Dental materials and radiology basics: denture acrylic porosity: 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: denture acrylic porosity

Sample item

A denture base is processed by plunging the flask straight into boiling water. After deflasking, voids are found in the thickest central part of the base. What caused them?

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

The answer and the reasoning

A. Monomer boiling as the exotherm overheated the thick core

Polymerisation of methyl methacrylate is exothermic, and in thick sections the heat cannot escape quickly. If the core exceeds the monomer boiling point of about 100.8 degrees C, bubbles form, giving gaseous porosity in the centre. A slow, gradual heating cycle avoids it.

Option by option

  • A. Monomer boiling as the exotherm overheated the thick core (correct)

    Correct. Rapid heating lets the core exceed the monomer boiling point and form gas bubbles.

  • B. Too little acrylic in the mould, causing shrinkage voids at the periphery

    Shrinkage porosity from insufficient material appears near the surface, not in the thick centre.

  • C. Excess powder in the mix leaving dry granular patches

    Dry patches from poor mixing look granular and are not central bubbles.

  • D. Air trapped by weak packing pressure along the cast surface

    Packing-pressure voids occur at the surface and are not confined to the thickest part.

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 A, Monomer boiling as the exotherm overheated the thick core. Polymerisation of methyl methacrylate is exothermic, and in thick sections the heat cannot escape quickly.

Why is "Too little acrylic in the mould, causing shrinkage voids at the perip…" not the answer?

Shrinkage porosity from insufficient material appears near the surface, not in the thick centre.

Why is "Excess powder in the mix leaving dry granular patches" not the answer?

Dry patches from poor mixing look granular and are not central bubbles.

Why is "Air trapped by weak packing pressure along the cast surface" not the answer?

Packing-pressure voids occur at the surface and are not confined to the thickest part.

What concept does this question test?

It tests Dental materials and radiology basics: denture acrylic porosity in Dentistry. If the core exceeds the monomer boiling point of about 100.8 degrees C, bubbles form, giving gaseous porosity in the centre. A slow, gradual heating cycle avoids it.

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: denture acrylic porosity?

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.