Dental Tribune International

Stairs to the Apex

By Dr Christophe Verbanck, Belgium
March 09, 2017

Sometimes endodontic specialists have to go the extra mile to save teeth. Only with the proper endodontic instruments success can be ensured in the most challenging situations. This case shows how the aid of HyFlex CM-files can help to deal with multiple iatrogenic deformations after several previous temporary root canal therapies. The use of these pre-bendable NiTi-files help us to get the root canal preparation “back on track”.

Sometimes endodontic specialists have to go the extra mile to save teeth. Only with the proper endodontic instruments success can be ensured in the most challenging situations. This case shows how the aid of HyFlex CM-files can help to deal with multiple iatrogenic deformations after several previous temporary root canal therapies. The use of these pre-bendable NiTi-files help us to get the root canal preparation “back on track”.

Endodontic intervention after a previous temporary treatment can sometimes pose a real challenge even for the most skilled endodontist. Some patients have a long history of unsuccessful root canal treatments. In a situation like this it becomes quite difficult to shape the canal when the natural path of the root canal is almost completely lost. The loss of dentin is often considerable after several dentists have literally tried to “push their luck”.

Iatrogenic damage
An 18-year old male patient presented with a painful lower right first molar. After thorough examination, both clinical and radiographic, tooth #46 was diagnosed to be the cause of his pain. On the pre-operative radiograph a (symptomatic) apical periodontitis could be recognized together with a leaky temporary restoration with decay underneath. Two mesial and a distal canal were filled with calcium hydroxide. Looking even more into detail a step could be observed in the distal root canal. Clinical the tooth was painful on percussion and biting forces, there was no reaction to cold or warmth and no pockets could be probed although the gum was inflamed due to the temporary restoration and decay that was left behind.

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After further examination the patient explained the tooth had been treated in the recent past by no less than three different dentists. Recurring pain had forced him to seek treatment time and again after each provisional non-surgical root canal treatment (nsRCT). Apparently, each colleague had tried to work his or her way around the imperfect preparation of their predecessors leading to a root canal with the shape of a staircase. The absence of a good coronal seal lead to improper healing and thus caused a chain reaction of re-interventions which resulted in iatrogenic damage of the root canal walls.

Re-shaping the root canal preparation
After applying a dental dam the first step was to remove the temporary filling and decay, the pulp floor was checked for perforations and all orifices were located. The canals were then scouted, patency was regained and with small hand files (K-flexofiles ISO 06 up to ISO 20) a manual glide path was established in all four root canals. After scouting it was clear that several steps, luckily without any perforation, were present in the distal and in the mesio-buccal canals. In a case like this it is important to redefine the shape of the previous preparation and first and foremost an endodontic file system is needed that is flexible and prevents further unproportional loss of tooth substance.

For the canal preparation a renowned nickel titanium file system by Swiss dental specialist COLTENE (Fig. 2) was used. Thanks to a clever combination of unique material properties, pre-bendable HyFlex CM files are virtually unbreakable. The reason for this phenomenon is simple: the well-known “Controlled Memory”-effect is flexible enough to find its way around the distorted canals. It improves certain physical qualities of the alloy itself. Similar to classical stainless steel files the instruments can be prebent, but they do not bounce back like conventional NiTi files. This typical characteristic makes “CM”-treated NiTi files extremely flexible. Highly versatile files are particularly helpful if you have to move around abrupt curves or—in this case—a mutilated anatomy. After usage their form adaptation can be quickly reversed in the sterilization process. During autoclaving the instruments turn back to their original shape (Fig. 3). The refined NiTi files are very resistant to cyclic fatigue and can be reused safely, as long as they are not plastically deformed.

The Hyflex CM-files respond to excessive resistance with straightening of the spirals, which avoids binding to the walls. To create any form of steps in the canal shape is incredibly hard and instrument separation is almost impossible, as long as the files are applied correctly. A good preparation technique is to move the file in a soft pecking motion through the canal. In addition to that it is highly advisable to irrigate the canal thoroughly every time a file in the sequence is changed.

