WROUGHT METAL ALLOYS AND BASE METAL ALLOYS USED IN DENTISTRY

1. PART II
WROUGHT BASE METAL ALLOYS

2. WROUGHT BASE METAL ALLOYS:-
INTRODUCTION
 Wrought alloys are worked and adapted in to
prefabricated forms for use in dental restorations.
(Wrought metal is a cast metal which has been
worked upon, in cold conditions, i.e. without
heating)

3.  Generally all metals and alloys are produced from
castings .
 Casting can be machined, forged, drawn, extruded ,or
mechanically worked in some manner to provide the
required article or appliance ,thereby becoming a wrought
metal .
Strain hardening(work hardening/cold working)
“Increase in strength and hardness and decrease in
ductility of a metal that is caused by plastic deformation
below the re-crystalization temperature”

4. DISLOCATION :-
 If large shear stress is applied across the top and bottom
faces of the metal crystal ,the bonds in the row of atoms
adjacent to dislocation are broken and new bond with new
row is established ,resulting in movement of dislocation by
one interatomic distance.
Continued application of this shear stress causes similar
movements of one interatomic distance untill the
dislocation reaches the boundry of crystal

5.  Cold working creates vast number of dislocations of
atoms within metal –these dislocation interact with
each other, mutually impeding their movements –
increase stress reqired for further dislocation
movement.
 Cold working also alter the shape of the grains and, in
the limit of wire , the grains are severely elongated
parallel to the wire axis.
 If cold work continued heavily deformed metal
fractured-ductile fracture

6. MECHANISMS OF STRENGTHENING IN METALS
1.Strengthening by Grain Size Reduction-
 Grain size can be controlled by the rate of solidification and by
plastic deformation.
2.-Solid-Solution Strengthening
 Adding another element that goes into interstitial or substitutional
positions in a solution increases strength. The impurity atoms
cause lattice strain - "anchor" dislocations.
 occurs when the strain caused by the alloying element
compensates that of the dislocation- costs strain energy for the
dislocation to move away from this state - scarcity of energy at
low temperatures - slip is hindered.
 3.-Strain Hardening

7.  After strain hardening ductility is decreased and
grains are distorted
Reversed by
Recovery heat treatment
Annealing
(controlled heating and cooling process designed to
produce desired properties in a metal)-
1. Recovery
2. Recrystalization
3. Grain growth

8. Recovery:-
regaining of properties of metal-no change in grain
structure-elimination of residual stress.
Recrystalization:-
Process of strengthening and forming a new stress
free crystals in a work-hardened metal-avoided for
orthodontic appliences
Grain growth-
Grain size change from fine to corase -

9. WROUGHT BASE METAL ALLOYS
1Wrought Stainless steel alloys
 Endodontic instruments
 Orthodontic wires and brackets
 Preformed crowns
2.Wrougt Co-cr-ni
 Orthodontic wires and endodontic files
3.Wrought Ni-ti
 Orthodontic wires and endodontic files
4.Wrought Titanium and titanium alloys:-
 Implants
 Crowns
 Bridges
5.Wrought Beta-titanium alloys
Orthodontic wires

10. STAINLESS STEEL-(FE-CR-NI)
 Steel is a iron- carbon based alloy which contains less
than 1.2 percent carbon.
 The term stainless steel is applied to alloys of iron and
carbon that contain chromium, nickel, manganese, and
perhaps other metals to improve properties and give
the stainless quality to the steel.

11. DIFFERENCE B/W CAST BASE METAL ALLOYS AND
STAINLESS STEEL ALLOY
 differ in composition
 Usually, stainless steel alloys are not cast, but instead
are used in the wrought form in dentistry
USES OF STAINLESS STEEL ALLOY:-
 Endodontic instruments
 Orthodontic wires brackets and appliances
 Preformed crowns

12.  These stainless steels are resistant to tarnish and
corrosion, because of the passivating effect of the
chromium.
 A thin, transparent but tough and impervious oxide
layer forms on the surface of the alloy when it is
subjected to an oxidizing atmosphere (air), which
protects against tarnish and corrosion.
 loses its protection if the oxide layer is ruptured by
mechanical or chemical factors.

13. TYPES: SS
 three types of stainless steel based upon the lattice
arrangements of iron.
Ferritic stainless steels:
 Pure iron at room temperature has a body centered cubic
(BCC) structure and is referred to as ferrite-
 stable up to 9120C.
 The ferric alloys have good corrosion resistance-less
strength and hardness- find little application in dentistry.
Composition: Chromium - 15– 25%
Carbon - 0.02%
Silicon and molybdenum

14. Austenitic stainless steels:
 At temperature between 9120C and 13940C the stable form of
iron is a face-centered cubic (FCC) structure called austenite.
 The austenitic stainless steel alloys are the most corrosion
resistant of the stainless steels.
Composition:
Chromium - 18%(13%-28%)
Nickel - 08%
Carbon - 0.08 – 0.20%
Ti, niobium and tantalum is also present
Balance-approx- 72% iron

15.  This alloys is also called as 18-8 stainless steel.
These are used most commonly by the orthodontist
in the form of bands and wires.
 Austenitic stainless steel is preferable to the ferritic
alloys because of;
1. Greater ductility and ability to undergo more cold work without
breaking.
2. Substantial strengthening during cold working.
3. Greater ease of welding.
4. The ability to readily overcome sensitization.
5. Less critical grain growth
6. Comparative ease in forming

16. Martensitic stainless steels:
 When austenite (Face-centered cubic structure) is cooled
very rapidly (quenched) it will undergo a spontaneous,
diffusion less transformation to a body-centered tetragonal
(BCT) structure called martensite-
 highly distorted and strained lattice, which results in a very
hard, strong and brittle alloy.

