BACKGROUND: This case report describes a 22-year-old female who was referred with a radiolucent lesion between her mandibular right molars. The original radiographic image suggested an odontogenic cyst. METHODS: The surgical enucleation and osteotomy of the residual cavity were performed with a piezoelectric knife. Histologic analysis revealed the lesion was a unicystic ameloblastoma that showed no evidence of epithelial invasion in the connective tissue wall, and it appeared to be contained within the cystic cavity with an intraluminal projection showing features of an ameloblastoma. The patient refused any further surgical treatment. In consideration of the pathological result (no presence of invasive epithelial cells in the connective tissue wall of the cyst), a wait-and-see policy was proposed to the patient, with more extensive surgical treatment only if a recurrence was noted. RESULTS: The patient has been followed clinically and radiographically at 6-month intervals for 5 years. There have been no signs of recurrence. CONCLUSION: Therefore, the piezoelectric knife could be considered a promising device in the treatment of odontogenic tumors.