Radiation-curing composition for production of dental components

Abstract

To provide a radiation-curing composition, the initiator system of which has fewer problems from an environmental and / or health standpoint.SOLUTION: Provided is a radiation-curing composition for the manufacture of dental components using the DLP process or SLA process, comprising, based on the total mass of the radiation-curing composition, i) one or more radically polymerizable monomers in a combined mass fraction of 60% or more, ii) one or more hexaarylbiimidazole compounds in a combined mass fraction in the range of 0.1 to 5%, and iii) one or more mercaptotetrazole compounds in a combined mass fraction in the range of 0.1 to 5%, wherein the combined mass fraction of fillers in the radiation-curing composition is less than 30%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to radiation-curable compositions for the production of dental components in the DLP or SLA process, dental components that can be produced by radiation-induced polymerization of such radiation-curable compositions, and the use of specific initiator systems in radiation-curable compositions to improve the mechanical properties of dental components that can be produced from radiation-curable compositions in the DLP or SLA process. [Background technology]

[0002] The technological advances and ongoing digitalization that have transformed the industrial landscape over the past decade have also had an impact on the field of dental technology, fundamentally changing the daily work of dentists and dental technicians. For decades, many types of tooth replacements, such as crowns, bridges, partial dentures, full dentures or inlays, as well as orthodontic appliances, such as splints, were mainly produced manually by dental technicians.

[0003] This traditional process is now increasingly being supported or even replaced by the use of computer-aided production and manufacturing processes, a technology sometimes referred to in the profession as digital prosthetics.

[0004] Here, so-called CAD / CAM methods are often an essential component of computer-aided production. The term CAD stands for "computer-aided design" and broadly refers to the creation of digital components that can be modified directly on the computer by the user as needed. The term CAM stands for "computer-aided manufacturing," i.e., the conversion of components created with CAD into code that can be used to control, for example, a milling machine or a 3D printer. In the field of dental technology, the creation of CAD components increasingly relies on the use of so-called intraoral scanners, which can transmit precise images of the patient's mouth to a computer without contact.

[0005] Of particular importance to dental technology are additive manufacturing methods, which produce products from formless materials without special tools and based on computer data sets generated by CAD. These 3D printing methods, sometimes called "rapid prototyping" methods based on the English expression, replace or complement many work steps in the production of dental components in the field of dental technology today.

[0006] So-called stereolithography (SLA) and digital light processing (DLP) play an important role in dental 3D printing. In these methods, a radiation-curable composition is applied and cured layer by layer by spatially resolved, targeted irradiation at the desired location. This allows the resulting components to, for example, sink into or rise from the composition step by step, so that after each increment, only a thin film of radiation-curable composition remains above the last layer formed. This thin film roughly corresponds to the thickness of the next polymerized layer. While SLA and DLP methods are similar in their basic principles, they differ significantly in terms of equipment design: in SLA, for example, a laser is used to scan the structure to be produced one after another, while in DLP, the entire surface is simultaneously exposed by a suitable projection technology. The principles of SLA and DLP are known from the prior art and are disclosed, for example, in US Pat. No. 4,575,330 A or WO 2014,078,537 A1. The use of additive manufacturing methods in dental technology is known, for example, from documents US 979554 B2, WO 2023126943 A2, DE 102016107935 A1 and DE 1020122011371 A1 and is also described in EP 3020361 B1.

[0007] Despite the increasing use of corresponding radiation-curable compositions, there is a continuing interest in the art in optimizing the materials used, in particular the processing characteristics of the radiation-curable compositions, while at the same time improving the properties of the materials that can be produced from the radiation-curable compositions by curing, in particular their mechanical properties.

[0008] When designing a radiation-curable composition for use in 3D printing, the initiator system always plays a decisive role. The initiator used must not only ensure good mechanical properties of the polymer, but also achieve a favorable polymerization rate. In addition to the polymerization rate achievable with the initiator used, the depth of polymerization is also an important issue. It also matters what initial radiation dose is required to initiate the polymerization reaction and what average layer thickness can be achieved with a given radiation dose. In this case, the depth of polymerization is in part correlated with the wavelength of the electromagnetic radiation used for initiation. However, this wavelength also has an even more important influence on the 3D printing device used. The efficiency of a radiation-curable composition in 3D printing depends largely on how well the 3D printing device can provide the optimal wavelength of the initiator system.

[0009] In view of the trade-offs between the various requirements mentioned above, a number of advantageous initiator systems have been identified in the past.

[0010] Phosphine oxide-based so-called Norrish Type I initiators, such as phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L), are widely used due to their broad absorption spectra. However, compared to so-called Norrish Type II initiators, such as the equally well-established camphorquinone / amine system, their absorption maxima are mostly localized in the short-wavelength ultraviolet region, limiting their use in some 3D printers. A large cure depth is advantageous, especially during post-curing, and improves the mechanical properties of the printed material.

[0011] A further drawback to using Norrish Type I initiators is that, because they are one-component initiator systems, the polymerization reactivity of the printed material is not well controlled.

