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By Barry Musikant, DMD
Conceptually the answer is very easy. We retreat a tooth when we believe such retreatment will lead to the successful function of the tooth for a long period of time. In reality the answer is far more difficult. Some of the questions that must be answered in the positive to do retreatments include the following:

1. Can retreatment lead to a better result? Were canals missed or instrumented short?
2. Is there new excessive decay that precludes a strong restoration?
3. Is adequate bone present to support the tooth?
4. Are there discernible fractures in the body of the tooth and if so how deep do they go?
5. Does a CBCT show any hidden bone loss not seen on periapical x-rays?
6. Are there any areas of root resorption that is occurring independent of a failing root canal?
7. Is the patient a clencher or grinder?
8. Does the patient have reasonably conscientious maintaining oral cleanliness?
9. Does the patient provide enough access for effective retreatment?
10. What is the overall health of the patient?

These are some of the questions that come to mind when retreatment is a consideration. Take question No. 1. If canals are missed and that led to periapical breakdown, say by not finding an mb2, that is the most likely candidate for retreatment. Find the canal, clean it out, perhaps redo the mb canal that is in close proximity and the problem should resolve. If canals are short that too may be a fairly easy problem to rectify. However, the canals may have been blocked by the first treatment that might present challenges when retreating. Nevertheless, these types of cases are routinely retreated providing the tooth has enough bone support and is structurally intact.

When cases present with a good deal of decay, it is highly likely that the previously done root canal is now contaminated. Retreatment under these circumstances would be based on the amount of tooth structure remaining after all the decay is removed. One should be able to imagine a minimum of two mms of tooth structure that can support a circumferential ferrule in the restoration even if the removal of surrounding gingiva is needed. If this goal cannot be attained, it is questionable whether the remaining tooth structure can support a new crown for any length of time. Again, we must consider the periodontal support and the overall integrity of the remaining tooth structure.

Whether the tooth is intact or not poor periodontal support does not make for a good prognosis. If a patient insists on an attempt to retreat such a tooth, it should be duly noted in the chart that the patient was told of the poor prognosis and chose to proceed despite the potential options of an implant being placed. While we want to save as many teeth as possible, we are doing the patient no favor if failure rapidly follows our course of treatment. Rapid failure reflects poorly on us too. On the other hand, I have seen many instances where teeth poorly supported by bone last for many years. So this is a real judgment call with the patient understanding all the options. Clincal experience over the years hopefully improves such judgments.

Once we get into the areas of vertical fractures we are really talking about their extent. If an occlusal fracture extends through the floor, it has a very poor prognosis and extraction should seriously be considered. If the fracture ends short of the floor, retreatment may be attempted with the clear understanding that the tooth if not supported by a crown with an excellent ferrule, must then have one soon after treatment. If the fracture is on the mesial or distal aspects of the tooth and again does not extend to the floor of the pulp chamber, retreatment may again be a viable option. By no means should a post be placed into any canal that is near the site of the vertical fracture. One should also be aware of a patient’s oral habits. If they are grinders, clenchers or bruxers, the fact that a vertical fracture to one degree or another already exists suggests a strong possibility that the fracture may propagate further in the near future. Such habits might mitigate against retreatment.

If the means are available a CBCT will show three-dimensional information about the tooth that is often not present on a periapical film. Such information may include missed canals, areas of root resorption, unseen periapical bone loss. While missed canals are the easiest problem to fix, resorptions and hidden bone losses may be so great that predicting success via retreatment is unlikely. The increased amount of information you have of both the bone support and the overall integrity of the tooth structure lets the dentist make a more informed decision on whether to retreat or extract. If the dentist does not have a CBCT he/she should have a professional relationship with someone who does and use that person as a source for better diagnoses.

Over the years I have seen patients with such destructive oral habits that they wear down their teeth excessively, have fractures in many of their teeth and destroy any tooth that has a post placed in it. I’ve repaired some of these post supported teeth by removing the segment fractured within the root and placing bigger posts only to have them also break or finally create a vertical fracture along the length of the root. If we are going to condemn such patients to extraction, we must fully explain why with the added proviso that the implants that may be subsequently placed are also subject to the same stresses as the natural teeth and may lead to further breakdown. Self-destructive habits are some of the most frustrating challenges we have in dentistry.

Ideally we want to treat a responsible patient who will then do the restorative work necessary to maximize their chances that the retreatment done will be successful. Patients who do not conscientiously follow up on their restorative work or fail to maintain proper hygiene will not have a good prognosis in the long run if they stop treatment as soon as the pain is gone. Responsible patients have a lot going for them simply by taking the proper steps to reinforce the retreated tooth with a solid well functioning restoration.

From a practical point of view, retreatment may be necessary because access the first time around was so limited that it was barely possible to perform any endodontic procedures. If this is the case, one must assess one’s own skills in measuring one’s ability to do a better job. If in doubt one way or the other, a referral to a specialist will shift the responsibility and the opportunity to an individual who due to specialization is more equipped to make the proper decision.

Finally we have to consider the overall health of the patient. I’ve worked on frail patients in their 90’s and have to assess if the retreatment procedure even if technically possible is subjecting them to too much stress. Is the tooth in question essential to their functioning? If not, perhaps it is the more humane thing to suggest extraction at far less cost in dollars and physical duress. Each patient and the difficulty of the procedure must be measured in these terms in determining if and when the effort should be made.

Many of the decisions are not black and white. There are many subtleties that can only be gained from experience and the care taken to make a good common sense decision that will benefit the patient the most whether it be retreatment or extraction.

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