Cellular kinetics of the bone remodeling sequence in the rat.

The kinetics of the bone remodeling sequence in the rat has been studied using a system in which well-synchronized remodeling units were induced along the periosteum of rat mandibles. Remodeling of the periosteal surface of the mandibles was induced according to Tran Van (1979) by extraction of the opposing row of teeth; namely, the right maxillary molars were extracted under light ether anesthesia, therefore allowing the right mandibular molars to egress; this, in turn, induced a wave of remodeling activity on the buccal side of the periosteal surface of the alveolar bone. The quantification of the different cellular activities involved in bone remodeling has been performed up to 16 days after induction. This allowed us to demonstrate the sequential activity of the different cell types involved in bone remodeling, to study the cellular kinetics of this sequence of events, and to directly measure the duration of each phase of the bone remodeling sequence. A single wave of osteoclasts appeared 3 days after induction, reached a peak of 4-5 days, and then decreased sharply. This was followed by a single wave of mononuclear cells (Baron et al., 1980) within remodeling sites during the reversal phase; they appeared 4 days after induction, reached a peak by day 7, and then decreased sharply. This reversal activity was then followed by osteoblasts forming new bone on top of a reversal cement line in the remodeling sites, starting 6 days after induction and increasing until the end of the experiment. In addition, the synchronization of the system used in this study allowed direct measurement of the duration of the successive steps of the remodeling sequence. The directly measured values have then been compared to previous data calculated from other systems.