Broken NiTi File LR7

There is a broken NiTi rotary file in the distal root canal of LR7.

It can be seen how the root canal deviates mesially in the middle third. It is possible that this sharp curve has resulted in flexural fatigue and failure of the instrument.

However torsional failure occurs more frequently than flexural fatigue. Applying too much apical pressure to a NiTi rotary instrument increases the likelihood of torsional failure.

It is important to establish a glide path with stainless steel files prior to using any rotary NiTi inside a root canal [minimum ISO20]. Furthermore, rotary NiTi instruments should be allowed to cut dentine with minimal loading. Excessive pushing on the instrument will increase the chance of file separation and should always be avoided. Copious use of a disinfecting irrigant will also reduce instrument loading.

Visualising The Broken Instrument X16

If the broken instrument cannot be bypassed it becomes necessary to remove it in order to gain access to the remaining root canal system.

Under high power, provided that the fractured instrument is not beyond a bend in the root canal, it is possible to assess its size, shape, position and its degree of freedom within the root canal. This assessment is best made at X16 magnification and by contacting the most coronal portion of the instrument using a DG16 endodontic explorer.

The broken instrument can be clearly seen in the distal root canal of the LR7.

Successful Removal of the
Broken Instrument X16

In this case a "modified" Gates Glidden was used to create a circumferential "staging platform" above the instrument. Ultrasonic energy is then used to trephine around the instrument exposing 1/3 to 1/2 its length.

In this example an RT3 ultrasonic tip [EMS] was used with a delicate, anticlockwise stroking motion, to release and eject the broken instrument. It is tempting to use high power settings to dislodge broken instruments. However, high power ultrasonic energy can cause the instrument to partially disintegrate.

It is more productive to begin with a lower power setting and gradually increase this towards medium power. In this manner ultrasonic energy is used to excite the instrument, encouraging its ejection from the root canal, rather than causing its break-up.

Cleaning And Shaping Of Root Canals

In general, the removal of broken instruments sacrifices radicular dentine. It is important to be aware of the remaining dentine thickness and root canal anatomy at the level of the fractured instrument. This assessment is best made from a radiograph. Whilst attempting to retrieve a broken instrument, it critical to avoid root perforation or over-enthusiastic canal enlargement These will compromise the prognosis.

During the creation of "staging platforms" for instrument removal, it is also easy to create a ledge. Such defects in canal shape should be refined where possible. This allows for the smooth passage of instruments beyond this position and will later facilitate 3D-obturation of the root canal system.

In this case a ledge was created distally by the "modified" gates glidden drill. Refinement of the canal shape and re-establishment of a smooth glide path was carried out with GT Hand files [Dentsply]

Post Operative Radiograph

Following the removal of the broken instrument: The entire root canal system is further shaped and disinfected in a conventional manner. The root canals can then be dried and obturated.

The root canal orifices are sealed with mineral trioxide aggregate and the core material is placed.

Notice the wine-glass silhouette in the middle third of the distal root canal. This is the position of the staging platform and dentine trephining. A common outcome of broken instrument retrieval is alteration of the root canal form.

Adopting correct technique and a safe discard strategy are still the best solutions for avoiding instrument failure. Should an instrument break however, then the use of a microscope in combination with ultrasonic energy can make its retrieval much easier and less stressful.