Effect of resorption rate and osteoconductivity of biodegradable calcium phosphate materials on the acquisition of natural bone strength in the repaired bone

The purpose of this study was to compare the biodegradation rate and quality of regenerated bone among four materials. A short time period of 8 weeks was chosen to examine early bone healing. The rod-shaped implants of commercially available two β-tricalcium phosphate (β-TCP) ceramics with porosity 60% and 71–80%, respectively, laboratory prepared octacalcium phosphate/gelatin composite (OCP/Gel), which has been proven to have a highly osteoconductive and biodegradable property in rat calvarial defect, and gelatin sponge (Gelatin) were implanted in rabbit tibia defect of 6 mm diameter and 7 mm depth for 2, 4 and 8 weeks. Analyses by μCT, histomorphometry and push-in test were carried out to evaluate the extent of the tissue regeneration and the material biodegradation in the long bone. OCP/Gel and Gelatin were completely resorbed but only OCP/Gel induced cortical bone bridge until 8 weeks that has strength compatible to that of the natural bone. β-TCP (71%-80%) and β-TCP (60%) were not completely resorbed and never induced the amount of new bone formation beyond that by OCP/Gel. The results indicate that the new bone having enough strength could be regenerated if the material shows not only higher biodegradation rate but also higher osteoconductivity.