INTRODUCTION
Unfortunately, every endodontic case that comes into a general dentist’s office is not always treatable. In some instances, the patient may present with challenges that are too serious to manage in the general practice office. The patient may have psychological or behavioral problems that are beyond the scope or ability of the dentist to overcome. In other instances, the tooth itself may present with treatment challenges that are too difficult and complex to treat. The tooth may be fractured, decayed, or perforated beyond the dentist’s ability to restore it. The tooth may also be of an anatomic variety that does not lend itself to routine endodontic treatment. This article will discuss this last group of teeth. The anatomic variations of these teeth make them very difficult and time consuming to treat. The dentist must decide, on a monetary and quality-outcome basis, if it is worthwhile to treat this patient. In other words, if the clinician decides to go ahead with the treatment, will money actually be made or lost on the quoted fee and, secondly, does the dentist have the necessary knowledge and skillset to complete the case successfully? Naturally, the trick is that one needs to know what the treatment involves, and what possible challenges might lie ahead, before beginning the work. This will enable the clinician to make the critical decision of whether to treat or to refer before investing a substantial amount of time into the treatment only to discover it is to no avail.
The MB2 Canal
One of the first anatomic variants that causes problems in endodontics is the MB2 canal. The existence of this canal first made an appearance in the literature during the late 1980s. It is found in maxillary first and second molars and sometimes in the maxillary third molar. In a literature review containing the most data on mesiobuccal (MB) root canal morphology (a total of 8,399 teeth from 34 studies), the incidence of MB roots having 2 canals was 56.8%, and those with one canal was 43.1%, in a weighted average of all reported studies.1 The Textbook of Endodontology2 states that, in the maxillary first molar, there are 2 MB canals 60% of the time, with 80% having one foramen and 20% having 2 foramina. If you draw a line between the MB and palatal canals, the MB2 will usually be found just mesial of that line somewhere near the MB canal (Figure 1). The canals are usually in the “A,” “B,” or “C” position. In the A position, the MB2 canal usually merges with the MB and there is only one foramen; in the B position, there often are 2 separate and distinct foramina; and, in the C position, there can be a separate, small root located between the MB root and the palatal root. The difficulty here (Figure 2) is in finding the MB2 canal and then instrumenting it. The problem, in both circumstances, is that it is very easy to leave a ledge of dentin on the mesial axial wall that will cover the MB2’s orifice (Figure 3).
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| Figure 1. An illustration showing the possible locations of the MB2 canal. | Figure 2. The canal in the “A” position merges with the MB canal. The canal in the “B” position has a separate apical terminus. The canal in the “C” position has a separate, small root. |
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| Figure 3. The arrow points to the dentin overhang. The MB2 is underneath the overhang. (Published with permission by the Academy of General Dentistry. Copyright 2009 by the Academy of General Dentistry. All rights reserved.) | Figure 4. An illustration showing the steps to create straight line access by removing the dentinal overhang. |
The orifice to the MB2 is located under the ledge. If the ledge is in place, it makes finding the MB2 difficult. If the orifice is found and the ledge is still in place, then the endodontic instruments must bend around the ledge in order to get into the canal. This is not straight-line access, and it puts an extra burden of stress on the instruments (Figure 4). Not only does it add stress to the instruments, but the dentist will be instrumenting this ledge as well. This is more dentin to cut, and the dentist will notice that, as larger size instruments are used, it will take more torque to prepare the extra length of canal that now exists by leaving the ledge in place. Therefore, it will seem harder to get down the canal to the working length. The author uses SafeSiders (Essential Dental Systems) reamers to gain access to the MB2 and all other canals because they can easily handle this extra stress when instrumenting the canals if some of this ledge is inadvertently left intact. However, it is much better to remove the ledge to more easily find and instrument the canal. If you are finding 50% or more of the MB2 canals in maxillary molars, go ahead and keep treating them. If you are not finding at least that many, perhaps you should consider referring these molars out.
