Cobalt-Chromium Alloy: Advantages and Disadvantages

Cobalt-Chromium Alloy: Advantages and Disadvantages

Base Metals used in dentistry. Describe chromium-cobalt alloy’s composition, advantages, and disadvantages as a denture base material.
Answer:

Base metals:

These are non-noble metals. They are important components of dental casting alloys because they influence physical properties, control of amount, type of oxidation, and their strengthening effects.

• Such metals are reactive with their environment and are referred to as “Base metals”.
• Some base metals, through a property known as “passivation,” can protect an alloy from corrosion.
• They are also called “Non-precious metals”.
• Examples: Chromium, cobalt, nickel, iron, copper, manganese, etc.

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 An alloy of Base metal is:

• Nickel: Chrome alloys.
• Cobalt-chromium alloys.
• Pure titanium and its alloys.
• Aluminum bronze alloys.

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Cobalt-Chromium Alloy

• They possess high strength; their excellent corrosion resistance, especially at high temperatures makes them useful for several applications.
• These alloys are also known as “satellites” because of their shiny, star-like appearance.
• They have bright, lustrous, hard, strong, and non-tarnishing qualities.

Uses Of Cobalt-Chromium Alloy

• Denture base
• Cast a removable partial denture framework
• Crown and bridges
• Bar connectors.

Composition Of Cobalt-Chromium Alloy

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Functions of Alloying Elements

• Cobalt:
  • Increase the hardness, strength, and rigidity of the alloy.
  • It has a high melting point.
• Chromium:
  • Its passivating effect ensures corrosion resistance.
  • It reduces the melting point.
  • It also acts in solid solution hardening with other elements.
• Nickel:
  • It decreases strength, hardness, modulus of elasticity, and fusion temperature.
  • It increases ductility.
• Molybdenum, Tungsten, Iron, Copper:
  • They are effective hardeners.
• Beryllium:
  • Hardener and reduce fusion temperature, and refine grain structure.
• Manganese and Silicon:
  • Primarily, oxide “scavengers” to prevent oxidation of other elements during melting.
  • They also act as hardeners.
• Boron:
  • Deoxidize and hardliner, but reduce ductility.
• Carbon:
  
  • Carbon content is most critical in small amounts.
  • It increases strength, hardness, and ductility.
  • However, excess carbon increases brittleness.

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Advantages Of Cobalt-Chromium Alloy

• Lighter in weight.
• Better mechanical properties.
• Corrosion resistance due to the passivating effect of chromium.
• Less expensive than gold alloys.

Disadvantages Of Cobalt-Chromium Alloy

• More techniques are sensitive.
• Complexity in the production of dental appliances.
• High fusion temperature.
• Greater casting shrinkage.
• Extremely hard, thus cutting, grinding, and finishing are difficult, so they require special equipment for finishing.
• The high hardness can cause excessive wear of restorations and natural teeth contacting the restorations.