by Richard Mounce, DDS
The CONSEQUENCES of a file protruding beyond the apex are dependent on a number of factors, only some of which are controlled by the clinician. To start, many endodontists -- including myself -- use patency as a guiding clinical philosophy. I believe, to the greatest degree possible, the clinician should attempt to be patent at all times. This begins with the insertion of the first hand file to reach the apex to the last finishing file at the TWL. Patency equates to fewer iatrogenic events. The converse is true.
The patency referenced above is generally achieved with a No. 6, 8, 10, or 15 hand file. The average minor constriction of the apical foramen is approximately .28 mm. Small hand fi les (Nos. 6 to 15) will not cause harm. This is especially true if the files are precurved with EndoBender pliers (SybronEndo, Orange, Calif.) if a small amount of the tip (1 to 2 mm) is extruded beyond the minor constriction of the apical foramen. Such small hand files pass unhindered through MC and are inconsequential.
The scenario changes, though, if larger hand files are used -- perhaps a No. 25 or larger. A larger file could potentially enlarge or transport the MC, especially if the hand file is large enough to engage the dentin along the walls of the MC. In addition, in some canals and apical foramina, larger hand files might propel pulpal remnants through the minor construction. In doing so, they may extrude irrigant.
Rotary nickel titanium files are not indicated beyond the MC. The ideal depth of instrumentation, irrigation, and obturation is the MC and not beyond this level. In practical terms, while the clinical reality is more complex, the conceptual model is that the RNT file tip should stop at the MC -- the narrowest diameter of the canal. While others sometimes have advocated taking the tip of an RNT instrument beyond the MC, in my empirical opinion, the risks -- transportation of the MC and iatrogenic issues of all types -- far exceed the benefits.
With these considerations in mind, factors that influence the outcome of placing a file through the apex include:
• the contents of the canal. If the canal is filled with an irrigant like sodium hypochlorite, bacteria, and necrotic tissue, the possibilities for extrusion, inflammation, and postoperative pain certainly are increased. Sodium hypochlorite is both bactericidal and dissolves tissue. While it is an excellent solution with which to digest pulpal tissue and kill bacteria, if extruded into apical tissues it initially is severely toxic. A file -- hand or RNT -- if used incorrectly in a canal filled with sodium hypochlorite, can act as a piston to drive irrigant, bacteria, and necrotic tissue apically. Proven methods to minimize debris buildup in the canal, as well as subsequent potential for extrusion of this material by file actions include visualizing treatment through a surgical microscope (Global Surgical, St. Louis, Mo.), optimal irrigation and recapitulation at all times, and utilizing a viscous EDTA gel -- like File Eze (Ultradent, South Jordan, Utah) -- to hold pulpal fragments in suspension until they can be flushed.
• if the apex of the root is open, resorbed or has been transported in some way. Placement of a large hand file or an RNT file beyond the apex enhances the chances for extrusion and subsequent inflammation. This is particularly so in the presence of an irrigant like sodium hypochlorite. Irrigants such as chlorhexidine and SmearClear (SybronEndo) for smear layer removal, or as a means to flush, are less toxic if extruded than sodium hypochlorite.
• the speed and manner of insertion. If an RNT file is taken beyond the apex unintentionally, the speed of file insertion, and whether the file has been used in a pumping manner, can propel irrigants beyond the MC, and cause inflammation. In essence, how an RNT file is used will determine the potential for extrusion. If the RNT file tip protruding beyond the MC is added to a pumping action, the potential for significant extrusion and postoperative inflammation is created.
• the anatomy of the root and canal system. For example, lower bicuspid roots, lower molar distal roots and many palatal roots are relatively straight, and as such, the possibility for extrusion of irrigant in the presence of a file being placed beyond the MC is increased.
Files beyond the apex -- drama, trauma, or non-event? There is no definite answer. If the file tip is a hand file, and if the hand file is used for achievement and maintenance of patency, desirable outcomes are created. Conversely, taking RNT files beyond the MC, or placing large hand files beyond the MC, creates hazards that can diminish clinical success.
Dr. Mounce has no commercial interest in any of the products mentioned in this article.
Dr. Richard Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash. Among other appointments, he is the endodontic consultant for the Belau National Hospital Dental Clinic in the Republic of Palau, Korror, Palau (Micronesia). He can be reached at [email protected].
