Basic Research—Technology

Removing Fractured Endodontic Instruments with a ModifiedTube Technique Using a Light-curing CompositeMichael Wefelmeier, DMD,* Maria Eveslage, Dipl-Stat,† Sebastian B€urklein, DMD,†‡

Klaus Ott, DMD,* and Markus Kaup, DMD*

Abstract

Introduction: The aim of this in vitro study was toassess an alternative method using light-curing compos-ite for removing fractured endodontic instruments witha tube technique.Methods: Two different stainless steelendodontic instruments (ISO 20: Hedstrom files, K-files;VDW, Munich, Germany) were cut at the diameter of0.4 mm. These fragments were fixed in a vise leaving afree end of 1 or 2 mm. Cyanoacrylate (Instant Fix; HenrySchein Dental, Melville, NY), dual-curing Rebilda DC(VOCO, Cuxhaven, Germany), and light-curing SureFilSDR (Dentsply, York, PA) were placed into microtubes(N’Durance Syringe Tips; Septodont, Saint-Maur, France)and shifted over the instruments (n = 20 in each group).After polymerization, pull-out testswere performedwith aconstant speed of 2 mm/min; failure load was measureddigitally. Data were analyzed using the Kruskal-Wallistest followed by the Dunn test for pairwise comparison.Results: The median failure load was up to 62.5 N forSDR, 35.8 N for Rebilda, and 14.7 N for cyanoacrylate,respectively. Both tested composites yielded significantlyhigher values in pull-out tests than cyanoacrylate. The dis-connecting force was highest when light-cured compositeSDR was used for fixation. Removing Hedstrom files re-sulted in higher values than removing K-files. The medianforce when using SDR was 79.7 N (interquartile range,66.0–86.8 N) in Hedstrom files and 53.3 N (interquartilerange, 47.1–58.5 N) in K-files. Conclusions: Withinthe limitations of this study, the use of light-curing com-posite inside of the microtube was superior comparedwith the use of cyanoacrylate or chemically cured com-posite, which are being used presently. (J Endod2015;41:733–736)

Key WordsEndodontic instrument, fractured, removal, tube tech-nique

From the *Department of Operative Dentistry, Universit€ats-klinikum M€unster; †Institute of Biostatistics and ClinicalResearch; and ‡Central Interdisciplinary Ambulance in theSchool of Dentistry, Universit€atsklinikum M€unster, M€unster,Germany.

Address requests for reprints to Dr Michael Wefelmeier,Department of Operative Dentistry, Albert-Schweitzer-Campus1, Building W30, Universit€atsklinikum M€unster, 48149,M€unster, Germany. E-mail address: mwefel@uni-muenster.de0099-2399/$ - see front matter

Copyright ª 2015 American Association of Endodontists.http://dx.doi.org/10.1016/j.joen.2015.01.018

JOE — Volume 41, Number 5, May 2015

Fracturing of endodontic instruments is a rare but annoying complication duringroot canal treatment with a reported prevalence between 1.83% (1) and 3.3%

(2). In retreatment cases, this incident occurs more often (1). Machtou and Reit(3) point out that removal of the separated instruments would be the best treatmentoption.

Even though modern techniques and advances in vision have improved clinicians’ability to remove fractured endodontic instruments, removal may not always bepossible or desirable. There is no sufficient information based on high-level evidenceabout the management of separated instruments, which complicates the decision-making process (4–6). All efforts in managing this complication should be basedon thorough knowledge of each treatment option, considering the success rateswell balanced against the potential risks of leaving or removing the fragment (7). Frac-tured endodontic instruments might not directly affect the prognosis (2, 4, 6, 8) of thetooth because the fractured instrument itself may not directly lead to infection.However, the fractured instrument may hinder chemomechanical disinfection of theentire root canal system and thus can limit the prognosis (3, 5, 6, 9–11)depending on the stage in the root canal treatment procedure when the separationoccurred (6, 12, 13). Because of the different situations after instrument fracture(eg, presence or absence of apical disease [6], type of tooth [14], location/length/type of the instrument [7, 14, 15], root canal curvature [14, 16], and time offracture [17]), there is no clinical evidence on the force required for its removal.Even the technique for the removal of fractured instruments has to be evaluated indi-vidually for each different situation (5).

