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Part 1: Access Procedures

Walking the Razor’s Edge Top

The more experience gained in endodontic therapy, the easier and faster most procedures go. But cutting an access cavity, even for the seasoned professional, is always an excellent opportunity for clinical disaster. And when an access procedure goes badly, the long-term prognosis of any given endodontic case can plummet within seconds. Perforations occurring during access procedures are typically located in the most difficult place to repair, the cervical region.

Beyond iatrogenic possibilities, access procedures set the stage for success or failure of the cleaning, shaping, and obturation procedures that follow. Of course inability to locate all of the canals in a tooth will usually result in short-term failure of treatment. While not an irreversible result like perforation, leaving canals untreated can embarrass clinicians and destroy patient confidence, if the patient has not been informed of the situation and the resulting impact on prognosis.

Faced with anatomic possibilities such as two canals in anteriors, three canals in premolars, and one to six canals in molars, clinicians who want to optimize their ability to find canals must enter pulp chambers with a suspicious, skeptical attitude.

More common, though less appreciated, is the lack of convenience form in access cavity design and execution. Although time spent in access saves time throughout the rest of the treatment flow, as it must be accomplished without the needless weakening of tooth structure caused by overenlarged preparations. Cutting an ideal access cavity clearly requires clinicians to walk a fine edge.

Doing No Harme Top

Perforation during access is always a threat, even in non-calcified teeth. Unlike restorative dentistry, all RCT occurs in internal spaces where visual information is limited. Although there are many external clues about the hidden root canal system, this surface morphology is of limited help at best, and on occasion, is the dentist’s worst enemy.

Many teeth are significantly tipped in one or more planes relative to the arch and adjacent teeth. This creates a challenge in entering even non-calcified pulp chambers. Most difficult yet are cases with severely calcified pulp chambers, tipped roots, and realigned coronal prostheses.

fig1

Incisor teeth are frequently perforated to the buccal because, for aesthetic reasons, these access cavities are skewed to the lingual (fig1). This less-than-ideal angle of entry tends to tip the cutting portion of the bur to the buccal, so clinicians must consciously avoid moving too far in that direction. Conversely, incisors are nearly impossible to perforate lingually. Therefore, when in doubt, err to the lingual.

Maxillary premolars are most easily perfed on their mesial surfaces as they are commonly tipped mesially. This occurs most often to mandibular premolars on their buccal surfaces, as the root is often in lingual version relative to the coronal structures. Premolars are challenging because of the widely angled emergence profile of their mesial and distal

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interproximal surfaces.

The occlusal surface of premolars is commonly one third larger than the narrow M-D width of these teeth at the cervical level. This sets one up for a false sense of security about the margin for error when accessing these teeth.Molars are most often perforated through their furcations, and less often through their mesial surfaces, due to their frequent mesial angulation.

If You Can’t Spend The Time, Don’t Do The Crime Top

While every dentist who does RCT has perforated a tooth during access, it should be a rare occurrence. To borrow a phrase from the NRA, handpiece burs don’t perforate teeth, dentists perforate teeth. All access perforations are essentially judgment errors, a result of not stopping soon enough, not taking the necessary x-rays, etc. If you don’t have the time or persistence to take a film every 1mm when burring toward a calcified pulp chamber, then you are not the right dentist to do the access.

Pre-op films are necessary from a straight-on angle, showing contacts and interproximal areas open, and from one or more angles, showing the third dimension. Working films easily show access entry angles in the mesial-to-distal plane, but the buccal-to-lingual plane is obviously more obscure. When burring deeply into calcified teeth, it is often necessary totake two films, straight-on and angled, every 1 mm. Again, if you can’t spend the time, don’t do the access.

After radiographs, cervical root contours are the most important landmarks in determining safe and accurate entry direction.

The following are aids to discerning those contours

Engage the rubber dam clamp as tight against the marginal gingiva as possible.

Place wedges in the mesial and distal interproximal areas.

Place a probe or root canal instrument in furcal areas.

For anteriors and premolars, center the clamp on buccal and lingual heights of contour as a mesial to distal sight-line.

When cervical contours are in doubt, take the dam off until the pulp chamber is located, then re-isolate and finish the access prep.

Overlay the bur on the pre-op radiograph to measure maximum safe depth.

Never forget that when burring beyond the furcational level in a multi-rooted tooth, or beyond the crestal level in single rooted tooth, the risk-to-benefit equation increases exponentially. As long as the entry path is on track (as proven by frequent films from different angles) in a deep access, you will tend to stay on track. As soon as you veer off even a bit, it becomes nearly impossible to reorient correctly, and it’s time to call it a day.

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Breaking and Entering Top

The most important tools needed to create the cleanest, most conservative paths into pulp chambers are hand-eye coordination, well-tuned mental imaging skills, and a lot of patience, thought and determination. Of secondary importance are the cutting tools we wield.

I would recommend the following access burs and ultrasonics tips

#2 round bur (surgical length, carbide) for anteriors and bicuspids.

#4 round bur (surgical length, carbide) for molars.

#2 round diamond bur with water spray for porcelain.

