Process for producing a dental zirconia article with a fast sintering process
The invention relates to a process of sintering a dental zirconia restoration, the process comprising a first step of heat-treating a porous dental zirconia article with a heating rate of at least 3 K/sec until a temperature level of 75 to 90% of the final sintering temperature is achieved to obtain a partially sintered dental zirconia article, the porous dental zirconia article having a BET surface of 5 to 12 m 2 /g and being composed of a 4 mol % yttria stabilized zirconia material and having an alumina content of utmost 0.15 wt. %.
1 . A process of sintering a porous dental zirconia article, the process comprising:
providing the porous dental zirconia article,
the porous dental zirconia article having been subjected to a pre-sintering heat treatment at a temperature of 960° C. to 980° C.,
the porous dental zirconia article characterized by a BET surface of 5 to 12 m 2 /g and being composed of a zirconia material containing about 4 mol % yttria and no greater than 0.15 wt. % alumina;
subjecting the porous dental zirconia article to:
a first segment of heat-treating, the first segment of heat-treating involving a heating rate of at least 3 K/sec until a temperature of 1,125° C. to 1,485° C. is achieved, and
a second segment of heat-treating, the second segment of heat-treating involving a heating rate of 2.5 K/sec until a final sintering temperature of 1,500° C. to 1650° C. is reached, to obtain a partially sintered dental zirconia article.
2 . The process according to claim 1 , further comprising a third segment of heat-treating, the third segment of heat-treating following the second heat-treating segment of heat-treating without interruption,
the third segment of heat-treating characterized by a dwell time at the final sintering temperature of utmost 8 min.
3 . The process according to claim 2 , further comprising a cooling-down segment, the cooling-down segment following the third segment of heat-treating without interruption,
the cooling-down segment being characterized by the following features alone or in combination:
cooling-down rate: 3K/sec or more until a temperature of 1,000° C. is reached;
duration: 6 min or less.
4 . The process according to claim 3 , the first segment of heat-treating, the second segment of heat-treating, the third segment of heating-treating, and the cooling-down segment having a total duration of 30 min or less.
5 . The process according to claim 1 , the process further comprising:
providing a porous dental zirconia mill blank,
machining the porous dental zirconia article from the porous zirconia dental mill blank.
6 . The process according to claim 1 , characterized by one or more of:
the first segment of heat-treating: heating rate of 3 to 7 K/sec and a duration of 8 min or less;
the second segment of heat-treating: heating rate of 2.5 K/sec and a duration of 25 min or less;
a third segment of heat-treating: heating rate of 0 K/sec and a duration of 8 min or less;
a cooling-down segment: cooling rate of 3 K/sec or more and a duration of 6 min or less.
7 . The process according to claim 1 , the porous dental zirconia article being characterized by one or more of:
density: 2.85 to 3.35 g/cm 3 ;
BET surface: 5.5 to 11 m 2 /g;
coefficient of thermal expansion: 8.5*10 −6 K −1 to 11.5*10 −6 K −1 .
8 . The process according to claim 1 , the porous dental zirconia article being characterized by the following features alone or in combination:
raw breaking resistance: 15 to 55 MPa, determined according to ISO 6872:2015 applying the punch on 3 balls test adapted to measurement in porous state;
Vickers hardness: 25 (HV 0.5) to 150 (HV 0.5).
9 . The process according to claim 1 , the porous dental zirconia article being characterized by the following features:
ZrO 2 +HfO 2 : 80 to 95 wt. %,
Al 2 O 3 : 0 to 0.15 wt. %,
colouring oxides: 0.01 to 1 wt. %,
wt. % with respect to a weight of the porous dental zirconia article.
10 . The process according to claim 1 , the porous dental zirconia article comprising coloring oxides selected from oxides of Fe, Mn, Cr, Ni, Co, Er, Pr, Nd, or any combination thereof.
11 . The process according to claim 1 , the porous dental zirconia article excluding one or more of: glass; glass ceramic; oxides of Si, Fe, K, Na; in an amount above 1 wt. % with respect to a weight of the porous zirconia dental article.
12 . The process according to claim 1 , for preparing a sintered dental zirconia restoration characterized by one or more of:
translucency: 25% or more, determined on a sample having a thickness of 1 mm in reflection mode at a wave length of 450 to 800 nm;
density: at least 98.5% of theoretical density;
phase content tetragonal phase: 10 to 80 wt. %;
phase content cubic phase: 10 to 80 wt. %;
biaxial flexural strength: 500 to 1,500 MPa, determined according to ISO 6872:2015.
13 . The process according to claim 1 , for preparing a sintered dental zirconia restoration having a shape of a dental bridge, a veneer, a facing, a coping, crown, an abutment, an inlay, an onlay, an implant, a monolithic dental restoration, or parts thereof.