Outline the standard irrigant sequence during chemomechanical preparation and the rationale for each step.

• A. Use NaOCl first, then EDTA, then saline.
• B. Rinse with saline to remove debris, rinse with NaOCl for disinfection, use EDTA to remove smear layer, followed by a final rinse.
• C. Use only saline as the irrigant.
• D. Rinse with chlorhexidine throughout the procedure.

Answer: (D)

Using a sequence of irrigants leverages the different strengths of each solution: first remove organic tissue and kill microbes that are most active during instrumentation, then dissolve the smear layer to expose dentinal tubules, and finally flush and neutralize residues to prepare for obturation. The standard approach begins with a tissue-dissolving, broad-spectrum irrigant—sodium hypochlorite—applied during shaping and cleaning to dissolve organic tissue and disrupt bacteria. After shaping, a rinse with an inorganic-smear-layer–removing agent, typically EDTA, is used to chelate calcium and other minerals, reducing the smear layer and opening tubules to improve disinfectant penetration. A final rinse with saline or sterile water then clears away residues and neutralizes the canal environment, leaving a clean space for obturation. Chlorhexidine has antimicrobial benefits, including substantivity, but it does not dissolve tissue or remove smear layer, and it can form precipitates if it contacts sodium hypochlorite; therefore rinsing with chlorhexidine throughout the procedure is not the standard sequence. If chlorhexidine is used, it should come after thorough flushing with NaOCl and EDTA, not as the sole or initial irrigant.