What is the function of an oxide layer on a metal surface in metal-ceramic restorations?

• A. It prevents bonding with ceramic
• B. It provides chemical bonding sites for ceramic veneer and should be formed and cleaned
• C. It is a cosmetic finish that enhances appearance
• D. It must be removed before applying ceramic veneer

Answer: (B)

In metal-ceramic restorations the bond between the porcelain veneer and the metal substructure relies on a chemical connection that forms at the metal surface. This is achieved by forming a controlled oxide layer on the metal. The oxide provides active chemical bonding sites that the ceramic can react with, creating a strong, durable bond. It also helps create a suitable surface texture for bonding.

For best results, the oxide layer is formed intentionally and then cleaned to remove contamination before applying the ceramic veneer. The oxide itself is not removed; if it’s absent or dirty, bonding is weak and porcelain may delaminate. So the oxide layer serves as the bonding bridge between metal and ceramic, and its proper formation and cleanliness are essential.