May 1, 2006
by Richard Mounce, DDS
We can learn more from our clinical failures than our successes. If we will allow it, the cases that have less success can be great teachers if we are open to their lessons. Such is a case pictured in Figure 1. What went wrong? How could this have been avoided? While the radiograph is in some ways self explanatory, it carries a number of lessons and subtle interpretations that can be derived from its careful evaluation.
The patient was an 82-year-old female whose medical history was non-contributory. The patient’s general dentist initiated the treatment on #28 and the patient was referred to the author in the condition pictured on the same day. The tooth was referred for completion of the root canal as well as removal of the separated file. There was a lack of clinical crown and yet the tooth could hold a rubber dam clamp. The tooth was within normal limits to percussion, palpation, mobility and probings. There was no apical lesion visible radiographically. The patient was aware that a rotary nickel titanium (RNT) file had separated in the tooth and yet did not have any idea of the degree of the extension of the file beyond the root end or the length of the separated fragment. The patient’s crown on #28 had come off some time before and the contemplated treatment plan was to place a post, crown the tooth again and use it for the distal abutment for a new partial denture. The patient was asymptomatic at the time she presented in my office. After obtaining consent (discussing the plan, alternatives, risks and answering the patients questions), an attempt to remove the file and complete treatment was made.
As an aside, #29 had been unsealed and broken off in its present condition for several months and was slated for extraction.
How the file came to rest in this position poses several excellent questions and reviews of what might have occurred, what did occur and how such events can be avoided.
1) The initial radiograph was not carefully evaluated. The length of the tooth was not estimated properly if at all. The initial length of any tooth to be treated endodontically should be evaluated to empirically give the clinician some idea of its future true working length (TWL) in addition to all of the anatomical and pathologic features which might be interpreted. If the initial length of the tooth is estimated from the pre operative x-rays, it is usually within 2mm of the final TWL. As such, the initial radiographs provide a “ball park” as to how deep within the root canal system any given instrumentation is proceeding, especially in the negotiation stage of the process. The estimated length of the tooth is one of several pieces of evidence that can be used to determine the TWL. The other evidential pieces are the use of an apex locator, tactile sense, a bleeding point, and as needed radiographically. Regardless of the methods used to determine TWL, they should be confirming and agreeing with one another.
As many methods as possible should be employed to confirm that the length achieved represents the position of the minor constriction of the apical foramen. Accurately determining the position of the minor constriction of the apical foramen can, in combination with appropriate instrumentation procedures, lead to the creation of an apical capture zone into which all obturation material can be condensed upon apical downpack of heated obturation materials. It is desirable to keep all RNT files and irrigants above the minor constriction of the apical foramen, if possible, so as to avoid canal transportation as well as extrusion of the irrigants.
In this particular clinical case, once the file violated the apical constricture as well as the apical foramen, one of the key principles in endodontic instrumentation, to keep the apical foramen at its original position and size, was lost. Had the file not separated, it is likely or at least very possible that the canal would have bled profusely due to apical transportation and violation of the periapical tissues making subsequent cleaning, shaping and obturation potentially much more difficult to perform. If the canal had bled profusely it would almost certainly required that the treatment take two visits. Such treatment can often require an interim dressing of calcium hydroxide or possibly MTA (Dentsply Tulsa Dental, Tulsa OK, USA) and ideally a surgical microscope for visualization.
It bears asking at what stage in the process the clinician should have determined the TWL. Ideally, aside from using the estimated working length from the initial radiograph, the clinician should have first negotiated the canal to determine either visually through radiographs or tactilely with small K files whether or not the canal was patent. If the canal were patent initially, which it was, the clinician could have either exposed a radiograph to determine TWL once the file would traverse the length of the canal to reach the estimated working length or taken an electronic apex locator reading or both. This could have been done after the coronal third and middle third were instrumented.
More specifically, in this hypothetical sequence, the clinician would instrument the coronal and middle thirds of the canal with orifice openers, and then, before instrumenting the apical third, the length would then be determined after the apical third had been negotiated with small hand files and canal patency assured prior to final instrumentation. Performing treatment in this manner would go far toward preventing the mishap of inserting the rotary file beyond the apical foramen.
It is noteworthy that many endodontists do not determine TWL until late in the instrumentation sequence. Said differently, many specialists will use the estimated length determined before treatment is initiated and blend it with the tactile sensation of the canal as shaping progresses and instrument the canal to within a mm or two of the estimated working length.
