Orthodontic Department, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Objective: Receptor activator for nuclear factor kappa B ligand (RANKL), which is also called osteoclast differentiation factor, is an important regulatory factor in osteoclast maturation. Knowledge of bone and cementum similarities and RANKL role in bone resorption suggests the possibility of a role for this protein in root resorption induced by orthodontic tooth movement. The aim of this study is to examine the expression of RANKL mRNA during root resorption induced by orthodontic tooth movement in rats. Materials and Methods: In order to move maxillary right first molars mesially fixed Ni-Ti closed coil springs (Dentaurum®-Germany) were tightened to the teeth. Sample consisted of 20 male seven week old Wistar rats. For each animal, the contralateral tooth was used as, an internal control. At day 21 the rats were sacrificed. Tissues from 10 rats were embedded in paraffin for histologic examination. Scratched material from resorptive lacunae on mesial sides of the roots of the other ten rats was used for extracting mRNA by RTPCR. Results: The histologic sections, analyzed histomorphometrically, showed a significant increase in root resorption in the case group as compared to the control (p<0.001). Densitometric studies of RANKL mRNA expression band on gel electrophoresis showed significantly increased RANKL expression in the resorptive lacunae of the case group (p<0.001). Conclusion: This observation indicates increased RANKL expression is associated with orthodontic tooth movement induced root resorption.