US 12,484,995 B2
Zirconia mill blank having layers with different contents of yttria and alumina
Kazumichi Nonaka, Kyoto (JP); Shuhei Takahashi, Kyoto (JP); and Mitsuji Teramae, Kyoto (JP)
Assigned to SHOFU INC., Kyoto (JP)
Filed by SHOFU INC., Kyoto (JP)
Filed on Mar. 5, 2021, as Appl. No. 17/193,466.
Claims priority of application No. 2020-039024 (JP), filed on Mar. 6, 2020.
Prior Publication US 2021/0401552 A1, Dec. 30, 2021
Int. Cl. A61C 13/00 (2006.01); A61C 13/083 (2006.01); B32B 18/00 (2006.01)
CPC A61C 13/0022 (2013.01) [A61C 13/0004 (2013.01); A61C 13/083 (2013.01); B32B 18/00 (2013.01)] 6 Claims
 
1. A zirconia mill blank for dental cutting and machining containing yttria and alumina, wherein
between two planes which are parallel and face each other in the zirconia mill blank for dental cutting and machining, a section in which a distance from one plane of the two planes is within 40% of the distance between the two planes is defined as section A, and a section in which a distance from the other plane is within 40% of the distance between the two planes is defined as section B, layer LA contained in the section A and layer LB contained in the section B satisfy the following Formula (1) and Formula (2),
wherein a sintered body prepared by sintering at 1550° C. a test specimen cut out from the layer LA is defined as sintered body SA, a sintered body prepared by sintering at 1550° C. a test specimen cut out from the layer LB is defined as a sintered body SB, a contrast ratio of the sintered body SA at a sample having a thickness of 1 mm is defined as contrast ratio CA and a contrast ratio of the sintered body SB at a sample having a thickness of 1 mm is defined as contrast ratio CB, the contrast ratio CA and the contrast ratio CB satisfy the following Formula (3),
the zirconia mill blank for dental cutting and machining comprises at least two intermediate layers between the layer LA and the layer LB, and
change directions of yttria concentration, alumina concentration and contrast ratio in a stacking direction are not changed by the at least two intermediate layers,
Yttria concentration of layer LA−Yttria concentration of layer LB>1.0 mol %  Formula (1):
0.0 wt. %<Alumina concentration of layer LB−Alumina concentration of layer LA<0.3 wt. %  Formula (2):
0.71≤(Contrast ratio CA)/(Contrast ratio CB)≤0.86,  Formula (3):
wherein the contrast ratio CA is 0.70 or less and/or the contrast ratio CB is 0.74 or more.