17.  Composition: Chromium - 12 – 18%
Nickel - 0 – 2.5%
Carbon - 0.15 – 0.25%
 Corrosion resistance of the martensitic stainless
steel is less than that of the other types.
 As having high strength and hardness, martensitic
stainless steels are used for surgical and cutting
instruments.

18. FUNCTIONS OF ALLOYING ELEMENT:--
CROMIUM-
 corrosion resistance-passivation-provides metallic luster
May lost due to-
1. heat treatment(during assembly),
2. alloy composition,
3. surface condition(abrasives) ,
4. stress in the appliance.
 chromium content is less than 13%, the adherent chromium
oxide layer does not form.
 Cr should not be more than 28%- cr oxide form at the grain
boundaries , embrittling the steel.

19.  Mo- increases the resistance to pitting corrosion.
 Carbon content should be in limit otherwise-
sensitization
 There are several methods by which sensitization
can be minimized;-stabilization

20. Sensitization:
 If amount of carbon is not controlled or stainless steel alloy is
heated between 4000 and 9000C, (temperature used during
soldering and welding)- - carbon will react with chromium, forming
these grain-boundary chromium-carbides, which lead to depletion
of grain-boundary chromium and decrease corrosion resistance in
a process known as sensitization

21. Stabilization:
 If we reduce the carbon content of the steel to such an extent
that carbide precipitation cannot occur- not economically
practicable.
 The elements present in small amounts tend to prevent the
formation of carbides between the carbon present in the alloy
and the iron or chromium and, as a result, often are described as
stabilizing elements-
 So stabilized stainless steels contain titanium, niobium, or
tantalum, so the carbides that do form are titanium carbides
and the precipitation of chromium carbide can be inhibited at
soldering temperatures.

22. CHEMICAL RESISTANCE:-SS
 improved if the surface is clean, smooth, and
polished.
 Irregularities promote electrochemical action on the
surface of the alloy.
 Soldering operations on stainless steel with gold and
silver solder may contribute to a reduction in
stainless qualities because of electrogalvanic action
between dissimilar metals or because of localized,
improper composition of the stainless steel wire.

23. RECOVERY HEAT TREATMENT(STRESS-RELIVIEING
TREATMENT)
 An increase in the elastic properties of a stainless steel wire
can be obtained by heating to temperature b/w 400dgr c -500
degr c for 5 to 120 seconds after it has been cold worked.
 It remove the effect of cold working during fabrication
,increase ductility, or promote some degree of hardening with
some alloys.
 It also establishes a uniformity of properties throughout the
appliance after adaptation and fabrication. which may reduce
the tendency towards breakage in service.

24. Manipulation of stainless steel wires and appliances
 Once an appliance is fabricated, it should be heat-treated for 1
minute at 450' C to relieve stresses created during fabrication.
 Soldering or brazing is the process of building up a localized
area with a filler metal or joining to a more metal component
by heating them to a temperature below their solidus
temperature and filling the gap b/w them using a molten metal
with a liquidus temp below 450 deg c.
 Solidus temp-temp at which alloy become solid on cooling and metal
begins to melt on heating.
 Liqidus temp-Temp at which an alloy begins to freeze on cooling or
which the metal is completely molten on heating.

25. WELDING-
“process of fusing two or more metal parts
through the application of heat ,pressure.
or both, with or without a filler metal ,to
produce a localized union across the
interface b/w the parts.”
 In welding fusion of the joined alloy parts
will be occurred while in soldering fusion of
the joined alloy parts does not usually
occur -bonding of the molten solder to the
metal parts result from flow by capillary
attraction b/w parts without appreciably
affecting the dimensions of the joined
structure.

26.  The electric spot welding apparatus produces a
large electric current that is forced to flow through
limited area (spot) on the overlapped materials that
are to be welded.
 The resistance of the material to the flow of current
produces intense localized heating and actual
fusion of the overlapped metals. The weld joints
become susceptible to corrosion, because of
chromium carbide precipitation and consequent
loss of passivation.

27. FLUXES
 Compound applied to the metal surfaces that
dissolve or prevent the formation of the oxides and
other undesirable substances that may reduce the
quality or strength of a soldered or brazed area.
 For stainless steel manipulation –flux are required
during soldering.
 Borax fluxes are not satisfactory- fluoride-
containing flux is required for a successful solder
joint.

28. SOLDERS FOR STAINLESS STEEL:
 Solder is the alloy which is being used in process of
soldering i’e for joining two or more cast or wrought
pieces.
 Silver solders are used:
It is alloy of;
 Silver
 Copper
 Zinc
 Tin
 Indium
 The soldering temperatures for orthodontic silver solders
are in the range of 620 to 6650C-
Adv-lower mp than gold solder-reduce the chance of
overheating the steel during soldering.

