Descriptive Histological and Histomorphometrical Comparison of Four Xenogeneic and Synthetic Bone Blocks for Mandibular Onlay Augmentation in Rabbits

Background: This exploratory study provided a primarily descriptive comparison of two xenogeneic and two synthetic blocks for mandibular onlay augmentation in rabbits. Methods: Twelve rabbits received bilateral block grafts, providing 24 sites allocated to Bio-Oss® Block, SP-Block, ReproBone® Block, or Alos Block (n = 6/material). After 10 weeks, undecalcified sections were evaluated within standardized inferior and superior regions. Newly formed bone was the primary outcome; secondary outcomes included residual graft, IBN-like tissue, soft-tissue components, and cross-sectional augmented area. Mixed-effects models accounted for clustering within animals. Results: No statistically significant difference in newly formed bone percentage was detected among biomaterials (p = 0.475). Residual graft differed significantly (p < 0.001) and was lower for all test materials than for Bio-Oss® Block. ReproBone® Block consistently exhibited IBN-like tissue (17.3 ± 2.9%). SP-Block showed more intra-compartment soft tissue than Bio-Oss® Block. Alos Block had the smallest augmented area (12.9 ± 6.1 mm2; adjusted p = 0.001 versus Bio-Oss® Block), and extra-compartment soft tissue was present in five of six sites. Conclusions: Although newly formed bone percentages did not differ significantly, the biomaterials displayed distinct profiles of scaffold persistence, incorporation, tissue organization, and cross-sectional augmented area at 10 weeks. These features should be considered together when evaluating block biomaterials for onlay augmentation.