[0012] As environmental and / or health concerns grow, selecting a suitable initiator becomes increasingly difficult. Many of the initiator systems known from the prior art are currently being criticized from environmental and / or health perspectives, and their use has already been restricted in some countries or is likely to be restricted in the near future. Despite their excellent mechanical and reactivity properties and wide application, phosphine oxide initiators are suspected of having reproductively toxic effects on the human body. For example, TPO is already included in the European Chemicals Agency's (ECHA) list of "substances of very high concern" and is classified as a potential carcinogen, mutagen, and reproductive toxicant (CMR) (Class 2). This calls into question the general use of substances in this category in medical products. Summary of the Invention [Problem to be solved by the invention]

[0013] The main object of the present invention is to eliminate or at least mitigate the drawbacks of the prior art.

[0014] In particular, it was an object of the present invention to provide a radiation-curable composition, the initiator system of which is less problematic from an environmental and / or health point of view than the solutions known from the prior art, a desirable requirement being that the initiator system be as free as possible from any regulatory restrictions worldwide, in particular in connection with additive manufacturing processes for medical products.

[0015] In this regard, one important objective of the present invention was that the radiation-curable compositions provided have an advantageous polymerization rate, in particular with respect to the radiation dose required for initiation and with respect to the average layer thickness that can be achieved with a given radiation dose.

[0016] A further object of the present invention was to make it possible to convert the radiation-curable compositions provided into advantageous polymers having advantageous mechanical properties that are also suitable for high-performance applications in the dental field.

[0017] In this respect, it was an object of the present invention to make the radiation-curable compositions provided as comparable as possible with respect to the rate of polymerization and mechanical properties of the polymer to radiation-curable compositions known from the prior art that use well-established initiator systems, in particular Norrish type I initiator systems, in that these properties are at least at a comparable level, and preferably these properties are at least partially improved so that the contradictions that exist in this respect are better resolved.

[0018] One desirable requirement of the present invention is that the radiation curable compositions provided are particularly efficiently processable in modern 3D printers, i.e., capable of being efficiently cured at wavelengths of 385 nm or less, a desirable property being that the initiator systems used have a sufficiently wide excitation range so that they can also be cured in a wide range of existing 3D printers, particularly those operating at wavelengths of around 405 nm.

[0019] An additional object of the present invention was to provide dental components that can be produced from the radiation-curable compositions provided, which not only can be produced in a particularly time- and cost-efficient manner, but also have excellent mechanical properties and are considered to be advantageous from an environmental and health perspective.

[0020] A further object of the present invention was to further provide the use of a particular initiator system for improving the mechanical properties of dental components manufactured by 3D printing.

[0021] The inventors of the present invention have surprisingly found that the above-mentioned problems can be solved by using an initiator system that uses a hexaarylbiimidazole compound in combination with a mercaptotetrazole compound in radiation-curable compositions having a high proportion of radically polymerizable monomer and a relatively low proportion of filler, as defined in the claims.

[0022] Surprisingly, when the corresponding initiator systems are used in certain low-filler radiation-curable compositions, advantageous cure speeds have been found, particularly with respect to the initial radiation dose required, and advantageous mechanical properties of the resulting polymers have also been identified. In combination with other components of the radiation-curable composition, the use of the initiator systems makes it possible to obtain, overall, performance properties that are at least comparable to, and in some cases even improved upon, well-established initiator systems known from the prior art. Here, the combination of a hexaarylbiimidazole compound and a mercaptotetrazole compound is preferable from an environmental and health perspective to many initiator systems known from the prior art, making the identified initiator systems particularly advantageous for use in additive manufacturing of medical products.

[0023] Therefore, the above-mentioned problem is solved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention are set out in the dependent claims and in the following description.

[0024] The embodiments described below as preferred are combined in particularly preferred embodiments with features of other embodiments described as preferred. Thus, it is particularly preferred to combine two or more of the embodiments described below as particularly preferred. Also preferred are embodiments in which a feature described as somewhat preferred in one embodiment is combined with one or more additional features of other embodiments described as somewhat preferred. The preferred dental component and use features result from the features of the preferred radiation-curable compositions.

[0025] Hereinafter, when a specific amount or ratio of a certain element, such as a radically polymerizable monomer or filler, and a preferred configuration of the element are disclosed, the specific amount or ratio of the element that is preferably implemented is also disclosed. Furthermore, it is disclosed that at least a portion of the element can be preferably implemented in the corresponding specific total amount or total ratio of the element, and that the element that is preferably implemented within the specific total amount or total ratio can also be present in the specific amount or ratio.

[0026] Particularly preferred embodiments of the present invention are disclosed in the Examples. Against this background, particularly preferred embodiments of the present invention comprise two or more, preferably three or more, and most preferably four or more of the preferred features of the present invention disclosed below, which features are also realized in the Examples. [Means for solving the problem]

[0027] The present invention relates in particular to a radiation-curable composition for the production of dental components in the DLP or SLA process, which comprises, with respect to the total weight of the radiation-curable composition: i) one or more radically polymerizable monomers having a total mass fraction of 60% or more; ii) one or more hexaarylbiimidazole compounds having a total mass fraction in the range of 0.1 to 5%; iii) one or more mercaptotetrazole compounds having a total mass fraction in the range of 0.1 to 5%, The radiation curable composition relates to a radiation curable composition, wherein the total mass fraction of fillers in the radiation curable composition is less than 30%.

