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Intermittent Force Induces High RANKL Expression in Human Periodontal Ligament Cells

Intermittent compressive force stimulates bone resorption in orthodontic treatment. This study examined the molecular mechanism in human periodontal ligament (PDL) cells stimulated by an intermittent force. PDL cells were subjected to compressive force (2.0 or 5.0 g/cm2) for 2–4 days. Continuous or intermittent force was applied all day or for 8 hrs per day, respectively. At days 3 and 4, cell damage was less with intermittent force than with continuous force. At day 4, RANKL and IL-1β expressions were greater with intermittent force than with continuous force. An IL-1 receptor antagonist inhibited the compressive force-induced RANKL expression. These findings indicate that IL-1β is an autocrine factor regulating compressive force-induced RANKL expression in PDL cells, and that intermittent force can effectively induce RANKL in PDL cells with less cell damage.