Dental materials and radiology basics: alginate imbibition: 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: alginate imbibition

Sample item

An alginate impression is stored under water for an hour before the cast is poured, and the cast turns out oversized and distorted. Which phenomenon explains this?

AImbibition, the uptake of water by the gelBSyneresis, the loss of fluid from the gel surfaceCHysteresis, the lag between gelation and meltingDThixotropy, the thinning of the gel under stress

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

The answer and the reasoning

A. Imbibition, the uptake of water by the gel

Alginate is a hydrocolloid gel. In water it takes up fluid and swells (imbibition), while in air it loses water and shrinks (syneresis). Both distort the impression, so it should be rinsed, disinfected briefly and poured promptly, ideally within minutes.

Option by option

A. Imbibition, the uptake of water by the gel (correct)
Correct. Water absorbed by the gel causes swelling and a distorted, enlarged impression.
B. Syneresis, the loss of fluid from the gel surface
Syneresis is fluid loss in air and produces shrinkage, the opposite of what is seen here.
C. Hysteresis, the lag between gelation and melting
Hysteresis describes the different temperatures of gelation and liquefaction of agar.
D. Thixotropy, the thinning of the gel under stress
Thixotropy is a flow property of some gels and is not the cause of swelling in water.

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 A, Imbibition, the uptake of water by the gel. Alginate is a hydrocolloid gel.

Why is "Syneresis, the loss of fluid from the gel surface" not the answer?

Syneresis is fluid loss in air and produces shrinkage, the opposite of what is seen here.

Why is "Hysteresis, the lag between gelation and melting" not the answer?

Hysteresis describes the different temperatures of gelation and liquefaction of agar.

Why is "Thixotropy, the thinning of the gel under stress" not the answer?

Thixotropy is a flow property of some gels and is not the cause of swelling in water.

What concept does this question test?

It tests Dental materials and radiology basics: alginate imbibition in Dentistry. In water it takes up fluid and swells (imbibition), while in air it loses water and shrinks (syneresis). Both distort the impression, so it should be rinsed, disinfected briefly and poured promptly, ideally within minutes.

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: alginate imbibition?

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.