A process for the preparation of a polymerisable dental composition comprising the steps of (a) preparing a liquid mixture comprising (i) 1 to 99% w/w of a hybrid monomer component containing at least one hybrid monomer compound having one hydrolysable siloxane group and at least one polymerisable organic moiety, and (ii) 99 to 1% w/w of a monomer component polymerisable with the polymerisable organic moiety of the hybrid monomer compounds; and (b) adding at least a stoichiometrically sufficient amount of water to the mixture to hydrolyse the hydrolysable siloxane group of the hybrid monomer compound and to form spherical polymerisable nanoparticles having an average particle size of from 1 to 100 nm dispersed in the monomer component, whereby the nanoparticles have a structure with Si-O-Si bonds and peripherally exposed polymerisable organic moieties.