Written by Richard E. Mounce, DDS Thursday, 30 April 2009 19:00
I have been blessed to be trained by, and cave dive with, 2 of the very best technical scuba cave divers and explorers in the world, Steve Bogearts (Mexico, aztecdiving.com) and Brian Kakuk (Bahamas, bahamasunderground.com). Integration of new equipment, techniques, and skills, be it in a cave under water or with a complex anatomy in a root canal can, at times, be difficult. Appreciating the risk present at any given time is essential to avoiding and/or overcoming these risks. Dive plans, especially in cave diving, should be carefully discussed beforehand amongst all team members. In caving, the skill sets and responses required for various scenarios should be reflexive. Interestingly, the conceptual strategies that make a safe and well-executed cave dive and a well-carried-out endodontic procedure are very much the same. These strategies and concepts are discussed below in the context of a clinical case that was referred to me recently. The comprehensive management of the situation is described along with the rationale behind the steps taken.
SLOWLY AND PROGRESSIVELY
Steve Bogearts suggested to me that in cave diving “slow is smooth and smooth is fast.” It is an idea that resonated with my experience in endodontics. In a cave diving context, each step in the dive builds positively upon the previous one to bring the dive to a safe conclusion. When problems occur in diving, they often multiply very quickly. This is just as true in endodontics. For example, a poor access cavity can easily lead to fractured rotary nickel titanium (RNT) instrument or apical blockage amongst many other problems. Alternatively, adequate straightline access and coronal third management can make apical enlargement much more streamline.
In moving through the tangible steps of the endodontic treatment, how many of us have, at one time or another, wished we could go back 5 minutes in time before a problem occurred or refer the case from the start? If we are wholly honest with ourselves, risk was there and predictable, we just may not have recognized it for what it is. Moving through the treatment process sequentially can mitigate many of these potential risks.
As a starting place, having the entire procedure rehearsed with our assistants as well as having all the needed supplies on the tray table placed in the expected order of use is essential for creating efficiency. Mentally, as well as tangibly, the entire procedure should be broken down in a larger number of very small steps that are moved through in a slow and yet intentional, deliberate, and focused manner. Making sure each success step is correctly accomplished before proceeding can prevent the clinician from having to back up, redo steps, and correct otherwise avoidable problems.
PLANNING AND DIAGNOSTIC STEPS
Several planning and diagnostic steps prior to treatment are axiomatic in avoiding iatrogenic outcomes and to make treatment flow smoothly.
A risk assessment of every case should be made for possible iatrogenic events as well as to decide how the treatment should be carried out in light of the challenges that the tooth presents. While a comprehensive discussion of the various instrumentation strategies is beyond the scope of this paper, decisions about the likely final taper and master apical diameter can often be made from the initial films. For example, complex root forms will generally have less final taper than simpler root forms. Complex root forms will also usually require more initial hand negotiation prior to the use of RNT files.
The patient must be well informed and give consent. Such informed consent is essential to build rapport and gain the patient’s trust. This informed consent is part of a larger examination that encompasses the patient’s medical and dental history and recording and duplicating the chief complaint. It also includes recording the objective and subjective findings amongst the other needed examination components. This consent stands in distinction to a procedure which is started and in which the patient does not know a root canal is being done or has been started until after the fact. The rubber dam should be used for all cases.
Optimal visualization and magnification should be employed; for example, by using the surgical operating microscope (SOM [Global Surgical]). Profound anesthesia should be achieved and tested before access.
A plan for treatment should be made for the entire procedure before starting. While not entirely rigid, this plan should be followed unless there is a significant finding in the middle of treatment that necessitates a change in approach. (For example, moving to a step back instrumentation technique from a crown down approach.)
|Figures 1a to 1c. The clinical case discussed. Note the initial fragment of nickel titanium present in the buccal root.|
Clinical Considerations in Managing This Case
It is essential to gain access to and remove the file fragment without making the root more susceptible to vertical fracture or possible perforation. It is not advisable to attempt removal of a RNT fragment unless the clinician is highly trained in such procedures.
