Presently described are methods of surface treating inorganic oxide particles, hardenable (e.g. dental) compositions comprising a polymerizable resin composition and surface treated particles, as well as surface treated (e.g. nanocluster) inorganic oxide particles, and silane surface treatment compounds. In one embodiment, the method comprises forming a surface treatment compound by reacting a first functional group of a (meth)acrylate monomer having a molecular weight of at least 350 g/mole with a second functional group of a silane compound wherein the first and second functional group react to form a covalent bond; and combining the surface treatment compound with inorganic oxide particles.