Comparison in physical properties of synthetic carbonate apatite and allogeneic bone graft substitute

Abstract: Objectives: Autogenous bone have been the gold standard for bone augmentation, but invasion to the healthy site remain as a concern. There has been a demand for bone graft substitutes which has potential to be replaced with autogenous bone. We have developed a novel bone graft substitutes "Cytrans Granules (Cyt)" consisting synthetic carbonate apatite, which is the main component of human bone. It is reported that Cyt shows osteoconductivity at similar or higher level of allogeneic bone graft substitutes, but the mechanism behind have not been clarified. In this study, we have compared the composition, crystal structure and resorption property of Cyt to synthetic Hydroxyapatite (HAp) and freeze-dried bone allograft (FDBA) as an allogeneic bone.Methods: Cyt was used as test sample, FDBA and three types of HAp (HAp-1, HAp-2, HAp-3) were used as control. Composition and crystal structure were evaluated by using Fourier transform infrared spectroscopy (FT-IR) and powder X-ray diffraction (XRD). Crushing strength was measured by universal testing machine. Resorption property was measured as amount of calcium ion dissolved from the samples in neutral solution (pH7.3) and weak acidic solution (pH5.5).Results: XRD pattern showed that all samples have apatitic crystal structure. FT-IR spectrum showed that Cyt and FDBA contains carbonate group. Synthetic Hydroxyapatite had higher crushing strength, followed by FDBA and Cyt. Among all samples, dissolution at neutral solution was at low level. In weak acidic solution, Cyt and FDBA showed higher rate of dissolution compared to synthetic Hydroxyapatite.Conclusions: It was confirmed that Cyt and FDBA are Hydroxyapatite containing carbonate group. Cyt had composition, crystal structure and mechanical properties similar to those of FDBA. From the result of dissolution test, Cyt and FDBA were stable in neutral body fluid, and were dissolved in weak acidic solution resembling the pH produced by osteoclast. These results indicate that these two materials could be resorbed by osteoclasts. It is suggested that Cyt has similar characteristics to allogeneic bone, which may be the reason for Cyt to exhibited osteoconductivity at similar or higher level compared to allogeneic bone.