Bone Healing Response to Different Concentrations of Nano-Hydroxyapatite Incorporated into Mineral Trioxide Aggregate and Bioceramic Sealers

Nano-engineering strategies have been increasingly applied to enhance the biological performance of calcium silicate–based materials; however, the optimal concentration of nano-hydroxyapatite (HANP) remains unclear. This study evaluated the bone-healing response to different concentrations of HANP incorporated into mineral trioxide aggregate (MTA) and bioceramic (BC) sealers in an experimental rabbit model. Thirty adult New Zealand white rabbits were allocated into two experimental groups according to sealer type: HANP-modified MTA and HANP-modified BC (n = 15 each). Two standardized circular intrabony defects were created bilaterally in the maxillary diastema of each rabbit. In the MTA group, the right-side defects were filled with 2% and 4% HANP-modified MTA, while on the left side one defect received 6% HANP-modified MTA and the adjacent defect was left as control. The same protocol was followed for the BC group using corresponding HANP concentrations. Five rabbits per group were sacrificed at 2, 4, and 8 weeks postoperatively for histopathological hematoxylin and eosin (H&E) and Masson trichrome staining. The results demonstrated significant differences among groups at all-time points, with 4% HANP showing the most favorable biological response, including reduced inflammatory cell infiltration, increased new bone formation, and improved collagen organization compared with lower and higher concentrations. Pairwise comparisons at matched HANP concentrations revealed no statistically significant differences between HANP-modified MTA and BC groups. These findings indicate that HANP incorporation enhances the biological performance of calcium silicate–based sealers in a concentration-dependent manner, with 4% representing an optimal formulation for promoting bone regeneration.