Applied Dental Material Second Year

1. ‫بسما اهللا الرحنمنا الرحمي ِ‬
‫ِ ِنمْ ِ ِ َّ ِنمْ ِ َّ ِ م‬
‫}وحاحللَدْ عقدة مل ن لسنان ي‬
‫ِناَ َدْقُ قُ َدْ ِناَ م ً ِّ ِّ ِناَ يِ‬
‫}يفقهوحا قول ي }82‬
‫ِناَ َدْ ِناَ قُ ِناَ َدْيِ‬
‫}72‬
‫ا الﻌﻅﻳما ا صدقا اهلل‬

2. Dental Casting Alloys II
Cast ‫ا‬Base ‫ا‬Metal ‫ا‬Alloy

3. Alternatives to Gold Alloys





Due ‫ا‬to ‫ا‬continuous ‫ا‬increased ‫ا‬price ‫ا‬of ‫ا‬gold, ‫ا‬
alternative ‫ا‬dental ‫ا‬casting ‫ا‬alloys ‫ا‬has ‫ا‬been ‫ا‬
introduced ‫ا‬for ‫ا‬Types ‫ا‬III ‫ا &ا‬IV ‫ا‬gold ‫ا‬alloys ‫ا‬
such ‫ا‬as:
Economy ‫ا‬gold ‫ا‬alloys
Silver ‫ا‬palladium ‫ا‬alloys
Palladium ‫ا‬silver ‫ا‬alloys
Base ‫ا‬metal ‫ا‬alloys

4. Definition:
Cast base metal alloys which do
not contain noble metals.
They are substitutes for gold
alloys type III & IV.

5. Uses in Dentistry
1. Removable partial denture framework.
2. Full denture bases.
3. Crown and bridge.
4. Dental implants.

6. Base Metal Alloys Used in Dentistry



Cobalt ‫ا‬chromium ‫ا‬alloy
Nickel ‫ا‬chromium ‫ا‬alloy
Titanium ‫ا‬and ‫ا‬titanium ‫ا‬alloys

7. Cobalt Chromium Alloys
Composition:
Major elements 90% by weight
Minor elements 10% by weight
1. Molybdenum: 3- ‫ا %6ا‬by ‫ا‬weight.
1. Cobalt: 35-65% ‫ا‬by ‫ا‬weight.
2. Silicon and Manganese.
2. Chromium: 28- ‫ا %03ا‬by ‫ا‬weight.
3. Nickel: 0-30% ‫(ا‬It ‫ا‬is ‫ا‬used ‫ا‬interchangeably ‫ .3 ا‬Carbon: 0. ‫ا %2ا‬by ‫ا‬weight.
with ‫ا‬Cobalt).
It is a substitute for Type IV gold alloy

8. Nickel Chromium Alloys
Composition:
Minor elements 10% by weight
Major elements 90% by weight
1. Nickel: 70-80%
2. Chromium: 12-20%.
1.
2.
3.
4.
Molybdenum: 3- 6%
Aluminum: 2-6%
Silicon and Manganese.
Beryllium: 0.5%.
It is a substitute for Type III gold alloy

9. Role of each element:
Major elements:
1- Cobalt
2- Nickel
Strength
Hardness
Modulus of elasticity
Strength
Hardness
Modulus of elasticity
Ductility
Nickel is allergic [female>male]
Therefore nickel free base metal alloys has been introduced

10. 3- Chromium:
It increases tarnish &corrosion resistance by formation of
passive layer
M
[oxide layer with specific properties]
M
a
A
j
o
r
Passive layer:
a- Thin
b- Uniform
c- Non porous
d- Adherent
e-Transparent

11. Minor Elements:
•
To increase strength, hardness & decrease ductility:
-Molybdenum as grain refiner
-Carbon 0.2% as discontinuous precipitate in the grain boundaries
-Aluminum reacts with nickel forming intermetallic compound
which precipitates inside the solid solution alloy
This causes precipitation hardening
•
To improve cast-ability:
-Silicone & Manganese
*Increase fluidity of molten alloy
*Act as deoxidizer
-Beryllium
*Decrease the melting temperature
Beryllium vapor is carcinogenic and may lead to fibrosis of the lungs.
Therefore many alloys are available now free of beryllium.

