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We used radiological and histological analyses to evaluate the effects of mechanical barrier permeability in a rat model of calvarial guided bone augmentation (GBA). The calvaria of 20 rats were exposed, and one of four types of plastic caps (an occlusive cylindrical plastic cap; a plastic cap with no top; a plastic cap with three holes; and a plastic cap with four holes) was randomly placed on both sides. Newly generated bone in the plastic caps was evaluated with micro-computed tomography (micro-CT) and histological analysis. Micro-CT volumetric analysis and decalcified hematoxylin and eosin-stained sections showed that GBA barrier permeability was inversely associated with the quantity of augmented bone obtained. Masson's trichrome staining showed that collagen in newly generated bony tissue was more mature in plastic caps with three holes than in those with more-permeable or more-occlusive barriers. Bone augmentation was inhibited in specimens exhibiting invasion of soft tissue through penetrating holes, and barrier permeability was associated with the quantity of augmented bone developed. In conclusion, moderate barrier permeability is optimal for development of mature augmented bone.

Background Osteoclast precursor cells are constitutively differentiated into mature osteoclasts on bone tissues. We previously reported that the continuous stimulation of RAW264.7 precursor cells with compressive force induces the formation of multinucleated giant cells via receptor activator of nuclear factor κB (RANK)-RANK ligand (RANKL) signaling. Here, we examined the bone resorptive function of multinucleated osteoclasts induced by continuous compressive force. Material/Methods Cells were continuously stimulated with 0.3, 0.6, and 1.1 g/cm 2 compressive force created by increasing the amount of the culture solution in the presence of RANKL. Actin ring organization was evaluated by fluorescence microscopy. mRNA expression of genes encoding osteoclastic bone resorption-related enzymes was examined by quantitative real-time reverse transcription-polymerase chain reaction. Mineral resorption was evaluated using calcium phosphate-coated plates. Results Multinucleated osteoclast-like cells with actin rings were observed for all three magnitudes of compressive force, and the area of actin rings increased as a function of the applied force. Carbonic anhydrase II expression as well as calcium elution from the calcium phosphate plate was markedly higher after stimulation with 0.6 and 1.1 g/cm 2 force than 0.3 g/cm 2 . Matrix metalloproteinase-9 expression decreased and cathepsin K expression increased slightly by the continuous application of compressive force. Conclusions Our study demonstrated that multinucleated osteoclast-like cells induced by the stimulation of RAW264.7 cells with continuous compressive force exhibit high dissolution of the inorganic phase of bone by upregulating carbonic anhydrase II expression and actin ring formation. These findings improve our understanding of the role of mechanical load in bone remodeling.

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