Carbide fissure bur (round-ended, cross-cut) for cast metal.

Water spray for porcelain metal to limit the heat transmitted.

Spartan Ultrasonic BUC-1 tip or narrow tapered diamond bur (round-ended, surgical length) for access refinement.

I strongly advise against using larger burs for initial entry or refinement as they weaken teeth needlessly and increase chances of perforation. As with any air flight, we are always slightly off course during access entry procedures. Because of frequent course corrections, we arrive at our destination with minor irregularities in the approach path. When we use small burs these course corrections cause insignificant irregularities in the access walls, but with large burs, a near miss becomes a perf.

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Access preps on anterior teeth should start with the #2 round bur penetrating the enamel in a narrow trough shape, from near the incisal edge to the cingulum. Once through the enamel it is critical that the angle of access penetration be directed apically and lingually to avoid buccal perforation. Once in the pulp chamber, refine the access cavity with a tapered diamond bur or with ultrasonics. Be sure to maintain a narrow mesial-to-distal form, but extend the buccal aspect right up to the incisal edge and the lingual aspect well into the cingulum (fig2) . Without this lingual extension into the cingulum, second canals in these teeth are even more difficult to find and treat.

fig3

Premolars with single canals require a round access form (fig3) .

fig4

Those with two canals need narrow, elongated accesses (fig4) . The unusual case with three canals should result in a triangular access outline form, much like a molar preparation. Remember to use a slightly lingual entry angle for mandibular first premolars, as they are easily perfed on the buccal.

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The most common molar access error is distal overextension. While this is not a result which will impact the prognosis of a case, it will certainly create difficulties for the operator whenever the distal canal orifices are approached with files, paper points, and gutta percha points.

To prevent distal overextension, access preps on maxillary molars should be started as a trough between the MB and P cusps and angled parallel to the mesial interproximal surface. After dropping into the pulp chamber, the distal access wall can then be gradually lifted back to gain entry to the DB canal. When the pulp chamber is totally calcified in maxillary molars, the first canal to look for is the MB 1, as it is easiest to locate relative to adjacent cervical root contours.

Mandibular molar access should be started distal to the mesial marginal ridge and no further distal than the bucco-lingual groove. Again, after penetration into the pulp chamber, the distal access wall can be gradually moved back to gain entry to the D canal(s). Be certain to visualize the angle of the mesial surface to allow the correct angle of entry. Mandibular molar accesses are commonly too constricted buccal-to-lingual at the mesial extent. Sometimes it is necessary to cut into MB cusps to gain the access needed to treat the MB canal.

Ergonomic Access Top

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The simplest description of access convenience form is the straightest possible entry angle into each canal, with the line angles of the access cavity smoothly dropping into canal orifices. Accesses which are too small (fig5) cause needless difficulty.

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Overenlargement, however, is to be as feared (fig6) . With the ideal RCT results available today, the greatest obstacle to long-term success is crown and root fracture. Overextended access preparations can easily increase that possibility.

The most elegant access preparations into upper and lower molars combine ideal convenience form with conservation of tooth structure. They have a mesially angled entry, just over the marginal ridge, for more direct entry into distally curving mesial canals. They are fully extended to the MB cusp (both maxillary and mandibular), and their distal walls are taken back barely beyond the mesial-to-distal center of the occlusal table. Although pulp chambers are found in the center of the tooth at the cervical level, access cavity design is at our discretion and the advantages of this path are obvious. When starting these accesses just over the mesial marginal ridge, always confirm the correct access angle, relative to the mesial aspect of cervical structures.

Cutting the Gordian Knot Top

G.V. Black said convenience form is not a luxury. When access preparations are designed and executed ideally, the most difficult cases are manageable. When accesses are sloppy, even simple cases become a struggle. Truly, time and effort spent during access pays dividends throughout the rest of the case.

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Access Refinement Using Ultrasonics Top

As I’ve said before, access is everything in endodontic therapy; it is also the most difficult, dangerous aspect of treatment. The question is, how can we turn the tables in our favor, and regain our sense of professional composure during difficult access procedures, especially in molars?

While there is the fundamental issue of the clinician’s ability (his or her knowledge of coronal and pulp chamber anatomy, hand-eye coordination and clinical judgement), visibility and cutting tool geometry can significantly improve procedural outcomes for dentists at any level of clinical skill. Until recently, it has been difficult to see deeply into molar root structure when hunting for calcified canals. Adding to this ubiquitous challenge is the greater appreciation of the high incidence of MB2 canals present in maxillary molars. Without magnification and ultrasonics, this higher level of clinical outcome is impossible.

Ultrasonic cutting instruments provide unbelievable visual access because there is no handpiece head to look around. This advantage is difficult to overstate. With loops or microscope to magnify the view, ultrasonic cutting tools allow clinicians to see and remove broken instruments in the apical thirds of straight roots. During access of calcified pulp chambers and canals, this improved visual access to the inside of teeth allows clinicians, for the first time in the practice of endodontics, to see the tip of a cutting instrument 12 mm into the center of a tooth. The time-consuming and anxiety-provoking days of cutting, drying and checking deep apical progress with a handpiece bur are gone for clinicians using this new application of ultrasonic technology.

