Patent Description:
The use of stereolithography and inkjet printing to produce three-dimensional articles has been known for a relatively long time, and these processes are generally known as methods of so called 3D printing (or additive manufacturing). In vat polymerization techniques (of which stereolithography is one type), the desired 3D article is built up from a liquid, curable composition with the aid of a recurring, alternating sequence of two steps: in the first step, a layer of the liquid, curable composition, one boundary of which is the surface of the composition, is cured with the aid of appropriate radiation within a surface region which corresponds to the desired cross-sectional area of the shaped article to be formed, at the height of this layer, and in the second step, the cured layer is covered with a new layer of the liquid, curable composition, and the sequence of steps is repeated until a so-called green body (i.e., gelled article) of the desired shape is finished. This green body is often not yet fully cured and must, usually, be subjected to post-curing. The mechanical strength of the green body immediately after curing, otherwise known as green strength, is relevant to further processing of the printed articles.

Other 3D printing techniques use inks that are jetted through a print head as a liquid to form various three-dimensional articles. In operation, the print head may deposit curable photopolymers in a layer-by-layer fashion. Some jet printers deposit a polymer in conjunction with a support material or a bonding agent. In some instances, the build material is solid at ambient temperatures and converts to liquid at elevated jetting temperatures. In other instances, the build material is liquid at ambient temperatures.

One particularly attractive opportunity for 3D printing is in the direct creation of orthodontic clear tray aligners. These trays, also known as aligners or polymeric or shell appliances, are provided in a series and are intended to be worn in succession, over a period of months, in order to gradually move the teeth in incremental steps towards a desired target arrangement. Some types of clear tray aligners have a row of tooth-shaped receptacles for receiving each tooth of the patient's dental arch, and the receptacles are oriented in slightly different positions from one appliance to the next in order to incrementally urge each tooth toward its desired target position by virtue of the resilient properties of the polymeric material. A variety of methods have been proposed in the past for manufacturing clear tray aligners and other resilient appliances. Typically, positive dental arch models are fabricated for each dental arch using additive manufacturing methods such as stereolithography described above. Subsequently, a sheet of polymeric material is placed over each of the arch models and formed under heat, pressure and/or vacuum to conform to the model teeth of each model arch. The formed sheet is cleaned and trimmed as needed and the resulting arch-shaped appliance is shipped along with the desired number of other appliances to the treating professional.

An aligner or other resilient appliance created directly by 3D printing would eliminate the need to print a mold of the dental arch and further thermoform the appliance. It also would allow new aligner designs and give more degrees of freedom in the treatment plan. Exemplary methods of direct printing clear tray aligners and other resilient orthodontic apparatuses are set forth in <CIT>), <CIT>), and <CIT>) as well as US Publication Nos. <CIT>) and <CIT>).

<CIT> discloses crosslinked polymers useful in orthodontic appliances, light polymerizable liquid compositions and formulations useful for making crosslinked polymers.

Existing printable/polymerizable resins tend to be too brittle (e.g., low elongation, short-chain crosslinked bonds, thermoset composition, and/or high glass transition temperature) for a resilient oral appliance such as an aligner. An aligner or other appliance prepared from such resins could easily break in the patient's mouth during treatment, creating material fragments that may abrade or puncture exposed tissue or be swallowed. These fractures at the very least interrupt treatment and could have serious health consequences for the patient. Thus, there is a need for curable liquid resin compositions that are tailored and well suited for creation of resilient articles using 3D printing (e.g., additive manufacturing) method. Preferably, curable liquid resin compositions to be used in the vat polymerization 3D printing process have low viscosity, a proper curing rate, and excellent mechanical properties in both the final cured article. In contrast, compositions for inkjet printing processes need to be much lower viscosity to be able to jetted through nozzles, which is not the case for most vat polymerization resins.

Urethane (meth)acrylates are a class of raw materials that have interesting properties, for example an elongation of over <NUM>% when cured, and very high toughness. But these resins also have a very high viscosity; at room temperature they are basically solids. Therefore, they only have been used in small amounts in photosensitive resin formulations for vat polymerization or stereolithography, and the properties of these resins are dominated by the other components.

In a first aspect of the invention, a photopolymerizable composition for an orthodontic article is provided. The photopolymerizable composition includes (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component and (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent, wherein the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, is free of any urethane functional groups, and comprises a methacrylate. The photopolymerizable composition further includes (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition. The photopolymerizable composition has a viscosity at a temperature of <NUM> degrees Celsius of <NUM> Pa s or less, as determined using a magnetic bearing rheometer using a <NUM> cone and plate measuring system at a shear rate of <NUM><NUM>/s. The photopolymerizable composition is free of monofunctional components. A reaction product of the photopolymerizable composition exhibits an elongation at break of <NUM>% or greater as determined according to ASTM D638-<NUM> using test specimen Type V. The at least one urethane comprises a high Mn urethane component and a low Mn urethane component. The ratio of the high Mn urethane component to the low Mn urethane component ranges from <NUM>:<NUM> high Mn urethane component to low Mn urethane component to <NUM>:<NUM> high Mn urethane component to low Mn urethane component. The high Mn urethane component has a number average molecular weight of <NUM>,<NUM> grams per mole (g/mol) or greater, with the proviso that all branches off the backbone of the compound, if present, have a Mn of no more than <NUM>/mol. The low Mn urethane component has either <NUM>) a number average molecular weight of <NUM>/mol or greater and up to but not including <NUM>,<NUM>/mol, or <NUM>) a number average molecular weight of <NUM>/mol or greater and <NUM>,<NUM>/mol or less, with the proviso that a number average molecular weight of any one or more linear portions between two reactive groups and/or branches is up to but not including <NUM>,<NUM>/mol.

In a second aspect of the invention, an orthodontic article is provided. The article includes a reaction product of a photopolymerizable composition including (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component and (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent, wherein the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, is free of any urethane functional groups, and comprises a methacrylate. The photopolymerizable composition further includes (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition. The photopolymerizable composition is free of monofunctional components. The article exhibits an elongation at break of <NUM>% or greater.

In a third aspect of the invention, a method of making an orthodontic article is provided. The method includes (i) providing a photopolymerizable composition and (ii) selectively curing the photopolymerizable composition to form an article. The method optionally also includes (iii) curing unpolymerized urethane component and/or reactive diluent remaining after step (ii). The photopolymerizable composition includes (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component; (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent, wherein the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, is free of any urethane functional groups, and comprises a methacrylate; (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator; and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition, wherein the photopolymerizable composition is free of monofunctional components. components and wherein the article exhibits an elongation at break of <NUM>% or greater.

In a fourth aspect of the disclosure, a non-transitory machine readable medium is provided. The non-transitory machine readable medium has data representing a three-dimensional model of an article, when accessed by one or more processors interfacing with a 3D printer, causes the 3D printer to create an orthodontic article. The article includes a reaction product of a photopolymerizable composition including (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component and (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent, wherein the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, is free of any urethane functional groups, and comprises a methacrylate. The photopolymerizable composition further includes (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition, wherein the photopolymerizable composition is free of monofunctional components. The article exhibits an elongation at break of <NUM>% or greater.

In a fifth aspect of the invention, a method is provided. The method includes retrieving, from a non-transitory machine readable medium, data representing a 3D model of an orthodontic article; executing, by one or more processors, a 3D printing application interfacing with a manufacturing device using the data; and generating, by the manufacturing device, a physical object of the article. The article includes a reaction product of a photopolymerizable composition including (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component and (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent, wherein the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, is free of any urethane functional groups, and comprises a methacrylate. The photopolymerizable composition further includes (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition, wherein the photopolymerizable composition is free of monofunctional components. The article exhibits an elongation at break of <NUM>% or greater.

In a sixth aspect of the invention, another method is provided. The method includes receiving, by a manufacturing device having one or more processors, a digital object comprising data specifying a plurality of layers of an orthodontic article; and generating, with the manufacturing device by an additive manufacturing process, the article based on the digital object. The article includes a reaction product of a photopolymerizable composition including (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component and (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent, wherein the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, is free of any urethane functional groups, and comprises a methacrylate. The photopolymerizable composition further includes (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition, wherein the photopolymerizable composition is free of monofunctional components. The article exhibits an elongation at break of <NUM>% or greater.

In a seventh aspect of the disclosure, a system is provided. The system includes a display that displays a 3D model of an orthodontic article; and one or more processors that, in response to the 3D model selected by a user, cause a 3D printer to create a physical object of an article. The article includes a reaction product of a photopolymerizable composition including (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component and (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent, wherein the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, is free of any urethane functional groups, and comprises a methacrylate. The photopolymerizable composition further includes (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition, wherein the photopolymerizable composition is free of monofunctional components. The article exhibits an elongation at break of <NUM>% or greater.

