Abstract: An apparatus for releasable fastening and for modifying the relative position of two components (1, 1?, Bf, G; 2, 2?, Bk, Br), which have a common connecting surface forming a contact surface (5, 5?), comprises two screws (3), which in coaction with specially configured V-shaped notch zones (9a1, 9a2; 9b1, 9b2; 9a3, 9a4; 9b3, 9b4) permit a relative positioning in zero-backlash and accurately aligned fashion, and serve as the fastening means. It is thereby possible to perform a linear displacement and/or a rotation and/or a tilt in simple fashion.

Abstract: The use is described of oxide ceramic materials for compression molds for shaping elements made from glass or a glass-containing ceramic and having high surface quality and tight tolerances. The materials are polycrystalline, monophasal or polyphasal materials which are contact-inert towards the optical elements to be pressed and which, in addition, have significantly better mechanical and thermal properties than monocrystalline substances, which, in principle, exhibit an anisotropic behavior as a consequence of their geometrical anisotropy. The material intended for use according to the invention can comprise a Al.sub.2 O.sub.3 ceramic or a ZrO.sub.2 -- and/or HfO.sub.2 -containing ceramic. The material can also be built up in several phases, i.e. can contain a matrix component and at least one particle component dispersed discretely in it. They are preferably ZrO.sub.

Abstract: The composite material for prosthetic purposes of the present invention is essentially composed of a plastic matrix, preferably of a methacrylate plastic, and at least one bioactive filler material, preferably a glass ceramic material of apatite crystal structure. The finely comminuted bioactive material may be homogeneously or nonhomogeneously incorporated in the plastic matrix. Reinforcing additives such as glass fibers and the like may also be incorporated into the mixture of plastic matrix and bioactive material in order to improve the mechanical strength properties. The bioactive material may be admixed to a mixture of methacrylate monomer and curing agent or to a prepolymer obtained therefrom. The composite material is useful as bone cement bone or tooth replacement material, and in general for prosthetic purposes in surgery and orthopedics.