Ceramics And Metal-Bonded Ceramics

Ceramics And Metal-Bonded Ceramics

Write a short note on metal-ceramic restorations.
Answer:

It is also known as porcelain fused to metal or metal bonded restoration or ceramometal.

Composition of Porcelain Powder for Metal Ceramics:

Types of Metal-ceramic Systems

As previously mentioned the metal-ceramic systems can be divided into:

• Cast metal-ceramic restorations:
  • Cast noble metal alloys
  • Cast base metal alloys
  • Cast titanium:
• Swaged metal-ceramic restorations:
  • Gold alloy foil coping
  • Bonded platinum foil coping.

Technical Consideration of Metal Ceramic Restoration:

• Because of the high melting temperature of the alloy, phosphate or silica-bonded investment material must be used.
• A gas-oxygen flame or induction is generally employed for melting the alloy.
• Surface treatment of metal casting before porcelain application is important for good bonding.
• This treatment is used to toughen the casting and form surface oxides.
• The surface may be roughened by sandblasting with a fie alumina abrasive.
• In most cases, the metal casting is heat treated either in air or under a partial vacuum to produce surface oxide to improve bonding.
• The opaque porcelain is condensed with a thickness of approximately 0.1-0.2 mm.
• It is then fired, the translucent enamel is applied and tooth form is built. The unit is again fied.
• A final glaze is then obtained.

Uses of Metal Ceramic Restoration:

• Single anterior and posterior crowns
• Short and long span anterior and posterior FPDs.

Advantages of Metal Ceramic Restoration:

• If proper fabrication of metal-ceramic crowns is done they are stronger and more durable than all ceramic crowns.
• Long-span bridges can be done with an excellent fit.
• In metal-ceramic restoration, tooth preparation should be less as compared to all-ceramic restorations.
• Metal ceramic restorations withstand the forces of occlusion without wear.
• Metal ceramic restorations do not undergo staining along the interface between metal and ceramic veneer.
• Metal ceramic restoration is hard and resists wear extremely well.
• Metal ceramic restoration is compatible with soft tissues.

Disadvantages of Metal Ceramic Restoration:

• If an adequate shoulder margin is not present mainly in anterior teeth, achieving the aesthetic margin without a dark shadow of metal is difficult.
• Metal base can affect the aesthetic of porcelain which makes its appearance unnatural because of decreased light transmission.
• Patients are allergic to metal and alloys which warrant the use of metal-free ceramic.
• Due to aesthetic demands, patients are opting for All ceramic restoration.
• There is a high degree of shrinkage on firing.
• Along with time metal gets discolored.
• The appearance of translucency is difficult to produce.