12. Carbon content is very critical
•If it is more than 0.2%
continuous carbide precipitation at the grain boundaries
Strength
Hardness
The alloy can not be used in dentistry
Ductility

13. Avoid carbon pick up by avoid using:
carbon containing investment
carbon crucible for melting
improper adjusted flame
ordinary casting atmosphere
Therefore we should use:
carbon free investment
ceramic crucible for melting
proper adjusted flame (acetylene & oxygen)
vacuum casting atmosphere

14. Pure Titanium and Titanium Alloys:
Composition:
1-Pure titanium:
There are 4 grades of pure
titanium according to:
N.B .Titanium has the property of allotropy
Its atoms are arranged in different
crystalline forms by changing the
surrounding temperatures
Oxygen 0.18- 0.4%
Iron 0.2- 0.5%
885°C
α Form
Stabilizer is aluminum
β form
Stabilizers are copper, palladium
and vanadium aluminum
Therefore titanium alloys have been introduced to stabilize either α , ß or both
to get different properties

15. CobaltNickelTitanium
chromium chromium
Biocompatibility
Nickel allergic
Gold type
III
IV
nobility
Beryllium vapor is carcinogenic
Excellent due to the presence
of Passive layer
Excellent due
to presence of
noble metals
Gold
Resistance to
tarnish &
corrosion
Re-passivate
in
nanosecond
if is
scratched
70% 65%
Pt 1% 2%
Pd 3% 3%

16. Cobaltchromium
Physical properties
Nickelchromium
Titanium &
Titanium
alloys
Color
Lustrous silvery white ,if properly finished
& polished
Melting temperature
Higher than gold
.˙.- Need complicated & expensive
technique for melting
- Highly reactive to atmosphere
. ˙.Vacuum casting is essential
Sag resistance during
-soldering
-ceramometallic
restoration
Higher sag resistance than gold,
since they have higher melting temperature
Density
They are lighter than gold
.˙.- Difficult in casting, they need higher casting
pressure.
- Comfortable in upper restorations

17. Mechanical
Properties
Cobaltchromium
Nickelchromium
Modulus of
elasticity
Double that of gold [stiffer]
Yield strength
Comparable to gold
Ultimate strength
Comparable to gold
Ductility
[%elongation]
Less ductile than gold
Hardness
.˙. used in thin section
.˙.Less burnish-able than gold
Harder than gold
.˙.Difficult in finishing &polishing
But retain this surface for longer
time
Titanium &
Titanium
alloys

18. Mechanical properties of pure Titanium are similar
to gold alloy type III and IV.
While those of Titanium alloy are similar to Cobalt
Chromium and Nickel chromium alloys.

19. Casting
Investment
Melting
Cobaltchromium
Nickelchromium
Carbon-free phosphate or
silicate investment with vents
Titanium
With very
stable oxides
Oxygen Acetylene- Electric Furnace
Quartz crucible
Casting
machines
Cooling
Centrifugal
under vacuum
Special casting
machine using
centrifugal + air
pressure under
vacuum
Bench cooling

20. CobaltCasting
chromium
Finishing &
polishing
Nickelchromium
Titanium &
Titanium
alloys
No pickling because it attack the passive
Difficult but retain their polished surface
Special technique for finishing & polishing
Sandblasting + Electrolytic Polishing
Recasting
Cannot be recast due to difficulties
during casting [technique sensitive]

21. Cobaltchromium
Microstructure
Heat
treatment
Joining
Nickelchromium
Titanium
&Titanium
alloys
Large grain
The alloys can not be heat-treated because the
mechanical properties are neither improved or
controlled by heat treatment.
By soldering using:
Hard low fusing solder
Fluoride containing flux [capable of removing
the passive layer at the site of soldering]
Anti-flux

22. Difficulties in casting titanium


Very high melting temperature when compared to other
base metal alloys
.˙. It needs
- special melting technique [electric]
- special investment [with very stable
oxides]
- vacuum
Very low density when compared to other base metal
alloys
.˙. It needs high casting pressure to fill the mold

23. Shaping of Titanium [Alternative to casting]


Milling the restoration from titanium piece
Spark erosion of titanium piece using
electric discharge to prepare the
restoration

26. Important Questions

1.
2.
3.
4.
5.
6.
7.
Give reason (s) for:
Dental casting alloys should be of solid solution
Ductility is essential for dental casting alloys
Stiffness is required in dental casting alloy
Increasing platinum & palladium % in noble ceramometallic alloys
Tin & Indium should be incorporated in noble ceramometallic
alloys
Construction of dental appliances from Type IV should be made
in thick section