Abstract: Compositions are used for coating teeth and dental prostheses based on a mixture of(a) at least one compound that is soluble in the reaction medium having the formula (I)MR.sub.x (I)in which M means Ti, Zr, Si, Ge, Sn or Al, R means halogen, hydroxy, alkoxy, acyloxy or a chelate ligand, and x means the valency of M, and(b) an organic silane having the formula (II)R".sub.n SiX.sub.4-n (II)in which R" means alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl or alkenylaryl, where said radicals may be interrupted by oxygen or sulfur atoms or --NH-- groups, X means hydrogen, halogen, hydroxy, alkoxy, acyloxy or the group --NR.sub.2 ' (R'=hydrogen and/or alkyl) and n has the value 1, 2 or 3, and/or(c) an organofunctional silane having the formula (III)R.sub.m "(R"'Y).sub.n SiX.sub.