BASE METAL ALLOYS IN PROSTHODONTICS

1. SE METAL
ALLOYS

2. 2
CONTENTS
 INTRODUCTION
 HISTORY
 CLASSIFICATION
 REQUIREMENTS
 PROPERTIES
 CAST BASE METAL ALLOYS
 WROUGHT BASE METAL ALLOYS
 DENTAL APPLICATIONS
 REFERENCE

3. INTRODUCTION
In dentistry, metals represent one of the three major classes of materials used for the reconstruction of
damaged or missing oral tissues. Although metals are readily distinguished from ceramics and
polymers.The wide varieties of complex dental alloy compositions consist of the following:
Dental amalgams containing the major elements mercury, silver, tin, and copper.
Noble metal alloys in which the major elements are some combination of gold, palladium, silver and
important secondary elements including copper, platinum, tin, indium and gallium.
Base metal alloys with a major element of nickel, cobalt, iron or titanium and many secondary elements
that are found in the alloy compositions.

4. HISTORICAL PERSPECTIVE ON DENTAL CASTING ALLOYS
Taggart’s presentation: 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
The 20th century generated substantially new changes to dental prosthetic materials. The major factors that
are driving new developments are:
i)Economy→ The new material performs the same function as the old material but at a lower cost.
ii)Performance → The new material performs better than the old product in some desirable way, such as ease
of processing, improved handlinig characteristics, or increased fracture resistance.
iii) Aesthetics → The new material Provides a more aesthetic result, such as increased translucency

5. 5
IDEAL REQUIREMENTS
• Should Not Produce Toxicological Or Allergic EffectS
• Provide Resistance To Corrosion And Physical Changes When In Oral Fluids
• Thermal Conductivity ,Melting Temperatures, Coefficient Of Thermal Expansion Should Be
Satisfactory.
• Use Should Be Feasible.
• Metals ,Alloys And Companion Materials Should Be Abundant, inexpensive And Readily
Available.

6. 6
COMPOSITION
• Cobalt, Chromium, And Nickel (82%-92%)
• Minor Alloying Elements- Carbon, Molybdenum ,beryllium ,tungsten And Aluminum.
• Carbon Upto 0.2 %,-Is Most Critical Small Amounts may Have Pronounced Effect on Strength ,Hardness
and Ductility.

7. 7
PHYSICAL PROPERTIES
1.Melting Temperature – most of the base metal alloys have at 1150-1500 c
•Though One Commonly Used Nickel Chromium Alloy [Ticonium] Melts At 1275C.
•Addition Of 1-2% Beryllium Lowers Melting Temperature Of Ticonium By About 100 c.
2.Density- The Average Density Of Cast Base Metal Alloys Is Between 7-8gms /Cm3
which is half the density of most dental gold alloys.

8. 8
MECHANICAL PROPERTIES
•Yield Strength:
•Gives an indication of when a permanent deformation of a part such as clasp will occur. •Base
metal dental alloys have greater than 600Mpa to Withstand Permanent Deformation When Used As Partial
Denture.
•Tensile Strength:
Greater Than 800 Mpa
•Elongation: Indication Of Relative Brittleness And Ductility. The combined effect of elongation and tensile
strength is an indication of toughness of material.
. • Increasing the nickel content with a corresponding reduction in cobalt generally increases the
ductility and elongation.
• High values of elongation are obtained by casting at the normal melting temperature. High
elongation is achieved without sacrificing strength and is the result of the precise and proper combination of
carbon, nitrogen, silicon, manganese, and molybdenum content

9. 9
HEAT TREATMENT OF BASE METAL ALLOYS
•Reduces The Yield Strength And Elongation.
•Soldering Or Welding Must Be Performed At The Lowest Possible Temperature with shortest possible time
of heating .
•Heat Treatment Of These Alloys At 100 C Upto 1 Hour Did Not Change Their Mechanical Properties.
PASSIVATION
• Elements In Some Base Metal Alloys Have High Affinity For Oxygen
,but The Oxide Film Formed Can Serve A Protective Layer Against Oxidation And
Corrosion. This Formation Of Protective Film By A Reactive Substance Is
Called Passsivation .

