Slip-casting method of fabricating zirconia blanks for milling into dental appliances
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; c) preparing a vacuum 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.
1 . A process for fabricating dental appliances of translucent zirconia; the process comprising the steps of:
a) preparing a slurry of binderless zirconia powder;
b) attrition milling the slurry;
c) slip casting the milled slurry in a vacuum assisted mold;
d) removing zirconia blanks formed in said slip casting step;
e) allowing the blanks to dry;
f) pre-sintering the dried blanks;
g) shaping the fully dried, pre-sintered blanks into a desired appliance form; and
h) sintering the appliance-shaped blanks to net shape and size.
2 . The process recited in claim 1 wherein step c) is performed in an openable silicone mold secured in surrounding engagement with a plaster of paris mold and attached to a vacuum.
3 . The process recited in claim 1 wherein step c) is performed wherein a polymer sleeve is in 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 1 wherein step a) is performed by dispersing the zirconia powder in water.
6 . The process recited in claim 1 wherein step a) is performed by dispersing the zirconia powder in water by controlled pH.
7 . The process recited in claim 1 wherein step a) comprises the additional step of ultra-sonicating the slurry to remove soft agglomerates for improved mixing of the powder.
8 . The process recited in claim 1 wherein step b) is performed using a zirconia bowl.
9 . The process recited in claim 1 wherein step f) is performed at a temperature in the range of about 850° C. to 1200° C.
10 . The process recited in claim 1 wherein step f) is performed at a temperature in the range of about 850° C. to 1200° C. for about two hours.
11 . A process for forming millable blanks of zirconia 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) mixing the slurry to form a homogeneous slurry;
c) pouring the mixed slurry into a vacuum-assisted slip casting assembly;
d) allowing zirconia blanks to form in said assembly and removing said blanks therefrom; and
e) subjecting said zirconia blanks to a presintering temperature to achieve partial densification of said blanks.
12 . The process recited in claim 11 wherein step c) is performed in an openable silicone mold secured in surrounding engagement with a plaster of paris mold and attached to a vacuum.
13 . The process recited in claim 11 wherein step c) is performed wherein a polymer sleeve is in radial surrounding engagement with a plaster of paris mold.
14 . The process recited in claim 11 wherein step a) is performed by dispersing the zirconia powder in water by controlled pH.
15 . The process recited in claim 11 wherein step a) comprises the additional step of ultra-sonicating the slurry to remove soft agglomerates for improved mixing of the powder.
16 . The process recited in claim 11 wherein step b) is performed using a zirconia bowl.
17 . The process recited in claim 11 wherein step f) is performed at a temperature in the range of about 850° C. to 1200° C.
18 . The process recited in claim 11 wherein step e) is performed at a temperature in the range of about 850° C. to 1200° C. for about two hours.
19 . The process in claim 11 wherein said chemical dispersants in step a) comprise tetramethyl ammonium hydroxide.