EP4673082A1

EP4673082A1 - Ceramic veneers and continuous additive manufacturing method for making ceramic veneers

Info

Publication number: EP4673082A1
Application number: EP24707953.6A
Authority: EP
Inventors: Martin Goetzinger; James D. Hansen; Gareth A. Hughes; John A. NORRIS
Original assignee: Solventum Intellectual Properties Co
Current assignee: Solventum Intellectual Properties Co
Priority date: 2023-03-01
Filing date: 2024-02-22
Publication date: 2026-01-07
Also published as: JP2026507104A; WO2024180438A1; CN120857914A

Abstract

The present disclosure provides a method of making a ceramic article. The method includes (a) obtaining a photopolymerizable slurry or sol including a plurality of ceramic particles distributed in the photopolymerizable slurry or sol and (b) selectively polymerizing the photopolymerizable slurry or sol using actinic radiation and continuous movement of a build substrate through the photopolymerizable slurry or sol to form a gelled article. The method also includes (c) extracting solvent from the gelled article to form an aerogel article or a xerogel article; (d) heat treating the aerogel article or the xerogel article to form a porous ceramic article; and (e) sintering the porous ceramic article to form a sintered ceramic article. The sintered ceramic article exhibits a particular density. Further, additive manufactured ceramic articles are provided that exhibit a particular density, opacity, or both.

