Nanocrystalline zirconia and methods of processing thereof

Abstract

Zirconia dental ceramics exhibiting opalescence and having a grain size in the range of 10 nm to 300 nm, a density of at least 99.5% of theoretical density, a visible light transmittance at or higher than 45% at 560 nm, and a strength of at least 800 MPa.

What is claimed is: 
     
         1 . A method of manufacturing an opalescent zirconia dental article comprising:
 providing a well-dispersed suspension of zirconia nanoparticles having an average particle size of less than 20 nm;   forming the suspension into a shape of the dental article or a blank to produce a wet zirconia green body;   drying the wet green body in a controlled humidity atmosphere to produce a zirconia green body;   heating the zirconia green body to provide a zirconia brown body, wherein the zirconia green body is shaped before heating, or the zirconia brown body is shaped after heating;   sintering the zirconia brown body at a temperature below or equal to 1200° C. to provide an opalescent zirconia sintered body;   wherein a resulting grain size of the sintered dental article is between 10 and 300 nm and an average grain size is between 40 nm and 150 nm.   
     
     
         2 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the heating step comprises heating up the zirconia green body at a temperature in the range of from 500 to 700° C. to remove any organic residuals to form a zirconia brown body. 
     
     
         3 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , further comprising pre-sintering the brown body at a temperature up to 850° C. prior to sintering. 
     
     
         4 . The method of manufacturing an opalescent zirconia dental article of  claim 3 , wherein the pre-sintering step and the heating step can be combined into one step. 
     
     
         5 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the step of forming the suspension into a shape comprises an isotropically enlarged, uniform shape. 
     
     
         6 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the dried green body or brown body is shaped by CAD/CAM, LPIM or dental heat-pressing. 
     
     
         7 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the zirconia nanoparticles have an average particle size less than 15 nm. 
     
     
         8 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the well-dispersed suspension of zirconia nanoparticles comprises a solids volume percent of particles in the range of 10 to 50 vol. %. 
     
     
         9 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the well-dispersed suspension further comprises a dispersant in an amount of not more than 10 wt. % of total solids in the suspension. 
     
     
         10 . The method of manufacturing an opalescent zirconia dental article of  claim 9 , wherein the dispersant comprises poly(ethyleneimine), 2-[2-(2-methoxyethoxy)ethoxy] acetic acid, or 2-(2-methoxyethoxy)acetic acid. 
     
     
         11 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the well-dispersed suspension is further de-agglomerated by attrition milling. 
     
     
         12 . The method of manufacturing an opalescent zirconia dental article of  claim 11 , wherein the suspension is further refined by centrifuging instead of, prior to, or after attrition milling. 
     
     
         13 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein sintering is conducted in conventional dental furnaces, high temperature furnaces, microwave dental furnaces or hybrid furnaces. 
     
     
         14 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the sintering temperature is below or equal to 1150° C. 
     
     
         15 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the sintering temperature is below or equal to 1125° C. 
     
     
         16 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein forming the suspension into blanks or the dental article comprises centrifugal casting, drop-casting, gel-casting, injection molding, slip casting, filter-pressing and/or electrophoretic deposition (EPD). 
     
     
         17 . The method of manufacturing an opalescent zirconia dental article of  claim 1 , wherein the well-dispersed suspensions comprises a liquid medium selected from the group consisting of water, ethanol, methanol, toluene, dimethylformamide, or mixtures thereof. 
     
     
         18 . A method of manufacturing an opalescent zirconia dental article comprising:
 providing a well-dispersed suspension of zirconia nanoparticles having an average particle size of less than 20 nm;   forming the suspension into a shape of the dental article or a blank to produce a wet zirconia green body;   drying the wet green body in a controlled humidity atmosphere to produce a zirconia green body;   heating the zirconia green body to provide a zirconia brown body, wherein the zirconia green body is shaped before heating, or the zirconia brown body is shaped after heating;   sintering the zirconia brown body at a temperature below or equal to 1200° C. to provide an opalescent zirconia sintered body;   wherein the majority of the pores are greater than 25 nm at a density of at least 99.5% theoretical density.   
     
     
         19 . The method of manufacturing a zirconia dental article of  claim 18 , wherein the majority of the pores are greater than 30 nm at a density of at least 99.5% theoretical density. 
     
     
         20 . A suspension for forming a zirconia dental article comprising:
 well-dispersed zirconia nanoparticles having an average particle size of less than 20 nm;   a solids volume percent of particles in the range of 10 to 50 vol. %;   wherein the resulting grain size of the of the zirconia dental article is between 10 and 300 nm and an average grain size is between 40 nm and 150 nm; and   wherein the zirconia dental article is opalescent.   
     
     
         21 . The suspension for forming a zirconia dental article of  claim 20 , wherein the solids volume percent of particles is at least 14 vol %. 
     
     
         22 . The suspension for forming a zirconia dental article of  claim 20 , wherein the solids volume percent of particles is at least 16 vol %. 
     
     
         23 . The suspension for forming a zirconia dental article of  claim 20 , wherein the solids volume percent of particles is at least 18 vol %. 
     
     
         24 . The suspension for forming a zirconia dental article of  claim 20 , having a viscosity of less than 100 cP at 25° C. 
     
     
         25 . The suspension for forming a zirconia dental article of  claim 24 , having a viscosity of less than 30 cP at 25° C. 
     
     
         26 . The suspension for forming a zirconia dental article of  claim 25 , having a viscosity of less than 15 cP at 25° C. 
     
     
         27 . The suspension for forming a zirconia dental article of  claim 23 , wherein the well-dispersed suspension is further de-agglomerated by attrition milling. 
     
     
         28 . A green body for forming a zirconia dental article comprising:
 zirconia nanoparticles having an average particle size of less than 20 nm;   wherein the resulting grain size of the of the zirconia dental article is between 10 and 300 nm and average grain size is between 40 nm and 150 nm; and   wherein the zirconia dental article is opalescent.   
     
     
         29 . The green body of  claim 28 , wherein the green body comprises a transmittance of 58% for a 2 mm thickness at 560 nm. 
     
     
         30 . A method of manufacturing an opalescent zirconia dental article comprising
 providing a zirconia green blank having zirconia nanoparticles having an average particle size of less than 20 nm;   shaping the zirconia green blank by CAD/CAM, LPIM, or dental heat-pressing, or heating the zirconia green blank to form a brown blank and shaping the brown blank by CAD/CAM machining;   sintering the shaped zirconia green blank or brown blank at a temperature below or equal to 1200° C. to provide an opalescent zirconia sintered body;   wherein the resulting grain size of the sintered dental article is between 10 and 300 nm and average grain size is between 40 nm and 150 nm.   
     
     
         31 . The method of manufacturing an opalescent zirconia dental article of  claim 30 , wherein the step of heating the zirconia green blank to form a brown blank comprises pre-sintering.