Successful and predictable endodontic treatment requires knowledge of root canal anatomy and morphology variations. In cases where X-ray images do not help to clarify the anatomy of the root canals, it is recommended to use magnifying devices. The second premolar of the lower jaw is one of the most diffcult teeth for endodontic treatment due to variations in internal morphology, additional root canals, apical deltas, and lateral canals. Diagnostic radiographs in different projections are important for getting an idea of the number of existing root canals. The purpose of root canal treatment is to clean the root canal of pathogenic microbes and infected pulp, prevent the formation of toxic products, and protect the periapical tissue. The presence of root canal variability increases the complexity of endodontic treatment. The complex anatomy of the root canals, the presence of additional channels, unnoticed by the dentist, can cause the failure of endodontic treatment.