Introduction: This case illustrates the healing of large trauma-induced periapical mandibular and maxillary pocket cysts in a 16-year-old female patient after a nonsurgical endodontic treatment. Dental pulp infection might be the result of tooth decay, trauma, and operative dental procedures. Pulp infection generally leads to the total pulpal necrosis. It stimulates the development of an immune response in the periapical region leading to the growth of periapical lesions with periapical bone resorption. Taking into account the crucial role of the microorganisms occupying the root canal in initiating and sustaining periradicular lesions, nonsurgical root canal treatment and proper infection control should be rule in the management of apical periodontitis. The outcome assessment of periapical lesions is based on clinical and radiographic criteria. Conclusion: In the present case, the CBCT periapical index was used to control bone healing and concluded that the lesion is considered “healing in progress.” This case confirms that even large periapical lesions could respond favorably to a well-performed nonsurgical root canal treatment.