Quantitative evaluation of newly formed bone in the alveolar wall surrounding the root during the initial stage of experimental tooth movement in the rat

By using a chronological lead-labelling technique and computer image analysis, the volume of this newly formed bone was evaluated. Rat maxillary first molars were moved mesially by a fixed, closed coil-spring appliance for 6 days using three different magnitudes of initial tensile force (27, 60 and 136 g). Sham-treated rats wearing an inactivated appliance were used for the control study. All animals were injected twice intraperitoneally with lead–disodium EDTA, 3 hr before the beginning and 3 hr before the end of treatment. The unit volumes of newly formed bone (mm3/mm2) were assessed with reference to lead-labelling lines in the alveolar walls of the root socket by computer image analysis. In the control group, two distinct lead-labelling lines indicated continuous bone formation on the mesial side of the root sockets, but only a jagged line was found on the distal side. After experimental mesial tooth movement, only a single lead line could be found on the mesial/pressure side of the root sockets; on the distal/tension side, a wide layer could be detected between the two lead lines. The volume of newly formed bone on the distal/tension side in the experimental groups was significantly greater than that in the control group. However, there was no significant difference in the volumes of newly formed bone among the three experimental groups. The study demonstrates that the volume of newly formed bone in the alveolar walls during the initial stage of tooth movement can be quantified and that the magnitude of the tensile force of tooth movement may not influence directly the volume of newly formed bone in the alveolar wall on the tension side.