Alloys For Cast Metal Restorations

Question 1

What is the reason behind using porcelain and metal alloy for a crown?

Answer 1

Porcelain has good aesthetics and withstands abrasion but micro cracks tend to form on fitting surface (brittle).
Alloys have good mechanical properties - strong, rigid, ductile

Question 2

Which part of the alloy does porcelain bond to?

Answer 2

The metal oxide - surface irregularities on oxide mechanical interlock with porcelain.

Question 3

Describe the bonding of porcelain to metal?

Answer 3

Mechanical bond between surface irregularities on metal oxide and porcelain.
Slight difference in thermal expansion- alloy contracts slightly more on cooling- compressive force on porcelain due to alloy gripping it.
Chemical bond between metal oxide and oxide in porcelain (during firing stage)

Question 4

What are the different types of metals that can’t be used with porcelain?

Answer 4

High gold (strongest however, creep)
Low gold (satisfactory)
Silver palladium (difficult to cast)
Nickel chromium (biocompatibility concerns, low bond strength)
Cobalt chromium (low bond strength)