title: Role of interleukin-6 in orthodontically induced inflammatory root resorption in humans.
abstract: 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.
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Kunii
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: Department of Dental Biomaterials, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tanimoto
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Asano
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Yamada
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
authors.forename: Takemi
authors.initials: T
authors.lastname: Goseki
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Kasai
keywords: Interleukin-6; Orthodontic force; Osteo/odontoclastogenesis; Root resorption