Evaluation of critical size defects of mouse calvarial bone: An organ culture study

Mouse calvarial organ culture has been used widely for the study of bone biology. The purpose of this study was to evaluate the healing potential of neonatal mouse parietal defects in different culture media. The critical size defect (CSD) was also investigated. The parietal bones of neonatal mice were used. Full-thickness, 0.8-mm circular defects were created through the bones from one litter of mice. The bones were divided into three groups: Dulbecco's Modified Eagle Medium (DMEM) group, DMEM/osteogenic medium (OM) group, and OM group. Cultures were analyzed with microcomputed-tomography, dissecting-microscope, phase-contrast-microscope, Von Kossa stain, scanning-electron-microscopy, and energy-dispersive-X-ray. Continuous bone formation of parietal bones was observed in all groups. Defects in the DMEM/OM group showed the highest healing potential and exhibited woven bone formation. Defects in the OM group showed limited bone healing at the defect edge. Defects in the DMEM group showed fibrous healing. The most effective culture medium (DMEM/OM) was used to determine the CSD of mouse calvaria in a separate experiment. Circular defects (diameters: 0.8, 1.0, and 1.5 mm) were made in the parietal bones from another litter of mice. The bones were analyzed with microcomputed-tomography, and phase-contrast-microscopy. The bone filling percentages of different size defects were statistically significant: 1.5-mm defects (4.49%), 1.0-mm defects (47.65%), and 0.8-mm defects (73.45%). In three culture conditions, DMEM/OM was the most effective approach to repair bone defects. A 1.5 mm in diameter, full-thickness parietal defect was found to be the CSD under the DMEM/OM culture conditions.