29. CLEANING AND POLISHING-SS
 Cleaning and polishing is necessary after soldering,
heat treating or period of service in mouth.
 The appliance is pickled in warmed nitric acid but a
gray satin finish will result-requires buffing or
mechanical brushing with a fine abrasive to restore
the luster of the original material.
 An electrolyte polishing bath ,also k/a anode polisher
–useful to restore the surface appearance

30. MECHANICAL PROPERTIES:
 the stainless steel wire has the highest values of yield strength,
elastic modulus, and spring rate and the lowest spring back
(yield strength/elastic modulus) than ni-ti and beta ti.
 In orthodontic wires, strength and hardness may increased with
a decrease in the diameter because of the amount of cold
working in forming the wire.
 Tensile strength - 2100 MPa
 Yield strength - 1400 MPa
 KHN - 600

32.  Soldering and spot welding can cause a deterioration in
properties if the wire is overheated or under heated.
 The low setting of the spot welder (under heating)
produced an inadequate joint, whereas the high setting
(overheating) caused excessive melting and
recrystallization of the wrought structure of the wire.

33. BRAIDED AND TWISTED WIRES (TRIPLE STANDARD
STAINLESS STEEL):
 Very small diameter stainless steel wires (about 0.16 mm) can
be braided or twisted together to form either round or
rectangular shaped (about 0.4 to 0.6 mm in cross section) wires.
 These braided or twisted wires, are able to sustain large elastic
deflections in bending, and apply low forces for a given
deflection when compared with solid stainless steel wire.

34.  K file and reamers are manufactured by machining
a stainless steel wire into a pyramidal blank, either
square or triangular in cross section, and then
twisting the blank to form a spiral cutting edge.
 Similar to orthodontic wires, mechanical properties
of endodontic files are dependent upon file
geometry,direction of loading and material
composition

35.  Sterilization by dry heat or salt has no effect on the
cutting ability of stainless steel files, but autoclave
sterilization causes a reduction.
 Irrigants such as sodium hypochlorite, hydrogen
peroxide, and EDTA-urea cause a reduction in cutting
ability, whereas a saline irrigant does not cause a
reduction in cutting ability.
 These solutions, excluding saline, also corrode
stainless steel at room temperature-irrigants should
be rinsed from the instruments as soon as possible
after use.

36. NICKEL-TITANIUM ENDODONTIC
INSTRUMENTS(NI-TI FILES)
 contain about 56% Ni and 44% Ti by weight, which
calculate to be 50% of each by atoms. In some
instances, <2% of cobalt may be substituted for nickel
 Can change their structure from austenitic (body-
centered cubic) to martensitic (close-packed
hexagonal) as a function of stress during root canal
preparation.
 the modulus of Ni-Ti austenite is 120 GPa, and that
of martensite is 50 GPa. This effect results in what is
termed super-elasticity,

37.  Ni-Ti alloys have higher strengths and lower moduli of
elasticity than stainless steel.
adv- in preparing curved root canals.
 Ni-Ti and stainless steel endodontic files do not differ
with respect to corrosion resistance-effectively used
as engine-driven, rotary instruments.

38. BASE-METAL PREFABRICATED CROWNS
 Stainless steel crowns were introduced in 1950 and are
recommended for the permanent restoration of primary
teeth.
 The mechanical properties of stainless steel and nickel-
based materials are similar- high ductility is important in
the clinical adaptation of the crowns.
 tin based and aluminum based alloys used for
temporary prefabricated crowns have high ductility, but
are soft and have lower yield and tensile strengths and
thus do not resist clinical wear as do the stainless steel
and nickel-based types.

40. WROUGHT COBALT CHROMIUM NICKEL ALLOYS:
 These wrought alloys were originally developed for use as
watch springs (Elgiloy).
 Elgiloy is a cobalt-chromium-nickel alloy - available in wire and
band form for various dental appliances.
Composition:
Co - 40%
Cr- 20%
Ni- 15%
Mo - 7%
Mn - 2%
C - 0.15%
Be - 0.4%
Fe - 15.4%

41. Heat treatment-
 The standard heat treatment ,similar to the treatment used to
relive stress in a stainless steel wire is 482 dgr c for 7 min.
Properties:-
 Proportional limit-1610mpa;.2%
 Yield strength-1930mpa
 Tensile strength-2540 mpa
 Vickers hardness number-700kg/mm squire

42. NICKEL-TITANIUM ALLOYS:
 These nickel-titanium alloy (Nitinol) wires have large elastic
deflections or working range and limited formability, because of
their low stiffness and moderately high strength.
 The industrial alloy is 55% nickel and 45% titanium and
possesses a temperature transition range (TTR).
 At temperatures below the TTR, the alloy
can be deformed plastically.

43.  This alloy exists in various crystallographic forms. At
high temperature stable body centered cubic lattice
(austenitic phase) exists.
 On appropriate cooling, or on application of stress, this
transforms to a close-packed hexagonal martensitic
lattice, associated with volumetric change.
 These characteristics of the austenite to martensite
phase transition results in two features of clinical
significance called as shape memory and
superelasticity, or pseudoelasticity.

