Some dentists state that root canals become a source of ongoing infection for the rest of the body. People with root canals should consider fungal candida as a source of ongoing problems in those teeth.
"Candidal organisms are commensals of the oral cavity and their opportunistic infection depends on the interplay of local and systemic factors. Endodontic treatment failure has been associated with the persistence of microbial flora following therapy in the root canal system, and this includes fungi like Candida, which are resistant to conventional root canal irrigants."
Presence of Candida albicans in Root Canals of Teeth with Apical Periodontitis and Evaluation of their Possible Role in Failure of Endodontic Treatment.http://www.ncbi.nlm.nih.gov/pubmed/25859106