Role of interleukin-6 in orthodontically induced inflammatory root resorption in humans

• Published in: Korean journal of orthodontics (2012) Vol. 43; no. 6; pp. 294 - 301
• Main Authors: Kunii, Ryuichi, Yamaguchi, Masaru, Tanimoto, Yasuhiro, Asano, Masaki, Yamada, Kunihiko, Goseki, Takemi, Kasai, Kazutaka
• Format: Journal Article
• Language: Korean
• Published: Korean Association of Orthodontists 31.12.2013; 대한치과교정학회
• Subjects: Root resorption; Orthodontic force; Osteo/odontoclastogenesis; Interleukin-6
• ISSN: 2234-7518; 2005-372X

Objective: To determine the interleukin (IL)-6 levels in gingival crevicular fluid (GCF) of patients with severe root resorption after orthodontic treatment and investigate the effects of different static compressive forces (CFs) on IL-6 production by human periodontal ligament (hPDL) cells and the influence of IL-6 on osteoclastic activation from human osteoclastic precursor (hOCP) cells in vitro. Methods: IL-6 levels in GCF samples collected from 20 patients (15 and 5 subjects without and with radiographic evidence of severe root resorption, respectively) who had undergone orthodontic treatment were measured by ELISA. The levels of IL-6 mRNA in hPDL cells and IL-6 protein in conditioned medium after the application of different uniform CFs (0, 1.0, 2.0, or 4.0 $g/cm^2$ for up to 72 h) were measured by real-time PCR and ELISA, respectively. Finally, the influence of IL-6 on mature osteoclasts was investigated by using hOCP cells on dentin slices in a pit-formation assay. Results: Clinically, the IL-6 levels were significantly higher in the resorption group than in the control group. In vitro, IL-6 mRNA expression significantly increased with increasing CF. IL-6 protein secretion also increased in a time- and magnitude-dependent manner. Resorbed areas on dentin slices were significantly greater in the recombinant human IL-6-treated group and group cultured in hPDL cell-conditioned medium with CF application (4.0 $g/cm^2$) than in the group cultured in hPDL cell-conditioned medium without CF application. Conclusions: IL-6 may play an important role in inducing or facilitating orthodontically induced inflammatory root resorption.