[0028] The radiation-curable compositions according to the invention are suitable and specified for producing dental components by 3D printing, i.e. DLP or SLA. Radiation-curable compositions for this purpose are as commonly known as the devices that can be used for DLP or SLA, and corresponding products and devices are commercially available from various suppliers, for example Kulzer.

[0029] The terms "DLP method" and "SLA method" refer to the aforementioned digital light processing and stereolithography methods, which are well known to those skilled in the art. The suitability of a radiation-curable composition for the production of dental components in such methods imposes functional requirements, particularly in that the viscosity of the material must be sufficiently low. This excludes many radiation-curable compositions used in other dental fields, particularly compositions with a high filler content, such as ceramic slurries. Regarding liquid properties, radiation-curable compositions according to the present invention are preferred that have a dynamic viscosity at 23°C in the range of 0.001 to 10 Pa·s, preferably 0.5 to 5 Pa·s, and particularly preferably 0.7 to 2.5 Pa·s. In the context of the present invention, the viscosity of uncured radiation-curable compositions is measured at 23°C using a flowmeter (Anton Paar Physica MCR301) (interchangeable plate I-PP-50 / SS smooth, measuring cone CP25-1.25 mm, 1°). The gap width is determined by the angle and diameter of the cone. Measurements are performed at a constant rotation speed and a shear rate of 100 (1 / s). A total of 10 measurement points are recorded. The duration of one measurement point is 6 seconds, and the interval time is 60 seconds.

[0030] However, the above-mentioned suitability does not exclude that the radiation-curable compositions according to the invention can also be used in other additive manufacturing processes, for example in the so-called "inkjet" technology. However, according to the inventors' assessment, radiation-curable compositions according to the invention are mainly used in DLP processes in later practice. Therefore, radiation-curable compositions according to the invention that are suitable for producing dental components in DLP processes are preferred.

[0031] Within the scope of the present invention, the components of the radiation-curable composition as defined are all referred to as "one or more" as understood by those skilled in the art, where the term "one or more" refers to the chemical nature of the corresponding compounds, as is commonly used in the art, and not to the quantity of the corresponding compounds.

[0032] When mass fractions are mentioned within the scope of the present invention, they are conventionally all mentioned as the total mass fraction of one or more components, thereby indicating that the mass fractions of the correspondingly formed components together satisfy the corresponding criteria.

[0033] Unless otherwise defined in a particular case, all mass fractions for components of the radiation-curable composition defined within the scope of the present invention relate to the total mass of the radiation-curable composition. Those skilled in the art will understand that mass fractions are defined in terms that add up to 100% of the total mass fractions of the radiation-curable composition, and therefore the upper limits of the defined components will be adjusted, if necessary, to add up to 100% together with the lower limits of other essential components.

[0034] Within the meaning of the present invention, the term "dental component" refers, in principle, to all components and three-dimensional structures primarily produced in dental technology as auxiliary, intermediate, or final products, i.e., regardless of the underlying dental indication. However, due to the advantageous mechanical properties of dental components that can be produced by curing radiation-curable compositions, the present invention is particularly suitable for producing dental components for permanent dental use, i.e., in the patient's oral cavity. Thus, examples include radiation-curable compositions according to the present invention, in which the dental component is selected from the group consisting of dental prostheses, dental models, gingival masks, bite splints, CAD-to-cast molds, impression trays, drill templates, temporary and permanent crowns, aligners, bridges, onlays, inlays, and veneers. However, radiation-curable compositions according to the present invention, in which the dental component is selected from the group consisting of dental prostheses, temporary and permanent crowns, aligners, bridges, onlays, inlays, and veneers, are preferred.

[0035] The term "radiation-curable" used above to characterize the present composition corresponds to a technical term commonly used in the industry. Alternatively, concepts such as "radiation-curable" or "radiation-crosslinkable" or similar terms are also used. This term is understood herein as the property of a composition that cures upon exposure to electromagnetic radiation, particularly electromagnetic radiation in the ultraviolet or visible light range, whereby polymerization of radically polymerizable monomers in the composition is induced by radiation using an initiator. The wavelength of the radiation used for this purpose is usually in the visible light range or in a wavelength range adjacent to the ultraviolet range, with wavelengths in the blue and ultraviolet ranges being particularly frequently used. As understood by those skilled in the art, radiation curability is achieved by combining the radically polymerizable monomers defined above with an initiator. In terms of the specific initiator, preferred radiation-curable compositions according to the present invention are configured to cure upon exposure to electromagnetic radiation in the wavelength range of 200 to 420 nm, preferably in the wavelength range of 250 to 415 nm, and particularly preferably in the wavelength range of 300 to 410 nm. In other words, a preferred radiation-curable composition according to the present invention is one in which the photoinitiator system comprising a hexaarylbiimidazole compound and a mercaptotetrazole compound is configured to initiate polymerization of the polymerizable monomer when the radiation-curable composition is irradiated with electromagnetic radiation in a wavelength range of 200 to 420 nm, preferably in a wavelength range of 250 to 415 nm, and particularly preferably in a wavelength range of 300 to 410 nm.

