Noel casting alloys , base metal casting alloys dental material

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Noel casting alloys , base metal casting alloys dental material

  1. 1. Nobel CastingNobel Casting alloysalloys
  2. 2. Silver-Palladium alloys Applications: 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 (900-1000o C)
  3. 3. 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
  4. 4. Base MetalBase Metal Casting AlloysCasting Alloys
  5. 5. Applications: 1. Complete denture bases & RPD Frameworks 2. Sub-periosteal implant 3. Bone plates and screws Composition: • Cobalt, Nickel, Chromium, Molybdenum, Carbon • Traces of Iron, Manganese, Tungsten, Silicone Cobalt-Chromium alloys
  6. 6. 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
  7. 7. Beryllium: Reduces the melting temperature (1 gm↓ 100o C) 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
  8. 8. Properties: Color: Silver white in color Melting Temp.: 1250-1450o C  Requires 1. Either phosphate or silica-bonded investment 2. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. Applications: 1. Full metal crown and bridge 2. 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
  13. 13. Properties: • Presence of nickel instead of cobalt renders the alloy; 1. Less hard 2. Of lower shrinkage rate 3. Of Lower melting temperature (nearly 1150o C) 4. Owns strength properties similar to type III gold alloys Nickel-Chromium alloys
  14. 14. Applications: 1. All-metallic restorations 2. Metal-ceramic restorations 3. 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
  15. 15. 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

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