Description

CERAMIC VENEERS AND CONTINUOUS ADDITIVE MANUFACTURING METHOD FOR MAKING CERAMIC VENEERS TECHNICAL FIELD The present disclosure broadly relates to ceramic dental veneers having desirable properties and geometries. The present disclosure also relates to an additive manufacturing method for producing such ceramic dental veneers. BACKGROUND A dental veneer is a thin layer of restorative material placed over a tooth surface or dental framework, to improve the aesthetics of the visible tooth, for instance, improving color or hiding staining. Veneers may be standardized or made custom for a particular patient’s one or more teeth. The dental veneer is preferably arranged at those parts of a dental restoration that are likely to be visible in a patient's mouth, or that in particular functionally co-operate with the adjacent or opposed teeth of a patient, for example. A dental veneer typically has a 3-dimensional inner and outer surface including convex and concave structures. The inner surface of the dental veneer typically corresponds essentially to the outer surface of a prepared tooth or tooth stump, whereas the outer surface of the dental veneer typically corresponds essentially to the final dental restoration (e.g., the desired final appearance of the patient’s tooth). A dental veneer may be temporary, in that it can be readily removed from the patient’s mouth by peeling of the underlying support structure. Such veneers typically do not require preparation and pre-shaping of the tooth, including cutting, drilling, grinding and other forms of permanently removing material from a tooth, as they are formed with a reduced cross-sectional thickness in the veneer body. For instance, US 2005/0227204 describes temporary veneers that can be made of porcelain, plastic, other semi-rigid composite materials, which can be removed by the use of a warm water rinse in the mouth and pulling the veneer off from the teeth. Other temporary veneers are formed of molded polymer or plastic materials. While a passable solution, temporary veneers can be deficient in aesthetics or possess insufficient material strength to withstand forces encountered in the patient’s mouth. Hence, there is a need in some cases for providing a permanent veneer. Permanent veneers are often formed from glass or glass ceramic materials and are created using at least one molding or milling process. US20120175799 features a method for producing an individualized tooth veneer with an individualized holder. The holder is complementary to shape of the veneer and provides stability to an otherwise thin and fragile article. Veneers obtained by the method of US20120175799 can purportedly be produced with mean thicknesses of 200 microns or less. SUMMARY Despite myriad options existing for veneers, the patient and practitioner still must engage in a series of tradeoffs: temporary or permanent; fragile or robust; custom-fit or standard; aesthetic or functional. What is needed is a veneer that combines the strength, aesthetic, and wear resistance of a ceramic veneer with the ease of manufacture of thin profile of a temporary veneer, along with the inclusion of surface features and elements that aid in the mimicking of a tooth surface and retention of the veneer on the tooth or other dental framework. In a first aspect, the present disclosure provides a monolithic veneer comprising: an incisal edge, a cervical edge, a body extending between the incisal edge region and cervical edge region, and opposing proximal edges, as well as a labial surface and an opposing tooth-facing surface. A cusp receptacle is provided adjacent the incisal edge, with a central window area defined between the incisal and cervical edges and offset from the proximal edges. The body of the veneer includes one or more architectural features selected from the group consisting of mamelons at least partially within the cusp receptacle, concave divots at least partially within the cusp receptacle, designed surface textures surface, and relief features. The thinnest portion of the body within the central window area is no greater than 400 microns. In a second aspect, the present disclosure provides method for making a dental veneer, comprising steps of: receiving a design for a dental veneer, comprising: an incisal edge, a cervical edge, opposing proximal edges, and a body extending between the edges; a labial surface and an opposing tooth-facing surface, and a cusp receptacle at the incisal edge; making the dental veneer as a single piece from a ceramic sol using additive manufacturing, wherein a thinnest portion of a central window area of the veneer is no greater than 400 microns, and wherein the veneer exhibits a density of 94% or greater with respect to a theoretical density of the ceramic material In a third aspect, an additive manufacturing method of making a ceramic veneer is provided. The method includes (a) obtaining a photopolymerizable slurry or sol including a plurality of ceramic particles distributed in the photopolymerizable slurry or sol and (b) selectively polymerizing the photopolymerizable slurry or sol using actinic radiation and movement of a build substrate through the photopolymerizable slurry or sol to form a gelled article. Next, the method includes (c) extracting solvent from the gelled article to form an aerogel article or a xerogel article; (d) heat treating the aerogel article or the xerogel article to form a porous ceramic article; and (e) sintering the porous ceramic article to form a sintered ceramic article. The sintered ceramic article exhibits a density of 94% or greater with respect to a theoretical density of the ceramic material. In a fourth aspect, an additively manufactured ceramic article is provided. The ceramic article exhibits a density of 94% or greater with respect to a theoretical density of the ceramic material, exhibits an opacity of 80% or less, or both. The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. For instance, the methods of the present disclosure can be adapted to produce dental and orthodontic articles in addition to veneers. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list. Brief Description of the Drawings FIG.1 is a perspective view of a veneer according to an embodiment of the present disclosure, looking towards the tooth-facing surface; FIG.2 is a perspective view of the veneer of FIG.1, looking towards the tooth-facing surface opposing the facial surface; FIG.3 is a perspective view of a veneer according to an embodiment of the present disclosure, looking towards the tooth-facing surface; FIG.4 is a cross-sectional view of the veneer of FIG.3; FIG.5 is a photograph of a sintered veneer according to Example 3; FIG. 6A-6C are perspective views of a veneer according to embodiments of the present disclosure, looking towards the tooth-facing surface; FIG.7 is a perspective view of a veneer according to an embodiment of the present disclosure, looking towards the facial surface; FIG.8 is a block diagram of a generalized system 600 for additive manufacturing of an article; FIG.9 is a block diagram of a generalized manufacturing process for an article; FIG.10 s a high-level flow chart of an exemplary article manufacturing process; FIG. 11 is a flowchart of a process for building an article using the photopolymerizable compositions disclosed herein; FIG.12A is a perspective view of a digital file for an article having the shape of a dental veneer; FIG.12B is a photograph of a gelled article in the shape of a veneer for the central incisor, an aerogel article in the shape of a veneer, a white body in the shape of a veneer, and a sintered veneer prepared from the digital file of article and according to the Example 2; FIG.12C is a photograph of a sintered ceramic veneer for a lateral tooth prepared according to Example 2; FIG.12D is a photograph of a set of sintered ceramic veneers for central and lateral teeth prepared according to Example 2. FIG.13 is a photograph of a series of veneers according to the prior art; FIG.14 is photograph of a portion of a sintered ceramic article of 12C with the support sprues removed; FIG.15 is a photograph of a series of gelled articles, each in the shape of a veneer, made according to Example 1; and FIG.16 is a photograph of a sintered ceramic veneer created from the gelled articles of FIG.16. While the above-identified figures set forth several embodiments of the disclosure other embodiments are also contemplated, as noted in the description. The figures are not necessarily drawn to scale. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. Glossary: As used herein, “ceramic” or “ceramic article” includes amorphous material, glass, crystalline ceramic, glass-ceramic, and combinations thereof, and refers to non-metallic materials produced by application of heat. Ceramics are usually classified as inorganic materials. The term “amorphous material” refers to material that lacks long range crystal structure as determined by X-ray diffraction and/or has an exothermic peak corresponding to the crystallization of the amorphous material as determined by DTA (differential thermal analysis). The term “glass” refers to amorphous material exhibiting a glass transition temperature. The term “glass-ceramic” refers to ceramics comprising crystals formed by heat-treating amorphous material. The term “crystalline ceramic” refers to a ceramic material exhibiting a discernible X-ray powder diffraction pattern. “Crystalline” means a solid composed of atoms arranged in a pattern periodic in three dimensions (i.e., has long-range crystal structure, which may be determined by techniques such as X-ray diffraction). A “crystallite” means a crystalline domain of a solid having a defined crystal structure. A crystallite can only have one crystal phase. As used herein, “ceramic particle” includes particles of amorphous material, glass, crystalline ceramic, glass-ceramic, and combinations thereof, and refers to non-metallic materials produced by application of heat or made by a chemical synthesis process. Ceramic particles are usually classified as inorganic materials. The term “amorphous material” with respect to ceramic particles refers to a material derived from a melt and/or a vapor phase as well as a material made from chemical synthesis, wherein the material lacks long range crystal structure as determined by X-ray diffraction and/or has an exothermic peak corresponding to the crystallization of the amorphous material as determined by DTA (differential thermal analysis). For instance, amorphous silica nanoparticles may be generated by condensation of silanes to form the nanoparticles. As used herein, “additive manufacturing” means processes used to make 3- dimensional articles. An example of an additive manufacturing technique is stereolithography (SLA), in which successive layers of material are laid down under computer control. The articles can be of almost any shape or geometry and are produced from a 3-dimensional model or other electronic data source. As used herein, “sol” refers to a continuous liquid phase containing discrete particles having sizes in a range from 1 nanometer (nm) to 100 nm. As used herein, “slurry” refers to a continuous liquid phase containing discrete particles having sizes in a range from greater than 100 nm to 50 micrometers or from greater than 100 nm to 10 micrometers. A slurry may optionally further contain discrete particles having sizes in a range from 1 nanometer (nm) to 100 nm. As used herein, “machining” refers to milling, grinding, cutting, carving, or shaping a material by a machine. Milling is usually faster and more cost effective than grinding. A “machinable article” is an article having a 3-dimensional shape and having sufficient strength to be machined. As used herein, a “powder” refers to a dry, bulk material composed of a large number of fine particles that may flow freely when shaken or tilted. As used herein, a “particle” refers to a substance being a solid having a shape which can be geometrically determined. The shape can be regular or irregular. Particles can typically be analyzed with respect to e.g., particle size and particle size distribution. A particle can comprise one or more crystallites. Thus, a particle can comprise one or more crystal phases. As used herein, “associated” refers to a grouping of two or more primary particles that are aggregated and/or agglomerated. Similarly, the term “non-associated” refers to two or more primary particles that are free or substantially free from aggregation and/or agglomeration. As used herein, “aggregation” refers to a strong association of two or more primary particles. For example, the primary particles may be chemically bound to one another. The breakdown of aggregates into smaller particles (e.g., primary particles) is generally difficult to achieve. As used herein, “agglomeration” refers to a weak association of two or more primary particles. For example, particles may be held together by charge or polarity. The breakdown of agglomerates into smaller particles (e.g., primary particles) is less difficult than the breakdown of aggregates into smaller particles. As used herein, “primary particle size” refers to the size of a non-associated single crystalline or single amorphous ceramic particle, which is considered to be a primary particle. X-ray diffraction (XRD) for crystalline particles and transmission electron microscopy (TEM) for amorphous particles are typically used to measure the primary particle size. As used herein, “essentially spherical” means that the shape of the particles is close to a sphere. It does not contain sharp edges, which may result from a milling process. As used herein, “soluble” means that a component (e.g., a solid) can be completely dissolved within a solvent. That is, the substance is able to form individual molecules (like glucose) or ions (like sodium chloride) when dispersed in water at 23°C. The solubilization process, however, might take some time, e.g. stirring the component over a couple of hours (e.g., 10 to 20 hours) might be required. As used herein, “density” means the ratio of mass to volume of an object. The unit of density is typically grams per cubic centimeter (g/cm³). The density of an object can be calculated e.g., by determining its volume (e.g., by calculation or applying the Archimedes principle or method) and measuring its mass. The volume of a sample can be determined based on the overall outer dimensions of the sample. The density of the sample can be calculated from the measured sample volume and the sample mass. The total volume of a material sample can be calculated from the mass of the sample and the density of the used material. The total volume of cells in the sample is assumed to be the remainder of the sample volume (100% minus the total volume of material). As used herein, “theoretical density” refers to the maximum possible density that would be obtained in a sintered article if all pores were removed. The percent of the theoretical density for a sintered article can be determined, for example, from electron micrographs of a cross-section of the sintered article. The percent of the area of the sintered article in the electron micrograph that is attributable to pores can be calculated. Stated differently, the percent of the theoretical density can be calculated by subtracting the percent voids from 100 percent. That is, if 1 percent of the area of the electron micrograph of the sintered article is attributable to pores, the sintered article is considered to have a density equal to 99 percent of the theoretical density. The density can also be determined by the Archimedes method. As used herein, “porous material” refers to a material comprising a partial volume that is formed by voids, pores, or cells in the technical field of ceramics. Accordingly, an “open-celled” structure of a material sometimes is referred to as “open-porous” structure, and a “closed-celled” material structure sometimes is referred to as a “closed-porous” structure. It may also be found that instead of the term “cell” sometimes “pore” is used in this technical field. The material structure categories “open-celled” and “closed-celled” can be determined for different porosities measured on different material samples (e.g., using a mercury “Poremaster 60-GT” from Quantachrome Inc., USA) according to DIN 66133. A material having an open-celled or open-porous structure can be passed through by e.g., gases. As used herein, “heat treating”, “calcining”, “binder burn out”, or “debindering” refers to a process of heating solid material to drive off at least 90 percent by weight of volatile chemically bound components (e.g., organic components) (versus, for example, drying, in which physically bonded water is driven off by heating). Heat treating is done at a temperature below a temperature needed to conduct a sintering step. As used herein, “sintering” and “firing” are used interchangeably. A porous (e.g., pre-sintered) ceramic article shrinks during a sintering step, that is, if an adequate temperature is applied. The sintering temperature to be applied depends on the ceramic material chosen. Sintering typically includes the densification of a porous material to a less porous material (or a material having less cells) having a higher density, in some cases sintering may also include changes of the material phase composition (for example, a partial conversion of an amorphous phase toward a crystalline phase). As used herein, “gel”, “gelled article”, and “gelled body” are used interchangeably and mean a three-dimensional gel resulting from the curing reaction of polymerizable components contained in a slurry or sol, including organic binder and solvent. As used herein, “aerogel” means a three-dimensional low-density solid. An aerogel is a porous material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The solvent removal is often done under supercritical conditions. During this process the network does not substantially shrink and a highly porous, low-density material can be obtained. As used herein, “xerogel” refers to a three-dimensional solid derived from a gel, in which the liquid component of the gel has been removed by evaporation under ambient conditions or at an elevated temperature. As used herein, “green body” means an un-sintered ceramic item, typically having an organic binder present. As used herein, “white body” and “porous ceramic article” are interchangeable and refer to an item that has had the binder burned out or to a pre-sintered ceramic item. As used herein, a “pre-sintered” ceramic item is an item that has had solvent and binder removed and exhibits a density of lower than 93% of its theoretical density. As used herein, “geometrically defined article” means an article the shape of which can be described with geometrical terms including 2-dimensional terms like circle, square, rectangle, and 3-dimensional terms like layer, cube, cuboid, sphere. As used herein, “isotropic linear sintering behavior” means that the sintering of a porous body during the sintering process occurs essentially invariant with respect to the directions x, y and z. “Essentially invariant” means that the difference in sintering behavior with respect to the directions x, y and z is in a range of not more than about +/- 5% or +/- 2% or +/- 1%. As used herein, the term “crack” refers to a material segregation or partitioning (i.e., defect) that is a ratio equal to at least 5:1, at least 6:1, at least 7:1, at least 8:1, at least 10:1, at least 12:1, or at least 15:1 in any two dimensions. The term “mass inertial force” as referred to herein may be specified as force per unit mass and therefore may be specified in the unit m/s². Further, the mass inertial force can be expressed by the G-force which is a factor of the acceleration of gravity. For the purposes of the present specification, the acceleration of gravity is 9.81 m/s². Consequently, for example, a mass inertial force of 9.81 m/s² can be expressed as 1 G. As used herein, a “dental article” means any article which can or is to be used in the dental or orthodontic field, especially for producing of or as dental restoration, a tooth model and parts thereof. Examples of dental articles include crowns (including monolithic crowns), bridges, inlays, onlays, veneers, facings, copings, crown and bridged framework, implants, abutments, orthodontic appliances (e.g. brackets, buccal tubes, cleats, attachments, and buttons) and parts thereof. The surface of a tooth is considered not to be a dental article. A material or composition is “essentially free” or “substantially free” of a certain component within the meaning of the invention, if the material or composition does not contain said component as an essential feature. Thus, said component is not willfully added to the composition or material either as such or in combination with other components or ingredient of other components. A composition or material being essentially free of a certain component usually contains the component in an amount of less than about 1 wt.%, or less than about 0.1 wt.%, or less than about 0.01 wt.