If removing is necessary, attempts to remove fractured instruments can lead toledge formation, overenlargement, canal transportation, or perforation (18). The chal-lenging steps in removing fractured instruments are the minimally invasive approachand exposure (5). For clinicians, several nonsurgical treatment options are available.Besides the ‘‘braiding technique’’ (19) in which small files are used to remove or at leastbypass the instrument, the use of ultrasonic devices is an effective way to expose andeventually remove fragments (14, 20). If ultrasonic procedures fail, the tubetechnique is the next best chance to remove fractured instruments (20). In these cases,it is helpful to be able to release as much force as possible with the minimally invasiveapproach.

For the successful use of commercial mechanical tube systems like the Masserannkit (Micro-Mega, Besancon, France) and the IRS Instrument Removal System (Jadent,Aalen, Germany), a straight-line access to the fractured instrument is necessary (21).Even the smallest diameter of the Masserann-kit (1.2 mm) is pretty wide compared withthe average root diameter (22, 23).

To approach the fractured instrument, the IRS Instrument Removal System onlyneeds 0.6 mm; however, the instrument needs to be exposed at least up to 2–3 mm(20). Alternatively, a microtube filled with cyanoacrylate or with dual-curing compositecan be shifted over the exposed end of the fractured instrument (24, 25). However, usingmicrotubes filled with adhesive materials is associated with disadvantages whencompared with mechanical systems (eg, the extended cyanoacrylate may set inside theroot canal) (20). Additionally, only relatively low tensile forces are achieved (20). Theaim of this in vitro pilot study was to compare the different well-established microtubetechniques with a new approach for instrument fixation.

Removing Fractured Endodontic Instruments 733

Basic Research—Technology

Materials and MethodsIn pull-out tests, the disconnecting force between 3 different

fixation materials and 2 different stainless steel endodontic instru-ments was determined. Twenty specimens were investigated in eachgroup.

Two different endodontic instruments (ISO 20: Hedstrom files,Kerr files; VDW Dental, Munich, Germany) were cut exactly at thesame diameter of 0.4 mm. These fragments were fixed in a vise withan overlap of either 1 or 2 mm. Microtubes (N’Durance syringe tips;Septodont, Saint-Maur, France) with an outer diameter of 0.85 mmand an inner diameter of 0.64 mm (22-G) were shifted over these in-struments and fixed as shown (Fig. 1).

In group 1, cyanoacrylate-based adhesive (Instant Fix; HenrySchein Dental, Melville, NY) was aspirated into the tubes before puttingthem over the endodontic instrument. For faster setting of the cyanoac-rylate, the tubes were stored in water for 30 minutes to guarantee a ho-mogenous setting and maximal adhesion.

In group 2, a dual-curing composite resin (Rebilda DC; VOCO,Cuxhaven, Germany) was used to fix the endodontic instrument inthe microtube. The setting time was 30 minutes to guarantee completepolymerization.

In group 3, a light-curing composite resin (Surefil SDR; Dentsply,York, PA) was used to fix the endodontic instruments inside of thetube. An optical fiber (Conrad Electronic SE, Hirschau, Germany)with a diameter of 0.5 mm was inserted into the microtube and pushedforward until the fiber got in contact with the endodontic instrument(Fig. 1). Then, the SDR was light polymerized by Smartlite PS (Dents-ply) through the optical fiber for 1.5 minutes. The light source wasapplied in contact to the fiber (Fig. 2).

After polymerization, the compound between the tubes and theendodontic instruments was used for pull-out tests. A total of 240 sam-ples were prepared as follows:

Figure 1. A schematic drawing showing the fixed instrument, metallic tube, and 2curing composite; upper right: SDR, smart dentin replacement, light-curing comp

