Non-microbial etiology: foreign body reaction maintaining post-treatment apical periodontitis

The polymerase chain reaction (PCR) is an elegant technology for faithfully replicating and amplifying the master molecule of life, but a valid scientific procedure remains essential without which the resulting data have only very limited value. The presence of microbial infection in the complex apical root canal system is the major cause of posttreatment apical periodontitis in well-treated teeth. However, in rare cases, non-microbial etiological factors, located beyond the root canal system (within the inflamed periapical tissues), can maintain the disease in root-filled teeth. These factors include foreign body reaction to exogenous materials or endogenous cholesterol crystals, a cystic condition of the lesion and extraradicular actinomycotic infections. This article addresses foreign body reaction at the periapex, as a pathobiological factor that maintains post-treatment apical periodontitis.