% (or less than about 0.05 mol/1 solvent, or less than about 0.005 mol/1 solvent, or less than about 0.0005 mol/1 solvent) with respect to the whole composition or material. Ideally the composition or material does not contain the said component at all. However, sometimes the presence of a small amount of the said component is not avoidable e.g., due to impurities. As used herein, “aliphatic group” means a saturated or unsaturated linear, branched, or cyclic hydrocarbon group. This term is used to encompass alkyl, alkenyl, and alkynyl groups, for example. As used herein, “alkyl” means a linear or branched, cyclic or acyclic, saturated monovalent hydrocarbon having from one to thirty-two carbon atoms, e.g., methyl, ethyl, 1-propyl, 2-propyl, pentyl, and the like. As used herein, “alkylene” means a linear saturated divalent hydrocarbon having from one to twelve carbon atoms or a branched saturated divalent hydrocarbon radical having from three to twelve carbon atoms, e.g., methylene, ethylene, propylene, 2- methylpropylene, pentylene, hexylene, and the like. As used herein, “alkenyl” refers to a monovalent linear or branched unsaturated aliphatic group with one or more carbon-carbon double bonds, e.g., vinyl. Unless otherwise indicated, the alkenyl groups typically contain from one to twenty carbon atoms. As used herein, “hardenable” refers to a material or composition that can be cured or solidified, e.g., by heating to remove solvent, heating to cause polymerization, chemical crosslinking, radiation-induced polymerization or crosslinking, or the like. As used herein, “curing” means the hardening or partial hardening of a composition by any mechanism, e.g., by heat, light, radiation, e-beam, microwave, chemical reaction, or combinations thereof. As used herein, “cured” refers to a material or composition that has been hardened or partially hardened (e.g., polymerized or crosslinked) by curing. As used herein, “integral” refers to being made at the same time or being incapable of being separated without damaging one or more of the (integral) parts, e.g., “unitary”. As used herein, “incisal” and “occlusal” are used interchangeably and refer to the cutting and/or chewing surfaces of the teeth located distal to the gingiva. As used herein, the term “(meth)acrylate” is a shorthand reference to acrylate, methacrylate, or combinations thereof, “(meth)acrylic” is a shorthand reference to acrylic, methacrylic, or combinations thereof, and “(meth)acryl” is a shorthand reference to acryl and methacryl groups. “Acryl” refers to derivatives of acrylic acid, such as acrylates, methacrylates, acrylamides, and methacrylamides. By “(meth)acryl” is meant a monomer or oligomer having at least one acryl or methacryl groups, and linked by an aliphatic segment if containing two or more groups. As used herein, “(meth)acrylate-functional compounds” are compounds that include, among other things, a (meth)acrylate moiety. As used herein, “non-crosslinkable” refers to a polymer that does not undergo crosslinking when exposed to actinic radiation or elevated heat. Typically, non- crosslinkable polymers are non-functionalized polymers such that they lack functional groups that would participate in crosslinking. As used herein, “polymerizable slurry or sol” and “polymerizable composition” each mean a hardenable composition that can undergo polymerization upon initiation (e.g., free-radical polymerization initiation). Typically, prior to polymerization (e.g., hardening), the polymerizable slurry/sol or composition has a viscosity profile consistent with the requirements and parameters of one or more additive manufacturing (e.g., 3D printing) systems. In some embodiments, for instance, hardening comprises irradiating with actinic radiation having sufficient energy to initiate a polymerization or cross-linking reaction, for a “photopolymerizable slurry or sol”. For instance, in some embodiments, ultraviolet (UV) radiation, visible radiation, e-beam radiation, or a combination, can be used. As used herein, a “resin” contains all polymerizable components (monomers, oligomers and/or polymers) being present in a hardenable slurry/sol or composition. The resin may contain only one polymerizable component compound or a mixture of different polymerizable compounds. As used herein, “sintered article” refers to a gelled article that has been dried, heated to remove the organic matrix, and then further heated to reduce porosity and to densify. The density after sintering is at least 40 percent of the theoretical density. Articles having a density in a range of 40 to 93 percent of the theoretical density typically have open porosity (pores open to surface). Above 93 percent or 95 percent of the theoretical density, there are typically closed pores (no pores open to the surface). As used herein, “thermoplastic” refers to a polymer that flows when heated sufficiently above its glass transition point and become solid when cooled. As used herein, “thermoset” refers to a polymer that permanently sets upon curing and does not flow upon subsequent heating. Thermoset polymers are typically crosslinked polymers. The words “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the disclosure. In this application, terms such as “a”, “an”, and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terms “a”, “an”, and “the” are used interchangeably with the term “at least one.” The phrases “at least one of” and “comprises at least one of” followed by a list refers to any one of the items in the list and any combination of two or more items in the list. As used herein, the term “or” is generally employed in its usual sense including “and/or” unless the content clearly dictates otherwise. The term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements. Also herein, all numbers are assumed to be modified by the term “about” and preferably by the term “exactly.” As used herein in connection with a measured quantity, the term “about” refers to that variation in the measured quantity as would be expected by the skilled artisan making the measurement and exercising a level of care commensurate with the objective of the measurement and the precision of the measuring equipment used. Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range as well as the endpoints (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). As used herein as a modifier to a property or attribute, the term “generally”, unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within +/- 20 % for quantifiable properties). The term “substantially”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within +/- 10% for quantifiable properties) but again without requiring absolute precision or a perfect match. Terms such as same, equal, uniform, constant, strictly, and the like, are understood to be within the usual tolerances or measuring error applicable to the particular circumstance rather than requiring absolute precision or a perfect match. Detailed Description of Illustrative Embodiments The present disclosure provides ceramic veneers having desirable optical and material properties. The veneers may be manufactured to have relatively thin wall sections while maintaining adequate if not desirable strength. Such veneers may include architectural features that, inter alia, aid in seating the veneer on the tooth surface, aid in the mimicking of the tooth anatomy, or better control the optical properties (e.g., opacity or translucency) of desired regions of the veneer body. The ceramic veneers of the present disclosure can be monolithically manufactured as a single piece from a particle loaded slurry or sol. Ceramic dental veneers of the present disclosure exhibit unique physical features and performance characteristics made possible by additive manufacturing. The present disclosure also provides a method to produce ceramic articles (e.g., parts) using additive manufacturing from a particle loaded slurry or sol. The articles can be made according to traditional stereolithography, where a digital object file is sliced into cross-sections, which are then used to illuminate each layer with a pause for motion in between each illumination step. Ceramic composite parts build this way are often post- processed to achieve a solid ceramic. An alternative approach to layer-wise stereolithography is to build a part continuously. The same slicing of a digital object into two-dimensional cross-sections is done, but the layers are illuminated without significant pauses between them. By (essentially) continuously moving the part away from the light source, a part without certain optical artifacts in its interior can be fabricated. Other additive manufacturing methods are also suitable, including inkjet printing and volumetric additive manufacturing (VAM) techniques. The present disclosure provides an additively manufactured ceramic veneer. The sintered ceramic veneer exhibits a density of 94% or greater, or even 98% or greater, with respect to a theoretical density of the ceramic material, exhibits an opacity of 80% or less, or both. In some embodiments, the sintered ceramic veneer advantageously exhibits an opacity of 80% or less, 75% or less, or 70% or less; and 1% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, or 60% or more. The opacity relates to the ceramic article’s ability to block transmission of light. As used herein, the term “light” refers to electromagnetic radiation, whether visible to the unaided human eye or not. Ultraviolet light is light having a wavelength in a range from about 250 nanometers (nm) to 380 nm. Visible light is light having a wavelength in a range from 380 nanometers (nm) to 700 nm. Infrared light has a wavelength in a range from about 700 nm to 300 micrometers. In some embodiments, suitable actinic radiation provides a wavelength in a range from 220 nm to 550 nm. Opacity measurements can be conducted according to ASTM E-284 using a Lab Scan XE spectrophotometer (Hunterlab, Reston, Va.). Opacity is measured using a spectrophotometer with the “L” value measured separately against a black background and against a white background, respectively. The opacity is calculated as (L measured against the black background/L measured against the white background) times 100, and reported in units of %. The “L” value is one of three standard parameters in the CIELAB color space scale established by the International Commission on Illumination. “L” is a brightness value, ranging from 0 (black) to 100 (highest intensity). In some embodiments, the opacity may vary across the surface the veneer. For instance, an architectural relief feature may be printed on a surface of the veneer to modify the opacity of the surrounding ceramic. The modified opacity can be advantageous in mimic decalcification or fluorosis of the underlying tooth or hiding an area of underlying discoloration. In some embodiments, the sintered ceramic veneer advantageously exhibits a flexural strength of 100 megaPascals (MPa) or greater, 200 MPa, 300 MPa, 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, 900 MPa, 1000 MPa, 1100 MPa, or 1200 MPa or greater; and 2000 MPa or less, 1900 MPa, 1800 MPa, 1700 MPa, 1600 MPa, 1500 MPa, 1400 MPa, or 1300 MPa or less. Flex strength can be determined using ISO 6872 (2008) after forming a sintered ceramic article in the shape of a test bar having dimensions of approximately 1 mm x 4 mm x 12 mm. Additional details of the test method are provided in the examples below. In many embodiments, the ceramic veneer comprises a shaped integral article, in which more than one variation in dimension or texture is provided by a single integral article. For example, the veneer can comprise one or more architectural features selected from the group consisting of mamelons, concave divots, designed surface textures, identification features, channels, and relief features. Such features are typically not possible to provide in an integral article using conventional molding or milling methods. In particular, the dimensions of the available milling burs are either too large to create the architectural feature or the surface of the veneer that would benefit from such features is nigh inaccessible. The veneer may be designed, and produced, to have a thickness of at least about 0.08 mm (80 microns) and less than 0.4 mm (400 microns), less than 0.3 mm, less than 0.2 mm or less than 0.1 mm after sintering. The thickness of the veneer can be a mean thickness. At various portions the veneer may be thinner or thicker. Typically, the veneers of the present disclosure are thinnest at the incisal, cervical, and proximal edges and thickest in the center of the veneer. As used herein, the center of the veneer means the region of the veneer located about 2 mm from the incisal and proximal edges, as further described below. In certain embodiments, the veneer can be a non-framework dental product, e.g., the veneer can be placed directly on to a tooth surface without any intermediate framework to strengthen the veneer. Other embodiments may utilize other dental prostheses, such as a dental crown or bridge, include a veneering layer on top of a framework, such as a coping or bridge framework. For certain embodiments, particularly those matching or accommodating a patient’s anatomical features, it may not be necessary to remove material from the tooth before install the veneer. In other embodiments, small portions of a tooth may be prepared, e.g. by grinding. This may be done to, for example, remove imperfections of a tooth surface or provide better mechanical retention. FIGS.1 and 2 depict a dental veneer according to embodiments of the present disclosure. FIG.1 depicts the facial surfaces of the veneer, while FIG.2 depicts the opposing, tooth-facing (e.g., lingual) surfaces. The facial surface 11 is typically flat or convex to simulate the curvature of a patient’s tooth, while the opposing surface 12 is generally flat or concave to fit over and accept the external surface of the patient’s tooth or dental framework. The tooth-facing surface 12 can also be designed to accommodate a bonding composition. Optionally, non-ceramic coloring and/or glazing layers may be added at least on one side of the veneer 10. The veneer 10 includes an incisal edge 20, a pair of proximal edges 21 and 22, and a cervical edge 23. The height and width of the veneer 10 is within the known ranges for adult human teeth, particularly the known dimensions for upper central incisors, laterals, cuspids and bicuspids. Heights ranging from 6 millimeters to 13 millimeters and widths of 6 millimeters to 11 millimeters are typical. A central region 14 of the veneer is a major surface area located between the incisal and cervical edges 20, 23 and offset from the proximal edges 21, 22. The central region 14 includes a portion of the veneer body that is typically, but not exclusively, thicker than the body at the edges 20, 21, 22, and 23. In some other embodiments, the thickness of the body in the central region 14 is substantially equal to the thickness at one or more of the edges 20, 21, 22, and 23. The thickness of any region of the veneer can be designed and dictated in the manufacturing process, or may be modified by e.g., grinding when the veneer is seated in the patient’s mouth or at another time prior to installation. The veneer 10 includes a cusp receptacle 30 near the incisal edge 20. The cusp receptacle 30 includes an incisal overhang 31 dimensioned to receive incisal surfaces of the patient’s tooth and/or framework restoration. Though not depicted in FIG.2, the cusp receptacle 30 may include regions that extend over the lingual surfaces of the patient’s tooth when the veneer is installed (see FIGS.3 and 4), such that the incisal overhang 31 is partially enclosed. The cusp receptacle 30 can be designed to include architectural features that mimic anatomical features of a patient’s tooth, that register with certain anatomical features to improve veneer seating, or combinations of both. The cusp receptacle 30 of veneer 10 includes two mamelons 33, 34 projecting from the incisal overhang 31 in the direction of the cervical edge 23. The mamelons 33, 34 can have a generally frusto-conical shape, with a largest cross-sectional dimension of no greater than 2mm and a height, as measured from the overhang 31 of about 500 microns to 1.5mm). In some embodiments, the mamelons can include a largest cross- sectional dimension of no greater than 1.75 mm, no greater than 1.5mm, no greater than 1.25 mm, and no greater than 1mm. For particular fine features used to mimic tooth anatomy and aid in retention, the mamelons may have a largest cross-sectional dimension of no greater than 750 microns, no greater than 600 microns, no greater than 550, and no greater than 500 microns. Height can also vary accordingly. Other shapes and dimensions for the mamelons are contemplated, including pyramidal, tetrahedral, circular cylindrical; elliptical cylindrical; cuboidal (e.g., square cube or rectangular cuboid); conical; truncated conical, and any other regular or irregular shape approximating an anatomical feature. In some embodiments where the veneer 10 is suitably translucent, the mamelons 33, 34 can impact the shading of the facial surface near the incisal edge 20. Such mamelons are challenging if not impossible to create via conventional milling or casting, due at least in part to the larger dimensions of conventional milling burrs and the difficulty of accessing the cusp receptacle surfaces. FIGS.3 and 4 depict another embodiment of a ceramic dental veneer according to the present disclosure. Ceramic dental veneer 100 is similar to veneer 10, in that it includes an incisal edge 120, a cusp receptacle 130, and a cervical edge 123. Unlike dental veneer 10, the dental veneer 100 of Figs.3 and 4 is a shell veneer with sidewalls 121a and 122b at the proximal edges 121, 122, respectively. The sidewalls 121a, 122b may extend partially into the interproximal spaces between adjacent teeth when the veneer 100 is seated, but this is not strictly necessary. The sidewalls 121a, 122b may be relatively thinner (e.g., about 200 microns or less) as compared to the central region 114 of the veneer 100. The cusp receptacle 130 may include a truncated wall section 132 opposite the tooth facing-surface 112, creating a pocket for receipt of incisal surfaces open primarily along an occluso-gingival axis. The truncated wall section 132 may be disposed adjacent or in contact with a lingual tooth surface when the veneer 100 is fixed to the patient’s tooth. The cusp receptacle 130 includes a plurality of mamelons 140 extending between the sidewalls 121a, 122a. The mamelons 140 define a series of concave divots 141 between the peaks 142 of the mamelons. Each divot 141 has a largest cross-sectional dimension, as measured in a plane substantially parallel to the overhang 131, of 200 microns or less, 175 microns or less, 150 microns or less, or in some embodiments 100 microns or less. The presence of the truncated wall section 132, along with dimensions and number of mamelons, renders the creation of such architectural features utterly impractical through conventional milling and casting methods. A further embodiment of a veneer according to the present disclosure is depicted in the image of FIG.5, which was created according to Example 3 below. The veneer 200 can include any of the features of the veneers 10 and 100. The veneer 200 includes an architectural feature 250 in relief on the tooth-facing surface 212, in this example a printed “3M” company name, at center region 214 of the veneer body. The appearance of the facial surface 211 is altered due to the presence of the architectural feature 250, which can be designed to hide disfavored aesthetics or identify parts for a patient or practitioner, in addition to the branding benefits provided. The architectural feature 250 can be intrusive or protrusive. Such identification or branding features are typically printed protruding from the tooth-facing surface a height of 100 microns and can have a dimension of about 1 mm, however the dimensions may vary according to the brand or the message borne. Bonding tooth identity, sub-brand, size, lot number, or custom case identification number, or any combination thereof, can be printed in a similar manner. Alternatively, the architectural features 250 can intrude into the tooth-facing surface 212, with similar dimensions. Architectural features are not limited to identification and branding marks. For instance, FIGs.6A-6C depicts arranged patterns of architectural features 350 on the tooth-facing surface 312 of a veneer 300. The veneer 300 can include any and all features of veneers 10, 100, and 200 in addition to the arranged pattern of architectural features. Like veneer 200, the architectural features 350 can be intrusive or protrusive. An "arranged pattern" is a plurality of architectural features (e.g., recesses, channels, protuberances, etc.) arranged at predetermined positions or arranged with some degree of regularity or deliberation. Such arranged architectural features can impart surface texture to the tooth-facing surface, which can aid in the retention of the bonding agent between the veneer and the tooth/framework. The surface texture provided by the arranged architectural features can also modify the translucency of the sintered veneer at desired locations. For example, the arranged pattern of architectural features can include an arranged row pattern, an arranged lattice pattern such as an arranged square lattice pattern, an arranged zigzag pattern, or an arranged radial pattern. The arranged pattern need not be formed evenly on the entire surface but may be formed in only a portion of a given veneer surface. The pattern of features may vary or remain the same over any portion of the article. The architectural features can take the form of any shape. Similarly, the three- dimensional geometry of the features is not particularly limited so long as the recess does not extend through the thickness of central veneer to the opposing major surface. Non- limiting examples of cross-sectional shapes that are suitable for features. include circles, triangles, squares, rectangles, and other polygons. The architectural features within the pattern can be of similar geometry or can have different geometries. The architectural features of Figs.6A-6C resemble channels in the tooth-facing surface. Such channels can follow any desired path and can be continuous or discontinuous across a surface of the core in any given direction. As depicted in FIGS.6A-6C, a surface can include architectural features of identifiable geometries arranged in repeating unit cell. The unit cell can be repeated in an arranged pattern of unit cells. A variety of shapes may be used to define the unit cell, including rectangles, circles, half-circles, ellipses, half-ellipses, triangles, trapezoids, and other polygons (e.g., pentagons, hexagons, octagons), etc., and combinations thereof. In such embodiments, each unit cell boundary is directly adjacent the boundary of a neighboring unit cell, so that the plurality of unit cells resembles, e.g., a grid or tessellation. The unit cells (or individual architectural features) may have similar dimensions across the printed surface (FIG.6A or 6B) or may have larger dimensions proximate the center region 314 of the veneer, offering smaller dimensions of the features at the edges 320, 321, 322, 323 are approached (FIG.6C). In certain embodiments, such gradients in feature geometry and arrangement may be useful in modifying at least one of the translucence and opacity of a specific region (e.g., central region) of the veneer body, and in improving the retention of the tooth-facing surface to the patient’s tooth and/or dental framework. Architectural features may also be created on facial surface of the veneer body to mimic or register with tooth anatomy. For instance, the veneer 500 of Fig.7 includes multiple classes of architectural features on the facial surface 511. The first architectural feature class includes a pair of troughs 550 extending occluso-gingivally from the incisal edge 520. The troughs 550 are dimensioned to correspond to primary tooth anatomy and do not extend over the full facial surface 511 of the veneer to the cervical edge 523. In other embodiments, the troughs may extend over a full or different portion of the facial surface 511. The second features class includes a series of mesio-distally extending channels 560 across the facial surface 511 substantially parallel to the troughs 550. The channels 560 are dimensioned to correspond with tertiary tooth anatomy, for instance perikyma. Accordingly, the channels 560 included smaller depth (i.e., distance into the facial surface 511) than the troughs 550, including less than about 100 microns. The channels are spaced from one another at a relatively tight pitch (e.g., a distance between channels valleys of less than 90 microns) and are arranged across on the full area of the facial surface 511, including the central region 514. In other embodiments, the veneer may feature only one of the first and second class of architectural features (e.g., only channels 560) on the facial or tooth-facing surface. Other surface textures described above with respect to veneers 300 may also be created on the facial surface 511. Veneers of the present disclosure may be manufactured individually or as part of a set, suitable for one or more patients. The veneers of the present disclosure may be provided as part of a kit. The contents of the kit can include one or more of the following: tooth veneers for each of the various teeth (centrals, laterals, cuspids, and bicuspids); adhesives, applicators, and brushes; files and shaping tools to shape the veneers; and color modifiers. The veneers of the present disclosure can be bonded to the teeth using conventional techniques and dental compositions, such as the RELYX Cements and SCOTCHBOND