[0036] In addition to the initiator, which will be further described below, the radically polymerizable monomer used in accordance with the present invention forms an important component determining radiation curability. Radical polymerizable monomers are characterized by their ability to crosslink with each other in a chain reaction after initiation by a radical initiator, which is usually provided by one or more initiators in a radiation-curable composition. Based on fundamental principles, the present invention is not limited to a specific radically polymerizable monomer but is applicable to any radically polymerizable monomer, which typically has a terminal unsaturated double bond through which radical polymerization can occur. These monomers, which may be monofunctional or polyfunctional, are selected by those skilled in the art based primarily on the physicochemical and application properties required for the dental component to be produced. In the field of dental chemistry, (meth)acrylates in particular are of great importance as monomers, and the term (meth)acrylate, as understood by those skilled in the art, refers to both acrylates and methacrylates. These monomers, frequently used in the field of dental chemistry, are known to those skilled in the art and are disclosed, for example, in EP 3020361B1 or DE 3941629C1. In light of this background, one example of a radiation-curable composition according to the present invention is one in which one or more radically polymerizable monomers are selected from the group consisting of (meth)acrylic acid, (meth)acrylates, (meth)acrylamides, and other vinyl compounds, preferably selected from the group consisting of (meth)acrylic acid, (meth)acrylates, and (meth)acrylamides, and particularly preferably selected from the group consisting of (meth)acrylates. Here, a preferred radiation-curable composition according to the present invention is one in which one or more radically polymerizable monomers are selected from the group consisting of monofunctional (meth)acrylates and polyfunctional (meth)acrylates.

[0037] Examples of suitable monofunctional (meth)acrylates are, for example, selected from the group consisting of substituted and unsubstituted alkyl (meth)acrylates and substituted and unsubstituted cycloalkyl (meth)acrylates, and preferably selected from the group consisting of dicyclopentanyl methyl acrylate, tertiary butyl cyclohexyl (meth)acrylate, 2(2-ethoxyethoxy)ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, octyldecyl (meth)acrylate, isobornyl (meth)acrylate, isodecyl (meth)acrylate, and alkyl (meth)acrylates having up to 12 carbon atoms in the alkyl radical.

[0038] Examples of suitable polyfunctional (meth)acrylates include, for example, urethane dimethacrylate, BisGMA, triethylene glycol di(meth)acrylate (TEGD[M]A), tricyclodecane dimethanol di(meth)acrylate (TCDDMD[M]A), bisphenol A-ethoxylates (various chain lengths) (Bis-EMA), 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, ester diol di(meth)acrylate, trimethylolpropane tri(meth)acrylate (TMPT[M]A), tris(2-hydroxyethyl)isocyanurate-tri(meth)acrylate, di-pentaerythritol-penta(meth)acrylate), ethoxylated or propoxylated trimethylolpropane-tr(meth)acrylate, 2-propenoic acid, 1,1'-[((octahydro-4,7,methano-1H-indene-5,diyl)bis(methyleneiminocarbonyloxy-2,1-ethanediyl)] ester (TCD-di-HEA; CAS 861437-11-8), 2-propionic acid, 1,1'[(octahydro-4,7-methano-1H-indene-5-diyl)bis(methyleneoxycarbonylamino-2,1-ethanediyl)] ester (TCD-di-UEA; CAS 945656-78-0), decanediol-1,10-dimethacrylate, and urethane dimethacrylates, as well as other urethane (meth)acrylates and thiourethane (meth)acrylates as disclosed, for example, in WO 2022248546 A1.

[0039] According to the inventors' evaluations, it is possible to obtain particularly high-performance radiation-curable compositions, particularly by using or combining monofunctional and difunctional (meth)acrylates. Accordingly, radiation-curable compositions according to the present invention that contain at least one radically polymerizable monomer selected from the group consisting of monofunctional (meth)acrylates and / or at least one radically polymerizable monomer selected from the group consisting of polyfunctional (meth)acrylates, preferably difunctional (meth)acrylates, are preferred. In the inventors' experiments, particularly in combination with the initiator system used according to the present invention, particularly advantageous property profiles were obtained when both monofunctional and difunctional monomers were used as monomer components.

[0040] Regarding the selection of the monomer, radiation-curable compositions according to the present invention are particularly preferred which contain at least one radically polymerizable monomer selected from the group consisting of ethoxylated 2-bisphenol-A-dimethacrylate, tricyclodecane methanol acrylate, urethane dimethacrylate, and carboxy-functionalized polyester acrylate, preferably two or more, more preferably three or more, and particularly four or more different types of these radically polymerizable monomers.

[0041] With respect to the basic content of the monomer components, the radiation-curable composition according to the present invention preferably contains one or more radically polymerizable monomers in a total mass fraction of 65% or more, preferably 70% or more, more preferably 75% or more, and most preferably 85% or more. Additionally or alternatively, the radiation-curable composition according to the present invention preferably contains one or more radically polymerizable monomers in a total mass fraction in the range of 60 to 96%, preferably 70 to 93%, and more preferably 80 to 90%.

