Orthodontics and paediatric dentistry: functional posterior crossbite: 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 · Orthodontics and paediatric dentistry: functional posterior crossbite

Sample item

An 8-year-old has a unilateral posterior crossbite. At first contact the midlines coincide, but on full closure the lower midline shifts towards the crossbite side. What is the likely cause?

AUnilateral early loss of lower primary molars in the archBA constricted maxilla causing an occlusal interferenceCTrue skeletal asymmetry from condylar overgrowth on one sideDHabitual chewing on one side of the mouth only

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

The answer and the reasoning

B. A constricted maxilla causing an occlusal interference

In a functional crossbite, a narrow maxilla produces cuspal interference so the mandible deviates to one side to reach maximum intercuspation, giving a midline shift only on closure. Treatment is by maxillary expansion. A true skeletal asymmetry has a shift that persists in all positions.

Option by option

A. Unilateral early loss of lower primary molars in the arch
Tooth loss on one side does not produce an interference with a closure shift of this kind.
B. A constricted maxilla causing an occlusal interference (correct)
Correct. A narrow maxilla forces the mandible sideways to reach occlusion.
C. True skeletal asymmetry from condylar overgrowth on one side
Condylar overgrowth gives a constant asymmetry that persists in all jaw positions.
D. Habitual chewing on one side of the mouth only
Chewing habits may contribute, but the constricted maxilla is the underlying cause.

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 B, A constricted maxilla causing an occlusal interference. In a functional crossbite, a narrow maxilla produces cuspal interference so the mandible deviates to one side to reach maximum intercuspation, giving a midline shift only on closure.

Why is "Unilateral early loss of lower primary molars in the arch" not the answer?

Tooth loss on one side does not produce an interference with a closure shift of this kind.

Why is "True skeletal asymmetry from condylar overgrowth on one side" not the answer?

Condylar overgrowth gives a constant asymmetry that persists in all jaw positions.

Why is "Habitual chewing on one side of the mouth only" not the answer?

Chewing habits may contribute, but the constricted maxilla is the underlying cause.

What concept does this question test?

It tests Orthodontics and paediatric dentistry: functional posterior crossbite in Dentistry. Treatment is by maxillary expansion. A true skeletal asymmetry has a shift that persists in all positions.

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 Orthodontics and paediatric dentistry: functional posterior crossbite?

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.