A photopolymerizable dental composition for application to and for the isolation and protection of gums and/or teeth during dental treatment is described. The composition can include (a) one or more photopolymerizable monomers selected from the group consisting of acrylates and methacrylates, (b) one or more photoinitiators, preferably selected from the group consisting of alpha-diketones, benzoin alkyl ethers, thioxanthones, benzophenones, acyl phosphine oxides, acetophenones, ketals, titanocenes, borates and sensitizing dyes, and (c) one or more molecular weight regulators selected from the group consisting of compounds which can be reacted with a radical of a monomer of component (a) with abstraction of an H radical from the molecular weight regulator in the allyl position. Also disclosed are kits comprising such a composition, methods for producing a corresponding protective layer, methods for treating one or more teeth, and methods of using the compositions as a masking compound.