Many prognostic studies have investigated the prevalence of apical periodontitis following endodontic treatments and tried to identify the potential risk factors affecting its outcomes. Factors such as preoperative apical disease, pulpal status, shaping and disinfection of the canal system, working length level, and the quality of obturation and restoration have been correlated to endodontic prognosis. The cause of an unsuccessful outcome following endodontic treatment is multifactorial. The importance of locating all existing canals within the root system to achieve optimal outcomes has been discussed, and
the potential adverse effects of missed and untreated canals on endodontic prognosis have been debated. Overwhelming clinical evidence of missed canals in failed cases requiring endodontic retreatment has been reported. However, the incidence of missed canals and its effect on endodontic prognosis has not been reported.

Karabucak et al from the University of Pennsylvania conducted a retrospective cohort study to evaluate both the incidence of missed canals in endodontically treated teeth and the effect of untreated canals on endodontic outcome. This study included all cone-beam computed tomography (CBCT) images taken from patients referred for dental treatment between January 2013 and July 2015. All axial, sagittal and coronal slices of each scan were
evaluated as a group by 2 readers-an endodontist experienced in reading CBCT images and a second/year endodontic resident.

All endodontically treated premolars and molars were included in the study. A periapical lesion was diagnosed when disruption of the lamina dura was detected and the low-density area associated with the radiographic apex was at least twice the width of the periodontal ligament space.

Excluded were scans of teeth with

  • perforation
  • extensive root resorption
  • previous periapical surgery with root-end resection
  • C-shaped anatomy
  • unsatisfactory image quality due to artifacts

The Fisher exact probability and odds ratio tests were used to assess the relationship between missed canals and the occurrence of apical periodontitis. The 655 scans included a total of 1137 endodontically treated teeth. Overall incidence of missed canals was 23.04%; the incidence of missed canals was highest in the maxillary molars (40.1%) and lowest in the maxillary premolars (9.5%; Table 1).

The results showed that the most frequently missed canals were

  • the second mesiobuccal canal in maxillary first molars (65%)
  • the second distal canal in mandibular first molars (62%)
  • a mesial canal in mandibular second molars (78%)

Overall prevalence of apical lesions was 59.5% (676/1137). The prevalence of lesions was highest in mandibular molars (64.9%) and maxillary molars (64.2%).

The prevalence of an apical lesion in teeth with a missed canal was 82.8% (217/262). All radiolucent lesions were associated with the root of a missed canal. There was a significant difference in lesion prevalence if a canal had been missed (p < .05).


Missed or untreated root canals appeared to have an adverse effect on endodontic outcomes. A tooth with a missed canal was 4.38x more likely to be associated with a periapical lesion.

Karabucak B, Bunes A, Chehoud C, et al. Prevalence of apical periodontitis in endodontically treated premolars and molars with untreated canal: a cone-beam computed tomography study. J Endod 2016;42:538-54l.