Nobel Casting alloysNobel Casting alloysNobel Casting alloysNobel Casting alloys

Silver-Palladium alloysApplications: Full metal crown and bridge

Composition:• Silver is predominant in the composition

(70-72%)• Palladium content 25% to provide nobility• May contain copper (<15%) and small

amount of gold

Casting temperature: In the range of gold alloys (900-

1000oC)

Properties:1. Color: Silver white in color

2. Physico-mechanical properties:• As type III Gold alloys• Some alloys (60% Ag + 25% Pd+ 15% Cu) show

properties similar to those of type IV gold alloys

3. Castability: • Poor due to low density of palladium

4. Tarnish and corrosion is the main drawback:

• Cu-containing > Cu-free alloys

Silver-Palladium alloys

Base Metal Casting Base Metal Casting AlloysAlloys

Base Metal Casting Base Metal Casting AlloysAlloys

Applications:1. Complete denture bases & RPD Frameworks2. Sub-periosteal implant3. Bone plates and screws

Composition:• Cobalt, Nickel, Chromium, Molybdenum, Carbon• Traces of Iron, Manganese, Tungsten, Silicone

Cobalt-Chromium alloys

Cobalt (35-65%)• Improve the strength, hardness and rigidity• Increase the melting range

Nickel (0-30%): As cobalt but by lower degree

Chromium (20-35%): Improve the tarnish and corrosion resistance by Forming passive oxide layer.

Molybdenum (0-7%): Improve the hardness and strength as it acts as grain refiner

Cobalt-Chromium alloys

Beryllium: Reduces the melting temperature (1 gm 100oC)

Carbon (0-0.4%): Improves the hardness, but it may brittle the alloy

Iron: • improves the ability of alloy to cold working• Reduce the strength and melting temperature

Tungsten, Manganese & Silicone:Increase the strength and hardness

Cobalt-Chromium alloys

Properties:Color: Silver white in color

Melting Temp.: 1250-1450oC Requires 1. Either phosphate or silica-bonded investment2. Ether Oxy-Acetylene gas torch or electric melting

Casting shrinkage: 2.3% • The highest rate of shrinkage between all casting

alloys • More mold expansion is required to compensate for

this shrinkage The alloy is not preferred for long-span bridges

Cobalt-Chromium alloys

Density: (7- gm/Cm3) 1. It is lower than that of gold alloys (15 gm/Cm3)2. More preferred for constructing maxillary dentures ,

but more casting force should be applied

Hardness: 370 BHN • 3 times more than that of type IV gold alloys• The alloy is difficult to be finished and polished

requires sand-blasting or electro-polishing• Could cause wear pf the opposing natural teeth

not used for crown and bridge construction

Cobalt-Chromium alloys

Strength: • Similar to that of type IV gold alloys

Modulus of elasticity (E): 3x106 Psi • 2 times more than that of type IV gold alloys• The alloy is highly rigid even in thin sections

Ductility (%elongation): 2-10% • The lower elongation value could be reflected as

clasp fracture

Cobalt-Chromium alloys

Heating: • Formation of chromium carbide is possible that

will render the material brittle, loss its strength, ductility, and reduces the tarnish and corrosion resistance

• Complicate the soldering and welding procedures (needs lowest temp. for shortest time)

Cobalt-Chromium alloys

Applications:1. Full metal crown and bridge2. Metal-ceramic restoration

Composition:The same as Co-Cr alloy except the % of

nickel is predominant (65-70%)Color:

The same as Co-Cr alloys

Nickel-Chromium alloys

Properties:• Presence of nickel instead of cobalt

renders the alloy;

1. Less hard2. Of lower shrinkage rate3. Of Lower melting temperature (nearly

1150oC)4. Owns strength properties similar to type III

gold alloys

Nickel-Chromium alloys

Applications:1. All-metallic restorations2. Metal-ceramic restorations3. RPD Frame works

Composition:• CP Titanium: pure metal has the ability to form

passive surface oxide layer in no time• The metal could also be alloyed with Aluminum

and vanadium (Ti.6Al.4V)

Color: Silver white

CP Titanium & Titanium alloys

Characters:1. Difficult to be cast because of low density and

high fusion temperature and high reactivity with the surrounding environment (Air & investment material)

2. Titanium cast is usually porous, so special casting equipments are required

3. Blocks of CP Ti or Ti-alloys could be milled into inlays or crowns using the CAD-CAM or copy milling technologies

CP Titanium & Titanium alloys