Low-energy laser irradiation stimulates tooth movement via RANK/RANKL and c-fms/M-CSF

Objectives: Recent studies have demonstrated that low-energy laser irradiation stimulates bone formation in vitro and in vivo. However, very little is known about the effects of laser irradiation on osteoclastogenesis. The receptor activator of the nuclear factor-kB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) system and c-fms/M-CSF system is essential and sufficient for osteoclastogenesis. The present study was designed to examine the effects of low-energy laser irradiation on expressions of RANK, RANKL, OPG, c-fms and M-CSF during experimental tooth movement.

Methods: To induce experimental tooth movement in rats, 10 g of orthodontic force was applied to the molars. Next, a Ga-Al-As diode laser was used to irradiate the area around the moved tooth and the amount of tooth movement was measured for 7 days. Immunohistochemical staining with RANK, RANKL, OPG, c-fms, M-CSF was performed. Real time PCR was also done to elucidate the expression of RANK and c-fms in irradiated rat osteoclast precursor cells in vitro.

Results: In the irradiation group, the amount of tooth movement in the irradiation group was significantly greater than that in the non-irradiation group by the end of the experimental period. Cells that showed positive immunoreactions to the primary antibodies of RANK, RANKL, c-fms, M-CSF were significantly increased in the irradiation group on days 2 and 3, as compared with the non-irradiation group. In contrast, the expression of OPG was not changed. Further, RANK and c-fms expressions in osteoclast precursor cells were detected at an early stage (days 2 and 3) in the irradiation group (P < 0.01, by one-way ANOVA).

Conclusion: These findings suggest that low-energy laser irradiation stimulates the velocity of tooth movement via induction of RANK/RANKL system and c-fms/M-CSF system.

This research was supported in part by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (C:18592252, C: 19592367).