The Buchanan Series Ultrasonics Tips Top

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Of secondary, but critical importance is the actual design of the ultrasonic access tips being used. Poorly designed tips will deliver lesser results, and will require more effort to achieve acceptable results. Ultrasonic tips must be designed specifically to their functional objectives. The clinician’s needs I’ve identified are, cutting, refining and digging (fig7)

The centerpiece of this ultrasonic access set is the BUC-1, tip. This instrument replaces the high-speed handpiece bur that I have used to cut 70% of my access cavities, a surgical length tapered diamond bur with a narrow round tip. The BUC-1 ultrasonic tip replicates that shape exactly, but with the added benefit of complete visibility. With a fine grit diamond coating, the BUC-1 allows for ideal cutting and refinement of access line angles so they drop smoothly into canal orifices without the irregular cutting results of other sharp tipped ultrasonic instruments on the market. This clean extension of the access line angles dropping nicely into each canal orifice allows files and obturation materials to be quickly and easily placed into canals without bringing a mirror into the field. Of critical importance is the refinement of the access line angle creating the convenience form required for safe rotary instrumentation.

Endodontic imperatives in the new millenium require the search for and the treatment of MB2 canals in maxillary molars. Anatomic research reveals that MB2 canals are present upwards of 70% of the time and that they have separate portals of exit more than 35% of the time. Yet the challenges of locating and entering MB2 canals are legendary. It’s hard to find them, then it’s hard to negotiate them. There is only one way to make this a consistently

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accomplished clinical objective. Magnification and ultrasonics.

However, ineffective tip geometries will make location of MB orifices difficult. Because, for example, sharp-ended ultrasonic tips create innumerable clefts and ditches in the pulp chamber floor, many of which have the appearance of a fin or MB2 canal orifice.

The BUC-1 has a diamond coating for gross dentin removal, moving access line angles, cutting a groove in the mesial access wall to drop into MB2 canals, and for quickly and carefully unroofing pulp chambers. As experienced endodontists know, there is great advantage to the creation of a smooth trough when looking for MB2 canals. A smooth trough, viewed with magnification, will show a distinct line extending from the MB1 orifice in a palatal direction to the MB2. Often the MB2 orifice is seen as a distinct white dot which is either negotiable with a #15 K-file or is calcified but thereby located. This gives the clinician an effective and safe road map to follow when cutting more apically to enter patent canal space.

Also needed is a way a to horizontally smooth pulp chamber floors without cutting past the floor. In molars it is necessary to plane through the lighter-colored calcific dentin to get to the darker colored pulp chamber floor dentin. With small tipped ultrasonic instruments ditching occurs which obscures pulp chamber floor anatomy. The BUC-2, with its disk-like radiused tip, smoothly and safely planes attached pulp stones from the pulp chamber floor without scoring it. Then, a BUC-1 can be easily used to follow pulp chamber floor anatomy to the canal orifices.

Occasionally a sharp digging tip is needed, hence the BUC-3, commonly referred to as the Digger. This extremely active tip is excellent for chasing canals halfway up a root or for digging around a post to remove it. The water port just near the tip allows perfect washing and cooling of the operative site. Keeping the tips cool also extends their life, but more importantly, the water wash allows instant view of the operative site after just a quick air blast.

In Summary Top

BUC-1 Fine Grit Cutter (tapered shape) – for cutting and refining line angles, smoothing access walls, cutting MB troughs

BUC-2 Disk Tipped Planer – for planing pulp chamber floors in molars

BUC-3 Sharp Tipped Digger – for aggressive apical cutting into calcified roots and around posts

Part 2: Negotiating Root Canals to Their Termini

A young endodontist approached me at one of my hands-on FastTrack courses and asked, “Isn’t it true that canals are commonly un-negotiable to their end points? Don’t you find that they are often calcified apically like the canal in this cuspid?” And I felt the gut wrench that usually follows that question.

My discomfort at this question comes from the realization that my easiest answer, “No,” is so easily misinterpreted as an arrogant reply. Instead, I asked for his extracted tooth with the straight #10 K-file in it. I moved the file in and out of the canal demonstrating the file’s loose resistance to apical file placement. It was loose, there was no binding of the file in the canal, but it felt like it was hitting a brick wall at the end of the canal.

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I explained that the sensation of “loose resistance to apical file placement” indicated that there was an impediment in the canal, and that in this case the impediment was most likely an abrupt canal curvature, not apical calcification. I bent the tip of the #10 K-file, adjusted the stop on the file to point to the bend, and re-entered the canal. Every time apical resistance was met, the file was withdrawn a millimeter, turned 10°, and watch-wound again. After three attempts, I got a catch, wiggled the file, slipped around the apical hook, and dropped through the terminus on the side of the root apex. Aaaah! The Holy Grail of Endo.

