Previous studies have suggested that the biodegradability of octacalcium phosphate-collagen (OCP/Col) composite by osteoclasts is accelerated in association with mechanical stress suffered by the host tissue around the implant. The present study was designed to investigate whether alleviation of mechanical stress restores the bone regenerative properties of OCP/Col, as previously shown in nonload-bearing sites. OCP/Col discs supported with a polytetrafluoroethylene (PTFE) ring, which has a higher modulus than OCP/Col, were implanted in a rat subperiosteal pocket for up to 12 weeks. The structural features of the implant and biological responses were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, histomorphometry, histochemistry, and tissue mRNA expression around the implants. The effect of compression was analyzed using mouse stromal ST-2 cells by deforming the cell-seeded OCP/Col discs in vitro with or without a PTFE ring. The results clearly indicated the restoration of bone formation by the alleviation of mechanical stress and the upregulation of osteoblast-related genes, such as osterix on the other hand, the implantation of OCP/Col on calvaria or in an in vitro test without PTFE support resulted in the upregulation of osteoclast-related genes, such as tartrate-resistant acid phosphatase (TRAP) and cathepsin K, in the tissues or receptor activator of the nuclear factor-κB ligand (RANKL) in ST-2 cells. The results confirmed that calvaria augmentation is enhanced by implanting OCP/Col if suitable conditions regarding mechanical stress are provided.
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