# US 9,434,651 B2 · Method of fabricating high light transmission zirconia blanks for milling into natural appearance dental appliances

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- Number: US 9,434,651 B2
- Document ID: US9434651B2
- Status: Granted
- Kind: B2
- Application number: 13/481,810
- Filed: 2012-05-26
- Published: 2013-11-28
- Granted: 2016-09-06
- Earliest claimed: 2012-05-26
- Assignees: James R. Glidewell Dental Ceramics, Inc.
- Applicants: Robin A. Carden
- Inventors: Robin A. Carden
- Web page: https://patentgrep.com/patent/US9434651B2

## CPC

- C04B 35/62625: {Wet mixtures}
- A61C 5/77: Methods or devices for making crowns
- A61C 13/0004: {Computer-assisted sizing or machining of dental prostheses}
- A61C 13/0006: {Production methods}
- A61C 13/0022: {Blanks or green, unfinished dental restoration parts}
- A61C 13/082: {Cosmetic aspects, e.g. inlays; Determination of the colour (A61C19/10 takes precedence)}
- A61C 13/083: Porcelain or ceramic teeth {(A61C13/081 takes precedence; preparations A61K6/80)}
- C04B 35/486: Fine ceramics
- C04B 35/62635: {Mixing details}
- C04B 2235/5454: nanometer sized, i.e. below 100 nm
- C04B 2235/549: the particle size being expressed by crystallite size or primary particle size
- C04B 2235/6026: Computer aided shaping, e.g. rapid prototyping
- C04B 2235/6027: Slip casting
- C04B 2235/612: Machining
- C04B: LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE {(roofing granules E04D7/005)}; CERAMICS (devitrified glass-ceramics C03C10/00); REFRACTORIES; TREATMENT OF NATURAL STONE
- A61C: DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE (non-driven toothbrushes A46B; {tongue scrapers A61B17/24;} preparations for dentistry A61K6/00; preparations for cleaning the teeth or mouth A61K8/00, A61Q11/00)

## 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

### Claim 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.

### Claim 2 (depends on 1)

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

### Claim 3 (depends on 1)

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.

### Claim 4 (depends on 1)

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

### Claim 5 (depends on 4)

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.

### Claim 6 (depends on 1)

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.

### Claim 7 (depends on 1)

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

### Claim 8 (depends on 1)

The process recited in claim 1 wherein step g) is performed at a temperature in the range of about 850° C. to 1200° C.

### Claim 9 (depends on 1)

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.

### Claim 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.

### Claim 11 (depends on 10)

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

### Claim 12 (depends on 10)

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.

### Claim 13 (depends on 10)

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

### Claim 14 (depends on 10)

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.

### Claim 15 (depends on 10)

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

### Claim 16 (depends on 10)

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.

### Claim 17 (depends on 10)

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.

### Claim 18 (depends on 10)

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.

### Claim 19 (depends on 10)

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

### Claim 20 (depends on 10)

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