10. 10
. BASE METAL ALLOYS
-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 Co-Cr-Mo Surgical
Implant Ni-Cr Co-Cr (Class-III) Fixed Partial denture Be. Cont.(Class-II) No Be. (Class-I)
Base metal Casting alloy
Removable Partial denture Co-Cr
Co-Cr-Ni Ni-Cr Co-Cr-Mo Co-Cr-
Mo Surgical Implant Ni-Cr Co-Cr
(Class-III) Fixed Partial denture
Be. Cont.(Class-II) No Be.
(Class-I)
Base
metal
Casting
alloy
BASE METAL ALLOYS
-Nickel based
-Cobalt based Alloys in both systems contain chromium as the second largest constituent.
A classification of base metal casting alloy

11. 11
Nickel-chromium (Ni-Cr) System
These metal-ceramic alloy offer such economy that they are also used for complete crown
and all metal fixed partial denture prosthesis (Bertolotti, 1983).
The major constituents are nickel and chromium, with a wide array of minor alloying elements.
The system contains two major groups:
-Beryllium free (class 1)
-Beryllium (class 2)
Of the two, Ni-Cr-Beryllium alloy are generally regarded as possessing superior properties
and have been more popular (Tuccillo and Cascone,1984).

12. 12
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. Difficult to solder retention
7. Ingots do not pool
8. Difficult to cut through cemented castings

13. 13
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.

14. 14
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.

15. 15
COBALT-CHROMIUM ALLOYS
COMPOSITION:
Cobalt : 35 to 65%
Chromium : 23 to 30%
Nickel : 0 to 20%
Molybdenum: 0 to 7%
Iron : 0 to 5%
Carbon : up to 0.4%
Tungsten, manganese, silicon and platinum in traces
PROPERTIES OF COBALT CHROMIUM
Cost Lower and good mechanical properties
Density: half that of gold alloys, lighter in weight (8 to 9 gm/cm3)
Fusion temperature: Type-1(high fusing)-liquidus temperature greater than 1300° c
Type-2(low fusing)-liquidus temperature not greater than 1300 °c
Yield strength : higher than the gold alloys
Elongation: ductility is lower
Modulus of elasticity: twice as stiff as gold alloys, casting made thinner,
the weight of the RPD Hardness: harder than gold alloys,cutting,grinding,finishing are difficult
Tarnish and corrosion resistance: Chromium oxide prevents tarnish and corrosion –
passivating effect Caution: hypochlorite denture cleaning cause corrosion ,should not be used to clean chromium based alloys
Casting shrinkage: shrinkage is much greater due to high fusion temperature
Porosity: is due to shrinkage of alloy and release of dissolved gases

16. TITANIUM AND TITANIUM ALLOYS :
✘ The most widely used titanium alloy in dentistry is Ti-6Al-4V (Ti- 10.2Al- 3.6V in atomic percent), which is an α-
alloy.
✘ Titanium derives its corrosion protection from a thin passivating oxide film (approximately 10 nm thick), which
forms spontaneously with surrounding oxygen .Titanium has a high melting point (1668 °C) and high rate of
oxidation above 900 °C.
✘ Greater strength than that of CP Ti.
16

17. 17
ADVANTAGES OF TITANIUM
High strength
Light weight
Bioinert
Low tarnish and corrosion because of ability to passivate
Can be laser welded
Limited thermal conductivity
DISADVANTAGES
Highly technique sensitive
Require expensive machines for casting and machining

18. 18
WROUGHT BASE METAL
ALLOYS
•Stainless Steel
•Cobalt Chromium Nickel
•Nickel –Titanium
•Beta- Titanium

19. 19
STAINLESS STEEL
• This was first discovered by Brearely of Sheffield, England in 1913.
• Stainless steel is an alloy of steel containing minimum of 13% chromium.
• It is chromium which makes the steel resistant to tarnish and corrosion.
FERRITIC (Alpha Form)
• Solid iron in which carbon is insoluble,because of small space in between atoms.
• It has a Body centered cubic structure
• This condition remains from room temperature to 912 C.
AUSTENITE(Gamma Form)
• Exists at Temperature Between 912- 1394 C As Face Centered Cubic Structure
in Which Carbon Is Soluble, Because the Space Between the Atoms Is Larger and So the Carbon Atoms Occupy These Spaces to
Form Interstitial Solid Solution.
MARTENSITE
• a Austenitic Steel at a Temperature Above 912 C Is Suddenly Cooled , It Undergoes Transformation in Its Structure to Form a Body
Centered Tetragonal Structure Called Martensite
• This Change Makes the Metal Hard,strong but Brittle.
.
.

