Objective      To investigate the effect of periodontal ligament stem cells (PDLSCs) on osteoclasts differentiation during periodontal remodeling in order to elucidate the roles of static force and inducible factors in the regulation of osteoclasts differentiation by PDLSCs.       Methods      PDLSCs were isolated and cultured from freshly extract teeth by using the limiting dilution technique. Mononuclear cells of umbilical cord blood (UBMC) were separated by density gradient centrifugation. After identif

ication

the two kinds of cells were co-cultured in direct- and in Transwell co-culture system. The co-culture system were further treated by static force (120 kPa for 1 h per day

for 3 d)

or inducible factors (1×10

-8

mol/L α-25(OH)

2

D

3

and 1×10

-6

mol/L PGE

2

for 7 d) to induce osteoclast-like cells (OLC). The cells without treatment served as control. Cell morphology was observed by phase contrast microscopy. TRAP staining was used to identify the OLCs. And the bone-resorption capacity was assessed by lacunae forming ability on bone slice.       Results      Under static force

there were more OLCs in direct co-culture system than in the Transwell co-culture system (P0.01). While

the treatment of inducible factors resulted more OLCs in the Transwell co-culture system than in direct co-culture system (P0.01).       Conclusion      PDLSCs promote mononuclear cells differentiate into OLC

especially under the continuous static force and the two cells contact directly.