44. PROPERTIES:-NI-TI
 Ni-ti has lowest elastic modulus and yield strength but
highest spring back.
 High spring back is important if large deflections are
needed such as poorly aligned teeth.
 highest resiliency in bending and torsion of the three
alloy(stainless steel ,ni-ti, beta ti) used for orthodontic
wires.
Clinical implication-Low elastic modulus and high
resiliency-more constant forces can be applied with
activations and an increased working range.
 Disadv-hard to bend and cannot be soldered, welded, or
heat treated.
.

46. WROUGHT BETA-TITANIUM
 Ti-Mo alloy-introduced at 1979
 Cp ti is hexagonal closed-packed(hcp) crystal
lattice k/a alpha phase
883 deg c
Body centered cubic (bcc)-beta phase
Stronger but brittle than alpha phase
 Beta form of titanium can be stabilized at room temp by
alloying with certain elements-

47. Composition :-
Ti -78%
Mo -11.5%
Zr -6%
Sn -4.5%

48. PROPERTIES- BETA TI
 Can be shaped easily, and wires can be soldered and
welded.
 Compared with SS and eligiloy wires beta ti has-
1. lower force magnitude, a
2. lower elastic modulous ,
3. higher spring back, a
4. lower yield strength and
5. good ductility, weldability and corrosion resistance.
 Its formability and weldability are advantages over nitinol
and it has large working range over stainless steel and
eligiloy wires.

50. RECENT ADVANCEMENTS
 Recent orthodontic wires include a titanium based alloys
–Ti-15V-3Cr-3Al-3Sn
Offers a yield strength/modulus ratio slightly grater than
that of beta Ti.
 Monel metal is alloy of Cu and Ni used for equipment
part because of its good physical property and resistance
to tarnish and corrosion.
Composition- approximately 28% copper, 68% nickel, 2%
iron, 1.5% manganese, and 0.2% silicon.

51.  An experimental Co-Cr alloy with addition of 4% to
6% Ti has been developed and reported to have
better fatigue resistance than the Co-Cr alloy alone.
 Zr-Pd-Ru-provide good wear resistance.
 The 30Ni-30Cu-40Mn alloy is an experimental
base-metal casting alloy.

52. CONCLUSION
 Many metals, such as tantalum, molybdenum,
columbium, vanadium,and gallium, are becoming
available in increasing quantities. These metals and
their alloys, along with chromium, nickel, cobalt,
titanium, stainless steel, and various copper,
aluminum, or magnesium alloys, may be developed
to possess physical and chemical qualities that
satisfy the requirements of various dental
applications.

53. REFERENCES
 Science of dental materials. Skinner, 9th Ed.
 Restorative dental materials. Craig, 10th Ed.
 Fundamentals of fixed prosthodontics. H.T. Shillingburg,
3rd Ed.
 Contemporary fixed prosthodontics. Rosenstiel, 3rd Ed.
 Theory and practice of fixed prosthodontics. Tylman, 8th
Ed.
 Dental material and their selection. J.O. Brien, 2nd Ed.
 Materials in dentistry. Jack L. Ferracane.
 Phillips science of dental material

56. BASE METAL ALLOYS
DR. KAUSHIK KR. PANDEY

57. INTRODUCTION
Alloys:-
 a mixture of two or more
metals or metalloids that are
mutually soluble in the molten
state; distinguished as binary,
ternary, quaternary, etc.,
depending on the number of
metals within the mixture.
Alloying elements are added
to alter the hardness,
strength, and toughness of a
metallic element, thus
obtaining properties not found
in a pure metal. GPT

58.  Casting alloys are used in the process
by which a wax pattern of a restoration
is converted to replicate in a dental
alloy.
 Wrought alloys are worked and
adapted in to prefabricated forms for
use in dental restorations.
(Wrought metal is a cast metal which has been
worked upon, in cold conditions, i.e. without
heating)

59.  Tarnish is surface discoloration on metal or even
slight loss or alteration of surface finish or lusture.
 Eg- formation of hard and soft deposits on the
suface of restoration-calculus,plaque,mucin
 Stain and formation of thin films of oxides,sulfides or
chlorides.
 Passivation-
In certain cases oxide film is protective in nature.
Eg-cr alloys are protected from corrosion by the
formation of an oxide layer on its surface-protect the
metal from further corrosion.

60. Corrosion:-
 it is not a surface
discoloration but actual
deterioration of metal by
reaction with the
environment
 Water, oxygen, chloride
ion ,sulfides like hydrogen
sulfide or ammonium
sulfide contribute to
corrosion attack in the oral
cavity.eg-formation of
sliver sulfide in dental
alloys containing silver.

61. NOBLE METALS
 Gold
 Platinum
 Palladium
 Rhodium
 Ruthenium
 Iridium
 Osmium
Resistance to oxidation, tarnish and corrosion during heating , casting,
soldering and in the mouth.
All noble metal alloys are based on gold or palladium as the principal
noble metal by weight percentage.

