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Endodontics · single question

At what concentration is EDTA conventionally used as an endodontic irrigant?

  1. 2%
  2. 35%
  3. 5.25%
  4. 17%
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Correct answer: D. 17%

  • A. 2% is the concentration associated with chlorhexidine, an antimicrobial irrigant with substantivity but no tissue-dissolving capacity.
  • B. 35% approximates phosphoric acid etchant concentrations and is not used as an endodontic chelator.
  • C. 5.25% is full-strength sodium hypochlorite, which dissolves ORGANIC tissue and kills bacteria but does not chelate.
  • D. CORRECT. EDTA is used at 17% as a final rinse. As a CHELATOR it binds calcium ions and removes the INORGANIC component of the smear layer, opening the dentinal tubules so that sealer and intracanal medicaments can penetrate. It is typically left for about one minute — prolonged application erodes peritubular dentine and weakens the root.

Note: The complementary pair: sodium hypochlorite dissolves the ORGANIC half of the smear layer; EDTA chelates the INORGANIC half. Both are needed, used alternately — but never mixed, as they inactivate one another and generate a precipitate.

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