Selective Laser Sintering of Calcium Phosphate Powders
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Since Dejong first observed the similarity between powder X - ray diffraction pattern ofthe in vivo mineral and the hydroxyapatite (Cas(OH)(P04h ,HA) in 1926, the calcium phosphate ceramics have received attention as a bone substitute material. Five calcium phosphates which exhibit different X-ray diffraction patterns are known to be precipitated from aqueous solution at normal pressure.  These are Ca(HzP04h, Ca(HzP04h-H20, CaHP04 , CaHP04-2H20, and crystalline precipitate of variable composition of hydroxyapatite with the base formula Cas(OH)(P04h. Various forms of calcium phosphate compounds, Ca/P ratio range from 0.5 to 1, are prepared from HA by reacting with phosphoric acid. Thermally dehydrated calcium phosphates are known to form a CaO and P20 S binary system. It is known that for the CaO and P20S binary system, the chain phosphates appear between the orthophosphate (mole ratio ofCaO/P20 S =3) and metaphosphate (mole ratio ofCaO/P20s =1) and ultraphosphate for which mole ratio ofCaO/P20 s iess than 1. Particularly in the case ofmetaphosphate, very high degree of polymerization and as a consequence, good mechanical properties are reported. In this binary system, mole ratio ofCaO/P20 S less than 55145 forms a glass-like structure from the melt, and its mechanical properties are known to be nearly same as those of natural teeth.