Which agent is used to remove smear layer?

• A. Citric acid
• B. Phosphoric acid
• C. Ethylenediaminetetraacetic acid (EDTA)
• D. Sodium hypochlorite

Answer: (C)

Removing the smear layer relies on agents that can dissolve the inorganic part of the debris left after instrumentation. The smear layer sits on dentin as a mix of organic material and inorganic salts, and opening the dentinal tubules helps with sealing and adhesion of fills and medicaments. Ethylenediaminetetraacetic acid, or EDTA, is a chelating agent that binds calcium ions from the hydroxyapatite in dentin. By chelating calcium, EDTA effectively dissolves the inorganic portion of the smear layer and exposes the tubules, allowing better penetration of sealers and bonding agents. In practice, EDTA is commonly used in a mild, controlled manner to achieve smear layer removal without excessive dentin erosion.

Citric acid can also chelate calcium and remove the smear layer, but it is less routinely used because it can be more erosive depending on concentration and exposure time. Phosphoric acid is a strong etchant used primarily for bonding procedures and enamel/dentin preparation, and it can over-etch dentin if used inappropriately for smear layer removal in canal areas. Sodium hypochlorite excels at dissolving organic tissue and biofilm but does not effectively remove the inorganic portion of the smear layer, so it alone does not accomplish complete smear layer removal.