Synergizing Macrogeometric Design and Nano-Hydroxyapatite Coatings to Enhance Early Implant Stability and Bone Maturation

Implant macrogeometry and surface microstructure represent fundamental pillars for accelerating and enhancing the quality of osseointegration. The objective of this study was to evaluate the synergistic effect of three distinct implant designs, Strong (hybrid with trapezoidal threads), Unitite (hybrid with healing chambers), and Epikut (hybrid with active double threads), associated with two surface configurations (dual acid-etched [DAE] and nanohydroxyapatite [NanoHA]) on bone regeneration at 3 and 8 weeks. Twenty-four male rabbits randomly received forty-eight implants in their tibiae, yielding an equal accounting of n = 12 animals per experimental healing period (3 and 8 weeks) to ensure a balanced longitudinal and structural analysis. Biomechanical monitoring included final insertion torque (IT) and resonance frequency analysis (ISQ) at installation and euthanasia, while high-resolution micro-computed tomography (µCT) quantified the 3D intersection surface index (IS/TS) and trabecular microarchitecture (BV/TV, Tb.Th, Tb.Sp, and Connectivity). Regarding insertion torque, no significant differences were observed between macrogeometries (p = 0.557), ensuring a standardized mechanical baseline for biological comparison. For clinical stability (ISQ), the Epikut and Unitite designs demonstrated significant stability gains as early as 3 weeks (p < 0.05). µCT data confirmed a progressive, time-dependent structural reorganization, presenting a significant increase in trabecular thickness (Tb.Th) over time (p < 0.001), while the overall bone volume fraction (BV/TV, p = 0.861) and IS/TS index (p = 0.774) maintained statistical uniformity across all studied models. In conclusion, implant macrogeometry and surface nanotopography exert a distinct, chronologically shifted synergy during osseointegration. Clinically, these findings dictate target-specific selection: macrogeometric innovations accelerate early secondary clinical stabilization, whereas bioactive NanoHA coatings optimize subsequent long-term trabecular thickening within the established peri-implant architecture.