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Receptor activator of nuclear factor kappa β ligand (RANKL) activates osteoclast differentiation, whereas this activity is blocked by osteoprotegrin (OPG), so that the relative expression of these 2 proteins might contribute to bone and root resorption during orthodontic tooth movement. We describe experiments with RANKL and OPG mRNA expression in rats subjected to orthodontic forces. It was hypothesized that the ratios of RANKL to OPG expression would increase during root resorption processes.

Fixed Sentalloy (GAC, Bohemia, NY) closed-coil springs capable of delivering approximately 100 g of force were applied for mesial movement of the mandibular left first molar in 9 male, 7-week-old Wistar rats; the right mandibular molar was used as an internal control for each animal. After 14 days, the rats were killed; tissues from 2 rats were examined by paraffin histology, and high-quality …