Solvents in Non-Surgical Endodontic Retreatment: Comparison
View Latest Version
Please note this is a comparison between Version 2 by Jason Zhu and Version 3 by Jason Zhu.

Non-surgical endodontic retreatment is a reliable conservative option for managing post-treatment apical periodontitis. However, effective microbial control, based on the maximization of filling removal and disinfection protocols, is not yet predictable. Traditional gutta-percha solvents, which are indistinctively used for both the core and sealer filling materials, became obsolete due to unprecedented advances in endodontic technology. Nonetheless, microtomography, scanning electronic microscopy findings, and histobacteriological analysis tend to confirm the persistence of filling materials and the lack of association between root canal enlargement and superior disinfection. There is a controversy regarding the most suitable clinical protocols surrounding the shaping procedures and the supplementary disinfection steps.

  • endodontics
  • filling materials
  • gutta-percha
  • solvents
  • non-surgical endodontic retreatment
  • sealers

1. Introduction

Non-surgical endodontic retreatment (NSER) is a conservative option for managing persistent apical periodontitis (AP) associated with root-filled teeth, or where a new disease has emerged after root canal filling. Its main objective is to reduce the interradicular bacterial load to levels that are compatible with periapical healing, relying on maximum filling removal, repreparation through the most complete and canal-centered shaping techniques, and disinfection protocols [1]. However, the current therapy still focuses on the main root canal.
Reducing old filling remnants is crucial, as they may harbor intraradicular biofilms, the main cause of post-treatment AP [2]. The relative difficulty of NSER is related to variables such as the design of the retreatment/instrumentation systems, the age and type of the root canal filling, and previous preparation errors, besides the complex root canal anatomy [3]. After regaining access to the apical foramen, chemo-mechanical preparation (repreparation) aims to further remove filling residues and disrupt persisting adhered biofilms. Current retreatment techniques include rotary files, ultrasonic instruments, heat, laser, hand files, and solvent solutions [3]. Although their combination is generally required, removing the bulk of the obturations has greatly improved with the development of nickel–titanium (NiTi) rotary systems. 

Two main strategies have been proposed to optimize disinfection before the new  filling: (i) a further apical enlargement [4], with the risk of weakening the root structure; or  (ii) using adjunctive procedures, such as sonic/ultrasonic processes or recently developed  finishing instruments, to activate the standard sodium hypochlorite (NaOCl) irrigating  solution.  Nonetheless, microtomography, scanning  electronic microscopy findings, and histobacteriological analysis tend to confirm the persistence of  filling materials and the lack of association between root canal enlargement and superior disinfection.

2. Moment of Use

Traditionally, solvents were applied at the initial stages of the NSER, when fillings are more compact, through the deposition of a few drops into the space created by the coronal filling removal [3]. The main objective was to soften gutta-percha, enabling the initial penetration of the file into the remaining obturation [4]. Some researchers reported a negative impact of the solvents’ deposition (chloroform and eucalyptol) in the medial and apical parts of the retreated ex-vivo canals, with reduced the filling remnants in the root canal surfaces of the nonsolvent groups [5]. Different methodologies, such as the type and moment of solvent deposition (before/after repreparation), may have influenced the results. Flooding the canal with solvent after removing the bulk of the remaining gutta-percha, and further enlargement, have also been investigated. One of the studies assessed the effect of xylene (1 min) on cleaning the root canal with paper points; the outcome was comparable to 2.5% ultrasonically activated NaOCl [6]. In turn, Fruchi et al. [7] emphasized the cleaning performance of the reciprocating instruments with xylene (1 min) and concluded that, even with passive ultrasonic agitation (PUI), the solvent did not improve filling removal. Similarly, Barreto et al. [8] also showed no improvement with PUI with OOil or NaOCl. Contrarily, Ferreira I et al. [9][10] showed promising results, advising specific solvents (MEK/TCE and MEK/OOil) as an additional step after the conventional repreparation and NaOCl/EDTA treatment. Due to their high dissolution rate in short periods, the same solvent mixtures might also be considered, to assist with the initial penetration of well-compacted obturations.

