dissolve the smear layer and concomitantly disinfect the root canal system [16, 36, 67].

Chlorhexidine Digluconate (CHX)

Chlorhexidine digluconate (CHX) should be used as the final irrigant. The use of CHX as an auxiliary irrigant in endodontic treatment has been suggested due to its antimicrobial nature and its ability to remain and have a long-lasting effect on the dentin, therefore preventing or delaying recontamination. This long-lasting effect is termed “substantivity.” In an in vivo study, Leonardo et al. [34] evaluated the antimicrobial substantivity of 2 % CHX in teeth with pulp necrosis and radiographically visible chronic periradicular lesions. The authors demonstrated that CHX prevented microbial activity in the root canal system with residual effects lasting for up to 48 h after application. When used as a supplemental irrigating solution, CHX has the capacity to reduce the bacterial load inside the root canals [47, 79].

Although CHX is effective against bacterial biofilms, NaOCl is still the only irrigation solution with the capacity of disrupting biofilms [41].

Concluding Remarks

In order to achieve optimal disinfection in retreatment cases, clinicians should be prepared to remove as much of the previous filling material as possible. This removal process may be tiring and time consuming. Solvents may be used if needed; however, caution is advised due to their toxicity. The combined use of the dental operating microscope (DOM) and ultrasonics may enhance the removal of filling material and increase the area of dentin that comes into contact with the disinfecting solutions. A combination of irrigating solutions is important to achieve the objective of ideal disinfection.

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