Community dentistry: dental unit waterlines: 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 · Community dentistry: dental unit waterlines

Sample item

Cultures of water from a dental unit's handpiece lines show high bacterial counts after the weekend. What best explains this?

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

The answer and the reasoning

D. Biofilm growth in the narrow-bore tubing

The narrow tubes and stagnant water favour biofilm, which sheds bacteria into the instrument water. Flushing, independent bottles and disinfectant reduce the load.

Option by option

  • A. Autoclave failure

    Autoclaving does not touch the unit water lines.

  • B. Mains water always carries a high bacterial load

    Mains water is usually of acceptable quality when it arrives.

  • C. Chlorine in tap water increases growth

    Chlorine reduces, not increases, microbial growth.

  • D. Biofilm growth in the narrow-bore tubing (correct)

    Correct. Stagnation and the tubing surface allow biofilm to form.

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 D, Biofilm growth in the narrow-bore tubing. The narrow tubes and stagnant water favour biofilm, which sheds bacteria into the instrument water.

Why is "Autoclave failure" not the answer?

Autoclaving does not touch the unit water lines.

Why is "Mains water always carries a high bacterial load" not the answer?

Mains water is usually of acceptable quality when it arrives.

Why is "Chlorine in tap water increases growth" not the answer?

Chlorine reduces, not increases, microbial growth.

What concept does this question test?

It tests Community dentistry: dental unit waterlines in Dentistry. Flushing, independent bottles and disinfectant reduce the load.

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 Community dentistry: dental unit waterlines?

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.