3. 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 [11]. 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 [12]. 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 [13]. 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. Barreto et al. [8] 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. Fruchi Lde et al. [7] 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 eucalyptol and OOil. However, independent of the solvent, the greatest dissolution was obtained with the ZOE sealer [14]. Another study [15] with chloroform and eucalyptol 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). Ferreira I et al. [16] 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 [17]. 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 [18]. 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 [10]. The researchers also found that the benefit of solvent agitation was independent of the device, whether ultrasonic or XP-endo Finisher R [9]. 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.

4. Effects on Dentin Structure

During NSER, solvents are inevitably in contact with dentin for some time. For a long time, investigations have highlighted a decrease in enamel and dentin hardness, due to the significant softening effects of chloroform, xylene, and halothane, with a time-dependent effect [19]; however, others do not confirm these findings [20][21]. Recent protocols suggest longer periods of dentin exposure to solvents after removing the bulk of the obturations. Some apprehension has, thus, arisen as to whether solvents can alter the dentin surface’s chemical composition, with potential changes in its microhardness, and consequences on the bond strength of the sealers [21][22]. A recent systematic research [23], including push-out assessments, has stressed that the heterogeneity of the studies prevented a reliable conclusion from being reached. However, chloroform and xylene seemed to raise further concerns. Despite reducing dentin’s hardness, the novel solvent proposals of MEK and ethyl acetate are reported as being preferred over chloroform, which caused the most significant decrease [24]. A different experimental design associating MEK with the specific co-solvents TCE and OOil significantly increased dentin hardness after NaOCl and EDTA treatment [25]. Regarding direct dentin exposure, the MEK/TCE group showed no significant differences from the control (saline). MEK/OOil produced a significant hardness increase, independently of being used directly or after the NaOCl/EDTA standard final irrigating protocol. The effect of solvent agitation on dentinal structure, per se, has been scarcely studied, and with ambiguous results. UA was reported to elicit a decline in dentin hardness when using MEK, ethyl acetate, and chloroform [24]. On the other hand, a study with the solvent mixtures MEK/TCE and MEK/OOil found no evidence of UA causing an additional decrease in dentin’s hardness [25]. Findings from endodontic irrigating solutions such as NaOCl, chlorhexidine, or EDTA also tend to diverge. Investigations on EDTA’s effect on dentin microhardness found that diode laser agitation caused higher hardness reduction than EDTA alone. However, there were no significant differences with UA or photon-induced photoacoustic streaming [26][27]. The different methodologies and chemistries regarding the compounds might explain the contradictory outcomes.

5. Antimicrobial/Antibiofilm Activity

AP is currently recognized as a biofilm-induced disease [28]. This causal link explains the increased resistance of endodontic intra-radicular infections to conventional disinfection procedures associated with the number of unprepared areas where root canal microorganisms, in planktonic and especially biofilm form, may persist [28][29]. These are considered to be the main causes of treatment failure. Moreover, the awareness that bacterial biofilms occur with particular relevance in the apical portion is crucial for the treatment, indicating the importance of primary and post-treatment AP therapeutics [30]. Research focusing on the antimicrobial properties of conventional gutta-percha solvents, such as halothane, eucalyptol, and OOil, has not been deep. The reported assays are almost exclusively against planktonic bacteria, such as Enterococcus faecalis (E. faecalis) and Staphylococcus aureus (S. aureus). In general, findings agree upon a stronger degree of antibacterial activity that is associated with the most cytotoxic solvents; OOil, for example, shows no antibacterial activity against the species mentioned [31]. Ex vivo studies emphasize that chloroform reduces intracanal levels of cultivable E. faecalis during endodontic retreatment [32]. By also stressing the role of E. faecalis as being the prime etiological agent of post-treatment infection, Subbiya A et al. [33] highlighted that RC Solve, a derivative of OOil, had superior antibacterial activity compared to xylene and EndoSolv E, which has tetrachloroethylene as its major compound. That study considered the minimal inhibitory concentration against E. faecalis ATCC and a clinical isolate from a failed root canal. Maximum antimicrobial activity against E. faecalis biofilm has been reported with the association of a surfactant, such as cetrimide, and with chloroform, eucalyptol, or OOil. Although the combinations with cetrimide achieved a 100% kill rate, cytotoxicity assessments or the dissolution efficacy of the suggested associations were missing [34]. Biofilm removal strategies include its disruption via chemo-mechanical preparation with specific shaping techniques, and antimicrobial irrigating solutions/dressings. Increased concern over its resistance to conventional antimicrobial drugs should be considered [35][36]. Supplementary procedures for activating the final irrigating protocol with NaOCl with recent devices, such as ultrasonics or XP-endo Finisher R, have been suggested [4][37]. However, microorganisms are reported to regrow after NaOCl treatment. Although the final exposure with the chelating EDTA had an additional antimicrobial effect, researchers claim there is a flaw in its ability to completely eliminate resistant biofilms, such as C. albicans, the most prevalent fungi isolated from persistent endodontic infections [38][39]. A recent study highlighted that the association of MEK/OOil could eradicate C. albicans biofilm cells remaining after the conventional NaOCl and EDTA final irrigating protocol [38].

