Almost a Case of Black and White
Every now and then a case comes along that dramatizes the ability and safety of a shaping system compared to one with a far narrower window of success. The patient in this case presented to us with a rotary nickel-titanium (NiTi) fragment in the distal root of a lower first molar. The fracture occurred in the apical third around a curve, making removal of the fragment virtually impossible (Figure 1). Attempts at negotiating it were unsuccessful and continued attempts could have lead to perforation.
As endodontists, we know that while rotary NiTi can be done in relative safety, curved canals subject rotary NiTi instruments to both torsional stress and cyclic fatigue. The only sure way to prevent separation is to not use them in these more challenging canals. This presents a dilemma because rotary NiTi was originally developed for just these situations and the justification of its use is the creation of smoothly shaped curved canals without distortion.
The time requirement for an endodontist with good microscope skills to remove a separated instrument that has broken around an apical curve is open ended. The authors have heard comments from rotary NiTi advocates that a broken instrument often is not a problem and even if it is, a simple apical procedure will solve the problem. If the consequences of broken instruments can be dismissed so lightly, then why all of the attention to the details of proper instrumentation? The greater the amount of pulpal tissue left behind, the poorer the debridement and the poorer the fill—which correlates to poorer success rates. Those writing the textbooks take great pains to familiarize us with periapical pathology and its root causes. Broken instruments are a major impediment to re-creating an environment that no longer fosters these pathologies.
As for a simple apical surgery, after decades of combined practice we do not believe any apical surgery, particularly on a lower molar, is simple—certainly not for the patient—and to casually describe “surgery” as a minor inconvenience is not, in our opinion, the best we can do for the patient.
That brings us back to our case. Conveniently, the mesial canals were not yet started by the referring dentist and we had the ability to tackle this case without any previous work being done. Our approach is entirely different than rotary NiTi. Our approach uses the EndoExpress Instrumentation System with SafeSiders® reamers (Essential Dental Systems, South Hackensack, NJ). We create the glide path first with regular k-reamers and then relieved k-reamers. Unlike k-files, the usual instrument recommended by rotary NiTi advocates for the mandatory creation of glide path, both non-relieved and relieved k-reamers have fewer flutes, and the flutes that are present are significantly more vertically oriented. By using SafeSiders, the end result is more efficient cutting combined with less engagement to give the dentist a superior tactile perception of what the tip of the instrument is encountering as it negotiates to the apex. Whether used manually or in an engine-driven reciprocating handpiece, the envelope of motion is limited to 30º or 1/12 of a circle, which is 5 minutes on the face of a clock. By limiting the arc of motion to 30º, the torsional stress and cyclic fatigue that are integral parts of rotary NiTi—and also are the two main causes of separation—are virtually eliminated.
The initial instrument (SafeSiders 08) was placed into the canal manually and emerged with a well-defined curve denoting the degree of curvature and, more im-portantly, the orientation of the curve. This was so pronounced that the subsequent instruments were pre-bent and oriented correctly within the canal to the initiation of the curve, where they were then connected to the reciprocating handpiece. Driven by a 30º reciprocating EndoExpress handpiece (Essential Dental Systems), the envelope of motion is so limited that a properly oriented reamer cannot distort the canal. This property is aided by the fact that within the confines of a narrow canal, the tip of the instrument makes barely more than a point contact with the 30º arc of motion presenting itself more conspicuously as the reciprocating motion travels more and more coronally.
With our approach, glide path creation is simply the initial part of the sequence and is constantly being refined throughout the entire shaping process. Stainless steel is often thought of as a material that is far stiffer than rotary NiTi and, as such, is inferior in its ability to shape canals. This would only be true if the stainless steel instruments were used in the same fashion as rotary—which they are not. In fact, stainless steel-relieved reamers have the ability to be pre-bent with excellent accuracy to reflect the anatomy they are traveling through. Unlike NiTi, which weakens significantly when it is pre-bent, stainless steel remains strong. With its pre-bent shape and proper orientation, the stainless steel-relieved reamer will accurately negotiate extreme curves without distortion as long as the driving force is limited to a 30º arc of motion. The unique blend of stainless steel and NiTi reamers provides numerous benefits to the Safe-Siders system.
We used the SafeSiders instruments to shape the curved mesial canals to a minimum of 35 at the apex, 40 1 mm back, and overlaid a 25/06 taper which allowed the canals to be filled with a medium gutta-percha point that was pre-fitted to ensure apical tugback. The patented EZ-Fill® Bi-Directional Spiral & Epoxy Root Canal Cement (Essential Dental Sys-tems) gives the dentist the ability to flood the canal with epoxy-resin, making sure that even a single-point fill becomes the equivalent of a 3-D fill. The low viscosity of the cement ensures its placement within any lateral canals that may be present along with its displacement into the dentinal tubules. The result is a mesial root that harbors two significantly curved canals that have been shaped without distortion and most obviously without any concern for separation. In fact, the distal canal produced a separated instrument even though that canal is both wider and less acutely curved than those present in the mesial root (Figure 2 and Figure 3).
SafeSiders allow for greater safety, which translates into greater predictability, and are based on sound rational grounds. If you want to reduce the chances of separation:
eliminate torsional stress and cyclic fatigue.
minimize the use of vulnerable metals like NiTi and eliminate their use in a rotational system.
create straight-line access for whatever system you are using.
use both non-relieved and relieved reamers to create and refine the glide path.
If you do not want to distort a canal:
use an instrument made from a metal that can easily and accurately be pre-bent.
limit its arc of motion to 30º.
use both non-relieved and relieved reamers.
use reamers with a cutting tip.
This short article cannot possibly show all of the factors that go into shaping highly curved canals to the apex without distortion. However, unlike the learning curve for rotary NiTi, the learning curve with SafeSiders used in a reciprocating handpiece does not consist of the need to learn where not to use them. Because separation is not an issue, all of the challenges of complicated cases can be addressed as a problem limited to the shaping of the canals without ever worrying about the impact of the canal anatomy on the integrity of the instruments. This fact alone is a vast change from what the typical dentist expects to encounter when learning a new system. Without the fear of separation, the dentist will feel more confident in tackling cases he or she would have shied away from with a more vulnerable and less predictable system.
This article was written by Barry Lee Musikant, DMD; Young Bui, DMD; and Allan S. Deutsch, DMD.
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Essential Dental Systems
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|Figure 2 and Figure 3 Radiographs showing shaped mesial canals.|
|Figure 1 Radiograph depicting rotary NiTi fragment lodged in the distal root.|