734 Wefelmeier et al.

1. Fixation material: cyanoacrylate, instrument: Hedstrom, and fixa-tion length: 1 mm

2. Fixation material: cyanoacrylate, instrument: Hedstrom, and fixa-tion length: 2 mm

3. Fixation material: cyanoacrylate, instrument: K-file, and fixationlength: 1 mm

4. Fixation material: cyanoacrylate, instrument: K-file, and fixationlength: 2 mm

5. Fixation material: Rebilda DC, instrument: Hedstrom, and fixationlength: 1 mm

6. Fixation material: Rebilda DC, instrument: Hedstrom, and fixationlength: 2 mm

7. Fixation material: Rebilda DC, instrument: K-file, and fixationlength: 1 mm

8. Fixation material: Rebilda DC, instrument: K-file, and fixationlength: 2 mm

9. Fixation material: SDR, instrument: Hedstrom, and fixation length:1 mm

10. Fixation material: SDR, instrument: Hedstrom, and fixation length:2 mm

11. Fixation material: SDR, instrument: K-file, and fixation length:1 mm

12. Fixation material: SDR, instrument: K-file, and fixation length: 2 mm

The tube on the one side and the endodontic instruments on theother side were fixed in a mount. The tubes were pulled with a constantspeed of 2 mm/min, and the resulting force was measured digitally (LFPlus; Lloyd Instruments, Bognor Regis, England).

StatisticsTo compare the different instruments, instrument lengths, and

fixation materials in regard to the force necessary to break the

different methods of adhesion (lower right: cyanoacrylate; Rebilda DC, dual-osite).

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Figure 2. Microtube and optical fiber to show the way of the light, which isnecessary for polymerization after shifting both over the tip of the endodonticinstrument.

Basic Research—Technology

adhesive joint, descriptive statistics were calculated. Values are pre-sented as median and interquartile range (IQR) throughout the text.Because normal distribution could not be assumed, the 3 groupswere compared using the Kruskal-Wallis (26) test followed by theDunn test (27) for pairwise comparison applying the closed testingprinciple (28). These comparisons were performed for the 2 instru-ments and 2 instruments lengths separately, and all P values weretherefore adjusted by the Bonferroni method to account for multipletesting. The multiple significance level was set to a = 0.05. Statisticalanalyses were conducted using IBM SPSS Statistics 22 (IBM Corp,Somers, NY) and R Version 3.1.0 (SAS Institute Inc, Cary, NC).

TABLE 1. Mean Force, Standard Deviation, and Range of All Pull-out Tests

Endodontic instrument Fixation length Fixation material

Hedstrom 1 mm cyanoacrylateRebilda DC

SDR2 mm cyanoacrylate

Rebilda DCSDR

K-file 1 mm cyanoacrylateRebilda DC

SDR2 mm cyanoacrylate

Rebilda DCSDR

Rebilda DC, dual-curing composite; SDR, smart dentin replacement light-curing composite.

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ResultsRegardless of the type of instrument or instrument length, the use

of light-curing SDR reached the highest median amount of force, whichwas necessary to break the connection between the microtube and theinstrument (Table 1). For all instruments and instrument lengths, sig-nificant differences between SDR and Rebilda as well as cyanoacrylatewere achieved (P < .0001).

In all pull-out tests with SDR and 2-mm Hedstrom files, theconnection between composite resin and the instrument did not fail.However, this was primarily because of previous fracturing of the end-odontic instrument itself.

Two different mechanisms of failure of the adhesive joint wereobserved when using Rebilda in 2-mm Hedstrom files or2-mm K-files. The connection between composite and the inner sur-face of the tube failed and led to total disconnection, which wasobserved in 20% (K-files) or 40% (Hedstrom) of the samples. Theincreased variance resulting from this phenomenon can clearly beseen in Table 1.

The glue or composite resin reacts differently with the 2 types ofinstruments. The adhesive joint seems to be more durable in Hedstromfiles for Rebilda and SDR (eg, the median force when using SDR was79.7 N [IQR = 66.0–86.8 N] in Hedstrom files and 53.3 N [IQR =47.1–58.5 N] in K-files). The connection is more durable in any com-bination of fixationmaterials and instruments with instrument lengths of2 mm compared with 1 mm (Table 1).

DiscussionAll tested parameters had a relevant influence on the durability of

the adhesive joint. The disconnecting force was highest when light-cured composite SDR was used for fixation. For the dual-curing com-posite resin Rebilda, the biggest variances of values were observed.Fixation with cyanoacrylate was the weakest (Table 1).

