Strategies for intracanal separated instrument removal: a review

Anatomic factors

Root anatomy, such as the diameter, length, canal curvature and thickness of the root dentine, has been reported to affect the ability to remove a SI safely.³³ The influence of anatomic factors can be explained in terms of visualization and access;³⁴ that is, the ability to see the separated segment, obtain clear access, and manipulate retrieval instruments/devices safely and effectively.

Canal curvature is one of the most important factors that influences the successful management of a SI. Some investigators reported that successful removal rates significantly decreased as the severity of curvature increased.^29,30,34 These studies demonstrate that the removal of SI from curved canals poses a particular challenge for clinicians. The problem with such cases is due to the tendency for the file to lie on its side, with the coronal portion of the fragment directed against one wall of the canal because of the natural tendency of the metal to straighten out as it exits a curved canal.³⁵

The removal of a SI is therefore more predictable in single-rooted teeth and teeth with uncomplicated root canal anatomy (eg incisors, canines, palatal roots of maxillary molars). The dimension and the internal anatomy of these roots makes fragment removal more straightforward.^2,29,30 On the other hand, the poorest rates for successful removal are associated with the mesiobuccal canals of maxillary molars and mandibular molars.³⁰ Somewhat surprisingly, some authors have reported lower success rates for maxillary and mandibular premolars due to narrow root canals and root canal irregularities.^2,29 By contrast, another study reported no statistical difference in removal success rates with regard to tooth and/or root type.¹⁵

Separated instrument factors

The chance of successfully removing a SI from the root canal depends also on factors relating to the instrument itself, such as the type of instrument, the location of the fragment, and its length.

Other factors

Preliminaries

Close inspection of pre-operative radiographs and knowledge of root anatomy is imperative before attempting the removal procedure in any tooth in order to ascertain the relative amount of surrounding dentine and the risk of perforation. Even then, a two-dimensional view of the root may provide an inaccurate estimate of dentine thickness.⁴⁶

After analysis of the radiograph, the first step is to eliminate any obstructions that prevent direct access to the SI. This is important since the main cause of instrument separation is often the presence of coronary interferences.^44,47,48 The clinician must consider the anatomy of the tooth being treated. For instance, in the case of the mesial root of a mandibular molar, a root in which instrument fracture frequently occurs,^29,37 there is almost always the presence of an isthmus connecting the mesiobuccal and mesiolingual canal. When attempting to locate the SI in this location, it would be easier and safer to remove dentine at the isthmus between the two mesial canals to free the fragment. Avoid targeting the furcal aspect of the root to prevent strip perforation. The same principle may be applied to the mesiobuccal root of a maxillary molar, where the presence of an MB2 (or mesiolingual) canal is quite common.⁴⁴

Removing fragments which extend into the pulp chamber

If a file has fractured with the fragment extending into the pulp chamber, or in a position where there is sufficient space around it, then quite often this can be simply removed by using mini-forceps,⁴⁹ such as Steiglitz forceps (Union Broach, York, PA), Peet silver point forceps (Silvermans, New York, NY), or Endo Forceps (Roydent, Johnson City, TN).

Removing separated instruments from the coronal third

When the SI is located within the root canal, it is generally impossible for the pliers to grip the instrument satisfactorily.²¹ Since this portion of the canal is generally wide and straight, using an extractor microtube is usually better and faster because it increases retention while gripping the embedded fragment.⁴⁵ There are several microtube removal methods, both old and new, and the choice is made depending on the diameter of the canal and separated instrument.

Microtube extraction is designed to engage an intracanal SI mechanically. It generally involves positioning the end of a narrow metal tube over the exposed coronal tip of the SI, a circumferential trough around the head of the fragment having previously been created by specialized trephine drills supplied with the system [Masserann^TM (Micro-Mega, Besançon, France); Endo Extractor^TM (Brassler, Savannah, GA, USA); Meitrac systems (Hager and Meisinger, Neuss, Germany); Endo Rescue^TM (Kome/Brasseler, Savannah, GA)] or ultrasonics [Cancellier^TM (SybronEndo, Orange, CA USA); iRS^TM (Instrument Removal System, Dentsply Endodontics, Tulsa, OK, USA); FRS^TM (File Removal System, Dentsply Tulsa Dental, Tulsa, OK, USA)]. The tube then engages the fragment mechanically (Masserann^TM, IRS^TM, Meitrac^TM, FRS^TM, Endo Rescue^TM) or with the aid of a cyanoacrylate glue (Cancellier^TM, Endo Extractor^TM).²¹ When the clinician feels that the tightest grip has been achieved, the entire assembly is rotated in a counterclockwise direction to unscrew the fragment from the dentine and remove it.⁵⁰

