Endodontic treatment of an abnormally shaped tooth is complicated by irregular tooth morphology. Furthermore, root canal fusions are known to occur in abnormal teeth. The placement of canal orifices is unusual and due to their depth, they are sometimes invisible to the naked eye. As a result of the difficulty in instrumentations and obturation, root canal treatment of teeth with an abnormality is difficult. When performing root canal treatment on abnormal teeth, complex anatomic variations of the root canal system should be investigated as thoroughly as possible. Cone-beam computed tomography is an effective method for assessing the morphology of the root canal by visualizing the canal of the tooth. The case reports that follow each describe a case of root canal treatment in a maxillary molar with an abnormality.