62. BASE METALS
 Ni-nickel
 Cu- copper
 Zn-zinc
 Ga-gallium
 Ag-silver
 Sn -tin
 In-indium
Invaluable components of dental casting alloys because of their low cost and
their influence on weight , strength, stiffness , and oxide formation(which is
required for bonding to porcelain)
Compared with noble metals, base metals are more reactive with their
enviournment-Co and Ni based alloy derived their corrosion resistance from the
passivating effect of chromium .

63. ELEMENT SYMBOL ATOMIC ATOMIC DENCITY MT COLOR COMMENTS
NUMBER MASS (G/CC) (O C)

64. Nickel(Ni) :-
 increases strength and hardness of alloy.
 White in color.
Tin(Sn):-
 Lustrous, soft, white metal –not subjected to tarnish and
corrosion in normal air.
 Some gold-based alloys contain limited quantities of tin, usually
less than 5% by weight.
 It combines with Pt and Pd to produce hardening effect-Also
increases brittleness.

65. Silver (Ag):-
 malleable , ductile, white metal
 common in gold- and palladium-based dental alloys
 Best known conductor of heat and electricity.
 stronger and harder than Au-softer than Cu
 Combines with sulfur, chlorine , phosphorous, and vapors
containing these elements or their compounds.
 Food containing Sulfur compounds causes severe tarnish
on silver-base metal

66. Cupper(Cu):-
 Malleable and ductile metal
 important component of noble dental alloys. When
added to gold-based alloys, copper imparts a
reddish color to the gold and hardens the alloy-40-
80%by wt
 Good conductor of heat and electricity
 Red in color
 In palladium based alloys it reduces the MP,
strengthen the alloy-15-55wt%

67. Zinc (Zn):-
 Blue-white metal
 Tendency to tarnish in moist air.
 In pure form soft, brittle metal with low strength.
 Acts as scavenger of oxygen when alloy is melted-deoxidizing
agent(1-2%)
 Because of its low density, the resulting zinc oxide lags behind the
denser molten mass during casting, and is therefore excluded from
the casting.
Gallium (Ga)
 Grayish metal-stable in dry air but tarnish in moist air.
 Has very low MP-29.8OC, Density -8.91 g/cm 3

68.  Gallium is not used in its pure form in dentistry, but is used as
a component of some gold- and palladium-based dental
alloys.
 oxides of gallium are important to the bonding of ceramic to
the metal
INDIUM (IN):-
 soft gray-white metal, with low MP-156O C
 not tarnished by air or water.
 Used in some gold alloys as replacement for Zn
 Recently indium has been used in greater amounts to(up to
30 % by weight) to impart a yellow color to Pd-Ag alloys.

69. “What we will be tomorrow is because of what we
are today, and what we are today is because of
what we were yesterday.”

70. HISTORY:-
 20Th century generated many changes in the dental
prosthetic materials
 Main factors that are driving new developments are
Economy
Performance
Aesthetics

71. PROCESS IN WHICH A WAX PATTERN ,PREPARED IN THE SHAPE OF MISSING TOOTH
STRUCTURE ,IS EMBEDDED IN A CASTING INVESTMENT AND BURN OUT TO
PRODUCE A MOLD CAVITY IN TO WHICH MOLTEN METAL IS CAST.
 Taggart – 1907 –
Demonstrated -Lost
wax technique

72.  The lost wax technique described by Taggart was an instant
success and it soon lead to the casting of complex
restorations such as inlays, onlays, crowns, fixed partial
dentures and removable partial denture frameworks.
 At the beginning of the twentieth century when dental casting
was evolving ,the alloys were predominantly gold based.
 In 1932 the dental materials Group at the National Bureau of
Standards surveyed the casting -gold alloys being used and
roughly classified them as a Type I, II, III and IV.

73.  Because pure gold did not have physical properties required for
those dental restorations existing jewelry alloys were quickly
adopted. These gold alloys were further strengthened with
copper, silver or platinum.
 At that time it was felt that alloy with a gold content ˂65% -
75% tarnished too easily in oral cavity.

74.  In 1948-palladium is added as substitute for platinum to
counteract the tarnish potential of silver, allowed the
alloys with a lower gold content to be used successfully.
 The base metal removable partial denture alloys were
introduced in the 1930s -(ni-cr and co-cr in compare
with type IV casting- gold alloys).

75.  1959-PFM PROCESS-
Successful veneering of a
metal substructure with dental
porcelain
 1978- the price of gold was
climbing so rapidly attention
focused on experimentation with
base metal alloys like ni-cr and
co-cr-to reduce the precious noble
metal content and yet retain the
advantages of noble metals for
dental use.

