Controversial effects of low level laser irradiation on the proliferation of human osteoblasts

Low level laser irradiation (LLLI) is the application of red or near infrared lasers irradiating between 600-1100 nm with an output power of 1-500 mW. Several researches indicate that LLLI modulates cellular mechanisms and leads to enhance proliferation. Although the biological mechanisms are not fully understood, it is known that the effects depend on several parameters such as wavelength, irradiation duration, energy level, beam type and energy density. The aim of this study is to investigate the effect of low level laser irradiation at varying energy densities with two different wavelengths (635 nm and 809 nm) on the proliferation of human osteoblasts in vitro. The cells are seeded on 96 well plates (105cells/well) and after 24 h incubation cells are irradiated at energy densities 0.5 J/cm2, 1 J/cm2 and 2 J/cm2. Cell viability test is applied after 24 h, 48 h and 72 h in order to examine effects of laser irradiation on osteoblast proliferation. 635 nm light irradiation did not appear to have significant effect on the proliferation of osteoblasts as compared to the control. On the other hand, 809 nm laser irradiation caused significant (p ≤ 0.01) biostimulation effect on the osteoblast cell cultures at 48 h and 72 h. In conclusion, irradiation of both wavelengths did not cause any cytotoxic effects. 809 nm light irradiation can promote proliferation of human osteoblasts in vitro. On the other hand, 635 nm light irradiation has no positive effect on osteoblast proliferation. As a result, LLLI applied using different wavelengths on the same cell type may lead to different biological effects.