The effect of low-power laser irradiation on bone formation in vitro were assessed. Osteoblast-like cells were isolated from rat calvariae of 21d rat fetuses. The cultured calvarial cells were irradiated with a low-power laser (830 nm, 60 mW) one time only or once daily for 21d at various energy doses (10.8-108 J/day). The number and the total area of mineralized bone modules that had developed in the culture dish on day 21 were evaluated. DNA content, alkaline phosphatase (ALP) activity and the amount of extra-cellular collagen were also measured. Calcium and phosphorus in bone nodules were examined with an X-ray microanalyzer. Laser irradiation significantly increased the number and the total area of bone nodules in a dose-dependent manner. Cell proliferation and ALP activity in the irradiation group were higher in the early and middle culture periods, while the collagen content was higher in the middle an late periods compared with the control. Calcium and phosphorus were both higher in the irradiation group. These findings indicate that laser irradiation may play a principal role in stimulating differentiation of osteoblasts during the early stage of the culture, resulting in increased bone formation through acceleration of bone nodule maturation.
The effects of low-power laser irradiation on prostaglandin (PG)E2 and interleukin(IL)-1(beta) production in stretched human periodontal ligament (PDL) cells were assessed in vitro. PDL cells derived from healthy premolars were utilized for these experiments. Cells were seeded in flexible-bottom culture plates and elongated (18% increase) under a vacuum at 6 cycles per minute for 1 to 5 days. The stretched cells were irradiated with a Ga-Al-As low-power diode laser (60 mW) once a day for 3 to 10 minutes for 1 to 5 days. PGE2 and IL-1(beta) levels in the medium were measured by radio immunoassay. Human PDL cells showed a marked elevation in PGE2 and IL-1(beta) production in response to mechanical stretching. 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 inhibited by laser irradiation, although the inhibition was only partial under this irradiation condition. Since high levels of PGE2 and IL-1(beta) are found in the PDL when teeth are moved during orthodontic treatment and since both factors are involved with the induction of pain, the inhibitory effects of laser irradiation on PGE2 and IL-1(beta) production suggest that laser irradiation may have therapeutic benefits in relieving the pain that accompanies orthodontic treatment.
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