Clear tray aligners and tensile bars made according to at least certain embodiments of this disclosure were found to show low brittleness, good resistance to water, and good toughness.

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 necessary drawn to scale. In all cases, this disclosure presents the invention by way of representation and not limitation.

As used herein, the terms "hardenable" refers to a material 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.

As used herein, the term "(meth)acrylate" is a shorthand reference to acrylate, methacrylate, or combinations thereof, and "(meth)acrylic" is a shorthand reference to acrylic, methacrylic, or combinations thereof. 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, "oligomer" refers to a molecule that has one or more properties that change upon the addition of a single further repeat unit.

As used herein, "polymer" refers to a molecule having one or more properties that do not change upon the addition of a single further repeat unit.

As used herein, "polymerizable composition" means a hardenable composition that can undergo polymerization upon initiation (e.g., free-radical polymerization initiation). Typically, prior to polymerization (e.g., hardening), the polymerizable composition has a viscosity profile consistent with the requirements and parameters of one or more 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 instance, in some embodiments, ultraviolet (UV) radiation, e-beam radiation, or both, can be used.

As used herein, a "resin" contains all polymerizable components (monomers, oligomers and/or polymers) being present in a hardenable composition. The resin may contain only one polymerizable component compound or a mixture of different polymerizable compounds.

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.

As used herein, "occlusal" means in a direction toward the outer tips of the patient's teeth; "facial" means in a direction toward the patient's lips or cheeks; and "lingual" means in a direction toward the patient's tongue.

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.

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., <NUM> to <NUM> includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, 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 +/- <NUM> % for quantifiable properties). The term "substantially", unless otherwise specifically defined, means to a high degree of approximation (e.g., within +/- <NUM>% 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.

In a first aspect, the present disclosure provides a photopolymerizable composition. The photopolymerizable composition comprises:.

The photopolymerizable compositions of the present disclosure include at least one urethane component. As used herein, a "urethane component" refers to a compound including one or more carbamate functionalities in the backbone of the compound. In certain embodiments, the carbamate functionality is of Formula I:.

Urethanes are prepared by the reaction of an isocyanate with an alcohol to form carbamate linkages. Moreover, the term "polyurethane" has been used more generically to refer to the reaction products of polyisocyanates with any polyactive hydrogen compound including polyfunctional alcohols, amines, and mercaptans.

The at least one urethane component provides both toughness (e.g., at least a minimum tensile strength and/or modulus) and flexibility (e.g., at least a minimum elongation at break) to the final article. In some embodiments, in addition to the urethane functionality, the urethane component further comprises one or more functional groups selected from hydroxyl groups, carboxyl groups, amino groups, and siloxane groups. These functional groups can be reactive with other components of the photopolymerizable composition during polymerization. The at least one urethane component often comprises a urethane (meth)acrylate, a urethane acrylamide, or combinations thereof, and wherein the at least one urethane component comprises a linking group selected from alkyl, polyalkylene, polyalkylene oxide, aryl, polycarbonate, polyester, polyamide, and combinations thereof. As used herein, "linking group" refers to a functional group that connects two or more urethane groups. The linking group may be divalent, trivalent, or tetravalent. In select embodiments, the at least one urethane component comprises a urethane (meth)acrylate comprising a polyalkylene oxide linking group, a polyamide linking group, or combinations thereof.

For example, the polymerizable component can include polyfunctional urethane acrylates or urethane methacrylates. These urethane (meth)acrylates are known to the person skilled in the art and can be prepared in a known manner by, for example, reacting a hydroxyl-terminated polyurethane with acrylic acid, methacrylic acid, or isocyanatoethyl methacrylate, or by reacting an isocyanate-terminated prepolymer with hydroxyalkyl (meth)acrylates to give the urethane (meth)acrylate. Suitable processes are disclosed, inter alia, in <CIT>) and <CIT>). Suitable urethane methacrylates can include PEGDMA (polyethyleneglycol dimethacrylate having a molecular weight of approximately <NUM>), aliphatic urethane methacrylates, aliphatic polyester urethane methacrylates, and aliphatic polyester triurethane acrylates.

Typically, the urethane component comprises a number average molecular weight (Mn) of <NUM> grams per mole to <NUM>,<NUM> grams per mole. The number average molecular weight may be measured by matrix assisted laser deposition ionization mass spectrometry (MALDI). The "urethane component" as used herein includes each of a "high Mn urethane component" and a "low Mn urethane component". The high Mn urethane component encompasses compounds including one or more urethane functionalities in the backbone of the compound and that have a number average molecular weight of <NUM>,<NUM> grams per mole (g/mol) or greater, with the proviso that all branches off the backbone of the compound, if present, have a Mn of no more than <NUM>/mol. Stated another way, the high Mn urethane component typically has a Mn of <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, <NUM>,<NUM>/mol or greater, or even <NUM>,<NUM>/mol or greater; and <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, or <NUM>,<NUM>/mol or less, or even <NUM>,<NUM>/mol or less.

The low Mn urethane component encompasses compounds including one or more urethane functionalities in the backbone of the compound and that have either <NUM>) a number average molecular weight of <NUM>/mol or greater and up to but not including <NUM>,<NUM>/mol, or <NUM>) a number average molecular weight of <NUM>/mol or greater and <NUM>,<NUM>/mol or less, with the proviso that a number average molecular weight of any one or more linear portions between two reactive groups and/or branches is up to but not including <NUM>,<NUM>/mol. For instance, a branched urethane component can have a total Mn of greater than <NUM>,<NUM>/mol but still be a low Mn urethane component due to having a linear segment between two branching points with a Mn of less than <NUM>,<NUM>/mol. Stated another way, the <NUM>) category of low Mn urethane components typically have a Mn of <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, or <NUM>/mol or greater; and up to but not including <NUM>,<NUM>/mol, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, or <NUM>/mol or less, or even <NUM>/mol or less. The <NUM>) category of low Mn urethane components typically have a Mn of <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, or <NUM>/mol or greater; and <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, or <NUM>/mol or less, or even <NUM>/mol or less. Each of the foregoing second category of low Mn urethane components includes the proviso that a number average molecular weight of any one or more linear portions between two reactive groups and/or branches is up to but not including <NUM>,<NUM>/mol, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, or <NUM>/mol or less; and a number average molecular weight of any one or more linear portions between two reactive groups and/or branches is <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, <NUM>/mol or greater, or <NUM>/mol or greater.

The use of high Mn urethane components having a number average molecular weight of <NUM>,<NUM>/mol or greater tend to provide a final article having at least a certain desirable minimum elongation at break (e.g., <NUM>% or greater). Eighty percent by weight or greater of the at least one urethane component is provided by one or more high Mn (e.g., long chain) urethane components. The ratio of the high number average molecular weight urethane component to the low number average molecular weight urethane component ranges from <NUM>:<NUM> high Mn urethane component to low Mn urethane component to <NUM>:<NUM> high Mn urethane component to low Mn urethane component. Stated another way, photopolymerizable compositions according to at least certain aspects of the disclosure include <NUM> wt. % or more of the total urethane component as a high Mn urethane component, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, or even <NUM> wt. % or more of the total urethane component as a high Mn urethane component; and <NUM>% or less of the total urethane component as a high Mn urethane component, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, or <NUM> wt. % or less of the total urethane component as a high Mn urethane component. Similarly, photopolymerizable compositions according to at least certain aspects of the disclosure can include <NUM> wt. % or more of the total urethane component as a low Mn urethane component, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, or even <NUM> wt. % or more of the total urethane component as a low Mn urethane component; and <NUM> wt. % or less of the total urethane component as a low Mn urethane component, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, or <NUM> wt. % or less of the total urethane component as a low Mn urethane component.

According to certain embodiments, at least one urethane component comprises at least one (meth)acrylate component having a urethane moiety, which may help to improve physical properties of the cured composition like flexural strength and/or elongation at break. Such a urethane component can be characterized by the following features alone or in combination:.

A combination of the features a) and b) or b) and c) or a) and d) can sometimes be preferred.

Urethane (meth)acrylates may be obtained by a number of processes known to the skilled person. The urethane(meth)acrylates are typically obtained by reacting an NCO-terminated compound with a suitable monofunctional (meth)acrylate monomer such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropylmethacrylate, preferably hydroxyethyl- and hydroxypropylmethacrylate. For example, a polyisocyanate and a polyol may be reacted to form an isocyanate-terminated urethane prepolymer that is subsequently reacted with a (meth)acrylate such as <NUM>-hydroxy ethyl(meth)acrylate. These types of reactions may be conducted at room temperature or higher temperature, optionally in the presence of catalysts such as tin catalysts, tertiary amines and the like.