76. CLASSIFICATION: BASED ON FUNCTION :
Classification of gold-based casting alloys-ADA -
5(1932)
 Type-1 –soft-low strength – Very slight stress- for
inlays
 Type-II–medium-Medium strength-moderate stress-
inlays, Onlays & full crowns
 Type-III-hard-High strength–High stress Onlays,
thin copings, pontics, crowns & full crowns
 Type-IV-extra hard-Extra high strength – Very high
stress-Saddles, bars, clasps, certain single units,
and partial denture frameworks

77.  Classification-ADA(1984)

78. RECENT ADA-5 CLASSIFICATION
Alloys Type Total Metal Content
1 High Noble Alloys Noble metal content ≥ 60% (
Gold + Platinum group) & Gold
≥ 40% )
2 Titanium &
Titanium Alloys
Titanium ≥ 85%
3 Noble Alloys Noble Metal content ≥ 25%
(Gold + Platinum group)
4 Predominantly Base
Metal Alloys
Noble metal content ≤ 25% (gold
+ Platinum group)

79.  Based on Description:
 1. All metal
 2. Metal ceramics
 3. Cast Partial Denture.
 4. Implant.

80. BASE METAL ALLOYS

81. DESIRABLE PROPERTIES OF
DENTAL CASTING ALLOYS
 BIOCOMPATIBILITY
 CORROSION RESISTANCE
 ALLERGENIC COMPONENTS IN CASTING ALLOYS
 ESTHETICS
 THERMAL PROPERTIES

82.  MELTING RANGE
 COMPENSATION FOR SOLIDIFICATION
 STRENGTH REQUIREMENTS
 CASTABILITY
 FINISHING OF CAST METALS
 PORCELAIN BONDING
 ECONOMIC CONSIDERATIONS

83. CAST BASE-METAL ALLOYS ACCORDING TO
DENTAL APPLICATION
1.Cast Co-cr-
 Removable partial denture frame work
 Ceramic-metal restoration
2. Cast Ni-cr-
 Removable partial denture framework
 Crowns and bridges
 Ceramic-metal restoration
3.Cast Titanium and titanium alloys-
 Crowns
 Bridges
 Removable partial-denture framework
 implants

84. CAST BASE METAL ALLOYS FOR
REMOVABLE PARTIAL DENTURE
FRAMEWORK

85. Additional requirement for rpd frame work alloys-
 Should be light in weight
 Should have high stiffness-prevents bending from
high occlusal load.
 Should have good fatigue resistance-important for
clasps.

86. CO-CR AND NI-CR CASTING ALLOYS
 Currently, almost all the metal frame works of
removable partial-dentures appliances are made from
Co-Cr or Ni-Cr alloys.
 Cr,Co,Ni compose about 85% of the total weight of
these alloys.
 Physical properties of these alloys are controlled by
the presence of minor alloying elements such as
carbon,molybedenum,beryllium,tunguston,magnese,ni
trogen,tantulum,gallium and aluminum

87. COMPOSITION:-
Ni-Cr ALLOYS:-
 Major components are about 70% nickel and 16%
chromium.
 Important minor components are about 2% aluminum and
0.5% beryllium.
 Other minor elements include molybdenum, tungsten,
manganese, cobalt, silicon, and carbon
 Aluminum and nickel form an intermetallic compound
(Ni3Al) that contributes to strength and hardness, and
beryllium lowers the melting range, enhances fluidity, and
improves grain structure.

88. CO-CR ALLOYS:-
 Also k/a stellite-shiny star like
 The major constituents are about 60% cobalt and 25% to
30% chromium,
 They may also contain minor quantities of molybdenum,
aluminum, tungsten, iron, gallium, copper, silicon, carbon,
and platinum.
 Possess high strength and excellent corrosion resistance.
 Manganese and silicon enhance fluidity of the molten
alloys; molybdenum, tungsten, and carbon are the
principal hardening and strengthening elements.

89. CROWN AND BRIDGE CASTING ALLOYS
 Castings of chromium-containing alloys are used as
substructures for porcelain-veneered fixed
restorations and, to a lesser extent, as all-metal
restorations.

90. NI-CR ALLOYS:-
 with beryllium or without beryllium.
 Available nickel-chromium products contain 62% to 82%
nickel and 11% to 22% chromium, 2-14% molybdenum.
 Common minor constituents are , aluminum, manganese,
silicon, cobalt, gallium, iron, niobium, titanium, and
zirconium.
 Beryllium, in amounts ranging from 0.5% to 2% by
weight, is a constituent of several commercial alloys.

91. CO-CR ALLOYS:-
 Typically, these products contain about 53% to 65% cobalt
and about 27% to 32% chromium.
 Some members of the cobalt-chromium alloy family
contain 2% to 6% molybdenum.
 Other minor components include tungsten, iron, copper,
silicon, tin, manganese, and ruthenium, a platinum group
metal.

92. FUNCTION OF VARIOUS ALLOYING COMPONENTS
OF NI-CR AND CO-CR ALLOYS:-
CROMIUM:-
 Passivity-tarnish and corrosion resistance.
 reduces m.pt.
 if content is more than 30%-difficult to cast and σ phage-brittle
phage is formed
CR should be less than 28-29%

93. COBALT :-
 Ni and co are interchangeable elements.
 Co increases the elastic modulus, strength, and hardness of the
alloy more than does the Ni.
CARBON :-
 Increase hardness of co based alloys .
 Up to-.4%,if increased .2 % over desired amount, alloy become
too hard and brittle and if decreased .2% it can also not be used
as it reduces tensile strength and yield strength .
 All most all elements in these alloys react with carbon to form
carbides, which changes the properties of alloy.

