It is well-known that orthodontic treatment usually causes some discomfort and pain to the patients. Recently, it has been reported that low-power laser irradiation is effective in reducing the pain accompanying tooth movement. However, the mechanism of such pain relief cannot be elucidated. Since high levels of prostaglandin (PG) E2 and interleukin (IL)-1 beta are found in the periodontal ligament (PDL) during tooth movement, and both factors are involved in the induction of pain, the effects of low-power laser irradiation on PGE2 and IL-1 beta production in stretched human PDL cells were studied in vitro. The PDL cells, derived from healthy premolars extracted for orthodontic treatment, were utilized for experiments. Cells were seeded in flexible-bottomed culture plates, and the bottom of each plate was elongated (18% increase) under vacuum at 6 cycles per min for 1, 3, or 5 days. The stretched cells were irradiated with a Ga-Al-As low-power diode laser (60 mW) once a day for 3, 6, or 10 min (from 10.8 to 36.0 J) for 1, 3, or 5 days. PGE2 and IL-1 beta levels in the medium were measured by radioimmunoassay. In response to mechanical stretching, human PDL cells showed a marked elevation in PGE2 production in a time-dependent manner. IL-1 beta production was also elevated, but this remained constant. The increase in PGE2 production was significantly inhibited by laser irradiation in a dose-dependent manner. The increase in IL-1 beta production was also significantly inhibited by laser irradiation, although the inhibition was only partial.(ABSTRACT TRUNCATED AT 250 WORDS)

Occlusal trauma is caused by excessive occlusal forces and is associated with alveolar bone loss. In the periodontal ligament (PDL), which primarily receives the occlusal force, there is increased prostaglandin E (PGE2) synthesis in response to mechanical stress, and many studies have shown that PGE2 is involved in the pathogenesis of periodontal diseases. Recently, two isozymes of cyclooxygenase, COX-1 and COX-2, which are key enzymes in prostaglandin (PG) biosynthesis, were identified and COX-2 was induced following the activation of cells by a variety of proinflammatory agents. However, the biosynthetic pathway of mechanical stress-dependent PGE2 from PDL cells has not been well understood. When cyclic tension force was applied to human PDL cells (18% increase in surface area), PGE2 release to the culture medium increased in a time-dependent manner. As analyzed by semi-quantitative PCR, COX-2 mRNAs, while hardly detectable in controls, increased dramatically on day 3 and 5 in response to tension force. In contrast, COX-1 mRNAs detected in controls were not affected by tension force. By immunocytochemical staining, COX-2 protein was significantly increased by tension force around the unstained cell nucleus in a time-dependent manner. When NS-398, a selective COX-2 inhibitor, was added to the medium, PGE2 synthesis increased by tension force was completely inhibited. These results indicate that tension force induces COX-2 in human PDL cells and that this induction is responsible for the augmentation of PGE2 production stimulated by tension force. Since selective COX-2 inhibitors have less adverse effects compared with those of non-steroidal anti-inflammatory drugs, they may be of therapeutic benefit for treatment of periodontal disease accompanying traumatic occlusion.

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ObjectiveTo 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.MethodsIL-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/cm2 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.ResultsClinically, 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/cm2) than in the group cultured in hPDL cell-conditioned medium without CF application.ConclusionsIL-6 may play an important role in inducing or facilitating orthodontically induced inflammatory root resorption.