Metal restorations, metal
ceramic restorations, and frameworks for removable
partial dentures.

17. Advantages of base metal
alloys:
High yield strength.
High elastic modulus.
High hardness.
Lower density.
Excellent sag resistance.
Lower cost alternative.

18. Disadvantages:
Have high liquidus temperatures making them difficult to
cast and ensure appropriate marginal fit of restorations.
They exhibit a greater casting shrinkage (about 2.3%) that
must be compensated for.
Because of their lower ductility and greater hardness, they
are less burnishable and more difficult to finish and polish.
Finally, beryllium and nickel can cause allergic reactions
and may have carcinogenic effects.

19. ItisusedasasubstitutefortypeIIIGold
alloys.
Thesystemcontainstwomajorgroups:
-Berylliumfree(classI)
-Beryllium(classII)
Ofthetwo,Ni-Cr-Berylliumalloyaregenerally
regardedaspossessingsuperiorpropertiesandhave
beenmorepopular.
“NICKEL CHROMIUM ALLOYS”

20. COMPOSITION:
Major contents (90%):
Nickel : 62-82% :
i.Increases hardness
ii.Increases modulus of elasticity (stiffness)
iii.Increases ductility
iv.Poor biocompatibility.
Chromium : 11-22% :
i.Increases tarnish and corrosion resistance
ii.Increases hardness.
iii.It reduces melting point.
When the chromium content of an alloy is over 30%, it is more
difficult to cast. It also forms a brittle phase, known as the sigma
phase. Therefore dental alloys of these types should not contain
more than 30% chromium.

21. Minor elements(10%) :
Molybdenum: 3-6% –Increases strength of the alloy.
Aluminium: 2-6% –Increases the tensile strength and yield
strength.
Silicon and Manganese–These are added to increase the
fluidity & castability of the alloys.
Beryllium: 0.5-2% (In Class II.)

22. If and when Berylliumis added :
Beryllium improves physical properties as it acts
as a grain refiner.
The Ni/Cr/Be alloy exhibit excellent sag resistance as well
as high strength and rigidity.
Small amounts of beryllium reduce the liquidus
temperature and, therefore, reducing the casting
shrinkage.This helps in easy casting.
Has mold-filling abilities that are superior to all other
groups. This ability permits easier casting of thin sections
and produces sharp margins on castings.
But unfortunately, beryllium increases corrosion.

23. Advantages:
Low density permits more casting per
ounce.
Can produce thin castings.
High sag resistance.
Poor thermal conductor.
Can be etched.
Low cost.

24. Disadvantages:
Cannot use with nickelsensitive patients
Beryllium exposure may be potentially harmful to
technicians.
Bond failure is more common in the oxide layer.
High hardness: May wear opposing teeth.
Difficult to solder.

25. Nickel chromium beryllium free alloy
Composition:
1.Nickel: 62-77%
2.Chromium: 11-22%
3.Boron, Iron, Molybdenum, Tantalum: Traces
DISADVANTAGE :
1.May not cast as well asNi-Cr-Be alloys.
2.Produce more oxides than Ni-Cr-Be alloys.

26. Comparative properties of Ni / Cr alloys and type III casting
gold alloys for small cast restorations
Property (Units)Ni/CrType III gold
alloy
Comments
Density (g/cm
3
) 8 15 More difficult to produce defect free
casting for Ni/Cr alloys.
Fusion
temperature
As high
as
1350°C
Normally
lower than
1000°C
Ni/Cr alloys require electrical induction
furnace or oxyacetylene equipment.
Casting shrinkage
(%)
2 1.4 Mostly compensated for by correct
choice of investment and using risers.

27. Comparative properties of Ni / Cr alloys and type III casting
gold alloys for small cast restorations(conti)
Property (Units)Ni/CrType III gold
alloy
Comments
Proportional limit
(MPa)
230 290 Both high enough to prevent distortion.
Modulus of
elasticity (GPa)
220 85 Higher modulus of Ni/Cr is an
advantage for large restoration e.g.
bridges and for porcelain bonded
restoration.
Hardness (VHN) 300 150 Ni/Cr more difficult to polish but
retains polish.
Ductility
(% elongation)
upto
30%
20% Relatively large values suggest that
burnishing is possible; however, large
proportional limit value suggests higher
forces would be require.

28. The Cobalt-Chromium alloys have replaced Type IV gold
alloys because of their lower cost and adequate mechanical
properties.
These have been available under the trade name Vitallium.
“Vitallium”was developed by Albert W. Merrick for the
Austenal Laboratories in 1932.
Itis a trademarkfor an alloyof
65% cobalt,
30% chromium,
5% molybdenum,
and other substances.
“COBALT CHROMIUM ALLOYS”
Cobalt-chromedisc with dental bridgesand
crownsmanufactured using WorkNC Dental
CAD/CAM.

29. COMPOSITION :
Major contents(90%) :
Cobalt : 35-65% :
1. increases hardness
2. increases melting point
Chromium : 28-30% :
1. increases tarnish and corrosion resistance
2. increases hardness.
3. it reduces melting point
Nickel : 0-20% :
1. increases hardness
2. high modulus of elasticity (stiffness)
3. increases ductility
4. poor biocompatibility.

