RESUMEN
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.
RESUMEN
The aim of this investigation was to examine the effects of experimental occlusal hypofunction, and recovery, on mandibular bone mineral density (BMD) using peripheral quantitative computed tomography. A metal cap was inserted between the upper and lower incisors of 40 male Wistar rats (aged 6 weeks) to prevent the molars from biting. The rats were divided into two equal groups: 'hypofunction' and 'recovery' animals. In addition, there was a third group comprising 20 control animals. The recovery animals were anaesthetized at 4 weeks in order to remove the metal cap using pliers. The rats were killed under deep anaesthesia, after which the mandibles were immediately removed and fixed in 10 per cent neutral formalin. After 2, 4, 6, and 8 weeks, BMD was measured in the cancellous and cortical bone in the first molar region. Data were analysed using one-way analysis of variance. At 6 and 8 weeks, in the hypofunction group, cancellous bone density decreased on the buccal and lingual sides, at the bifurcation of the root and at the root apex. In the recovery group, the density on the buccal and lingual sides had recovered to the normal levels, compared with the control group. However, density of the bifurcation of the root and the root apex recovered by only 30 and 50 per cent, respectively. At 6 and 8 weeks, cortical bone density in the hypofunction group had reduced in the lingual basal and lingual middle cortical bone areas. Cortical bone density in the lingual basal and lingual areas recovered to control group levels at 6 weeks. Recovery of occlusal hypofunction may restore decreased BMD of both cancellous and cortical bone.