This clinical report describes a relatively infrequent patient with inferior alveolar nerve damage caused by foreign material within the mandibular canal, which is one of the most severe complications of endodontic therapy. Although the circumstance is uncommon, it can have extremely unfavorable consequences for patients, such as anesthesia and paresthesia. In the present case, a patient suffered pain and severe paresthesia in the corresponding area after routine endodontic therapy. Several treatments were conducted to relieve the patient's symptoms, ranging from medication to tooth extraction, but all were of no avail. Ultimately, surgical exploration and debridement were performed with assistance of a customized surgical template. Once the foreign material was excavated, the exacerbation of condition was terminated and gradually reverted. This patient illustrates that special attention is required when undertaking intracanal procedures of lower posterior teeth so as to avoid iatrogenic damage to inferior alveolar nerve. Even more significant, when above-mentioned condition occurs, prompt surgical intervention is essential for recovery of sensation. It also demonstrates the advantages of applying surgical template and piezosurgery in removal of foreign material within the mandibular canal.