Patients are keeping their teeth longer. As life expectancies increase, more and more patients are asking us to try to help them retain heavily worn and heavily restored teeth. This often involves Class V restorations on the labial or lingual (due to recession, root caries or abrasion) or replacement of restorations that may have already had two or more major restorations during the patient's lifetime. Unfortunately, financial constraints can sometimes force us to place restorations along crown margins or to patch restorations rather than replacing them completely. All these factors add up to possible exposures, greater deposition of secondary dentin and reduction in the space of the chambers and canals. These cases can often be very challenging when they involve endodontic treatment. Before attempting to treat such teeth, it is important to recognize certain fundamental concepts that play a role in successful treatment.
Rule #1 - A Vital Pulp Test Means Vital Tissue in the Canals. Pulp tests should be routinely be performed.
A vital pulp test means that the coronal pulp is responsive. With extremely rare exceptions, a vital pulp chamber means vital tissue in all the canals, all the way to the foramen. This also means that because vascularity is present in all canals, they SHOULD be able to be negotiated to the terminus. In other words, THERE IS NO SUCH THING AS A "CALCIFIED" APEX IN A VITAL CASE. Clinicians who insist that the reason that they were unable to negotiate to working length because the canal was "calcified" at the midroot or apex are misguided. Yes, deposition of secondary dentin can certainly restrict the diameter of such canals and you can easily become ledged or blocked out. However, blaming these procedural errors on "calcified canals" is simply wrong.
Rule #2 -Use Radiographs to Determine the Difficulty of the Case Before You Start
Well angulated periapical and bite wing radiographs are important. Not only do they indicate whether roots and canals are radiographically present (or absent), they give you important information as to the RELATIVE position of canal orifices in calcified cases. In molar teeth this is crucial in preventing furca perforations during access and exploration of calcified chambers. Of particular importance are the relationship of the crown axis to the axis of the root and the proximity of proximal restorations to canals. Failure to recognize changes in the axis of the tooth that occur during crown restoration can easily lead to access perforation. Proximal restorations can be used as guides to locate canals e.g./ a deep distal proximal box of a mandibular molar often is quite close to one of the distal pulp horns. Unfortunately, due to the geometry of radiography, films are of little assistance in determining small changes in the bucco-lingual position of orifices and canals. CL V amalgam restorations can also render films almost useless for locating a canal orifice.
Rule #3 -Carefully consider the consequences of anesthetizing the case
Although it may seem unusual, NOT anesthetizing patients does have distinct advantages. It should only be used in those cases where canals are virtually invisible on a film or difficult to discern. The keys to use of this technique are to explain to the patient what you are trying to do and to work quickly and efficiently. Patients should be told to indicate when they feel a sharp sensation during access with a bur. At that point a sharp DG 16 Endo explorer should be used to locate the canal. Patients need to be reassured that once you confirm that you in the canal (and not in a perf!) anesthesia will be immediately provided. It is easy to tell the difference between PDL and pulp with a small (.06 or .08) file. If it is inserted only a mm or two into the pulp, the reaction will be sharp. If it is in the PDL, the reaction is often less sharp. If a perforation is suspected, an apex locator is then used to confirm the presence of a perforation since it will immediately read "long" if this is the case. Occasionally, application of topical anesthetic on a file can also be used to make this initial canal probing more comfortable. I find that once the entrance to the orifice can be reamed out with a #20 or 25 reamer, it is easy to use a fast intrapulpal injection to provide profound anesthesia. Many elderly patients do not seem to react or have minimal discomfort to this injection technique. It is important to remember NOT to do this is necrotic teeth because this can force bacteria and canal contents into the periapex.
Rule #4 -Use magnification - Loupes at a minimum
You cannot treat what you cannot see. Although experienced clinicians will instinctively know when a canal "should be there" (They factor in radiographic appearance, clinical appearance, crown shape, root thickness, "centering" of a canal in a film vs. "off center 2nd canal") it all comes down to being able to see the orifice and negotiating a file to the terminus. Magnification is essential. Dental Operating Microscopes (DOMs) have become a routine part of endodontics but costs are still very high and most general dentists will not be willing to spend $25-30 K per room to have one installed. Still, it is important to understand that the unaided naked eye is not sufficiently acute to see the fine structures that must be recognized in order to treat cases like these. Companies like Orascoptic and Designs for Vision offer finely made Loupes that enhance vision. These can cost from $1500- 2000 CDN but are absolutely essential. If you are not using Loupes (at the bare minimum) then you are NOT seeing what you need to see.
Rule #5 -Avoid buring out the access and losing any landmarks.
They are your Roadmap!One of the most frequent mistakes occurs when clinicians remove large amounts of dentin in the hope of finding a canal orifice. Having had no luck, the case is then referred. By that time all pulp floor landmarks have disappeared and the strength and dentinal thickness have been compromised. Risk of perforation now becomes a real problem. By first unroofing the chamber and then examining the access for the pulpal floor grooves, it is most often possible to tell where the canal orifices "should be". At that point a fresh, sharp, DG16 Endo explorer should be used to examine for a "sticking point", that offers resistance to removal. Small (#4 and 2 round) burs are then used to create a "Glidepath" to the orifice. This will further ease the instrument into the proper lane to allow effortless introduction of files into the canal.
Rule #6-Sometimes you MUST remove the restoration in its entirety
Occasionally, you will run into a tooth where castings or restorations make access or visibility impossible. This frequently occurs with long crowns and in teeth that have deeply restored cervical abrasion. There is no advantage to be gained by preserving the restoration when it can contribute to eventual perforation of the tooth. As much as I'd like to preserve the existing restoration, endodontic failure and a symptomatic tooth mean that extraction will be necessary. The restoration will have little value at that point. Attempting to work "through" or around these confining structures will only serve limit visibility, deflect files and make the working length "longer" than necessary. Shorter files are much easier to control than long files, therefore, at times it is necessary to remove castings or restorations, or even reduce the crown, to allow you better access and visibility.
Rule #7-Consider Closing the case and Working on it at the Next appointment
Sometimes even with the most careful examination, you still can't find the orifice. This may be because it is covered by a restoration, because of secondary dentin or simply because you have lost the ability to concentrate on the access. (THIS HAPPENS TO ALL OF US!!) I refer to that phenomenon as "Needing a Fresh Pair of Eyes". It is similar to the concept of "Can't see the forest for the trees". At that point, it is easy to become disoriented. As frustration mounts you begin to consider removing dentin in areas far removed from where you think the orifice may be. STOP! Close the case and reappoint. Many times, you will find that by getting a "Fresh pair of eyes", you will find that elusive orifice within a few minutes of accessing the case in the subsequent appointment. It was there all the time, but you could not "see" it because of this phenomenon. Try it. You'll be amazed at what you now see with a new perspective at the next appointment.
Rule #8-Know when to quit and consider a surgical alternative
There reaches a point at which continuing to search for the orifice or canal will result in imminent perforation or serious weakening of the root dentin. Frequent radiographs should be taken to know exactly "where you are" with respect to furcations and the root face. (Take the dam/clamp off if necessary!!) If you see that your access is not traveling in the right direction and the root is narrow, resist the urge to hollow out the rest of the root. At that point it is time to consider a referral or a surgical alternative if pathology is present. If pathology is not present, the canal space should be filled as is. No further attempts at treatment should be made but the patient told about the possibility of requiring further treatment in the future. Know your limits. Don't risk losing a tooth just to be able to say you found and filled the canal(s).