Eliminating the Ding of Endodontics by Brett Rosenberg, DDS

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Ding! The wretched sound of a nickeltitanium (NiTi) file breaking in a patient’s tooth. Ding! That was the sound of the cash register when it came to pay for NiTi files. For many years that was the duality of nickel titanium instruments. You had these wonderfully efficient files that far surpassed the shaping instruments before them, but that still had two major flaws— breakage and cost.

In 1988, Dr. Harmeet Walia presented the modern use of NiTI rotary instruments in endodontic therapy and the path of future treatment changed forever. The benefits of NiTi, such as the ability to negotiate curved canals and reduce transportation made the shaping of root canals significantly more efficient and predictable. Early NiTi rotary instruments were fairly rigid and lacked the advances in metal chemistry that exist today. Because most root canal systems are dynamic and not straight, early NiTi files had the propensity to fracture during use. This tragic event is called cyclic fatigue and is thought to be brought on from crack initiation on a surface irregularity during manufacturing.2,3 When the material has reached its elastic limit, it breaks. This is not dissimilar to a paper clip being broken after repeated movement. Many studies have shown that as the angle of the curve increases, the time to fail decreases.4 Therefore, as the number of rotations or the amount of curvature increase, the chance of fracture increases and the time for the instrument to reach its elastic limit greatly decreases. Thus the goal of any advances in NiTi rotary design would address the amount of stiffness and flexibility of the instrument as well as the mean seconds to fracture.

In the past two years a new advance in endodontic NiTi instrumentation has taken place. Addressing many of the negatives of previous systems, the EdgeEndo files have made a monstrous jump in our ability to clean and shape curved canals quickly, efficiently and in a cost effective manner. The files utilize heat treatment as well as advanced metallurgy to significantly alter the ability of the files to shape curved canals, and do so with almost zero risk of separation. Edgefiles have a high fatigue threshold (655.6 seconds). This extra time gives the operator a safety cushion when shaping cases. They also have flexibility–.0047nm according to an ISO stiffness test, which tests ductility or flexure.

So what does all this mean, and how does this translate to clinical endodontics? Well, when I first started using these files after over 10 years of GT files, I was awestruck at just how efficient these files were. After treating one of my patient’s first lower molars with two files, I went and used the same files on six more extracted teeth without the instrument showing any signs of cyclic fatigue. And after almost a year and a half of use I haven’t seen one separation, and as an endodontist practicing in the state of Florida, I live in calcified canals all day. It is only one in 50 cases that is truly “open.” The Edge files have really changed the way I perform my shaping procedures and are so efficient that I find I have to have patients sit for additional time to allow the sodium hypochlorite to have enough exposure time to be fully effective.

A further benefit of the Edgefile system is that it allows conservation of dentin. Older systems required very large initial tapers used in a crown down manner. The GT file system for example required the use of a .12, .10, .08, and then a .06 taper instrument. The use of such large initially tapered instruments places the tooth at risk for fracture and loss of retention. The Edgefiles allow a single .06 taper to fully shape the canal while not removing excess dentin. While there aren’t any current studies that can quantify just how much dentin removal causes a certain proclivity to fracture, all studies point to the conservation of dentin being paramount to tooth retention and prevention of vertical root fractures.

Clinically the Edgefiles couldn’t be easier for a general dentist or endodontist to integrate into the current technique. I have tried all current file systems and have come up with an extremely simple system which can be used in the majority of cases.

After access is made (preferably under a microscope), length is obtained using an electronic apex locator with a 10- C file followed by a 15 Hedstrom file. Now the case is ready for the Edgefiles. While keeping the chamber flooded with 8% NaOCL (for organic tissue removal and lubrication) a 30 .04 Edgefile X5 is taken to length. Next a 30 .06 Edgefile X5 is taken to length. If the 30 .06 file won’t go to length after two passes, a 25 Hedstrom file can be used to open up a large glide path. If the canal is wide enough to warrant further apical enlargement (such as palatal roots and distal canals of lower molars) a 40 .06 can be used as a final shape. This technique is almost foolproof and fully reproducible in most of the cases I see. My goal is to fully instrument to the anatomic apex (0.0 on the apex locator), although the literature shows this might be past the actual foramen. By instrumenting in this manner it allows the custom fit .06 gutta percha to exhibit a very strong tugback without false binding coronal to the apical 2-3mm. After using sonics and ultrasonics to activate 8% NaOCL, 17% EDTA and 2% CHX, the case is ready to be filled. Here are six cases that exhibit the benefit of flexibility and resistance to fracture.




One of the dings of nickel titanium is breakage, but let’s spend a moment discussing the elephant in the room: cost. For years, nickel-titanium patents were controlled by one company and prices were on an ever-lasting slope. The ding of the cash register! This was the other main disadvantage of utilizing rotary instruments. A busy endodontic practice might be spending upwards of $20,000 per year on rotary instruments. With the Edgefiles being priced at a third of the cost of competitors’ files, the practitioner will be saving a tremendous amount of money. It’s a win-win for the practitioner. Ding!

References
  1. Walia H, BrantleyWA,GersteinH.Aninitialinvestigationofthebendingandtorsional properties of nitinol root canal files. J Endod 1988;14:346
  2. Haikel Y, Serfaty R, Bateman G, Senger B, Allenmann C. Dynamic and cyclic fatigue of enginedriven rotary nickel-titanium endodontic instruments. J Endod 1999;25:434 – 40. –51.
  3. SattapanB,NervoG,PalamaraJ,MesserH.Defectsinrotarynickeltitaniumfileafter clinical use. J Endod 2000;26:161–5.
  4. LiU,LeeB,ShihC,LanW,LinC.Cyclicfatigueofendodonticnickel-titaniumrotary instruments: static and dynamic tests. J Endod 2002;28:448 –51.

  Author's Bio
Dr. Brett Rosenberg has been practicing microscopic endodontics for over 10 years in Jupiter, Florida. He is board certified endodontist who prides himself on performing the absolute highest quality endodontics possible. Dr. Rosenberg can be reached at 561-575-4556 or by email at rosenbergendo@comcast.net.

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