Simultaneous Implant Placement After One-Stage Management of a Chronic Schneiderian Membrane Defect in the Posterior Maxilla with Less Than 4 mm of Residual Bone Height: An 8-Year Follow-Up Case Report

Abstract

Maxillary sinus floor augmentation is an established treatment for vertical bone deficiency in the posterior maxilla. Management of a chronic Schneiderian membrane defect associated with a pre-existing lateral sinus wall defect following previous sinus augmentation may present additional surgical challenges, particularly when simultaneous implant placement is planned in sites with very limited residual bone height (RBH). A 58-year-old systemically healthy male presented with tooth loss in the left posterior maxilla and a history of an unsuccessful sinus augmentation and bone grafting procedure performed two years previously at another clinic. Preoperative cone-beam computed tomography (CBCT) demonstrated a chronic circular defect measuring approximately 6 × 10 mm in the anterior lateral wall of the left maxillary sinus. Severe vertical resorption of the posterior maxillary alveolar ridge was also present, with an RBH of 3.7 mm at site #25 and 2.6 mm at site #27, according to the FDI two-digit tooth-numbering system. A one-stage surgical approach was performed using a customized lateral window created through intact lateral sinus wall bone immediately adjacent to the pre-existing defect. This access was adapted intraoperatively after visualization of the chronic defect and allowed initial elevation of the Schneiderian membrane from a relatively non-scarred region before controlled dissection toward the defective area. The continuity of the Schneiderian membrane could not be reliably assessed on preoperative CBCT; the associated membrane defect was therefore identified and confirmed intraoperatively under direct visualization. The membrane defect was managed using a resorbable collagen membrane (GuidOss®, NIBEC Co., Ltd., Korea; 25 × 30 mm, adapted intraoperatively to approximately 20 × 20 mm). The collagen membrane was not independently fixed with pins, screws, tacks, or other fixation devices; following implant placement, the implants provided mechanical support for the elevated membrane and maintained the created subantral space. Two implants were placed simultaneously: a 4.0 × 10 mm implant at site #25 and a 5.0 × 10 mm implant at site #27. Both implants achieved a final insertion torque of 35 Ncm. Approximately 1 cc of particulate bone allograft (Sure-Oss®, HansBioMed, Seoul, Republic of Korea) was used for sinus augmentation. A second resorbable collagen membrane was placed over the lateral access window. Postoperative healing was uneventful. Five-month CBCT demonstrated radiographic bone formation surrounding both implants, incorporation of the grafted compartment, and radiographic resolution of the pre-existing lateral sinus wall defect. At the 8-year follow-up, both implants remained functionally loaded and clinically stable, with no documented implant mobility, clinically evident peri-implantitis, progressive peri-implant bone loss, or mechanical complications. This case describes the technical feasibility of one-stage management of a chronic Schneiderian membrane defect with very limited residual bone height, using an adjacent lateral window approach combined with sinus augmentation and simultaneous implant placement. The 8-year clinical and radiographic follow-up documents sustained implant function in this individual case. Further clinical studies are required to determine the reproducibility and appropriate indications of this approach in similar clinical situations.