Ceramic filler compositions of customized shapes (FIGS. 1-30) according to the present invention, includes ceramic and glass-ceramic particles having a customized shape which provides mechanical locking within a resin matrix giving significantly improved fracture toughness performance for a resin/glass or ceramic composite system. The material has particular application as a tooth filling material with significantly improved wear resistance. The wide range of unique-shaped filler particles are produced using wet chemistry methods according to the invention of preparing the ceramic particles for use in a resin matrix composite material. Such composite materials have a very wide application, especially as a dental composite filling material for restoring a tooth.