The C-Shaped Canal Configuration
The next anatomical variation to be considered is the c-shaped canal configuration. It is most often found in the mandibular second molars (teeth Nos. 18 and 31). On a radiograph, the root is seen as a conical root form with no furcation (Figures 5 and 6). The MB, mesiolingual (ML), and distal canals can be connected with a sheath of pulp tissue from the chamber down to the apex. Some canals may connect to one another, and some may not; the configuration varies from tooth to tooth. It is difficult to instrument these connected webs of tissue and even more difficult to obturate them. Figure 7 shows a typical c-shaped canal system initially and after gutta-percha and sealer obturation. Since these teeth can be identified on a radiograph by their conical root shape, we can make the decision to treat or refer before we commit to investing a lot of time and energy in the case (Figure 8).
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| Figure 5. A typical single root morphology on a radiograph for a c-shaped canal. |
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| Figure 6. A radiograph showing c-shaped canals (conical root shape). |
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| Figure 7. (Left) The initial access of a second molar, showing elongated canals. (Right) Gutta-percha in canals, demonstrating a C shape. |
Radix Entomolaris
Another anatomical variety that we encounter is the mandibular 3-rooted first molar, which has recently been named Radix Entomolaris (RE). This extra root and corresponding canal are found on the distal lingual aspect of mandibular first molars. It is found in varying percentages for different populations. The RE is found most often in Southeast Asians, particularly in the Taiwanese (Figure 9).3 The root and canal are difficult to visualize on the preoperative radiograph since their visibility depends on the angle of the x-ray (Figures 10 and 11). In the buccal view of Figure 10, you will not be able to see the RE because it is hidden behind the distal root. In most cases, the canal must be found clinically. If the location of the distal canal is skewed to the buccal, then the RE canal orifice will be skewed toward the lingual (Figure 11). In Figure 12, we cannot see the RE root on the preoperative radiograph; however, the RE root becomes apparent once the gutta-percha is in place. In Figure 13, which shows the root canal filling in place, the RE root is obvious in the postoperative radiograph. The question now becomes, “Would you feel confident in finding the RE canal clinically?” (The more you do, the easier it becomes!) If you see it on the pre-op radiograph, you know it is there. Then, if you are confident, do it; if not, then refer to the endodontist.
Anatomic Variance in Bicuspids
The last anatomic variation we will discuss occurs in the bicuspids. Premolars are variable and can present with many variations. The first bicuspid can often have 2 canals that merge into one, and the second premolar frequently has 2 canals instead of one (Figures 14 and 15). First and second premolars often develop as if they were “mini molars.” This means they have 3 canals, just like a maxillary molar (Figures 16 and 17). On the pre-op radiograph, if something doesn’t look “just right,” it may mean that there are 3 roots (Figure 18). The buccal canals are usually found close together on the buccal aspect of the root (Figure 19).4 In a patient case done by a friend of mine, Dr. Adham A. Azim, one can see how closely the 2 buccal canals are located to one another (Figure 20).
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| Figure 8. A radiograph showing the anatomy of a c-shaped canal and conical root. | Figure 9. Bains et al showed that the occurrence of a separate Radix Entomolaris (RE) in the first mandibular molar is associated with certain ethnic groups and as follows: (1) Africans: 3%; (2) Eurasians/Indians: < 5%; (3) East Asians, Southeast Asians, and people of the Arctic region of North America: 5% to 30%; (4) Caucasians: 4.2%; and (5) Taiwanese: 21% (normal anatomy). |
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| Figure 10. The buccal-view radiograph will often not show the RE because of angulation. | Figure 11. The arrow on the left is the RE canal (skewed to the lingual); the arrow on the right is the RE root. |
Another anatomic variant occurs mainly in mandibular bicuspids and can be one of the most difficult teeth in the mouth to treat endodontically. The good news is that the astute clinician can spot this anatomic variant on the radiograph. When looking at the radiograph, one sees a large chamber and/or canal. As this radiolucent space proceeds apically, it will suddenly disappear or get drastically reduced in size (Figures 21 and 22). Figure 23 demonstrates what is actually happening from an anatomic perspective. If the root is rotated 90°, one can see that the reason the pulp chamber/canal disappears or gets drastically reduced in size is because it is bifurcating into 2 canals (and sometimes roots) at this level. The level in the root of the bifurcation of the canal determines how difficult it is to treat that root canal system. The closer to the apex the root splits, the more difficult it is to treat that particular tooth. If the bifurcation split is in the apical half of the root, it is the author’s opinion that it is best to refer the case to the specialist.