Figure 2. The M4 Safety Handpiece (SybronEndo).
Other than the obvious removal of dentin in the coronal third, it is unknown what steps were made to remove the file. In this case, once the fracture occurred, immediately, it had value for the clinician to attempt to bypass the fragment with a small precurved hand file (a No. 6, 8, 10 hand K file) and see if the canal was still negotiable. If the fragment could be bypassed by hand to create a pathway alongside the instrument, it may have been possible to remove the file without a microsurgical intervention. Progressively larger hand files, starting with a No. 6 or 8 hand K file, creating space alongside the fragment in this manner, might allow the canal to be enlarged to a diameter where the use of a Hedstrom file might allow the fragment to be lifted out of the canal. A reciprocating handpiece such as the M4 Safety Handpiece (SybronEndo) can be invaluable when used for such a purpose (amongst the others described below). If the fragment can be initially bypassed, the M4 can efficiently make the pathway alongside the fragment larger to make way for the Hedstrom file that might allow a purchase and coronal delivery (Figure 2).
If the fragment cannot be easily bypassed (and immediately) and this type of removal is not easily feasible, the case should be referred to a specialist. Removal of dentin from the cervical area of the tooth, especially without the SOM, places the tooth at high risk of perforation. Dentin removal for the purpose of gaining access to a fracture file segment is problematic in that it is dentin that otherwise would not need removal and as such represents a compromise under any circumstances.
The File Fragment: Clinical Implications
Given the length of this fragment as well as the relatively linear nature of its position in the root, it is very likely that this file fractured from cyclic fatigue failure. Cyclic fatigue failure occurs when an instrument is rotating in a canal with tension (the file is being pulled apart) being placed on one side of the file and compression on the other (the file is being pushed in) with these forces working simultaneously to propagate micro fractures, which can develop into a fractured instrument. The endodontic literature shows cyclic fatigue to occur more frequently when files of relatively larger diameter are used compared to those of a smaller diameter. New files have greater resistance to cyclic fatigue than used files. A smaller radius of canal curvature also is consistent with greater risk of cyclic fatigue failure.
In any event, appreciating the source of the failure has a direct impact on removal potential. An instrument that has fractured from cyclic fatigue will be less likely to have been screwed into the dentin with force. Alternatively, a file which has been inserted with undue force into canals and is restrained until failure (torsional failure), (ie, the file is locked in dentin and rotational forces are continually placed upon it) may prove to be harder to remove than a file which fails by cyclic fatigue. File fragments from torsional failure are generally much smaller than their cyclic fatigue counterparts. In essence, fragments that fail due to cyclic fatigue are longer and generally have been subjected to little, if any, screwing in. As a result, they are generally somewhat easier to remove because they were not locked into the canal walls.
Cyclic fatigue fragments are often located around or beyond a curvature complicating removal. Fragments that result from torsional failure, being smaller, tend to occur more at, or above, the point of greatest root curvature. They are easier to remove from the perspective that there is less metal to retrieve from the canal. This said, the degree to which these fragments have been screwed into the root will, in part, affect their relative ease or challenge in removal.
Fracture of the instrument in this clinical case could have resulted from using the file too many times, a combination of excessive use and excessive force or possibly using the file after signs of deformation (an indication that it should have been discarded). It is unknown what taper, tip size, or brand of RNT file fragment this was.
It should be appreciated that the existing coronal third dentin removal is more than adequate. Removal of more dentin might predispose the tooth to either peroration or subsequent vertical fracture. Clinically, this meant that the use of an orifice opener such as a .12 tapered RNT file was contraindicated as was the use of Gates Glidden drills or Peezo reamers, all of which might remove more dentin and make an iatrogenic outcome more likely.
Clinical Management: Instrumentation and Obturation
After removal of the existing temporary and cotton pellets present, the fragment was immediately visible under the SOM. Because the fragment appears straight in the radiograph, it must be appreciated that this does not have to be the case. It is certainly possible that it could curve in a buccal to lingual direction and in essence complicate removal.
