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1. A comparative evaluation of the resistance to vertical root fracture after removal of separated instruments using three instrument retrieval systems: An in vitro study P.RAJA RAJESWARI, THIRD YEAR POST GRADUATE, DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS Lobo WM, Sayed A, Sapkale K, Ramugade M, Benavides AC. A comparative evaluation of the resistance to vertical root fracture after removal of separated instruments using three instrument retrieval systems: An in vitro study. Journal of Conservative Dentistry and Endodontics. 2025 Feb 1;28(2):182-6. 1

2. Successful endodontic treatment comprises the thorough debridement of the pulpal tissue, cleaning and shaping and three-dimensional filling of the canal. Hand or rotary files, gates glidden burs, lentulo spirals, pluggers and spreaders - made of different materials. Improper handling, limited physical properties, inadequate straight-line access, complex root canal anatomy, debris accumulation, choice of instruments, excessive force and manufacturing defects - causes for file separation. introduction 2

3. Frequent accident with rotary instruments ( 1.83%) > manual ( 8.2%) Highest frequency of instrument separation - molars (77% - 89%) Lower molars (50% - 55%), compared to upper molars (25% - 33.3%) Mesio-buccal root canals > disto-buccal ones - upper molars Mesio-buccal root canals > mesio-lingual ones - lower molars Frequency of endodontic instrument separation Vouzara T, Lyroudia K. Separated instrument in endodontics: Frequency, treatment and prognosis. Balkan Journal of Dental Medicine. 2018;22(3):123-32. 3

4. 7% in straight root canals, 35% in curved ones, and 58% in intensely curved ones A higher rate of separation is observed in the apical third (41% - 82.7%) The most common separation site is 2mm from the tip of the instrument The most common sizes of instruments undergoing separation - no 20-40 (ISO) As to taper, separation most commonly happens in files with a taper between 4% and 9% Frequency of endodontic instrument separation Vouzara T, Lyroudia K. Separated instrument in endodontics: Frequency, treatment and prognosis. Balkan Journal of Dental Medicine. 2018;22(3):123-32. 4

5. MANAGEMENT OF instrument separation 5

6. Techniques and systems used for the removal of separated instruments 6

7. Complications during MANAGEMENT OF instrument separation 7

8. Prognosis after removal of separated instrument 8

9. To evaluate and compare the vertical root fracture resistance after using three commonly used retrieval systems: Ultrasonic U Files, ET25 Retreatment Ultrasonic Tip, and Endo Rescue system. AIM 9

10. T o evaluate the resistance to vertical root fracture after retrieval of separated instruments from the root canal using Ultrasonic U Files under magnification of the dental operating microscope. T o evaluate the resistance to vertical root fracture after retrieval of separated instruments from the root canal using Ultrasonic Tip (Acteon Endo Success ET25 Retreatment Tip under magnification of the dental operating microscope. OBJECTIVES 10

11. OBJECTIVES T o evaluate the resistance to vertical root fracture after retrieval of separated instruments from the root canal using the Endo Rescue System under magnification of the dental operating microscope. T o evaluate and compare the resistance to vertical root fracture after retrieval of separated instruments from the root canal using Ultrasonic U Files, Ultrasonic Tip (Acteon Endo Success ET25 Retreatment Tip), or the Endo Rescue System under magnification of the dental operating microscope. 11

12. Sample selection Freshly extracted sample teeth were placed in a 2.5% sodium hypochlorite solution for 15 min for the dissolution of soft tissue remnants. Later, the teeth were stored in 10% formalin solution. 12

13. Inclusion criteria 1. Mandibular first molar teeth with sound crown and root 2. The mesial root is moderately curved (Schneider’s classification) 3. Mature apex. 13

14. Exclusion criteria 1. Endodontically treated teeth 2. External or internal resorption 3. Teeth with developmental anomalies 4. Teeth with preexisting root fractures, cracks, or root caries. 14

15. Sample preparation 15

16. Intracanal fracture of instruments 16

17. SAMPLE GROUPING 17

18. The samples were mounted in a custom box filled with self‑cure acrylic resin and tested with a universal testing machine accurate to ±1%. The samples were fixed so that a 5‑mm diameter flat plugger applied axial force to the root at a crosshead speed of 1 mm/min Preparation for mechanical testing 18

19. results n Mean SD SE Median χ2 P value of Kruskal–Wallis test A 14 826.214 296.2172 79.1674 730 10.133 0.006** B 14 538.964 133.9031 35.7871 546.75 C 14 727.321 332.0970 88.7567 745.50 Total 42 697.500 288.1304 44.4595 Intergroup comparison of fracture load Intergroup comparison between Ultrasonic U Files (Group A), Ultrasonic ET25Retreatment Tip (Group B), and Endo Rescue System (Group C) 19

