In vitro study results of the tooth cavity walls’ microstructure after mechanical and ultrasonic treatment of the root canals

AIM. To evaluate the root canals’ microstructure using mechanical and ultrasonic treatment by examining the tooth cavity hard tissues under experimental conditions using scanning electron microscopy (SEM) and atomic force microscopy (AFM).

MATERIALS AND METHODS. The study included extracted single-root premolars that had not undergone endodontic treatment. After creating endodontic access, apical patency was confirmed using No. 15 K-file. Then UltraPath Files and Ultrataper Next files were used to shape the root canal. Irrigation in each group was performed with 3.25% sodium hypochlorite and 17% EDTA solution. In the second group, the EDTA solution was activated with an ultrasonic tip for 2 minutes. Subsequently longitudinal sections (for scanning electron microscopy) and transverse sections (for atomic force scanning) were obtained. Afterwards a qualitative comparative analysis of the microstructure of the root canals’ middle third was performed.

RESULTS. When using ultrasonic (US) activation, an increase in dentin roughness was observed. The number of open dentinal tubules was also higher in second group. According to SEM data, the amount of smear layer and dentin debris without US activation was greater than with additional treatment using ultrasound. According to AFM and SEM data, the US removal of mineralized areas revealed depressions and microcracks connecting the dentinal tubules. The presence of microcracks in samples without US activation was not detected.

CONCLUSION. The root canal wall surface is more defined and roughened when using ultrasound, which can impact material retention during obturation. Almost complete absence of a smear layer when using ultrasound can reduce the risk of biofilm formation and root canal reinfection and improve the adherence of the obturation material. Increasing the time or force of ultrasound exposure can cause the microcracks between dentinal tubules to develop into larger cracks visible using an operating microscope.

1. Paqué F., Ganahl D., Peters O.A. Effects of root canal preparation on apical geometry assessed by microcomputed tomography. J Endod. 2009;35(7):1056–1059. https://doi.org/10.1016/j.joen.2009.04.020

2. Peters O.A., Schönenberger K., Laib A. Effects of four Ni-Ti preparation techniques on root canal geometry assessed by micro computed tomography. Int Endod J. 2001;34(3):221–230. https://doi.org/10.1046/j.1365-2591.2001.00373.x

3. Nusstein J.M. Endodontic sonic and ultrasonic irrigant activation. Clin Dent Rev. 2018;2(1):22. https://doi.org/10.1007/s41894-018-0037-1

4. Orekhova L.Y., Porkhun T.V., Vashneva V.Y., Rubezhova E.A. Use of vibration methods in endodontic treatment. Journal of Scientific Articles Health and Education Millennium. 2018;20(2):65–69. (In Russ.).

5. Urban K., Donnermeyer D., Schäfer E., Bürklein S. Canal cleanliness using different irrigation activation systems: a SEM evaluation. Clin Oral Investig. 2017;21(9):2681–2687. https://doi.org/10.1007/s00784-017-2070-x

6. Hülsmann M. A critical appraisal of research methods and experimental models for studies on root canal preparation. Int Endod J. 2022;55(Suppl. 1):95–118. https://doi.org/10.1111/iej.13665

7. Binnig G., Quate C.F., Gerber Ch. Atomic Force Microscope. Phys Rev Lett. 1986;56(9):930–933. https://doi.org/10.1103/PhysRevLett.56.930

8. Hu X., Ling J., Gao Y. Effects of irrigation solutions on dentin wettability and roughness. J Endod. 2010;36(6):1064–1067. https://doi.org/10.1016/j.joen.2010.03.007

9. Tsenova-Ilieva I., Simeonova S., Karova E. Atomic force microscopy study on the effect of different irrigation regimens on the surface roughness of human root canal dentin. Niger J Clin Pract. 2022;25(3):261–266. https://doi.org/10.4103/njcp.njcp_1379_21

10. Antonova I.N., Goncharov V.D., Kipchuk A.V., Bobrova E.A. Evaluation of dental hard tissues by means of atomic force microscopy. Stomatology. 2014;93(4):11–14. (In Russ.) Available at: https://www.mediasphera.ru/issues/stomatologiya/2014/4/030039-1735201443 (accessed: 19.03.2026).

11. Güngördü Z.S., Tufenkci P., Sarı M. The effectiveness of endoactivator, EDDY, passive ultrasonic irrigation, and XP-Endo finisher r in removing filling materials from retreated root canals. BMC Oral Health. 2025;25(1):1656. https://doi.org/10.1186/s12903-025-06877-4

12. Gündüz H., Özlek E., Baş Z. Influence of passive ultrasonic irrigation cycles on the penetration depth of sodium hypochlorite into root dentin. Sci Rep. 2025;15(1):35213. https://doi.org/10.1038/s41598-025-19716-x

13. John J., Singh V.P.P., Karuveettil V., M R., Subramanian D., Haridas K. Comparison of crack formation induced by ultrasonic tips and burs during root-end preparation: a systematic review and meta-analysis. Evid Based Dent. 2022. https://doi.org/10.1038/s41432-022-0823-0