Dental materials and radiology basics: oxygen inhibition layer: 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: oxygen inhibition layer

Sample item

After light-curing the first increment of a composite, the surface remains slightly sticky. Why is this layer left in place before adding the next increment?

ALoose filler that supports the next incrementBTrapped water that helps the next increment to wetCUnreacted monomer that bonds the next incrementDResidual photoinitiator that speeds up the next cure

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

The answer and the reasoning

C. Unreacted monomer that bonds the next increment

Oxygen in air inhibits free-radical polymerisation at the surface, leaving a thin layer of unreacted monomer. When the next increment is placed it copolymerises with this layer, giving a good chemical bond between layers. The final surface layer is removed by finishing and polishing.

Option by option

A. Loose filler that supports the next increment
The sticky surface is monomer-rich resin, not a supportive loose filler.
B. Trapped water that helps the next increment to wet
The layer is unreacted resin, not water; moisture would weaken the bond.
C. Unreacted monomer that bonds the next increment (correct)
Correct. The unreacted monomer layer copolymerises with the next increment.
D. Residual photoinitiator that speeds up the next cure
Photoinitiator is consumed during curing and does not accelerate the next increment.

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 C, Unreacted monomer that bonds the next increment. Oxygen in air inhibits free-radical polymerisation at the surface, leaving a thin layer of unreacted monomer.

Why is "Loose filler that supports the next increment" not the answer?

The sticky surface is monomer-rich resin, not a supportive loose filler.

Why is "Trapped water that helps the next increment to wet" not the answer?

The layer is unreacted resin, not water; moisture would weaken the bond.

Why is "Residual photoinitiator that speeds up the next cure" not the answer?

Photoinitiator is consumed during curing and does not accelerate the next increment.

What concept does this question test?

It tests Dental materials and radiology basics: oxygen inhibition layer in Dentistry. When the next increment is placed it copolymerises with this layer, giving a good chemical bond between layers. The final surface layer is removed by finishing and polishing.

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: oxygen inhibition layer?

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.