Regarding rubber dam placement, all of the following are correct EXCEPT:

Correct answer: B. The whole quadrant must always be isolated

• A. This IS correct. The rubber dam is the standard of care for moisture control, soft-tissue retraction, improved visibility, infection control, and — critically — protection of the airway from aspirated or swallowed instruments and irrigants. Its role as an airway barrier is why it is mandatory for endodontics.
• B. CORRECT — this is the EXCEPTION. Isolation is dictated by the PROCEDURE, not by a fixed rule. Single-tooth isolation is standard for endodontics; a multiple-tooth ('split dam') isolation is used for anterior composites and quadrant dentistry. There is no requirement to isolate an entire quadrant every time.
• C. This IS correct. The clamp jaws must engage the tooth at or below the height of contour without traumatising the attached gingiva, which would cause post-operative pain and recession.
• D. This IS correct practice. Flossing each contact before placement confirms the floss will pass, identifies overhangs or rough margins that would shred the dam, and prevents wasting time struggling with the sheet after the clamp is seated.

Note: Flossing AFTER treatment is also done, to verify contacts and remove debris — but the item hinges on the universal-quadrant claim, which is simply false.