Dental materials and radiology basics: amalgam corrosion: practice question

A Dentistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Dentistry · Dental materials and radiology basics: amalgam corrosion

Sample item

Conventional low-copper dental amalgam fails early at the margins from corrosion and creep. Which phase is the weakest and most corrodible, and is eliminated in high-copper amalgams?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Gamma-2 (tin-mercury) phase

The gamma-2 tin-mercury phase corrodes readily and has poor strength, causing marginal breakdown. High-copper alloys bind tin into copper-tin phases and avoid forming gamma-2.

Option by option

  • A. Gamma (silver-tin) phase

    Gamma is the unreacted silver-tin alloy particle, which is the strongest component.

  • B. Epsilon (copper-tin) phase

    The copper-tin phase is the corrosion-resistant product in high-copper amalgam.

  • C. Gamma-1 (silver-mercury) phase

    Gamma-1 is the strong matrix phase and is relatively corrosion resistant.

  • D. Gamma-2 (tin-mercury) phase (correct)

    Correct. Gamma-2 is the weak, corrodible phase.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Dentistry question

What is the answer to this Dentistry question?

The best answer is D, Gamma-2 (tin-mercury) phase. The gamma-2 tin-mercury phase corrodes readily and has poor strength, causing marginal breakdown.

Why is "Gamma (silver-tin) phase" not the answer?

Gamma is the unreacted silver-tin alloy particle, which is the strongest component.

Why is "Epsilon (copper-tin) phase" not the answer?

The copper-tin phase is the corrosion-resistant product in high-copper amalgam.

Why is "Gamma-1 (silver-mercury) phase" not the answer?

Gamma-1 is the strong matrix phase and is relatively corrosion resistant.

What concept does this question test?

It tests Dental materials and radiology basics: amalgam corrosion in Dentistry. High-copper alloys bind tin into copper-tin phases and avoid forming gamma-2.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Dental materials and radiology basics: amalgam corrosion?

Learn the dental formula, eruption ages and tooth structure once, as tables. Then use the flashcards and the other Dentistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.