Endodontic postoperative pain is a common unexpected complication. This problem is not well understood and its incidence varies widely from one study to another. The hypothetical mechanisms for this complication include chemical, mechanical or microbial injury to the periradicular tissue. Instrumentation beyond the apical foramen and apical extrusion of the infected debris seem to be the most important causative factors by stimulation of an acute immune response in the periapical area. The reported incidence of this phenomenon varied from 1.7 to 70%. This wide range of the reported incidence is due to different study designs, pre-operative condition of the teeth, treatment procedure or technique, timing of recording pain experience, index of pain measurement and severity of pain included in the statistical analysis. Although some studies found a correlation between this phenomenon and presence of preoperative pain, presence of periapical lesion, pulpal necrosis, number of visits, technique of instrumentation, age, gender, other studies have failed to find this correlation.. No specific procedure, systemic or localized medication has been found to prevent its occurrence. Knowledge about the etiology of flare-ups and adoption of appropriate preventive measures can significantly reduce the incidence of this highly distressing and undesirable clinical phenomenon.

endodontic flare-ups, postoperative pain, etiology, related factors