The quality of smear layer removal in the root canal in in vitro studies (literature review)

   Introduction. The treatment of chronic apical periodontitis remains a relevant issue in dentistry.

   A key stage of endodontic treatment is the removal of the smear layer (SL), which forms during mechanical root canal instrumentation and prevents adequate disinfection.

   Traditional chelating agents, such as EDTA, have limited effectiveness in the apical third and may damage dentin. Etidronic acid (HEBP) is considered a promising alternative, as it allows continuous chelation simultaneously with antiseptic irrigation.

   Aim. To evaluate the effectiveness of smear layer removal in the root canal using various chelating agents according to in vitro studies.

   Materials and methods. A literature review was conducted in the Scopus, PubMed, Web of Science, eLIBRARY.RU, and Google databases for the period 2015–2025 using the following keywords: HEBP, EDTA, etidronate, smear layer, in vitro study. Out of 1,218 identified publications, after excluding duplicates, reviews, clinical cases, and studies with non uniform irrigant activation, 23 full text articles were selected for analysis.

   Results. EDTA is effective in the coronal and middle thirds but removes the smear layer less effectively in the apical part. Activation (ultrasonic, sonic) improves its performance; however, the risk of reduced dentin strength remains. HEBP, especially in combination with sodium hypochlorite, provides stable smear layer removal throughout the entire canal, including the apical third, and prevents debris accumulation. At the same time, HEBP solutions are less effective in dissolving pulp compared to pure hypochlorite.

   Conclusions. HEBP in a continuous chelation protocol has advantages over EDTA in terms of cleaning uniformity and dentin safety, but it requires consideration of its impact on the organic tissue dissolution ability of sodium hypochlorite.

1. Nocini R., Lippi G., Mattiuzzi C. Periodontal Disease: The Portrait of an Epidemic. J. Public Health Emerg. 2020;(4):10. doi: 10.21037/jphe.2020.03.01.

2. Yanushevich O.O. (Ed.). Therapeutic Dentistry: National Guideline. — 3^rd ed., rev. and expanded. – Moscow: GEOTAR-Media, 2024. – 1024 p. – ISBN 978-5-9704-8385-5.

3. Yusupov F.A., Yuldashev A A., Yusupov A. F., Abdykadyrov M. Sh. The influence of oral microbiota on the prognosis and severity of stroke. Bulletin of Science and Practice. 2025;(1):124–145.

4. Apanasovich M. V., Apanasovich V. G., Gorodetskaya O. S., Solomevich A. S. Periodontitis and rheumatoid arthritis: searching for the relationship. Modern Dentistry. 2018;(71):34–38.

5. Blinova A. V., Rumyantsev V. A. Destructive lesions of the apical periodontium: achievements of fundamental and applied science in modern approaches to solving the problem. Science of the Young (Eruditio Juvenium). 2021; (3): 471–480. doi: 10.23888/HMJ202193471-480.

6. Kuratov I.A., Nagaeva M.O., Korneeva M.V., Surkov M.A. Analysis of the causes of endodontic treatment failures and tooth extractions diagnosed with chronic apical periodontitis. Problems of Dentistry. 2019;(1):52–56. doi: 10.18481/2077-7566-2019-15-1-52-56.

7. da Silva Magalhães K., Kuerten Gil A.C., Goulart T.S., Schuldt D.P.V., Coelho B. S., Figueiredo D.R., Garcia L.D.F.R., de Almeida J. Efficacy of disinfection procedures performed prior to regenerative endodontic therapy : An integrative review. Australian Endodontic Journal. 2023;(49):418–427. doi: 10.1111/aej.12670.

8. Kuratov I. A., Nagaeva M. O. Review of means and methods of root canal irrigation during endodontic treatment. Medical Science and Education of the Urals. 2014;15(80):142–145. EDN: TDXCJX.

9. Paqué F., Laib A., Gautschi H., Zehnder M. Hard-tissue debris accumulation analysis by high-resolution computed tomography scans. Journal of Endodontics. 2009 (35):1044–1047. doi: 10.1016/j.joen.2009.04.026.

10. Tonini R., Salvadori M., Audino E., Sauro S., Garo M. L., Salgarello S. Irrigating Solutions and Activation Methods Used in Clinical Endodontics : A Systematic Review. Frontiers in Oral Health. 2022;(3):838043. doi: 10.3389/froh.2022.838043.

11. Wilkoński W., Jamróz-Wilkońska L., Zapotoczny S., Opiła J., Giardino L. Real-time co-site optical microscopy study on the morphological changes of the dentine’s surface after citric acid and sodium hypochlorite: a single-tooth model. BMC Oral Health. 2021 (21):454. doi: 10.1186/s12903-021-01815-6.