When instrumentation is virtually complete, they will take an electronic apex locator reading and then create their final apical shape. Doing so provides an element of safety in that the actual shaping of the apical third is done so passively, by intention and gently with special emphasis on finishing the apical third as safely and efficiently as possible. This method would stand in distinction to the clinician who might rush to the apex. Such a rush to the apex, in trying to shape the apical third before the coronal two thirds are instrumented, risks ledges, obstructions, canal deviations, and other such iatrogenic events.
2) The tactile feedback of the canal was ignored. The touch and insertion of the RNT file was likely too forceful and performed too quickly. The canal was not instrumented in a rational sequential order maximizing safety. In other words, the RNT was pressed apically both too rapidly and from the forearm instead of gently from the fingers. As one gets deeper in a canal especially early in the instrumentation sequence, the resistance encountered is greater and especially as one enters the apical third, such resistance can become quite acute. Not taking into account the amount of increased pressure that such apical advancement requires can easily lead to torsional failure of the RNT as well as blockage of the canal with debris and canal transportation if not cleared.
Coincident to considering the tactile feedback the canal gives, it is vital to negotiate all canal spaces by hand as well as create a glide path before the placement of RNT files into any given canal third, especially the middle and apical third. Said differently, ideally, this canal would have been explored by hand first to determine the canal length, calcification, diameter, and curvature.
Once these baseline pieces of information were determined, the clinician would have then obtained the TWL and maintained all the file insertions up above the minor constriction of the apical foramen. Ideally, irrespective of the given canal third, the clinician would have negotiated each canal space first with small hand files to
determine its patency and negotiability and subsequently created a glide path and then in a crown down fashion instrumented the canal with rotary files.
Such a crown down approach to instrumentation would have used the RNT files from larger taper to smaller tapers and larger tip sizes to smaller tip sizes, all used in a manner that minimized the engagement of the file along the canal walls, ideally to 1-2mm, and be done so with the gentlest touch so as to be able to interpret the canals tactile feedback. This stands in distinction to the clinician who pushes rotary files apically without regard for all the radiographic, clinical and tactile signs that would argue against such insertion.
3) The risks of cyclic fatigue were ignored either because the clinician was not aware of the phenomenon or was relying on the auto reverse function of the given electric motor being used to tell them when to remove the given rotary. It is very possible that this clinician was relying upon the electric motor being used to tell them when to remove the rotary file from the canal by virtue of the auto reverse function as well as some audible alarm. Said differently, using the electric motor and relying upon the motor to tell the clinician when they should pull the file out is problematic in the extreme.
Empirically, the author uses the TCM III electric motor with the torque control off and K3 rotary files at a speed of 900 RPM both SybronEndo, Orange, CA, USA.
Manufacturers’ instructions for RNT files generally range from 350-500 RPM with exceptions. A search of the “PubMed” website for references for K3 yields the attached references for further information. In the author’s empirical opinion, running RNT with an electric motor with the torque control off allows the clinician to have full control over the file and allows the clinician to utilize the files to its greatest safety.
Relying on auto reverse set to diminished torque limits will in practice lengthen the learning curve by potentially reversing the file without taking advantage of the files greatest efficiency or rotational speed as well as cutting to it fullest capability.
Conversely, cutting with the correct RPM’s and without torque control can put the greatest function, efficiency and ultimately safety into the files use. This can give the clinician total control over the file and if the touch used in file function is ideal, the need to rely upon torque control limits is eliminated. The correct touch in RNT use is gentle, from the fingers, passive, done in increments of cutting 1-2mm per insertion and is done so in a controlled single continuous motion. Once the file engages 1-2mm of dentin wall or wont advance apically in a passive manner, the file can be removed and the next file can be inserted.
4) The clinician did not use a rubber dam. Simply put, there is no defence for neglecting to use a rubber dam. It is the standard of care in the United States for endodontic treatment and should morbidity occur due to a lack of rubber dam (aside for the quality of care issues that are significant), the clinician cannot be defended should the patient sue. If a tooth won’t accept a rubber dam clamp, either crown lengthening surgery should be performed to make it ready for one or the tooth should be extracted.
If the patient refuses a rubber dam, the tooth should be extracted. Lack of a rubber dam allows saliva to drip into the tooth defeating antimicrobial irrigation, risks instruments and liquids from falling into the patient’s throat in addition to a wide variety of other possible problems.
