Pattern of endodontic instrument separation and factors affecting its retrieval: a 10-year retrospective observational study in a postgraduate institute

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Restor Dent Endod. 2025;50.rde.2025.50.e7

Publication date (electronic) : 2025 February 19

doi : https://doi.org/10.5395/rde.2025.50.e7

Velmurugan Natanasabapathy^1,, Aswathi Varghese¹, Paul Kevin Abishek Karthikeyan¹, Srinivasan Narasimhan²

¹Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Meenakshi Academy of Higher Education and Research (MAHER) University, Maduravoyal, Chennai, India

²Specialist – Endodontics, Hamad Dental Center, Hamad Medical Corporation, Doha, Qatar

Citation: Natanasabapathy V, Varghese A, Karthikeyan PKA, Narasimhan S. Pattern of endodontic instrument separation and factors affecting its retrieval: a 10-year retrospective observational study in a postgraduate institute. Restor Dent Endod 2024;50(1):e7.

^*Correspondence to Velmurugan Natanasabapathy, BDS, MDS, PhD Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Meenakshi Academy of Higher Education and Research (MAHER) University, No. 1, Alapakkam Main Road, Maduravoyal, Chennai 600 095, Tamil Nadu, India Email: vel9911@yahoo.com

Received 2024 September 18; Revised 2024 October 13; Accepted 2024 November 22.

Abstract

INTRODUCTION

Separated endodontic instruments (SEI) during cleaning and shaping, is a challenging clinical situation. Disinfection of the root canal system is affected by the presence of a SEI, which can ultimately compromise the treatment outcome [1]. To date, mechanical enlargement of the root canals is mostly done using nickel-titanium (NiTi) instruments. These instruments have a higher incidence of separation inside the root canal than stainless steel instruments [2]. Previous literature has shown the prevalence of SEI ranging from 0.4% to 5% [3,4].

The recent NiTi files are manufactured using heat-treated alloys, which are claimed to have superior fracture resistance and enhanced flexibility [5]. Apart from these, changes in NiTi file design elements like variable taper, asymmetrical cross-section, and newer motion kinematics like, torque control motors with auto reverse function, reciprocation, and self-adjusting files are other methods that have been introduced to decrease the incidence of file separation [6–10]. The clinical incidence of SEI for rotary motion is 2.43%, while for reciprocation it is 1% [11]. Previous studies have reported, SEI to occur more commonly in the mesial roots of molars and the apical third of the root canal [12,13]. It is still unclear if this pattern of separation is seen with the newer generation NiTi files.

SEI can be retrieved using nonsurgical or surgical techniques. With advances in technology, newer techniques, and microscopic instruments are available for instrument retrieval which can give a predictable outcome [14–18]. Knowing the pattern of separation and the factors affecting the retrieval of separated instruments in such scenarios will be interesting.

Hence, the aim of this retrospective observational study was, to assess the pattern of instrument separation (level and length), the type of tooth/root canal, the technique used for retrieval, retrieval success, and factors that influence retrieval of SEI. The secondary aim was to assess any difference between newer generation heat-treated NiTi files and conventional NiTi files in terms of SEI pattern and retrieval.

METHODS

This observational study has been reported according to the STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) guidelines [19] (Figure 1). This study was conducted in the Department of Conservative Dentistry and Endodontics. Ethical approval for this study was granted by the Institutional Ethical Committee (No. MADC/IEC/III/89/2023) of the dental college. The study population comprised patients who had been treated for SEI between 2013 and 2023 in the postgraduate department. The record of 190 patients who had a SEI during their root canal procedure or were referred to the department for management of SEI was considered for this study. The data was collected using a pre-piloted data sheet using Microsoft Excel. It was divided into, demographic data (age and sex), tooth-related data (diagnosis of the tooth, primary/secondary treatment tooth, arch, curvature, presence of calcification, canal, level of fracture, curvature), file-related data (type of file, kinematics, material, file size, length of file, taper). Additionally, if the retrieval was attempted, the technique used for retrieval, success or failure of retrieval, final intervention (extracted, bypassed and obturated, obturated till the level of separation), and adverse outcomes if any were recorded.

Figure 1.

STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) flowchart. SEI, separated endodontic instrument.

