Abstract: A deproteinization filler comprises an aggregate of hydroxyapatite fibers having a three dimensional network structure. The mean radius of pores defined by the aggregate is approximately 0.02 .mu.m to approximately 0.08 .mu.m, the specific surface of the aggregate is approximately 25 m.sup.2 /g to approximately 65 m.sup.2 /g and the mean diameter of particles defined by the aggregate is approximately 1 .mu.m to approximately 30 .mu.m. The filler is produced by a given method. The filler may be contained in a throwaway cartridge.

Abstract: An alkali monofluorophosphate expressed by the formula M.sub.2 PO.sub.3 F, where M represents Na or K, can readily be synthesized under a relatively mild reaction condition by making HF gas contact with powdery or fine granular M.sub.4 P.sub.2 O.sub.7 or M.sub.2 HPO.sub.4 placed in a reaction vessel and maintained at a temperature in the range from about 200.degree. C. to about 450.degree. C., and more preferably in the range of 280.degree.-360.degree. C. It is suitable to make HF gas continuously flow into and pass through the reaction vessel until the total quantity of HF flowed into the vessel amounts to 100 to 150% of the theoretical value for conversion of M.sub.4 P.sub.2 O.sub.7 or M.sub.2 HPO.sub.4 to M.sub.2 PO.sub.3 F.