Chemical root canal dilatation. Location of canal entrances. Citric acid is a mild, slightly antibacterial, biocompatible chelating agent that forms a relatively stable chelate complex with the calcium ions in the dentine (action similar to EDTA preparations). This demineralizes and softens hard dental substance and removes the smear layer on the canal wall, thus opening the dentine tubuli and even widening them. Residual citric acid must be thoroughly flushed out to prevent continuing demineralization along the length of the tubuli. Opening up the dentine tubuli facilitates adaptation of the root canal sealer, generally improving the sealing of the root canal filling. This effect is further enhanced by activating the solution with ultrasound. Calcium hydroxide residues can also be reliably removed (for instance from a medical inlay).