Autoradiographic Study on Tissue Response to Hydroxyapatite Ceramics Utilizing Tritiated Thymidine

The objective of this study was to examine the kinetics of mesenchymal cells derived from the periosteum to apatite particles with autoradiographical evaluation using tritiated thymidine. A circular hole 4.5mm in diameter was made in each rat's parietal bone. Apatite particles were implanted on one side as the experimental group, while the other was left empty as the control group. 1.0μCi/gram body weight of tritiated thymidine was injected intraperitoneally 1 hour before the rats were sacrificed, and 12 rats were sacrificed from 6 hours to 28 days after operation. On the other group, to clarify cell differentiation of labeled cells, 3.0μCi/gram body weight of tritiated thymidine was injected intraperitoneally at 4 days afterthe operation and sacrificed at 28 days after the operation. Percentage of population labeling gave a highest value at 2 days after operation at each measured area, and was slightly higher inthe experimental group than in the control. The labeled cells were mainly seen close to some cells but away fromthe bone surface and the apatite particles. From the results of long term labeling, the labeled cells were seen in the newly formed bone around the apatite particles and in the area where there was no bone formation, the labeled cells were seen in the surface of the apatite particles. From these results, it is suggested that bone formation at the surface of the apatite particles originated from the osteoprogenitor cell in the mesenchymal cells which is derived from the periosteum differentiated to osteoblasts.