Bicyclic cyclopropane derivatives of the general Formula (I) ##STR00001## in which n+m is 0 to 8; r is 1 to 4; R.sup.1 is absent or is a C.sub.1-C.sub.20 alkylene radical which can be interrupted by O or S, a cycloaliphatic C.sub.4-C.sub.12 radical, a bicyclic C.sub.4-C.sub.12 radical, a C.sub.6-C.sub.14 arylene or C.sub.7-C.sub.20 alkylenearylene radical; R.sup.2 is for r=1 a C.sub.1-C.sub.20 alkyl radical which can be interrupted by O or S, a cycloaliphatic C.sub.4-C.sub.12 radical, a bicyclic C.sub.4-C.sub.12 radical, a C.sub.6-C.sub.14 aryl or a C.sub.7-C.sub.20 alkylaryl radical; is for r>1 an r-times substituted aliphatic C.sub.1 to C.sub.20 radical which can be interrupted by O or S, a cycloaliphatic C.sub.4-C.sub.12 radical, an aromatic C.sub.6-C.sub.14 radical or aliphatic-aromatic C.sub.7-C.sub.20 radical; X is absent or is --CO--O--, --CO--NH-- or --O--CO--NH--, and Y is CH.sub.2, O or S which is suitable in particular for the preparation of dental materials.