Cobalt-Chromium Alloy — MFDS Part 1 MCQ

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ModerateDental MaterialsCobalt-Chromium AlloyMFDS Part 1

A cobalt-chromium removable partial denture framework is adjusted, exposing fresh alloy. In the oral environment, its corrosion resistance is restored by formation of a stable passive surface film. Which alloying element is primarily responsible for this protection?

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Correct answer: E — Chromium

Chromium is the principal element responsible for corrosion resistance. It forms a thin, adherent and self-repairing passive surface film composed predominantly of chromium(III) oxide (Cr2O3), which limits further electrochemical dissolution in the oral environment. Cobalt forms the main alloy matrix but is not the principal passivating element. Molybdenum contributes to strength and may improve resistance to localised corrosion, but it is not primarily responsible for passivation. Carbon contributes to carbide formation, hardness and strength. Nickel may occur in other dental alloy systems but does not provide the characteristic corrosion protection of cobalt-chromium frameworks.

Reference: Reclaru L et al. Corrosion Behavior and Ion Release of Co-Cr Dental Alloys Fabricated by Casting, CAD/CAM, SLM and DMLS: Influence of Manufacturing Route and Microstructure. Bioengineering. 2026;13(4):406. https://pubmed.ncbi.nlm.nih.gov/42072200/