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Precurving a NiTi Handfile to Correct Ledges

A Simple and Practical Technique

Many dentists who have performed endodontic treatment know that the correction of a ledge, as created along the radicular wall during cleaning and shaping, presents a challenging dilemma. Of course, prevention of a ledge is the best strategy, but is there a predictable technique that the clinician can use once the ledge is formed?1 This article discusses a simple technique to effectively remove the ledge.

 

Presentation of the Dilemma 

 In endodontic cleaning and shaping mechanics, a ledge in the canal wall can be created via the use of instruments too large for the canal or through the use of too much force. Ledges are iatrogenic. Subsequent shaping and cone-fit procedures become difficult and sometimes impossible to correct. Files tend to have “memory” as they follow down the existing canal. When these files reach the ledge, they bump into it, instead of glancing off and over it. At the start of ledge formation, it may be extremely small and thus easily overlooked. If the clinician neglects to completely and immediately remove the ledge, it will inevitably become larger and could actually prevent proper apical cleaning and shaping beyond the ledge. In addition, the cone-fit could fail and the finished obturation may fall several millimeters short of the original portal of exit apical constriction.2 Viable and nonviable irritants within the apical “dentin mud” could then be a source of endodontic failure.

 

Precurving NiTi Hand Files 

The predominant method for removal of ledges is through the use of precurved stainless steel hand files. Nickel-titanium (NiTi) files are a more effective and efficient means to remove ledges if an initial “glide path” has first been established.3  

When precurved conventional stainless steel hand files fail to remove ledges from the canal, the clinician may use a simple technique that involves precurving NiTi manual hand files. In the author’s experience, the most effective instrument to use is a F1 finishing file. This instrument is small enough to finesse around a curve and large enough to effectively remove the curve and create the desired apical shape at the same time. The clinician can use basic metal cotton pliers to curve the NiTi file. The curve will be preserved, and then the manual instrument can be followed around the ledge, rotated, and removed. The dentin that made up the ledge will be cut away by the blades of the curved file and the apical shape will be complete. This may take a single pass or several passes to finish.

 

Application of the Files 

A patient presented with an endodontic failure of tooth #30(46). After removal of gutta-percha, a #10 file could be followed to the radiographic terminus of the distolingual canal (Figure 1). An S1 shaping file could not follow around the previous ledge formation. The file instead continued to rest on the ledge itself (Figure 2). The goal was to wear away enough of the shelf so that a cone could slide around the shelf into the apical constriction. Using orthodontic bird beak pliers, the file’s apical several millimeters were curved by “walking” the bird beaks toward the tip of the F1 NiTi file (FIgure 3). The apical turn was preserved even in the nickel-titanium material. Cotton pliers could have been used in place of the bird beak pliers (FIgure 4). Again, the apical turn would be preserved, regardless of the curving technique. The curved NiTi file then easily followed manually past the shelf to the radiographic terminus (Figure 5). The flutes of the file then contained the dentin of the shelf as well as the apical preparation (Figure 6), and a cone-fit was then made in the distolingual root canal and successfully down-packed.

 

Conclusion 

A simple and effective method for removing radicular shelf formation using NiTi instruments has been described. While ledge prevention is the best technique of all, it is reassuring that ledges can be predictably removed by using an efficient rotary device with minimal effort.

 

*Private practice, Tacoma, WA.

References 

  1. West JD. Perforations, blocks, ledges, and transportations: Overcoming barriers to endodontic finishing. Dent Today Jan 2005:68-73.
  2. West JD. The cone fit: An essential step in creating exceptional endodontic obturation. Dent Today May, 2005;102-105.
  3. West JD. Cleaning and shaping the root canal system. In Cohen S, Burns RC, eds. Pathways of the Pulp 7th Ed. St. Louis, Mosby 1998:244-248.
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