Evaluation of the Osteoconductive Capacity of Micro-Hydroxyapatite and Nano-Hydroxyapatite Associated with Beta-Tricalcium Phosphate: Experimental Study in Critical Calvarial Defects in Rats

Among the biomaterials used in grafting techniques for bone rehabilitation and subsequent dental implant placement, biphasic ceramics have emerged as promising alternatives, prompting investigations into their structural and biological properties. The objective of this study was to evaluate bone repair in critical-size calvarial defects in rats using two particulate biphasic ceramics composed of micro- or nano-hydroxyapatite associated with βtricalcium phosphate in different proportions. Seventy-two Wistar rats were used, distributed into four groups: blood clot (BC); GenPhos® 70/30 (GP), containing micro-HA; Blue Bone® 80/20 (BB), containing nano-HA; and Bio-Oss® (BO). In each rat, a critical defect was created in the calvaria, filled according to the group and covered with a collagen membrane. The animals were euthanized at 7, 14, and 28 days. Histomorphometric analysis was performed, quantifying newly formed bone, biomaterial, and connective tissue, in addition to microcomputed tomography (Micro-CT), adopting p < 0.05, and qualitative histological analysis. In the Micro-CT analysis, no significant differences in bone volume were observed among the groups, although the BB group exhibited a more pronounced trabecular microarchitecture. Histomorphometrically, all biomaterial groups were superior to BC (p < 0.001). The BB group showed similar mean new bone formation (45.03%) compared to the BO group (46.62%), at 28 days, with no statistically significant difference, exhibiting an intraparticular osteoconduction pattern. The GP group demonstrated greater resorption dynamics (17.22%), whereas BO remained the most stable (44.22%). The BC group showed the highest connective tissue persistence (68.07%). It is concluded that the biphasic ceramics and the xenogeneic biomaterial promoted defect closure, with nano-hydroxyapatite (BB) demonstrating great qualitative performance in trabecular organization and initial vascularization, indicating that the nanometric scale and the bioactivity of β-TCP favor a dynamic tissue replacement in critical defects.