RESULTS

A total of 190 cases of SEI were reported during the study period. The age of the study population was 39.08 ± 12.9 years. In eight cases, the nature of the file type was unknown as these were referred from outside the department for retrieval and so their data was used only to determine the pattern of separation and not for determining the generation of NiTi instruments. Among the NiTi files, 55.3% were conventional NiTi and 40.5% were heat-treated NiTi files. SEI occurred more commonly in posterior teeth (86.8%) than anterior teeth (13.2%) and more often in mandibular teeth (59.5%) than in maxillary teeth (40.5%).

With regard to the sizes of the SEI, 11.5% were below size 15, 56.5% were between 15 and 25, 29.2% were between 25 and 40, and 2.8% were above size 40. With regards to taper, the SEI prevalence of 2%, 4%, 6%, and >6% tapered instruments were 31.5%, 27.9%, 23.8%, and 16.6%, respectively. The length of the SEI was <5 mm in 77.9%, 6–10 mm in 16.8%, and >10 mm in 5.3%.

The maximum number of SEI occurred in the apical third region (46.8%) and the least in the coronal third region (6.3%). The prevalence in the middle third was 16.3%. Apart from this SEI were located, in the cervico-middle and apical-middle levels in 2.6% and 15.3% of the cases, respectively. In 4.7% of the cases, SEI occurred along the full length of the root canal and in another 7.9% of the cases, the files were separated beyond the apex. In 84.2% of the cases, the instrument separation occurred in teeth with moderate to severe curvature and 15.8% in cases with mild curvature. The pattern of instrument separation was similar with both conventional NiTi files and newer generation heat-treated NiTi files.

A total of 88 patients opted for removal of SEI and complete retrieval was possible in 70 of these cases (79.5%). A few of the successful cases have been represented in Figures 2 and 3. In the remaining 18 cases (20.5%), retrieval was unsuccessful. Of those 18 cases, in 11 cases the SEI was bypassed and obturated and in seven cases the teeth were obturated at the level of SEI (Table 1). Of the 102 patients who did not want retrieval, 41 of them did not report back for any further treatment, and in all the remaining cases, the root canals were either bypassed or obturated till the level permissible.

Figure 2.

Retrieval of separated endodontic instruments (A–D, Case I; E–H, Case II; I–L, Case III). (A) Separated instrument in the apical third. (E) Full-length separation of the instrument. (I) Full-length separation of instrument. (B, F, J) Separated instrument viewed under a dental operating microscope (arrows). (C, G, K) After retrieval. (D, H) Retrieved instrument. (L) Retrieved instrument with fractured ultrasonic tip.

Figure 3.

Retrieval of separated endodontic instruments using a broken tool removal (BTR) pen (A–D, Case I; E–H, Case II; I–L, Case III). (A) Separated instrument beyond the apex. (E) Separated instrument in middle third. (I) Separated instrument in the middle third of the crowned tooth. (B, F, J) Separated instrument viewed under a dental operating microscope (arrows). (C, G, K) After retrieval. (D, H, L) Retrieved using BTR pen.

Table 1.

Descriptive statistics: distribution of the separated endodontic instruments across various independent factors (n = 190)

Ultrasonics was the most commonly used method for the retrieval of SEI in 73.9% of the cases (Figure 2). In 22.8% of the cases, ultrasonics and BTR were used (Figure 3). The iatrogenic events that occurred during retrieval were perforations (<1%), secondary fracture of SEI (11.4%), fracture of ultrasonic tips (17.0%), and ledge formation (<1%) (Figure 4). There was no difference in retrievability between conventional NiTi files and newer generation heat-treated NiTi files.

Figure 4.

(A) Separated instrument in apical two-thirds. (B) Secondary fracture of the separated instrument. (C) Separated instrument in the apical third. (D) Separated instrument with lateral strip perforation, (E) Separated instrument in the apical third. (F) Secondary fracture of the separated instrument and lateral perforation.

Various independent factors such as the position of the tooth, arch, file size, curvature, length of file, and file type did not affect the outcome of retrieval (Table 2). The odds ratio (OR) of failure and its 95% CI values for all the prognostic variables are presented in Table 3. Of the eight prognostic factors included in the model, only two (taper and level of the separated instrument) were found to be statistically significant (p < 0.05) and to have influenced the retrieval. An increase in the taper by every unit was associated with increased odds of failure by 1.494 times (OR, 1.494; p = 0.022). In addition, the apical position of the instrument was associated with increased odds of failure by 8.761 times (OR, 8.761; p = 0.013) compared to the coronal two-thirds level. Additionally, our bootstrapped analysis provided further insights into the reliability of our regression coefficients as the estimated 95% CIs for the two predictors (taper and level of the separated instrument) remained significant (Table 4).

