Delayed Complications After Maxillary Sinus Floor Augmentation with a Bovine Xenohybrid Bone Graft: A Retrospective Clinical Case Series.

Background/Objectives: Maxillary sinus floor augmentation (MSFA) via the lateral approach is a well-established procedure for prosthetic rehabilitation of atrophic posterior maxillae. However, late complications are often nonspecific, with an incompletely understood aetiology. We evaluated patients with atypical late complications post-MSFA with bovine xenohybrid bone substitute NaturesQue SemOss B (BEGO GmbH, Bremen, Germany), describing their presentation, management, and outcomes. Methods: This retrospective, complication-selected clinical case series examined 47 patients who underwent lateral window MSFA with this graft from September 2020 to March 2023 in a single university department. Twelve complication cases were identified during the study period. Atypical late complications were defined as graft-associated clinical and/or radiological adverse outcomes, excluding peri-implantitis, that first manifested > 6 mo postoperatively. Baseline characteristics, perioperative findings, conservative and surgical management (including graft removal and reaugmentation), histology, and follow-up were assessed. Results: Twelve complication cases were identified among 47 patients treated during the study period. Seven experienced implant loss; seven, partial or complete lack of graft osseointegration; six, pain; and seven, signs of sinus infection. Histological analysis (6/12) revealed lymphocytes, plasma cells, and fibroblastic changes without detectable macrophages. No intraoperative complications were observed. Conclusions: Atypical late complications affected 25.5% of the patients. Despite comprehensive clinical, radiological, and histological assessments, the aetiology remained unclear, and the findings did not indicate a peri-implantitis-type infection; we hypothesised impaired early phase wound healing These patients were amenable to repeat augmentation post-non-osseointegrated graft removal, although larger studies are required.