A composition for restoring defects in calcified tissues comprises an amorphous bioactive particulate consisting essentially of calcium, silicon and oxygen. Said agent may be selected from the group consisting of : a) a reaction product of an organic silicate source and a source of calcium; b) a calcium containing hydrolysis product of tetraethylorthosilicate; c) a calcium containing silica sol-gel; d) a binary calcium oxide and silicate precipitated material; e) a synthetic analog of a naturally occurring wollastonite-like calcium silicate; and f) a precipitated reaction product of soluble calcium source and a silicate solution. A process for producing the amorphous bioactive particulate consists essentially of adding a sufficient amount of a solution of a soluble calcium source to a solution of a silicate or silicate precursor to cause a precipitation of calcium-containing silicate particulate.