In this clinical case, I could not bypass the fragment with hand files. The immediate goal after fragment removal was to achieve patency and instrument the canal to the minor constriction (MC) of the apical foramen.
Using the SOM and ultrasonic tips, the file fragment was removed using a counterclockwise motion with water coolant around the fragment. The tip was focused on selective dentin removal and not vibration of the fragment itself. Removing dentin around the file allows the restrictive dentin that is locking the file in place to be removed and allow the file a path of exit. The lingual canal showed minimal enlargement upon access and was relatively untouched.
Figure 3. The Twisted File (SybronEndo).
After removal of the fragment, small hand files were inserted to assure apical patency in both canals. The M4 Safety Handpiece was employed (as described below) in order to prepare the glide path that made way for the use of the Twisted File (TF) (SybronEndo) to instrument the canals (Figure 3). The M4 reciprocates a hand K file 30° clockwise and 30° counterclockwise. I utilize the M4 for the initial enlargement of the canal and glide path creation, not for the entire canal preparation. The M4 is very safe, efficient to use and simple in both concept and application. It mimics the manual use of a hand K file with a watch-winding motion. It saves time and hand fatigue and yet is very safe in that fracture of a stainless steel hand file, used in the manner described, is very rare.
Specifically, for this tooth, after the removal of the file fragment, the No. 8 hand K file was able to be inserted with some resistance in the apical third of both roots until a tangible “pop” could be felt at the MC. The electronic apex locator (SybronEndo) was then used to verify the position of the MC, hence, provide the true working length (TWL). Clinically, in this case when the No. 8 reached the MC and the aforementioned “pop” was felt, the file was left in the tooth (under the rubber dam) and the M4 was attached. The M4 was used with the No. 8 for about 15 seconds with a vertical amplitude of about 1 to 3 mm. The M4 Safety handpiece attachment couples with an E-type coupling and is used in an endodontic motor at the 18 to 1 setting at 900 rpm. Used in this manner, the canal is able to be taken from the size of a No. 8 to that of a No. 10 hand K file. After this application of the M4, the No. 10 hand K file can be placed to the same length and reciprocated with the M4 in the same manner. Reciprocating a No. 10 hand K file will create a glide path (a canal enlarged to the size of a No. 15 hand K file), making way for RNT canal enlargement.
After the creation of the glide path with the M4, TF was used to prepare the canal. Two tapers of TF (.10 and .08) were used in approximately 8 total insertions to shape these roots. TF is available in 5 tapers (.12, .10, .08, .06, and .04). At the time this case was treated, TF was only available to a No. 25 at the tip. TF is now available in .06-30, .06-35, .04-40, and .04-50. This case, if done today, could be enlarged apically with these larger TF sizes. TF is never ground against the grain structure of the metal of the file in its manufacture. Created by the twisting of nickel titanium in its rhombohedral crystalline phase configuration (an intermediate phase between austenite and martensite) the properties of TF are remarkable relative to ground RNT files. For example, the number of insertions needed for TF relative to the alternatives is much fewer (3 to 4), the tapers that can be prepared are much larger (.08 to 10 taper around a multi planar curvature) as a result of the cutting efficiency, flexibility, and fracture resistance of TF.
Figures 4 and 5. The RealSeal One Bonded Obturator (RSOBO) and Oven (SybronEndo).
TF technique requires fewer files than the alternatives. TF was used crown down in this case from the larger taper (.10) to smaller (.08), alternating between these 2 tapers after glide path creation to the TWL. While many clinicians in daily practice chose to create relatively small apical diameters (20 to 30), the endodontic literature is very clear that the preparation of larger apical diameters creates cleaner canals. As a result of this literature basis, in this clinical case, after preparation with TF, the apices were gauged and larger apical preparation ensued using K3 with a step back method (25, 30, 35, 40, 45, 50, 55, 60) in the .04-tapered variety.
Figure 6. SOM of the bonding achieved with the RSOBO.
|Figure 7. Additional cases obturated with RSOBO.|
Figure 8. Maxcem Elite (Kerr) self-etch self-adhesive resin cement was used in the coronal build-up of this clinical case.