[0042] An essential aspect of the radiation-curable compositions of the present invention is that the total mass fraction of filler is selected to be relatively low, but the inventors believe that trends toward even lower filler contents are favorable. It is also conceivable, and in some applications preferable, to implement radiation-curable compositions of the present invention completely free of fillers. Therefore, radiation-curable compositions of the present invention in which the total mass fraction of fillers in the radiation-curable composition is 25% or less, preferably 20% or less, and particularly preferably 15% or less, are preferred.

[0043] Although it is conceivable, as mentioned above, that the radiation curable composition according to the invention may be implemented without a filler, the inventors consider it particularly preferable to intentionally add a filler to the radiation curable composition in order to achieve advantageous mechanical properties. iv) A radiation-curable composition further comprising one or more fillers in a total mass fraction ranging from 0.05 to 29% is preferred.

[0044] In their own experiments, the inventors have succeeded in identifying particularly suitable mass fractions of fillers used, i.e., mass fractions that, in combination with the initiator system used according to the invention, allow for advantageous polymerization rates combined with excellent mechanical properties. Therefore, radiation-curable compositions according to the invention that contain one or more fillers in a total mass fraction of less than 25%, preferably less than 20%, and more preferably less than 15% are preferred. Additionally or alternatively, radiation-curable compositions according to the invention that contain one or more fillers in a total mass fraction ranging from 0.1 to 25%, preferably from 0.5 to 22.5%, more preferably from 1 to 20%, particularly preferably from 2 to 17.5%, and most preferably from 5 to 15% are also preferred.

[0045] According to the inventors' evaluation, in principle, fillers frequently used in comparable dental products, such as dental glass, can be used in the practice of the present invention. However, the inventors' experiments have shown that particularly advantageous properties can be obtained using fillers consisting of silicon dioxide and zirconium dioxide, especially fillers also known as "precipitated silica." Therefore, radiation-curable compositions according to the present invention are preferred, in which one or more fillers are selected from the group consisting of oxide fillers, preferably selected from the group consisting of silicon dioxide and zirconium dioxide, more preferably selected from the group consisting of amorphous silicon dioxide, and in particular selected from the group consisting of precipitated amorphous silicon dioxide. Here, for substantially all embodiments, radiation-curable compositions according to the present invention are preferred, in which one or more fillers are selected from the group consisting of particulate fillers.

[0046] An essential aspect of the present invention is the interaction of two specific classes of compounds in the initiator system of the radiation-curable composition of the present invention: a hexaarylbiimidazole compound is combined with a mercaptotetrazole compound, which together function as photoinitiators or coinitiators and determine the radiation curability of the radiation-curable composition of the present invention.

[0047] Through extensive independent experiments, the present inventors have successfully identified preferred ranges for the content of the components of the initiator system used according to the present invention, which provide excellent results when used in DLP or SLA systems. During these studies, it was determined that using these two compounds in at least equal mass fractions is particularly advantageous, but that adding a larger amount of the mercaptotetrazole compound is preferable. Here, radiation-curable compositions according to the present invention are preferred, comprising one or more hexaarylbiimidazole compounds in a total mass fraction ranging from 0.15 to 4.5%, preferably from 0.2 to 4.0%, more preferably from 0.25 to 3.5%, and most preferably from 0.3 to 3.0%. Additionally or alternatively, radiation-curable compositions according to the present invention are also preferred, comprising one or more mercaptotetrazole compounds in a total mass fraction ranging from 0.15 to 4.5%, preferably from 0.2 to 4.0%, more preferably from 0.25 to 3.5%, and particularly preferably from 0.3 to 3.0%. Additionally or alternatively, the radiation-curable composition according to the present invention is preferably one in which the quotient obtained by dividing the total molar fraction of the one or more hexaarylbiimidazole compounds by the total molar fraction of the one or more mercaptotetrazole compounds is 1.0 or less, preferably 0.8 or less, more preferably 0.6 or less, and particularly preferably 0.4 or less.

[0048] Hexaarylbiimidazole compounds and their use as photoinitiators are known in the prior art and are disclosed, for example, in US 2017 / 0266081 A1. Experiments by the present inventors have shown that substituted hexaarylbiimidazole compounds provide particularly high-performance systems. Therefore, radiation-curable compositions according to the present invention are preferred, in which one or more hexaarylbiimidazole compounds are selected from the group consisting of hexaarylbiimidazole compounds having one or more, preferably two or more, more preferably three or more, and most preferably four or more, aryl groups substituted with substituents. Particularly preferred are radiation-curable compositions according to the present invention, in which the substituents are selected from the group consisting of halogen atoms and alkoxy groups, preferably chlorine atoms and methoxy groups.

[0049] The present inventors have now achieved particularly favorable results in terms of overall performance properties, especially by using two or more different hexaarylbiimidazole compounds in combination, which in particular allows the polymerization properties of the radiation-curable composition according to the invention to be specifically adapted to the requirements of each application. Therefore, radiation-curable compositions according to the invention that comprise two or more different hexaarylbiimidazole compounds are preferred.

