Effects of continuous and released compressive force on osteoclastogenesis invitro.

Objective: Compressive force has been found to be catabolic to alveolar bone during orthodontic tooth movement. This study quantified the fusion of mononuclear RAW 264.7 cells (a murine osteoclastic-like cell line) into multinucleated osteoclasts under a hydrostatic pressure-generated mechanical compression-the new model of various magnitudes and durations. Methods: RAW 264.7 cells were subjected to 0.3, 0.6 or 0.9 g/cm2 of compressive force by an acrylic cylinder custom-made by laser cutting or no compressive force for 4 days during osteoclastogenic induction. TRAP-positive multinucleated cells were quantified. For the release from force experiment, osteoclastogenesis was induced by 0.6 g/cm2 mechanical stimuli for 0, 1, 2, 3 or 4 days. Cell viability, TRAP-positive multinucleated cells, DCSTAMP and Cathepsin K (CTSK) gene expression were evaluated 4 days after release from force. Results: Compressive force at 0.6 and 0.9 g/cm2 significantly increase the number of TRAP-positive multinucleated cells (P < 0.05). Release from continuous mechanical compression after 4 days significantly elevated the number of TRAP-positive multinucleated cells and DCSTAMP and CTSK mRNA expression, with no adverse effects on cell viability (P < 0.05). Conclusions: Continuous stimulation with compressive force induced osteoclastogenesis in RAW 264.7 cells by enhancing DCSTAMP and CTSK expression, which provides new understanding of bone remodeling during orthodontic treatment.

Effects of compressive stress combined with mechanical vibration on osteoclastogenesis in RAW 264.7 cells.

OBJECTIVES: To investigate the effects of compressive force and/or mechanical vibration on NFATc1, DCSTAMP, and CTSK (cathepsin K) gene expression and the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells in RAW 264.7 cells, a murine osteoclastic-like cell line. MATERIALS AND METHODS: RAW 264.7 cells were subjected to mechanical vibration, compressive force, or compressive force combined with vibration. Cell viability and the numbers of TRAP-positive multinucleated cells were evaluated. NFATc1, DCSTAMP, and CTSK gene expressions were analyzed using real-time quantitative reverse transcription polymerase chain reaction. RESULTS: Compressive force combined with mechanical vibration significantly increased the numbers of TRAP-positive multinucleated cells but did not significantly affect cell viability. In addition, compressive force combined with mechanical vibration significantly increased NFATc1, DCSTAMP, and CTSK mRNA expression compared with compressive force or vibration alone. CONCLUSIONS: Compressive force combined with mechanical vibration induces osteoclastogenesis and upregulates NFATc1, DCSTAMP, and CTSK gene expression in RAW 264.7 cells. These results provide more insight into the mechanisms by which vibratory force accelerates orthodontic tooth movement.