Set of colored porous zirconia dental mill blanks and process of production

A set of porous zirconia dental mill blanks comprising at least two differently colored porous zirconia dental mill blanks,

• the porous zirconia dental mill blanks
• comprising zirconia, yttria, coloring ions, and optionally alumina,
• comprising multiple layers with different yttria content,
• having a bottom layer, at least one intermediate layer, and a top layer,
• the content of yttria and coloring ions in mol % changing in opposite direction to each other from the bottom layer to the top layer, and
• wherein the multiple layers comprise a gradient in yttria and coloring ion content, with the content of yttria and coloring ions changing in opposite directions from the bottom layer to the top layer, wherein each layer differs in the content of yttria by not more than 0.5 mol % relative to a respective adjacent layer in the multiple layers,
• the content of yttria and coloring ions in mol % being adjusted to provide an essentially constant ratio of the sum of yttria and coloring ions in mol % between the top layer and the bottom layer for the differently colored zirconia dental mill blanks, the essentially constant ratio defined as varying by a deviation Dn that is not more than 2.70 for all colored mill blanks of the set, Dn is calculated from the ratios Rn of the sum of yttria and coloring ions in mol % between the top layer and the bottom layer with the formula
• Dn=((Rmax−Rn)/Rmax*100)/Rmax2,
• with Dn being not more than 2.70 for the differently colored porous zirconia dental mill blanks within the set containing N different colors with Rmax being the highest ratio found within the set and N≥2, n=1, 2, . . . , N,
• wherein the dental mill blanks comprise a ratio Rn of (amount of yttria+amount of coloring ions in the top layer in mol %)/(amount of yttria+amount of coloring ions in the bottom layer in mol %) being
• in a range of 1.83 to 1.67 for a porous zirconia dental mill blank having an yttria gradient from 3.0 to 5.5 mol % from the bottom layer to the top layer,
• in a range of 1.37 to 1.31 for a porous zirconia dental mill blank having an yttria gradient from 4.0 to 5.5 mol % from the bottom layer to the top layer,
• in a range of 1.66 to 1.54 for a porous zirconia dental mill blank having an yttria gradient from 3.0 to 5.0 mol % from the bottom layer to the top layer,
• in a range of 1.25 to 1.20 for a porous zirconia dental mill blank having an yttria gradient from 4.0 to 5.0 mol % from the bottom layer to the top layer, or
• in a range of 1.76 to 1.62 for a porous zirconia dental mill blank having an yttria gradient from 3.2 to 5.65 mol % from the bottom layer to the top layer.