Which bacteria are most commonly associated with failed endodontic cases?

Three species of bacteria are most commonly implicated in the failure of endodontic treatment. The microorganisms colonize dentinal walls and any debris that is pushed through the apex as well as dentine tubules of pulpless necrotic teeth.

Enterococcus faecalis

• Associated with 30-40% of failed root canal treatments
• May be resistant to calcium hydroxide as well as chemomechanical endodontic processes
• Increased tendency to be resistant to antibiotics

Actinomyces

• Can survive for long periods of time without causing host responses and is therefore, considered to have low pathogenicity
• Causes chronic infections
• Lives in necrotic pulpal and infected periapical tissues

Streptococcus anginosus, Streptococcus intermedius, Streptococcus constellatus

• Has symbiotic relationship with other microorganisms
• Considered to be part of the flora normally found in the mouth
• Commonly found in both acute and chronic periapical endodontic lesions as well as purulent infections

Source: Dental Secrets, Elsevier 2015.