References

  1. Siqueira, J.F., Jr.; Rôças, I.N. Clinical implications and microbiology of bacterial persistence after treatment procedures. J. Endod. 2008, 34, 1291–1301.e3.
  2. Ricucci, D.; Siqueira, J.F., Jr.; Bate, A.L.; Pitt Ford, T.R. Histologic investigation of root canal-treated teeth with apical periodontitis: A retrospective study from twenty-four patients. J. Endod. 2009, 35, 493–502.
  3. Duncan, H.F.; Chong, B.S. Removal of root filling materials. Endod. Top. 2008, 19, 33–57.
  4. Martins, M.P.; Duarte, M.A.H.; Cavenago, B.C.; Kato, A.S.; da Silveira Bueno, C.E. Effectiveness of the ProTaper Next and Reciproc Systems in Removing Root Canal Filling Material with Sonic or Ultrasonic Irrigation: A Micro-computed Tomographic Study. J. Endod. 2017, 43, 467–471.
  5. Horvath, S.D.; Altenburger, M.J.; Naumann, M.; Wolkewitz, M.; Schirrmeister, J.F. Cleanliness of dentinal tubules following gutta-percha removal with and without solvents: A scanning electron microscopic study. Int. Endod. J. 2009, 42, 1032–1038.
  6. Cavenago, B.C.; Ordinola-Zapata, R.; Duarte, M.A.; del Carpio-Perochena, A.E.; Villas-Boas, M.H.; Marciano, M.A.; Bramante, C.M.; Moraes, I.G. Efficacy of xylene and passive ultrasonic irrigation on remaining root filling material during retreatment of anatomically complex teeth. Int. Endod. J. 2014, 47, 1078–1083.
  7. Fruchi Lde, C.; Ordinola-Zapata, R.; Cavenago, B.C.; Hungaro Duarte, M.A.; Bueno, C.E.; De Martin, A.S. Efficacy of reciprocating instruments for removing filling material in curved canals obturated with a single-cone technique: A micro-computed tomographic analysis. J. Endod. 2014, 40, 1000–1004.
  8. Barreto, M.S.; Rosa, R.A.; Santini, M.F.; Cavenago, B.C.; Duarte, M.A.; Bier, C.A.; So, M.V. Efficacy of ultrasonic activation of NaOCl and orange oil in removing filling material from mesial canals of mandibular molars with and without isthmus. J. Appl. Oral Sci. 2016, 24, 37–44.
  9. Ferreira, I.; Babo, P.S.; Braga, A.C.; Lopes, M.A.; Gomes, M.E.; Pina-Vaz, I. Supplementary solvent irrigation efficacy on filling remnants removal comparing XP-endo Finisher R vs IrriSafe. Sci. Rep. 2021, 11, 12659.
  10. Ferreira, I.; Babo, P.S.; Braga, A.C.; Gomes, M.E.; Pina-Vaz, I. Effect of Sonic Agitation of a Binary Mixture of Solvents on Filling Remnants Removal as an Alternative to Apical Enlargement-A Micro-CT Study. J. Clin. Med. 2020, 9, 2465.
  11. Macedo, R.G.; Robinson, J.P.; Verhaagen, B.; Walmsley, A.D.; Versluis, M.; Cooper, P.R.; van der Sluis, L.W. A novel methodology providing insights into removal of biofilm-mimicking hydrogel from lateral morphological features of the root canal during irrigation procedures. Int. Endod. J. 2014, 47, 1040–1051.