Adhesives, each available from 3M Oral Care (St. Paul, MN). Suitable bonding techniques are described in EP2272458 (Karlsson et al.). Systems and methods for creating the veneers of the present disclosure are explored in more detail below. In general, the methods for creating a dental veneer include receiving digital 3D models of intra-oral structures or parameters for a preformed restoration including a veneer; generating a design of the veneer; generating instructions for a 3D printer (or other additive manufacturing equipment) to make the veneer; outputting the instructions to the 3D printer for making the veneer; making the veneer; and possibly performing post-processing of the 3D printed veneer. Methods and Systems for Additively Manufacturing Veneers The functions or algorithms described herein may be implemented in software in one embodiment. The software may consist of computer executable instructions stored on computer readable media or computer readable storage device such as one or more non-transitory memories or other type of hardware-based storage devices, either local or networked. Further, such functions correspond to modules, which may be software, hardware, firmware or any combination thereof. Multiple functions may be performed in one or more modules as desired, and the embodiments described are merely examples. The software may be executed on a digital signal processor, ASIC, microprocessor, or other type of processor operating on a computer system, such as a personal computer, server or other computer system, turning such computer system into a specifically programmed machine. The term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated software modules or hardware modules configured for performing the techniques of this disclosure. Even if implemented in software, the techniques may use hardware such as a processor to execute the software, and a memory to store the software. In any such cases, the computers described herein may define a specific machine that is capable of executing the specific functions described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements, which could also be considered a processor. Often, computer readable media are provided as part of a computing device. The computing device may have one or more processors, volatile memory (RAM), a device for reading machine-readable media, and input/output devices, such as a display, a keyboard, and a pointing device. Further, a computing device may also include other software, firmware, or combinations thereof, such as an operating system and other application software. A computing device may be, for example, a workstation, a laptop, a tablet, a smart phone, a personal digital assistant (PDA), a server, a mainframe or any other general-purpose or application-specific computing device. A computing device may read executable software instructions from a computer-readable medium (such as a hard drive, a CD-ROM, or a computer memory), or may receive instructions from another source logically connected to computer, such as another networked computer. Data can be communicated directly to an application, e.g., on a mobile device and/or directly to a cloud platform system via cellular connection, a Wi-Fi router or a hub. FIG. 8 is a diagram of a system 600 for generating additively manufactured 3D dental veneers. System 600 includes a processor 610 receiving digital 3D models 612 of teeth from intra-oral 3D scans or scans of impressions of teeth, or in other embodiments the system receives user manual input. System 600 can also include an electronic display device 616, such as a liquid crystal display (LCD) device, and an input device 618 for receiving user commands or other information, for example to design dental veneers. Display device 616 can be implemented with any electronic display, for example a Cathode Ray Tube (CRT), a liquid crystal display (LCD), light emitting diode (LED) display, or organic light emitting diode (OLED) display. Input device 618 can be implemented with any device for entering information or commands, for example a keyboard, microphone, cursor-control device, or touch screen. These systems can use an intra-oral scanner to obtain digital images from multiple views of teeth or other intra-oral structures, and those digital images can then be processed to generate a digital 3D model representing the scanned teeth and gingiva. System 600 can be implemented with, for example, a desktop, notebook, or tablet computer. System 600 can receive the 3D scans locally or remotely via a network. System 600 also includes a 3D printer 614, or other additive manufacturing device, to make the dental restorations. Data representing a veneer may be generated using computer modeling, such as computer aided design (CAD) data. Image data representing the veneer design can be exported in STL format, or in any other suitable computer processable format, to the additive manufacturing equipment. Scanning methods to scan a three-dimensional object may also be employed to create the data representing the article. One exemplary technique for acquiring the data is digital scanning. Digital scanning can capture information related to the spatial color variation in anatomy of interest (e.g., labial tooth surfaces), along with identification of anatomical features and margins for incorporation into a veneer design. A particularly suitable color scanner for capturing such information is the TRIOS scanner available from 3Shape A/S (Copenhagen, DK). Any other suitable scanning technique may be used for scanning an article, including X-ray radiography, laser scanning, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound imaging. Other possible scanning methods are described, e.g., in U.S. Patent Application Publication No.2007/0031791 (Cinader, Jr., et al.). The initial digital data set, which may include both raw data from scanning operations and data representing articles derived from the raw data, can be processed to segment an article design from any surrounding structures (e.g., a support for the article). FIG.9 is a flow chart representing a method for making dental veneers using additive manufacturing. This method includes receiving digital 3D models of intra-oral structures, such as models 612, or parameters for a preformed veneer (step 722), generating a design of the veneer (step 724), generating instructions for a 3D printer to make the veneer (step 726), outputting the instructions to the 3D printer to cause the 3D printer to make the veneer (step 728), and possibly performing post-processing of the 3D printed veneer (step 732). Some steps of this method, such as steps 722, 724, 726, and 728, can be implemented in software or firmware modules for execution by a processor such as processor 720, and the method can possibly be implemented using cloud computing. The designed veneer can be displayed on a display device such as display device 716, and a user may interact with the designed restoration via display device 716 and input device 718. Step 724 to design the veneer to be 3D printed can be implemented with software applications, including those for computer-aided design (CAD) and finite element analysis (FEA). Examples of CAD applications to design veneers, either standard or patient- specific or both, include the software products from SOLIDWORKS Corp. (Waltham, Mass.), Dental Wings Inc. (Montreal, Canada), and Exocad GmbH (Darmstadt, Germany). Non dental-specific CAD design software may be used as well, especially when designing standard preformed crown shapes, including the Unigraphics product from Siemens PLM Software (Plano, Tex.), the products from SOLIDWORKS Corp., and the Pro/ENGINEER product from PTC (Needham, Mass.). Topology optimization software can be used to engineer the architectural features and specify parameters such a unit cell geometry, scale, location, and gradient parameters; nTopology, available from nTopology, Inc. (New York, NY) is suitable for this purpose. Stress analysis via FEA or modeling can be used to predict performance, such as stress and deflection, during the design, and an example of an FEA application is the software product from ANSYS, Inc. (Canonsburg, Pa.). Generative design software can be used to optimize the structure of the veneer for desired response (e.g., flexibility, feature size, location, and volume) under simulated use conditions, and an example of such software application is the AUTODESK Within product from Autodesk Inc. (San Rafael, Calif.). The veneer may be designed on the basis of the digital representation of the patient’s tooth or based on standardized geometries. Steps 726 and 728 can use software applications to convert the designed veneer into instructions, for example a stereolithography (STL) file, for a 3D printer or other additive manufacturing device. The instructions can include slicing the design into layers to additively build up the restoration possibly with supporting layers. An example of 3D printing is the vat polymerization method using the Pico 3D printer from Asiga (Sydney, Australia). Other types of additive manufacturing to form a gel body or ceramic body include the following: inkjet printing; powderbed printing; selective laser sintering; fuse deposition modeling; and laminated object manufacturing. Examples of materials and processes for additive manufacturing, including 3D printable materials, are disclosed in the following: US Patent No.10532,088, entitled “High Strength and Translucency Dental Zirconia, Ceramic Materials, Devices, and Methods,”; International Publication No. WO2016/191162, entitled “Additive Manufacturing Process for Producing Ceramic Articles Using a Sol Containing Nano-Sized Particles,”; International Publication No. WO2016/191534, entitled “Sol Containing Nano Zirconia Particles for Use in Additive Manufacturing Processes for the Production of 3-Dimensional Articles,”; International Publication No. WO2017/011388, entitled “A Method of Making a Dental Article,”; International Publication No. WO2016/140840, entitled “Gel Compositions, Shaped Gel Articles and a Method of Making a Sintered Article”; and International Publication No. WO2021/024162, entitled “Continuous Additive Manufacturing Method for Making Ceramic Articles, and Ceramic Articles”. The post-processing for step 730 can include post-curing, support removal, extraction, and/or burn out, and then sintering and finishing of the 3D printed veneer. Further details regarding the additive manufacturing process are detailed below. In presently preferred embodiments, the additive manufacturing step 728 results in a gelled article obtained by selectively curing a photopolymerizable slurry or sol. The photopolymerizable slurry or sol typically includes ceramic particles; at least one radiation curable monomer; a solvent; a photoinitiator; and an inhibitor. Referring to FIG.10, for example and without limitation, an additive manufacturing method comprises retrieving 810, from a (e.g., non-transitory) machine-readable medium, data representing a 3D model of an article (e.g., a dental veneer) according to at least one embodiment of the present disclosure. The method further includes executing 820, by one or more processors, an additive manufacturing application interfacing with a manufacturing device using the data; and generating 830, by the manufacturing device, a physical object of the article. The method may optionally include receiving a 3D digital object comprising data specifying an article; and generating, with the manufacturing device by an additive manufacturing process, the article based on the digital object. The additive manufacturing equipment can selectively cure a photopolymerizable slurry or sol to form a gelled article. The photopolymerizable slurry or sol typically includes ceramic particles; at least one radiation curable monomer; a solvent; a photoinitiator; and an inhibitor. The components of ceramic particles, radiation curable monomer, solvent, photoinitiator, and inhibitor, are as discussed in detail below. One or more various optional post-processing steps 840 may be undertaken. Typically, the gelled article is dried, heat treated, and sintered to form a ceramic article. In presently preferred implementations, the generating step 830 typically comprises: a) obtaining a photopolymerizable slurry or sol comprising a plurality of ceramic particles distributed in the photopolymerizable slurry or sol; b) selectively polymerizing the photopolymerizable slurry or sol using actinic radiation and continuous movement of a build substrate through the photopolymerizable slurry or sol to form a gelled article; c) extracting solvent from the gelled article to form an aerogel article or a xerogel article; d) heat treating the aerogel article or the xerogel article to form a porous ceramic article; and e) sintering the porous ceramic article to form a sintered ceramic article; wherein the sintered ceramic article exhibits a density of 94% or greater with respect to a theoretical density of the ceramic material. Stated another way, and referring to FIG.11, a method of generating a ceramic veneer includes the step 1010 of obtaining a photopolymerizable slurry or sol and the step 1020 of selectively curing (e.g., polymerizing) the photopolymerizable slurry or sol to obtain a gelled article using actinic radiation and movement of a (e.g., build) substrate through the photopolymerizable slurry or sol. The photopolymerizable slurry or sol is typically introduced into a reservoir, cartridge, or other suitable container for use by or in an additive manufacturing device. The additive manufacturing device selectively cures the photopolymerizable slurry or sol according to a set of computerized design instructions. Referring again to FIG.11, the method further includes either the step 1040a of extracting solvent from (e.g., drying) the gelled article to form an aerogel article or the step 1040b of extracting solvent from the gelled article to form a xerogel article. Optionally, the solvent extraction is performed by applying a supercritical fluid drying step. The method further includes either the step 1050a of heat treating the aerogel article to form a porous ceramic article or the step 1050b of heat treating the xerogel article to form a porous ceramic article; as well as the step 1060 of sintering the porous ceramic article to obtain a sintered ceramic article. The photopolymerizable slurry or sol includes ceramic particles distributed in the photopolymerizable slurry or sol, which often comprises at least one radiation curable monomer, a solvent, a photoinitiator, and an inhibitor. Additionally, it is to be understood that methods of manufacturing a 3D article described herein can include so-called “stereolithography/vat polymerization” 3D printing methods, and the selective curing step may employ stereolithographic printing. Other techniques for three-dimensional manufacturing are known, and may be suitably adapted to use in the applications described herein. More generally, three-dimensional fabrication techniques continue to become available. All such techniques may be adapted to use with photopolymerizable slurries and sols described herein, provided they offer compatible fabrication viscosities and resolutions for the specified article properties. Fabrication may be performed using any of the fabrication technologies described herein, either alone or in various combinations, using data representing a three-dimensional object, which may be reformatted or otherwise adapted as necessary for a particular printing or other fabrication technology. Preferably, vat (co)polymerization with a two-dimensional cross section projection is employed in methods according to the present disclosure. This technology also includes a container of curable slurry or sol (e.g., photopolymerizable composition). However, a two-dimensional cross section is projected onto the curable composition by a computer controlled digital light processing (“DLP”), liquid crystal display (LCD), laser scanning system, or a photomask, or the like, to cure the desired section of an entire plane transverse to the projected beam at one time. Continuous printing in machines with these basic printer configurations is enabled, for example, by projecting a continuous series of cross-sectional images onto the vat while (e.g., essentially) continuously advancing the build platform away from the surface of the polymerizing liquid such that additional liquid photopolymerizable composition is drawn into the build area during the polymerization process. A two-dimensional pattern either blocks actinic irradiation from passing through all of the regions of the exposure image except for the pattern (e.g., as with a combination of light source and photomask), or provides actinic irradiation in the shape of the pattern (e.g., as with a laser or an array of pixels). When the exposure image includes a photomask, the positioning of the exposure image is typically a physical positioning of the photomask adjacent to the vat. In contrast, when the exposure image includes actinic irradiation in the shape of the pattern (e.g., via digital projection or laser scanning), the positioning of the exposure image is typically a positioning of the irradiation source, and the irradiation source is directed towards the vat. Sequential cross-sections of the 3D article can be bonded or adhered to one another in the z-direction (or build direction corresponding to the direction of raising or lowering recited above) by the application of the energy for solidifying the photopolymerizable composition. Moreover, selectively applying energy to the photopolymerizable composition in the container can comprise applying actinic radiation, such as UV radiation, visible radiation, e-beam radiation, or any combination thereof, having a sufficient energy to cure the photopolymerizable composition. The skilled practitioner can select a suitable radiation source and range of wavelengths for a particular application without undue experimentation. In some embodiments, the actinic radiation provides a wavelength in a range from 220 nm to 550 nm. Optionally, the actinic radiation is provided at an intensity of 1 to 50 milliwatts per square centimeter (mW/cm²). It is to be understood that one or more steps of a method described herein, such as a step of selectively applying energy to a layer of photopolymerizable composition, can be carried out according to an image of the 3D article in a computer-readable format. In certain embodiments, an apparatus adapted to be used in a continuous mode may be employed, such as the ASIGA PICO PLUS 39, available from Asiga USA, Anaheim Hills, CA, or an apparatus commercially available from Carbon (Redwood City, CA), for instance as described in U.S. Patent Nos.9,205,601 and 9,360,757 (both to DeSimone et al.). Suitable commercially available continuous printers include the M2 from Carbon, the ProMaker L8000 from Prodways Technologies (Les Mureaux, France), the Vida UHD cDLM from EnvisionTEC Inc. (Dearborn, MI), and the FIGURE 4 from 3D Systems (Rock Hill, SC). A suitable apparatus can also be assembled from individual components, for instance as described in the examples below. DLPs are well-known in the art, for instance and without limitation, the apparatuses described in U.S. Patent Nos.5,658,063 (Nasserbakht), 5,905,545 (Poradish et al.), 6,587,159 (Dewald), 7,164,397 (Pettitt et al.), 7,360,905 (Davis et al.), 8,705,133 (Lieb et al.), and 8,820,944 (Vasquez). Suitable DLPs are commercially available, such as from Texas Instruments (Dallas, TX). As indicated above, either an LED or a lamp may be employed with a DLP. Suitable lamps may include a flash lamp, a low pressure mercury lamp, a medium pressure mercury lamp, and/or a microwave driven lamp. The skilled practitioner can select a suitable LED or lamp light source to provide the actinic radiation required to initiate polymerization for a particular polymerizable composition, for instance, the UV LED CBT-39-UV, available from Luminus Inc. (Sunnyvale, CA). Suitable photomasks are commercially available, for instance, NanoSculpt Photomasks from Infinite Graphics (Minneapolis, MN). Similar to using a DLP, either an LED or a lamp may be employed with a photomask. A benefit of employing a digital photomask is that the individual pixels are readily adjustable (e.g., using computer controls) to change the irradiation location and dosage and thereby the shape of the resulting gel as needed without requiring a significant equipment alteration. Suitable LCDs are commercially available, for instance, the LCD LQ043T1DG28, available from Sharp Corporation (Osaka, Japan). A method described herein can also comprise planarizing a new layer of fluid photopolymerizable composition provided by raising or lowering an elevator platform. Planarization in continuous methods is typically only carried out when different sections are being formed, in between curing the composition for distinct sections. Such planarization can be carried out, in some cases, by utilizing a wiper or roller or a recoater. Planarization corrects the thickness of one or more fluid layers prior to curing the composition by evening the dispensed material to remove excess material and create a uniformly smooth exposed or flat up-facing surface on the support platform of the printer. In other alternative embodiments, the methods of manufacturing a 3D article described herein can include so-called “volumetric additive manufacturing methods (Volumetric AM). Here a gel body representing the core of the restoration may be printed, typically with a composition that yields inner tooth (i.e. dentin) properties such as color and translucency. Afterward, the liquid printing medium can be exchanged for one design to yield outer tooth (i.e. enamel) properties. Likewise, many series, or continuous, modifications to the composition of printing bath can be made to create a gel that is later post processed into a fully dense restoration. Exemplary processes for volumetric AM useful in the present disclosure can be found in US Patent No.10,647,061 (Kelly et al.) and Madrid-Wolff et al., “Controlling Light in Scattering Materials for Volumetric Additive Manufacturing”. Adv. Sci.2022, 9, 2105144 and US Publication No.20220350127 (Huffman et al). As another alternative, the methods of manufacturing a 3D article described herein can include inkjet printing. For instance, the methods may include inkjetting a sol through a nozzle to form a plurality of droplets of printed sol; wherein the sol comprises: i) metal oxide particles; ii) a solvent; iii) a surface modifying agent; and iv) optionally a polymerizable component. The method can further include to solidifying the printed sol to form a portion of the three-dimensional veneer. Exemplary details of inkjet printing of sols may be found in International Publication No. WO2022136969 (Korten et al.). After the 3D article has been formed, it is typically removed from the additive manufacturing apparatus, and at least some uncured photopolymerizable slurry or sol is removed from the surface of the gelled article. Referring again to FIG.11, the method optionally includes rinsing the gelled article, (e.g., an ultrasonic, or bubbling, or spray rinse) in a solvent, which would dissolve a portion of the uncured photopolymerizable slurry or sol but not the cured, solid state article (e.g., gel). In some embodiments, step 1030 of the method comprises, (e.g., prior to step c), step f) of moving the gelled article