Missed canal systems are the most likely basis for endodontic retreatment of molars.

Unfortunately, a small percentage of endodontically treated teeth do not respond favorably to non-surgical root canal treatment. Failure to cate and treat an additional nal system is cited as the principle basis for endodontic retreatment. The aim of this retrospective clinical study was to identify the incidence of additional or missed canal systems in molar retreatment cases in a private practice setting. Missed canals were identified in 64 of the 133 previously treated teeth (48%). Of the total missed canals, 11% involved a maxillary second molar and 44% involved a maxillary first molar. For the maxillary first molars, 93% of all missed canal were identified in the mesiobuccal root. In the mandibular second molars, 29% of missed canals were identified in the distal and 71% were identified in the mesial root. In the mandibular first molars, 86% of missed canals were identified in the distal and 14% were identified in the mesial root. The results of the current study support the findings of previous studies and confirm the importance of locating, instrumenting and obturating the endodontic treatment. Given that failure to locate all canal systems of a tooth contributes significantly to unsuccessful endodontic treatment, all measures available to the clinician to maximize canal identification should be used.