From incidence to therapeutic approach concerning endodontic instrument fracture Part 2

Methods of solving endodontic separated files cases

The possibilities of solving a clinical situation characterized by the existence of a separated instrument may involve several possible approaches:

• removal of the fragment
  • represents the ideal solution
  • requires the use of dedicated instrumentation and kits
  • involves the association of ultrasonic means, considered indispensable
  • there are also attempts to use Nd: YAG laser devices with inconsistent results

• bypass
  • consists of overcoming the obstacle, “bypassing” the metallic fragment, by instrumenting the root canal so as to allow the passage over the fractured instrument, in order to reach the entire working length
  • the separated fragment remains into the root canal, subsequently being included in the root canal filling
  • such a therapeutic attitude is not without risks, being able to endanger the root resistance and even favor the fracture of other instruments

• instrumentation and filling of the root canal coronal of the the fractured fragment
  • not recommended
  • in this case, part of the endodontic system remains untreated, which may cause the development or persistance of periapical pathology

• surgical methods, depending on the location of the fractured fragment and the endodontic pathology
  • depending on the geometry of the respective root canal, it may be the only option in the case of the existence of a fractured instrument in the apical third or that exceeds the apical constriction

In the situation of a fractured instrument at the level of the endodontic system the prognosis is dependent on a number of factors:

• initial diagnosis
• the moment during the endodontic treatment ehen fracture occurred: early or late
• dimensions of the fragment
• its location
• the degree of curvature of the root canal
• the possibility of direct visibility
• the possibility to create a straight line access to the separated instrument
• the morphological characteristics of the respective root
• the experience and the endowment of the clinician.

Statistical studies concerning fractured endodontic instruments that could not be removed or “bypassed”, with the endodontic treatment and root canal filling performed only up to their level, have shown the following aspects:

• the prognosis is all the more favorable as the fracture occurred later in the course of chemo-mechanical treatment; a fracture that occurs during the early stages of treatment blocks the access to the rest of the root canal, at which level instrumentation, debridement, irrigation and of course root canal filling can no longer be achieved;
• the prognosis is also more favorable in the situation of a vital tooth, in which the microbial flora at the endodontic level is absent or present to a much smaller extent than in the situation of a nonvital tooth;
• the most reserved prognosis occurs in the presence of chronic apical pathology.

Maintaining an obstacle represented by a fragment of separated endodontic instrument often makes it impossible to fully and correctly approach the entire endodontic system, in terms of instrumentation, root canal filling or both stages of treatment. The partial or complete blocked access apically of this obstacle allows the existence of an environment that favors the development of microbial flora and its organization in the form of biofilm. Thus, the conditions of occurrence or persistence and evolution of a periapical pathology are met, which complicates root canal treatment and diminishes the possibilities of maintaining the tooth in functional conditions.

It is therefore obvious that the main objective, to perform an endodontic treatment over the entire working length, finalized with a three-dimensional root canal filling, allowing the entire endodontic system to be sealed, is practically impossible to achieve if the fractured fragment prevents complete access throughout working length.

Viewed from this perspective, the orthograde endodontic approach should aim to remove the obstacle and permeabilize the entire root canal. Maintaining the fractured fragment under the conditions of performing a bypass is a compromise solution, which is resorted to in the event of the impossibility of safely removing it. This choice is also not without risks, as there are authors who believe that the successful completion of a bypass would indicate the existence of considerable chances of successfully removing the fragment, which would obviously be preferable from all points of view.

The removal of the fractured endodontic instrument is therefore the optimal solution, in the context of the clinical situations in which the following conditions are met:

• direct access, as close as possible to the straight line, with sufficient root canal width to allow the necessary instrumentation to be used
• perfect visibility, requiring illumination and magnification – offered by the operating microscope
• use of instruments, kits and methods specifically dedicated to the removal of fractured instruments
• the application of ultrasonic vibrations at the level of the fragment, which will contribute to its removal.

All of the above require a realistic appreciation of the possibilities specific to the respective clinical case, correlated with the endowment and the expertise of the operator.

The location of the fragment at the level of the apical third of the root canal, with or without exceeding the apical constriction, or apical of very sharp root curvatures, makes it practically impossible to apply methods of removing it through orthograde endodontic access. In such conditions, the only approach remains the retrograde one, using endodontic surgery, which indications and chances of success must be evaluated according to a series of elements represented by: the level at which the fragment is located, the existence of a periapical pathology, the implantation of the respective tooth, the possibilities of apical sealing and the benefit / risk ratio.

