Base Metal Alloys Used for Dental Restorations and Implants

Base Metal Alloys

Write briefly on base metal alloys.
Or
Write short notes on base metal alloys.
Answer:

Base metal refers to the metal elements that are chemically reactive to their environment.

• Base metal alloys are those which contain little or no noble metals.
• The first base metal alloys were cobalt-chromium alloys primarily used for removable partial denture alloys.
• Later on, nickel-chromium alloys were used and recently titanium and its alloys are used.

Cobalt-Chromium Alloys

• Cobalt-chromium alloys were the oldest and possess high strength.
• They have the best corrosion resistance at high temperatures which makes these alloys useful for many applications.
• Cobalt-chromium alloys have a shiny, star-like appearance.
• They are bright, lustrous, hard, strong, and have non-tarnishing qualities.

Uses Of Cobalt-Chromium Alloys

• In denture base
• In casting removable partial denture framework
• In crowns and fixed partial dentures
• Bar connectors.

Composition Of Cobalt-Chromium Alloys

• Cobalt − 35 to 65%
• Chromium − 23 to 30%
• Nicke − 0 to 20%
• Molybdenum − 0 to 7%
• Iron − 0 to 5%
• Carbon − Upto 0.4%
• Tungsten, manganese, silicon, and platinum − Traces.

Functions of Alloy Elements

• Cobalt: Provide hardness, strength, and rigidity. Has a high melting point.
• Chromium: Gives corrosion resistance and helps in the reduction of melting point.
• Nickel: Increases ductility and decreases modulus of elasticity, strength, hardness, and fusion temperature.
• Molybdenum: Acts as hardener, and reduces ductility.
• Iron, copper, and beryllium: These are hardliners, beryllium decreases fusion temperature and refine grain structure.
• Manganese and Silicon: Prevent oxidation of other elements during melting.
• Boron: Harder and reduces ductility.
• Carbon: Strengthen the alloy.

Properties Of Cobalt-Chromium Alloys

• Cobalt-Chromium Alloys Density: Light in weight, i.e. 8 to 9 g/cm3
• Cobalt-Chromium Alloys Fusion temperature: It is high 1250°C to 1480°C.
• Cobalt-Chromium Alloys Yield strength: It is 710 MPa.
• Cobalt-Chromium Alloys Elongation: It is 1 to 12%.
• Cobalt-Chromium Alloys Modulus of elasticity: Their stiffness is twice the stiffness of gold alloys.
• Cobalt-Chromium Alloys Hardness: Very hard compared to gold alloys. Cutting, grinding and finishing are difficult.
• Cobalt-Chromium Alloys Casting shrinkage: It is high almost 2.3%.

Nickel-Chromium Alloys

Composition Of Nickel-Chromium Alloys :

• Nickel-Chromium Alloys  Basic Elements:
  • Nickel–61 to 81 wt%
  • Chromium–11 to 27 wt%
  • Molybdenum–2 to 9 wt%.
• Nickel-Chromium Alloys  Minor Elements:
  • Beryllium–0.5 to 2 wt%
  • Aluminium–0.2 to 4.2 wt%
  • Iron–0.1 to 0.5 wt%
  • Silicon–0.2 to 2.8 wt%
  • Copper–0.1 to 1.6 wt%
  • Manganese–0.1 to 3 wt%
  • Cobalt–0.4 to 0.5 wt%
  • Tin–1.25 wt%.

Properties Of Nickel-Chromium Alloys 

• The color is white.
• Density: Light in weight, i.e. 7.8 to 8.4 g/cm3
• Yield strength: It is 310 to 828 MPa.
• Modulus of elasticity: It is 150-218 GPa.
• Casting shrinkage: It is high.
• Melting range: It is 1155 to 13040C.
• Hardness: Hardness ranges from 175 to 360 VHN.
• Sag resistance: It is high, i.e. materials are stable at firing temperatures.
• Tarnish and corrosion resistance is high because of passivation.
• Biological Consideration: Nickel can lead to allergic reactions. It can be a potent carcinogen.

Titanium and its Alloys

• Uses Of Titanium and its Alloys:
  • As dental implant
  • As metal-ceramic restoration
  • A complete denture base
  • As a partial denture frame
  • As bar connectors.

Properties Of Titanium and its Alloys

• The color is white.
• Density: Light in weight, i.e. 4.5 g/cm3
• Yield Strength: It is 460 to 600 MPa.
• Tensile strength: It is 560 to 680 MPa.
• Modulus of elasticity: It is 110 GPa.
• Melting range: It is 1668°C.
• Tarnish and corrosion resistance is high because of self-passivation.
• Biological Consideration: Excellent biocompatibility

Advantages of Base Metal Alloys

• They are lighter in weight.
• Mechanical properties are good.
• They are corrosion-resistant because of the passivating effect.
• They are cheaper.

Disadvantages of Base Metal Alloys

• They are technique-sensitive.
• Their fusing temperatures are high.
• They are hard and require special equipment for finishing.