RATIONALE: Tooth extraction is a common surgical procedure in oral and maxillofacial surgery. Extraction of the upper molar teeth may result in root fracture for anatomical reasons, leading to the migration of fractured roots into the maxillary sinus. This can cause serious complications such as oroantral fistula, sinusitis, cellulitis, and subdural abscesses. To mitigate the risk of these complications, it is important to promptly remove the root stumps from the maxillary sinus and preserve alveolar bone for subsequent prosthetic rehabilitation. PATIENT CONCERNS: A 30-year-old male patient presented for the removal of a root stump that had migrated into the maxillary sinus following the extraction of a right upper posterior tooth. A 28-year-old male patient sought dental implant restoration following the extraction of an upper left posterior tooth. Imaging revealed a residual root in the maxillary sinus, which could affect subsequent restoration. DIAGNOSES: Residual root in the maxillary sinus. INTERVENTIONS: Two cases of root stumps displaced into the maxillary sinus were treated using the modified lateral window technique, with good recovery. Besides, the second patient underwent a successful implant placement 4 months postoperatively. OUTCOMES: Two cases of root stumps displaced into the maxillary sinus were removed though the modified lateral window technique, with good recovery. The second patient, who underwent implant restoration 4 months postoperatively, demonstrated good implant stability during subsequent follow-up assessments. LESSONS: This paper presents a modified lateral window technique, which is used to remove the stump in the maxillary sinus, resulting in a good postoperative recovery and providing sufficient bone for implant placement. It should be noted that this surgical approach is not applicable to the scenario "the root is free within the sinus", precise localization of the foreign body becomes challenging, and alternative surgical methods may need to be considered.