Abstract: A thermosetting organopolysiloxane and organohydrogenpolysiloxane mixture containsa catalytic amount of platinum or a platinum compound finely dispersed in a solid substance at a concentration of 0.01-5% by weight calculated as platinum metal and based on the total weight of catalyst and solid substance, wherein the solid platinum-containing catalyst material has a melting point or softening point between 70.degree. and 250.degree. C., is practically immiscible with the organopolysiloxane and organohydrogenpolysiloxane mixture below the melting point or the softening point, and is finely dispersible therein.

Abstract: In a polysiloxane-based dental composition which crosslinks by an addition reaction and hardens at room temperature, the composition comprising(a) an organopolysiloxane with at least two vinyl groups in the molecule,(b) an organohydridopolysiloxane,(c) a catalyst to accelerate the addition reaction, and(d) a hydrophobic filler, the improvement which comprises including therein(e) an aluminosilicate containing finely divided palladium. This removes any by-product hydrogen and results in a smoother surface on any plaster of Paris moldings made from the hardened composition.