Effects of a Xenogeneic Bone Graft Combined with Platelet-Rich Fibrin Obtained Using Two Distinct Centrifugation Protocols on Critical-Size Rat Calvarial Defects: A Microtomographic, Histomorphometric, and Confocal Laser Scanning Microscopy Analysis

This study aimed to evaluate bone regeneration in critical-size rat calvarial defects treated with a xenogeneic bone graft alone or combined with autologous platelet concentrates prepared using two distinct centrifugation protocols, one based on horizontal centrifugation to produce horizontal platelet-rich fibrin (H-PRF) and the other based on vertical fixed-angle centrifugation to produce leukocyte–platelet-rich fibrin (L-PRF). Calvarial defects were created in 24 rats and allocated to four groups: blood clot (C), xenograft (XEN), xenograft plus L-PRF (XEN+L-PRF), and xenograft plus H-PRF (XEN+H-PRF) (n = 6/group). Calcein and alizarin were administered at 14 and 30 days, respectively. After 35 days, specimens were analyzed by micro-computed tomography, confocal laser scanning microscopy, histomorphometry, and histopathology. Data were analyzed using ANOVA and Tukey’s post hoc test (p < 0.05). All treated groups showed higher bone volume and lower trabecular separation than group C. The XEN+L-PRF group showed significantly higher bone volume than the XEN group. The XEN+H-PRF group showed higher bone volume, connectivity density, alizarin labeling, mineral apposition rate, and newly formed bone area, as well as lower trabecular separation, than the other groups (p < 0.05). Under the experimental conditions evaluated, both PRF protocols improved bone regeneration when combined with a xenogeneic bone graft, whereas the H-PRF protocol was associated with superior structural and histomorphometric bone regeneration outcomes and with more favorable spatiotemporal mineralization kinetics.