Understanding Endodontic Failure
To describe the reasons why root canal treatment fails in practice.
At the end of this chapter, the practitioner should be able to identify the possible reasons for root canal treatment failure and understand how failure may be converted to success.
When failure has occurred or if a periapical lesion does not heal after root canal treatment, there are four possible ways of dealing with the problem:
wait, watch and reassess
As patients increasingly express a preference for retaining their natural dentition, non-surgical or surgical retreatment offers the patient another chance of saving their root treated tooth. The first practical step in managing endodontic failure is to identify the cause. Only then is it possible to retreat a tooth with confidence. Unless the cause of failure is properly addressed, there is a risk of perpetuating or compounding the problem.
The commonest reason for endodontic failure is infection, caused by the presence of microorganisms and their by-products, inside or outside the root canal system. This may be a result of new infection being introduced or a failure of the original treatment to manage the pre-existing infection.
Persistent intraradicular infection occurs most frequently when the original treatment falls short of acceptable technical standards (Fig 2-1a). Cross-sectional surveys from various countries have revealed that, on average, 30% of endodontically treated teeth are associated with periapical radiolucencies and there is a positive correlation with poor technical quality of the root filling. Unfortunately, radiographs, typically taken in a buccolingual direction, rarely tell the whole story. Apparently well-treated cases may have, for example, obvious deficiencies in the third dimension or missed canals (Fig 2-2). Failures associated with technical deficiencies are usually amenable to non-surgical retreatment (Fig 2-1b).
Failures in cases in which a high technical standard of treatment has been attained are more challenging to handle and resolve. Often, it is difficult to identify the reason for this type of failure. Studies have suggested that therapy-resistant cases may be associated with some form of extraradicular recalcitrant infection – an established infection colonising the external root face, forming a biofilm and persisting in periapical tissues. Inaccessible and unresponsive to conventional root canal treatment, the infection also resists the efforts of the host defences. Actinomyces israelii (Fig 2-3) and Propionibacterium propionicum have been reported to be associated with extraradicular infections.
Typically, a radical approach, including a combination of surgical and non-surgical retreatment, may be required to deal with therapy-resistant cases (Fig 2-4). Even then, not all affected teeth can be saved. It should be noted, however, that non-surgical retreatment is almost always justified as a first-line approach for managing failures associated with apparently well root treated teeth (see Chapter 3 and Fig 2-5).