# The Novel Role of Solvents in Non-Surgical Endodontic Retreatment
## 5 Solvent Agitation  
The goal of combining solvents with ultrasonic agitation (UA) was for endodontic instruments to reach difficult-to-access areas, enhancing their effectiveness, as with the current irrigating protocol [39]. Moreover, the apical root canal, which is considered a \"critical zone\" due to its strategic position for microorganisms, remains a challenge for several instrumentation techniques or irrigating/dressing proposals [40].  
SEM assessments found no improvement in root canal walls cleanliness using PUI with EndoSolv R as a final step after further enlargement (repreparation), independent of the root canal thirds; thus, its efficacy remains unclear [41]. Additionally, with contradictory outcomes, a few ex-vivo studies with microtomography quantified the volume of the remnants of filling materials after retreatment protocols with solvent agitation. [PERSON] et al. [36] found no significant differences between static NaOCl, PUI/NaOCl, and PUI/OOil, but stressed that all groups showed a significant reduction in filling residuals (gutta-percha and epoxy resin-based sealer). The lack of superiority of the solvent group was justified with the formation of a paste that penetrated the dentinal tubules and canal irregularities, making its removal harder. [PERSON] et al. [35] concluded that solvent agitation (PUI for 1 min, with xylene) slightly increased filling material removal, but without statically significant results.  
On the other hand, in vitro studies assessing the dissolution rate using a sample weight comparison concluded that UA increased the efficacy of solvents such as eucalypt and OOil. However, independent of the solvent, the greatest dissolution was obtained with the ZOE sealer [42]. Another study [43] with chloroform and eucalypt corroborated an increased efficiency of solvents in the dissolution of sealers with UA, although with a significant decrease concerning the mineral trioxide aggregate sealer (MTA Fillapex). [PERSON] et al. [12] also reported a positive impact of UA on solvent efficacy, which was first evidenced with MEK over an epoxy resin-based sealer (AH-Plus). Similarly, traditionally milder solvents, such as OOil, were clearly improved via UA with regard to gutta-percha dissolution [28].  
Because MEK had little effect on gutta-percha dissolution, studies with the MEK/TCE and MEK/OOil associations have confirmed previous findings and a clear benefit of UA in filling dissolution [13]. The suggested protocol assessed in ex-vivo studies with microtomography, including MEK/TCE, and claimed to target the most common filling materials: gutta-percha and epoxy resin-based sealer (AH-Plus). These performances was reported as being similar to a further enlargement to the next file size, thus preventing an excessive reduction in the thickness of the root canals [38]. The authors also found that the benefit of solvent agitation was independent of the device, whether ultrasonic or XP-endo Finisher R [37]. The specificity and synergism of the solvents in the mixture, their moment of use, and the exposure time, as well as sonic/ultrasonic agitation, were given as explanations for the performance obtained.