Dental blank comprising a pre-sintered porous zirconia material, process of its production and dental article formed from said dental blank

1. A dental mill blank comprising a porous pre-sintered zirconia material, comprising:

the porous pre-sintered zirconia material showing a N 2 adsorption and/or desorption of isotherm type IV according to IUPAC classification;

the porous pre-sintered zirconia material having a Vickers hardness from about 25 to about 150; and

an attachment for reversibly attaching the dental mill blank to a machining device.

2. The dental mill blank of claim 1 , the porous pre-sintered zirconia material being characterized by at least one of the following features:

showing a nitrogen adsorption and desorption isotherm with hysteresis loop;

showing a hysteresis loop of type H 1 according to IUPAC classification;

showing a N 2 adsorption and desorption isotherm with a hysteresis loop in a p/p 0 range of 0.70 to 0.95;

average connected pore diameter: from about 10 to about 100 nm;

average grain size: less than about 100 nm;

BET surface: from about 10 to about 200 m 2 /g;

Biaxial flexural strength: from about 10 MPa to about 40 MPa;

x, y, z dimension: at least about 5 mm;

Vickers hardness: from about 35 to about 140;

density: about 30 to about 95% of theoretical density;

having an isotropic shrinkage behaviour.

3. The dental mill blank according to claim 2 , the porous pre-sintered zirconia material being further characterized by at least one of the following features:

ZrO 2 content: from about 70 to about 98 mol %;

HfO 2 content: from about 0 to about 2 mol %;

Y 2 O 3 content: from about 1 to about 15 mol %;

Al 2 O 3 content: from about 0 to about 1 mol %.

4. The dental mill blank according to claim 1 having the shape of a disc or block.

5. The dental mill blank according to claim 1 , the attachment for reversibly attaching the dental mill blank to a machining device being selected from frame(s), stump(s) and combinations thereof.

6. The dental article according to claim 1 , the attachment for reversibly attaching the dental mill blank to a machining device being selected from groove(s), notch(es), recess(es), stamp(s), and combinations thereof.

7. The dental mill blank according to claim 1 , the porous pre-sintered zirconia material being obtained by a process comprising the step of heat treating an aerogel.

8. The dental mill blank according to claim 7 , the aerogel being characterized by at least one of the following features:

comprising crystalline zirconia particles having an average primary particle diameter in a range from about 2 nm to about 50 nm;

content of crystalline zirconia particles: at least about 85 mol.-%;

having a surface area in the range of 100 m 2 /g to 300 m 2 /g;

having an organic content of at least about 3 wt.-%.

9. The dental mill blank according to claim 7 , the aerogel having been heat treated to a temperature of about 900 to about 1100° C.

10. The dental mill blank according to claim 1 , the porous pre-sintered zirconia material being obtained by a process comprising the steps of

providing a zirconia sol comprising crystalline metal oxide particles,

optionally concentrating the first zirconia sol to provide a concentrated zirconia sol,

adding a radically reactive surface modifier to the zirconia sol to provide surface-modified particles of the zirconia sol and adding a radical initiator to the radically polymerizable surface-modified particles of the zirconia sol,

casting the zirconia sol into a mold to provide a casted zirconia sol,

curing the radically polymerizable surface-modified particles of the zirconia sol to form a gel,

optionally removing water, if present, from the gel via a solvent exchange to provide an at least partially de-watered, solvent containing gel,

extracting solvent, if present, from the gel by super critical extraction to provide an aerogel,

optionally cutting the aerogel into smaller pieces,

heat treating the aerogel.

11. A process of producing a zirconia dental article comprising the steps of:

providing a dental mill blank comprising a porous pre-sintered zirconia material comprising:

the porous pre-sintered zirconia material showing a N 2 adsorption and/or desorption of isotherm type IV according to IUPAC classification;

the porous pre-sintered zirconia material having a Vickers hardness from about 25 to about 150; and

an attachment for reversibly attaching it to a machining device;

placing the dental mill blank in a machining device; and

machining the porous zirconia material.

12. The process according to claim 11 , the machining step being done with a milling, drilling, cutting, carving, or grinding device.

13. The process according to claim 11 comprising the additional step of sintering the machined porous zirconia material.

14. A dental article obtained by the process described in claim 11 .

15. The dental article of claim 14 having the shape of a crown, bridge, inlay, onlay, veneer, facing, coping, crown and bridged framework, implant, abutment, orthodontic appliances and parts thereof.