146: Compression force induces inflammatory cytokines via notch signaling in periodontal ligament cells

Abstract

Objective: Orthodontically induced inflammatory root resorption (OIIRR) is one of the most difficult to predict accidental symptom in orthodontic treatment. Orthodontic forces are known to produce mechanical damage and inflammatory reactions in the periodontal ligament (PDL). Notch signaling pathway is a highly conserved cell signaling system that plays an important role in various cell differentiation processes including bone homeostasis. However, the role of Notch signaling in tooth movement and root resorption in orthodontic treatment has not fully understood. We examined the effects of orthodontic force on Notch and Jagged1(Notch ligand) expression in human PDL (hPDL) cells in vitro, andthe expression of Jagged1, RANKL and IL-6 in root resorption area during experimental tooth movement in rats. Materials and Methods: Different compression forces (CF) were applied to hPDL cells for up to 24 h. With/without γ -secretase inhibitor (GSI; inhibitor of Notch signaling). The expression of Jagged1, RANKL and IL-6 mRNA was determined by using real-time PCR. In animal study, rats were subjected to an orthodontic force of 10 or 50 g with a closed coil spring. Experimental tooth movement was undertaken for 7 days. Each sample was prepared for HE and immunohistochemistry staining for TRAP, Jagged1, RANKL and IL-6 in root resorption area. Results: CF increased the expression of Jagged1, RANKL and IL-6mRNA from hPDL cells. Moreover, GSI suppresses CF-induced expression of these mRNA. On days 7, immunoreactivity for Jagged1, RANKL and IL-6 was detected in odontoclasts with an orthodontic force of 50 g, but not 10 g. Conclusions: These results indicate that CF may modulate the mRNA expression of RANKL and IL-6 via Notch signaling in hPDL cells. Notch signaling might be involved in the progress of inflammation in PDL tissue and the incidence of severe root resorption during orthodontic treatment.