12. Keine K. C., Kuga M. C., Tormin F. B. C., Venção A. C., Duarte M. A. H., Chávez-Andrade G. M., Faria G. Effect of peracetic acid used as single irrigant on the smear layer, adhesion, and penetrability of AH Plus. Brazilian Oral Research. 2019;(33):e057. doi: 10.1590/1807-3107bor-2019.vol33.0057.

13. Murugesan K., Vishwanath S., Kadandale S., Thanikachalam Y., Parthasarathy R., Ilango S. Comparative Evaluation of Smear Layer Removal in Apical Third Using Four Different Irrigants With Ultrasonic Agitation: An In Vitro Scanning Electron Microscopy (SEM) Analysis. Cureus. 2022;(14):e23142. doi: 10.7759/cureus.23142.

14. Biel P., Mohn D., Attin T., Zehnder M. Interactions between the Tetrasodium Salts of EDTA and 1-Hydroxyethane 1,1-Diphosphonic Acid with Sodium Hypochlorite Irrigants. Journal of Endodontics. 2017;(43):657–661. doi: 10.1016/j.joen.2016.12.006.

15. Razumova S. N., Brago A. S., Barakat H. B., Kozlova Yu. S., Velichko E. V., Vasiliev Yu. L. Microbiological protocol for the effectiveness of root canal treatment with erbium laser. Biomedical Photonics. 2019;(8):11–16. doi: 10.24931/2413-9432-2019-8-4-11-16.

16. De-Deus G., Namen F., Galan J. Jr., Zehnder M. Soft chelating irrigation protocol optimizes bonding quality of Resilon/Epiphany root fillings. Journal of Endodontics. 2008 (34):703–705. doi: 10.1016/j.joen.2008.02.024.

17. Mukherjee M., Kalita T., Barua P., Barman A., Thonai S., Mahanta P. Sr., Medhi H. Efficacy of Smear Layer Removal of Human Teeth Root Canals Using Herbal and Chemical Irrigants: An In Vitro Study. Cureus. 2023;(15):e40467. doi: 10.7759/cureus.40467.

18. Veeraiyan M., Kumar Y. P., Chandhar C. Y., Priyanka Y., Jaiswal M., Kemasaram D. Evaluation of Smear Layer Removal and Micro Hardness Alteration of Radicular Dentin after Using Various Chelating Agents – An Atomic Force Microscopic Study. Journal of Pharmacy and Bioallied Sciences. 2023;(15):S582–S587. doi: 10.4103/jpbs.jpbs_29_23.

19. Ballal N. V., Jain I., Tay F. R. Evaluation of the smear layer removal and decalcification effect of QMix, maleic acid and EDTA on root canal dentine. Journal of Dentistry. 2016;(51):62–68. doi: 10.1016/j.jdent.2016.06.001.

20. Deari S., Mohn D., Zehnder M. Dentine decalcification and smear layer removal by different ethylenediaminetetraacetic acid and 1-hydroxyethane-1,1-diphosphonic acid species. International Endodontic Journal. 2019;(52):237–243. doi: 10.1111/iej.12987.

21. Ulusoy Ö. İ., Mantı A. Ş., Çelik B. Nanohardness reduction and root dentine erosion after final irrigation with ethylenediaminetetraacetic, etidronic and peracetic acids. International Endodontic Journal. 2020;(53):1549–1558. doi: 10.1111/iej.13372.

22. Morago A., Ordinola-Zapata R., Ferrer-Luque C. M., Baca P., Ruiz-Linares M., Arias-Moliz M. T. Influence of Smear Layer on the Antimicrobial Activity of a Sodium Hypochlorite/Etidronic Acid Irrigating Solution in Infected Dentin. Journal of Endodontics. 2016;(42):1647–1650. doi: 10.1016/j.joen.2016.07.023.

23. Razumova S., Brago A., Kryuchkova A., Barakat H., Ovchinnikov M. Evaluation of the efficiency of smear layer removal during endodontic treatment using scanning electron microscopy: an in vitro study. BMC Oral Health. 2025;(25):151. doi: 10.1186/s12903-024-04444-x.

24. Kamil A. A., Ali A. H., Foschi F., Mannocci F. Effectiveness of Continuous and Sequential Chelation and Different Agitation Techniques on Smear Layer Removal and Microhardness of Root Canal Dentin (An In Vitro Study). Dentistry Journal. 2025;(13):221. doi: 10.3390/dj13050221.

25. Rath P.P., Yiu C.K.Y., Matinlinna J.P., Kishen A., Neelakantan P. The effects of sequential and continuous chelation on dentin. Dental Materials. 2020;(36):1655–1665. doi: 10.1016/j.dental.2020.10.010.

