Histomorphometric and transcriptome evaluation of early healing bone treated with a novel human particulate dentin powder

Human particulate dentin (HPD) shows potential as an alternative bone grafting material. However, the mechanism of bone healing at the molecular level after grafting with HPD is unclear. This study assessed the histological and global gene expression of bone tissues grafted with HPD. The HPD was prepared to 250-500m in size. X-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDX) were performed to confirm the crystal structure, organic compound residues, and surface morphology, respectively. Bony defects were created on the heads of 24 New Zealand White rabbits. Sterilized HPD was used as the grafting material. The quality and quantity of new bone formation was evaluated using micro-CT and histologic analyses during the 8 week experimental periods. For microarray assay, bone tissue and blood samples were taken at 3, 5 and 7 d post-implantation. The results of XRD and EDX showed that HPD exhibited physical and chemical properties similar to natural hydroxyapatite. New bone formation was observed after HPD implantation compared to the controls, as shown on hematoxylin and eosin staining and micro-CT. The bone volume of HPD treated animals was higher than that of the control group at all observation times. Microarray analysis showed that vascular development coupled with immune and inflammatory related genes were expressed in the early healing stage. The gene coding for the IL-1 antagonist, IL1RN, was expressed to inhibit the inflammatory response, and at the same time, the CCL2 gene was activated to 2.3 times the normal level. BMP2, RUNX2, COL1A, and OPN expression were also up-regulated. CCL2 predominated in osteoblastogenesis of the HPD-treated bony defect in the early stage of healing. HPD accelerated bone regeneration and augmentation. These results suggested that HPD provided potential as a bone graft resource during the bone healing process.