Comparative Histological and Histomorphometric Analysis of Xenografts and Synthetic Biomaterials in Rabbit Sinus Floor Elevation

Background: This study compared four biomaterials after maxillary sinus floor elevation in rabbits, focusing on graft persistence, tissue organization, space maintenance, and Schneiderian membrane response. Methods: Thirteen adult New Zealand White rabbits were enrolled, including 12 males and one female replacement animal; 12 animals provided evaluable specimens, with six assigned to each healing interval. Four elevated sinus compartments per evaluable animal were randomly allocated to Bio-Oss®, mp3®, ReproBone® novo Paste, or Alos Granular. Specimens were collected after 2 or 10 weeks (n = 6 each). Histomorphometry quantified new bone, residual graft, soft tissue, elevated area, mucosal alterations, and IBN-like tissue, defined as areas in which biomaterial and bone could not be reliably separated. A combined graft and IBN percentage was calculated. Results: At 10 weeks, materials differed in residual graft (p = 0.0040) and combined graft and IBN percentage (p = 0.0218); Bio-Oss® showed higher values than Alos Granular for both outcomes (adjusted p = 0.0024 and 0.0219, respectively). IBN-like tissue was higher in ReproBone® novo Paste and Alos Granular than in Bio-Oss® (adjusted p = 0.0219 and 0.0417), whereas only a small proportion occurred in mp3®. New bone did not differ among materials at either interval. Bio-Oss® and mp3® showed predominantly conventional osteoconduction. Alos Granular showed extensive degradation, whereas ReproBone® novo Paste exhibited irregular graft and IBN regions. In the descriptive mucosal assessment, thinning was observed in all groups, whereas perforations were observed only at Bio-Oss®-treated sites; no inferential comparisons were performed for these outcomes. Conclusions: The materials differed in graft persistence, tissue architecture, dimensional stability, and mucosal response. Sinus graft evaluation should extend beyond new bone formation to include residual graft, IBN-like tissue, space maintenance, and mucosal compatibility.