21 October 2022

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What factors influence the removal of broken instruments in root canals?

Simona Chirico

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When using rotary nickel-titanium (NiTi) instruments for root canal shaping, the fracture incidence of rotary files varies from 0.4% to 5%. The presence of fractured endodontic instruments within the root canal system, preventing adequate disinfection and elimination of infected pulp tissues, can adversely affect the result of orthograde treatment. 

The success rate for removing such separate tools or instruments varies widely from 48% to 95% and appears to be related to the techniques used in a complex range of cases. The technique of using ultrasonic tips and a dental operating microscope (DOM) is considered by many to be the optimal strategy for the successful removal of separate instruments. However, there is currently no standardized procedure for predictable removal.

Materials and methods

In the study led by Teurachi et al. and published in the Journal of Endodontics, the authors evaluated how much the curvature of the root canals and the length of the broken instrument inside the canal can affect the time required to loosen and recover the broken fragments. Retrieval procedures of 128 separate instruments were evaluated in patients monitored for a minimum of six months. Preoperative Cone Beam tomographic images were used to measure the length of the separate instrument fragments in relation to the degree of curvature of the canal. In the initial phase, ultrasonic instruments were used to remove some of the root dentin to free the fractured piece of instrument. 

In the second step, ultrasonic instruments, wire loops or XP Shapers (FKG Dentaire SA, La Chaux-de-Fonds, Switzerland) were used for the removal of the fragments. 

The time periods to complete all procedures were recorded. The statistical analysis was completed by applying log-normal regression, modeling of structural equations and linear regression using Stata software version 14.2 (StataCorp LLC, College Station, TX).

Results

All the fractured instruments were successfully recovered. Almost 90% of the instruments were removed using only ultrasonic instruments with an average time of 221 seconds. The time to remove the instrument depended on both the length of the instrument and the curvature of the root canal. Furthermore, the preparation times were proportionally longer as the length of the fractured instrument increased when the microscope was required.

Conclusions

From the study data, the preparation phase seems to have a decisive role in the recovery of fractured instruments. The time required for the removal of the fractured instruments proved to be more prolonged with the increase in the length of the broken files and with the increase in the degree of curvature of the canal.

Yoshi Terauchi, Christopher Sexton, Leif K. Bakland and George Bogen. "Factors Affecting the Removal Time of Separated Instruments." J Endod August 2021;47:1245–1252. DOI: 10.1016/j.joen.2021.05.003 https://pubmed.ncbi.nlm.nih.gov/34000326/