Ultimately, the external diameter of a device dictates how deep it can be safely introduced into a canal, while the internal diameter is selected to be slightly larger than the diameter of the fragment (Table 1).

If the operator does not have access to microtube extraction, other techniques may be considered. A wire loop can be formed by passing the two free ends of a 0.14-mm wire through a 25-gauge injection needle from the open end until they slide out of the hub end. By using a small mosquito hemostat, the wire loop can be tightened around the upper free part of the fragment, and then the whole assembly can be extracted from the root canal. The loop can be either small and circular or long and elliptical in shape, according to canal size and the location of the fragment.^26,54

Another technique is the use of a hypodermic needle to trephine around the coronal aspect of the fragment manually.⁵⁵ The beveled tip of a hypodermic needle can be shortened to cut a groove around the coronal part of the fragment by rotating the needle under light apical pressure. The needle size should allow its lumen to encase the coronal tip of the fragment entirely, which guides the needle tip while cutting so as to remove the minimum amount of dentine.⁵⁵ To remove the fragment, a cyanoacrylate glue or strong dental cement (eg polycarboxylate) can be inserted into the hypodermic needle and, when set, the complex (needle-adhesive-fragment) can be pulled out delicately in a clockwise or counterclockwise rotational movement. Roughening the smooth lumen by creating small burs can enhance the bond.⁵⁶ For cases in which glue cannot be used, a Hedstrom file can be pushed in a clockwise turning motion through the needle to wedge the upper part of the fragment against the needle's inner wall.⁵⁷ When the fragment and the Hedstrom file are interlocked, both can then be gently pulled out of the root canal.⁴¹

If the SI is a barbed broach and is not tightly wedged in the root canal, the easiest and fastest technique is to use another small barbed broach with a small piece of cotton twisted around it, which can then be inserted inside the root canal to engage the fragment; then the whole assembly is withdrawn.⁴⁹

Removing separated instruments from the middle third

When the fragment is located deep in the middle third, the sequence of steps for instrument removal is as follows.

After creating straight-line access to all canals, radicular access to the obstruction is prepared. If radicular access is limited, NiTi rotary or hand files are used to create sufficient space to introduce Gates Glidden drills into the canal orifice safely. The drills are then used in a brush-like manner to create additional space and allow maximum visibility of the obstruction.⁴³

Going in the first time, bypassing may be carried out using stainless-steel hand K-files^TM. The majority of root canal lumens are elliptical in cross-section, which facilitates the bypassing of a SI with a hand K-file^TM; especially when it is lodged in the middle or coronal third.^29,58,59 Bypassing attempts should be made with a small hand K-file^TM on the buccal and/or lingual aspect with frequent radiographs to follow the progress of instrumentation and prevent perforations.

Once bypassed, the fragment may be dislodged using an endosonic file. Before activating the file, it is generally recommended that a cotton plug be placed in other canal orifices to prevent the removed segment from lodging in another canal. A K-file^TM is mounted on an ultrasonic handpiece, which is then inserted into the root canal between the fragment and the root canal wall in order to penetrate alongside the broken fragment. The file can then be ultrasonically energized. It is necessary for the K-files^TM mounted on the ultrasonic handpiece to be thinner than the last hand K-files^TM used. The ultrasonic K-file^TM is gently pushed up and down 1 or 2 mm between the fragment and the root canal wall. The broken instrument is usually loosened from the root canal wall because of the ultrasonic vibrations of the energized file. The SI can then be washed out with the irrigant. This method allows for the conservation of the remaining dentine wall of the root canals and can also save time.⁶⁰