Polyisocyanates which can be employed to form isocyanate-functional urethane prepolymers can be any organic isocyanate having at least two free isocyanate groups. Included are aliphatic cycloaliphatic, aromatic and araliphatic isocyanates. Any of the known polyisocyanates such as alkyl and alkylene polyisocyanates, cycloalkyl and cycloalkylene polyisocyanates, and combinations such as alkylene and cycloalkylene polyisocyanates can be employed. Preferably, diisocyanates having the formula X(NCO)<NUM> can be used, with X representing an aliphatic hydrocarbon radical with <NUM> to <NUM> C atoms, a cycloaliphatic hydrocarbon radical with <NUM> to <NUM> C atoms, an aromatic hydrocarbon radical with <NUM> to <NUM> C atoms and/or an aliphatic hydrocarbon radical with <NUM> to <NUM> C atoms.

Examples of suitable polyisocyanates include <NUM>,<NUM>,<NUM>-trimethylhexamethylene-<NUM>,<NUM>-diisocyanate, hexamethylene-<NUM>,<NUM>-diisocyanate (HDI), cyclohexyl-<NUM>,<NUM>-diisocyanate, <NUM>,<NUM>'-methylene-bis(cyclohexyl isocyanate), <NUM>,<NUM>'-methylenebis(<NUM>-isocyanato) cyclohexane, isophorone diisocyanate, <NUM>,<NUM>'-methylene diphenyl diisocyanate, <NUM>,<NUM>-tetramethylene diisocycanate, meta- and para-tetra¬methylxylene diisocycanate, <NUM>,<NUM>-phenylene diisocycanate, <NUM>,<NUM>- and <NUM>,<NUM>-toluene diisocycanate, <NUM>,<NUM>-naphthylene diisocycanate, <NUM>,<NUM>' and <NUM>,<NUM>'-diphenylmethane diisocycanate and mixtures thereof.

It is also possible to use higher-functional polyisocyanates known from polyurethane chemistry or else modified polyisocyanates, for example containing carbodiimide groups, allophanate groups, isocyanurate groups and/or biuret groups. Particularly preferred isocyanates are isophorone diisocyanate, <NUM>,<NUM>,<NUM>-trimethyl-hexamethylene diisocyanate and higher-functional polyisocyanates with isocyanurate structure.

The isocyanate terminated urethane compound is capped with a (meth)acrylate to produce a urethane(meth)acrylate compound. In general, any (meth)acrylate-type capping agent having a terminal hydroxyl group and also having an acrylic or methacrylic moiety can be employed, with the methacrylic moiety being preferred. Examples of suitable capping agents include <NUM>-hydroxyethyl(meth)acrylate, <NUM>-hydroxypropyl (meth)acrylate, glycerol di(meth)acrylate and/or trimethylolpropane di(meth)acrylate. Particularly preferred are <NUM>-hydroxyethyl methacrylate (HEMA) and/or <NUM>-hydroxyethyl acrylate (HEA).

The equivalence ratio of isocyanate groups to compounds reactive vis-à-vis isocyanate groups is <NUM>:<NUM> to <NUM>: <NUM>, preferably <NUM>:<NUM> to <NUM>: <NUM>.

The isocyanate polyaddition reaction can take place in the presence of catalysts known from polyurethane chemistry, for example organotin compounds such as dibutyltin dilaurate or amine catalysts such as diazabicyclo[<NUM>. <NUM>]octane. Furthermore, the synthesis can take place both in the melt or in a suitable solvent which can be added before or during the prepolymer preparation. Suitable solvents are for example acetone, <NUM>-butanone, tetrahydrofurane, dioxane, dimethylformamide, N-methyl-<NUM>-pyrrolidone (NMP), ethyl acetate, alkyl ethers of ethylene and propylene glycol and aromatic hydrocarbons. The use of ethyl acetate as solvent is particularly preferred.

According to select embodiments the urethane dimethacrylate of the following Formulas I and II are preferred:
<CHM>
wherein n = <NUM> or <NUM>;
<CHM>.

Examples of commercially available urethane components include those available under the trade designations of EXOTHANE <NUM> (e.g., Formula I), EXOTHANE <NUM>, and EXOTHANE <NUM> (e.g., Formula II) from Esstech Inc, and DESMA from <NUM> Company. DESMA is described in, e.g., paragraph [<NUM>] and Table <NUM> of <CIT>).

The urethane component is included in the photopolymerizable composition in an amount of <NUM> to <NUM> wt. %, inclusive, based on the total weight of the photopolymerizable composition, such as <NUM> to <NUM> wt. %, inclusive. Typically, the urethane component is included in the photopolymerizable composition in an amount of <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, or <NUM> wt% or more; and <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, or <NUM> wt. % or less, based on the total weight of the photopolymerizable composition.

The photopolymerizable compositions of the present disclosure include at least one reactive diluent. A "reactive diluent," for reference purposes herein, is a component that contains at least one free radically reactive group (e.g., an ethylenically-unsaturated group) that can co-react with the at least one urethane component (e.g., is capable of undergoing addition polymerization). The reactive diluent has a smaller molecular weight than at least one (e.g., high Mn) urethane component. The reactive diluent has a molecular weight of <NUM> grams per mole or less, and does not contain any urethane functional groups (e.g., is free of any urethane functional groups). The at least one reactive diluent comprises a methacrylate.

In select embodiments, the at least one reactive diluent comprises a (meth)acrylate, a polyalkylene oxide di(meth)acrylate, an alkane diol di(meth)acrylate, or combinations thereof, such as a (meth)acrylate.

Suitable free-radically polymerizable reactant diluents include di-, tri-, or other polyacrylates and methacrylates such as glycerol diacrylate, ethoxylated bisphenol A dimethacrylate (D-zethacrylate), tetraethylene glycol dimethacrylate (TEGDMA), glycerol triacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate, triethyleneglycol dimethacrylate, <NUM>,<NUM>-propanediol diacrylate, <NUM>,<NUM>-propanediol dimethacrylate, trimethylolpropane triacrylate, <NUM>,<NUM>,<NUM>-butanetriol trimethacrylate, <NUM>,<NUM>-cyclohexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, sorbitol hexacrylate, bis[<NUM>-(<NUM>-acryloxy)] -p-ethoxyphenyldimethylmethane, bis [<NUM>-(<NUM>-acryloxy-<NUM>-hydroxy)]-p-propoxyphenyl-dimethylmethane, and trishydroxyethyl-isocyanurate trimethacrylate; the bis-acrylates and bis-methacrylates of polyethylene glycols of molecular weight <NUM>-<NUM>, copolymerizable mixtures of acrylated monomers such as those in <CIT>, and acrylated oligomers such as those of <CIT>); polyfunctional (meth)acrylates comprising urea or amide groups, such as those of <CIT>).

The reactive diluent can comprise one or more poly(meth)acrylates, for example, di-, tri-, tetra- or pentafunctional monomeric or oligomeric aliphatic, cycloaliphatic or aromatic acrylates or methacrylates.

Examples of suitable aliphatic poly(meth)acrylates having more than two (meth)acrylate groups in their molecules are the triacrylates and trimethacrylates of hexane-<NUM>,<NUM>,<NUM>-triol; glycerol or <NUM>,<NUM>,<NUM>-trimethylolpropane; ethoxylated or propoxylated glycerol or <NUM>,<NUM>,<NUM>-trimethylolpropane; and the hydroxyl-containing tri(meth)acrylates which are obtained by reacting triepoxide compounds, for example the triglycidyl ethers of said triols, with (meth)acrylic acid. It is also possible to use, for example, pentaerythritol tetraacrylate, bistrimethylolpropane tetraacrylate, pentaerythritol monohydroxytriacrylate or -methacrylate, or dipentaerythritol monohydroxypentaacrylate or - methacrylate.

Another suitable class of free radical polymerizable compounds includes aromatic di(meth)acrylate compounds and trifunctional or higher functionality (meth)acrylate compound. Trifunctional or higher functionality meth(acrylates) can be tri-, tetra- or pentafunctional monomeric or oligomeric aliphatic, cycloaliphatic or aromatic acrylates or methacrylates.