94. MOLYBDENUM:-
 - 3-6%
 contributes to the strength of the alloy.
ALUMINUM :-
 Forms a compound with Ni-(Ni3Al)-increases the tensile
strength and yield strength of the alloy

95. SILCON AND MAGNESE:-
 Added to increase the fluidity and castability of these
alloys.
BERYLLIUM:-
 Addition of 1-2% be in Ni based alloys lowers the
fusion range by about 100deg c
 ductility and corrosion resistance is compromised if
amount is increased.

96. PHYSICAL PROPERTIES:-
Melting temperature:-
 Higher (1150o -1500 o ) than gold based alloys(800o -1050 o
)
 Melting temp is important in selection of casting equipment
,investment, and control of casting technique.
Density :-
 b/w 7-8 gram/cm 3
 Half the density of most dental gold alloys.

97.  More density-more bulky appliance-in case of maxillary
appliances relative weight of casting to place additional force
on the supporting teeth
 Lower density of cast base metal alloys can be considered
as advantage
Casting shrinkage:-
 Linear casting shrinkage is relatively high, 2.05% to 2.33%-
more than gold alloys-greater mould expansion is needed to
compensate for this.
Color:-
 Polished cobalt-chromium and nickel-chromium prostheses
are lustrous and silvery white.

98. MECHENICAL PROPERTIES
HARDNESS:-
 380-340kg/meter square.
 about 1/3 greater than gold alloys(220-250).
 ADV-ease of finishing and resistance to scratching in service.
 Disadv-requires different polishing equipments and
compounds.
POLISHING-
 done by electrolyte polishing-alloy to be polished is
made the anode.

99.  Cast base metal restoration are deplated and only a very
small amount of alloy(a few angstrom) is removed from the
surface.
 The deplating exposes a new surface which is soother than
a cast surface.
FATIGUE:-
Co-Cr alloys possess superior fatigue resistance.

100. ELASTIC MODULUS:-
 186-218 gpa.
 Elastic modulus is double the modulus of type IV cast dental gold
alloys.
 Higher the elastic modulus –rigid the structure-can make thinner
copings and lighter castings.
ELONGATION:-
 Chromium-type alloys are quite brittle.
 Available cobalt-chromium alloys exhibit elongation values
of 1% to 2%.
 cobalt-chromium-nickel alloy, which contains lesser
amounts of molybdenum and carbon than the other cobalt-
based materials, shows an elongation of 10%.
 Increasing the Ni content in Co-Ni-Cr alloys increases the
ductility and elongation.

101. TENSILE STRENGTH:-
 Greater than 800mpa
 hardened partial-denture gold alloys can have ultimate tensile
strengths almost equal to those of cast base-metal alloys.
YIELD STRENGTH:-
 Dental alloys should have at least 415mpa to withstand
permanent deformation when used as partial denture clasps
 Base metal alloys have yield strength greater than
(644mpa-700mpa) gold based alloys(480-510)

103. CHEMICAL PROPERTIES
 Exhibit a reasonable degree of intra-oral corrosion
resistance.
 The surfaces of these alloys are made passive in air
by the spontaneous development of a thin,
transparent, and contiguous chromium oxide film

104. SOLDERING-
 Modification or repair of a cobalt-chromium-molybdenum RPD
framework should not be accomplished with a different alloy
(cobalt-chromium-nickel, for instance).
If a gold braze were used to join these dissimilar alloys, the
least noble component (cobalt-chromium-nickel) would undergo
corrosion in a galvanic couple with the gold brazing alloy.
 Base metal alloys are much more difficult to solder than gold
alloys
 All chromium-type alloys are attacked vigorously by chlorine;
household bleaches should not be used for cleaning appliances
made from chromium alloys.

105. DISADVANTAGES OF CAST BASE METAL
ALLOYS
 Allergic responses to the constituents of base metal alloys,
especially nickel, are observed occasionally- incidence of
allergic sensitivity to nickel has been reported to be from 5
to 10 times more in females has in males.
 Most adverse tissue reactions attributed to the wearing of a
base metal removable prosthesis, however, are
manifestations of improper design or poor fit.

106.  Clasps cast from relatively non-ductile base metal alloys can
break in service; some break within a short period of time.
 Apparently, fatigue causes clasp failure. When tested in the dry
state, cobalt-chromium-molybdenum specimen bars can
sustain 78,000 loading cycles. Similar tests performed in
artificial saliva or water show resistance to fatigue up to 59,000
and 36,000 loading cycles, respectively.


107.  Minor but necessary adjustments required on delivery of
a base metal RPD can be made difficult by the alloy's
high hardness, strength, and accompanying low
elongation-consume inordinate amounts of the dentist's
valuable chair time.
 High hardness of the alloy can cause excessive wear of
restorations or natural teeth that contact the cast
framework.

108.  Beryllium is toxic metal - main risk occurs primarily in the
vapor form ,which is concern for technician who melt and
cast large quantities of Ni-Cr-be alloys without adequate
ventilation or fumes hoods in the melting area- berylliosis
of lungs
 Occupational safety and health administration(osha)-
recent content of beryllium should be less than .02%-
drastically impact the marketability of beryllium-containing
alloys.

109. SURGICAL BASE METAL ALLOYS
 Bone plates , screws, various fracture appliances, and
splints, metallic obturators and implants for various
purposes can be formed from cast base-metal alloys.
 Two chromium-type alloy systems are available.
1. about 60% cobalt and 32% chromium (Vitallium,
Austenal Dental)
2. about 54% nickel, 25% chromium, and 15% cobalt
(Surgical Ticonium, Ticonium).

