Abstract: Objective: To explore the etiology and treatment of one case of bilateral mandibular second molar impaction with paradental cyst, and to provide a reference for its diagnosis and treatment. Methods: Root canal treatment of the left mandibular first molar of the patient was performed before operation.The left mandibular second molar of the patient was removed; the residual dental follicle, the granulation tissue and the cyst wall were stroken off under local anesthesia.The diamond ball was used to polish the wound cavity and sharp bone edge, and to mill the distal apical part of left mandibular first molar.The tissue removed during the procedure was used for the pathological examination. Results: The X-ray image showed that the bilateral mandibular second molar was impacted with the left mandibular first molar root's absorption, and there was a clear round-like density reduction zone around the second molar crown.The pathologic result was paradental cyst. Conclusion: Dental impaction complicated with paradental cyst could occur in other tooth position except for the third molar.Its diagnosis should be combined with the clinical manifestations, the pathologic manifestations and the medical imaging.Multidisciplinary consultation is in favor of its diagnosis and treatment.

Key words: paradental cyst, mandibular second molar, impaction, case report