Dental compositions are described comprising an addition-fragmentation agent of the formula: wherein R1, R2 and R3 are each independently Zm-Q-, a (hetero)alkyl group or a (hetero)aryl group with the proviso that at least one of R1, R2 and R3 is Zm-Q-; Q is a linking group have a valence of m+1; Z is an ethylenically unsaturated polymerizable group; m is 1 to 6; each X1 is independently —O— or —NR4—, where R4 is H or C1-C4 alkyl; and n is 0 or 1. Also described are dental articles prepared from a dental composition comprising an addition-fragmentation agent and methods of treating a tooth surface.