  12. Ricucci, D.; Loghin, S.; Gonçalves, L.S.; Rôças, I.N.; Siqueira, J.F., Jr. Histobacteriologic Conditions of the Apical Root Canal System and Periapical Tissues in Teeth Associated with Sinus Tracts. J. Endod. 2018, 44, 405–413.
  13. Müller, G.G.; Schönhofen, Â.P.; Móra, P.M.; Grecca, F.S.; Só, M.V.; Bodanezi, A. Efficacy of an organic solvent and ultrasound for filling material removal. Braz. Dent. J. 2013, 24, 585–590.
  14. Trevisan, L.; Huerta, I.R.; Michelon, C.; Bello, M.C.; Pillar, R.; Souza Bier, C.A. The Efficacy of Passive Ultrasonic Activation of Organic Solvents on Dissolving Two Root Canal Sealers. Iran. Endod. J. 2017, 12, 25–28.
  15. Alzraikat, H.; Taha, N.A.; Hassouneh, L. Dissolution of a mineral trioxide aggregate sealer in endodontic solvents compared to conventional sealers. Braz. Oral Res. 2016, 30.
  16. Ferreira, I.; Soares, S.; Sousa, J.; Barros, J.; Braga, A.C.; Lopes, M.A.; Pina-Vaz, I. New Insight into the Dissolution of Epoxy Resin-based Sealers. J. Endod. 2017, 43, 1505–1510.
  17. Ferreira, I.; Braga, A.; Lopes, M.; Pina-Vaz, I. Improvement of the efficacy of endodontic solvents by ultrasonic agitation. Saudi Dent. J. 2021, 33, 39–43.
  18. Ferreira, I.; Grenho, L.; Gomes, P.; Braga, A.C.; Fernandes, M.H.; Lopes, M.A.; Pina-Vaz, I. Efficacy and Cytotoxicity of Binary Mixtures as Root Canal Filling Solvents. Materials 2020, 13, 3237.
  19. Rotstein, I.; Cohenca, N.; Teperovich, E.; Moshonov, J.; Mor, C.; Roman, I.; Gedalia, I. Effect of chloroform, xylene, and halothane on enamel and dentin microhardness of human teeth. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 1999, 87, 366–368.
  20. Erdemir, A.; Eldeniz, A.U.; Belli, S. Effect of the gutta-percha solvents on the microhardness and the roughness of human root dentine. J. Oral Rehabil. 2004, 31, 1145–1148.
  21. Khedmat, S.; Hashemi, A.; Dibaji, F.; Kharrazifard, M.J. Effect of chloroform, eucalyptol and orange oil solvents on the microhardness of human root dentin. J. Dent. 2015, 12, 25–30.
  22. Topcuoglu, H.S.; Demirbuga, S.; Tuncay, O.; Arslan, H.; Kesim, B.; Yasa, B. The bond strength of endodontic sealers to root dentine exposed to different gutta-percha solvents. Int. Endod. J. 2014, 47, 1100–1106.
  23. Ferreira, I.; Braga, A.C.; Pina-Vaz, I. Effect of Gutta-percha Solvents on the Bond Strength of Sealers to Intraradicular Dentin: A Systematic Review. Iran. Endod. J. 2021, 16, 17–25.
  24. Nalci, G.; Alaçam, T.; Altukaynak, B. Microhardness evaluation of root dentin after using resin sealer solvents. J. Dent. Res. Dent. Clin. Dent. Prospects 2021, 15, 256–261.
  25. Ferreira, I.; Braga, A.C.; Lopes, M.A.; Pina-Vaz, I. Adjunctive procedure with solvent mixtures in non-surgical endodontic retreatment: Does it affect root dentin hardness? Odontology 2021, 109, 812–818.
