Objective To evaluate the effect of the pulsed Nd:YAG laser irradiation on the survival rate of human periodontal ligament fibroblast (PDLF) at different power and irradiation time settings, and to compare the morphological change of cells before and after irradiation.Methods The cells were cultured and placed into the 96-well tissue culture plates. Cells were divided into groups according to the irradiation time (10 s,20 s,40 s,60 s) and the output energy (0·5 W,1·0 W,1·5 W,2·0 W,2·5 W). After the irradiation, the cell numberwere counted and the survival rateswere calculated. The correlation between the survival rate and irradiation time as well as power output was analyzed.Results No significant reduction of survival rates were found in 10 s group, as well as in 20 s group with 0·5 W, 1.0 W setting·The increase of the power output and increase of the irradiation time caused significant reduction of cell survival rate (P
