Endodontic failure that is limited to a radiolucency around the MB root of a maxillary molar has a differential diagnosis that includes a missed MB2 canal. Where such diagnosis is suspected, the clinician has the option of apicoectomy vs. non-surgical retreatment. Since apicoectomy in a non treated canal leaves a large volume of bacteria behind in the coronal portion of the canal, this options has been demonstrated to have a limited long term prognosis. In such cases, endodontic retreatment is the best option. Where well fitting, recent crowns with cast posts and other obstacles are present in canals that do not demonstrate any clinical signs of periapical infection, a conservative approach that entails access over the MB root alone may be taken to address the missed MB2 and retreat the entire MB root. Such cases generally do well if the canals are adequately enlarged and other canals were originally well treated. The current video shows one such case.