Caries, pulp and periodontal disease: critical pH: 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 · Caries, pulp and periodontal disease: critical pH

Sample item

Below which approximate plaque pH does enamel begin to dissolve?

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

The answer and the reasoning

C. 5.5

The critical pH for enamel demineralisation is about 5.5, since below this the saliva and plaque fluid become undersaturated with respect to hydroxyapatite. Dentine and cementum have a higher critical pH of about 6.2 to 6.7.

Option by option

  • A. 7.0

    A pH of 7.0 is neutral and does not demineralise enamel.

  • B. 4.0

    4.0 is far below the threshold, which is crossed well before this value.

  • C. 5.5 (correct)

    Correct. Enamel demineralises below approximately 5.5.

  • D. 6.8

    6.8 is within the safe range for enamel.

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 C, 5.5. The critical pH for enamel demineralisation is about 5.

Why is "7.0" not the answer?

A pH of 7.0 is neutral and does not demineralise enamel.

Why is "4.0" not the answer?

4.0 is far below the threshold, which is crossed well before this value.

Why is "6.8" not the answer?

6.8 is within the safe range for enamel.

What concept does this question test?

It tests Caries, pulp and periodontal disease: critical pH in Dentistry. 5, since below this the saliva and plaque fluid become undersaturated with respect to hydroxyapatite. Dentine and cementum have a higher critical pH of about 6.2 to 6.7.

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 Caries, pulp and periodontal disease: critical pH?

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.