Effects of X-irradiation on mineralized nodules of MC3T3-E1 cells. MC3T3-E1 cells were exposed to 0, 0.1, 0.5 and 1.0 Gy of X-irradiation respectively and von Kossa staining was performed on day 14 after irradiation. A represented microscope images. The number of mineralized nodules of osteoblasts was counted and shown in B. Data were expressed as mean ± SD of 3 wells. Significant difference in 0.5 and 1.0 Gy groups was observed compared with the control group (0 Gy) (**p<0.01).