If the attempt to bypass the broken file with K-files^TM fails, the second option is to create a circumferential ‘staging platform’ around the coronal end of the SI. Select an ultrasonic tip that can access the depth of the obstruction and allow contact alongside the fragment. The ultrasonic tip is activated at the lowest possible power setting and used dry. This allows the clinician constant microscopic vision of the energized tip and the SI. An unobstructed view is also essential to maximize success, since ultrasonic tips are most effective when used alongside the SI. Without the microscope, it is easy to come into contact with the top of the SI and push it further into the canal. Careful washing and drying of the operating field is also essential to maintain visibility at all times to prevent procedural accidents.⁴³ For this, a dental assistant uses a triplex syringe to direct a continuous stream of air to blow away dentinal dust, allowing an uninterrupted view of the procedure. The selected ultrasonic tip is then used in a counterclockwise direction around the obstruction, removing dentine and lightly trephining in order to expose the coronal portion. Once the coronal portion of the obstruction is exposed, gently wedge the energized tip between the obstruction and the canal wall while using a sodium hypochlorite irrigating solution in the canal, which will often cause the SI to be freed and removed.

When ultrasonic vibration is ineffective, the next attempt can be to remove the SI with a tube-extractor that has been selected based on the diameters of the canal and SI (Table 2). The periphery of the fragment is exposed and gripped with the tube-extractor. However, if the fragment is tightly wedged into the dentine and efforts to loosen it with manual pressure are unsuccessful, the ultrasonic tip can be applied directly against the exposed end of the fragment and activated under the microscope. The alternate application of the ultrasonic vibration and counterclockwise rotation with the extractor allows the SI to be removed.

If visualization is not possible with magnification and/or after attempting to establish straight-line access to the SI, the procedure described above is not recommended because of the risk of perforation and extensive canal damage. This is also the case if the clinician does not have ultrasonics.³⁵ In these cases, the remaining option is ‘braiding’ with Hedstrom files^TM. The first Hedstrom file^TM is gently screwed into the canal alongside the SI, and two further Hedstrom files^TM are introduced to wind around one another, all of which are then withdrawn together. The largest possible size of files should be used with caution because of the possibility of separation of the braided files.⁶¹

Removing separated instruments from the apical third

In general, removing SI from the apical third is unsuccessful and may lead to undesired effects.^{15,31,38,42,43} This is due to the fact that the use of fine ultrasonically-activated instruments is not always possible in more apically located root canal sections because of limited space and visibility.²⁴ Any approach to removing SI in the apical third should always prioritize safety. Therefore, the safest technique is to use a ‘softened gutta-percha point’ as described by Rahimi and Parashos.⁶¹ The technique begins with the use of SS Hedstrom files^TM 8, 10 and 15, which can reveal if the instrument could be partially bypassed and whether it is loose within the root canal. Following this, the apical 2–3 mm of a size 40, 0.04 taper gutta-percha point is dipped in chloroform for approximately 30 seconds. The softened gutta-percha is then inserted into the distobuccal canal and allowed to harden for approximately 3 minutes. The gutta-percha point and SI are then successfully removed using careful and delicate clockwise and counterclockwise pulling action.⁶¹

‘Braiding of Endodontic Files’ can be used when the fragment is positioned deeply in the canal and not visible and the clinician is relying on tactile sense, or the fragment is loose but cannot be retrieved by using other means.^15,29

The ‘Braiding of Endodontic Files’ can also be used when the fragment is not visible because it is positioned deep in the canal, leaving the clinician to rely on touch. This technique can also be used if the fragment is loose but cannot be retrieved by other means.^15,29

Removing separated instruments from curved canals

Since curved canals often curve in more than one plane, a significant amount of dentine has to be sacrificed in order to establish straight-line access to the SI, especially in the apical one third of the canal.³⁵ These situations present a particular dilemma for the clinician since no device or instrument removal technique has been described that can result in the successful and conservative removal of SI in the hard-to-reach areas of the canal system.⁶¹

The softened gutta-percha removal technique may be tried in this situation since this conservative technique does not require direct vision or straight-line access.⁵ If this attempt is unsuccessful, it is recommended to leave the fragment in situ, when appropriate, as this is a less destructive option, conserving tooth substance, time and money.²³