Cone‐beam computed tomography and clinical examinations including pulp vital testing and pocket probing depth showed a cemental tear with a severe labial alveolar bony defect, but no endodontic lesions, in #25, which had a sinus tract at the labial site, in a 75‐year‐old woman.

Key Clinical Message: Dental radiography and cone‐beam computed tomography revealed the left mandibular first molar in a 68‐year‐old female patient with Heithersay Class 3 invasive cervical resorption ( ICR ). The inhibition of ICR progression and environmental improvement in and around the affected tooth through combined endodontic and periodontal treatments led to a favorable clinical outcome.

The present case report describes the clinical detection and root canal management of a rare middle mesial canal of a Japanese mandibular second molar by troughing preparation using an operating microscope and cone‐beam computed tomography.

Key Clinical Message: Endodontists should be aware that some maxillary second molars can have more than three roots. If any unusual anatomical features are detected during dental radiography or endodontic procedures, it is necessary to conduct cone‐beam computed tomography (CBCT) scanning to prevent procedural mishaps. CBCT can provide three‐dimensional reconstructed images of the root canal system. With the help of CBCT, variations in tooth root number and root canal morphology, such as extra canals, apical ramifications, apical deltas, and lateral canals, can be identified. Knowledge of the variations is very important for the success of endodontic treatment. This report suggests that endodontists must not assume that a MSM has only three tooth roots, which is the most prevalent number.