ABSTRACT
Objective To study the effects of early mechanical strain magnitude on formation and differentiation of osteoclasts. Methods RAW 264.7 cells induced by macrophage colony-stimulating factors and osteoclast differentiation factors were subjected to 0, 1 000, 1 500, 2 000, 2 500 and 5 000 με mechanical straining for three days. The morphological changes, number of osteoclasts and proliferation of precursor cells were determined at day 7. The activity of the tartrate-reaistant acid phosphatase (TRAP) in the culture medium was detected at days 4 and 7. Results The number of osteoclasts was decreased in 2 500 με group, while it was increased in 5 000 με group. The proliferation of precursor cells was increased in 2 000 and 2 500 με group, while it was decreased significantly in 5 000 με group. There was no significant difference in the number of osteoclasts and proliferation of precursor cells among 1 000 με group, 1 500 με group and 0 με group. The activity of TRAP was decreased in 1 000, 1 500, 2 000, 2500 and 5 000 με groups at days 4 and 7 when compared with με group. Conclusions Early mechanical straining plays a direct role in formation and differentiation of osteoclasts. The high strain magnitude within physiological load inhibits osteoclast formation, while high strain magnitude beyond physiological load stimulates osteoclast formation. Low strain magnitude has nearly no impact on formation of osteoclasts. Early mechanical straining may inhibit differentiation of osteoclasts.