Abstract: This invention sets forth an agent for filling bone and tooth defects, for building up bone, for bone-contact layers and for the replacement of bones and the roots of teeth, which contains calcium phosphate apatite having carbonate and alkali portions, all ions being definedly integrated in the crystal lattice; use is optionally made together with additives and/or diluents both tolerated by the body. Furthermore, it sets forth the use of this apatite for filling bone and tooth defects, for building up bone, for bone-contact layers, as a replacement for bones and the roots of teeth and as an implant article consisting completely or partially of this apatite or consisting of a material known for implant articles and being coated completely or partially with a layer of this apatite.