TNF-<i>α</i> and RANKL facilitates the development of orthodontically-induced inflammatory root resorption

Abstract

Background: The objective of this study was to determine the levels of tumor necrosis factor-alpha (TNF-α) and receptor activator of NF-kB ligand (RANKL) in the gingival crevicular fluid (GCF) in patients with severe root resorption after orthodontic treatment. Materials and Methods: Ten patients who had been receiving orthodontic treatment (5-control subjects and 5-severe root resorption subjects) participated in this study. GCF was collected from all patients. Subjects with severe root resorption (>1/3 of the original root length) were identified. Control group subjects with no loss of the root structure undergoing orthodontic treatment were also identified. The GCF was collected non-invasively from the mesial and distal sides of each of the upper central and lateral incisors using filter paper strips. The eluted GCF was used for a Western blot analysis with Antibodies against TNF-α and soluble RANKL (sRANKL). Ten male 6-week-old Wistar rats were subjected to orthodontic force of 50 g to induce a mesially tipping movement of the upper first molars for 7 days. The expression levels of TNF-α and RANKL proteins were determined in periodontal ligament (PDL) by immunohistochemical analysis. Results: The Western blot analysis showed that the TNF-α and sRANKL expressions were significantly higher in the severe root resorption group than in the control group. In the experimental tooth movement in vivo, resorption lacunae with multinucleated cells were observed in 50 g group. The immunoreactivity for TNF-α and RANKL was detected in PDL tissue subjected to the orthodontic force on day 7. Conclusion: These results suggest that TNF-α and RANKL play important roles in inducing or facilitating the development of orthodontically-induced inflammatory root resorption (OIIRR).