May 1, 2006
by Rich Mounce, DDS and Gary Glassman, DDS, FRCD(C)
At hands on courses, we are frequently asked how to remove separated rotary nickel titanium files (RNT). It is a skill that has taken years to learn and will continually evolve. Removal of separated rotary files can be addressed from many perspectives, materials science, ultrasonic tip choice, risk of iatrogenic events, clinical technique, etc. Suffice it to say that the only clinicians who don’t break RNT files are those who don’t utilize them! Prevention is the key with regard to avoiding this problematic event. In our hands the avoidance of separation is enhanced by minimizing engagement of the file against the canal walls, gentle use of apical pressure, never forcing a file where it doesn’t want to go passively, using crown down instrumentation techniques and creating a glide path with small K files up to a size 15 K file prior to placing a rotary file into any given canal third, amongst other strategies. In addition, empirically we have found the K3 system by SybronEndo (Orange, CA, USA) to create the best blend of cutting efficiency, tactile sense and fracture resistance amongst the many brands of files available in North America.
What follows is our chosen method for removal of separated RNT files. There are other methods available and many individuals who will champion those methods. As a result, we will present what, empirically, has been the most predictable in our hands.
Removal methods must be carefully chosen, as the clinician should attempt to remove the fragment without pushing the fragment apically and creating a worse situation relative to the initial one. It is very easily to create perforations, blocked canals, push fragments apically if the forces applied are not appropriate, as well as overheat roots and cause tissue necrosis if roots are overheated.
Once fracture has occurred, irrespective of the cause, location of the fracture or other circumstances, decisions must be made quickly to address the situation productively. Simply put, at this stage the clinician must decide and honestly, whether they have the equipment, skills and time to remove the fragment in the best interest of the patient. At the very least, a surgical operating microscope and extensive experience with ultrasonic tips (their uses, when coolant is required, which tips are appropriate for what applications, etc) are required. If these factors are not present, the tooth should be referred to a specialist who has the experience required (Fig. 1). A file fragment, once present, irrespective of location can either be bypassed easily with hand files or not. In our experience, very few fragments, especially those beyond the orifice level can be easily bypassed with K files. Even if a fragment can be easily bypassed, it is challenging to not dislodge the fragment from its position and cause it to rest in a different (more apical) position that then prevents its being bypassed. Irrespective of the given situation, copious irrigation, ideally with sodium hypochlorite under a rubber dam is absolutely vital for visualization of the present state of the files position within the canal.
In the most general sense, removal of the fragment should be done without changing he morphology of the canal to the greatest extent possible. In other words file removal should require the minimum required removal of dentin and such dentin removal should be taken from areas of the canal that keep perforation risk to a minimum. Having removed a large number of separated files, if any portion of the file is resting in a straightaway linear path to the orifice, i.e. it is above the most significant curvature of the root in a straight line with the orifice there is an excellence chance that the file can be removed. If the entire file is beyond the curvature, chances for removal, while not impossible, will drop. There must be a significant benefit to risk ratio assessment made with regard to how much dentin will be removed in order to facilitate file removal before any procedures of any type are undertaken to remove the file. In our opinion, to leave a file in place because a clinician simply does not have the will, time, desire or integrity to refer the patient (given the particulars of the clinical situation where referral or removal was a viable option) or address the problem is a genuine disservice to the patient.
In the example that follows, a lower molar mesial root fragment will be described with regard to removal of the file. Application of these principles and ideas to other teeth and clinical situations is straightforward.
Once it is decided that the given clinician will attempt to remove the file, straight-line access is essential. Orifice shapers can be used to fully define and enlarge the orifices of the canal to create the best initial visualization and clearing of the canal with regard to irrigation. Removal of dentin with ultrasonic tips is almost always (with some exceptions) away from the “danger zone” i.e. the furcal aspect of the mesial roots of lower molars. Lack of judicious removal of dentin in this delicate area can easily cause strip perforation severely compromising the case. Dentin should be removed as needed at the area of greatest bulk of dentin, which, for example, in the mesial root of lower molars will be the mesial aspect of the mesial root, away from the furcation and/or toward the isthmus between the two mesial canals. Below the orifice, removal of dentin to facilitate removal would ideally never be accomplished with a bur, ever. Risk of perforation is simply too high, even under a surgical microscope. Coronal access will often need to be accentuated to allow the ultrasonic tips utilized to be free to work at their tips without touching the walls of the access at the occlusal level. While tooth structure should always be conserved while possible, risk of perforation from attempted file removal rises exponentially if the occlusal access is too small. Simply put, in attempted file removal, arbitrary conservation of tooth structure is counterproductive.
Several issues must ideally be appreciated before removal of RNT file fragments is attempted. First off, files separate because of either torsional forces and cyclic fatigue or some combination of the two. A description of these sources of instrument fracture has been detailed elsewhere.1-5 Suffice it to say that removal of RNT segments is slightly different based on the source of the failure. Segments that have fractured as a result of torsional failure tend to be smaller 1-3mm and wedged very tightly into canal fins, acute canal curvatures, and narrow restrictions that may not have previously be opened up with a hand created glide path. The source of the torsional failure is instructive. Often such torsional failure arises because the largest diameter of the file has enough power behind it provided by the electric motor to allow that portion of the file to cut and should the tip of the file become locked in a canal, it can very easily snap. As a clinical aside, it is important for clinicians to not depend on the auto reverse function of the given electric motor to let them know when it is time to remove the file from the canal. In essence, the clinician should not use the auto reverse alarm like a “speed limit” up to which they believe they may force the file to length.