[0050] In principle, hexaarylbiimidazole compounds can be designed differently with regard to the connection of the imidazole rings. In this regard, the inventors have obtained particularly good results with compounds in which the connection is via an N-N or C-N bond. Overall, a C-N bond has shown particularly advantageous results. Preferred for some applications is a radiation-curable composition according to the invention, in which one or more hexaarylbiimidazole compounds are selected from the group consisting of hexaaryl-1,1'-biimidazole compounds and / or one or more hexaarylbiimidazole compounds are selected from the group consisting of hexaarylbiimidazole compounds in which the imidazole rings are connected via a C-C bond. However, preferred for many purposes are radiation-curable compositions according to the present invention, wherein the one or more hexaarylbiimidazole compounds are selected from the group consisting of hexaaryl-1,2'-biimidazole compounds and / or the one or more hexaarylbiimidazole compounds are selected from the group consisting of hexaarylbiimidazole compounds in which the imidazole rings are linked via C-N bonds.

[0051] In the course of the experiments carried out, the inventors were able to identify particularly suitable hexaarylbiimidazole compounds and, among these suitable compounds, three particularly high performance representatives of this compound class. First, the radiation-curable composition according to the present invention, wherein the one or more hexaarylbiimidazole compounds are 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole (o-Cl-HABI), 2,2'-bis(2,4-dichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole (2,4-Cl-HABI), 2,2'-bis(3-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole (3-Cl-HABI), 2,2'-bis(4-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole (4-Cl-HABI), 2,2'-bis(phenyl

[0033] Preferred are radiation-curable compositions selected from the group consisting of 2,2'-bis(phenyl)-4,4'-biphenyl-5,5'-bi(2-chlorophenyl)-1,2'-biimidazole, 2,2'-bis(phenyl)-4,4',5,5'-tetra(2-chlorophenyl)-1,2'-biimidazole, 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,2'-biimidazole, and 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,1'-biimidazole. Additionally or alternatively, radiation-curable compositions according to the present invention, wherein the one or more hexaarylbiimidazole compounds are selected from the group consisting of 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,2'-biimidazole, and 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,1'-biimidazole, are also particularly preferred.Additionally or alternatively, the radiation-curable composition according to the present invention may comprise, as the hexaarylbiimidazole compound, 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole and / or 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,2'-biimidazole and / or 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,2'-biimidazole. Particularly preferred are radiation-curable compositions comprising 2,2'-bis(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,1'-biimidazole, preferably 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, and 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,2'-biimidazole.

[0052] In the prior art according to US 2017 / 0266081 A1, hexaarylbiimidazole compounds were used in combination with coinitiators that were heteroaromatic compounds containing thiol groups, in particular benzothiazole- and triazole-based compounds, namely MMT (3-mercapto-4-methyl-4H-1,2,4-triazole) and MBT (2-mercaptobenzothiazole).

[0053] Within the scope of the present invention, the inventors have found that the above-mentioned problems are advantageously solved by using mercaptotetrazole compounds instead of coinitiators known from the prior art, whereas corresponding mercaptotetrazole compounds from other fields of application are generally known and commercially available from various manufacturers, for example Merck.

[0054] The present inventors have found, through their own development process, that the use of a substituted mercaptotetrazole compound, in particular, provides an advantageous initiator system. Therefore, preferred radiation-curable compositions according to the present invention are those in which one or more mercaptotetrazole compounds are selected from the group consisting of mercaptotetrazole compounds having at least one substituent on the tetrazole ring, preferably mercaptotetrazole compounds having exactly one substituent on the tetrazole ring, and preferably mercaptotetrazole compounds having exactly one substituent adjacent to the thiol group. Particularly preferred are radiation-curable compositions according to the present invention in which the substituent is selected from the group consisting of substituents having a +M effect and / or the substituent is selected from the group consisting of unsubstituted or substituted aryl groups, preferably substituted aryl groups having one substituent in the para position relative to the tetrazole ring, and the substituent is preferably selected from the group consisting of hydroxy groups and alkoxy groups, preferably selected from the group consisting of hydroxy groups and alkoxy groups having 1 to 3 carbon atoms, and preferably selected from the group consisting of hydroxy groups and alkoxy groups having 1 or 2 carbon atoms.

[0055] Among the mercaptotetrazole compounds, the inventors have been able to identify compounds that have proven to be particularly advantageous in combination with the hexaarylbiimidazole compounds used according to the invention, especially in radiation-curable compositions of the invention that are low in certain fillers. That is, the radiation-curable composition according to the present invention is preferably a radiation-curable composition in which the one or more mercaptotetrazole compounds are selected from the group consisting of 5-mercapto-1-phenyl-1H-tetrazole (MPHTA), 1-(4-hydroxyphenyl)-5-mercapto-1H-tetrazole (HPMTA), 1-(4-ethoxyphenyl)-5-mercapto-1H-tetrazole (EPMATA), 1-(4-carboxyphenyl)-5-mercapto-1H-tetrazole, 4-(5-sulfanyl-1H-1,2,3,4-tetrazol-1yl)benzonitrile (STABN), and 1-[4-(5-mercapto-1H-tetrazol-1-yl)phenyl]ethanone (MTPE). Additionally or alternatively, preferred is a radiation-curable composition according to the present invention, wherein the one or more mercaptotetrazole compounds are selected from the group consisting of 5-mercapto-1-phenyl-1H-tetrazole (MPHTA), 1-(4-hydroxyphenyl)-5-mercapto-1H-tetrazole (HPMTA), and 1-(4-ethoxyphenyl)-5-mercapto-1H-tetrazole (EPMTA).

