A process for the preparation of a dental impression comprisingA) forming a mixture of a polyaddition product which contains ether, urethane and urea groups,B) mixing therewith water of proton donor-containing aqueous solution in a weight ratio of A:B of from 1:0.01 to 1:40 and in at least catalytically active amount, the weight ratio of water plus proton donor to the balance of the composition exclusive of the filler ranging from about 0.01:1 to 1:1, andC) applying the mixture formed in B intraorally to a patient to make a negative copy of the patient's teeth.