What can cause root canal treatments to fail?
Root canal treatment failures can be attributed to two main causes: microbial or non-microbial.
MICROBIAL causes can either be intra- or extra-radicular in nature
Intraradicular
Microorganisms found in root-canal-treated teeth with persisting periapical disease are different from those found in untreated teeth. The majority of bacteria found in treated teeth are Gram positive facultative anaerobes which reside in accessory canals, along the root-filling material in the main canal and in the dentinal tubules.
There is no evidence to suggest that certain bacterial species are resistant to treatment. However, the existence of bacteria in treated teeth could mean that they have survived from the original infection or could be contaminants that were introduced into the canal.
Extra-radicular
Periapical tissues can not only be infected by bacteria in the root canal, but also can introduce bacterial contamination into the root canal system. The microorganisms found in extra-radicular infections include predominantly Actinomyces, Propionibacterium as well as Fusobacterium, Prevotella and Staphylococcus.
NON-MICROBIAL causes of root canal failures include cysts and the host’s foreign body reaction to materials, such as root-filling materials, medicaments and sealers, amalgam, cellulose components from cotton or paper points.
Cysts
While granulomatous tissues in the periapical region of the treated tooth may respond to conventional root canal treatment, a cyst is unlikely to resolve. It is also difficult to differentiate a cyst from a granuloma clinically. As such, it is preferable to treat a lesion, associated with an infected and necrotic pulp, endodontically first and if it does not resolv after adequate follow-up, a surgical approach may be indicated.
Response to Foreign Bodies
Foreign materials can enter into an open tooth either before or after treatment and travel into the periapical tissues. Usually, any small amounts of debris are removed naturally by the host’s response; however, any material which causes chronic symptoms or pathology should be removed surgically.
Source: Endodontics, 4th Edition, Elsevier 2014.
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Interesting article – relevant – except, that it is the failure to find all of the canals in the root canal system that is greatest vector of failure – the article and the need to appreciate the labyrinthine complexity of the root canal system go hand in hand with an equally profound understanding of irrigation methodology.
I disagree that missed canals is the greatest vector for failure. Maxillary laterals and mandibular premolars have the highest failure rate in the literature yet are predominantly single canal teeth. (90-100% of the time).
The literature most assuredly does not indicate that mandibular bicuspids predominately are single canals – again, I reference the microCT work of both Drs. Versiani and Zapata. In regard to the lateral incisors, the failure to negotiate the apical curvature adequately is the primary reason for treatment outcome failure……..in both cases, these are outlier situations. The teeth that are most commonly treated are mandibular and maxillary molars and the failure to identify multiple canal systems in the MB root of the maxillary 6’s and 7’s and the prevalence of middle mesial canals in mandibular molars estimated to be as high as 40% represent the most significant areas of failure concern. Failure is a multivariate problem – number of canals is but one variable…..