The influence of parathyroid hormone-related protein (PTHrP) on tooth-germ development and osteoclastogenesis in alveolar bone of PTHrP-knock out and wild-type mice in vitro.

In a previous study, it was shown that tooth germs of neonatal homozygous parathyroid hormone-related protein (PTHrP)-knockout mice are penetrated or compressed by the surrounding alveolar bone, suggesting an important role for PTHrP in the formation and activation of osteoclasts around growing tooth germs. In order to elucidate the role of PTHrP during the development of the tooth germ and related structures, mandibular explants containing cap stage tooth germs of embryonic day 14, homozygous mice were here cultured with or without surrounding alveolar bone. There was no difference in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclastic cells around the first molars of homozygous and wild-type mice. After 10 days of culture, osteoclastic cells were rarely present in explants from homozygous mice and penetration of alveolar bone into the dental papilla was observed. The decline in osteoclast number was partly restored by the addition of PTHrP to the culture. Tooth germs of both wild-type and homozygous mice cultured without alveolar bone developed well, with no apparent structural abnormality; dentine formation was evident after 10 days. These data suggest that PTHrP is not required for the development of the tooth germ proper but is indispensable in promoting the osteoclast formation required to accommodate that development.

Polycaprolactone/hydroxyapatite composite scaffolds: preparation, characterization, and in vitro and in vivo biological responses of human primary bone cells.

Polycaprolactone (PCL) is a synthetic biodegradable polymer that has been approved for use as bone graft substitutes. In this study, PCL scaffolds incorporating hydroxyapatite (HAp) particles were fabricated by combined solvent casting and particulate leaching techniques. The average pore dimension was in the range of about 480-500 microm. The porosity, water absorption, and compressive modulus of the scaffold were evaluated. The responses of primary bone cells cultured on the PCL and PCL/HAp scaffolds were examined both in vitro and invivo. In comparison with the cells grown on the PCL scaffold, those cultured on the PCL/HAp counterpart positively expressed the markers of osteogenic differentiation. Cells increased the mRNA expressions of type I collagen and osteocalcin on day 10 and demonstrated a significant increase in calcium deposition. In coherence with the in vitro appearance, histomorphometric analysis in a mouse calvarial model showed a significantly greater amount of new bone formation. The results demonstrated that the prepared PCL/HAp scaffold could be a good candidate as synthetic substitute for bone tissue engineering. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.