[0056] Based on the above explanations regarding the combined use of two or more different hexaarylbiimidazole compounds, the present inventors propose that different mercaptotetrazole compounds can also be used, in particular to precisely adapt the polymerization behavior to the requirements of each application. Therefore, radiation-curable compositions according to the present invention comprising two or more different mercaptotetrazole compounds are preferred.

[0057] Additionally or alternatively, preferred is a radiation-curable composition according to the present invention, which comprises 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole as the hexaarylbiimidazole compound and 5-mercapto-1-phenyl-1H-tetrazole (MPHTA) as the mercaptotetrazole compound.

[0058] The advantage of the radiation-curable composition according to the present invention can be considered to be that it is highly compatible with the presence of common additives, and that the use of such additives allows the setting of an advantageous property profile suited to each application. Thus, in many cases, the radiation-curable composition according to the present invention further comprises one or more additives, preferably in a total mass fraction ranging from 0.01 to 10%, preferably from 0.05 to 5%, particularly preferably from 0.1 to 2%, where the additives are preferably selected from the group consisting of colorants, flow improvers, thixotropic agents, thickeners, stabilizers, and UV protection agents.

[0059] Below we disclose radiation curable compositions which, based on the inventors' assessment, are particularly preferred, in particularly highly preferred embodiments, which combine one, two or more of the features described as preferred.

[0060] A first preferred embodiment is a radiation-curable composition according to the invention, which comprises, with respect to the total weight of the radiation-curable composition: i) one or more radically polymerizable monomers having a total mass fraction of 70% or more; ii) one or more fillers having a total mass fraction ranging from 0.05 to 29%; iii) one or more hexaarylbiimidazole compounds having a total mass fraction in the range of 0.1 to 5%; iiiv) one or more mercaptotetrazole compounds having a total mass fraction in the range of 0.1 to 5%, The radiation curable composition has a total mass fraction of filler in the radiation curable composition of less than 30%.

[0061] A second preferred embodiment is a radiation curable composition according to the invention, which comprises, with respect to the total weight of the radiation curable composition: i) one or more radical polymerizable monomers having a total mass fraction of 70% or more, the one or more radical polymerizable monomers being selected from the group consisting of (meth)acrylic acid, (meth)acrylate, (meth)acrylamide, and other vinyl compounds; ii) one or more fillers having a total mass fraction ranging from 0.5 to 22.5%; iii) one or more hexaarylbiimidazole compounds having a total mass fraction in the range of 0.1 to 5%, the one or more hexaarylbiimidazole compounds being selected from the group consisting of 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,2'-biimidazole, and 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,1'-biimidazole; iiiv) one or more mercaptotetrazole compounds having a total mass fraction in the range of 0.1 to 5%, the one or more mercaptotetrazole compounds being selected from the group consisting of 5-mercapto-1-phenyl-1H-tetrazole (MPHTA), 1-(4-hydroxyphenyl)-5-mercapto-1H-tetrazole (HPMTA), and 1-(4-ethoxyphenyl)-5-mercapto-1H-tetrazole (EPMTA), The radiation curable composition has a total mass fraction of filler in the radiation curable composition of less than 25%.

[0062] A third preferred embodiment is a radiation curable composition according to the invention, which comprises, with respect to the total weight of the radiation curable composition: i) one or more radical polymerizable monomers having a total mass fraction of 75% or more, the one or more radical polymerizable monomers being selected from the group consisting of monofunctional (meth)acrylates and polyfunctional (meth)acrylates; ii) one or more fillers having a total mass fraction in the range of 1 to 20%; iii) one or more hexaarylbiimidazole compounds having a total mass fraction in the range of 0.2 to 4%, the one or more hexaarylbiimidazole compounds being selected from the group consisting of 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,2'-biimidazole, and 2,2',4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4',5'-diphenyl-1,1'-biimidazole; iiiv) one or more mercaptotetrazole compounds having a total mass fraction in the range of 0.2 to 4%, the one or more mercaptotetrazole compounds being selected from the group consisting of 5-mercapto-1-phenyl-1H-tetrazole (MPHTA), 1-(4-hydroxyphenyl)-5-mercapto-1H-tetrazole (HPMTA), and 1-(4-ethoxyphenyl)-5-mercapto-1H-tetrazole (EPMTA), the total mass fraction of fillers in the radiation-curable composition is less than 25%; The radiation-curable composition has a dynamic viscosity at 23°C in the range of 0.001 to 10 Pa·s.

[0063] The present invention also relates to dental components produced or producible by radiation curing the radiation-curable compositions according to the present invention, in particular the preferred radiation-curable compositions according to the present invention, in the DLP or SLA process.