A Good News/Bad News Story Top

In a way, I felt sorry for the guy, because he had just been disabused of the classic excuse for short treatment. The good news was that nearly all canals can be negotiated to their termini, they aren’t calcified in their apical regions. (Reference1) Calcification occurs coronally, where pulps begin their degenerative process.

fig8

fig9

The bad news is that it isn’t necessarily easy to get to the end of root canals. In fact it’s sometimes incredibly difficult. In the first cut, root canals are hidden from direct view and are microscopic in size. “Hidden and microscopic” is literally what makes endodontic therapy different from any other part of dentistry. More difficult yet, root canals accelerate in curvature and exhibit their greatest anatomic complexity as you approach their endpoints (fig8) (fig9) .While root canals are not calcified apically, they are tough to thread files through and they are easily blocked with pulp tissue. Further bad news is that without successfully negotiating to canal termini, the outcome of all treatment to follow is in doubt, regardless of how advanced the instruments and techniques used. (Reference2-5)

There are, however, signposts to follow into this maze. The most important precursor to successful negotiation procedures is the sophistication of the clinician’s endodontic anatomic knowledge, especially the clinician’s anatomic knowledge of the case at hand. You must become a student of endodontic anatomy in your own practices, as you shape, clean, and fill canals in all their complexity. Get to know root canals on an intimate level, and you can learn to sneak through them at will.

The payoff to operating at this level is predictability. Once the primary canal of a root canal system has been negotiated to patency and the pulp has been removed, the expected outcome of the endodontic procedure goes way, way up. At this point much of the artful aspect of procedural endodontics is complete and everything to follow should be straightforward, regardless of which shaping or filling technique is used.

Basic Negotiation Technique and Radiographic Imaging Top

The history of the field of endodontics shows that endodontic procedures are fundamentally plagued by the obscurity of root canal systems. Endodontic therapy, as a respected part of dentistry, only took off in the late 1800’s after Dr. Roentgen invented X-ray imaging. Likewise today, X-ray imaging is absolutely key to understanding the anatomic challenges of any given case and our endodontic treatment results greatly depend on the quality of those images and our interpretive skills in reading them.

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Even though we often cannot see root canal complexities on our pre-op radiographs, we can see apical root outlines and the anatomy of periradicular lesions. Apical root outlines become very revealing when imaged with a file placed to length in the canal. Since Hertwig’s epithelial sheath forms roots from their periphery inward, it stands to reason that canals are to be found centered in the root structure. In the coronal two-thirds of roots, this Law of Centrality (Reference6) reveals the presence of additional canals when an off-angle radiograph is taken (fig10a) (fig10b).

fig10a fig10b

In the apical thirds of roots, file position relative to the outline enables clinicians to discern many apical anatomic irregularities (fig11a) (fig11b) .

fig11a fig11b

Necrotic canals with periradicular lesions are the easiest to map pre-operatively. Periradicular “lesions of endodontic” origin develop in response to infectious pathogens emanating from root canal openings, described as “portals of exit” by Schilder (fig12a) (fig12b) (fig12c) .

fig12a fig12b fig12c

fig13

Ipso loquitor, where you find a lesion of endodontic origin, you should find a portal of exit. The presence of asymmetrical apical lesions is a beautiful tip-off that there is an abrupt apical canal curvature near the end of a relatively straight root (fig13) .

All pre-operative X-ray images should be taken with a holder and cone positioning device, such as the Rinn XCP, which ensures that the X-ray beam is perpendicular to the film or digital sensor, thereby eliminating elongation error. The next variable to consider is the angulation of this imaging set, the film/sensor and X-ray head, relative to the tooth being treated.

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fig14a

A typical imaging error is the foreshortening of roots (fig14a) .

fig14b

Assistants quickly learn that it is better to foreshorten teeth and get the root apices on the image, rather than miss the apices and have to take the film over. We need radiographs that include root apices and periapical bone, but which also represent teeth and their roots in their correct dimensions (fig14b) . This is accomplished by careful placement of the film/sensor holder and with clear instructions to the patient to bite or hold it firmly in place.

X-ray positioning is critical to radiographic visualization during root canal therapy, unfortunately it is probably the most difficult skill to teach to dental assistants. Digital radiography is most helpful here because the sensor and X-ray head can easily stay in position for the 15 seconds it takes to see the image on the computer screen. If the view is not optimal, the X-ray head can be moved precisely from the previous position, allowing the ideal angle within 2-3 attempts. With conventional X-ray film, which must be removed to develop and view, the Dr. and assistant may give up after 2-3 attempts since the 4th attempt is no more likely to be ideal.

Digital X-ray imaging has just about hit it’s inflection point for large-scale adoption into themarketplace due to it’s speed and ease of image capture, storage, and retrieval. Another advantage of digital radiography is that it allows dentists to image process (zoom, change the contrast, brightness, gamma levels, etc.) radiographs to ideally visualize apical structures, for instance, and then be able to change those settings to ideally visualize the osseous crest or the pulp chamber. The final threshold to widespread use of this technology will follow the introduction of electronic dental charts for the simple reason that digital radiography is a primary requirement to go paperless in the clinical environment.

