Biologic properties of nano-hydroxyapatite: An in vivo study of calvarial defects, ectopic bone formation and bone implantation

This study investigated the biologic properties of nano-hydroxyapatite (nHAp) using the rat calvarial defect, ectopic bone formation, and rabbit tibia implant installation models. Animals were divided into two groups: those implanted with nHAp, and negative controls (Collagen). Eight weeks after creating an 8 mm calvarial defect, bone regeneration was evaluated radiographically and histologically. To investigate ectopic bone formation, materials were injected into the right thigh muscle and were evaluated after 8 weeks. nHAp coated implant and conventional titanium implant were placed bilaterally in rabbit tibias. After 4 weeks, bone-implant contact (BIC), new bone area inside the thread, and removal torque were measured. In the calvarial defect model, radiographic and histologic analysis showed more bone formation in the nHAp Group; particularly, histologically assessed bone area (p = 0.034) and microcomputed tomography assessed bone mineral density (p = 0.034). In the ectopic bone formation model, calcification and expression of osteogenic biomarkers were seen in the nHAp-injected samples but in none of the controls. nHAp coated implant resulted in increased BIC, new bone area, and increased removal torque, with statistical significance for BIC (p = 0.034). This study suggests that nHAp has potential as a coating material for dental implant surfaces and as a bone graft material.