Tuesday, December 4, 2012
Figure 1: Separated RNT file in the mesial root of tooth #30 as referred to the author.
In Part 1 of this 2-part article described a clinical case of rotary nickel titanium (RNT) instrument separation in the mesial root of tooth #30, as well as many of the causes of RNT file separation.
In this case the patient was referred to me for removal of the separated RNT file and completion of endodontic treatment.
Here in Part 2 of the article, I describe how this and similar cases should be assessed pre-operatively and how this case was subsequently treated.
Assessment of this RNT fracture for treatment required evaluation of the following (among other issues):
The design/geometry of the fractured file as well as it’s taper and tip size.
The type of RNT that fractured was unknown, but it appeared from the pre-operative radiograph to be an orifice opener, approximately a .08/25 taper and tip size. In all probability, the instrument was inserted too far apically—given the location of the fragment in the canal—too rapidly in the sequence—restrictive dentin coronal to the file was not removed, creating an undue torque force on the instrument—and probably without an adequate glide path. As a result, the file fragment was anticipated to be screwed into dentin and not lying loose in the canal.
Fracture location and specifically, how much of the file was above and below the point of greatest root curvature.
The more coronal the segment, the greater the chance of retrieval. Given the location of this fracture, it was 50-50 the file could be retrieved in one piece using ultrasonics in experienced hands with a surgical microscope.
Whether fracture was the result of cyclic fatigue or torque failure because the type of failure that occurred influences the removal technique.
Based on the length of the fragment, it is possible that this was a purely cyclic fatigue failure—despite the opinion above that this may have been a torque related failure. In reality, it was probably both.
The experience of the clinician and the equipment and supplies at hand.
Only those trained and experienced should attempt such cases. This clinical situation has an extreme risk of perforation given the thin lateral root walls.
Tooth position in the arch.
Were this scenario to present in the mesial root of a lower second molar, the chances for removal would be reduced. In this case, access to the fragment is improved given that it occurred in the mesial root of the first molar.
Rotation, tipping and possible co-morbidities such as secondary perforation, canal blockages, canal transportations or a second separated file, etc.
Fortunately in this case none of these were an issue and the tooth was restorable. In addition, there was neither co-existing resorption nor anatomical anomalies. The tooth was periodontally sound.
Limited opening, gagging, and other behavioral issues.
Fortunately this patient had no limitations with opening, gagging or behavioral issues that limited treatment.
The patient’s risk tolerance for retreatment.
After informed consent, this patient wished to have the file removed if possible.
Case Study
Clinically, the previous access was quite small through the existing crown.
Figure 2: A radiograph was taken confirming the RNT file fragment was successfully bypassed.
The patient was informed that the access would be expanded considerably and that the porcelain might fracture as a result of this expansion. (In this instance it did not).
Straight-line access was obtained and using the CT4 ultrasonic insert from SybronEndo, and the orifice was enlarged concentrically to reveal the most coronal aspect of the file fragment.
Stainless steel hand files—in this case Mani D finders—were used to bypass the fragment until patency was achieved, and subsequently safe ended stainless steel hand K files—Mani SEC O K files—were reciprocated to the apex with a Synea W&H reciprocating handpiece.
Figure 3:The Safe-Ended Mani Hand SEC O K File used for this case.
Figure 4:The Synea W&H WA-62_A reciprocating handpiece used for this case.
Using the SEC O K file in this manner alongside the file fragment created space next to the instrument into which it was delivered during irrigation.
Figure 5: A radiograph showing the canal obstruction has been removed.
After removal, the canal was shaped with MounceFile Controlled Memory Nickel Titanium Files and obturated using gutta percha with a continuous wave of condensation via SybronEndo’s Elements Obturation Unit, SybronEndo.
The entire procedure was accomplished under the surgical operating microscope from Global Surgical that I use in my practice.
Conclusion
In summary, preventing fracture is key. Prevention of instrument fracture is enhanced by the following strategies, among others, in the coronal and middle third before addressing the apical third:
- Preparing straight-line access
- Using a viscous EDTA gel such as File-Eze from Ultradent to emulsify the pulp tissue (i.e. hold it in suspension), especially in vital cases where abundant tissue is present in the chamber. Such tissue, if pushed apically can lead to canal blockage.
- Removing the cervical dentinal triangle with orifice openers
- Negotiating the canal to the apex with hand files followed by glide path creation
- Irrigating copiously at all stages in the treatment process
- Removing restrictive dentin coronally before moving apically—moving crown down, depending on the degree of canal curvature and calcification
- Minimizing engagement of each RNT file to 4-6 mm per insertion
As an aside, when confronted with significant curvature and calcification, aside from the above strategies, using a step back approach is often fruitful.
This in essence means enlarging the canal from smaller tapers and tip sizes to larger tapers and tip sizes as opposed to strictly using a crown down approach. Clinically, with an instrument system such as MounceFiles, this means using the .02/25 first, followed by the .03/25, .04/25, .06/25 and .08/25, with a .03/30 instrument for apical finishing.
Figure 6: The files for the sequence explained above are all a part of the MounceFile Controlled Memory Assorted Pack.
The clinician can enlarge the apex to a larger diameter as desired. Such an approach in complex anatomies minimizes the torque load on instruments and reduces possibilities for canal transportations relative to a strictly crown down approach.
I welcome your feedback.