The invention relates to plastics which are self-disinfecting. The invention relates in particular to polyether or silicone based dental plastics and impression materials in which a biocidal material is incorporated. The dental impression material ace. to the invention comprises at least a polymerizable base paste BP and a non-aqueous catalyst paste CP, wherein the base paste BP comprises about 0.001 to about 10% by weight of a water-stable anti-microbial agent. Preferred anti-microbial agents are selected from the group consisting of Hexitidin, Cetypyridininumcloride (CPC), Chlorhexidine and its derivates (CHX) and Triclosan.