, Volume 107, Issue 2, pp 142–149 | Cite as

Effectiveness of irrigation strategies on the removal of the smear layer from root canal dentin

  • Prasanna NeelakantanEmail author
  • Hani F. Ounsi
  • Sharmila Devaraj
  • Gary S. P. Cheung
  • Simone Grandini
Original Article


The aim of this study was to evaluate the removal of the smear layer by some commonly used (needle-and-syringe irrigation, sonic activation, ultrasonically activated irrigation) and new root canal irrigation strategies (negative pressure irrigation and polymer rotary file) using a novel approach by comparing pre- and post-experimental images. Prepared root canals (n = 50) were subjected to a split tooth model and divided into 5 groups (n = 10): (1) needle-and-syringe irrigation (control); (2) sonic activation (SA); (3) negative pressure irrigation with continuous warm activated irrigation and evacuation (CWA); (4) polymer finishing file (FF); (5) ultrasonically activated irrigation (UAI). Smear layer scores and percentage of open dentinal tubules (%ODT) were evaluated by 2 examiners before and after irrigation procedures, from the middle and apical thirds of the root canal, on scanning electron microscopic images. Data were analysed using Kruskal–Wallis and post hoc tests at P = 0.05. Needle-and-syringe irrigation (control) showed no significant difference (both smear score and %ODT) compared to the pre-experimental value (P > 0.05). All other groups showed lower smear scores and higher %ODT, compared to the control (P < 0.05). The lowest smear score and highest %ODT were observed in the CWA group, which was significantly different from all other groups (P < 0.05). SA group showed significantly higher smear scores and lower %ODT than FF or UAI (P < 0.05). CWA showed superior removal of smear layer in the middle and apical thirds of the root canal compared to the other irrigation strategies.


Negative pressure Polymer finishing file Scanning electron microscopy Sonic Ultrasonic 



The authors sincerely thank Ms. Samantha Kar Yan Li, Centralized Research Laboratories, Faculty of Dentistry, The University of Hong Kong for the data analysis.


This study did not receive any funding from internal or external sources.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