110.  Chromium-type surgical alloy systems employ about 4%
molybdenum, 0.5% silicon, and 0.6% iron, manganese and
carbon.
 These can be implanted directly in to the bone structure for
long periods without harmful reactions-due to low solubility
and inert behavior of metal .
 Primary metal today used for oral implant logy is titanium.

111.  Failure can be seen due to corrosion and release of
metal ion -can affect various organs.
 Large metallic implants are more likely to elicit signs
of clinical failure than are smaller ones.
 Sharp edges and protuberances can injure
intervening soft tissue. Movement of the implant
resulting from improper stabilization may produce
painful bursae (fluid filled cyst formed due to friction)
and decubitus ulcers (inflammation caused by
pressure).

112.  Continued irritation by corrosion or movement can
cause pain, swelling, and necrosis, thereby
necessitating removal of the implant.
 Complete rejection is manifested by the formation of
fistulae or by frank extrusion.
 The most toxic individual alloying elements are
hexavalent chromium > nickel > cobalt.

113. COMMERCIALLY PURE TITANIUM AND ITS
ALLOYS
 The following features make commercially pure (cp)
titanium an attractive alternative to chromium-type
surgical, RPD, and FPD alloys:
1. low cost, low density, good
2. mechanical properties that resemble those of hard and
extra hard casting gold.
3. high corrosion resistance, and remarkable
biocompatibility.
Titanium forms a very stable oxide layer with a thickness
on the order of angustram-provides corrosion resistance
and biocompatibility to the titanium.

114. USES:-
 Dental implants, surface coatings.
 recently for crowns.
 partial denture frames.
 complete dentures bases.
 Wrought alloys of Ti and Ni and Ti and Mo are used for
orthodontic wires.
 In surgical cases –artificial hip joint, bone splints,
artificial heart pumps, artificial heart valve
parts,pacemaker cases.

115. COMMERCIALLY PURE TITANIUM(CP TI)
 Commercially pure Ti disclaims 100% purity and
acknowledges that small amounts of oxygen (0.18%
to 0.40% by weight) and iron (0.20% to 0.50% by
weight) are combined with titanium.

116.  Cp ti is hexagonal closed-packed(hcp) crystal lattice
k/a alpha phase
883 deg c
Body centered cubic (bcc)-beta phase
Stronger but brittle than alpha phase

117. TITANIUM ALLOYS(TI-6AL-4V)
 Titanium alloys of interest include Ti-30Pd, Ti-20Cu, Ti-
15V, and Ti-6Al-4V.
 Alloying other metals with titanium enables attainment of
the benefits of lower melting and casting temperatures.
Also, it provides a means to stabilize, or expand, either
the alpha phase field or the beta phase field.

118.  At room temp- it is a two phase ( +ß) alloy
 In Ti-6Al-4V, aluminum is an alpha stabilizer because it
increases the ( +ß) to ß transformation temperature and
thereby expands the phase field
 vanadium, cupper and palladium expand the beta phase
field by decreasing the ( +ß) to ß transformation
temperature.

119.  In gernal alpha Ti is weldable but difficult to form or
work with at the room temperature while beta Ti is
malleable at room temperature –used in
orthodontics.
 The mechanical properties of (alpha+beta) titanium
alloys are depicted by the amount size ,shape ,and
morphology of alpha phage and density of
alpha/beta interfaces.

120. CAST TITANIUM
 Due to high melting point (1700 deg c) and chemical
reactivity ,special melting procedures, cooling cycles, mold
material, and casting equipment to prevent metal
contamination are required.
 Titanium reacts with hydrogen, oxygen, and nitrogen at high
temperature (˃600 dgr c) so during manipulation vacuum is
required.
 If contaminated- oxigen enriched and hardened surface
layer of 100micron meter is formed.-ductility and strength
decrease –cracking
 Tech required to overcome these factors makes ti
expensive.

121.  Investment materials using a combination of ZrO2
type face coat that is backed up a phosphate
bonded silica investment or phosphate investment
material involving silica fillers(ZrO2,AL2O3,MgO)

122. SURFACE COATED TITANIUM
 The newer implant design use titanium that is
coated with a material that bonds and promotes
bone growth (bioactive).-thin layer of tricalsium
phosphate or hydroxyappetite or has been plasma
sprayed.

123. PROPERTIES OF COMMERCIALLY PURE
TITANIUM
 Mechanical properties of cp Ti is similar to type 3 and
type 4 gold alloys and alloy TI-6AL-4V have properties
same as co-cr and ni-cr alloys except for modulus.
 Density of CP Ti -4.5g/cm cube and modulus -100 Ga
is about half the value of the other base metals.
 Yield strength-170 to 480 mpa.
 Color- white in color.

124.  Melting point-high-approx-1668 degree c
 Modulus of elasticity-100gpa –makes it only half
rigid as base metal alloys –this appears sufficient
for more dental use.
 Coefficient of thermal expansion-low(8.4X10-6
/degr c)
Low fusing porcelains have been develop for this to
be compatible with porcelains.