In the not-so-distant future dentists will be able to click off four angles of registered digital X-ray images, reconstruct those images in their chairside workstation, and be able to view a dimensionally accurate 3D model of the tooth to be treated. (Reference7) In the immediate future, expert-knowledge electronic charts and digital radiography will allow for dimensional analysis of the morphology of roots, root canals, and periradicular lesions to aid treatment planning and outcomes tracking in digital detail.

Electronic Apex Locators: Working in the Z Plane Top

Apex locators are indispensable aids in length determination, but they should be a part of initial negotiation procedures for more than just length determination. As I mentioned at the beginning of this article, clinicians must know root canals intimately to successfully find their way through them. Knowing root canals at this level involves putting together every bit of information you can gather to create an accurate mental construct of canals in which you are working.

Traditionally, this has been done by combining radiographic data with tactile feedback from file handles during their movement through the canal space, however, when an electronic apex locator is added to the feedback loop there is a much richer data pool. With an apex locator we can discern the 3rd dimension of root canals in real-time. We can connect our

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tactile feedback to a position in the canal, and more accurately map that region as a result.

While apex locators are really good at some functions, they are dreadfully inadequate at others. Apex locators cannot accurately tell you how far short of the canal terminus you are. They are very, very good at telling you when you are at the terminus or beyond. Again, they cannot tell you how far you are beyond the terminus. Therefore, they should not be used if you fear taking a small file passively through the end of a root canal.

I recommend using an apex locator with each negotiation instrument as this offers many advantages. First, it allows for greater control and less over-extension of initial negotiating files as well as eliminating unnecessary films when files aren’t yet to length. Second, it adds a layer of confidence to the accuracy of apex locator readings when the #08, #10, and #15 files all read to the same or nearly the same length in the canal.

When small files give “squirrelly” readings with an apex locator, simply moving up one or two file sizes provides a more stable indication of the canal terminus. Be aware that apex locators most often err by placing the file long, rather than short. This occurs most often in vital cases where the root apex is embedded in less conductive cortical bone or projects into the maxillary sinus. In both cases, clinicians will usually get one accurate reading of canal length when the first file to length hits the PDL, before getting patent into these less-conductive periapical regions. This is of no endodontic consequence other than requiring the treating dentist to stay alert to catch that single fleeting-but-accurate apex locator reading.

Without an apex locator, lengths in at least 20% of canals will be mis-determined (long) and canals will be over-treated as a result. With an apex locator in the treatment loop, this 80% accuracy goes to 95%. It is my opinion that treating root canals without an apex locator is like flying an airplane without an altimeter, and I wouldn’t do either.

Getting to Length… Once Top

You cannot predictably negotiate canals to their terminal points if blockage is a possibility. Unfortunately, this is extremely common due to inaccurate conceptual models of apical blockage and the erroneous treatment strategies taught to us as a result.

Here’s the experience. You irrigate with NaOCl, just like you were taught, and you watch-wind a #08 K-file to estimated length. You push-pull it until it’s loose in the canal. You irrigate, cut the #10 file to length and work it until it’s loose, you irrigate. Everything is just going great until you put the #15 file in the canal and it hangs up. Hunh. You put the #10 in, the #08 in, the #06 in. Darn, you’re blocked!

This event is only mysterious because apical blockage has been historically mis-described as being caused by the apical collection and compaction of dentin mud. While blockage with dentin mud does occur (especially with push-pull filing) it seldom causes the irreversible blockage that clinicians most fear. The breakthrough came for me in 1983 when I realized that I didn’t fear the necrotic case, only the vital ones. The epiphany was that this unpredictable and irreversible blockage was caused by pulp tissue, not dentinal debris. (Reference4)

In retrospect, it was obvious that when the #08 and #10 files bound in the canal and then loosened up, they were not binding at their tips. The tip diameters of these files, .08 and .10 millimeters, respectively, are smaller than the terminal diameters of most canals (.15mm and larger), allowing them to act as swords cutting through apical pulp tissue. When a pulp

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stump is pierced by small files in the presence of an aqueous irrigant, the cut tissue can subsequently re-adhere to itself and immediately meld into a solid mass of collagen if it is pushed into the apical constricture by the tip of a larger file. This type of blockage usually occurs with the #15 file in a Small-Root canal because it is the first file that approximates the terminal diameter of the canal, causing it to act as a piston rather than a sword.

For all the hell that this common problem has caused, the resolution is remarkably simple. Never negotiate a root canal without a lubricant in the pulp chamber. Not only does this work; it works 100% of the time. (Reference4) As each file passes through the access cavity it is coated with lubricant. When small files coated with a lubricant pierce apical pulp tissue, the cuts are coated as well, preventing re-adherence of this tissue if compacted. In effect, this tissue becomes emulsified.

Any lubricant, including Glide, RC Prep, Endo-Eze or KY Jelly, may be used effectively, although my favorite is Pro-Lube by Tulsa Dentsply because of it’s single-use packaging.

Patency Top

I find it hard to believe, but the myth of failure caused by small files passively slipping through the apical foramina of root canals, is still with us. Despite decades of wanking about the horrors of patency instruments taken long, the Scandinavian School of Endodontics has yet to show a single study proving this point, and in fact, all clinical experience proves just the opposite. Without patency file use, consistent apical control is impossible. Without patency confirmation, you will be long, short, ripped, blocked, or ledged; everything but in control of the case.

