Dental materials and radiology basics: C-factor in composite: 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: C-factor in composite

Sample item

Polymerisation shrinkage stress and the risk of debonding are greatest when the ratio of bonded to free surfaces of a composite restoration is high. Which cavity has the highest such ratio?

AClass I occlusal cavity with five bonded wallsBClass IV incisal restoration with few bonded surfacesCClass III proximal cavity open to the palatal sideDClass V cervical cavity with a wide open surface

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

The answer and the reasoning

A. Class I occlusal cavity with five bonded walls

The configuration factor is the ratio of bonded to unbonded surfaces. A Class I box has five bonded walls and one free surface, so shrinkage cannot be relieved by flow and stress at the interface is high. Cervical and other open cavities have a low factor, and incremental placement helps lower the stress.

Option by option

A. Class I occlusal cavity with five bonded walls (correct)
Correct. A Class I box has the highest ratio, so stress is highest at the interface.
B. Class IV incisal restoration with few bonded surfaces
A Class IV is largely unbonded surface and so has a low ratio.
C. Class III proximal cavity open to the palatal side
A Class III open on one side has relatively more free surface, so the ratio is lower.
D. Class V cervical cavity with a wide open surface
A broad, shallow Class V has few bonded walls relative to its free surface, giving a low ratio.

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, Class I occlusal cavity with five bonded walls. The configuration factor is the ratio of bonded to unbonded surfaces.

Why is "Class IV incisal restoration with few bonded surfaces" not the answer?

A Class IV is largely unbonded surface and so has a low ratio.

Why is "Class III proximal cavity open to the palatal side" not the answer?

A Class III open on one side has relatively more free surface, so the ratio is lower.

Why is "Class V cervical cavity with a wide open surface" not the answer?

A broad, shallow Class V has few bonded walls relative to its free surface, giving a low ratio.

What concept does this question test?

It tests Dental materials and radiology basics: C-factor in composite in Dentistry. A Class I box has five bonded walls and one free surface, so shrinkage cannot be relieved by flow and stress at the interface is high. Cervical and other open cavities have a low factor, and incremental placement helps lower the stress.

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: C-factor in composite?

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.