  1. 1.
    Wang Z, Shen Y, Haapasalo M. Effect of smear layer against disinfection protocols on Enterococcus faecalis-infected dentin. J Endod. 2013;39:1395–400.CrossRefPubMedGoogle Scholar
  2. 2.
    Violich DR, Chandler NP. The smear layer in endodontics—a review. Int Endod J. 2010;43:2–15.CrossRefGoogle Scholar
  3. 3.
    Carvalho AS, Camargo CH, Valera MC, Camargo SE, Mancini MN. Smear layer removal by auxiliary chemical substances in biomechanical preparation: a scanning electron microscope study. J Endod. 2008;34:1396–400.CrossRefPubMedGoogle Scholar
  4. 4.
    Ng YL, Mann V, Gulabivala K. A prospective study of the factors affecting outcomes of nonsurgical root canal treatment: part 1: periapical health. Int Endod J. 2011;44:583–609.CrossRefGoogle Scholar
  5. 5.
    Pintor AV, Dos Santos MR, Ferreira DM, Barcelos R, Primo LG, Maia LC. Does smear layer removal influence root canal therapy outcome? A systematic review. J Clin Pediatr Dent. 2016;40:1–7.CrossRefPubMedGoogle Scholar
  6. 6.
    Neelakantan P, Devaraj S, Jagannathan N. Histologic assessment of debridement of the root canal isthmus of mandibular molars by irrigant activation techniques ex vivo. J Endod. 2016;42:1268–72.CrossRefPubMedGoogle Scholar
  7. 7.
    De-Deus G, Reis C, Paciornik S. Critical appraisal of published smear layer-removal studies: methodological issues. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011;112:531–43.CrossRefPubMedGoogle Scholar
  8. 8.
    Lottanti S, Gautschi H, Sener B, Zehnder M. Effects of ethylenediaminetetraacetic, etidronic and peracetic acid irrigation on human root dentin and the smear layer. Int Endod J. 2009;42:335–43.CrossRefPubMedGoogle Scholar
  9. 9.
    Mancini M, Cerroni L, Iorio L, Armellin E, Conte G, Cianconi L. Smear layer removal and canal cleanliness using different irrigation systems (EndoActivator, EndoVac, and passive ultrasonic irrigation): field emission scanning electron microscopic evaluation in an in vitro study. J Endod. 2013;39:1456–60.CrossRefGoogle Scholar
  10. 10.
    Blank-Goncalves LM, Nabeshima CK, Martins GH, Machado ME. Qualitative analysis of the removal of the smear layer in the apical third of curved roots: conventional irrigation versus activation systems. J Endod. 2011;37:1268–71.CrossRefPubMedGoogle Scholar
  11. 11.
    Schmidt TF, Teixeira CS, Felippe MC, Felippe WT, Pashley DH, Bortoluzzi EA. Effect of ultrasonic activation of irrigants on smear layer removal. J Endod. 2015;41:1359–63.CrossRefPubMedGoogle Scholar
  12. 12.
    Tay FR, Gu LS, Schoeffel GJ, Wimmer C, Susin L, Zhang K, Arun SN, Kim J, Looney SW, Pashley DH. Effect of vapor lock on root canal debridement by using a side-vented needle for positive-pressure irrigant delivery. J Endod. 2010;36:745–50.CrossRefPubMedPubMedCentralGoogle Scholar
  13. 13.
    Hulsmann M, Rummelin C, Schafers F. Root canal cleanliness after preparation with different endodontic handpieces and hand instruments: a comparative SEM investigation. J Endod. 1997;23:301–6.CrossRefPubMedGoogle Scholar
  14. 14.
    Vasiliadis L, Darling AI, Levers BG. The amount and distribution of sclerotic human root dentin. Arch Oral Biol. 1983;28:645–9.CrossRefPubMedGoogle Scholar
  15. 15.
    Basmadjian-Charles CL, Farge P, Bourgeois DM, Lebrun T. Factors influencing the long-term results of endodontic treatment: a review of the literature. Int Dent J. 2002;52:81–6.CrossRefPubMedGoogle Scholar
  16. 16.
    Gu LS, Kim JR, Ling J, Choi KK, Pashley DH, Tay FR. Review of contemporary irrigant agitation techniques and devices. J Endod. 2009;35:791–804.CrossRefGoogle Scholar
  17. 17.
    George S, Kishen A, Song KP. The role of environmental changes on monospecies biofilm formation on root canal wall by Enterococcus faecalis. J Endod. 2005;31:867–72.CrossRefPubMedGoogle Scholar
  18. 18.
    Baumgartner JC, Mader CL. A scanning electron microscopic evaluation of four root canal irrigation regimens. J Endod. 1987;13:147–57.CrossRefPubMedGoogle Scholar
  19. 19.
    Saunders WP, Saunders EM. The effect of smear layer upon the coronal leakage of gutta-percha fillings and a glass ionomer sealer. Int Endod J. 1992;25:245–9.CrossRefPubMedGoogle Scholar
  20. 20.
    Yang SE, Bae KS. Scanning electron microscopy study of the adhesion of Prevotella nigrescens to the dentin of prepared root canals. J Endod. 2002;28:433–7.CrossRefPubMedGoogle Scholar
  21. 21.