Table 2.

Outcome of retrieval (count and percentage) based on various independent factors (n = 88)

Table 3.

Logistic regression: various prognostic factors influencing the instrument retrieval

Table 4.

Bootstrapped logistic regression

DISCUSSION

This study was a 10-year retrospective observational study done to determine the pattern of separated instruments and their management in a postgraduate institute in Chennai, India. The postgraduates were asked to complete root canal instrumentation in 10 extracted teeth before starting a clinical case. The students were instructed to pre-enlarge the root canal using stainless steel hand instruments to size 20 K-file before the use of NiTi instruments. All students performed the instrumentation using endo motors with torque control.

In the event of an instrument separation, the patients were informed about the incident and given the option of retrieval. Retrieval was done by a senior endodontist with more than 15 years of experience, under a dental operating microscope, with rubber dam isolation.

A total of 190 SEI was reported during the 10 years from 2013 to 2023. Nonsurgical instrument retrieval was attempted in 88 cases and the SEI was retrieved successfully in 70 cases (79.5%). A total of 21.6% of the patients did not report back for any further treatment once they were informed about the presence of SEI inside the root canal. The patients would have been apprehensive about the chances of failure and this could have resulted in them not reporting for any further management. A detailed explanation by the concerned clinician is necessary to educate the patients regarding the management of such iatrogenic errors, which could reduce the fallout.

SEI occurred most often in posterior teeth when compared to anterior teeth. The frequency of separation was highest in mandibular molars followed by maxillary molars [13]. Similar to earlier clinical studies, instrument separation occurred more often in the apical third region, followed by the middle region, and least in the coronal third region [2,12] in the current study [2,13]. A study from Türkiye reported that the frequency of file separation was higher in the mesiobuccal canal and apical one-third of the root canal. They also reported separation to be frequent in teeth with moderate to severe curvature (82%) which is similar to the current study (84%) [12].

Another interesting aspect seen in the current study was the length of the separated instrument. Earlier laboratory studies indicated that the length of SEI was mostly below 5 mm, but contrary to this, SEI longer than 5 mm were also noticed. In 18% of the cases, SEI was seen to include multiple levels (corono-apical, middle-apical) and in 5% of the cases, it occurred along the entire length of the root canal. This could have probably been due to excessive torsional loading [20]. Longer fragments could pose additional challenges to retrieval in the form of secondary fracture, which necessitated more chair side time and additional dentin removal to retrieve these fragments [21]. The pattern of instrument separation was also similar between conventional NiTi files and newer generation heat-treated NiTi files.

Retrieval was successful in 79.5% of cases in the current clinical study, which was similar to the success rate reported for retrieval of broken instruments using ultrasonics alone in a previous study [22]. This is slightly lower than the values reported by Malentacca et al. (83%) [17] and Fu et al. (88%) [4]. While Fu et al. [4] used the same staging platform (Ruddle’s technique) as the current study, Malentacca et al. [17] used a modified spinal tap needle for the retrieval of hand files. Another study by Nevares et al. [23] reported a lower success rate of 33% for retrieving SEI in 112 of their cases using the Ruddle’s technique. Retrieval in that study was done, only if the separated fragment was visible under the microscope. The higher success rate for retrieval in a study by Cuje et al. (95%) [24] is attributed to the fact that 52% of the instruments retrieved were stainless steel instruments. In contrast, in the present study, the vast majority were NiTi rotary instruments, excluding eight cases which were stainless steel files. Ward et al. [25] reported a success rate of only 67% and the authors attempted retrieval under a dental operating microscope but used CPR (controlled penetration removal) ultrasonic tips. Souter and Messer [26] reported a success rate of 70% for retrieval of hand and rotary instruments which is slightly lower than the current study. The difference in success rates for retrieval among studies might have occurred, due to different ultrasonic tips, varied techniques used, and also the operator skill. The retrieval in the current study was attempted by a senior endodontist, who had prior training in instrument retrieval. If multiple operators were to be involved in retrieval attempts, the success rates could differ and this needs to be studied in the future.

