A composition for use as a dental impression material including a polymerizable resin consisting of oligomers or polymers functionalized with groups curable by ring opening metathesis polymerization. These oligomers or polymers are end-capped and/or tethered with said functional groups. The composition also includes a ruthenium carbene complex catalyst, whereby the catalyst initiates ring-opening metathesis polymerization of the composition. The invention includes a paste/paste system in which a base paste includes the polymerizable oligomer or polymer and an inorganic dental filler system and in which a catalyst paste includes the catalyst dissolved in an inert solvent and an inorganic dental filler system. The oligomer or polymer may be, for example, one or a combination of a telechelic polydimethylsiloxane end-capped with norbornenyl groups, a polydimethylsiloxane tethered and end-capped with norbornenyl groups, a tri-functional polydimethylsiloxane end-capped with norbornenyl groups, or a quadri-functional polydimethylsiloxane end-capped with norbornenyl groups. The catalyst may be, for example, a ruthenium carbene complex with a ligand having a basicity higher than tricyclohexylphosphine. The composition of the present invention exhibits reduced sensitivity to sulfur impurities.