Xenograft-Induced Damage and Synechiae Formation in the Maxillary Sinus Mucosa: A Retrospective Histological Analysis in Rabbits

<b>Background</b>: During maxillary sinus floor augmentation, the elevated sinus mucosa may come into close contact with the pristine mucosa. The presence of xenograft granules can lead to unintended mechanical and biological interactions between the two layers, and the resulting tissue damage remains poorly understood. The aim of this study was to perform a focused histological evaluation of graft-mediated interactions between the elevated and pristine sinus mucosae. <b>Methods</b>: Histological slides from five previously published rabbit sinus augmentation studies using grafts with different resorption rates were retrospectively analyzed. The following main patterns of tissue alteration were identified: (1) Proximity stage, characterized by epithelial thickening, goblet cell hyperactivity, and ciliary shortening; (2) Fusion stage, with epithelial interpenetration and loss of distinct mucosal boundaries; (3) Synechiae stage, featuring connective tissue bridges linking the two mucosae; and (4) Pristine mucosa lesions, caused by direct contact between residual graft particles and the pristine sinus mucosa. <b>Results</b>: A total of 192 sinuses were evaluated. Sinuses augmented with slowly resorbable grafts showed proximity stage in 22.3% of cases, fusion in 7.7%, direct lesions in 9.6%, and only one instance of synechia. In contrast, the faster resorbable xenograft presented only 11.1% of proximity stage, without further alterations. <b>Conclusions</b>: In this rabbit model, xenografts were associated with histological alterations of the sinus mucosa, while synechiae formation was rare. These preclinical findings should not be directly extrapolated to humans but may provide a basis for future investigations.