  26. Arslan, H.; Yeter, K.Y.; Karatas, E.; Yilmaz, C.B.; Ayranci, L.B.; Ozsu, D. Effect of agitation of EDTA with 808-nm diode laser on dentin microhardness. Lasers Med. Sci. 2015, 30, 599–604.
  27. Akbulut, M.B.; Terlemez, A. Does the Photon-Induced Photoacoustic Streaming Activation of Irrigation Solutions Alter the Dentin Microhardness? Photomed. Laser Surg. 2019, 37, 38–44.
  28. Ricucci, D.; Siqueira, J.F., Jr. Biofilms and apical periodontitis: Study of prevalence and association with clinical and histopathologic findings. J. Endod. 2010, 36, 1277–1288.
  29. Arias, A.; Peters, O.A. Present status and future directions: Canal shaping. Int. Endod. J. 2022. Online ahead of print.
  30. Siqueira, J.F., Jr.; Rôças, I.N. Present status and future directions: Microbiology of endodontic infections. Int. Endod. J. 2021. Online ahead of print.
  31. Karlovic, Z.; Anic, I.; Miletic, I.; Prpic-Mehicic, G.; Pezelj-Ribaric, S.; Marπan, T. Antibacterial Activity of Halothane, Eucalyptol and Orange Oil. Acta Stomat. Croat. 2000, 34, 307–309.
  32. Edgar, S.W.; Marshall, J.G.; Baumgartner, J.C. The antimicrobial effect of chloroform on Enterococcus faecalis after gutta-percha removal. J. Endod. 2006, 32, 1185–1187.
  33. Subbiya, A.; Padmavathy, K.; Mahalakshmi, K. Evaluation of the antibacterial activity of three gutta-percha solvents against Enterococcus faecalis. Int. J. Artif. Organs 2013, 36, 358–362.
  34. Martos, J.; Ferrer Luque, C.M.; González-Rodríguez, M.P.; Arias-Moliz, M.T.; Baca, P. Antimicrobial activity of essential oils and chloroform alone and combinated with cetrimide against Enterococcus faecalis biofilm. Eur. J. Microbiol. Immunol. 2013, 3, 44–48.
  35. Zancan, R.F.; Calefi, P.H.S.; Borges, M.M.B.; Lopes, M.R.M.; de Andrade, F.B.; Vivan, R.R.; Duarte, M.A.H. Antimicrobial activity of intracanal medications against both Enterococcus faecalis and Candida albicans biofilm. Microsc. Res. Tech. 2019, 82, 494–500.
  36. Alves, F.R.; Almeida, B.M.; Neves, M.A.; Moreno, J.O.; Rocas, I.N.; Siqueira, J.F., Jr. Disinfecting oval-shaped root canals: Effectiveness of different supplementary approaches. J. Endod. 2011, 37, 496–501.
  37. Silva, E.; Belladonna, F.G.; Zuolo, A.S.; Rodrigues, E.; Ehrhardt, I.C.; Souza, E.M.; De-Deus, G. Effectiveness of XP-endo Finisher and XP-endo Finisher R in removing root filling remnants: A micro-CT study. Int. Endod. J. 2018, 51, 86–91.
  38. Ferreira, I.; Rodrigues, M.E.; Fernandes, L.; Henriques, M.; Pina-Vaz, I. Candida albicans Antimicrobial and Antibiofilm Activity of Novel Endodontic Solvents. Appl. Sci. 2021, 11, 7748.
  39. Alshanta, O.A.; Shaban, S.; Nile, C.J.; McLean, W.; Ramage, G. Candida albicans Biofilm Heterogeneity and Tolerance of Clinical Isolates: Implications for Secondary Endodontic Infections. Antibiotics 2019, 8, 204.
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)
ScholarVision Creations
Feedback