What is the composition of metals in base metal PFM copings regarding oxidation during casting?

The composition of metals in base metal porcelain-fused-to-metal (PFM) copings is characterized by the inclusion of metals that might oxidize during the casting process. Base metals, such as nickel and chromium, are commonly used due to their cost-effectiveness and desirable mechanical properties. However, these metals have a higher tendency to form oxides when exposed to elevated temperatures during casting.

The oxidation of these metals can affect the bond strength between the metal coping and the porcelain layer, as well as the overall aesthetic appearance of the final restoration. The presence of oxides can create a barrier that may prevent proper adherence of the porcelain to the metal, which is critical for both function and esthetics.

In contrast, noble metals, which are mentioned in the other options, are less likely to oxidize due to their inherent chemical properties, making them more stable under casting conditions. High noble metals, while also resistant to oxidation, are not typically used in the same way as base metals for PFM copings, which focus on cost-effectiveness alongside performance. Therefore, the correct understanding of base metal PFM copings' composition highlights their potential to oxidize during the casting process.