The invention relates to a composition comprising an ethylenically unsaturated acidic compound, water, a functionalized silane, an initiator, optionally comprising a sensitising agent, a non-surface treated filler, optionally a solvent, optionally an ethylenically unsaturated compound, optionally additives selected from the group consisting of stabilizer(s), photobleachable colorant(s), fluoride release agent(s), pigments. The invention also relates to a process of producing such a composition by in-situ silanization of the non-surface treated filler.