26. Mankeliya S., Singhal R.K., Gupta A., Jaiswal N., Pathak V.K., Kushwah A. A Comparative Evaluation of Smear Layer Removal by Using Four Different Irrigation Solutions like Root Canal Irrigants: An In Vitro SEM Study. Journal of Contemporary Dental Practice. 2021;(22):527–531.

27. El-Banna A., Elmesellawy M. Y., Elsayed M. A. Flexural strength and microhardness of human radicular dentin sticks after conditioning with different endodontic chelating agents. Journal of Conservative Dentistry. 2023;(26):344–348. doi: 10.4103/jcd.jcd_173_23.

28. Chodankar S. S., Ashwini P., Meena N., Gowda V., D’souza N. Assessment of smear layer removing efficacy of different irrigation activation devices in mandibular premolar teeth using a scanning electron microscope: An in vitro comparative study. Endodontology. 2023;(35):210–216. doi: 10.4103/endo.endo_98_22.

29. Hegde V., Thakkar P. Effect of continuous soft chelating irrigation protocol on removal of smear layer. Endodontology. 2019;(31):63–67. doi: 10.4103/endo.endo_58_18.

30. Jaiswal S., Gupta S., Nikhil V., Bhadoria A., Raj S. Effect of intracanal and extracanal heating on pulp dissolution property of continuous chelation irrigant. Journal of Conservative Dentistry. 2021;(24):544–548. doi: 10.4103/jcd.jcd_230_21.

31. Tartari T., Borges M. M. B., de Araújo L. B. B., Vivan R. R., Bonjardim L. R., Duarte M. A. H. Effects of heat in the properties of NaOCl alone and mixed with etidronate and alkaline tetrasodium EDTA. International Endodontic Journal. 2021;(54):616–627 doi: 10.1111/iej.13450.

32. Kucuk M., Tunca Y. M., Erdem O., Cetinkaya S., Demirkaya K. Efficacy of preheated chelating agents on calcium ion removal from instrumented root canals. Journal of Clinical and Experimental Dentistry. 2021;(13):e1015–e1020. doi: 10.4317/jced.58539.

33. Kfir A., Goldenberg C., Metzger Z., Hülsmann M., Baxter S. Cleanliness and erosion of root canal walls after irrigation with a new HEDP-based solution vs. traditional sodium hypochlorite followed by EDTA. A scanning electron microscope study. Clinical Oral Investigations. 2020;(24):3699–3706. doi: 10.1007/s00784-020-03249-w.

34. Wigler R., Srour Y., Wilchfort Y., Metzger Z., Kfir A. Debris and Smear Layer Removal in Curved Root Canals: A Comparative Study of Ultrasonic and Sonic Irrigant Activation Techniques. Dentistry Journal. 2024;(12):51. doi: 10.3390/dj12030051.

35. Kaushal R., Bansal R., Malhan S. A comparative evaluation of smear layer removal by using ethylenediamine tetraacetic acid, citric acid, and maleic acid as root canal irrigants: An in vitro scanning electron microscopic study. Journal of Conservative Dentistry. 2020;(23):71–78. doi: 10.4103/JCD.JCD_43_20.

36. Nanda Z., Singh R., Kamble P. P., Deshmukh G., Patil N., Patil A. B., Banerjee S. Efficacy of Different Root Canal Irrigating Solutions in Removing Smear Layer: A Scanning Electron Microscopic Study. Cureus. 2023;(15):e44618. doi: 10.7759/cureus.44618.

37. Arun D. R., Sujatha V., Mahalaxmi S. Effect of 5 % Carbohydrate Derived-Fulvic Acid on Smear Layer Removal and Root Dentin Microhardness – An In Vitro study. European Endodontic Journal. 2022;(7):156–160. doi: 10.14744/eej.2022.97759.

38. Alhat M. B., Mattigatti S. B., Mahaparale R. R., Wahane K. D., Jadhav A. Comparative Evaluation of Different Methods of Activation of Chelating Solution for Smear Layer Removal in the Apical Portion of the Root Canal Using a Scanning Electron Microscopy: An In Vitro Study. Cureus. 2024;(16):e66622. doi: 10.7759/cureus.66622.

39. Alakshar A., Saleh A. R. M., Gorduysus M. O. Debris and Smear Layer Removal from Oval Root Canals Comparing XP-Endo Finisher, EndoActivator, and Manual Irrigation: A SEM Evaluation. European Journal of Dentistry. 2020;(14):626–633. doi: 10.1055/s-0040-1714762.

40. Aoun C., Rechenberg D. K., Karam M., Mhanna R., Plotino G., Zogheib C. Effect of Continuous Chelation Irrigation Using DualRinse HEDP+3 % NaOCl with or with-out High-power Sonic Activation on Debris and Smear Layer Removal. European Endodontic Journal. 2023;(8):162–169. doi: 10.14744/eej.2022.93064.