5) The clinician did not phone the specialist to tell them what had happened. Communication between generalist and specialist is a key feature to allowing the patient to get the best possible clinical service. Some patients have special needs and most specifically with iatrogenic events of all types, knowing what has occurred, what the patient has been told can all make a very big difference in allaying patient fears, treating the problem and making the experience as atraumatic as possible.
Prior to appearing in my office, the referring doctor did not (among other things):
a) Appreciate that they ideally should have used a rubber dam.
b) Have a conversation with the patient with regard to restorability before treatment.
c) Discuss how the tooth would be restored with the patient, i.e. would it be posted, built up, crowned.
d) Discuss the periodontal status of the tooth.
e) Discuss whether the tooth would need periodontal treatment of any kind or if periodontal treatment would be needed so as to make the tooth restorable.
f) There was no consent preoperatively that a file could break and what might happen if file breakage should occur.
Ironically, this patient had the tooth extracted when it become evident that after consenting to treatment with the author that they would not tolerate a rubber dam. It is likely that had the patient and referring doctor discussed the rubber dam (in addition to the other challenges this tooth presented) prior to treatment that this patient may have had the tooth removed from the very beginning or after separation. The case review underscores the vital importance of a focussed and methodical pre-operative assessment of both the tooth and the patient.
Dr. 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. Mounce has no commercial interest in any of the products mentioned in this paper.
Oral Health welcomes this original article.
1.Yao JH, Schwartz SA, Beeson TJ. Cyclic fatigue of three types of rotary nickel-titanium files in a dynamic model. J Endod. 2006 Jan; 32(1). 55-7.
2.Guelzow A, Stamm O, Martus P, Kielbassa AM. Comparative study of six rotary nickel-titanium systems and hand instrumentation for root canal preparation. Int Endod J. 2005 Oct;38(10).743-52.
3.Yoshimine Y, Ono M, Akamine A. The shaping effects of three nickel-titanium rotary instruments in simulated S-shaped canals. J Endod. 2005 May;31(5):373-5.
4.Patino PV, Biedma BM, Liebana CR, Cantatore G, Bahillo JG. The influence of a manual glide path on the separation rate of NiTi rotary instruments. J Endod. 2005 Feb;31(2):114-6.
5.Masiero AV, Barletta FB. Effectiveness of different techniques for removing gutta-percha during retreatment. Int Endod J. 2005 Jan; 38(1): 2-7.
6.Ayar LR, Love RM. Shaping ability of ProFile and K3 rotary Ni-Ti instruments when used in a variable tip sequence in simulated curved root canals. Int Endod J. 2004 Sep; 37(9): 593-601.
7.Ankrum MT, Hartwell GR, Truitt JE. K3 Endo, ProTaper, and ProFile systems: breakage and distortion in severely curved roots of molars. J Endod. 2004 Apr;30(4):234-7.
8.Prati C, Foschi F, Nucci C, Montebugnoli L, Marchionni S. Appearance of the root canal walls after preparation with NiTi rotary instruments: a comparative SEM investigation. Clin Oral Investig. 2004 Jun;8(2):102-10. Epub 2004 Feb 4.
9.Schafer E, Dzepina A, Danesh G. Bending properties of rotary nickel-titanium instruments. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003 Dec;96(6):757-63.
10.Yared G, Kulkarni GK, Ghossayn F. Related Articles, Links Torsional properties of new and used rotary K3 NiTi files. Aust Endod J. 2003 Aug; 29(2): 75-8.
11.Bergmans L, Van Cleynenbreugel J, Beullens M, Wevers M, Van Meerbeek B, Lambrechts P. Progressive versus constant tapered shaft design using NiTi rotary instruments. Int Endod J. 2003 Apr; 36(4): 288-95.
12.Martin B, Zelada G, Varela P, Bahillo JG, Magan F, Ahn S, Rodriguez C. Factors influencing the fracture of nickel-titanium rotary instruments. Int Endod J. 2003 Apr; 36(4): 262-6.
Schlingemann R. Efficiency of rotary nickel-titanium K3 instruments compared with stainless steel hand K-Flexofile. Part 2. Cleaning effectiveness and shaping ability in severely curved root canals of extracted teeth. Int Endod J. 2003 Mar;36(3):208-17.
Your email address will not be published. Required fields are marked *
Save my name, email, and website in this browser for the next time I comment.