20. results Group Versus Mann–Whitney U Z P value of Mann–Whitney U ‑test A B 16.000 − 3.768 0.000** A C 85.000 − 0.597 0.550# B C 70.000 − 1.287 0.198# Intergroup pairwise comparison using Mann– Whitney U‑test **Statistically highly significant difference seen ( P <0.01) between group A vs B. #Statistically non-significant difference seen ( P >0.05) for the values between groups A vs C. #Statistically non-significant difference seen ( P >0.05) for the values between groups B vs C 20

21. Graph 1: Intergroup comparison between Ultrasonic U Files (Group A), Ultrasonic ET25Retreatment Tip (Group B), and Endo Rescue System (Group C) results 21

22. Graph 2: Intergroup comparison between Ultrasonic U Files (Group A) and Ultrasonic ET25 Retreatment Tip (Group B) results 22

23. Graph 3: Intergroup comparison between Ultrasonic U Files (Group A) and Endo Rescue System (Group C) results 23

24. Graph 4: Intergroup comparison between Ultrasonic ET25 Retreatment Tip. (Group B) and Endo Rescue System (Group C) results 24

25. discussion Hulsmann . ,Ward et al ., Wu et al .,and Bardsen et al . noted that the severe lingual curvature of the mesiobuccal root canal increases the likelihood of instrument separation. Ungerechts C, Bårdsen A, Fristad I. Instrument fracture in root canals‐where, why, when and what? A study from a student clinic. International endodontic journal. 2014 Feb;47(2):183-90. . 25

26. discussion After removing the separated instruments, samples were tested for vertical root fracture resistance directly as obturation could lead to dentinal defects, as noted by Blum et al .,Shemesh et al .,and Kumaran et al . wherein it was concluded that teeth subjected to both lateral compaction and warm vertical condensation resulted in defects. Blum JY, Machtou P, Micallef JP. Analysis of forces developed during obturations. Wedging effect: Part II. Journal of Endodontics. 1998 Apr 1;24(4):223-8. 26

27. discussion The superior performance of Group A is attributed to the small tip diameter (0.2 mm) and the absence of a need for a staging platform, which minimizes radicular dentin loss . 27

28. discussion The Endo Rescue System (Group C) exhibited moderate fracture resistance, with no statistically significant difference ( P > 0.05) compared to the other groups. holding techniques to be more aggressive while removing separated instruments from the root canal as compared to ultrasonics. Gerek M, Başer ED, Kayahan MB, Sunay H, Kaptan RF, Bayırlı G. Comparison of the force required to fracture roots vertically after ultrasonic and Masserann removal of broken instruments. International endodontic journal. 2012 May;45(5):429-34. 28

29. discussion The least resistance to vertical root - Ultrasonic ET 25 retreatment tip (Group B). which stated that use of this ultrasonic tip evidently increases the root canal volume owing to the need for the creation of a staging platform to gain access to the separated instrument, leading to microcrack formation, with the former being the primary reason for decreased vertical root fracture resistance Fu M, Huang X, Zhang K, Hou B. Effects of ultrasonic removal of fractured files from the middle third of root canals on the resistance to vertical root fracture. Journal of endodontics. 2019 Nov 1;45(11):1365-70. 29

30. Ultrasonic U files demonstrated the least reduction in vertical root fracture resistance after the removal of separated instruments, followed by the Endo Rescue System and Ultrasonic ET25 retreatment tips. Given the variability in root anatomy, instrument type, location, size, pulpal status, and operator skill, no single retrieval system is universally ideal. Clinicians should choose their treatment protocols based on a thorough assessment of the tooth’s future prognosis. conclusion 30

31. REFERENCES Vouzara T, Lyroudia K. Separated instrument in endodontics: Frequency, treatment and prognosis. Balkan Journal of Dental Medicine. 2018;22(3):123-32. Ungerechts C, Bårdsen A, Fristad I. Instrument fracture in root canals‐where, why, when and what? A study from a student clinic. International endodontic journal. 2014 Feb;47(2):183-90. Blum JY, Machtou P, Micallef JP. Analysis of forces developed during obturations. Wedging effect: Part II. Journal of Endodontics. 1998 Apr 1;24(4):223-8. Gerek M, Başer ED, Kayahan MB, Sunay H, Kaptan RF, Bayırlı G. Comparison of the force required to fracture roots vertically after ultrasonic and Masserann removal of broken instruments. International endodontic journal. 2012 May;45(5):429-34. Fu M, Huang X, Zhang K, Hou B. Effects of ultrasonic removal of fractured files from the middle third of root canals on the resistance to vertical root fracture. Journal of endodontics. 2019 Nov 1;45(11):1365-70. 31

32. THANK YOU 32