and thereby generating a mass inertial force in uncured photopolymerizable composition disposed on the gelled article, thereby forming a coating layer of uncured photopolymerizable composition on the gelled article, wherein the mass inertial force is generated using a centrifuge, a shaker, or a mixer that spins along one or more axes. Suitable ways of generating a mass inertial force are described, for instance, in International Publication No. WO2020157598, entitled “Orthodontic Articles and Methods of Making and Postprocessing the Same”. For instance, the source of the mass inertial force may be generated using a centrifuge, a shaker, or a mixer that spins along one or more axes. In some embodiments, the moving of the object is a rotation or spinning of the object. Accordingly, the mass inertial force may be generated by a centrifugal force. One suitable mixer that spins along more than one axis is a dual asymmetric centrifugal mixer, such as the DAC 400 FVZ available from Flacktek (Landrum, SC). A dual asymmetric centrifugal mixer provides simultaneous dual axis spinning that automatically reorients the article during spinning, which tends to pull uncured composition out of concave features of the article in a short period of time (e.g., 20, 15, or 10 seconds or less). Any other conventional method for cleaning the article and removing uncured material at the article surface may also be utilized. At this stage, the three-dimensional article typically has sufficient green strength for handling in the remaining steps of the method. A photopolymerizable slurry or sol described herein in a cured state (e.g., a gelled body), in some embodiments, can exhibit one or more desired properties. The article surface, as well as the bulk article itself, typically still retain uncured photopolymerizable slurry or sol, suggesting a need for further curing. Removing residual uncured photopolymerizable composition is particularly useful when the article is going to subsequently be post-cured, to minimize uncured residual photopolymerizable composition from undesirably curing directly onto the article. A photopolymerizable slurry or sol in a “cured” state can comprise a photopolymerizable composition that includes a polymerizable component that has been at least partially polymerized and/or crosslinked. For instance, in some instances, a gelled article is at least about 10% polymerized or crosslinked or at least about 30% polymerized or crosslinked. In some cases, a gelled article is at least about 50%, at least about 70%, at least about 80%, or at least about 90% polymerized or crosslinked. A gelled article can also be between about 10% and about 99% polymerized or crosslinked. Further curing can be accomplished by further irradiating with actinic radiation, heating, or both. Optionally, that can be followed by soaking the gelled article with another solvent (e.g., diethylene glycol ethyl ether or ethanol). Exposure to actinic radiation can be accomplished with any convenient radiation source, generally UV radiation, visible radiation, and/or e-beam radiation, for a time ranging from about 10 seconds to over 60 minutes. Heating is generally carried out at a temperature in the range of about 35-80°C, for a time ranging from about 10 to over 60 minutes in an inert atmosphere. So called post-cure ovens, which combine UV radiation and thermal energy, are particularly well suited for use in the post-cure process(es). In general, post curing improves the mechanical properties and stability of the three-dimensional article relative to the same three-dimensional article that is not post cured. Referring to FIG.12A, an image is shown of a digital file for an article having the shape of a dental veneer. FIG.12B shows, from left to right, a gelled article 1100 prepared according to an embodiment of the present disclosure using the digital file of FIG.12A, an aerogel article 1101 prepared from the gelled article 1100, a white body or pre-sintered article 1103 prepared from the aerogel article 1101, and a sintered dental veneer 1105 prepared from the pre-sintered article 1103. The veneer articles of FIG.12B are shaped for a central tooth made according to Example 2 below. FIG.12C shows another sintered dental veneer 1105 prepared according to Example 2 below and designed for a lateral tooth. FIG.12D depicts a set of sintered veneers prepared according to Example 2 and designed for a patient’s central and lateral teeth. Certain articles of FIG.12B - D include a plurality of support structures 1170 arranged on the incisal edge 1120 of the veneer. The support structures 1170 can include thicknesses for at least one of the base 1171 and tip 1172 of less than 200 microns, or in some embodiments less than 150 microns. The series of fine support structures 1170 can provide adequate stability during printing and processing, while be readily removable by conventional grinding or milling methods without leaving noticeable vestiges or burrs. This stands in contrast to the supports of prior art veneers, depicted in FIG.13, which are considerably larger to allow for investment casting and handling of otherwise remarkably fragile veneer. Removal of such structures risks unsightly vestiges or fractures in the veneer body, neither of which are probable with veneer 1100 including the support structures 1170. Referring to FIG.14, a ceramic article is shown having a shape of a dental veneer. The ceramic article has been post-processed after the additive manufacturing formation of a gelled article (e.g., including removing support structures from the gelled article). The components of the photopolymerizable slurry or sol (e.g., ceramic particles, solvent, radiation curable monomer, photoinitiator, and inhibitor) are each discussed in detail below. Ceramic Particles The photopolymerizable compositions of the present disclosure include particles of at least one ceramic material. In many embodiments, the ceramic particles comprise metal oxide ceramic particles, non-oxide ceramic particles, or any combination thereof. Preferably, the ceramic particles are selected from the group consisting of zirconia (ZrO2), silica (SiO2), alumina (Al2O3), yttria (Y2O3), ceria (CeO2), magnesium-magnesia aluminate (MMA), magnesium oxide (MgO), hydroxyapatite (Ca5(PO4)3OH), fluorapatite (Ca5(PO4)3F), chlorapatite (Ca5(PO4)3Cl), calcite (CaCO3), cordierite (Mg2Al4Si5O18), silicon carbide (SiC), silicon nitride (Si3N4), boron carbide (B4C), titanium diboride (TiB2), zirconium diboride (ZrB2), boron nitride (BN), titanium carbide (TiC), zirconium carbide (ZrC), aluminium nitride (AlN), calcium hexaboride (CaB6), MAX phase (Mn+1AXn), and any combination thereof. In select embodiments, high-purity particles are used, in which the total content of metal impurities is preferably less than 100 ppm, particularly preferably less than 50 ppm. In alternate embodiments, particles are used having a total content of metal impurities of about 2,000 ppm. Suitable zirconia particles include for instance and without limitation, nano-sized zirconia particles(s) having at least one and up to all of the following parameters or features: • Primary particle size XRD (diameter): from 2 to 100 nm, 2 to 50 nm, 2 to 20 nm, 2 to 15 nm, or 4 to 15 nm; • being essentially spherical, cuboid or a mixture of spherical and cuboid; • being non-associated; • being crystalline; • not being coated with an inorganic coloring agent. Suitable nano-sized zirconia particles can have at least one and up to all of the following features: • ZrO2 content: from 70 to 100 mol% or 80 to 97 mol%; • HfO₂ content: from 0 to 4.5 mol%, 0 to 3 mol%, or 0.1 to 2.8 mol%; • Stabilizer selected from Y₂O₃, CeO₂, MgO, CaO, La₂O₃ or a combination thereof in an amount from 0 to 30 mol%, 1.5 to 16 mol%, 2 to 10 mol%, or 2 to 5 mol%; • Al2O3 content: from 0 to 1 mol% or from 0.005 to 0.5 mol% or from 0.01 to 0.2 mol%. According to one embodiment, the nano-sized zirconia particles are characterized as follows: ZrO2 content: from 70 to 98.4 mol%; HfO2 content: from 0.1 to 2.8 mol%; Y2O3 content: from 1.5 to 28 mol%. Nano-sized zirconia particles can be obtained or are obtainable by a process comprising the steps of hydrothermal treatment of an aqueous metal salt solution or suspension (e.g. zirconium salt, yttrium salt). Such a process is described in WO 2013/055432 (Kolb et al.). Suitable silica particles include for instance and without limitation spherical silica particles and non-spherical silica particles. Spherical silica particles in aqueous media (sols) are well known in the art and are available commercially; for example, as silica sols in water or aqueous alcohol solutions under the trade designations LUDOX from W.R. Grace & Co. (Columbia, MD), NYACOL from Nyacol Nanotechnologies Inc. (Ashland, MA), or NALCO from Nalco Company (Naperville, IL). One useful silica sol with a volume average particle size of 5 nm, a pH of 10.5, and a nominal solids content of 15 percent by weight, is available as NALCO 2326 from Nalco Company. Other useful commercially available silica sols include those available as NALCO 1115 and NALCO 1130 from Nalco Company, as REMASOL SP30 from Remet Corp. (Utica, NY), and as LUDOX SM from W.R. Grace & Co. Other suitable silica particles include fumed silica. Agglomerated silica particles are commercially available e.g. from Degussa, Cabot Corp or Wacker under the product designation AEROSIL, CAB-O-SIL and HDK. The specific surface of the hydrophobic fumed silica is typically from 100 to 300 m²/g or from 150 to 250 m²/g. A mixture of different fumed silica can be used, if desired. For example, a mixture of fumed silica the surface of which has been treated with a hydrophobic surface treating agent and fumed silica the surface of which has been treated with a hydrophilic surface treating agent can be used. A suitable nano-silica comprising aggregated nano-sized particles can be produced according to the processes described e.g. in US 6,730,156 (Zhang et al; preparatory example A). Suitable alumina particles include for instance and without limitation aqueous alumina dispersions (e.g., average particle size of 500 nm alumina particles available from Sumitomo Chemicals (New York, NY)) and alumina particles from Saint-Gobain Surface Conditioning Group (Anaheim, CA). Suitable yttria particles include for instance and without limitation yttrium oxide available from Treibacher Industrie AG (Althofen, Austria). Suitable ceria particles include for instance and without limitation colloidal cerium oxide in the form of colloidal sols and nano-structured powders available from NYACOL Nano Technologies, Inc (Ashland, MA). NYACO CDP, for example, has a particle size of 25–30 nm and is a dispersible ceria powder, while NYACOL Ce120/10 is colloidal ceria having a particle size of 100–140 nm and water as a carrier. In some embodiments, the photopolymerizable slurry or sol comprises 20 wt.% or greater ceramic particles, based on the total weight of the photopolymerizable slurry or sol, 21 wt.% or greater, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, 30 wt.%, 32 wt.% or 35 wt.% or greater; and 60 wt.% or less, 29.5 wt.% or less, 28.5 wt.% or less, 27.5 wt.% or less, 26.5 wt.% or less, 25.5 wt.% or less, or 24.5 wt.% or less ceramic particles, based on the total weight of the photopolymerizable slurry or sol. Stated another way, the photopolymerizable slurry or sol can include between 20 percent by weight and 60 percent by weight of ceramic particles, based on the total weight of the photopolymerizable slurry or sol. In some embodiments, the photopolymerizable slurry or sol comprises 3 volume percent (vol.%) or greater ceramic particles, based on the total volume of the photopolymerizable slurry or sol, 4 vol.%, 5 vol.%, 6 vol.%, 7 vol.%, 8 vol.%, 9 vol.%, 10 vol.%, 11 vol.%, 12 vol.%, 13 vol.%, 14 vol.%, 15 vol.%, 17 vol. %, 19 vol.%, 21 vol.%, 23 vol.%, 25 vol.% or 29 vol.% or greater; and 45 vol.% or less, 44 vol.%, 42 vol.%, 40 vol.%, 38 vol.%, 36 vol.%, 34 vol.%, 32 vol.%, or 30 vol.% or less ceramic particles, based on the total volume of the photopolymerizable slurry or sol. Stated another way, the photopolymerizable slurry or sol can include for instance, between 3 percent by volume and 45 percent by volume of ceramic particles, 5 vol.% to 45 vol.%, or 10 vol.% to 45 vol.% ceramic particles, based on the total volume of the photopolymerizable slurry or sol. The ceramic particles typically comprise an average (mean) particle size diameter (i.e., D₅₀) of 1 nanometer (nm) or greater, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 12 nm, 15 nm, 17 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 75 nm, 90 nm, 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, 250 nm, 350 nm, 500 nm, 750 nm, 1 micrometer, 1.25 micrometers, 1.5 micrometers, 1.75 micrometers, 2 micrometers, 2.5 micrometers, 3.0 micrometers, 3.5 micrometers, 4.0 micrometers, or 4.5 micrometers or greater; and a D₅₀ of 10 micrometers or less, 9.5 micrometers, 9 micrometers, 8.5 micrometers, 8 micrometers, 7.5 micrometers, 7 micrometers, 6.5 micrometers, 6 micrometers, 5.5 micrometers, 5 micrometers, 4.5 micrometers, 3 micrometers, 2 micrometers, 1.5 micrometers, 1 micrometer, 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, or 250 nm or less. Stated another way, the ceramic particles may have an average particle size diameter (D₅₀) of 1 nm to 900 nm, 1 nm to 500 nm, 1 nm to 250 nm, 250 nm to 10 micrometers, 1 micrometer to 10 micrometers, 500 nanometers to 1.5 micrometers, or of 250 nm to 1 micrometer. The average (mean) particle size (D₅₀) refers to that particle diameter at which 50 percent by volume of the particles in a distribution of particles have that diameter or a smaller diameter, as measured by laser diffraction. Preferably, the average particle size is of the primary particles. Sintering Aid The photopolymerizable compositions of the present disclosure optionally include at least one sintering aid. Often, sintering aids assist by removing oxygen during the sintering process. Also, a sintering aid may provide a phase that melts from a solid to a liquid at a lower temperature than the ceramic material, or may provide some alternate mechanism that improves transport of ceramic ions and thus increases densification as compared to a composition not containing the sintering aid. Suitable sintering aids are not particularly limited, and may include rare earth oxides, alkaline earth oxides, alkali oxides, and combinations thereof. Materials that yield liquids at the sintering temperature of the ceramic particles can be useful. Rare earth oxides include cerium oxide (e.g., CeO2), dysprosium oxide (e.g., Dy2O3), erbium oxide (e.g., Er2O3), europium oxide (e.g., Eu2O3), gadolinium oxide (e.g., Gd2O3), holmium oxide (e.g., Ho2O3), lanthanum oxide (e.g., La2O3), lanthanum aluminum oxide (LaAlO3), lutetium oxide (e.g., Lu2O3), neodymium oxide (e.g., Nd2O3), praseodymium oxide (e.g., Pr₆O₁₁), samarium oxide (e.g., Sm₂O₃), terbium oxide (e.g., Tb2O3), thorium oxide (e.g., Th4O7), thulium oxide (e.g., Tm2O3), ytterbium oxide (e.g., Yb2O3), and yttrium oxide (e.g., Y2O3), and combinations thereof. Alkaline earth oxides include barium oxide (BaO), calcium oxide (CaO), strontium oxide (SrO), magnesium oxide (MgO), and beryllium oxide (BeO), and combinations thereof. Alkali oxides include lithium oxide (Li₂O₂), sodium oxide (Na₂O₂), potassium oxide (K₂O), rubidium oxide (Rb₂O), and cesium oxide (Cs₂O), and combinations thereof. In some embodiments, a mixture of an alkaline earth oxide and a rare earth oxide is preferable, such as a combination of aluminum oxide and yttrium oxide. Additional suitable sintering aids include for instance and without limitation, boron, carbon, magnesium, aluminum, silicon, titanium, vanadium, chromium, iron, nickel, copper, aluminum nitride, alumina, yttria, ethyl silicate, sodium silicate with Mg(NO₃)₂, other glasses, Fe₂O₃, MgF₂, and combinations thereof. In some embodiments, suitable sintering aids comprise aluminum oxide, yttrium oxide, zirconium oxide, silicon oxide, titanium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, lithium oxide, sodium oxide, potassium oxide, carbon, boron, boron carbide, aluminum, aluminum nitride, or combinations thereof. For instance, suitable commercially available sintering aids include Calcined Alumina from Almatis (Ludwigshafen, Germany) and Yttrium Oxide from Treibacher Industrie AG (Althofen, Austria). Coloring Agents Photopolymerizable compositions according to embodiments of the present disclosure may further comprise one or more inorganic coloring agent(s). The nature and structure of the inorganic coloring agent(s) is not particularly limited, unless the desired result cannot be achieved. In preferred embodiments, the metal ion is not a free salt, but rather is incorporated into the ceramic particles. Up to 30 mole %, up to 25 mole %, up to 20 mole %, up to 10 mole %, up to 5 mole %, up to 2 mole %, or up to 1 mole % of the ceramic particles can be Y2O3, La2O3, Al2O3, CeO2, Pr2O3, Nd2O3, Pm2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Fe2O3, MnO2, Co2O3, Cr2O3, NiO, CuO, V2O3, Bi2O3, Ga2O3, Lu2O3, HfO2, or mixtures thereof. Inorganic oxides such as Fe2O3, MnO2, Co2O3, Cr2O3, NiO, CuO, Ga2O3, Er2O3, Pr2O3, Eu2O3, Dy2O3, Sm2O3, V2O3, or W2O3 may be added, for example, to alter the color of the ceramic article to be produced. If the slurry or sol is to be used for producing dental or orthodontic articles, the following inorganic coloring agent(s) were found to be useful: salts of Mn, Fe, Cu, Pr, Nd, Sm, Eu, Tb, Dy, Er, Bi and mixtures thereof, preferably Er, Tb, Mn, Bi, Nd or Fe, Pr, Co, Cr or V, Cu, Eu, Sm, Dy, with Er, Tb, Mn, Bi, Nd being sometimes particularly preferred. Including a coloring agent may be particularly desirable when the ceramic particles comprise zirconia. If present, the inorganic coloring agent(s) is present in an amount, based on the moles of the coloring ion being present in the coloring agent and with respect to the total moles of inorganic oxide in the ceramic particles, of 0.001 mole % or greater, 0.005 mole %, or 0.01 mole % or greater; and 0.02 mole % or less, 0.05 mole %, or 0.5 mole % or less. Solvent In many embodiments, the photopolymerizable slurry or sol according to the present disclosure further comprises at least one (e.g., organic or aqueous) solvent. Suitable solvents are typically selected to be miscible with water. Further, these solvents are often selected to be soluble in supercritical carbon dioxide or liquid carbon dioxide. The molecular weight of the solvent is usually at least 25 grams/mole (g/mol), 30 g/mol, 40 g/mol, 45 g/mol, 50 g/mol, 75 g/mol, or at least 100 g/mol. The molecular weight can be up to 300 g/mol, 250 g/mol, 225 g/mol, 200 g/mol, 175 g/mol, or up to 150 g/mol. The molecular weight is often in a range of 25 to 300 g/mol, 40 to 300 g/mol, 50 to 200 g/mol, or 75 to 175 g/mol. It is particularly preferable that the one or more solvents have a boiling point above a temperature employed during the additive manufacturing process to minimize solvent evaporation from the sol, slurry, or gelled article. For instance, at least one solvent may be used having a boiling point of 150°C or greater, 160°C, 170°C, 180°C, or 190°C or greater. In certain embodiments, the amount of one or more solvents in a photopolymerizable slurry or sol is 10 wt.% or more, 15 wt.%, 20 wt.%, 25 wt.%, 30 wt.%, 35 wt.%, 40 wt.%, or 45 wt.% or more, based on the total weight of the photopolymerizable slurry or sol; and 70 wt.% or less, 65 wt.%, 60 wt.%, 55 wt.%, or 50 wt.% or less, based on the total weight of the photopolymerizable slurry or sol. Stated another way, the photopolymerizable slurry or sol may contain 10 to 70 wt.% solvent, or 20 to 50 wt.% solvent, based on the total weight of the photopolymerizable slurry or sol. Advantageously, in certain embodiments, the presence of solvent can assist in maintaining a pore structure in an article for removing organic material from the article. Suitable solvents include for instance and without limitation, diethylene glycol monoethyl ether, ethanol, l-methoxy-2-propanol (i.e., methoxy propanol), isopropanol, ethylene glycol, N,N-dimethylacetamide, N-methyl pyrrolidone, water, and combinations thereof. A suitable solvent is often a glycol or polyglycol, mono-ether glycol or mono- ether polyglycol, di-ether glycol or di-ether polyglycol, ether ester glycol or ether ester polyglycol, carbonate, amide, or sulfoxide (e.g., dimethyl sulfoxide). The solvent usually has one or more polar groups. The solvent does not have a polymerizable group; that is, the (e.g., organic) solvent is free of a group that can undergo free radical polymerization. Further, no component of the solvent medium has a polymerizable group that can undergo free radical polymerization. In some embodiments, the solvent contains less than 15 weight percent water, less than 10 percent water, less than 5 percent water, less than 3 percent water, less than 2 percent water, less than 1 weight percent, or even less than 0.5 weight percent water. Suitable glycols or polyglycols, mono-ether glycols or mono-ether polyglycols, di- ether glycols or di-ether polyglycols, and ether ester glycols or ether ester polyglycols are often of Formula (I). R¹O-(R²O)_n-R¹ (I) In Formula (I), each R¹ independently is hydrogen, alkyl, aryl, or acyl. Suitable alkyl groups often have 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms. Suitable aryl groups often have 6 to 10 carbon atoms and are often phenyl or phenyl substituted with an alkyl group having 1 to 4 carbon atoms. Suitable acyl groups are often of formula –(CO)R³ where R³ is an alkyl having 1 to 10 carbon atoms, 1 to 6 carbon atoms, 1 to 4 carbon atoms, 2 carbon atoms, or 1 carbon atom. The acyl is often an acetate group (–(CO)CH3). In Formula (I), each R² is typically ethylene or propylene. The variable n is at least 1 and can be in a range of 1 to 10, 1 to 6, 1 to 4, or 1 to 3. Glycols or polyglycols of Formula (I) have two R¹ groups equal to hydrogen. Examples of glycols include, but are not limited to, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol. Mono-ether glycols or mono-ether polyglycols of Formula (I) have a first R¹ group equal to hydrogen and a second R¹ group equal to alkyl or aryl. Examples of mono-ether glycols or mono-ether polyglycols include, but are not limited to, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, propylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether. Di-ether glycols or di-ether polyglycols of Formula (I) have two R¹ groups equal to alkyl or aryl. Examples of di-ether glycols or di-ether polyglycols include, but are not limited to, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, dipropylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and pentaethylene glycol dimethyl ether. Ether ester glycols or ether ester polyglycols of Formula (I) have a first R¹ group equal to an alkyl or aryl and a second R¹ group equal to an acyl. Examples of ether ester glycols or ether ester polyglycols include, but are not limited to, ethylene glycol butyl ether acetate, diethylene glycol butyl ether acetate, and diethylene glycol ethyl ether acetate. Other suitable solvents are carbonates of Formula (II). In Formula (II), R⁴ is hydrogen or an alkyl such as an alkyl having 1 to 4 carbon atoms, 1 to 3 carbon atoms, or 1 carbon atom. Examples include ethylene carbonate and propylene carbonate. Yet other suitable solvents are amides of Formula (III).