Fixation with cyanoacrylate led to slightly higher values for instru-ments with a larger core diameter (K-file > Hedstrom). The strength ofthe adhesive bond seems to be higher when the layer of cyanoacrylate inthe gap between the instrument and the tube is spread out relatively uni-formly. Cyanoacrylate adhesives are not designed to bridge a gap>.1 mm and thus cannot create a secure adhesive connection.

In general, significantly higher values in pull-out tests wereachieved with both tested composites than with cyanoacrylate. Usingground-twisted K-files resulted in lower values compared withmachined Hedstrom files with a smaller core diameter and a more pos-itive rake angle (29), resulting in more room for the fixation material.Furthermore, the angulation of the instruments’ cutting edges may affectthe resulting data. If the angle is more parallel to the direction of force

Mean Standard deviation Range (minimum–maximum)

11.24 N 3.83 N 4.93–18.50 N32.42 N 11.30 N 11.69–51.67 N64.66 N 9.13 N 49.13–81.47 N17.69 N 7.42 N 6.16–30.88 N55.82 N 25.51 N 14.17–96.59 N86.15 N 4.33 N 78.91–93.60 N11.56 N 4.44 N 2.85–18.86 N29.83 N 7.35 N 18.20–42.12 N47.67 N 7.07 N 33.42–58.83 N27.59 N 5.55 N 18.54–36.31 N43.20 N 17.28 N 10.34–64.36 N59.79 N 9.45 N 45.62–76.15 N

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Basic Research—Technology

(K-files), the resistance of the connection between composite resin andfractured instrument seems to be lower.

The application of chemically polymerized Rebilda DC showedsignificantly lower values and greater standard deviations than light-cured SDR. This could be explained by different shrinkage of the testedcomposites (30) and the content of filler but not a lack of polymeriza-tion or other physical properties. In their studies, axial shrinkage of SDRwas 2.26% and Rebilda DC reached 2.96%. The shrinkage forceamounted to 20 N for SDR in average and about 37 N for RebildaDC (30).

During polymerization, the composite seems to shrink towardthe structured surface of the endodontic instrument. As a result ofthis, the connection between the composite and the inner surfaceof the tube failed using Rebilda DC for fixation and led to totaldisconnection. These observations may elucidate the standard devia-tions in Table 1.

Using this modified microtube technique may offer some advan-tages compared with other tube techniques. Within the limitations ofthe results of this experiment, the following aspects about the clinicalrelevancy might be considered:

1. The microtubes can be bent in any desirable direction or a Cancel-lier instrument (SybronEndo, Orange, CA) might be used for placingthe tubes over the instrument so that nothing will interfere with thestraight line of sight a microscope requires.

2. Both microtubes and optical fibers are available in a wide range ofdiameters down to 0.25 mm. Because of this fact, the size of the tubecan be adapted individually, and additional reduction of radiculardentine is minimized.

3. A circumferential staging platform facilitates the removal of frac-tured endodontic instruments with ultrasonic devices or microtubes(13). The more radicular dentin can be saved; the lower is at risk ofperforation (23). For this modified tube technique, high forces canbe transferred to the fractured instrument with an exposure of1–2 mm.

4. Furthermore, there are huge differences in application time.Although the polymerization of SDR can be controlled by the clini-cian and is induced by light for 1.5 minutes, longer setting times forthe other materials were necessary. Preliminary tests showed a con-stant level of maximal fixation after 20 minutes for cyanoacrylate andRebilda.

5. In addition, the polymerization of SDR only depends on the in-tensity of light, which is inside and in front of the tube. Materialoutside of the tube will not polymerize and can be removedeasily.

The investigation of additional rotational forces and different typesof endodontic instruments will have to show whether this technique is ameaningful rewarding addition to the standard techniques frequentlyused by clinicians. Further studies concerning rotary nickel-titanium in-struments are necessary to elucidate if the results can be extrapolated toinstruments with other metallurgical properties and cross-sectional de-signs.

ConclusionWithin the limitations of this in vitro pilot study, the use of light-

curing composite resin inside of the microtube was superior comparedwith the use of cyanoacrylate or chemically cured composite resin.The applicable forces differed significantly (SDR > RebildaDC > cyanoacrylate, Hedstrom file > K-file).

736 Wefelmeier et al.

AcknowledgmentsThe authors deny any conflicts of interest related to this study.

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