Furthermore, these academics claim that root canals should be treated a certain distance from the end of the root canal, but it is impossible to treat to any specific distance from the root canal terminus unless you have been there at least once. Also ironic is the belief that vital pulp tissue left at the ends of root canals is healthy and will remain healthy. Nowhere, in any other part of healthcare is it recommended that pathologic tissue be excised shy of a healthy margin, yet that is what we have been told to do in endodontics. As an aside, Torabinijad and others showed that there was no difference in post-operative pain between cases treated with all files held within the canal and those where small files were taken long. (Reference8)

A very common approach when you first accept the need for patency is to timidly go through the terminus 1/4 to 1/2mm. And you will still block yourself out by packing pulp tissue against the lamina dura instead of against the apical constricture. Being kind of patent is like being kind of pregnant. Until you are willing to take the #08, #10, and #15 files a full millimeter long, you will struggle. When you accomplish definitive patency by taking these files at least 1mm long, instrumentation becomes a predictable event and conefit takes less than 30 seconds.

File Selection Top

Negotiation instruments are typically thought of as sizes #15 and smaller. In standard ISO sizes this would be file #’s 06, 08, 10, and 15. While the flexibility of nickel titanium makes it the ideal metal for shaping files, the stiffness of stainless steel files makes them the ideal instruments for the negotiation of canals. Beware of using stainless steel files with lathe-cut flutes for negotiating procedures, they aren’t as stiff as twisted flute instruments.

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I know of three manufacturers who make twisted stainless steel files: VDW (Verienigte Dental Werke) from Germany, Maillefer from Switzerland, and Kerr from the US. VDW sells files through the dental supply companies Schwed, Chige, Royco, and Premier under the brand names Anteos, Beutlerock and Zipperer, Maillefer sells through Dentsply, and Kerr sells as Kerr. I prefer VDW’s negotiating files, as they are the stiffest on the market.

I begin negotiating Small-Root canals, specifically canals in mandibular incisors, multi-canalled premolars, buccal roots of maxillary molars, and mesial roots of mandibular molars, with a #08 K-file. I start with a #10 K-file in Large-Root canals, which include mandibular cuspids, maxillary anteriors, single-canalled premolars, palatal roots of maxillary molars, and distal roots of mandibular molars. Obviously, if my initial negotiating file hangs up prematurely, the next smaller file can be brought in.

File Motions Top

Buying a Skilsaw does not make you a carpenter, just as buying the right file does not insure that you will get to length. It can make a huge difference in results when even a subtle technical nuance is not respected during a procedure. As I’ve often said, I would rather have root canal therapy done on my tooth by an experienced, skilled clinician using the most mundane instruments than by an inexperienced dentist using the hottest innovations in endodontics.

The primary file motions used during negotiation procedures are watch-winding and push-pull. During watch-winding, the reciprocating 90° back and forth rotational motion alternately pulls the file into the canal (clockwise), and then (counter-clockwise) cuts the engaged dentin - in-cut, in-cut, in- cut. Those with quartz watches may have difficulty with this concept, but it is simple and almost magical, as it literally sucks small instruments into canals when done correctly. At a certain point, watch-winding will not advance the file further into the canal. In many cases, 3-5 push-pull filing strokes will loosen the file and allow watch-winding to advance the file further apically.

The terminal diameter of root canals is usually .15mm or larger, therefore the #08 and #10 files are seldom binding at their tips. Using a #15, #20, and #25 (with big step-back increments) cuts a coronal shape large enough to release the shank portions of the #08 and #10 files from binding, allowing their tips to slip passively to and through the apical foramen. Recapitulation is the most powerful strategy when negotiation or shaping files stall out short of intended length. When small files bind at their tips, watch-winding will no longer advance these instruments because the file tips hang tight in the canal while the shank flutes flex and unflex.

At this point the Balanced Force file motion using a triangular-bladed file is the most effective way to cut dentin. (Reference9) In this technique the file is threaded into the canal with a light clockwise rotation, apical pressure is applied to the file and it is counter-rotated at least 360°. By turning the file beyond the 90° of watch-winding, the tip is moved and cuts, allowing rapid apical advancement upon rethreading the file clockwise again, to set up for the CCW cut stroke to follow. In, push, and cut; in, push, and cut; etc. This file motion will rapidly create space with the #20 and #25 files, effectively removing any cervical canal constrictions.

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Serial Step-Back Negotiation Top

As great as Crown-Down instrumentatiion is for the shaping of root canals (especially with rotary files), it is a bit scary as a negotiation procedure. If the #15 file is taken just 2mm too deep early in the procedure, blockage can occur in a heartbeat. Craig Baumgartner, Department Chair of Endodontics at OHSU (where the Crown-Down concept was developed), saw a high frequency of apical blockage created by students using Crown-Down negotiation procedures. He then saw resolution of that problem when students were redirected to accomplish the negotiation phase of treatment with a Serial Step-Back technique.

