Dental materials and radiology basics: zinc phosphate cement acidity: 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: zinc phosphate cement acidity

Sample item

A crown is to be luted with zinc phosphate cement onto a vital tooth with a deep preparation. The freshly mixed cement is strongly acidic. Which step best limits pulpal irritation?

ADry the dentine thoroughly with a long air blastBAdd a few drops of eugenol to the cement liquidCMix the powder into the liquid in one large incrementDLine the dentine with varnish or a liner first

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

The answer and the reasoning

D. Line the dentine with varnish or a liner first

Zinc phosphate cement has a very low pH when first mixed, rising towards neutral over about a day, and it has no sealing or adhesive action. A cavity varnish or liner on deep dentine protects the pulp. Powder should be added slowly in small increments to a cool slab.

Option by option

A. Dry the dentine thoroughly with a long air blast
Over-drying the dentine desiccates odontoblast processes and increases pulpal damage.
B. Add a few drops of eugenol to the cement liquid
Eugenol does not buffer the phosphoric acid and would interfere with setting.
C. Mix the powder into the liquid in one large increment
Adding the powder at once raises the setting temperature and acidity and shortens working time.
D. Line the dentine with varnish or a liner first (correct)
Correct. A varnish or liner shields the dentinal tubules from the acid while the cement matures.

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.

Questions about this Dentistry question

What is the answer to this Dentistry question?

The best answer is D, Line the dentine with varnish or a liner first. Zinc phosphate cement has a very low pH when first mixed, rising towards neutral over about a day, and it has no sealing or adhesive action.

Why is "Dry the dentine thoroughly with a long air blast" not the answer?

Over-drying the dentine desiccates odontoblast processes and increases pulpal damage.

Why is "Add a few drops of eugenol to the cement liquid" not the answer?

Eugenol does not buffer the phosphoric acid and would interfere with setting.

Why is "Mix the powder into the liquid in one large increment" not the answer?

Adding the powder at once raises the setting temperature and acidity and shortens working time.

What concept does this question test?

It tests Dental materials and radiology basics: zinc phosphate cement acidity in Dentistry. A cavity varnish or liner on deep dentine protects the pulp. Powder should be added slowly in small increments to a cool slab.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: zinc phosphate cement acidity?

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.