摘要： Low-level laser irradiation (LLLI) could be useful for the stimulation of stem-cell proliferation. LLLI has important physiological properties which increase the mitochondrial activity of cells. This study aimed to evaluate the biological effect of LLLI on cryopreserved stem cell from human exfoliated deciduous teeth (SHEDs). Cryopreserved and characterised SHEDs from a previous study were used for this study. The SHEDs were exposed to GaAlAs diode laser with energy densities of 1.2 (Group 2) and 2 J cm?2 (Group 3). For the control group (Group 1), SHEDs were cultured in culture medium including Dulbecco’s modified Eagle’s Medium supplemented with 15% foetal bovine serum, 1% L-glutamine, 1% penicillin-streptomycin, 1% gentamycin, and amphotericin-B. The cells in the experimental groups were irradiated as previously indicated, and after the irradiation were incubated for 0, 24, 48, and 72 h at 37 °C in 5% CO2. Proliferation of SHEDs was analysed by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay at incubation periods of 0, 24, 48, and 72 h after the single-laser irradiation. The effects of laser irradiation on apoptosis of SHEDs at the last incubation period (72 h) were detected with the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) method. Group 2 showed increased TUNEL-positive cells compared to Groups 1 and 3, but no significant differences between the three groups were observed (p > 0.05). Comparing Groups 2 and 3 to Group 1, the proliferation of SHEDs significantly increased after 24, 48, and 72 h (p < 0.05), but no significant differences were observed between the groups at 0 h (p > 0.05). In addition to this, at 72 h, Group 3 showed significantly higher proliferative effect on SHEDs compared to Group 2 (p > 0.05). In terms of clinical usage of long-term cryopreserved SHEDs, we can recommend to clinicians and researchers that prior to their use, LLLI may be used to increase the proliferation rate.