Another common error made during negotiation procedures is to over-use each file in the series. A #08 file will not make shape half as fast as quickly using file #’s 10, 15, and 20 to cut more coronal shape, stepping back in big increments. The #08 file, which was balking at further apical advancement, usually then drops passively to length because it no longer is binding on it’s shank-end flutes. This is much preferred to endless push-pull filing with the #08.

The #08 and #10 files are each taken to the terminus using an apex locator, and then the stop is adjusted to the reference point. These files are taken at least one millimeter long to insure patency. When a #15 file or larger has been cut to the terminus as indicated, a length confirmation x-ray is taken. Canals with large apical diameters may evoke an unsteady, ambivalent apex locator reading with relatively small files. Simply going up in file size invariably delivers a more stable and accurate reading.

If a “Rubber Band” sensation is felt in the canal after negotiating and measuring it, pulp tissue remains in the canal and must be broached. While most Small-Root canals have been effectively broached by the time a #15 file has been taken to length, a bent #25 broach will often be necessary to The #08 and #10 files are each taken to the terminus using an apex locator, and then the stop is adjusted to the reference point. These files are taken at least one millimeter long to insure patency. When a #15 file or larger has been cut to the terminus as indicated, a length confirmation x-ray is taken. Canals with large apical diameters may evoke an unsteady, ambivalent apex locator reading with relatively small files. Simply going up in file size invariably delivers a more stable and accurate reading.

After initial negotiation and length determination procedures are completed, the air/water syringe is used to remove the lubricant from the access cavity prior to irrigation with sodium hypochlorite and the start of shaping procedures.

Strategies for Negotiation of Calcified Canals Top

I believe that we are obligated to attempt a conventional approach to obviously-calcified root canal systems because: a) nine times out of ten the canal can be found with a microscope and, b) because clinical success is higher when canals are treated throughout their length rather than just at their root ends. When a #15 or #20 cannot be picked into a canal orifice, a handpiece bur or ultrasonic tip must be used with magnification to drill into the root structure in an attempt to intersect a less obstructed region of the canal.

As mentioned before, calcification is a degenerative process that starts near the site of injury, the pulp chamber, and progresses apically. Therefore, there is always an apical point in any calcified canal that is not obstructed, if you can just get to that level in the root. Obviously, the deeper dentists drill into the tooth, the greater chance they will perforate a root. Radiographs should be shot from two angles after every 1-2mm advance in access

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depth. There is a conceptual truism when accessing calcified teeth that says as long as you are on track as you drill apically, you will tend to stay on track, but as soon as you get off-track, it becomes exponentially harder to get back on track. Dentists must decide when the risk- to-benefit ratio goes upside down, and abort further drilling. It is far easier to place an apical retroseal at the end of an un-negotiated canal than it is to repair a cervical or furcational perforation. Generalists should strongly consider referral at this point.

Stiff negotiation instruments are imperative in constricted canals, as clinicians must literally grind open the orifices of even slightly calcified canals. Initially attempt to enter these small canals with a 21mm stainless steel #15 K-file. Narrower files lack the stiffness required to probe for calcified orifices. Bouncing the tip of a new #08 file off a pulp chamber floor is a sure waste of a good instrument when it buckles. Simply entering an orifice once with a 21mm #15 K-file, followed by just a few push-pull strokes, opens it enough to then easily enter it with a #06 or #08 K-file and negotiate closer to the canal terminus. Be certain to stay out of the apical half of the canal during initial use of the #l5, as blockage could result.

Once a file can be threaded into the barest hint of a canal, the game changes. Picking a negotiation instrument into a “stick,” or a point of tight resistance to withdrawal, is the Holy Grail of obstructed canals. This is about the only useful time to use 1/4 turn-pull file motion, as you must literally pick your way through this wood-like connective tissue to get the first file to length. Once a “stick” is caught and further picking into the canal is unproductive, clinicians should step down or up in file size and continuing picking.

Fibrous pulp stumps inadvertently packed into apical constrictures is not the same as apical calcification, neither in factual description nor in their ability to seal root canals. As pulp stumps are made of organic tissue, they are unpredictable as apical sealants. They may be infected or become infected; they are prone to necrosis, creating a substrate for bacteria -the most potent periradicular pathogen.

When picking files into calcified canals, they are used in a crown-down series, then a step-back series, followed by crown-down, etc. The #15, #10,# 08, and #06 files each pick deeper, then the #08, #10, and #15 pick to this new length, and so on to length. Clinicians working in an obstructed molar can easily go through two to four six-packs of negotiation instruments before reaching the terminus.

Unfortunately, there are no silver bullet answers to the challenges of calcified canal negotiation. They are, without a doubt, the most difficult of all endodontic cases. They always present a fine line of opportunity between being a hero or the goat. These techniques must be used in each calcified canal coupled with good judgment, strong intention, and persistence.

I don’t know an endodontist in practice who wouldn’t love to refer these cases if they could. Generalists who tackle calcified root canal systems should examine their decisions from a totally self-interested standpoint. Of all the work they can do in their practices, surely these are the most difficult and the least remunerative to treat. These tough cases can take 3-4 times the clinical effort and must be charged accordingly.