Examples of suitable aliphatic tri-, tetra- and pentafunctional (meth)acrylates are the triacrylates and trimethacrylates of hexane-<NUM>,<NUM>,<NUM>-triol; glycerol or <NUM>,<NUM>,<NUM>-trimethylolpropane; ethoxylated or propoxylated glycerol or <NUM>,<NUM>,<NUM>-trimethylolpropane; and the hydroxyl-containing tri(meth)acrylates which are obtained by reacting triepoxide compounds, for example the triglycidyl ethers of said triols, with (meth)acrylic acid. It is also possible to use, for example, pentaerythritol tetraacrylate, bistrimethylolpropane tetraacrylate, pentaerythritol monohydroxytriacrylate or -methacrylate, or dipentaerythritol monohydroxypentaacrylate or - methacrylate. In some embodiments, tri(meth)acrylates comprise <NUM>,<NUM>-trimethylolpropane triacrylate or methacrylate, ethoxylated or propoxylated <NUM>,<NUM>,<NUM>-trimethylolpropanetriacrylate or methacrylate, ethoxylated or propoxylated glycerol triacrylate, pentaerythritol monohydroxy triacrylate or methacrylate, or tris(<NUM>-hydroxy ethyl) isocyanurate triacrylate. Further examples of suitable aromatic tri(meth)acrylates are the reaction products of triglycidyl ethers of trihydroxy benzene and phenol or cresol novolaks containing three hydroxyl groups, with (meth)acrylic acid.

In some cases, a reactive diluent comprises diacrylate and/or dimethacrylate esters of aliphatic, cycloaliphatic or aromatic diols, including <NUM>,<NUM>- or <NUM>,<NUM>-butanediol, neopentyl glycol, <NUM>,<NUM>-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, tripropylene glycol, ethoxylated or propoxylated neopentyl glycol, <NUM>,<NUM>-dihydroxymethylcyclohexane, <NUM>,<NUM>-bis(<NUM>-hydroxycyclohexyl)propane or bis(<NUM>-hydroxycyclohexyl)methane, hydroquinone, <NUM>,<NUM>'-dihydroxybiphenyl, bisphenol A, bisphenol F, bisphenol S, ethoxylated or propoxylated bisphenol A, ethoxylated or propoxylated bisphenol F or ethoxylated or propoxylated bisphenol S. In some cases, a reactive diluent described herein comprises one or more higher functional acrylates or methacrylates such as dipentaerythritol monohydroxy pentaacrylate or bis(trimethylolpropane)tetraacrylate.

In certain embodiments, the photopolymerizable composition consists essentially of multifunctional components or is free of monofunctional components. This means that the photopolymerizable composition contains <NUM> wt. % or less of monofunctional components. An advantage of such photopolymerizable compositions is that they tend to contain a minimal to zero amount of unreacted reactive diluent that is capable of leaching out of an article following cure. For applications in which the article is an orthodontic article, this minimizes release of unreacted reactive diluent into a patient's mouth.

In certain embodiments, the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, <NUM>/mol or less, or <NUM>/mol or less. Including one or more reactive diluents with such molecular weights can assist in providing a photopolymerizable composition that has a sufficiently low viscosity for use with vat polymerization methods. In certain embodiments, the at least one reactive diluent comprises a molecular weight of <NUM>/mol to <NUM>/mol, inclusive.

The reactive diluent is included in the photopolymerizable composition in an amount of <NUM> to <NUM> wt. %, inclusive, based on the total weight of the photopolymerizable composition, such as <NUM> to <NUM> wt. %, inclusive. Typically, the reactive diluent is included in the photopolymerizable composition in an amount of <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, <NUM> wt. % or more, or <NUM> wt. % or more; and <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, <NUM> wt. % or less, or <NUM> wt. % or less, based on the total weight of the photopolymerizable composition.

Photopolymerizable compositions described herein, in some instances, further comprise one or more additives, such as one or more additives selected from the group consisting of photoinitiators, inhibitors, stabilizing agents, sensitizers, absorption modifiers, fillers and combinations thereof. For example, the photopolymerizable composition further comprises one or more photoinitiators. Suitable exemplary photoinitiators are those available under the trade designations IRGACURE and DAROCUR from BASF (Ludwigshafen, Germany) and include <NUM>-hydroxycyclohexyl phenyl ketone (IRGACURE <NUM>), <NUM>,<NUM>-dimethoxy-<NUM>,<NUM>-diphenylethan-<NUM>-one (IRGACURE <NUM>), bis(<NUM>,<NUM>,<NUM> trimethylbenzoyl)phenylphosphineoxide (IRGACURE <NUM>), <NUM>-[<NUM>-(<NUM>-hydroxyethoxy)phenyl]-<NUM>-hydroxy-<NUM>-methyl-<NUM>-propane-<NUM>-one (IRGACURE <NUM>), <NUM>-benzyl-<NUM>-dimethylamino-<NUM>-(<NUM>-morpholinophenyl)butanone (IRGACURE <NUM>), <NUM>-methyl-<NUM>-[<NUM>-(methylthio)phenyl]-<NUM>-morpholinopropan-<NUM>-one (IRGACURE <NUM>), Oligo[<NUM>-hydroxy-<NUM>-methyl-<NUM>-[<NUM>- (<NUM>-methylvinyl)phenyl]propanone] ESACURE ONE (Lamberti S. , Gallarate, Italy), <NUM>-hydroxy-<NUM>-methyl-<NUM>-phenyl propan-<NUM>-one (DAROCUR <NUM>), <NUM>, <NUM>, <NUM>-trimethylbenzoyldiphenylphosphine oxide (IRGACURE TPO), and <NUM>, <NUM>, <NUM>-trimethylbenzoylphenyl phosphinate (IRGACURE TPO-L). Additional suitable photoinitiators include for example and without limitation, benzyl dimethyl ketal, <NUM>-methyl-<NUM>-hydroxypropiophenone, benzoin methyl ether, benzoin isopropyl ether, anisoin methyl ether, aromatic sulfonyl chlorides, photoactive oximes, and combinations thereof.

A photoinitiator can be present in a photopolymerizable composition 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 composition in an amount of up to about <NUM>% by weight, based on the total weight of the photopolymerizable composition. In some cases, a photoinitiator is present in an amount of about <NUM>-<NUM>% by weight, based on the total weight of the photopolymerizable composition.

In addition, a photopolymerizable material composition 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 <NUM>-chlorothioxanthone (CTX). Other sensitizers may also be used. If used in the photopolymerizable composition, a sensitizer can be present in an amount ranging of about <NUM>% by weight or about <NUM>% by weight, based on the total weight of the photopolymerizable composition.

A photopolymerizable composition described herein optionally also comprises one or more polymerization inhibitors or stabilizing agents. A polymerization inhibitor is often included in a photopolymerizable composition to provide additional thermal stability to the composition. A stabilizing agent, in some instances, comprises one or more anti-oxidants. Any anti-oxidant not inconsistent with the objectives of the present disclosure may be used. In some embodiments, for example, suitable anti-oxidants include various aryl compounds, including butylated hydroxytoluene (BHT), which can also be used as a polymerization inhibitor in embodiments described herein. In addition to or as an alternative, a polymerization inhibitor comprises methoxyhydroquinone (MEHQ).

In some embodiments, a polymerization inhibitor, if used, is present in an amount of about <NUM>-<NUM>% by weight, <NUM> to <NUM>% by weight, or <NUM>-<NUM>% by weight, based on the total weight of the photopolymerizable composition. Further, if used, a stabilizing agent is present in a photopolymerizable composition described herein in an amount of about <NUM>-<NUM>% by weight, about <NUM>-<NUM>% by weight, or about <NUM>-<NUM>% by weight, based on the total weight of the photopolymerizable composition.

A photopolymerizable composition as described herein can also comprise one or more absorption modifiers (e.g., dyes, optical brighteners, pigments, particulate fillers, etc.) to control the penetration depth of actinic radiation. One particularly suitable absorption modifier is Tinopal OB, a benzoxazole, <NUM>,<NUM>'-(<NUM>,<NUM>-thiophenediyl)bis[<NUM>-(<NUM>,<NUM>-dimethylethyl)], available from BASF Corporation, Florham Park, NJ. The absorption modifier, if used, can be present in an amount of about <NUM>-<NUM>% by weight, about <NUM>-<NUM>% by weight, about <NUM>-<NUM>% by weight, or about <NUM>-<NUM>% by weight, based on the total weight of the photopolymerizable composition.

Photopolymerizable compositions may include fillers, including nano-scale fillers. Examples of suitable fillers are naturally occurring or synthetic materials including, but not limited to: silica (SiO<NUM> (e.g., quartz)); alumina (Al<NUM>O<NUM>), zirconia, nitrides (e.g., silicon nitride); glasses and fillers derived from, for example, Zr, Sr, Ce, Sb, Sn, Ba, Zn, and Al; feldspar; borosilicate glass; kaolin (china clay); talc; zirconia; titania; and submicron silica particles (e.g., pyrogenic silicas such as those available under the trade designations AEROSIL, including "OX <NUM>," "<NUM>," "<NUM>" and "<NUM>" silicas from Degussa Corp. , Akron, OH and CAB-O-SIL M5 and TS-<NUM> silica from Cabot Corp. , Tuscola, IL). Organic fillers made from polymeric materials are also possible, such as those disclosed in International Publication No. <CIT>).

