Elaboration of high temperature sintered hydroxyapatite for odontological applications

Abstract

Stoichiometric hydroxyapatite is a bioreabsorbable material and has been used for bone repair and shot blasting of titanium implants. However, the stoichiometric hydroxyapatite is not stable above 1130oC to 1200oC, limiting the heat treatment performed on the biomaterial to increase the mechanical strength of the granules obtained from the synthesis process at room temperature. Therefore, the aim of this work was the elaboration of calcium phosphate with Ca/P molar ratio of 1.7. With this Ca/P molar ratio, the formation of stable hydroxyapatite is possible up to approximately 1360oC, according to the CaO-P2O5 equilibrium diagram. Calcium phosphate was prepared by the wet method of synthesis using calcium carbonate and phosphoric acid as raw materials. The material obtained from the synthesis consists of agglomerated particles with a size between 20 nm and 70 nm, while the size of the agglomerates varied from a few microns to approximately 200 µm. The results of the thermal analysis and X-ray diffraction showed that the hydroxyapatite is stable between 750oC and 1350oC. The heat treatment performed at 1300oC confirmed that there is no transformation of hydroxyapatite into tricalcium phosphate above 1130oC to 1200oC as it happens for stoichiometric hydroxyapatite. In the heat treatment carried out at 1300oC for 1 hour, hydroxyapatite was obtained with 67 % of porosity whereas in the treatment of 4 hours at the same temperature the porosity was 17 %. Hydroxyapatite with high porosity has applications in bone repair whereas the more compact hydroxyapatite can be used in the blasting of titanium implants. These applications are discussed in the work.