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Strategies for Negotiation of Tortuous Canals Top

fig15

Not only do canals become more complex in their apical thirds relative to the incidence of lateral and accessory canals; they also become more complex in this region in terms of their curvature. It is commonplace to see the rate of canal curvature accelerate as the terminus is approached. These apical curvatures may move in radiographically hidden directions and they are often multi-planar, curving in several different directions (fig15) .

Occasionally these apical curvatures are so severe that they can only be fully negotiated after coronal shaping is completed. Certainly, the key to negotiating irregular canal paths lies in accurate mental imaging, file bending, and a lot of patience. But file bending is more difficult than most clinicians realize.

Bending files in a cotton roll or between gloved fingers won’t impart the file curvature necessary to sneak a #08 around a 110° apical hook. Bends that are imparted short of the file tip result in a file that is “functionally straight.” The part of the file that is relatively straight, the tip, will encounter the curved part of the canal. The part of the file that is bent will usually be traversing the straighter part of the canal.

fig16

Files bent to negotiate severely curved canals must be smoothly bent, not kinked, and they must be bent to the last flute. K-file sizes #06-10 are so flexible that the only part of those instruments that needs to be bent is the last 1mm. If only the last few flutes are bent to allow the file tip to sneak around abrupt canal curvatures, the rest of the file will easily flex and follow it’s tip around that curve. A helpful device to use when imparting smooth but severe file bends is the Endobender plier (fig16).

It is also important to use teardrop stops on files, with the point of the stop directed toward the file bend. Then, as the file moves through hidden canal curvatures, the canal path can be accurately mapped by watching the point of the stop, rather than having to hunt around each time a new file is introduced.

fig17

A canal curvature that is seldom considered is common to MB2 canals, severe cervical curvature as the canal enters the pulp chamber (fig17) . This can be frustrating to untrained clinicians, as the canal orifice can be seen and probed with a DG16 explorer. However, when a #15 file is placed in the orifice, loose resistance to apical file placement is immediately felt a millimeter or two into the canal. The strategy here is easy. Simply bend a #15 file at it’s tip, just as you would for an abrupt apical canal curvature, place the file in the orifice with the bend to the mesial, flip it around and watch-wind it beyond the impediment.

A tip for wild canals: if you have to battle to get a file to length through a tortuous canalform, be certain to take the file 2-3mm’s long and work it with 20 or 30 push-pull strokes before taking it out of the canal. Premature removal may preclude never getting back to length again. In cervically-bent MB2 canals, just 4-5 push-pull strokes with a #15 file will rip the orifice path straight, making it easier to re-enter without file bending.

Finally, if you are doing surgery on more than 0.5% of your own virgin cases, you have not

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yet hit your potential in negotiating root canal systems to their termini. This can be difficult so we must take all possible advantage. We must demand ideal pre-operative radiographs and study them carefully for anatomic anomalies. We must discipline ourselves to only negotiate canals in the presence of a lubricating solution to avoid blockage. We must use the best quality of twisted-flute stainless steel negotiation instruments available. They must be brand new, and we must be willing to go through 10 or 15 negotiation files to get to length.

Most important, we must be persistent and get to the terminus or inform our patients that the case has a guarded prognosis. This is what our patients are paying us for…to do the hard thing when it’s in their best interest (fig18a) (fig18b). If you can’t get paid enough to spend the time, don’t do the crime. Refer.

fig18a fig18b

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References: Top

1. Blayney, JR: Tissue reaction in the apical region to known types of treatment, Dental Cosmos, 221-242, 1930.

2. Andreason, JO, Rud, J: Modes of healing histologically after endodontic surgery in 70 cases, Int. J. oral Surg. 1:148-160, 1972.

3. Schilder, H.: Cleaning and shaping the root canal, Dent. Clin. North Amer. 18:269, 1974.

4. Buchanan, L.S.: Chapter 7: Cleaning and shaping the root canal system, Pathways of the Pulp, 5th ed., 1991, Mosby-Yearbook, St. Louis.

5. Sjogren,U, Figdor,D, Persson,S, Sundquist,G: Influence of infection at the time of root filling on the outcome of endodontic treatment fo teeth with apical periodontitis, Int. Endo. J., 30:297-306, 1997.

6. Krasner, P.: Clinical Concepts of Endodontics, Lecture, Temple University, 1979.

7. Hatcher,D. Craniofacial imaging: Historical perspective, current status, and future development, The Angle Orthodontist, 69:6, 491-505, 1999.

8. Torebinejad, M., Kettering, J.B., McGraw, J.C., Cummings, R.R., Dwyer, T.G., Tobias, T.S.: Factors associated with endodontic interappointment emergencies of teeth with necrotic pulps, J. Endod., 14(5): 261-266, May, 1988

9. Roane, J.B., Sabala, C.L., and Duncanson, M.G. Jr.: The “Balanced Force” concept for instrumentation of curved canals, J. Endod. 11:203, 1985.