The compositions may further contain fibrous reinforcement and colorants such as dyes, pigments, and pigment dyes. Examples of suitable fibrous reinforcement include PGA microfibrils, collagen microfibrils, and others as described in <CIT>). Examples of suitable colorants as described in <CIT>) include <NUM>-hydroxy-<NUM>-[<NUM>-methylphenylamino]-<NUM>,<NUM>-anthracenedione (FD&C violet No. <NUM>); disodium salt of <NUM>-hydroxy-<NUM>-[(<NUM>-sulfophenyl)oxo]-<NUM>-naphthalenesulfonic acid (FD&C Yellow No. <NUM>); <NUM>-(o-carboxyphenyl)-<NUM>-hydroxy-<NUM>,<NUM>,<NUM>,<NUM>-tetraiodo-<NUM>-xanthen-<NUM>-one, disodium salt, monohydrate (FD&C Red No. <NUM>); and the like.

Discontinuous fibers are also suitable fillers, such as fibers comprising carbon, ceramic, glass, or combinations thereof. Suitable discontinuous fibers can have a variety of compositions, such as ceramic fibers. The ceramic fibers can be produced in continuous lengths, which are chopped or sheared to provide the discontinuous ceramic fibers. The ceramic fibers can be produced from a variety of commercially available ceramic filaments. Examples of filaments useful in forming the ceramic fibers include the ceramic oxide fibers sold under the trademark NEXTEL (<NUM> Company, St. NEXTEL is a continuous filament ceramic oxide fiber having low elongation and shrinkage at operating temperatures, and offers good chemical resistance, low thermal conductivity, thermal shock resistance, and low porosity. Specific examples of NEXTEL fibers include NEXTEL <NUM>, NEXTEL <NUM>, NEXTEL <NUM>, NEXTEL <NUM> and NEXTEL <NUM>. NEXTEL <NUM> and NEXTEL <NUM> are refractory aluminoborosilicate that includes Al<NUM>O<NUM>, SiO<NUM> and B<NUM>O<NUM>. NEXTEL <NUM> and NEXTEL <NUM> are aluminosilica and NEXTEL <NUM> is alumina. During manufacture, the NEXTEL filaments are coated with organic sizings or finishes which serves as aids in textile processing. Sizing can include the use of starch, oil, wax or other organic ingredients applied to the filament strand to protect and aid handling. The sizing can be removed from the ceramic filaments by heat cleaning the filaments or ceramic fibers as a temperature of <NUM> for one to four hours.

The ceramic fibers can be cut, milled, or chopped so as to provide relatively uniform lengths, which can be accomplished by cutting continuous filaments of the ceramic material in a mechanical shearing operation or laser cutting operation, among other cutting operations. Given the highly controlled nature of certain cutting operations, the size distribution of the ceramic fibers is very narrow and allow to control the composite property. The length of the ceramic fiber can be determined, for instance, using an optical microscope (Olympus MX61, Tokyo, Japan) fit with a CCD Camera (Olympus DP72, Tokyo, Japan) and analytic software (Olympus Stream Essentials, Tokyo, Japan). Samples may be prepared by spreading representative samplings of the ceramic fiber on a glass slide and measuring the lengths of at least <NUM> ceramic fibers at 10X magnification.

Suitable fibers include for instance ceramic fibers available under the trade name NEXTEL (available from <NUM> Company, St. Paul, MN), such as NEXTEL <NUM>, <NUM>, <NUM> and <NUM>. One presently preferred ceramic fiber comprises polycrystalline α-Al<NUM>O<NUM>. Suitable alumina fibers are described, for example, in <CIT>) and <CIT>). Exemplary alpha alumina fibers are marketed under the trade designation NEXTEL <NUM> (<NUM> Company, St. In some embodiments, the alumina fibers are polycrystalline alpha alumina fibers and comprise, on a theoretical oxide basis, greater than <NUM> percent by weight Al<NUM>O<NUM> and <NUM>-<NUM> percent by weight SiO<NUM>, based on the total weight of the alumina fibers. In other embodiments, some desirable polycrystalline, alpha alumina fibers comprise alpha alumina having an average grain size of less than one micrometer (or even, in some embodiments, less than <NUM> micrometer). In some embodiments, polycrystalline, alpha alumina fibers have an average tensile strength of at least <NUM> GPa (in some embodiments, at least <NUM> GPa, or even, at least <NUM> GPa). Suitable aluminosilicate fibers are described, for example, in <CIT>). Exemplary aluminosilicate fibers are marketed under the trade designations NEXTEL <NUM>, and NEXTEL <NUM>, by <NUM> Company (St. Aluminoborosilicate fibers are described, for example, in <CIT>). Exemplary aluminoborosilicate fibers are marketed under the trade designation NEXTEL <NUM> by <NUM> Company. Boron nitride fibers can be made, for example, as described in <CIT>) and <CIT>).

Ceramic fibers can also be formed from other suitable ceramic oxide filaments. Examples of such ceramic oxide filaments include those available from Central Glass Fiber Co. (e.g., EFH75-<NUM>, EFH150-<NUM>). Also preferred are aluminoborosilicate glass fibers, which contain less than about <NUM>% alkali or are substantially free of alkali (i.e., "E-glass" fibers). E-glass fibers are available from numerous commercial suppliers.

Examples of useful pigments include, without limitation: white pigments, such as titanium oxide, zinc phosphate, zinc sulfide, zinc oxide and lithopone; red and red-orange pigments, such as iron oxide (maroon, red, light red), iron/chrome oxide, cadmium sulfoselenide and cadmium mercury (maroon, red, orange); ultramarine (blue, pink and violet), chrome-tin (pink) manganese (violet), cobalt (violet); orange, yellow and buff pigments such as barium titanate, cadmium sulfide (yellow), chrome (orange, yellow), molybdate (orange), zinc chromate (yellow), nickel titanate (yellow), iron oxide (yellow), nickel tungsten titanium, zinc ferrite and chrome titanate; brown pigments such as iron oxide (buff, brown), manganese/antimony/titanium oxide, manganese titanate, natural siennas (umbers), titanium tungsten manganese; blue-green pigments, such as chrome aluminate (blue), chrome cobalt-alumina (turquoise), iron blue (blue), manganese (blue), chrome and chrome oxide (green) and titanium green; as well as black pigments, such as iron oxide black and carbon black. Combinations of pigments are generally used to achieve the desired color tone in the cured composition.

The use of florescent dyes and pigments can also be beneficial in enabling the printed composition to be viewed under black-light. A particularly useful hydrocarbon soluble fluorescing dye is <NUM>,<NUM>-bis(<NUM>-tert-butyl-<NUM>-benzoxazolyl) <NUM> thiophene. Fluorescing dyes, such as rhodamine, may also be bound to cationic polymers and incorporated as part of the resin.

If desired, the compositions of the disclosure may contain other additives such as indicators, accelerators, surfactants, wetting agents, antioxidants, tartaric acid, chelating agents, buffering agents, and other similar ingredients that will be apparent to those skilled in the art. Additionally, medicaments or other therapeutic substances can be optionally added to the photopolymerizable compositions. Examples include, but are not limited to, fluoride sources, whitening agents, anticaries agents (e.g., xylitol), remineralizing agents (e.g., calcium phosphate compounds and other calcium sources and phosphate sources), enzymes, breath fresheners, anesthetics, clotting agents, acid neutralizers, chemotherapeutic agents, immune response modifiers, thixotropes, polyols, anti-inflammatory agents, antimicrobial agents, antifungal agents, agents for treating xerostomia, desensitizers, and the like, of the type often used in dental compositions.

Combinations of any of the above additives may also be employed. The selection and amount of any one such additive can be selected by one of skill in the art to accomplish the desired result without undue experimentation.

Photopolymerizable compositions materials herein can also exhibit a variety of desirable properties, non-cured, cured, and as post-cured articles. A photopolymerizable composition, when non-cured, has a viscosity profile consistent with the requirements and parameters of one or more additive manufacturing devices (e.g., 3D printing systems). In some instances, a photopolymerizable composition described herein when non-cured exhibits a dynamic viscosity of about <NUM>-<NUM>,<NUM> Pa·s, about <NUM>-<NUM> Pa·s, or about <NUM>-<NUM> Pa·s using a TA Instruments AR-G2 magnetic bearing rheometer using a <NUM> cone and plate measuring system at <NUM> degrees Celsius and at a shear rate of <NUM><NUM>/s, when measured according to ASTM D4287, as set forth in the Example Test Method below. In some cases, a photopolymerizable composition described herein when non-cured exhibits a dynamic viscosity of less than about <NUM> Pa·s, when measured according to modified ASTM D4287.

