Fig. 2

Effect of different preconditioning strategies on apoptosis of PDLSCs. Preconditioned and non-preconditioned PDLSCs were collected and passaged to the 4th generation. After 3 days of cultivation only supplemented with 10% FBS, the cells were collected and stained with annexin V-FITC and propidium iodide (PI). Apoptosis was tested by flow cytometry. A–D Apoptosis images of four groups. E Significant difference could be found between control group and pretreatment groups while no significant difference was noted among three pretreatment groups. (No matching letters (e.g.: a, b) above any two column charts represents a significant difference between these two groups (p < 0.05), while the appearance of any matching letters (e.g.: a, a) means that there is no significant difference among groups (p > 0.05). Data are expressed as mean ± SD)