Bulk Carbonate Apatite Materials Prepared From Calcium Phosphate Cements

Objectives: Phase pure bulk carbonate apatite materials prepared at ambient temperatures are useful for several applications including as bio-dosimeters and as references for human enamel, dentin, and bone minerals. This study was conducted to determine the feasibility of preparing bulk carbonate apatite with a wide range of carbonate contents.
Methods: A calcium phosphate cement system, previously developed for bone defect repair applications (Chow and Takagi 2001), was used to prepare bulk carbonate apatite. The cement uses tetracalcium phosphate and dicalcium phosphate as starting materials and forms nano-sized hydroxyapatite crystals as the only product. When carbonate and sodium are included in the cement ingredients, these components are also incorporated into the apatite crystal structure of the product. In the present study, various amounts of NaHCO₃, KHCO₃ or combinations thereof are included in the cement powder, and a phosphate solution was used as the cement liquid. Hardened cement samples were incubated in a physiological-like solution for 24h and then dried in air before being characterized by XRD, FTIR and analyzed for carbonate and sodium contents.
Results: (1) XRD results showed that in all instances a low crystalline apatite was the only product formed, (2) a wide range of carbonate (1.08 mass% to 5.80%) was incorporated into the apatite structure, (3) FTIR analysis suggests that the carbonate was type-b carbonate, (4) a wide range of sodium (0% to 2.87%) also was incorporated into the apatite structure, (5) it is possible to control the amounts of carbonate and sodium incorporation independently.
Conclusions: The results suggest that this method can be used to prepare bulk carbonate apatite materials for dosimetry purposes and as test substrates that have carbonate and sodium contents nearly identical to those in human hard tissue minerals.