Abstract: An impression composition which is based on an aziridine-free composition which can be vulcanized at room temperature, and which comprises wax is provided according to the invention. The wax increases the dimensional stability of the composition during mixing and curing. The invention furthermore provides a kit for the preparation of such compositions and a process for the preparation of the wax-containing components of these kits. The wax is dispersed throughout the composition and is prepared by shock-cooling. The wax forms a crystalline network.

Abstract: Plastics with at least one polyaddition product which contains silane, ether, urethane and optionally urea groups and has the following features: a content of terminally located alkoxysilyl groups of the formula --NR--(CH.sub.2).sub.m --SiR.sup.1 R.sup.2 R.sup.3, in which m is the number 3, R is hydrogen or a group of the formula --(CH.sub.2).sub.m --SiR.sup.1 R.sup.2 R.sup.3 and at least one of the groups R.sup.1, R.sup.2 and R.sup.3 is a group of the formula --(O--C.sub.p H.sub.2p).sub.q --O--A--R.sup.4, in which p is the number 3, q is a number in the range from 1 to 100 and A is a single bond and R.sup.4 is an organic radical defined in more detail; and the remaining groups R.sup.1, R.sup.2 and R.sup.3 are methyl, ethyl or C.sub.1 - to C.sub.4 -alkoxy, the plastics furthermore comprising at least one catalyst for condensation of the silane groups, are suitable as impression, duplicating and modelling compositions, in particular for dental purposes.