Effects of heat treatment of spherical shape tetracalcium phosphate on the reactivity and injectability of apatite cement

Although injectability through syringe is one of the key advantages of apatite cement (AC), injectability of current AC is not satisfactory for its clinical use. In this investigation, therefore, effects of powder shape on injectability were studied using spherical tetracalcium phosphate (s-TTCP) prepared with plasma melting method. Bulk density of AC using s-TTCP (s-AC) was 1.13 ± 0.04g/cc and this value was significantly larger than AC using irregular TTCP (i-TTCP) (i-AC) which was 0.61 ± 0.02 (g/cc). Also we found better injectability in the case of i-AC. For example, cement spread area used as an index of consistency of the s-AC paste was 512 mm² whereas that of ordinary AC with irregular TTCP (i-AC) was 158 mm² when powder to liquid mixing ratio was 2.5. However, diametral tensile strength of set s-AC (1.4 MPa) was significantly lower than i-AC (10.7 MPa). X-ray powder diffraction (XRD) analysis revealed limited transformation to apatite in the case of set s-AC. XRD analysis also revealed that trace amount of thermal decomposition products were formed in the case of s-TTCP. To avoid the drawback due to plasma melting method, s-TTCP was again heated to 1500 degree for four hours and quenched to room temperature (q-TTCP). AC using q-TTCP (q-AC) transformed to apatitic mineral and showed the similar DTS value with i-AC. We concluded, therefore, spherical powder is very useful to improve the injectability of AC. Also, we found re-heat treatment of TTCP is useful if s-TTCP is prepared using plasma melting method.