Figure 24 shows one such case; here one can see it is a trifurcated, 3-canaled root. The arrow on the radiograph on the left shows the level of the splitting of the canals. This is an extremely difficult case to treat (as is shown by the result), even for an endodontist. Each canal must be found and instrumented separately, and, in this case, the apical roots are also very curved. Once all canals are instrumented, they must be filled separately. Gutta-percha is used to fill one canal first, then it is seared off at the level of the split so that the next canal can be obturated, and so forth. One must realize that this is no easy task! Teeth with this type of anatomy often have apicoectomies or are extracted and restored with implants in order to realize a good long-term treatment result. The author’s suggestion for the GP is to send these to the endodontist for treatment.
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| Figure 12. The RE root on the preoperative radiograph can’t be seen. The RE root and canal on the postoperative radiograph can be seen. | Figure 13. A long RE root is visible on the post-op radiograph. |
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| Figure 14. Two canals merge into one in this radiograph of a maxillary first premolar. | Figure 15. A radiograph of a maxillary second bicuspid showing 2 separate canals. |
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| Figure 16. A radiograph showing a 3-rooted maxillary first bicuspid. | Figure 17. A radiograph showing 3 canals in a premolar. |
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| Figure 18. Midway up the root, there is a bulge in its appearance. | Figure 19. This illustration shows the anatomy of a 3-rooted bicuspid. |
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| Figure 20. These images show how closely together the 2 buccal canals are located. (Image courtesy of Dr. Adham A. Azim, Buffalo.) | Figure 21. On the tooth on the left, the canal disappears about one third of the way down the root. |
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| Figure 22. In both of these bicuspids, the canals disappear or get narrow about one fourth of the way down the root. | Figure 23. An illustration showing the bifurcation (splitting) of canals. Upon evaluation of the radiograph, the canal narrows or disappears at the point of bifurcation (A-A). |
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| Figure 24. An exceedingly difficult or impossible tooth to treat. | Figure 25. The canal splits high up on the root; this case would be much easier to treat and to get an acceptable result. |
Figure 25 demonstrates a simpler bifurcated bicuspid. Here the split from one canal to 2 canals occurs in the top coronal one third of the canal (arrow on left). Both canals are easily found, instrumented, and obturated. This could all be determined from the position of the splitting of the canals on the pre-op radiograph. In summary, if the canal splits in the top one-third to one-fourth of the canal, treat it; and, if it splits anywhere in the apical half of the root, refer it out.
CLOSING COMMENTS
First, philosophically speaking, I believe that we should render the best treatment possible to our patients in order to achieve the highest procedural success rates for their conditions. Second, we also need to make a profit on the procedure in order to remain in business. If only one or neither of these objectives can be met, then it is time to refer the treatment to a specialist. Luckily, with the anatomic variants that have been discussed herein, this determination can often be made by carefully reviewing and evaluating the pre-op radiograph before we have invested a lot of time and energy in the case. Therefore, after the diagnosis is made, and before you lift up the handpiece, take at least a minute or 2 to look carefully at the radiograph. The investment of this small amount of time will help you determine whether you should treat this tooth or if it might be best to refer the case out to an endodontist.
References
- Cleghorn BM, Christie WH, Dong CC. Root and root canal morphology of the human permanent maxillary first molar: a literature review. J Endod. 2006;32:813-821.
- Bergenholtz G, Hørsted-Bindslev P, Reit C, eds. Textbook of Endodontology. Oxford, England: Blackwell Publishing; 2003:240.
- Bains R, Loomba K, Chandra A, et al. The radix entomolaris: a case report. ENDO (Lond Engl). 2009;3:121-125.
- Woodmansey KF. Endodontic treatment of a three-rooted maxillary first premolar: a case report. Gen Dent. 2006;54:420-424.
Dr. Deutsch co-operates an endodontic practice in New York City. He holds 18 patents for co-inventing endodontic products for Essential Dental Systems. He is one of the leading authorities in endodontics, having lectured at more than 150 worldwide locations, and has co-authored more than 200 dental articles. He can be reached at (800) 223-5394, via email at info@essentialseminars.org, or via the website essentialseminars.org.
Disclosure: Dr. Deutsch is vice president of Essential Dental Systems.
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