A coating composition comprising (a) a matrix mixture, wherein said matrix mixture comprises (i) 30% to 95% one or more urethane multi(meth)acrylates having exactly two groups of structure II: wherein R 5 is hydrogen or methyl, by weight based on the weight of said matrix mixture; (ii) 4% to 50% one or more non-urethane multi(meth)acrylates having three or more groups of structure II: wherein R 5 is hydrogen or methyl, by weight based on the weight of said matrix mixture; (iii) 0 to 35% one or more mono(meth)acrylates, by weight based on the weight of said matrix mixture; (iv) 1% to 10% one or more initiators, by weight based on the weight of said matrix mixture; (b) zirconia, (i) wherein said zirconia is in the form of a collection of zirconia particles having number-average diameter of 100 nm or less as measured by forming a dispersion of 0.1% by weight particles in solvent, casting a film on a grid suitable for transmission electron microscopy, allowing the film to dry, obtaining an image of the film by TEM, then analyzing the image to determine distribution of particle diameters; (ii) wherein said collection of zirconia particles has a distribution of diameters that has a breadth parameter defined by BP = N 75 − N 25 of 5 nm or less; and wherein the weight ratio of (a) to (b) is from 0.06:1 to 2.8:1, and wherein the amount of (a) plus the amount of (b) is 1% to 100% by weight based on the weight of said coating composition. (a) a matrix mixture, wherein said matrix mixture comprises (i) 30% to 95% one or more urethane multi(meth)acrylates having exactly two groups of structure II: wherein R 5 is hydrogen or methyl, by weight based on the weight of said matrix mixture; (ii) 4% to 50% one or more non-urethane multi(meth)acrylates having three or more groups of structure II: wherein R 5 is hydrogen or methyl, by weight based on the weight of said matrix mixture; (iii) 0 to 35% one or more mono(meth)acrylates, by weight based on the weight of said matrix mixture; (iv) 1% to 10% one or more initiators, by weight based on the weight of said matrix mixture; (i) 30% to 95% one or more urethane multi(meth)acrylates having exactly two groups of structure II: wherein R 5 is hydrogen or methyl, by weight based on the weight of said matrix mixture; (ii) 4% to 50% one or more non-urethane multi(meth)acrylates having three or more groups of structure II: wherein R 5 is hydrogen or methyl, by weight based on the weight of said matrix mixture; (iii) 0 to 35% one or more mono(meth)acrylates, by weight based on the weight of said matrix mixture; (iv) 1% to 10% one or more initiators, by weight based on the weight of said matrix mixture; (b) zirconia, (i) wherein said zirconia is in the form of a collection of zirconia particles having number-average diameter of 100 nm or less as measured by forming a dispersion of 0.1% by weight particles in solvent, casting a film on a grid suitable for transmission electron microscopy, allowing the film to dry, obtaining an image of the film by TEM, then analyzing the image to determine distribution of particle diameters; (ii) wherein said collection of zirconia particles has a distribution of diameters that has a breadth parameter defined by BP = N 75 − N 25 of 5 nm or less; and (i) wherein said zirconia is in the form of a collection of zirconia particles having number-average diameter of 100 nm or less as measured by forming a dispersion of 0.1% by weight particles in solvent, casting a film on a grid suitable for transmission electron microscopy, allowing the film to dry, obtaining an image of the film by TEM, then analyzing the image to determine distribution of particle diameters; (ii) wherein said collection of zirconia particles has a distribution of diameters that has a breadth parameter defined by BP = N 75 − N 25 of 5 nm or less; and