30. Minor contents(10%)
Molybdenum: 3-6% : Increases strength of the alloy.
Tungsten : Traces:
1. increases hardness
2. reduces melting point
3. act as grain refiner
Manganese & Silicon : Traces:These are added to increase
the fluidity & castability of the alloys.
A.D.A. specification No. 14divides this alloy into two
types, based on fusion temperature (which is defined as
the liquidus temperature):
Type-I (High fusing) –liquidus temperature greater than
1300
o
C.
Type-II (Low fusing) –liquidus temperature lower than
1300
o
C

31. Advantages :
1.Their resistance to corrosion is due to a large percentage
of Chromium present. It quickly forms an inert or passive
chromium oxide (Cr
2
O
3)
layer over it surface.
2.When used, they are most frequently chosen as an
alternative to the nickel-based alloys for patients allergic to
nickel.
Disadvantages:
1.They are more difficult to work with due to their high melting
temperatures which necessitate the use of special casting
equipment such as electrical induction furnace or
oxyacetylene equipment.
2.Their high hardness and low ductility make them difficult to
finish and polish.

32. Comparative properties of Co / Cr alloys and type IV casting gold
alloys for partial denture
Property (Units) Co/Cr Type IV gold
alloy
Comments
Density (g/cm
3
) 8-9 15 Moredifficulttoproducedefectfree
castingforCo/Cralloysbutdenture
frameworksarelighter
Fusion temperature as high
as
1500°C
Normally lower
than 1000°C
Co/Cralloysrequireelectricalinduction
furnaceoroxyacetyleneequipment.
Can notusegypsum bonded
investmentsforCo/Cralloys
Casting shrinkage
(%)
2.3 1.4 Mostlycompensatedforbycorrect
choiceofinvestment

33. Comparative properties of Co / Cr alloys and type IV casting gold
alloys for partial denture (conti)
Property (Units) Co/Cr Type IV gold
alloy
Comments
Proportional limit
(MPa)
710 500 Bothacceptable;canresiststresses
withoutdeformation
Modulus of
elasticity (GPa)
225 100 Co/Crmorerigidforequivalentthickness;
advantageforconnectors;disadvantage
forclasps
Hardness (Vickers) 432 250 Co/Crmoredifficulttopolishbutretains
polishduringservice
Ductility (%
elongation)
2 15 (as cast)
8 (hardened)
Co/Crclaspsmay fracturedif
adjustmentsareattempted.

34. Titanium Alloys
Titanium was discovered in
Cornwall, Great Britain, by William
Gregorin 1791.
And named by Martin.H.Klaproth
after the Titansof Greek
mythology.
The oxide formation property
forms basis for corrosion
resistance and biocompatibility of
this material.
The term 'titanium' is used for all
types of pure and alloyed titanium.
Titanium
Sir.Martin.H.Klaproth

35. The physical and mechanical properties of titanium and its
alloys vary greatly with the addition of traces of other
elements such as oxygen, iron and nitrogen etc.
According to the American Society for Testing and
Materials (ASTM), there are 4 unalloyed grades of
commercially Pure Ti, based on the concentration of :
Oxygen : 0.18-0.40 wt%
Iron : 0.2-0.5 wt%
Nitrogen : 0.03-0.05 wt%
Carbon : 0.1 m%
Hydrogen : 0.015 wt%
The most commonly used and important Ti alloy is Ti-6Al-
4Valloy because of its desirable proportion and predictable
producibility.

36. Uses:
Pure titanium is used for dental implants, crowns, partial
dentures, complete dentures and orthodontic wires.
Composition of Cp Titanium and alloy (wt%)

37. Titanium Alloy:
Alloying elements are added to stabilize alpha or the
beta phase in Ti-6Al-4V.
Aluminum is an alpha stabilizer; whereas
Vanadium, 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 but is
difficult to weld.(used in orthodontics.)

38. Properties.
Most biocompatible material.
High melting & boiling point of 1668°C & 3260°C
respectively.
Highly resistant to tarnish and corrosion due to titanium
oxide layer on its surface.
Relatively light weight.
Low density (4.5 g/cm3)
Low modulus of elasticity: 100 GPa
High Yield strength: 170-480 Mpa.

39. Disadvantages:
Requires expensive equipments: Ti readily reacts with
hydrogen,oxygen and nitrogen at temperatures greater
than 600°C. So casting is done in a vacuum or inert
gas(Argon) atmosphere.
High melting point
High reactivity
Low casting efficiency
Casting porosity.
Difficulty in finishing
Difficulty in welding

40. Properties High Noble Co-Cr Ni-Co CPTi
BiocompatibilityExcellent Excellent Fair Excellent
Density 15 8 9 4.5
Elastic Modulus 90 225 207 103
Sag resistance Poor Excellent Excellent Good
Technique
Sensitivity
Minimal
Moderately
high.
Moderately Extremely
Porcelain BondingExcellent Fair High High
COMPARISON OF PROPERTIES OF DIFFERENT BASE METAL
ALLOYS

41. Conclusion:
Based metal alloys have been used in dentistry since
1930s. Ever since efforts are taken to modify them for our
use.
Metal alloys forms one of the most important class for
providing restorations in prosthodontic treatment
modalities.
Therefore the properties of metal and alloy should be
thoroughly understood and their manipulative details has to
be understood so has to have best results.
Finally it is important for the dentist to remember and take
up the responsibility of being responsible for the safety and
efficacy of any restoration.

42. References:
Anusavice . K .J :Phillips' Science of Dental
Materials,8
th
edition :
Anusavice . K .J :Phillips' Science of Dental
Materials,11
th
edition :
Anusavice . K .J :Phillips' Science of Dental
Materials,12
th
edition :
Craig .R : Dental Materials: Properties and
Manipulation, 8
th
edition
Craig.R : Restorative Dental Materials,13
th
edition.
McCabe .J .F & Wells.G .W .A : Applied Dental
Materials, 7
th
edition
Gladwin .M & Bagby .M : Clinical Aspects of Dental
Materials ,1
st
edition

43. Wataha JC. Alloys for prosthodontic restorations. J
Prosthet Dent 2002;87:351-363.
O’Brien WJ. Dental Materials and Their Selection.
Carol Stream, IL: Quintessence, 1997.

44. Thank You.