fa Radiology Radiology Case report <strong><span dir="LTR">Background:</span></strong><span dir="LTR"> A correct diagnosis of the morphology of the root canal system is crucial in order to ensure a successful root canal treatment. The incidence of mandibular first premolars with three root canals has been reported to be low. This clinical case report describes a case of a successful nonsurgical endodontic management of a mandibular first premolar with three root canals. </span><br> <strong><span dir="LTR">Case presentation:</span></strong><span dir="LTR"> A 27-year-old man presented to our clinic with pain in the left mandibular premolar. The diagnosis was irreversible pulpitis based on the clinical and radiographic examinations. Hence, root canal treatment was recommended. After preparing the access cavity, the orifices were found by removing the dentinal shelves. The root canals were treated by rotary files and were obturated using the cold lateral compaction technique.</span><br> <strong>Conclusion:</strong> Mandibular premolars can present with an extremely complex root canal morphology, which if not considered during the treatment, it can lead to post-treatment complications, failure, or flare-ups. Abnormality, Bicuspids, Dental Pulp Cavity, Mandible, Root Canal Therapy 50 54 http://jrdms.dentaliau.ac.ir/browse.php?a_code=A-10-391-1&slc_lang=fa&sid=1 N Hoshyari narjeshoshyari@rocketmail.com 100319475328460010673 100319475328460010673 Yes Assistant professor, Endodontics Dept ,School of Dentistry, A Haddadi haddadi-azam@yahoo.com 100319475328460010674 100319475328460010674 No Assistant professor, Endodontics Dept, School of Dentistry,