Obturation was performed with the RealSeal One Bonded Obturators (RSOBO [SybronEndo]) (Figures 4 to 7). RealSeal is a synthetic polymer of polyester that includes a methacrylate component, which is chemically similar to the methacrylate component of the self-etching sealer of the system. This chemical similarity allows the core filling material to be chemically bonded to the sealer and into the resin tags that penetrate the dentinal tubules after smear layer removal.
RealSeal has been available since 2004 in a master cone variety that is virtually identical in delivery and appearance to gutta-percha. I have bonded all of my obturation since January 2004 with RealSeal. RealSeal looks, handles, is applied, and re-treated like gutta-percha. Previously, it was not possible to use RealSeal bonded obturation technology in warm carrier based form. RSOBO are now available in .04 taper in tip sizes from 20 to 90.
Gutta-percha has no ability to bond to neither sealer nor dentin. Gutta-percha requires the use of a coronal restoration to prevent the migration of bacteria in a coronal to apical direction. Gutta-percha has no inherent ability to seal canals. The endodontic literature is quiet clear that the placement of a coronal restoration is correlated with clinical success with gutta-percha and vice versa. On balance, the endodontic literature has overwhelmingly shown, across the totality of the canal, that RealSeal resists coronal leakage (in vitro and in vivo) to a greater degree than gutta-percha.
RSOBO has advantages over other variations of warm carrier based obturation. First off, all of the obturators can be dissolved in a solvent such as chloroform. Second, these obturators can be easily removed with TF as needed in retreatment using TF with enhanced speeds (greater than 900 rpm). Third, for clinicians already using warm carrier based techniques, they can now bond their obturation without any significant deviation from what they are doing now. Fourth, for the clinician who has been hesitant to use a warm obturation technique, this gives another option that is simple, efficient, and easily retreated, in addition to the advantage of being bonded. And finally, post space is simple to make using RSOBO, as a heat source such as the Elements Obturation Unit (EOU [SybronEndo]) heat source can easily melt the carrier to the desired level of post space depth.
RSOBO come with an oven that is used only for these obturators. It is not appropriate to use the ovens from other systems with RSOBO as the temperatures required for different systems are not the same.
To utilize RealSeal or RSOBO, the final irrigation rinse is a liquid EDTA solution. In this case, that solution was SmearClear (SybronEndo) which was used to remove the smear layer and facilitate the bonding of the obturation. The SmearClear is left in the canals for approximately 2 minutes before it is flushed out with water and obturation commences.
Obturation of this clinical case with RSOBO was simple. The final TF taper was .10 and both canals passively accepted the No. 60 size verifier indicating that the No. 60 RSOBO was appropriate for the canals. As per the manufacturer’s instructions, the obturators were heated in the RSOBO oven and placed to length in the canal and seared off with the heat source of the EOU at the orifice.
Figures 9a and 9b. The Skini syringe and Micro 20 gauge (Ultradent Products) syringe tip was used to apply the Maxcem Elite resin cement.
After insertion of the RSOBO, Maxcem Elite (Kerr) self-etch self-adhesive resin cement was placed utilizing the Skini syringe and the Micro 20 gauge tip (Ultradent) under the SOM. The tooth was rough-prepped for a crown and the occlusion reduced (Figures 8 and 9).
Each stage in the process of evaluation and subsequent treatment should be performed both slowly and progressively. In this example, first to appreciate the challenges in fragment removal, then to remove the fragment (or refer), achieve patency, shape the canals, obturate, and place a coronal restoration. Much like a cave dive that is highly planned and rehearsed and carried out in successive and progressively building steps, to the greatest extent possible so should our endodontic procedures. Ideally, there should be no surprises. Once begun, performing every step in a sequential order allows the process (whether it’s cave diving or endodontics), to be at first slow, then smooth, and ultimately fast.
Disclosure: Dr. Mounce is on the Advisory Board for SybronEndo. He receives honorariums for some aspects of this work, lectures for example.
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