## 4 Discussion
In the current study, the wavelength of 808 nm was significantly different from the control group on days 1 and 3. Furthermore, on the fifth day, the energy densities of 1, 1.5, and 2.5 J/cm\({}^{2}\) of the wavelength of 808 nm were significant compared to the control group. Therefore, lower energy densities can be effective in the long-term. Research conducted by [PERSON] et al. in 2015 aimed to investigate the effect of PBMT on the proliferation and viability of dental pulp stem cells. In this research, cells were isolated from two third molars. The laser used in this research was InGaIP with a wavelength of 660 nm and a power of 30 mW, and densities of 0.5 J/cm\({}^{2}\) and 1 J/cm\({}^{2}\). Proliferation, viability, and mitochondrial activity were evaluated 24, 48, 72, and 96 h later. In addition,apoptosis and events related to the cell cycle were investigated by flow cytometry. In this research, they concluded that the group that was irradiated with an energy density of 1 J/cm\({}^{2}\) had increased proliferation and had a significant difference at 72 h and 96 h compared to the control group [42]. In our study, although a different cell source was used, the laser had a similar wavelength (660 nm) and energy densities (1, 1.5, 2.5, 4 J/cm\({}^{2}\)). However, the power we used was 150 mW, and MTT was checked 1, 3, and 5 days after laser irradiation. In the current study, it was observed that the results obtained from the wavelength of 660 nm with an energy density of 1 J/cm\({}^{2}\) on days 1, 3, and 5 were insignificant compared to the control group, which is in line with the previous study. In addition, at the wavelength of 660 nm at any time, the difference in energy densities was not significant. These results can be attributed to the lower power of the laser device and the lower penetration of this wavelength. In the study by [PERSON] et al., the effect of different wavelengths on the proliferation and differentiation of bone marrow stem cells was investigated. This research extracted mesenchymal stem cells from rabbit iliac bone marrow. A control group and eight laser groups were considered: Infrared (810 nm), Red (660 nm), Green (532 nm), Blue (485 nm), IR-R, IR-B, R-G, and B-G. The energy density was 4 J/cm\({}^{2}\). Laser therapy was repeated every day for 21 days, and proliferation, bone, and cartilage differentiation were checked. Cell proliferation was evaluated after 10 days. The combination of 532 nm and 485 nm had the most cell proliferation, and 532 nm without any combination decreased proliferation. There was no significant difference between the control and other groups except for the 485 nm and 532 nm groups. Wavelengths at 660 nm and 810 nm increased proliferation, and 660 nm had a better effect. Wavelengths at 660 nm and 810 nm had a stimulating effect on osteogenesis, but the impact of the wavelength at 532 nm was inhibitory [33]. In the current study, BFP stem cells with wavelengths of 635, 660, 808, and 980 nm were used during two sessions of laser therapy with a similar energy density, and we concluded that the wavelength of 808 nm was significant on the first and third days compared to the control group which was in line with the mentioned study. On the fifth day, the wavelength of 808 nm with energy densities of 1, 1.5, and 2.5 J/cm\({}^{2}\) was significant compared to the control group, and the wavelength of 980 nm was significant compared to the other wavelengths, showing that higher wavelengths in the near-infrared region are more effective. This can be related to the different mechanisms of signaling pathways and needs further study in the future. The study of [PERSON] et al. investigated the effect of PBMT on the proliferation and differentiation of HDPSC isolated from Healthy Dental Pulp and inflamed pulp. Healthy and inflamed dental pulp stem cells were prepared from different patients and were exposed to laser radiation at a wavelength of 660 nm with four densities of 0.05, 0.30, 7, and 42 J/cm\({}^{2}\).