In a second aspect, the present disclosure provides an orthodontic article. The article comprises a reaction product of a photopolymerizable composition, the photopolymerizable composition comprising:.

The shape of the article is not limited, and may comprise a film or a shaped integral article. For instance, a film may readily be prepared by casting the photopolymerizable composition according to the first aspect, then subjecting the cast composition to actinic radiation to polymerize the photopolymerizable composition. In many embodiments, the article comprises a shaped integral article, in which more than one variation in dimension is provided by a single integral article. For example, the article can comprise one or more channels, one or more undercuts, one or more perforations, or combinations thereof. Such features are typically not possible to provide in an integral article using conventional molding methods. In select embodiments, the article comprises an orthodontic article. Orthodontic articles are described in further detail below.

In a third aspect, the present disclosure provides a method of making an orthodontic article. The method comprises:.

In many embodiments, the photopolymerizable composition is cured using actinic radiation comprising UV radiation, e-beam radiation, visible radiation, or a combination thereof. Moreover, the method optionally further comprises postcuring the article using actinic radiation or heat.

In additive manufacturing methods, the method further comprises (iv) repeating steps (i) and (ii) to form multiple layers and create the article comprising a three dimensional structure prior to step (iii). In certain embodiments, the method comprises vat polymerization of the photopolymerizable composition. When vat polymerization is employed, the radiation may be directed through a wall of a container (e.g., a vat) holding the photopolymerizable composition, such as a side wall or a bottom wall.

A photopolymerizable composition described herein in a cured state, in some embodiments, can exhibit one or more desired properties. A photopolymerizable composition 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 cured article is at least about <NUM>% polymerized or crosslinked or at least about <NUM>% polymerized or crosslinked. In some cases, a cured photopolymerizable composition is at least about <NUM>%, at least about <NUM>%, at least about <NUM>%, or at least about <NUM>% polymerized or crosslinked. A cured photopolymerizable composition can also be between about <NUM>% and about <NUM>% polymerized or crosslinked.

The conformability and durability of a cured article made from the photopolymerizable compositions of the present disclosure can be determined in part by standard tensile, modulus, and/or elongation testing. The photopolymerizable compositions can typically be characterized by at least one of the following parameters after hardening. Advantageously, the elongation at break is typically <NUM>% or greater, <NUM>% or greater, <NUM>% or greater, <NUM>% or greater, <NUM>% or greater, <NUM>% or greater, <NUM>% or greater, <NUM>% or greater, <NUM>% or greater, or <NUM>% or greater; and <NUM>% or less, <NUM>% or less, <NUM>% or less, <NUM>% or less, or <NUM>% or less. Stated another way, the elongation at break of the cured article can range from <NUM>% to <NUM>%. In some embodiments, the elongation at break is at least <NUM>% and no greater than <NUM>%. The ultimate tensile strength is typically <NUM> MegaPascals (MPa) or greater, <NUM> MPa or greater, <NUM> MPa or greater, or <NUM> MPa or greater, and is typically <NUM> MPa or less, each as determined according to ASTM D638-<NUM>. While the urethane component has the greatest effect on the elongation at break of an article, other components of the photopolymerizable composition also impact the elongation at break, e.g., the length of a linear chain or branch of a reactive diluent tends to be positively correlated to the elongation at break of the final article. The tensile modulus is typically <NUM> MPa or greater, as determined according to ASTM D638-<NUM>. Such elongation properties can be measured, for example, by the methods outlined in ASTM D638-<NUM>, using test specimen Type V. The mechanical properties above are particularly well suited for articles that require resiliency and flexibility, along with adequate wear strength and low hygroscopicity.

Photopolymerizable compositions described herein can be mixed by known techniques. In some embodiments, for instance, a method for the preparation of a photopolymerizable composition described herein comprises the steps of mixing all or substantially all of the components of the photopolymerizable composition, heating the mixture, and optionally filtering the heated mixture. Softening the mixture, in some embodiments, is carried out at a temperature of about <NUM> or in a range from about <NUM> to about <NUM>. In some embodiments, a photopolymerizable composition described herein is produced by placing all or substantially all components of the composition in a reaction vessel and heating the resulting mixture to a temperature ranging from about <NUM> to about <NUM> with stirring. The heating and stirring are continued until the mixture attains a substantially homogenized state.

Once prepared as set forth above, the photopolymerizable compositions of the present disclosure may be used in myriad additive manufacturing processes to create a variety of articles, including casting a film as noted above. A generalized method <NUM> for creating three-dimensional articles is illustrated in <FIG>. Each step in the method will be discussed in greater detail below. First, in Step <NUM> the desired photopolymerizable composition (e.g., comprising at least one urethane component, at least one reactive diluent, and a photoinitiator) is provided and 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 composition according to a set of computerized design instructions in Step <NUM>. In Step <NUM>, Step <NUM> and/or Step <NUM> is repeated to form multiple layers to create the article comprising a three dimensional structure (e.g., an orthodontic aligner). Optionally uncured photopolymerizable composition is removed from the article in Step <NUM>, and further optionally, the article is subjected to additional curing to polymerize remaining uncured photopolymerizable components in the article in Step <NUM>.

Methods of printing a three dimensional article or object described herein can include forming the article from a plurality of layers of a photopolymerizable composition described herein in a layer-by-layer manner. Further, the layers of a build material composition can be deposited according to an image of the three dimensional article in a computer readable format. In some or all embodiments, the photopolymerizable composition is deposited according to preselected computer aided design (CAD) parameters.

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. 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 compositions 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.

It is entirely possible to form a 3D article from a photopolymerizable composition described herein using vat polymerization (e.g., stereolithography). For example, in some cases, a method of printing a 3D article comprises retaining a photopolymerizable composition described herein in a fluid state in a container and selectively applying energy to the photopolymerizable composition in the container to solidify at least a portion of a fluid layer of the photopolymerizable composition, thereby forming a hardened layer that defines a cross-section of the 3D article. Additionally, a method described herein can further comprise raising or lowering the hardened layer of photopolymerizable composition to provide a new or second fluid layer of unhardened photopolymerizable composition at the surface of the fluid in the container, followed by again selectively applying energy to the photopolymerizable composition in the container to solidify at least a portion of the new or second fluid layer of the photopolymerizable composition to form a second solidified layer that defines a second cross-section of the 3D article. Further, the first and second 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, or e-beam radiation, having a sufficient energy to cure the photopolymerizable composition. A method described herein can also comprise planarizing a new layer of fluid photopolymerizable composition provided by raising or lowering an elevator platform. Such planarization can be carried out, in some cases, by utilizing a wiper or roller or a recoater bead. Planarization corrects the thickness of one or more layers prior to curing the material 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.

It is further to be understood that the foregoing process can be repeated a selected number of times to provide the 3D article. For example, in some cases, this process can be repeated "n" number of times. Further, 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. Suitable stereolithography printers include the Viper Pro SLA, available from 3D Systems, Rock Hill, SC and the Asiga Pico Plus39, available from Asiga USA, Anaheim Hills, CA.

<FIG> shows an exemplary stereolithography apparatus ("SLA") that may be used with the photopolymerizable compositions and methods described herein. In general, the SLA <NUM> may include a laser <NUM>, optics <NUM>, a steering lens <NUM>, an elevator <NUM>, a platform <NUM>, and a straight edge <NUM>, within a vat <NUM> filled with the photopolymerizable composition. In operation, the laser <NUM> is steered across a surface of the photopolymerizable composition to cure a cross-section of the photopolymerizable composition, after which the elevator <NUM> slightly lowers the platform <NUM> and another cross section is cured. The straight edge <NUM> may sweep the surface of the cured composition between layers to smooth and normalize the surface prior to addition of a new layer. In other embodiments, the vat <NUM> may be slowly filled with liquid resin while an article is drawn, layer by layer, onto the top surface of the photopolymerizable composition.

A related technology, vat polymerization with Digital Light Processing ("DLP"), also employs a container of curable polymer (e.g., photopolymerizable composition). However, in a DLP based system, a two-dimensional cross section is projected onto the curable material to cure the desired section of an entire plane transverse to the projected beam at one time. All such curable polymer systems as may be adapted to use with the photopolymerizable compositions described herein are intended to fall within the scope of the term "vat polymerization system" as used herein. In certain embodiments, an apparatus adapted to be used in a continuous mode may be employed, such as an apparatus commercially available from Carbon 3D, Inc. (Redwood City, CA), for instance as described in <CIT> and <CIT>).