Once the manual glide path was created, it was very easy to bypass the various steps and ledges with the pre-bendable HyFlex files (Fig. 4). The mechanical rotation was started on the endodontic motor only after the insertion of the pre-bent instrument in the canal beyond the step. By this approach the risk of perforation is generally eliminated and no further damage of the root canal wall takes place at the level of the step. Beyond the step we used the rotating files as usual at the normal operating mode of 500 rpm. With only a few files per canal it was possible to instrument the root canal up to a working length of 21 mm. The mesio-lingual canal was finally instrumented with a pre-bent .35/0.06 file (Fig. 5). The file was inserted into the canal with two to three subtle movements, then withdrawn before it re-entered the canal. Similarly, the mesio-buccal canal was shaped with a size .35 file with a taper of 0.04 (Fig. 6). To enlarge the apical aspect of both the disto-lingual and the disto-buccal canal a 45/0.04 file was used (Fig. 7).

All files kept their pre-bent shape during the procedure and moved safely in the centre of the canal. Even unexpected angles could be managed almost effortlessly with the swift moving instruments. Despite the numerous steps that got sculptured into the root canal before a smooth shape was finally regained, which would ensure a tight and reliable obturation of the root canal system (Fig. 8).

Successfully preventing re-infection
As mentioned above, a thorough rinsing protocol was performed throughout the whole nsRCT. The constant copious irrigation helped to clear the canal of remaining debris or necrotic tissue. As cleaning irrigants we used sodium hypochlorite (NaOCl) in a concentration of 5.25 % and citric acid (40 %). Both irrigants were activated by ultrasound as well as manual dynamic activation (cone pumping). Corresponding paper points were inserted to dry the canals afterwards.

In the end a bioceramic sealer and gutta percha were used in the hydraulic condensation technique for permanent obturation (Fig. 9). After curing, bioactive filling material can form so-called hydroxyapatite crystals on the surface. The crystals help to stimulate the regeneration of bone and dentin tissue in particular. The coronal restoration was topped off with a composite and a core build-up of glass fibre reinforced composite. Further indirect restoration is planned to be done by the referring dentist.

The post-operative X-rays illustrate two interesting aspects (Figs. 10 & 11): first of all, the obturation material was safe in place and together with the tight seal of the coronal restoration should keep another reinfection at bay. Secondly, the steps were still visible. Especially the mesio-buccal and distal canals looked imposing in relation to their normal size. However, the composition as a whole appeared to be stable with enough dentine surrounding the apex. We were able to save the tooth and the patient left our endodontic practice with an uplifting prognosis despite his unfortunate entry.

Experts for root canal treatment
In our line of work, we often witness patients that dread visiting an endodontic specialist. This sometimes leads to a situation were the general practitioner tries to perform a complex nsRCT himself turning it in an even more complex treatment. Of course, the enormous technical progress in endodontic instruments helps dentists to work professionally and confidently—almost irrespective of their level of experience. Modern endo equipment like a state of- the-art NiTi system allows newcomers and colleagues who do not perform endodontic treatments on a regular basis to create convincing results in a short period of time.

Dentists who have not got the time or desire to personally invest in endo should nevertheless improve the service level of their practice by cooperating with a skilled and well-versed endodontic practice. In Belgium, dentists specialize in a three year intensive course to become experts in root canal treatments. Equipped with the latest instruments experienced endodontists therefore can offer a lot of advice and help with cases that are otherwise deemed to be untreatable. A good working referral system can bring huge benefits for both general practitioners and endodontists who know their way around the root canal.

Modern rotating instruments help the endodontist and general dentist to operate both confidently and safely. Refined NiTi systems with “Controlled Memory”- effect are extremely flexible and fracture resistant due to their special material properties. With pre-bendable files root canals can be shaped efficiently without making any concessions to the natural anatomy of a given root canal. Even referral cases with an eventful history can have a promising prognosis, if the RCT is performed according to the rules, i.e step by step.

Editorial note: This article was published in roots - international magazine of endodontology No. 04/2016.

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