Removing a fractured endodontic instrument is one of the most difficult endodontic approaches, due to a multitude of factors:

• requires specific training of the clinician
• involves advanced equipment and techniques
• is time and resource consuming
• presents risks: fracture of other instruments, formation of thresholds, perforations, cracks or root fractures by weakening the parietal walls
• the success rate is very variable, the numerous studies conducted indicating values ​​between 53% – 95% depending on:
  • location, fragment length and type of fractured instrument
  • tooth and root canal involved
  • training and technical equipment of the clinician.

Most methods of removing separated endodontic instruments are based on the following elements:

• direct access
• obtaining the space necessary to penetrate the instrumentation used (creating a so-called “platform”) by widening the root canal in the corono-apical direction to the level of the fractured fragment
• the application of ultrasonic vibrations on the fractured fragment by placing the tip in direct contact or mediated through another instrument
• use of systems specifically designed: Instrument Removal System (IRS – Clifford Ruddle), File Removal System Kit (Dentsply Sirona), Terauchi File Retrieval Kit (TFRK – Yoshi Terauchi), Masseran, Meitrac, Endo Rescue Kit ( Komet), etc.

Each of the existing systems is based on the application of one of the well known methods – the microtubular method and that of the “lasso” (or loop). Each of these methods require the necessity of sufficient enlargement of the segment of the root canal coronally located respective of the fractured fragment, in order to obtain the necessary space (called platform) to introduce the instruments of the kits and the ultrasonic tips.

The microtubular system is based on the use of a tube of inner diameter immediately superior to that of the separated fragment, which will be inserted into the root canal to a level that apically exceeds the coronary end of the fragment, thus being concentric with it. The space necessary for circumscribing the fractured fragment by the microtube is created by selectively enlarging the root canal with the help of a microtrephine bur performing a circular groove around it.

Through the tube is inserted of the kit corresponding to the diameter of the tube, which slides in an apical direction until contact with the respective fragment is achieved. By further pushing the plunger rod in the apical direction its sharp tip will “force” the angulation of the fragment and its locking inside the tube.

The lasso or loop method is based on the existence of a kit containing a device that allows the retrieving the separated fragment and its extraction by means of a very thin wire loop that is wrapped around it.

In order to reach the level of the fragment, it is proceeded as with the microtubular method, first achieving a sufficient enlargement of the root canal and the a circular groove around the coronary end of the fractured fragment.

This is then followed by the insertion of the loop at the level of the circular groove created circumferentially of the fragment and its tightening around it.

Each method of retrieving a separated endodontic instrument is also based on ultrasonic vibrations transmitted to the fragment by use of ultrasonic tips dedicated to this purpose.

Made of different alloys (steel, nickel-titanium, titanium-niobium) and in a wide range of tapers and axial dimensions, these are used by insinuating the tip at the level of the internal curvature, between the parietal wall of the root canal and the separated instrument, the operator simultaneously rotating the tip counterclockwise.

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Figure 13. Ultrasonic tips meant to dislocate the separated instrument

Sometimes the simple ultrasonic vibration is sufficient to dislocate the fragment, but in most cases it is indispensable to use the systems dedicated to this purpose.

Conclusions

Endodontic treatment requires specific equipment and expertise.

In particular, the removal of separated instruments implies using specific instruments and especially specially designed kits, by applying different methods: microtubular, lasso, etc.

The realization of a “platform”, representing the enlargement of the root canal segment located coronally of the fragment, represents an intermediate stage, preceding the use of the specific systems. This “pre-instrumentation” is conditioned by a correct appreciation of the root cross-sectional diameter, especially in the situation of the location of the fractured fragment in the middle or apical thirds.

Any method applied is associated with the use of ultrasonic vibrations, considered indispensable for the dislocation of the fractured fragments, their application being realized by using dedicated tips.

The clinical approach involved requires an operating field that is perfectly magnified and illuminated by means of the operating microscope.

Successful removal of a separated endodontic instrument depends on the selection of the optimal method, with correct evaluation of the benefit-risk ratio and taking into account the uniqueness that each clinical case.

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