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Avoiding iatrogenic errors in endodontics

Nov. 5, 2010
Dr. Richard Mounce offers general practitioners clinical strategies to avoid iatrogenic outcomes. Emphasis is placed on achievement and maintenance of apical patency, accurate location of the MC, and preserving the MC at its original position and size.
By Richard E. Mounce, DDSAn excellent endodontic case outcome has several components, one of which is using correct strategies and principles in its active treatment. The corresponding flip side to active treatment is the avoidance of iatrogenic events. Avoiding iatrogenic events builds a platform for obtaining desirable and predictable results. This article was written to specifically discuss strategies for avoidance of several types of iatrogenic misadventures. Iatrogenic misadventures are prevented by (among other strategies) enhanced visualization, lighting, and magnification in the form of the surgical operating microscope (SOM) (Global Surgical, St. Louis, MO, USA) and/or loupes (4.8x HiRes Class IV) (Orascoptic, Middleton, WI, USA). The value of the SOM and loupes cannot be overstated in its value to provide visual and tactile control. Prior to making access, the clinical case should be carefully evaluated for possible iatrogenic events. Is the furcation thin? Is the root significantly curved at the apex? By taking multiple radiographic angles or possibly using cone beam (CBCT) technology, the clinician can observe the anatomic factors that will put the risk of iatrogenic misadventure clearly into focus. Specifically, the following factors that represent an iatrogenic risk when observed radiographically (among many others) should be considered: a) Canal curvatureb) Canal calcificationc) Number of rootsd) Root lengthe) Rotated and tipped teethf) Resorptiong) Dens in dentae and other atypical anatomyh) Arch position if access is limitedi) Material being accessed through, especially if the furcation is obscuredj) Severe flutingk) Thin furcationl) Teeth with previous root canal therapy, especially cases with previous iatrogenic events and/or postsm) Immature apicesn) Trauma casesSeeing these risks, the clinician can decide on strategies to help optimize the final result. Several clinical questions should be asked in conjunction with observing the risk factors above: a) What is the optimal taper of the canal?b) What is the optimal master apical diameter?c) What is the flexibility, fracture resistance, cutting ability of the clinician’s file system to address the possible iatrogenic risk as well as prepare the parameters listed in a and b above?d) What level of experience do I have to manage the iatrogenic risks observed? e) What level of lighting and magnification do I have to have tactile and visual control over in the clinical case? f) Would referral be a better option? As mentioned, at times the clinician must take into account iatrogenic risks and sometimes these risks might modify common treatment sequences.For example, the mesial buccal root of an upper molar often has moderate mid-root curvature. Using a rotary nickel titanium (RNT) system like the Twisted File* (TF), it is possible to prepare a .08 taper throughout of the root with the .08/25 TF. It is not possible to prepare a .08 taper along the length of the root predictably using RNT files that are manufactured by a grinding process. Using ground files, the final prepared taper is likely to be .06 or even possibly .04. Hence, knowing the capabilities of the instruments being used has significant implications as to the sequence used, number of files required, and number of insertions required to prepare the final taper, whether a taper of .04, .06, or .08. Using TF (or any RNT system, irrespective of its manufacture), the common “crown down” instrumentation sequence might be modified slightly in that with severe curvature, the clinician might prepare the smaller taper first and the larger tapers later throughout the length of the root. Using TF, this might mean that the canal is taken to a .04 taper first (with the .04/25 TF), the .06 taper second (with the .06/25 TF), and finally the .08 taper (with the .08/25 TF). One common iatrogenic error (preventable with a correct RNT sequence) is the blockage of a small canal orifice using Gates Glidden (GG) drills after access. Forceful and rapid insertion of GGs can lead to transportation and blockage of the orifice and subsequent lost time trying to negotiate the canal with hand K files (HKF). Unnecessary dentin removal often results from attempts to gain canal patency after blockage that can lead to long-term vertical root fracture. As an aside, it is more challenging to prepare a continuous taper using GG drills than using RNT files as orifice openers as the various GG drills must be taken to different levels in the canal to produce a continuous taper and avoid a “Coke bottle” preparation. An alternative to this challenge presented by GG drills is to use TF in lieu of both GG drills and other RNT classes of orifice openers. The .08/25 TF can be used both as an orifice opener and as the primary file to shape the canal to entire taper before preparation of the master apical diameter. Once straight-line access is prepared, the cervical dentinal triangle is removed, brushing up and away from the furcation with the .08/25 TF. Once the canal is negotiated with HKF, apical patency achieved, and the glide path prepared, if the same .08/25 TF will advance to the apex in a series of passive insertions taken to resistance (irrigating and recapitulating between each insertion), the file is taken to the apex (assuming the .08 taper is the correct taper for the entire canal preparation).One important means of iatrogenic avoidance is determination of an estimated working length (EWL) before access. Having some idea of the initial length of the root can go far toward telling the clinician how to correlate the tactile feedback from file insertion relative to its distance from the apex. For example, as the clinician inserts both HKF and RNT files closer to the apex, increasing resistance and needed pressure for insertion tells the clinician how close he or she is to the apex. Once the clinician feels a tangible “pop” at the apex, he or she can correlate the length of the canal that was initially estimated to the tactile “pop.” Once the