Incomplete removal of bacteria, pulp debris and dentinal shavings is commonly caused by inadequate irrigation. Another important cause is failure to:

Correct answer: D. Obtain straight-line access

• A. Working length determines how FAR you instrument, not how thoroughly the walls are debrided.
• B. Barbed broaches remove bulk vital pulp tissue but do not clean the canal walls; they are a convenience, not a determinant of cleanliness.
• C. A chelator helps remove the inorganic smear layer, but poor access defeats even excellent irrigation.
• D. CORRECT. STRAIGHT-LINE ACCESS is the foundation of everything that follows. Without it, files bind against the coronal walls and are deflected, so they never engage the canal walls evenly. The result is uninstrumented recesses harbouring tissue and bacteria, plus a greatly increased risk of ledging, transportation and instrument separation. Remove all overhanging coronal dentine and unroof the chamber completely before instrumenting.

Note: The sequence that governs endodontic success: access first, then patency, then irrigation, then shaping. An inadequate access compromises every step downstream.