Referring to <FIG>, a general schematic is provided of another SLA apparatus that may be used with photopolymerizable compositions and methods described herein. In general, the apparatus <NUM> may include a laser <NUM>, optics <NUM>, a steering lens <NUM>, an elevator <NUM>, and a platform <NUM>, within a vat <NUM> filled with the photopolymerizable composition <NUM>. In operation, the laser <NUM> is steered through a wall <NUM> (e.g., the floor) of the vat <NUM> and into the photopolymerizable composition to cure a cross-section of the photopolymerizable composition <NUM> to form an article <NUM>, after which the elevator <NUM> slightly raises the platform <NUM> and another cross section is cured.

More generally, the photopolymerizable composition is typically cured using actinic radiation, such as UV radiation, e-beam radiation, visible radiation, or any combination thereof. The skilled practitioner can select a suitable radiation source and range of wavelengths for a particular application without undue experimentation.

After the 3D article has been formed, it is typically removed from the additive manufacturing apparatus and rinsed, (e.g., an ultrasonic, or bubbling, or spray rinse in a solvent, which would dissolve a portion of the uncured photopolymerizable composition but not the cured, solid state article (e.g., green body). 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 optional steps of method <NUM>.

It is expected in certain embodiments of the present disclosure that the formed article obtained in Step <NUM> will shrink (i.e., reduce in volume) such that the dimensions of the article after (optional) Step <NUM> will be smaller than expected. For example, a cured article may shrink less than <NUM>% in volume, less than <NUM>%, less than <NUM>%, less than <NUM>%, or even less than <NUM>% in volume, which is contrast to other compositions that provide articles that shrink about <NUM>-<NUM>% in volume upon optional postcuring. The amount of volume percent shrinkage will not typically result in a significant distortion in the shape of the final object. It is particularly contemplated, therefore, that dimensions in the digital representation of the eventual cured article may be scaled according to a global scale factor to compensate for this shrinkage. For example, in some embodiments, at least a portion of the digital article representation can be at least <NUM>% of the desired size of the printed appliance, in some embodiments at least <NUM>%, in some embodiments at least <NUM>%, in some embodiments, at least <NUM>%, and in some embodiments, at least <NUM>%.

A global scale factor may be calculated for any given photopolymerizable composition formulation by creating a calibration part according to Steps <NUM> and <NUM> above. The dimensions of the calibration article can be measured prior to postcuring.

In general, the three-dimensional article formed by initial additive manufacturing in Step <NUM>, as discussed above, is not fully cured, by which is meant that not all of the photopolymerizable material in the composition has polymerized even after rinsing. Some uncured photopolymerizable material is typically removed from the surface of the printed article during a cleaning process (e.g., optional Step <NUM>). The article surface, as well as the bulk article itself, typically still retains uncured photopolymerizable material, suggesting further cure. Removing residual uncured photopolymerizable composition is particularly useful when the article is going to subsequently be postcured, to minimize uncured residual photopolymerizable composition from undesirably curing directly onto the article.

Further curing can be accomplished by further irradiating with actinic radiation, heating, or both. 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 <NUM> to over <NUM> minutes. Heating is generally carried out at a temperature in the range of about <NUM>-<NUM>, for a time ranging from about <NUM> to over <NUM> 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 postcure process of Step <NUM>. In general, postcuring improves the mechanical properties and stability of the three-dimensional article relative to the same three-dimensional article that is not postcured.

The following describes general methods for creating a clear tray aligner as printed appliance <NUM>. However, other dental and orthodontic articles can be created using similar techniques and the photopolymerizable compositions of the present disclosure. Representative examples include, but are not limited to, the removable appliances having occlusal windows described in International Application Publication No. <CIT>), the removable appliances with a palatal plate described in <CIT>); and the resilient polymeric arch members described in International Application Nos. <CIT> and <CIT>); as well as <CIT>). Moreover, the photopolymerizable compositions can be used in the creation of indirect bonding trays, such as those described in International Publication No. <CIT>) and <CIT>) and other dental articles, including but not limited to crowns, bridges, veneers, inlays, onlays, fillings, and prostheses (e.g., partial or full dentures). Other orthodontic appliances and devices include, but not limited to, orthodontic brackets, buccal tubes, lingual retainers, orthodontic bands, class II and class III correctors, sleep apnea devices, bite openers, buttons, cleats, and other attachment devices.

Alternatively, the photopolymerizable compositions can be used in other industries, such as aerospace, animation and entertainment, architecture and art, automotive, consumer goods and packaging, education, electronics, hearing aids, sporting goods, jewelry, medical, manufacturing, etc..

One particularly interesting implementation of an article is generally depicted in <FIG>. The additive manufactured article <NUM> is a clear tray aligner and is removably positionable over some or all of a patient's teeth. In some embodiments, the appliance <NUM> is one of a plurality of incremental adjustment appliances. The appliance <NUM> may comprise a shell having an inner cavity. The inner cavity is shaped to receive and resiliently reposition teeth from one tooth arrangement to a successive tooth arrangement. The inner cavity may include a plurality of receptacles, each of which is adapted to connect to and receive a respective tooth of the patient's dental arch. The receptacles are spaced apart from each other along the length of the cavity, although adjoining regions of adjacent receptacles can be in communication with each other. In some embodiments, the shell fits over all teeth present in the upper jaw or lower jaw. Typically, only certain one(s) of the teeth will be repositioned while others of the teeth will provide a base or anchor region for holding the dental appliance in place as it applies the resilient repositioning force against the tooth or teeth to be treated.

In order to facilitate positioning of the teeth of the patient, at least one of receptacles may be misaligned as compared to the corresponding tooth of the patient. In this manner, the appliance <NUM> may be configured to apply rotational and/or translational forces to the corresponding tooth of the patient when the appliance <NUM> is worn by the patient. In some particular examples, the appliance <NUM> may be configured to provide only compressive or linear forces. In the same or different examples, the appliance <NUM> may be configured to apply translational forces to one or more of the teeth within receptacles.

In some embodiments, the shell of the appliance <NUM> fits over some or all anterior teeth present in an upper jaw or lower jaw. Typically, only certain one(s) of the teeth will be repositioned while others of the teeth will provide a base or anchor region for holding the appliance in place as it applies the resilient repositioning force against the tooth or teeth to be repositioned. An appliance <NUM> can accordingly be designed such that any receptacle is shaped to facilitate retention of the tooth in a particular position in order to maintain the current position of the tooth.

A method <NUM> of creating an orthodontic appliance using the photopolymerizable compositions of the present disclosure can include general steps as outlined in <FIG>. Individual aspects of the process are discussed in further detail below. The process includes generating a treatment plan for repositioning a patient's teeth. Briefly, a treatment plan can include obtaining data representing an initial arrangement of the patient's teeth (Step <NUM>), which typically includes obtaining an impression or scan of the patient's teeth prior to the onset of treatment. The treatment plan will also include identifying a final or target arrangement of the patient's anterior and posterior teeth as desired (Step <NUM>), as well as a plurality of planned successive or intermediary tooth arrangements for moving at least the anterior teeth along a treatment path from the initial arrangement toward the selected final or target arrangement (Step <NUM>). One or more appliances can be virtually designed based on the treatment plan (Step <NUM>), and image data representing the appliance designs can exported in STL format, or in any other suitable computer processable format, to an additive manufacturing device (e.g., a 3D printer system) (Step <NUM>). An appliance can be manufactured using a photopolymerizable composition of the present disclosure retained in the additive manufacturing device (Step <NUM>).

In some embodiments, a (e.g., non-transitory) machine-readable medium is employed in additive manufacturing of articles according to at least certain aspects of the present disclosure. Data is typically stored on the machine-readable medium. The data represents a three-dimensional model of an article, which can be accessed by at least one computer processor interfacing with additive manufacturing equipment (e.g., a 3D printer, a manufacturing device, etc.). The data is used to cause the additive manufacturing equipment to create an article comprising a reaction product of a photopolymerizable composition, the photopolymerizable composition comprising: (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component; (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent; (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator; and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition. In certain embodiments, the article is an orthodontic article. Preferably, the article has an elongation at break of <NUM>% or greater.

Data representing an article may be generated using computer modeling such as computer aided design (CAD) data. Image data representing the (e.g., polymeric) article 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. 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 <CIT>). 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). In embodiments wherein the article is an orthodontic article, scanning techniques may include, for example, scanning a patient's mouth to customize an orthodontic article for the patient.

Often, machine-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 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. Referring to <FIG>, a computing device <NUM> often includes an internal processor <NUM>, a display <NUM> (e.g., a monitor), and one or more input devices such as a keyboard <NUM> and a mouse <NUM>. In <FIG>, an aligner <NUM> is shown on the display <NUM>.

