Cell turnover in the periodontal ligament determined by continuous infusion of H3‐thymidine using osmotic minipumps

Previous methods of determining the labelling index (LI) of periodontal ligament (PDL) over an extended period of time have required multiple injections of isotope or addition of isotope to the animal's drinking water. Problems with these techniques are overcome to a great extent by the use of osmotic minipumps. Male Syrian hamsters had minipumps which had been filled with 2μCiH3‐TdR implanted intraperitoneally. Animals were killed at 2,4,7,21. and 42 days. Specimens were embedded in plastic and 1 μm sections prepared forradioautography. Results show that the LI rose from less than 1% to reach over 50% by the end of the experiment. It is concluded that cells of the PDL are a slowly renewing population.