In Formula (III), group R⁵ is hydrogen, alkyl, or combines with R⁶ to form a five-membered ring including the carbonyl attached to R⁵ and the nitrogen atom attached to R⁶. Group R⁶ is hydrogen, alkyl, or combines with R⁵ to form a five-membered ring including the carbonyl attached to R⁵ and the nitrogen atom attached to R⁶. Group R⁷ is hydrogen or alkyl. Suitable alkyl groups for R⁵, R⁶, and R⁷ have 1 to 6 carbon atoms, 1 to 4 carbon atoms, 1 to 3 carbon atoms, or 1 carbon atom. Examples of amide organic solvents of Formula (III) include, but are not limited to, formamide, N,N-dimethylformamide, N,N- dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2- pyrrolidone. Additionally, in certain embodiments, the photopolymerizable slurry or sol further comprises a dispersant to assist in distributing the ceramic particles in the photopolymerizable slurry or sol. Typically, one or more dispersants can be present in a photopolymerizable slurry or sol in an amount of 0.5 wt.% or greater, based on the total weight of the photopolymerizable slurry or sol, 0.55 wt.% or greater, 0.60 wt.%, 0.65 wt.%, or 0.70 wt.% or greater; and 5.0 wt.% or less, 4.0 wt.%, 3.0 wt.%, 2.0 wt.%, 1.0 wt.%, 0.95 wt.%, 0.90 wt.%, 0.85 wt.%, 0.80 wt.%, or 0.75 wt.% or less, based on the total weight of the photopolymerizable slurry or sol. Stated another way, the optional dispersant may be present in an amount of 0.5 wt.% to 5.0 wt.%, based on the total weight of the photopolymerizable slurry or sol. Suitable dispersants include for instance and without limitation, dispersants available under the trade designations SOLPLUS or SOLSPERSE from Lubrizol (Wickliffe, OH), such as SOLPLUS D510, R700, R720, D540, D545, and D570, SOLSPERSE 20000, S71000, M387, M389, S41000, and S79000, and combinations thereof. Radiation Curable Monomer The photopolymerizable slurry or sol described in the present text comprises one or more radiation curable monomers being part of or forming an organic matrix. The radiation curable monomer(s) being present in the photopolymerizable slurry or sol can be described as first, second, third, etc., monomer. The nature and structure of the radiation curable monomer(s) is not particularly limited unless the desired result cannot be achieved. In some embodiments, the at least one radiation curable monomer comprises an acrylate. Preferably, the at least one radiation curable monomer includes a (meth)acrylate, an epoxy, a silane, or combinations thereof. In some embodiments, upon polymerization, the radiation curable monomers form a network with the (preferably) homogeneously dispersed ceramic particles. According to one embodiment, the photopolymerizable slurry or sol contains as a first monomer a polymerizable surface modification agent. Optionally, at least a portion of the ceramic particles in the photopolymerizable slurry or sol may comprise a surface modifier attached to a surface of the ceramic particles. A surface modifier may help to improve compatibility of the particles contained in the slurry or sol with an organic matrix material also present in the slurry or sol. Surface modifiers may be represented by the formula A-B, where the A group is capable of attaching to the surface of a ceramic particle and the B group is radiation curable. Group A can be attached to the surface of the ceramic particle by adsorption, formation of an ionic bond, formation of a covalent bond, or a combination thereof. Examples of suitable Group A moieties include acidic moieties (like carboxylic acid groups, phosphoric acid groups, sulfonic acid groups and anions thereof) and silanes. Group B comprises a radiation curable moiety. Examples of suitable Group B moieties include vinyl, in particular acryl or methacryl moieties. Suitable surface modifiers comprise polymerizable carboxylic acids and/or anions thereof, polymerizable sulfonic acids and/or anions thereof, polymerizable phosphoric acids and/or anions thereof, and polymerizable silanes. Suitable surface modification agents are further described, for example, in WO 2009/085926 (Kolb et al.), the disclosure of which is incorporated herein by reference. An example of a radically polymerizable surface modifier is a polymerizable surface modification agent comprising an acidic moiety or anion thereof, e.g. a carboxylic acid group. Exemplary acidic radically polymerizable surface modifiers include acrylic acid, methacrylic acid, beta-carboxyethyl acrylate, and mono-2- (methacryloxyethyl)succinate. Exemplary radically polymerizable surface modifiers can be reaction products of hydroxyl-containing polymerizable monomers with cyclic anhydrides such as succinic anhydride, maleic anhydride and phthalic anhydride. Exemplary polymerizable hydroxyl- containing monomers include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, and hydroxybutyl methacrylate. Acryloxy and methacryloxy functional polyethylene oxide and polypropylene oxide may also be used as the polymerizable hydroxyl-containing monomers. An exemplary radically polymerizable surface modifier for imparting both polar character and reactivity to the ceramic nanoparticles is mono(methacryloxypolyethyleneglycol) succinate. Another example of a radically polymerizable surface modifier is a polymerizable silane. Exemplary polymerizable silanes include methacryloxyalkyltrialkoxysilanes or acryloxyalkyltrialkoxysilanes (e.g., 3-methacryloxypropyltrimethoxysilane, 3- acryloxypropyltrimethoxysilane, and 3-(methacryloxy)propyltriethoxysilane); methacryloxyalkylalkyldialkoxysilanes or acryloxyalkylalkyldialkoxysilanes (e.g., 3- (methacryloxy)propylmethyldimethoxysilane and 3- (acryloxypropyl)methyldimethoxysilane); methacryloxyalkyldialkylalkoxysilanes or acyrloxyalkyldialkylalkoxysilanes (e.g., 3-(methacryloxy)propyldimethylethoxysilane); mercaptoalkyltrialkoxylsilanes (e.g., 3-mercaptopropyltrimethoxysilane); aryltrialkoxysilanes (e.g., styrylethyltrimethoxysilane); vinylsilanes (e.g., vinylmethyldiacetoxysilane, vinyldimethylethoxysilane, vinylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltriisopropoxysilane, and vinyltris(2- methoxyethoxy)silane). A surface modifier can be added to the ceramic particles using conventional techniques. The organic matrix can be added before or after surface modification or simultaneously with surface modification. Various methods of adding the surface modification agent are further described, for example, in WO 2009/085926 (Kolb et al.), the disclosure of which is incorporated herein by reference. The surface modification reactions can occur at room temperature (e.g., 20°C to 25°C) or at an elevated temperature (e.g., up to 95°C). When the surface modifiers are acids such as carboxylic acids, the ceramic particles typically can be surface-modified at room temperature. When the surface modification agents are silanes, the ceramic particles are typically surface modified at elevated temperatures. The optional first monomer can function as a polymerizable surface modification agent. Multiple first monomers can be used. The first monomer can be the only kind of surface modifier or can be combined with one or more other non-polymerizable surface modifiers. In some embodiments, the amount of the first monomer is at least 20 wt.% based on a total weight of polymerizable material (radiation curable monomers). For example, if present, the amount of the first monomer is often at least 25 wt.%, at least 30 wt.%, at least 35 wt.%, or at least 40 wt.%. The amount of the first monomer can be up to 100 wt.%, up to 90 wt.%, up to 80 wt.%, up to 70 wt.%, up to 60 wt.%, or up to 50 wt.%. Some photopolymerizable slurries or sols contain 20 to 100 wt.%, 20 to 80 wt.%, 20 to 60 wt.%, 20 to 50 wt.%, or 30 to 50 wt.% of the first monomer based on a total weight of polymerizable material. The optional first monomer (i.e., the polymerizable surface modification agent) can be the only monomer in the polymerizable material or it can be combined with one or more second monomers, as described in further detail below. According to one embodiment, the photopolymerizable slurry or sol comprises one or more second monomers comprising at least one or two radiation curable moieties. In particular, the second monomers comprising at least two radiation curable moieties may act as crosslinker(s) during the gel-forming step. Any suitable second monomer that does not have a surface modification group can be used. The second monomer does not have a group being capable of attaching to the surface of a ceramic particle. That is, the optional second monomer does not have a carboxylic acid group or a silyl group. The second monomers are often polar monomers (e.g., non-acidic polar monomers), monomers having a plurality of polymerizable groups, alkyl (meth)acrylates and mixtures thereof. A successful build typically requires a certain level of gel strength as well as shape resolution, and adding a second monomer comprising at least two radiation curable moieties to the photopolymerizable slurry or sol described herein may facilitate the optimization both properties. A crosslinked approach often allows for greater gel strength to be realized at a lower energy dose since the polymerization creates a stronger network. In some examples, higher energy doses have been applied to increase layer adhesion of non-crosslinked systems. While an article is successfully built, the higher energy often impacts the resolution of the final article, causing overbuild to potentially occur, especially in the case of highly translucent materials where the light, and with it the cure depth, can penetrate further into the material. The presence of a monomer having a plurality of polymerizable groups tends to enhance the strength of the gel composition formed when the photopolymerizable slurry or sol is polymerized. The amount of the monomer with a plurality of polymerizable groups can be used to adjust the flexibility and the strength of the gelled body, and indirectly optimize the gelled body resolution and final article resolution. Such gel compositions can be easier to process without cracking, and in the case of transforming the gel into a fully dense ceramic, increased gel strength aids in the robustness of the post-building procedures. In many embodiments, the second monomer includes a monomer having a plurality of polymerizable groups. The number of polymerizable groups can be in a range of 2 to 6 or even higher. In many embodiments, the number of polymerizable groups is in a range of 2 to 5 or 2 to 4. The polymerizable groups are typically (meth)acryloyl groups. Exemplary monomers with two (meth)acryloyl groups include 1,2-ethanediol diacrylate, 1,3-propanediol diacrylate, 1,9-nonanediol diacrylate, 1,12-dodecanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, butylene glycol diacrylate, bisphenol A diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, polyethylene/polypropylene copolymer diacrylate, polybutadiene di(meth)acrylate, propoxylated glycerin tri(meth)acrylate, and neopentylglycol hydroxypivalate diacrylate modified caprolactone. Exemplary monomers with three or four (meth)acryloyl groups include, but are not limited to, trimethylolpropane triacrylate (e.g., commercially available under the trade designation TMPTA-N from Cytec Industries, Inc. (Smyrna, GA, USA) and under the trade designation SR-351 from Sartomer (Exton, PA, USA)), pentaerythritol triacrylate (e.g., commercially available under the trade designation SR-444 from Sartomer), ethoxylated (3) trimethylolpropane triacrylate (e.g., commercially available under the trade designation SR-454 from Sartomer), ethoxylated (4) pentaerythritol tetraacrylate (e.g., commercially available under the trade designation SR-494 from Sartomer), tris(2- hydroxyethylisocyanurate) triacrylate (e.g., commercially available under the trade designation SR-368 from Sartomer), a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (e.g., commercially available from Cytec Industries, Inc., under the trade designation PETIA with an approximately 1:1 ratio of tetraacrylate to triacrylate and under the trade designation PETA-K with an approximately 3:1 ratio of tetraacrylate to triacrylate), pentaerythritol tetraacrylate (e.g., commercially available under the trade designation SR-295 from Sartomer), and di-trimethylolpropane tetraacrylate (e.g., commercially available under the trade designation SR-355 from Sartomer). Exemplary monomers with five or six (meth)acryloyl groups include, but are not limited to, dipentaerythritol pentaacrylate (e.g., commercially available under the trade designation SR-399 from Sartomer) and a hexa-functional urethane acrylate (e.g., commercially available under the trade designation CN975 from Sartomer). In some embodiments, the radiation curable monomer comprises an epoxy. Epoxy compounds which are suitable for use as photopolymerizable slurries or sols include, for instance and without limitation, cycloaliphatic oxiranes, aliphatic oxiranes, aromatic oxiranes, or a combination thereof. These compounds, which are widely known as epoxy compounds, can be monomeric, polymeric, or mixtures thereof. These materials generally have, on the average, at least one polymerizable epoxy group (oxirane unit) per molecule, and preferably at least about 1.5 polymerizable epoxy groups per molecule. The polymeric epoxides include linear polymers having terminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymers having skeletal oxirane units (e.g., polybutadiene polyepoxide), and polymers having pendent epoxy groups (e.g., a glycidyl methacrylate polymer or copolymer). The epoxides may be pure compounds or may be mixtures containing one, two, or more epoxy groups per molecule. The “average” number of epoxy groups per molecule is determined by dividing the total number of epoxy groups in epoxy-containing material by the total number of epoxy molecules present. The epoxy compounds may have a molecular weight of from about 58 to about 100,000 or more. Suitable epoxy compounds include those which contain cyclohexene oxide groups, such as the epoxycyclohexanecarboxylates, for example, 3,4- epoxycyclohexylmethyl-3,4-epoxy cyclohexanecarboxylate, 3,4-epoxy-2- methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexane carboxylate, and bis(3,4-epoxy- 6-methylcyclohexylmethyl) adipate. A more detailed list of useful epoxides of this nature is provided in U.S. Patent No.3,117,099 (Proops et al.). Suitable epoxy compounds also include glycidyl ether compounds, such as glycidoxyalkyl and glycidoxyaryl compounds containing 1 to 6 glycidoxy groups. Examples include glycidyl ethers of polyhydric phenols, which can be obtained by reacting the polyhydric phenol with an excess of epichlorohydrin to provide, for example, 2,2-bis(2,3-epoxypropoxyphenyl)propane. Additional epoxides of this type are described in U.S. Patent No.3,018,262 (Schroeder), and in “Handbook of Epoxy Resins” by Lee and Neville, McGraw-hill Book Co., New York (1967). Many suitable epoxy compounds are commercially available and are listed in U.S. Patent No.6,187,833 (Oxman et al.). Some photopolymerizable slurry or sol compositions contain 0 to 80 wt.% of a second monomer having a plurality of polymerizable groups based on a total weight of the polymerizable material. For example, the amount can be in a range of 10 to 80 wt.%, 20 to 80 wt.%, 30 to 80 wt.%, 40 to 80 wt.%, 10 to 70 wt.%, 10 to 50 wt.%, 10 to 40 wt.%, or 10 to 30 wt.%. The overall composition of the polymerizable material is often selected so that the polymerized material is soluble in a solvent medium. Homogeneity of the organic phase is often preferable to avoid phase separation of the organic component in the gel composition. This tends to result in the formation of smaller and more homogeneous pores (pores with a narrower size distribution) in the subsequently formed aerogel or xerogel. Further, the overall composition of the polymerizable material can be selected to adjust compatibility with a solvent medium and to adjust the strength, flexibility, and uniformity of the gel composition. Still further, the overall composition of the polymerizable material can be selected to adjust the burnout characteristics of the organic material prior to sintering. In some embodiments, the optional second monomer is a polar monomer. As used herein, the term “polar monomer” refers to a monomer having a free radical polymerizable group and a polar group. The polar group is typically non-acidic and often contains a hydroxyl group, a primary amido group, a secondary amido group, a tertiary amido group, an amino group, or an ether group (i.e., a group containing at least one alkylene-oxy-alkylene group of formula –R-O-R- where each R is an alkylene having 1 to 4 carbon atoms). Suitable optional polar monomers having a hydroxyl group include, but are not limited to, hydroxyalkyl (meth)acrylates (e.g., 2-hydroxyethyl (meth)acrylate, 2- hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate), and hydroxyalkyl (meth)acrylamides (e.g., 2-hydroxyethyl (meth)acrylamide or 3-hydroxypropyl (meth)acrylamide), ethoxylated hydroxyethyl (meth)acrylate (e.g., monomers commercially available from Sartomer under the trade designation CD570, CD571, and CD572), and aryloxy substituted hydroxyalkyl (meth)acrylates (e.g., 2-hydroxy-2-phenoxypropyl (meth)acrylate). Exemplary polar monomers with a primary amido group include (meth)acrylamide. Exemplary polar monomers with secondary amido groups include, but are not limited to, N-alkyl (meth)acrylamides such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-tert-octyl (meth)acrylamide, and N-octyl (meth)acrylamide. Exemplary polar monomers with a tertiary amido group include, but are not limited to, N-vinyl caprolactam, N-vinyl-2-pyrrolidone, (meth)acryloyl morpholine, and N,N-dialkyl (meth)acrylamides such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, and N,N-dibutyl (meth)acrylamide. Polar monomers with an amino group include various N,N-dialkylaminoalkyl (meth)acrylates and N,N-dialkylaminoalkyl (meth)acrylamides. Examples include, but are not limited to, N,N-dimethyl aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylamide, N,N-diethylaminopropyl (meth)acrylate, and N,N-diethylaminopropyl (meth)acrylamide. Exemplary polar monomers with an ether group include, but are not limited to, alkoxylated alkyl (meth)acrylates such as ethoxyethoxyethyl (meth)acrylate, 2- methoxyethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate; and poly(alkylene oxide) (meth)acrylates such as poly(ethylene oxide) (meth)acrylates, and poly(propylene oxide) (meth)acrylates. The poly(alkylene oxide) acrylates are often referred to as poly(alkylene glycol) (meth)acrylates. These monomers can have any suitable end group such as a hydroxyl group or an alkoxy group. For example, when the end group is a methoxy group, the monomer can be referred to as methoxy poly(ethylene glycol) (meth)acrylate. Suitable alkyl (meth)acrylates that can be used as a second monomer can have an alkyl group with a linear, branched, or cyclic structure. Examples of suitable alkyl (meth)acrylates include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-methylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-octyl (meth)acrylate, isononyl (meth)acrylate, isoamyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, isobornyl (meth)acrylate, 2-propylheptyl (meth)acrylate, isotridecyl (meth)acrylate, isostearyl (meth)acrylate, octadecyl (meth)acrylate, 2-octyldecyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, and heptadecanyl (meth)acrylate. In some embodiments, the alkyl (meth)acrylates are a mixture of various isomers having the same number of carbon atoms as described in PCT Patent Application Publication WO 2014/151179 (Colby et al.). For example, an isomer mixture of octyl (meth)acrylate can be used. The amount of a second monomer that is a polar monomer and/or an alkyl (meth)acrylate monomer is often in a range of 0 to 40 wt.%, 0 to 35 wt.%, 0 to 30 wt.%, 5 to 40 wt.%, or 10 to 40 wt.% based on a total weight of the polymerizable material. The total amount of polymerizable material is often at least 10 wt.%, at least 12 wt.%, at least 15 wt.%, or at least 18 wt.% based on the total weight of the photopolymerizable sol or slurry. The amount of polymerizable material can be up to 50 wt.%, up to 40 wt.%, up to 30 wt.%, or up to 20 wt.%, based on the total weight of the photopolymerizable sol or slurry. For example, the amount of polymerizable material can be in a range of 10-50 wt.%, 15-40 wt.%, 15-30 wt.%, or 10-20 wt.% based on the total weight of the photopolymerizable sol or slurry. In some embodiments, the polymerizable material contains 20 to 100 wt.% first monomer and 0 to 80 wt.% second monomer based on a total weight of polymerizable material. For example, polymerizable material includes 30 to 100 wt.% first monomer and 0 to 70 wt.% second monomer, 30 to 90 wt.% first monomer and 10 to 70 wt.% second monomer, 30 to 80 wt.% first monomer and 20 to 70 wt.% second monomer, 30 to 70 wt.% first monomer and 30 to 70 wt.% second monomer, 40 to 90 wt.% first monomer and 10 to 60 wt.% second monomer, 40 to 80 wt.% first monomer and 20 to 60 wt.% second monomer, 50 to 90 wt.% first monomer and 10 to 50 wt.% second monomer, or 60 to 90 wt.% first monomer and 10 to 40 wt.% second monomer. In some embodiments, the polymerizable material contains 0 wt.% first monomer and 100 wt.% second monomer based on a total weight of the polymerizable material. Photoinitiator Photopolymerizable slurries or sols described herein typically further comprise one or more photoinitiators. In certain embodiments the photoinitiator(s) can be characterized by being soluble in a solvent contained in the slurry or sol and/or absorbing radiation within a range from 200 to 500 nm or from 300 to 450 nm. The photoinitiator should be able to start or initiate the curing or hardening reaction of the radiation curable component(s) being present in the photopolymerizable slurries or sols. The following classes of photoinitiator(s) can be used: a) two-component system where a radical is generated through abstraction of a hydrogen atom from a donor compound; b) one component system where two radicals are generated by cleavage; and/or c) a system comprising an iodonium salt, a visible light sensitizer, and an electron donor compound. Examples of photoinitiators according to type (a) typically contain a moiety selected from benzophenone, xanthone or quinone in combination with an aliphatic amine. Examples of photoinitiators according to type (b) typically contain a moiety selected form benzoin ether, acetophenone, benzoyl oxime or acyl phosphine. Suitable exemplary photoinitiators are those available under the trade designation OMNIRAD from IGM Resins (Waalwijk, The Netherlands) and include 1-hydroxycyclohexyl phenyl ketone (OMNIRAD 184), 2,2-dimethoxy-1,2-diphenylethan-1-one (OMNIRAD 651), bis(2,4,6 trimethylbenzoyl)phenylphosphineoxide (OMNIRAD 819), 1-[4-(2-hydroxyethoxy)phenyl]- 2-hydroxy-2-methyl-1-propane-1-one (OMNIRAD 2959), 2-benzyl-2-dimethylamino-1-(4- morpholinophenyl)butanone (OMNIRAD 369), 2-methyl-1-[4-(methylthio)phenyl]-2- morpholinopropan-1-one (OMNIRAD 907), 2-hydroxy-2-methyl-1-phenyl propan-1-one (OMNIRAD 1173), 2, 4, 6-trimethylbenzoyldiphenylphosphine oxide (OMNIRAD TPO), and 2, 4, 6-trimethylbenzoylphenyl phosphinate (OMNIRAD TPO-L). Additional suitable photoinitiators include for example and without limitation, Oligo[2-hydroxy-2-methyl-1-[4- (1-methylvinyl)phenyl]propanone] ESACURE ONE (Lamberti S.p.A., Gallarate, Italy), 2- hydroxy-2-methylpropiophenone, benzyl dimethyl ketal, 2-methyl-2- hydroxypropiophenone, benzoin methyl ether, benzoin isopropyl ether, anisoin methyl ether, aromatic sulfonyl chlorides, photoactive oximes, and combinations thereof. Examples of photoinitiators according to type (c) typically contain the following moieties for each component: Suitable iodonium salts are described in U.S. Pat. Nos. 3,729,313, 3,741,769, 3,808,006, 4,250,053 and 4,394,403, the iodonium salt disclosures of which are incorporated herein by reference. The iodonium salt can be a simple salt, containing an anion such as Cl-, Br-, I- or C₄H₅SO₃-; or a metal complex salt containing an antimonate, arsenate, phosphate or borate such as SbF₅OH- or AsF₆-. Mixtures of iodonium salts can be used if desired. For instance, suitable iodonium salts include each of diphenyliodonium hexafluorophosphate and diphenyliodonium chloride, both commercially available from Sigma-Aldrich (St. Louis, MO). The visible light sensitizer may be selected from ketones, coumarin dyes (e.g., ketocoumarins), xanthene dyes, acridine dyes, thiazole dyes, thiazine dyes, oxazine dyes, azine dyes, aminoketone dyes, porphyrins, aromatic polycyclic hydrocarbons, p-substituted aminostyryl ketone compounds, aminotriaryl methanes, merocyanines, squarylium dyes and pyridinium dyes. Preferably, the visible light sensitizer is an alpha-diketone; camphorquinone is particularly preferred and commercially available from Sigma-Aldrich. The electron donor compound is typically an alkyl aromatic polyether or an alkyl, aryl amino compound wherein the aryl group is substituted by one or more electron withdrawing groups. Examples of suitable electron withdrawing groups include carboxylic acid, carboxylic acid ester, ketone, aldehyde, sulfonic acid, sulfonate and nitrile groups. The electron donor compound may be selected from polycylic aromatic compounds (such as biphenylenes, naphthalenes, anthracenes, benzanthracenes, pyrenes, azulenes, pentacenes, decacyclenes, and derivatives (e.g., acenaphthenes) and combinations thereof), and N-alkyl carbazole compounds (e.g., N-methyl carbazole). Preferred donor compounds include 4- dimethylaminobenzoic acid, ethyl 4-dimethylaminobenzoate, 3-dimethylaminobenzoic acid, 4-dimethylaminobenzoin, 4-dimethylaminobenzaldehyde, 4- dimethylaminobenzonitrile and 1,2,4-trimethoxybenzene. Photoinitiators according to type (c) are described in detail, for instance, in co-owned U.S. Patent No.6,187,833 (Oxman et al.). A photoinitiator can be present in a photopolymerizable slurry or sol described herein in any amount according to the particular constraints of the additive manufacturing process. In some embodiments, a photoinitiator is present in a photopolymerizable slurry or sol in an amount of 0.005 wt.% or more, 0.01 wt.% or more, 0.05 wt.% or more, 0.1 wt.% or more, or 0.3 wt.% or more; and 5% wt.% or less, 4 wt.% or less, 3 wt.% or less, 2 wt.% or less, 1 wt.% or less, or 0.5 wt.% or less, based on the total weight of the photopolymerizable slurry or sol. In some cases, a photoinitiator is present in an amount of about 0.005-5 wt.%, or 0.1-2 wt.%, based on the total weight of the photopolymerizable slurry or sol. In addition, a photopolymerizable slurry or sol described herein can further comprise one or more sensitizers to increase the effectiveness of one or more photoinitiators that may also be present. In some embodiments, a sensitizer comprises isopropylthioxanthone (ITX) or 2-chlorothioxanthone (CTX). Other sensitizers may also be used. If used in the photopolymerizable composition, a sensitizer can be present in an amount of about 0.001% by weight or more, 0.01% by weight or more, or about 1% by weight or more, based on the total weight of the photopolymerizable slurry or sol. Inhibitor A photopolymerizable slurry or sol described herein optionally also comprises one or more polymerization inhibitors (e.g., photoinhibitors). A polymerization inhibitor is often included in a photopolymerizable slurry or sol to provide additional thermal or photo stability to the composition. An inhibitor may extend the shelf life of the photopolymerizable slurry or sol, help prevent undesired side reactions, and adjust the polymerization process of the radiation curable component(s) present in the slurry or sol. Adding one or more inhibitor(s) to the photopolymerizable slurry or sol may further help to improving the accuracy or detail resolution of the surface of the ceramic article. Specific examples of inhibitor(s) which can be used include: p-methoxyphenol (MOP), hydroquinone monomethylether (MEHQ), 2,6-di-tert-butyl-4-methyl-phenol (BHT; Ionol), phenothiazine, 2,2,6,6-tetramethyl-piperidine-1-oxyl radical (TEMPO) and mixtures thereof. In some embodiments, a polymerization inhibitor, if used, is present in an amount of about 0.001-5 wt.%, 0.001-1 wt.%, or 0.01-1 wt.%, based on the total weight of the photopolymerizable slurry or sol. A photopolymerizable slurry or sol as described herein can also comprise one or more absorption modifiers (e.g., dyes, optical brighteners, pigments, etc.) to control the penetration depth of actinic radiation. One suitable optical brightener is Tinopal OB, a benzoxazole, 2,2'-(2,5-thiophenediyl)bis[5-(1,1-dimethylethyl)], available from BASF Corporation (Florham Park, NJ). The absorption modifier, if used, can be present in an amount of about 0.001-5 wt.%, about 0.01-1 wt.%, about 0.1-3 wt.%, or about 0.1-1 wt.