    Cameron JA. The use of ultrasound for the removal of the smear layer. The effect of sodium hypochlorite concentration; SEM study. Aust Dent J. 1988;33:193–200.CrossRefPubMedGoogle Scholar
  22. 22.
    Rodig T, Dollmann S, Konietschke F, Drebenstedt S, Hulsmann M. Effectiveness of different irrigant agitation techniques on debris and smear layer removal in curved root canals: a scanning electron microscopy study. J Endod. 2010;36:1983–7.CrossRefPubMedGoogle Scholar
  23. 23.
    Prado M, Gusman H, Gomes BP, Simao RA. Scanning electron microscopic investigation of the effectiveness of phosphoric acid in smear layer removal when compared with EDTA and citric acid. J Endod. 2011;37:255–8.CrossRefPubMedGoogle Scholar
  24. 24.
    de Gregorio C, Estevez R, Cisneros R, Paranjpe A, Cohenca N. Efficacy of different irrigation and activation systems on the penetration of sodium hypochlorite into simulated lateral canals and up to working length: an in vitro study. J Endod. 2010;36:1216–21.CrossRefGoogle Scholar
  25. 25.
    Haapasalo M, Shen Y, Wang Z, Gao Y. Irrigation in endodontics. Br Dent J. 2014;216:299–303.CrossRefPubMedGoogle Scholar
  26. 26.
    Mozo S, Llena C, Forner L. Review of ultrasonic irrigation in endodontics: increasing action of irrigating solutions. Med Oral Patol Oral Cir Bucal. 2012;17:e512-6.PubMedGoogle Scholar
  27. 27.
    Jiang LM, Verhaagen B, Versluis M, van der Sluis LW. Evaluation of a sonic device designed to activate irrigant in the root canal. J Endod. 2010;36:143–6.CrossRefPubMedGoogle Scholar
  28. 28.
    Moorer WR, Wesselink PR. Factors promoting the tissue dissolving capability of sodium hypochlorite. Int Endod J. 1982;15:187–96.CrossRefPubMedGoogle Scholar
  29. 29.
    Saber Sel D, Hashem AA. Efficacy of different final irrigation activation techniques on smear layer removal. J Endod. 2011;37:1272–5.CrossRefGoogle Scholar
  30. 30.
    Wu L, Mu Y, Deng X, Zhang S, Zhou D. Comparison of the effect of four decalcifying agents combined with 60 °C 3% sodium hypochlorite on smear layer removal. J Endod. 2012;38:381–4.CrossRefPubMedGoogle Scholar
  31. 31.
    Khademi A, Yazdizadeh M, Feizianfard M. Determination of the minimum instrumentation size for penetration of irrigants to the apical third of root canal systems. J Endod. 2006;32:417–20.CrossRefPubMedGoogle Scholar
  32. 32.
    Lee SJ, Wu MK, Wesselink PR. The efficacy of ultrasonic irrigation to remove artificially placed dentin debris from different-sized simulated plastic root canals. Int Endod J. 2004;37:607–12.CrossRefPubMedGoogle Scholar
  33. 33.
    Capar ID, Aydinbelge HA. Effectiveness of various irrigation activation protocols and the self-adjusting file system on smear layer and debris removal. Scanning. 2014;36:640–7.CrossRefPubMedGoogle Scholar
  34. 34.
    Malki M, Verhaagen B, Jiang LM, Nehme W, Naaman A, Versluis M, Wesselink P, van der Sluis L. Irrigant flow beyond the insertion depth of an ultrasonically oscillating file in straight and curved root canals: visualization and cleaning efficacy. J Endod. 2012;38:657–61.CrossRefPubMedGoogle Scholar
  35. 35.
    Sabins RA, Johnson JD, Hellstein JW. A comparison of the cleaning efficacy of short-term sonic and ultrasonic passive irrigation after hand instrumentation in molar root canals. J Endod. 2003;29:674–8.CrossRefPubMedGoogle Scholar
  36. 36.
    Klyn SL, Kirkpatrick TC, Rutledge RE. In vitro comparisons of debris removal of the EndoActivator system, the F file, ultrasonic irrigation, and NaOCl irrigation alone after hand-rotary instrumentation in human mandibular molars. J Endod. 2010;36:1367–71.CrossRefPubMedGoogle Scholar
  37. 37.
    Mader CL, Baumgartner JC, Peters DD. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endod. 1984;10:477–83.CrossRefPubMedGoogle Scholar
  38. 38.
    White RR, Goldman M, Lin PS. The influence of the smeared layer upon dentinal tubule penetration by endodontic filling materials. Part II. J Endod. 1987;13:369–74.CrossRefPubMedGoogle Scholar

Copyright information

© The Society of The Nippon Dental University 2018

Authors and Affiliations

  1. 1.Discipline of Endodontology, Faculty of DentistryThe University of Hong KongPok Fu LamHong Kong
  2. 2.Department of Endodontics and Restorative DentistryUniversity of SienaSienaItaly
  3. 3.Department of Endodontics, School of Dental MedicineLebanese UniversityBeirutLebanon
  4. 4.Private PracticeChennaiIndia

Personalised recommendations