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Bone-forming osteoblasts and bone-resorbing osteoclasts play an important role during maintenance, adaptation and healing of bone, and both cell types are influenced by physical activity. The aim of the present study was to investigate the effect of a narrow mechanical stimulation window on osteoblast- and osteoclast-like cells. Primary human cells were cultured on a bone-like structure (dentine) and three-point bending with approximately 1,100 microstrain was applied to the dentine at varying frequencies (0.1 and 0.3 Hz) and duration (1, 3 and 5 min daily over 5 days) resulting in different patterns of mechanical stimulation of osteoblast- and osteoclast-like cells. The longest stimulation (5 min at 0.1 Hz) induced a significant increase in osteoblast alkaline phosphatase activity and a significant decrease in osteoprotegerin (OPG) production, and resulted in a significant increase in the soluble receptor activator of NF-κB ligand (sRANKL)/OPG ratio towards sRANKL in comparison to the unstimulated osteoblast-like cells. All stimulations caused a significant decrease in collagen type 1 synthesis. Stimulation for 1 min at 0.3 Hz decreased the fusion and resorption activity of the osteoclast-like cells. These results demonstrate a direct effect of mechanical stimuli on osteoblast-like cells as well as on osteoclast formation and activity in vitro. The change in the sRANKL/OPG ratio towards the stimulation of osteoclastogenesis stresses the necessity to investigate the effect of the same stimulation parameter on the co-culture of both cell types.

Proliferation was significantly enhanced by the native cancellous bone, Allomatrix, and BMP-2 and decreased by the PES-processed cancellous bone. The osteogenic differentiation was significantly enhanced by BMP-2 and the two commercial DBM products and decreased by PES-sterilized cancellous bone. All tested materials revealed a high donor-dependent variability. This is the first comparative study on the osteoinductivity of bony allografts frequently used in clinic.