The length of the SEI has not been taken into consideration in previous studies, 11% of longer SEI underwent secondary fracture and this further increased the retrieval time. Longer fragments were successfully removed using a combination of ultrasonics and looping techniques in 80% of the cases. This method can decrease the treatment time and reduce the incidence of secondary fractures. According to Terauchi et al. [27], any SEI, longer than 4.5 mm can be removed easily using looping systems. The BTR loop device was used for retrieval in this study. This device allows for a loop of 0.5 mm diameter to be used inside the root canal.

Ultrasonic ET 40 and 20 tips (Acteon Endo Success tips, Eighteeth Medical Ultra X Tip; distributed by Orikam Healthcare, India) were used during the first 5 years of the study. During the next 5 years, the Terauchi file retrieval kit’s ultrasonic tips 87,88, and 89 (Dental Engineering Laboratories) were used, as these tips allowed for precise dentin removal due to their longer and smaller dimensions. Besides this U files sizes 15 and 20 (Mani Inc.) were used in select cases to free the separated instrument from dentin if the file was not retrieved using the former ultrasonic tips. The most common iatrogenic error that occurred was the fracture of the ultrasonic tip itself, which occurred in 15 cases, but all of those were removed easily using ultrasonic vibrations with larger tips. But the chair side time was increased in all cases. In 11% of the cases, the SEI itself underwent a secondary fracture, which was also removed subsequently. The other iatrogenic errors that occurred, were perforation and ledge formation which occurred in one case each and were managed accordingly.

Among the various factors influencing instrument retrieval, the taper and apical positioning of the SEI were the ones that negatively impacted instrument retrieval [21]. The chances for failure to retrieval is 1.4 times more with every increase in taper. Previous studies have reported more fracture in files with larger taper than in files with smaller taper, due to increased stress intensity at the point of flexure [28]. The increased cross-section of the file will limit the potential space available for ultrasonic vibrations and also hamper the enveloping of the instrument using the looping device.

Failure to retrieve was eight times more if the files were placed apically. Two earlier studies have reported difficulty and inability to retrieve instruments separated in the apical third [25,26]. Similarly, Dioguardi et al. [29] in their trial sequencing analysis reported that increased failure rates were seen when instruments were located more apically when compared to middle and coronal thirds. The narrow dimensions of the root canal and lack of clear visibility of the SEI make retrieval difficult in the apical portion of the root canal. Besides this, clinicians often limit the use of ultrasonic instruments in the apical portion for fear of perforation [25,26].

The use of the gold standard ‘Ruddle’s technique’ for retrieval has proven effective and successful based on the previous literature and in this current study [4,23]. It is important to highlight that the newer generation heat-treated NiTi files can be retrieved similarly to the conventional NiTi files using the current microscopic instruments. In the vast majority of cases, the retrieval was done in a single appointment, but in a few cases multiple appointments were required and this extended chair side time required for retrieval could pose a problem in pediatric or geriatric patients. While most of the separated instruments in this study could be retrieved, the process requires significant time and resources. Therefore, clinicians should take extra precautions to prevent SEI from occurring. Special care is essential during instrumentation in root canals, particularly in posterior teeth of the mandibular arch and in teeth with moderate to severe curvature.

The study has certain limitations, including a small sample size and the fact that all retrieval procedures were conducted by a single operator, which affects the generalizability of the findings. While the evidence presented is classified as observational, conducting a clinical trial on this issue would have posed significant challenges. Nonetheless, the credibility of the results remains intact. Given that only one trained endodontist performed the retrievals, varying success rates might be observed with multiple operators. Therefore, future research should focus on larger sample sizes, involve multiple operators, and explore the impact of different motion kinematics, such as reciprocation.

CONCLUSIONS

SEI was more frequently observed in the mesiobuccal roots of mandibular and maxillary molars with moderate curvature. Instrument separation occurred more frequently in the apical portion of the root canal. There was no difference in the pattern of SEI between the conventional NiTi and newer generation heat-treated NiTi files. The great majority of cases had successful instrument retrieval. The instrument taper and apical location of the SEI had a negative impact on instrument retrieval.

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