HKF reaches the EWL, an electronic length is taken to provide the first determination of true working length (TWL). Knowing the position of the TWL early and accurately and preserving the position and size of the minor constriction of the apical foramen (MC) and avoiding transportation of the apex are key strategies to avoid iatrogenic events. Knowing exactly where the preparation should end also tells the clinician exactly where irrigation and obturation should terminate. To work apically with HKF and RNT files without an exact TWL measurement is to invite apical transportation, blockage ... in essence, to leave bacteria, uncleaned and unfilled space after canal preparation. Transportation makes possible significant extrusion of irrigants, sealer, obturation material, and reduces the chances of long-term clinical success. Preserving the MC also provides an apical barrier or stop into which a thermally softened master cone or obturator can be placed. This action focuses the hydraulic forces of obturation apically and vertically, and moves obturation material into all of the cleared ramifications of the canal space because it cannot escape to any significant degree apically. In order to avoid all manner of iatrogenic extrusion of obturation materials, cone fit should provide tugback. Cone fit assures that the master cone is only in intimate contact in the apical 4 to 5 mm of the canal. Without tugback, once heat and pressure are placed on the cone during thermal down packing, gross overfilling is predictable if the MC has been violated. This underscores the vital importance of only taking the instrumentation, irrigation, and obturation to the MC and not further. Summarizing several concepts above, it is crucial that the clinician determine the TWL early and accurately, that cone fit be taken only to the MC (and not beyond), and that all parameters of obturation using a technique like SystemB are performed correctly; i.e., using the correct heat plugger, depth, time, and rate of heat plugger insertion, etc. When any one of these variables is inaccurate, the chances for unnecessary extrusion rise exponentially. Avoidance of iatrogenic transportation of the MC is more predictable when the laser marks are used on the RNT files (such as TF) for length referencing, rather than relying on rubber stoppers to gauge the depth of insertion. When TF is entered into the canal using these laser markings, they should be carefully inserted only to the depth of the MC and not further. An excellent fulcrum during insertion provides tactile control over the file and prevents the file from “screwing into” the root. Irrespective of the RNT file used, insertion should be a single continuous and controlled insertion to resistance. The file should not be pumped up and down (inserted and withdrawn) into the canal. Pumping any RNT file into the canal repeatedly increases the chance of locking the tip and risks torsional failure. The above strategies notwithstanding, the single most important strategy for iatrogenic avoidance is achievement and maintenance of apical patency with HKF. The tactile feedback provided by HKFs cannot be overstated in value. Using HKF to their greatest effect can go far toward avoidance of all manner of iatrogenic issues, including blockage. Blocked canals are dirty canals. “Dirty” in this context means pulp and dentin debris that has not been removed and has been allowed to be compacted into the apical third. Alternatively, canals that are open and negotiable to the apex can be prepared without compromise. Canals that have been blocked with debris are much more likely to become transported and/or contribute to the separation of RNT. Aside from obtaining patency, avoidance of blockage requires that the canal be recapitulated after every RNT insertion in combination with copious irrigation.Clinically, HKF should be trimmed and precurved where needed. Trimming HKF is simple. HKF can be customized to the needed length to provide optimal tactile control to enable the clinician to gain patency and bypass existing blockages. As an aside, when the clinician is having challenges getting patent, often, when using #6, #8, and #10 HKF, the clinician needs to push harder on the file and/or reinsert the precurved HKF file in numerous orientations to make apical progress. Once apical patency is achieved, using the reciprocating M4 Safety Handpiece* is very efficient and safe in taking the canal from its initial diameter to that of a #15 HKF; in essence, to prepare a glide path and make the canal ready for RNT files. The M4 reciprocates a HKF 30 degrees clockwise and 30 degrees counterclockwise; it replicates the manual use of HKFs. It is also helpful in avoiding blockage to employ viscous EDTA gels in vital cases that have a significant amount of pulp tissue in the chamber upon access. Leaving the pulp tissue in the chamber as HKFs are inserted below the orifice can easily lead to apical blockage. Viscous EDTA gels (such as SlickGel*) act to hold pulp tissue in suspension in the chamber until the tissue is removed. This action helps prevent the tissue from being pumped apically and forming a blockage. Once the pulp tissue is cleared from the pulp chamber, and the clinician has shaped the coronal third using a file like the .08/25 TF (as mentioned above), the clinician can switch to a tissue-dissolving liquid irrigant, optimally 5.25% sodium hypochlorite and the use of the viscous EDTA gel is discontinued. This article was written to provide general practitioners clinical strategies to avoid iatrogenic outcomes. Emphasis has been placed on achievement and maintenance of apical patency, accurate location of the MC, and preserving the MC at its original position and size. I welcome your feedback. *SybronEndo (Orange, CA, USA)
Richard E. Mounce, DDS, is the author of the nonfiction book “Dead Stuck” — “one man's stories of adventure, parenting, and marriage told without heaping platitudes of political correctness.” Pacific Sky Publishing. Dr. Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash. Contact him at [email protected].Figures 1 through 4: Clinical cases treated in the manner described using Twisted Files* avoiding iatrogenic misadventures. Obturation was performed with SystemB technique via the Elements Obturation System* using RealSeal.*
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