Achieving access to the most coronal aspect of the file can be accomplished several ways. First off, the method of easiest access depends largely on the level in the canal at which the file rests. If the file is in the coronal third of a root, it may be possible to simply take a small ultrasonic tip and with a gentle counter clockwise motion around the coronal aspect of the file unwind the fragment out of the canal.
Separations of the file that are in the middle and apical thirds of roots are obviously more complex. Middle third separations usually first require the use of orifice openers to remove coronal third dentin above the file. The Shaper K3 files (SybronEndo, Orange, CA, USA) of .12, .10 and .08 taper all could be used to accomplish such a fu
nction. It is noteworthy that the Shapers, or any such orifice opener will only create a tapered funnel down to the level of the most coronal aspect of the separation and will not usually allow visualization of the file head. Usually, some removal of dentin circumferentially with an ultrasonic tip is required to fully visualize the file head.
File separations in the apical third of roots are more challenging. In the most general terms, if the file separation lies beyond the point of greatest root curvature, its removal is doubtful, as, access to achieve removal is vital to visualize the file above the point of greatest curvature. Through minimal dentin removal over the most coronal aspect of such a file, if a portion of the head can be exposed, chances for removal increase.
Ultrasonic tips of all types when placed onto the separated rotary NiTi file directly often lead to breakage of the exposed portion of the file leaving a more apical fragment in place which is most often much harder to remove. It is important to realize that the file is removed by elimination of the forces placed upon it by the canal walls and not by direct vibration of the file. Said differently, it is removal of dentin (around the file) that frees up the file and allows it to move coronally. Several noteworthy issues are worthy of mention at this point.
As mentioned, as much as possible, removal of dentin must always be away from the furcation and towards the wall of the canal with the greatest bulk of dentin. Second, pulses of ultrasonic energy during removal are brief and require the lightest touch. It is not necessary to remove large amounts of dentin to remove most separations. In reality, many file fragments can be removed with only the smallest amount of dentin removal preformed selectively. Such removal is more dependent on placement of ultrasonic energy and type of ultrasonic tip rather than the sheer amount of energy and/or the duration of ultrasonic use. Such pulses of ultrasonic energy are usually 1-2 seconds at a time with pauses followed by irrigation and drying and/or the entire process can be carried out with light water spray to avoid heat build up in the root. It is entirely possible to push too hard on a file and either break the file as mentioned or actually push the file apically and make removal less likely and more complex.
It is important to have ideal visualization during the entire process. It is possible to either use the Stropko Irrigator to pulse a significantly reduced pressure air down such a canal blocked by a separated file or to irrigate frequently with either SmearClear (SybronEndo, Orange, CA, USA), sodium hypochlorite, or chlorhexidine (2%, Vista Dental Products, Racine, WI, USA) and dried with paper points (Fig. 2). Clinician personal preference guides which method might be used. The important point is that removal of the file is accomplished through direct visualization and the ultrasonic tips are never used without being able to directly visualize the file whose removal is being attempted. The motion of ultrasonic file use is counter clockwise and if possible, as mentioned; the RNT file is not touched if it can be avoided.
The challenge in knowing where to remove dentin for file removal stems from appreciating the path of the separated file which is unseen because it is embedded in the canal. In other words, the portion of the file that may appear to be straight given the orientation of the head of the file that is visualized may be anything but. As mentioned, removal of tooth structure must respect the furcation and any thin “danger” areas of dentin thickness where removal of dentin excessively and/or unnecessarily can lead to perforation.
During the application of ultrasonic energy it is vital to have the ultrasonic tip not touch any canal walls of the access so as to not reduce the amount of energy applied to the tip.
After circumferential removal of dentin in the given third of the canal around the head of the file, often times the file will begin to move and may even spring upward and straighten out in the canal and removal can be complicated because the file needs a straight line path of exit to be removed from the canal. When the file pops up, it is easiest to actually separate the head of the file that is now lying on the opposite canal wall and irrigate out this portion of the file and then “pop up” the remaining fragment. Alternatively, sometimes application of greater ultrasonic energy for short pulses (1-2 seconds) on the file itself can make the file exit from the canal entirely (in the authors empirical opinion, this is the only indication to touch the file directly with an ultrasonic tip). Alternatively, if the file lifts out of the canal partially, it is often possibly to then bypass the file with a hedstrom file and “pick the file up” and carry it out of the canal. In addition, once the file has lifted out of the canal somewhat, it is also possible occasionally to irrigate the remaining segment out of the canal.
Irrespective of the particular method of attempted file removal it is very important to attempt to maintain as much of the dentin along the canal path as possible and do everything possible to minimize the chances for perforation or subsequent root fracture due to overzealous removal of tooth structure even if the root is not perforated. This skill of removal of rotary nickel titanium files is a highest order skill requiring practice, ideally on extracted teeth, most certainly a surgical microscope for the greatest visualization and command over the operative site and ideal irrigation and a variety of ultrasonic tips. It requires time, patience and focus to perform each subsequent step to the highest standard to achieve the intended goal of removal of the separated rotary (Fig. 3).
Dr. Richard Mounce is in private endodontic practice in Portland, Oregon, USA. Dr. Mounce is the author of a comprehensive DVD on cleansing, shaping and packing the root canal system for the general practitioner. The material is also available as audio CD’s and as a web cast pay per view. For information: Comfort@MounceEndo.com
Dr. Gary Glassman is the endodontic editor for Oral Health Dental Journal, a Fellow and endodontic examiner for the Royal College of Dentists of Canada, Past President of the George Hare Endodontic Study Club and the H.M.Worth Radiology Study Club. He maintains a private practice, Endodontic Specialists in Toronto, Ontario. He can be reached through his website www.rootcanals.ca.
Dr. Mounce and Glassman have no commercial interest in any of the products mentioned in this paper.
Oral Health welcomes this original article. References available upon request.