Success of endodontic treatment depends on proper identification and localization of all the canals, thorough chemo- mechanical preparation followed by three-dimensional obturation with hermetic seal. Failure of any of these steps may occur due to unusual tooth morphology. Mandibular first molar can show significant anatomical variations in number of roots, root canals and morphology. Mandibular first molar sometimes have an additional root located lingually (the radix entomolaris) or buccally (the radix paramolaris). So, proper awareness and understanding of this unusual root and its canal morphology can contribute to the successful outcome of root canal treatment. This case series discusses endodontic treatment of mandibular first molar with radix entomolaris, which is rare entity and poses as an endodontic challenge for clinician to diagnose and further treatment. Clinician should be aware of this unusual root morphology in mandibular first molar which needs strategic treatment as unfilled canals remains a nidus for infection and can compromise treatment outcome.
