Method of fabricating high light transmission zirconia blanks for milling into natural appearance dental appliances

• US 9,434,651 B2
• Filed: 05/26/2012
• Issued: 09/06/2016
• Est. Priority Date: 05/26/2012
• Status: Active Grant

• Current Assignee: James R Glidewell Dental Ceramics Incorporated
• Original Assignee: James R Glidewell Dental Ceramics Incorporated
• Inventors: Carden, Robin A.
• Primary Examiner(s): Sultana, Nahida
• Application Number:
  US13/481,810
• Publication Number:
  US 20130313738A1
• Time in Patent Office: 1,564 Days
• Field of Search: 264/16, 264/86, 264/299, 264/636, 264/637, 264/651
• US Class Current: 1/1
• CPC Class Codes: A61C 13/0004 Computer-assisted sizing or machining of dental prostheses
• CPC Class Codes: A61C 13/0006 Production methods
• CPC Class Codes: A61C 13/0022 Blanks or green, unfinished dental restoration parts
• CPC Class Codes: A61C 13/082 Cosmetic aspects, e.g. inlays; Determination of the colour A61C19/10 takes precedence
• CPC Class Codes: A61C 13/083 Porcelain or ceramic teeth A61C13/081 takes precedence; preparations A61K6/80
• CPC Class Codes: A61C 5/77 Methods or devices for making crowns
• CPC Class Codes: C04B 2235/5454 nanometer sized, i.e. below 100 nm
• CPC Class Codes: C04B 2235/549 the particle size being expressed by crystallite size or primary particle size
• CPC Class Codes: C04B 2235/6026 Computer aided shaping, e.g. rapid prototyping
• CPC Class Codes: C04B 2235/6027 Slip casting
• CPC Class Codes: C04B 2235/612 Machining
• CPC Class Codes: C04B 35/486 Fine ceramics
• CPC Class Codes: C04B 35/62625 Wet mixtures
• CPC Class Codes: C04B 35/62635 Mixing details

Abstract

A process for fabricating pre-sintered zirconia blanks that are then computer machined and sintered to form dental appliances having highly advantageous features. The principal steps of a preferred embodiment of that process comprise a) preparing a ceramic slurry of binderless zirconia powder; b) subjecting the slurry to attrition milling down to about a 5-29 nm crystallite size; c) preparing a vacuum assisted and pressure assisted slip casting mold and pouring the milled slurry into the slip-casting mold; d) after casting, excess slurry is poured from the mold and a consolidated zirconia blank is removed; e) drying the blank and pre-sintering it to form solid blanks ready for CAD/CAM machining and sintering to net shape. The attrition is run with ball bearings that are of the sample material to prevent contamination. It also is run, up to 24 hours, to break down the crystallites to overcome the high density of zirconia.

Claims

1. A process for fabricating dental appliances of translucent zirconia;

the process comprising the steps of;

a) preparing a ceramic slurry comprising mixing binderless zirconia powder, water and a dispersant;

b) attrition milling the ceramic slurry to a crystallite size in the range of about 5 nm to about 29 nm;

c) slip casting the milled ceramic slurry in a vacuum-assisted mold;

d) removing water from the milled ceramic slurry and consolidating the zirconia powder to form zirconia blanks by subjecting one end of the vacuum-assisted mold to an evacuating pressure in a range of −

5 to −

40 psi and subjecting another end of the vacuum-assisted mold to a positive pressure in a range of 1 to 30 psi;

e) removing zirconia blanks formed in said slip casting step;

f) allowing the zirconia blanks to dry;

g) pre-sintering the dried zirconia blanks to form dried, pre-sintered zirconia blanks;

h) shaping the dried, pre-sintered zirconia blanks into appliance-shaped blanks; and

i) sintering the appliance-shaped blanks to net shape and size.

2. The process recited in claim 1 wherein the step of preparing the ceramic slurry comprises dispersing zirconia powder in tetra ethyl ammonium hydroxide.

3. The process recited in claim 1 wherein the vacuum-assisted mold comprises a polymer sleeve in a radial surrounding engagement with a plaster of paris mold.

4. The process recited in claim 1 wherein step a) is performed by dispersing the zirconia powder in deionized water.

5. The process recited in claim 4 wherein the step of preparing the slurry comprises dispersing zirconia powder in acid with pH of 1-3.9.

6. The process recited in claim 1 wherein step a) comprises the additional step of ultra-sonicating the ceramic slurry to remove soft agglomerates for improved mixing of the powder zirconia.

7. Process recited in claim 1 wherein step b) is performed using a zirconia bowl.

8. The process recited in claim 1 wherein step g) is performed at a temperature in the range of about 850°

C. to 1200°

C.

9. The process recited in claim 1 wherein the pre-sintering step is conducted at a temperature in the range of about 850°

C. to 1200°

C. for about two hours.

10. A process for forming zirconia blanks for use in fabricating dental appliances;

the process comprising the steps of;

a) preparing a slurry of zirconia powder dispersed by chemical dispersants in deionized water;

b) attriting the slurry to form a homogeneous, mixed slurry having a range of crystallite sizes of about 5 nm to about 29 nm;

c) pouring the mixed slurry into a vacuum-assisted assembly;

d) removing water from the milled slurry and consolidating the zirconia powder to form zirconia blanks by subjecting one end of the vacuum-assisted assembly to an evacuating pressure from −

5 to −

40 psi and another end of the vacuum-assisted assembly to a positive pressure of from 1 to 30 psi;

e) removing said zirconia blanks from the vacuum-assisted assembly;

f) subjecting said zirconia blanks to a presintering temperature to achieve partial densification of said zirconia blanks.

11. The process recited in claim 10 wherein the dispersant comprises tetramethyl ammonium hydroxide.

12. The process recited in claim 10 wherein the vacuum-assisted assembly comprises a polymer sleeve in radial surrounding engagement with a plaster of paris mold.

13. The process recited in claim 10 wherein step a) is performed by dispersing the zirconia powder in water by controlled pH.

14. The process recited in claim 10 wherein step a) comprises the additional step of ultra-sonicating the slurry to remove soft agglomerates for improved mixing of the powder.

15. The process recited in claim 10 wherein step b) is performed using a zirconia bowl and attriting for up to 24 hours.

16. The process recited in claim 10 wherein the pre-sintering is performed at a temperature in the range of about 850°

C. to 1200°

C.

17. The process recited in claim 10 wherein step f) is performed at a temperature in the range of about 850°

C. to 1200°

C. for about two hours.

18. The process in claim 10 wherein said chemical dispersants in step a) comprises at least one dispersant selected from an acid which comprises a nitric acid, and a base which comprises sodium hydroxide.

19. The process in claim 10 wherein the vacuum-assisted assembly is a slip casting assembly.

20. The process of claim 10 wherein the zirconia blanks are millable blanks.