%, based on the total weight of the photopolymerizable slurry or sol. Slurries and Sols The preparation of photopolymerizable slurries or sols is typically conducted under light-restricted conditions to avoid an undesired early polymerization. In some embodiments, the photopolymerizable slurry or sol is prepared by speed mixing the components to form a preferably homogenous slurry or sol. The slurry or sol is typically stored in a suitable device like a vessel, a bottle, cartridge or container before use. A photopolymerizable slurry or sol (e.g., uncured) has a viscosity profile consistent with the requirements and parameters of one or more additive manufacturing devices (e.g., 3D printing systems). In certain embodiments, the photopolymerizable slurry or sol exhibits a dynamic viscosity at 23 degrees Celsius of 500 milliPascals seconds (mPa·s) or less, 400 mPa·s, 300 mPa·s, 200 mPa·s, 100 mPa·s, 50 mPa·s, or 25 mPa·s or less. In some instances, a photopolymerizable slurry or sol described herein when uncured exhibits a dynamic viscosity of 1 to 500 mPa·s, 1 to 100 mPa·s, or 1 to 50 mPa·s using a Brookfield DV-E Viscometer (Brookfield Engineering Laboratories, Middleboro, MA) using disc and cylinder spindles at 23 degrees Celsius and at shear rates of 21/s to 201/s. In some cases, a photopolymerizable composition described herein when uncured exhibits a dynamic viscosity of less than about 50 mPa·s. The photopolymerizable slurry or sol containing ceramic particles is solidified by curing (e.g., gelation). Preferably, the gelation process allows gels to be formed of any shape without cracks and provide gelled bodies that can be further processed without inducing cracks. For example, preferably, the gelation process leads to a gelled body having a structure that will not collapse when the solvent is removed; so-called “free- standing gel”. It is preferable that the gel contain the minimum amount of organic material or polymer modifiers. After processing the photopolymerizable slurry or sol to form a gel, the gelled article is typically removed from the device used for conducting the additive manufacturing process. If desired, the surface of the gelled article is cleaned, e.g., by rinsing with a solvent, soaking in a solvent, and/or subjecting the gelled article to mass inertial force. Suitable solvents preferably include mixtures thereof or the same solvent(s) described above in the present text. As noted above, an aerogel is a porous material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The solvent removal (e.g., extraction) is often done under supercritical conditions. There is no capillary effect for this type of drying, and the linear shrinkage is often in a range of 0 to 25%, 0 to 20%, 0 to 15%, 5 to 15%, or 0 to 10%. The density typically remains uniform throughout the structure. In contrast, a xerogel is a three-dimensional solid derived from a gel, in which the liquid component of the gel has been removed (e.g., extracted) by evaporation under ambient conditions or at an elevated temperature. In some embodiments, the gelled body structure is compatible with and stable in a variety of solvents and conditions that may be necessary for supercritical extraction. Furthermore, the gel structure should be compatible with supercritical extraction fluids (e.g., supercritical carbon dioxide). In other words, the gels should be stable and strong enough to withstand drying, so as to produce stable aerogels and/or xerogels and give materials that can be heated to burn out the organics, pre-sintered, and densified without inducing cracks. Preferably, the resulting aerogels and/or xerogels have relatively small and uniform pore sizes to aid in sintering them to high density at low sintering temperatures. However, preferably the pores are large enough to allow product gases of organic burnout to escape without leading to cracking of the aerogel or xerogel. It is believed that the rapid nature of the gelation step results in an essentially homogeneous distribution of the ceramic particles throughout the gel, which can aid in the subsequent processing steps such as supercritical extraction, organic burnout, and sintering. If applied, the supercritical drying step can be characterized by at least one, more or all of the following features: a) Temperature: 20°C to 100°C, 30°C to 80°C, or 15°C to 150°C; b) Pressure: 5 to 200 MPa, 10 to 100 MPa, 1 to 20 MPa, or 5 to 15 MPa; c) Duration: 2 to 175 hours, 5 to 25 hours, or 1 to 5 hours; and d) Extraction or drying medium: carbon dioxide in its supercritical stage. A combination of features (a), (b), (c), and (d) is sometimes preferred. Supercritical extraction can remove all or most of the (e.g., organic) solvent in the printed gel article. In some embodiments, the aerogels contain some residual solvent. The residual solvent can be up to 6 wt.% based on the total weight of the aerogel. For example, the aerogel can contain up to 5 wt.%, up to 4 wt.%, up to 3 wt.%, up to 2 wt.%, or up to 1 wt.% (e.g., organic) solvent. The article obtained after having conducted the supercritical drying step can typically be characterized by at least one or more of the following properties: • showing a N₂ adsorption and/or desorption isotherm with a hysteresis loop; • showing a N2 adsorption and desorption of isotherm type IV according to IUPAC classification and a hysteresis loop; • showing a N2 adsorption and desorption isotherm of type IV with a hysteresis loop of type H1 according to IUPAC classification; • showing a N₂ adsorption and desorption isotherm of type IV with a hysteresis loop of type H1 according to IUPAC classification in a p/p0 range of 0.70 to 0.99; Heat treating of an aerogel article or xerogel article to form a porous ceramic article may be performed (usually in an atmosphere that includes oxygen) at a temperature of 70 degrees Celsius (°C) or greater, 80°C or greater, 90°C or greater, 100°C or greater, 125°C or greater, 150°C or greater, 175°C or greater, 200°C or greater, 250°C or greater, 300°C or greater, 400°C or greater, 500°C or greater, 600°C or greater, or 700°C or greater; and 1200°C or less, 1100°C or less, 1000°C or less, 900°C or less, or 800°C or less. Stated another way, heat treating may be performed at a temperature of 70°C to 1200°C. In some embodiments, the porous ceramic article has a sulfate equivalent less than 5 ppm and/or a chloride equivalent less than 5 ppm. The raw material used to prepare a zirconia sol, for instance, often contains chloride and sulfate impurities. Several thousand ppm by weight of these ions can be present in the porous ceramic article. If not removed, these impurities can volatilize at the temperatures used for sintering and become entrapped in the sintered body as pores. The chloride and sulfate impurities can be removed prior to sintering, for example, using ion exchange treatment. Ion exchange is optionally performed by infiltrating the porous ceramic article with a solution of ammonia in water, allowing it to sand overnight, then exchanging the ammonia solution with water several times. During this treatment ammonia reacts with the chloride and sulfate impurities to form soluble ammonia salts. These are removed by diffusion into the water. It is also possible to remove these impurities by adjusting the heating profile so that sufficient volatilization occurs in the thermal treatment used to form the porous ceramic article. A sintering step is finally carried out to obtain a ceramic article having a density of 94% or greater, 95% or greater, 96% or greater, 97% or greater, 98% or greater, 99% or greater, 99.5% or greater, or 99.9% or greater, of the theoretical density. Sintering of the porous ceramic article is typically carried out under the flowing conditions: • Temperature: from 900°C to 2300°C, from 100°C to 2000°C, from 2050°C to 2300°C or from 1800°C to 2100°C or from 1000°C to 1300°C; or 900°C or greater, 1200°C or greater, 1400°C or greater, above 1600°C or greater, or 1900°C or greater; and 2300°C or less, 2250°C or less, 2200°C or less, 2150°C or less, 2100°C or less, 2050°C or less, or 2000°C or less; • Atmosphere: air or inert gas (e.g., nitrogen, argon); • Pressure: ambient pressure (e.g., 1013 mbar); and • Duration: until a density of 94% to 100% of the final density of the material has been reached. Alternatively to ambient pressure, the sintering may be carried out at elevated pressure or decreased pressure. Examples Objects and advantages of this disclosure are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure. Unless otherwise indicated, all parts and percentages are on a weight basis, all water is de-ionized water, and all molecular weights are weight average molecular weight. Moreover, unless otherwise indicated all experiments were conducted at ambient conditions (23°C; 1013 mbar). Materials Material or Description abbreviation Zirconium acetate An aqueous solution of zirconium acetate containing nominally 16.3 weight percent zirconium obtained from Magnesium Elektron, Inc. (Flemington, NJ, USA). The aqueous solution was exposed to an ion exchange resin (obtained under the trade designation “AMBERLYTE IR 120” from Rohm and Haas Company (Philadelphia, PA, USA) before use (oxide content 21.55 wt.%). Yttrium acetate Yttrium (III) acetate tetrahydrate obtained from Molycorp Inc. (Mountain Pass, CA) (oxide content 34.65 wt.%). Iron acetate Iron (II) acetate anhydrous obtained from Alfa Aesar (Ward Hill, MA, USA) (oxide content 40.84%). Erbium acetate Erbium (III) acetate tetrahydrate 99% (REO) obtained from Alfa Aesar (Ward Hill, MA, USA) (oxide content 46.48%). DI water De-ionized water. Diethylene glycol Diethylene glycol monoethyl ether obtained from Alfa Aesar monoethyl ether (Ward Hill, MA, USA). “OMNIRAD 819” UV/Visible photoinitiator obtained from IGM Resins (Waalwijk, The Netherlands) under the trade designation “OMNIRAD 819”. MEEAA 2-[2-(2-Methoxyethoxy)ethoxy]acetic acid obtained from Sigma-Aldrich (St. Louis, MO, USA). Acrylic acid Acrylic acid obtained from Alfa Aesar (Ward Hill, MA, USA). HEA Hydroxyethyl acrylate obtained from Alfa Aesar (Ward Hill, MA, USA). “SR351 H” Trimethylolpropane triacrylate obtained from Sartomer USA (Exton, PA, USA) under the trade designation “SR351 H”. “CN975” Hexafunctional urethane acrylate obtained from Sartomer USA (Exton, PA, USA) under the trade designation “CN975”. “CN9031” Aliphatic Urethane Acrylate Oligomer obtained from Sartomer USA (Exton, PA, USA) under the trade designation “CN9031” BHT 2,6-Di-tert-butyl-4-methyl-phenol (Butylated hydroxytoluene) obtained from Fluka Analytical (St. Louis, MO, USA). Isatin Isatin 98%, ACROS Organics AC151491000 obtained from Fisher Scientific (Waltham, MA) Ammonium Hydroxide Ammonium Hydroxide (assay 28-30 wt.% as NH3) obtained from EMD Chemicals Inc. (Gibbstown, NJ, USA). Methods Method for Crystalline Structure and Size (XRD Analysis) Dried zirconia samples were ground by hand using an agate mortar and pestle. A liberal amount of the sample was applied by spatula to a glass microscope slide on which a section of double-sided adhesive tape had been adhered. The sample was pressed into the adhesive on the tape by forcing the sample against the adhesive with the spatula blade. Excess sample was removed by scraping the sample area with the edge of the spatula blade, leaving a thin layer of particles adhered to the adhesive. Loosely adhered materials remaining after the scraping were removed by forcefully tapping the microscope slide against a hard surface. In a similar manner, corundum (Linde 1.0 µm alumina polishing powder, Lot Number C062, Union Carbide, Indianapolis, IN) was prepared and used to calibrate the X-ray diffractometer for instrumental broadening. X-ray diffraction scans were obtained using a Philips vertical diffractometer having a reflection geometry, copper K ^ radiation, and a proportional detector registry of the scattered radiation. The diffractometer was fitted with variable incident beam slits, fixed diffracted beam slits, and a graphite diffracted beam monochromator. The survey scan was recorded from 25 to 55 degrees two theta (2 ^) using a step size of 0.04 degrees and a dwell time of 8 seconds. X-ray generator settings of 45 kV and 35 mA were used. Data for the corundum standard was collected on three separate areas of several individual corundum mounts. Likewise, data was collected on three separate areas of the thin layer sample mount. The observed diffraction peaks were identified by comparison to reference diffraction patterns contained within the International Center for Diffraction Data (ICDD) powder diffraction database (sets 1-47, ICDD, Newton Square, PA, USA). The diffraction peaks for the samples were attributed to either cubic/tetragonal (C/T) or monoclinic (M) forms of zirconia. For zirconia-based particles, the (111) peak for the cubic phase and (101) peak for the tetragonal phase could not be separated so these phases were reported together. The amounts of each zirconia form were evaluated on a relative basis and the form of zirconia having the most intense diffraction peak was assigned the relative intensity value of 100. The strongest line of the remaining crystalline zirconia form was scaled relative to the most intense line and given a value between 1 and 100. Peak widths for the observed diffraction maxima due to corundum were measured by profile fitting. The relationship between mean corundum peak widths and corundum peak position (2 ^) was determined by fitting a polynomial to these data to produce a continuous function used to evaluate the instrumental breadth at any peak position within the corundum testing range. Peak widths for the observed diffraction maxima due to zirconia were measured by profile fitting the observed diffraction peaks. The following peak widths were evaluated depending on the zirconia phase found to be present: Cubic/Tetragonal (C/T): (111) Monoclinic (M): (-111), and (111) A Pearson VII peak shape model with K _^1 and K _^2 wavelength components and linear background model were used for all measurements. Widths were calculated as the peak full width at half maximum (FWHM) having units of degrees. The profile fitting was accomplished by use of the capabilities of the JADE diffraction software suite. Sample peak widths were evaluated for the three separate data collections obtained for the same thin layer sample mount. Sample peaks were corrected for instrumental broadening by interpolation of instrumental breadth values from corundum instrument calibration and corrected peak widths converted to units of radians. The Scherrer equation was used to calculate the primary crystal size. Crystallite Size (D) = K ^/ ^ (cos ^) In the Scherrer equation, K is the form factor (here 0.9), ^ is the wavelength (1.540598 Å), ^ is the calculated peak width after correction for instrumental broadening (in radians), and ^ equals half the peak position (scattering angle). ^ is equal to [calculated peak FWHM – instrumental breadth] (converted to radians) where FWHM is full width at half maximum. The cubic/tetragonal (C/T) mean crystallite size was measured as the average of three measurements using (111) peak. That is, C/T mean crystallite size = [D(111) _{area 1} + D(111) _{area 2} + D(111) _{area 3}] / 3. Method for Photon Correlation Spectroscopy (PCS) Particle size measurements were made using a light scattering particle sizer equipped with a red laser having a 633 nm wavelength of light (obtained under the trade designation “ZETA SIZER - Nano Series, Model ZEN3600” from Malvern Instruments Inc., Westborough, MA). Each sample was analyzed in a one centimeter square polystyrene sample cuvette. The sample cuvette was filled with about 1 gram of deionized water, and then a few drops (about 0.1 gram) of the zirconia-based sol were added. The composition (e.g., sample) within each sample cuvette was mixed by drawing the composition into a clean pipette and discharging the composition back into the sample cuvette several times. The sample cuvette was then placed in the instrument and equilibrated at 25°C. The instrument parameters were set as follows: dispersant refractive index 1.330, dispersant viscosity 0.8872 MPa-second, material refractive index 2.10, and material absorption value 0.10 units. The automatic size-measurement procedure was then run. The instrument automatically adjusted the laser-beam position and attenuator setting to obtain the best measurement of particle size. The light scattering particle sizer illuminated the sample with a laser and analyzed the intensity fluctuations of the light scattered from the particles at an angle of 173 degrees. The method of Photon Correlation Spectroscopy (PCS) was used by the instrument to calculate the particle size. PCS uses the fluctuating light intensity to measure Brownian motion of the particles in the liquid. The particle size is then calculated to be the diameter of sphere that moves at the measured speed. The intensity of the light scattered by the particle is proportional to the sixth power of the particle diameter. The Z-average size or cumulant mean is a mean calculated from the intensity distribution and the calculation is based on assumptions that the particles are mono-modal, mono-disperse, and spherical. Related functions calculated from the fluctuating light intensity are the Intensity Distribution and its mean. The mean of the Intensity Distribution is calculated based on the assumption that the particles are spherical. Both the Z-average size and the Intensity Distribution mean are more sensitive to larger particles than smaller ones. The Volume Distribution gives the percentage of the total volume of particles corresponding to particles in a given size range. The volume-average size is the size of a particle that corresponds to the mean of the Volume Distribution. Since the volume of a particle is proportional to the third power of the diameter, this distribution is less sensitive to larger particles than the Z-average size. Thus, the volume-average will typically be a smaller value than the Z-average size. Method for Measuring Oxide Content The oxide content was measured via thermal gravimetric analysis (obtained under the trade designation “TGA Q500” from TA Instruments, New Castle, DE, USA). The sample (about 50 mg) was loaded into the TGA and the temperature was taken to 900°C in air. The oxide content of the sample was equal to the residual weight after heating to 900°C. Sol Batch Preparation Zirconia-based sols Sol-I(a)–Sol-IV(a) were prepared as described in WO2016191534 (Examples Section – Processing: Preparation of Sol-S1) except that the feed composition was varied. The target compositions for Sol-I(a)–Sol-IV(a) are listed in Table 1, below. Table 1. Mole % Mole % Mole % Mole % Sol ZrO₂ Y₂O₃ Er₂O₃ Fe₂O₃ Sol-I(a) 95.0 5.0 - - Sol-II(a) 92.0 8.0 - - Sol-III(a) 96.8 3.0 - 0.2 Sol-IV(a) 93.8 5.0 1.2 - The properties of Sol-I(a)–Sol-IV(a) were determined using the methods described above. Table 2, below, summarizes the crystallite size from XRD analysis as well as the PCS data, including the volume-average size and the Z-average size. Table 2. X^{RD PCS} C/T size Volume-Average Size Z-Average Size Sol (nm) (nm) (nm) S^ol-I(b) _{5.5 10.38 18.40} S^ol-II(b) _{5.4 12.11 19.05} S^ol-III(b) _{6.7 9.85 21.27} S^ol-IV(b) _{5.5 10.56 18.76} Sol-I(a)–Sol-IV(a) were further processed to increase their concentration and/or remove acetic acid (AcOH). A combination of one or more of ultrafiltration, diafiltration and distillation were used. The diafiltration and ultrafiltration were performed using a membrane cartridge (obtained under the trade designation “M21S-100-01P” from Spectrum Laboratories Inc., Rancho Dominguez, CA). Distillation was performed using rotary evaporation. Diethylene glycol monoethyl ether-based sols, Sol-I(b)–Sol-IV(b), were prepared from Sol-I(a)–Sol-IV(a) by adding 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA) (3.5–7.2 wt.% with respect to the grams of oxide in the sol) as well as the appropriate amount of diethylene glycol monoethyl ether (adjusted to the intended final oxide concentration in the sol, e.g, 55 wt.%) and concentrating each sol via rotary evaporation. The resulting weight percents of oxide, acetic acid (AcOH), and 2-[2-(2- methoxyethoxy)ethoxy]acetic acid (MEEAA) in each sol are given Table 3. Table 3. wt.% wt.% Sol wt.% oxide AcOH MEEAA Sol-I(b) 55.66% 7.55% 2.98% Sol-II(b) 54.05% 6.78% 3.85% Sol-III(b) 55.60% 5.70% 1.98% Sol-IV(b) 47.96% 5.92% 2.56% To prepare precursor-sol S1, 1303.4 grams of Sol-I(b) were charged to a 1-L bottle and combined with acrylic acid (77.66 grams) and diethylene glycol monoethyl ether (125.75 grams). To prepare precursor-sol S2, 147.87 grams of Sol-II(b), 7.28 grams of Sol-III(b), and 2.15 grams of Sol-IV(b) were charged to a 250-mL bottle and combined with 2-[2-(2- methoxyethoxy)ethoxy]acetic acid (MEEAA) (0.16 grams), acrylic acid (9.19 grams), and diethylene glycol monoethyl ether (11.09 grams). Printing Sol Preparation Preparation of Printing Sol PS1 To prepare printing sol PS1, a portion of precursor-sol S1 (500 grams) was charged to a 1-liter bottle and combined with diethylene glycol monoethyl ether (33.5 grams), hydroxyethyl acrylate (HEA) (2.2 grams), trimethylolpropane triacrylate (“SR351H”) (47.1 grams), and two different urethane acrylates: CN975 (15.7 grams) and CN9031 (7.8 grams). Prior to printing, OMNIRAD 819 (0.1 wt.% with respect to the weight of the sol), butylated hydroxytoluene (BHT) (0.1 wt.% with respect to the weight of the sol), and isatin (0.05 wt% with respect to the weight of the sol) were dissolved in the sol. The printing sol was then passed through a 1-µm filter. Preparation of Printing Sol PS2 To prepare printing sol PS2, a portion of precursor-sol S2 (100 grams) was charged to a 250-mL bottle and combined with diethylene glycol monoethyl ether (6.7 grams), hydroxyethyl acrylate (HEA) (0.44 grams), trimethylolpropane triacrylate (“SR351H”) (9.42 grams), and two different urethane acrylates: CN975 (3.14 grams) and CN9031 (1.56 grams). Prior to printing, OMNIRAD 819 (0.1 wt.% with respect to the weight of the sol), butylated hydroxytoluene (BHT) (0.1 wt.% with respect to the weight of the sol), and isatin (0.05 wt% with respect to the weight of the sol) were dissolved in the sol. The printing sol was then passed through a 1-µm filter. Method for Layer-by-Layer 3D Printing To print objects from ceramic sol with layer-by-layer DLP stereolithography 3D printing, the following procedure was used. A build tray was assembled with a fluoropolymer release film. Approximately 50 mL of a sol was loaded into the build tray at room temperature. Caution was taken to prevent light exposure by performing procedures in a UV-filtered room (yellow lights), or in low-light conditions when UV-filtering was not available. The build platform was abraded with sandpaper and cleaned with IPA as needed. A .STL file was loaded into the software and support structures were applied as required. The settings for printing in the ASIGA MAX-X43 UV stereolithography printer (from Asiga, Sydney, Australia) are listed in Table 4, below. Table 4: Standard settings for build using the ASIGA MAX-X43 UV printer. Setting Min Max Typical Units Slice Thickness 0.001 0.05 0.05 mm Separation 4 Distance 2 10 mm After building, Separation Velocity 0.15 15 1 mm/s the gel sample Approach Velocity .5 15 2 mm/s was Exposure Time 0.5 45 1.5 s Power 15 30 25 mW/cm² immediately removed from the build platform and submerged in 2 used and one fresh diethylene glycol monoethyl ether solvent bath. The washed parts were post-cured in a Clearstone Technologies CA3200 inerted UV cure chamber for 1 minute of 385nm LED exposure at 20% power under nitrogen. It was then placed in a sealed container until the next step. Method for Supercritical Fluid Extraction The printed gel body was dried via supercritical fluid extraction, for example as described in the Method for Supercritical Extraction of Gels in the Examples section of WO 2016/191534 (Mayr et al). Method for Burnout and Pre-sinter The dried gel body was placed on a bed of zirconia beads in an alumina crucible. The crucible was covered with alumina plates and then fired in air according to the following schedule: 1- Heat from 20°C to 220°C at 18°C/hour rate, 2- Heat from 220°C to 244°C at 1°C/hour rate, 3- Heat from 244°C to 400°C at 6°C/hour rate, 4- Heat from 400°C to 1020°C at 60°C/hour rate, 5- Cool from 1020°C to 20°C at 120°C/hour rate. Method for Ion Exchange The pre-sintered body was placed in a 118-ml glass jar containing 1.0N NH₄OH at a depth of about 2.5 cm and soaked for at least 16 hours. The NH₄OH was then poured off and the jar was filled with distilled water. The body was soaked in the distilled water for 1 hour. The water was then replaced with fresh distilled water. This step was repeated until the pH of the soak water was equal to that of fresh distilled water. The body was then dried at 90-125°C for a minimum of 15 minutes. Method for Sintering The pre-sintered, ion-exchanged body was placed on a bed of zirconia beads in an alumina crucible. The crucible was covered with alumina plates, and the sample was sintered in air according to the following schedule: 1- Heat from 20°C to 1020°C at 500°C/hour rate, 2- Heat from 1020°C to 1225°C at 120°C/hour rate, 3- Hold at 1225°C for 2 hours, 4- Cool down from 1225°C to 20°C at 500°C/hour rate. Method for Measuring Archimedes Density The density of the sintered material may be measured by the Archimedes technique. The measurements can be made on a precision balance (identified as “XSE204” from Mettler-Toledo, LLC, Columbus, OH, USA) using a density determination kit (identified as “Density Determination Kit for Excellence XP/XS Analytical Balances” from Mettler-Toledo, LLC, Columbus, OH, USA). The sample can be first weighed in air (A), then immersed in water and weighed (B). The water can be distilled and deionized. Three drops of a wetting agent (obtained under trade designation “PERVITRO 75%” from Mettler-Toledo, LLC, Columbus, OH, USA) can then be added to 250 ml of water. The density can be calculated using the balance density function, which used the formula ρ = (A/(A-B)) (ρ0-ρL) + ρL, where ρ0 is the density of water and ρL is the density of air (0.0012 g/cm³). The relative density can be calculated by reference to the theoretical density (ρt) of the material, ρrel = (ρ/ρt)*100. Method for Measuring Flexural Strength of Ceramic Articles The flexural strength may be determined according to ISO 6872 (2008). The printed ceramic test piece will be in the shape of a flex bar, with dimensions of approximately 1 millimeter (mm) x 4 mm x 12 mm after sintering. The parallel large faces of the flex bar can be polished to a surface finish of 15 microns using diamond lapping film (668X Diamond Lapping Film PSA, 3M, St. Paul, MN) on a Beta, Grinder-Polisher (Buehler, Lake Bluff, IL), operating at 100 rpm and lubricated with water. Each of the 4 edges along the length of the flex bar can be chamfered, meaning to create a bevel on the edges of the specimens along the length, to a 45 degree angle. A 3-point beam bend test configuration with a span of 10.0 mm may be employed. The crosshead test speed is 1 mm/minute. An Instron 5954 test frame (Instron Corporation, Canton, MA) can be utilized for testing. Method for Measuring Opacity of Ceramic Articles The opacity of a ceramic article may be evaluated with the following procedure. After sintering, the dimensions of the printed ceramic test piece may be approximately 1 mm ± 0.03 mm thick x 13 mm x 13 mm. The parallel large faces of the sample may be polished to a surface finish of 15 micron grade diamond lapping film (668X Diamond Lapping Film PSA, 3M, St. Paul, MN) on a Beta, Grinder-Polisher (Buehler, Lake Bluff, IL), operating at 100 rpm and lubricated with water. The polished sample can be measured with a spectrophotometer (X-Rite Color i7, Grand Rapids, MI, USA) in reflectance mode. Translucency (T) was determined according to T = 1-RB/RW where RB is the reflectance through a ceramic sample on a black substrate and RW is the reflectance through the same sample on a white substrate. Higher values of translucency are indicative of greater transmission of light, and less opacity. Opacity (O) is accordingly determined by the formula O = 100-T. Examples 1–3 Ceramic test pieces were printed according to the Method for Layer-by-Layer 3D Printing. The printed samples were dried according to the Method for Supercritical Fluid Extraction, and subsequently processed according to the Method for Burnout and Pre- sinter, the Method for Ion Exchange, and the Method for Sintering to form fully dense ceramic articles. Example 1 Example 1 exhibits mamelon features partially within the cusp receptacle as well as thicknesses less than 300 microns in central regions away from the proximal edges. Three separate veneer samples from a single batch had thickness of 198 microns, 195 microns, and 200 microns at the thinnest parts. It was produced as detailed above with printing sol PS1. The gelled articles are depicted in FIG.15, while a sintered veneer is depicted in FIG.16. Example 2 Example 2 exhibits regions with thickness less than 300 microns away from proximal edges. Precise thickness varies across the face. Three separate veneer samples from a single batch had thicknesses of 278, 274, and 258 microns at the thinnest parts. The veneers were produced as detailed above with printing sol PS2. The resulting articles, including support sprues, are depicted in FIG.12C and 12D. Example 3 Example 3, depicted in FIG.5, exhibits a central inset region with higher surface roughness than the surrounding surface. The region having higher surface roughness depicts a recreation of the 3M brand. It was produced as detailed above with printing sol PS2. The patents, patent documents, and patent applications cited herein are incorporated by reference in their entirety as if each were individually incorporated by reference. It will be apparent to those of ordinary skill in the art that various changes and modifications may be made without deviating from the inventing concepts set from above. Thus, the scope of the present disclosure should not be limited to the structures described herein. Those having skill in the art will appreciate that many changes may be made to the details of the above-described embodiments and implementations without departing from the underlying principles thereof. Further, various modifications and alterations of the present invention will become apparent to those skilled in the art without departing from the spirit and scope of the invention. The scope of the present application should, therefore, be determined only by the following claims and equivalents thereof.

