Abstract: Abstract: Objective To provide fundamental data for understanding the difference between various treatment fluids and to investigate the best treatment fluid for teeth replantation. Methods 277 premolars extracted for orthodontics will be collected to simulate the avulsed teeth and then soaked in HBSS, milk and 2% NaF at different drying time. Trypan blue staining technique will be used to detect the viability of PDL cells, and then subjected to statistical analysis using analysis of variance. And the morphologic changes of PDL will be observed under the microscope. Results The viability of PDL cells soaked in HBSS showed higher viability（94.60±0.72）than that in 2%NaF（84.37±3.98) at 30mins; At 60mins and 120mins, the viability of PDL cells soaked in HBSS(63.03±3.05、13.38±1.04) was higher than that in milk(48.9±3.47、5.73±1.29) and 2%NaF(51.93±1.72、8.60±0.74) respectively. Conclusions All the three solutions have repaired effect on viability of the PDL cells ,and HBSS is the best one.

Key words: avulsed teeth, periodontal ligament, treating solution