Referring to <FIG>, in certain embodiments, the present disclosure provides a system <NUM>. The system <NUM> comprises a display <NUM> that displays a 3D model <NUM> of an article (e.g., an aligner <NUM> as shown on the display <NUM> of <FIG>); and one or more processors <NUM> that, in response to the 3D model <NUM> selected by a user, cause a 3D printer / additive manufacturing device <NUM> to create a physical object of the article <NUM>. Often, an input device <NUM> (e.g., keyboard and/or mouse) is employed with the display <NUM> and the at least one processor <NUM>, particularly for the user to select the 3D model <NUM>. The article <NUM> comprises a reaction product of a photopolymerizable composition, the photopolymerizable composition comprising: (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component; (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent; (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator; and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition.

Referring to <FIG>, a processor <NUM> (or more than one processor) is in communication with each of a machine-readable medium <NUM> (e.g., a non-transitory medium), a 3D printer / additive manufacturing device <NUM>, and optionally a display <NUM> for viewing by a user. The 3D printer / additive manufacturing device <NUM> is configured to make one or more articles <NUM> based on instructions from the processor <NUM> providing data representing a 3D model of the article <NUM> (e.g., an aligner <NUM> as shown on the display <NUM> of <FIG>) from the machine-readable medium <NUM>.

Referring to <FIG>, for example and without limitation, an additive manufacturing method comprises retrieving <NUM>, from a (e.g., non-transitory) machine-readable medium, data representing a 3D model of an article according to at least one embodiment of the present disclosure. The method further includes executing <NUM>, by one or more processors, an additive manufacturing application interfacing with a manufacturing device using the data; and generating <NUM>, by the manufacturing device, a physical object of the article. The additive manufacturing equipment can selectively cure a photopolymerizable composition to form an article. The article comprises a reaction product of a photopolymerizable composition, the photopolymerizable composition comprising: (a) <NUM> to <NUM> wt. %, inclusive, of at least one urethane component; (b) <NUM> to <NUM> wt. %, inclusive, of at least one reactive diluent; (c) <NUM> to <NUM> wt. %, inclusive, of a photoinitiator; and (d) an optional inhibitor in an amount of <NUM> to <NUM> wt. %, inclusive, if present; based on the total weight of the photopolymerizable composition. One or more various optional post-processing steps <NUM> may be undertaken. Typically, remaining unpolymerized photopolymerizable component may be cured. In certain embodiments, the article comprises an orthodontic article. Additionally, referring to <FIG>, a method of making an article comprises receiving <NUM>, by a manufacturing device having one or more processors, a digital object comprising data specifying a plurality of layers of an article; and generating <NUM>, with the manufacturing device by an additive manufacturing process, the article based on the digital object. Again, the article may undergo one or more steps of post-processing <NUM>.

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.

The materials used in the following examples are summarized in Table <NUM>.

Unless otherwise noted, all printed Examples were printed on an Asiga PicoPlus39, a vat polymerization 3D printer available from Asiga USA, Anaheim Hills, CA.

Resins were prepared according to the formulations listed in Table <NUM> below, by roller mixing the components overnight to ensure thorough mixing.

Absolute (e.g., dynamic) viscosities of the example resins were measured using a TA Instruments AR-G2 magnetic bearing rheometer using a <NUM> cone and plate measuring system at <NUM> at a shear rate of <NUM><NUM>/s. Two replicates were measured and the average value was reported as the viscosity, in Pa·s, in Table <NUM> below.

The Example <NUM> (E-<NUM>) formulation shown in Table <NUM> was mixed in a glass jar. The E-<NUM> mixture was placed on a rolling mixer to make a homogenous mixture. The mixture was degassed and speed mixed in THINKY planetary mixer (Thinky Corporation, Tokyo, Japan), at <NUM> rpm for <NUM> seconds under vacuum. The mixture was then poured in a silicone dogbone mold (Type V mold, ASTM D638-<NUM>). The filled mold was placed between two glass plates and cured in a broad spectrum UV chamber (Dymax Light Curing Systems Model <NUM> Flood) for <NUM> minutes. The sample was demolded and cured for another <NUM> minutes in the chamber, according to ASTM D638-<NUM>. These dogbones were tested on an Insight MTS with <NUM> kN load cell at the rate of <NUM>/minute. Five replicate samples were tested, and the average and standard deviation are reported. The tensile strength, tensile modulus and elongation at break of the samples were determined according to ASTM D638-<NUM> and shown in Table <NUM> below.

Subsequent examples, E-<NUM>-E-<NUM> and CE-<NUM>-CE-<NUM>, were made by the same method (the formulations for these examples are summarized in Table <NUM> above) and tested. The test results of the cast samples are summarized in Table <NUM> below.

The formulations of E-<NUM> and E-<NUM> resins were photopolymerized on the Asiga Pico <NUM> printer with a LED light source of <NUM> and ~<NUM> mW/cm<NUM> of power. Tensile test bars of Type V according to ASTM D638-<NUM> were manufactured. The resin bath of the printer was heated to <NUM>-<NUM> before photopolymerization to reduce the viscosity to be able to manufacture the tensile test bars. The following settings were used: Slice thickness = <NUM>, Burn-In Layers = <NUM>, Separation Velocity = <NUM>/s, Slides per Layer = <NUM>, Burn-In Exposure Time = <NUM>, Normal Exposure Time = <NUM>. The test bars were then cleaned in isopropanol to remove unreacted resin. The test bars were then post-cured under fusion lamps for <NUM> minutes on each side. The post-cured dogbones were tested on an Insight MTS with <NUM> kN load cell at the rate of <NUM>/minute. Five replicate samples were tested, and the average and standard deviation are reported. The tensile strength of the samples was determined according to ASTM D638-<NUM> and shown in Table <NUM> below.

The formulation of E-<NUM> was photopolymerized on the Asiga Pico <NUM> HD printer with a LED light source of <NUM> and ~<NUM> mW/cm<NUM> of power. An STL file of the aligner was loaded into the software and support structures were generated. The resin bath of the printer was heated to <NUM>-<NUM> before photopolymerization to reduce the viscosity to be able to manufacture the article. The following settings were used: Slice thickness = <NUM>, Burn-In Layers = <NUM>, Separation Velocity = <NUM>/s, Slides per Layer = <NUM>, Burn-In Exposure Time = <NUM>, Normal Exposure Time = <NUM>. The photopolymerized aligners were then cleaned in isopropanol to remove unreacted resin and then post-cured under fusion lamps for <NUM> minutes on each side. The photopolymerized aligners fit the models, showing precision of the additive manufacture part. The aligners also had acceptable strength and flexibility.

Claim 1:
A photopolymerizable composition for an orthodontic article comprising:
(a) <NUM> to <NUM> wt.%, inclusive, of at least one urethane component;
(b) <NUM> to <NUM> wt.%, inclusive, of at least one reactive diluent, wherein the at least one reactive diluent has a molecular weight of <NUM> grams per mole or less, is free of any urethane functional groups, and comprises a methacrylate;
(c) <NUM> to <NUM> wt.%, inclusive, of a photoinitiator; and
(d) an optional inhibitor in an amount of <NUM> to <NUM> wt.%, inclusive, if present; based on the total weight of the photopolymerizable composition,
wherein the photopolymerizable composition has a viscosity at a temperature of <NUM> degrees Celsius of <NUM> Pa·s or less, as determined using a magnetic bearing rheometer using a <NUM> cone and plate measuring system at a shear rate of <NUM><NUM>/s, wherein the photopolymerizable composition is free of monofunctional components, and wherein a reaction product of the photopolymerizable composition exhibits an elongation at break of <NUM>% or greater as determined according to ASTM D638-<NUM> using test specimen Type V; and
wherein the at least one urethane comprises a high Mn urethane component and a low Mn urethane component, wherein a ratio of the high Mn urethane component to the low Mn urethane component ranges from <NUM>:<NUM> high Mn urethane component to low Mn urethane component to <NUM>:<NUM> high Mn urethane component to low Mn urethane component, wherein the high Mn urethane component has a number average molecular weight of <NUM>,<NUM> grams per mole (g/mol) or greater, with the proviso that all branches off the backbone of the compound, if present, have a Mn of no more than <NUM>/mol, and wherein the low Mn urethane component has either <NUM>) a number average molecular weight of <NUM>/mol or greater and up to but not including <NUM>,<NUM>/mol, or <NUM>) a number average molecular weight of <NUM>/mol or greater and <NUM>,<NUM>/mol or less, with the proviso that a number average molecular weight of any one or more linear portions between two reactive groups and/or branches is up to but not including <NUM>,<NUM>/mol, wherein number average molecular weight is as measured by matrix assisted laser deposition ionization mass spectrometry.