Claims

CLAIMS: 1. A monolithic veneer comprising: an incisal edge, a cervical edge, a body extending between the incisal edge region and cervical edge, and opposing proximal edges; a labial surface and an opposing tooth-facing surface; and a cusp receptacle adjacent the incisal edge; wherein the body includes one or more architectural features selected from the group consisting of mamelons at least partially within the cusp receptacle, concave divots at least partially within the cusp receptacle, designed surface textures, and relief features, wherein a thinnest portion of the body in a central window area is no greater than 400 microns.

2. The veneer of claim 1, wherein the tooth-facing surface substantially matches the contours of a patient’s labial tooth surface.

3. The veneer of claim 1, wherein the designed surface textures include one or more channels complementary to perikyma on the patient’s labial tooth surface.

4. The veneer of claim 3, wherein the channels have a depth of no greater than 100 microns.

5. The veneer of claims 1-3, wherein the cusp receptacle includes one or more mamelons.

6. The veneer of any one of the previous claims, wherein the cusp receptacle includes a surface of the body having a series of concave divots.

7. The veneer of claim 7, wherein each divot of the series of divots has a radius of no greater than 100 microns, and wherein the divots are configured to register with one or more features on a patient’s tooth surface.

8. The veneer of any one of the previous claims, wherein the cusp receptacle includes a lingual wall surface opposing the tooth-facing surface of the body.

9. The veneer of claim 9, wherein at least some of the architectural features are disposed on the lingual wall of the cusp receptacle.

10. The veneer of any one of the previous claims, wherein the veneer is monolithically formed from a sol including ceramic particles, wherein the sol includes at least one of zirconia and silica particles.

11. The veneer of any one of the previous claims, wherein the sol includes zirconia particles.

12. The veneer of any one of the previous claims, wherein the body includes one or more translucent regions.

13. The veneer of any one of the previous claims, wherein the central window area of the body has a cross-sectional thickness of no more than 200 microns.

14. The veneer of any one of the previous claims, wherein an exterior surface of the veneer includes a plurality of support sprues, and wherein the plurality of support sprues are located on the incisal edge or on the cervical edge.

15. The veneer of any one of the previous claims, wherein the support sprues include a shaft having a cross-sectional thickness adjacent to the veneer which is not greater than 100 microns.

16. The veneer of any one of the previous claims, wherein the veneer exhibits a flex strength of 100 megapascals (MPa) or greater, 200 MPa or greater, 300 MPa or greater, 400 MPa or greater, 500 MPa or greater, 600 MPa or greater, 700 MPa or greater, 800 MPa or greater, 900 MPa or greater, 1000 MPa or greater, 1100 MPa or greater, or 1200 MPa or greater.

17. The veneer of claim 1, wherein the architectural features include a repeating pattern of surface texture elements, the elements arranged in unit cells.

18. The veneer of any one of the previous claims, wherein the veneer exhibits a density of 98% or greater with respect to a theoretical density of the ceramic material.

19. A method for making a dental veneer, comprising steps of: receiving a design for a dental veneer, comprising: an incisal edge, a cervical edge, opposing proximal edges, and a body extending between the edges; a labial surface and an opposing tooth-facing surface, and a cusp receptacle at the incisal edge; making the dental veneer as a single piece from a ceramic sol using additive manufacturing, wherein a thinnest portion of a central window area of the veneer is no greater than 400 microns, and wherein the veneer exhibits a density of 94% or greater with respect to a theoretical density of the ceramic material.

20. The method of claim 19, wherein the veneer exhibits a density of 98% or greater with respect to a theoretical density of the ceramic material.

21. The method of claim 19, and further comprising receiving a model of the patient’s tooth surface and designing the veneer to substantially match at least a portion of the model.

22. The method of claim 19, wherein the model is a 3D model.

23. The method of any one of the previous claims, wherein the ceramic sol is a zirconia sol.

24. The method of any one of the previous claims, wherein a thinnest portion of the additively manufactured veneer has a thickness of less than 200 microns.

25. The method of the any one of the previous claims, wherein the incisal edge of the veneer design includes a hollow cusp receptacle.

26. The method of any one of the previous claims, wherein the cusp receptacle includes one or more mamelons.

27. The method of any one of the previous claims, wherein the body includes one or more architectural features selected from the group consisting of mamelons at least partially within the cusp receptacle, concave divots at least partially within the cusp receptacle, designed surface textures, and relief features.

28. The method of any one of the previous claims, wherein additively manufacturing the veneer comprises: a) obtaining a photopolymerizable sol comprising a plurality of ceramic particles distributed in the photopolymerizable sol, wherein the ceramic particles have an average particle size diameter of 1 nanometer (nm) to 100 nm; b) selectively polymerizing the photopolymerizable sol using actinic radiation and continuous movement of a build substrate through the photopolymerizable sol to form a gelled article; c) extracting solvent from the gelled article to form an aerogel article or a xerogel article; d) heat treating the aerogel article or the xerogel article to form a porous ceramic article e) sintering the porous ceramic article to form a sintered ceramic article.

29. The method of any one of the previous claims, wherein the body includes one or more architectural features selected from the group consisting of mamelons at least partially within the cusp receptacle, concave divots at least partially within the cusp receptacle, designed surface textures, and relief features, wherein creation of the features occurs before step (e).

30. A kit comprising: A plurality of veneers, each veneer comprising: an incisal edge, a cervical edge, opposing proximal edges, and a body extending between the edges; a labial surface and an opposing tooth-facing surface, wherein the body includes one or more architectural features selected from the group consisting of mamelons, concave divots, patterned surface textures on the tooth-facing surface, and printed relief features on the tooth-facing surface, wherein a thinnest portion of the thickness of the veneer at the proximal edges is no greater than 300 microns. a bonding agent for securing at least one veneer to a tooth surface.