20. 20
USES OF 18-8 STAINLESS STEEL
• In Prosthetics For Partial Denture Clasps ,Bars For Swaged Plates,implants.
• In Orthodontics For Wires, Ribbons, Bands, Bows, Hooks, Springs.
ADVANTAGES OF 18-8 STAINLESS STEEL
• Heat and Corrosion Resistance.
• More Ductile and Can Be Cold Worked.
• Can Be Easily Welded.
• Hardened by Cold Working.
• Can Be Stabilized Against Corrosion.

21. 21
NICKEL- TITANIUM ALLOYS (NITINOL)
COMPOSITION: Ni-54%, Ti-44%, Co-2%
•was introduced in 1972 , characterized by high resiliency,limited
formability,thermal memory
Properties
• Shape Memory effect- it is the ability of the alloy to retain and memorize a
particular shape given to it
• Mechanism of shape memory
Structure of nitinol at room temperature is BCC(austentic phase) when
this is heated it changes to HCP(martensitic phase).This change is responsible
for shape memory effect.
• Superelasticity

22. 22
WROUGHT Co-Cr- Ni ALLOYS (ELGILOY)
COMPOSITION:
CO-40% Mn-2%
Cr-20% C-0.15%
NI-15% Be-0.04%
Mo-7% Fe-15.8%
Excellent Tarnish And Corrosion Resistance.
WROUGHT BETA -TITANIUM ALLOY
COMPOSITION: : Ti-78% Mo-11.55% Zr-6% Sn-4.5%
PROPERTIES: : •Lower Elastic Modulus
•Lower Yield Strength
•Good Ductility
•Good Weldability

23. 23
RECENT ALLOYS
Palladium- Copper- Gallium
Palladium- 75%
Copper- 10%
Gallium- 5-10%
Palladium –Gallium- Silver
Palladium- 80-85%
Gallium- 5-10%
Silver- 0.5-8%
Cobalt-Chromium-Neobium-Molybdenum-Zirconia-
an increased corrosion resistance and overall biocompatibility Co 60% Cr 26.5%
Mo 4.5% Nb 6.0% Zr 0.8%
These alloys have superior mechanical properties.

24. 24

25. 25
Cast Cobalt Chromium Alloys .
( Vitalium &Nobilium).
Partial Denture Framework ,Porcelain Metal Restorations
• Cast Nickel Chromium Alloys
(Ticonium).
Partial Denture Framework Crowns & Bridges Porcelain Metal Restorations
• Cast Titanium and Titanium Alloys
Implants, Crowns, Bridges
• Wrought Stainless Steel
Endodontic Instruments , Orthodontic Brackets ,Preformed Crowns
• Wrought Cobalt- Chromium -Nickel Alloys
Orthodontic wires
Endodontic files
• Wrought Nickel -Titanium Alloys
Orthodontic wires
Endodontic files
• Wrought Beta- Titanium Alloys
Orthodontic wires

26. 26
METALLIC DENTURE BASE MATERIALS
• Used In Clinical Situations Where a Single Maxillary CD Opposes a Partial
Component of Natural Mandibular Teeth. Heavy Masticatory Load Directed in to
a Thin Palatal Resin Plate Which May Result in Denture Fracture.
TECHNIQUE
• Relatively Thin Metal Base Is Cast to Contact Denture Bearing Surface. Acrylic
Resin Is Used to Retain the Denture Teeth and Provide Buccal and Labial Flanges
That Enhances Esthetic Quality .The Processed Resin Is Attached to Cast Metal
Base by a Retentive Meshwork.
• MATERIALS used :
Cobalt chromium alloys, Nickel chromium alloys, Titanium alloys .
Cobalt and nickel containing alloys could be potential allergens ,biological risks
of metal ions being released suggests use of titanium.

27. 27
OTHER APPLICATIONS OF BASE METALALLOYS
•In Surgical Repair Of Bone Fracture .
•Metallic Obturators And Implants.
•Cobalt Chromium Alloys Have Been Implanted Directly Into Bone Structure For Long Periods With Favorable
Response Of The Tissue, Probably Due To Low Solubility And Electro- Galvanic Action Of The Alloy. The Product
Known As Surgical Vitalliun Is Used Extensively For This Purpose .

28. 28

29. 29
REFERENCES:
•Craig R.G., Restorative Dental Materials, 11th Edition, 2002,
India.
•Anusavice, Science of Dental Materials, 10th Edition, 1998,
India
•Micheal McCcracken

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