[0064] In view of the above-described embodiments, preferred dental components according to the present invention are those that have been produced or can be produced by radiation curing using a DLP system or an SLA system, in which a radiation-curable composition is irradiated with electromagnetic radiation in the wavelength range of 200 to 420 nm, preferably in the wavelength range of 250 to 415 nm, and particularly preferably in the wavelength range of 300 to 410 nm.

[0065] The present invention also relates to the use of an initiator system in a radiation-curable composition to improve the mechanical properties and reduce health concerns of dental components that can be produced from the radiation-curable composition in a DLP or SLA process, wherein the radiation-curable composition comprises, with respect to the total weight of the radiation-curable composition: i) containing one or more radical polymerizable monomers in a total mass fraction of 60% or more, the total mass fraction of fillers in the radiation-curable composition is less than 30%; The initiator system comprises, with respect to the total weight of the radiation-curable composition: x) one or more hexaarylbiimidazole compounds having a total mass fraction in the range of 0.1 to 5%; y) one or more mercaptotetrazole compounds having a total mass fraction in the range of 0.1 to 5%. DETAILED DESCRIPTION OF THE INVENTION

[0066] In the following, the present invention and preferred embodiments thereof will be explained and described in more detail with reference to experiments.

[0067] A. Preparation of the Radiation-Curable Composition The radiation curable compositions were prepared by mixing the components in the usual way.

[0068] The influence of the initiator system was investigated on the basis of a model system M1 not according to the invention, which, in the inventors' experience, is very suitable, in terms of its composition, to serve as a starting point for studies on the behavior of initiator systems. Model system M1 had the composition listed in Table 1. [Table 1]

[0069] Based on this model system, radiation-curable compositions were prepared by replacing phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide with other initiator systems. When the total mass fraction of the initiator system was increased, the relative mass fractions of the other components were correspondingly reduced. The amounts of coinitiators (MTA, MPHTA, HPMTA, and EPMTA) added relative to the amount of sensitizer (HABI) were calculated and added, thereby partially changing the ratio of the amounts of the co-initiators.

[0070] Radiation curable compositions Z1 to Z17 were prepared, as summarized in Table 2, where composition Z1 is not according to the invention. [Table 2]

[0071] The abbreviations used above correspond to the compounds shown in Table 3. [Table 3]

[0072] B. Reactivity Experiments The produced samples were first analyzed for reactivity and curing speed by exposing the radiation-curable compositions to different doses of radiation and measuring the resulting average layer thickness.

[0073] The DLP printer (cara® Print 4.0 pro) was started at least 5 minutes before use. Measurements were performed at an ambient temperature of 21°C to 25°C, ensuring that the temperature of the composition being measured did not drop below 21°C or exceed 25°C. A vat with a coated glass exposure window, i.e., a container for the photopolymer to be printed, was placed in the printer, and a Hostaphan film (3 cm x 6 cm) was placed in the center of the vat film. First, the exposure intensity was measured using a suitable radiometer (Opsytec Dr. Groebel RM 12), both with and without the Hostaphan film. Next, a pea-sized drop of composition was applied to the Hostaphan film using a disposable plastic pipette and irradiated at a predetermined exposure dose. Immediately after the exposure process was completed, the Hostaphan film with the partially cured material was removed from the vat and placed under a digital dial gauge (Sylvac S_Dial Work Nano) set to zero relative to the Hostaphan film. After 1 minute, the measurement value was read and recorded in the form of the resulting layer thickness. Four measurements were taken for each irradiation dose, and the average layer thickness was calculated from the arithmetic mean of the measured layer thicknesses.

[0074] The results obtained are summarized in Table 4 below. [Table 4-1] [Table 4-2] [Table 4-3]

[0075] From these measurements, a linear regression of the plot of layer thickness against In (dose) can derive the minimum exposure dose Emin (as the intersection point with the x-axis of the linear regression) and the resulting layer thickness vs. light dose relationship dp (as the slope of the linear regression). The results are summarized in Table 5. [Table 5]

[0076] From the above data it can be seen that excellent results can be achieved with the radiation curable compositions according to the invention, and in particular the curing speed can be targeted over a wide range to suit the application requirements.

[0077] In particular, E min It is even possible to achieve values ​​for dp comparable to those of the well-established phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. In particular, the combination of two hexaarylbiimidazole compounds in Z12, Z13, and Z14 yields excellent values ​​for both parameters that are very close to the optimum. These optimum values ​​must not be too high or too low, for example, to prevent undesirable premature curing. The combination of two hexaarylbiimidazole compounds, particularly in samples Z13 and Z14, allows for a reduction in the total content while still providing favorable curing properties, which is not only favorable from the standpoint of manufacturing technology but also advantageous in terms of the color properties of the composition.

[0078] C. Mechanical property testing In addition to the above experiments, selected radiation-curable compositions were analyzed for mechanical properties. To this end, the radiation-curable compositions were cured (DLP printer: cara® Print 4.0 pro; post-cure: HiLite® power 3D for 5 minutes twice), and the flexural strength, modulus, work of fracture, and fracture toughness were measured as follows:

[0079] The preparation of the bending bars and the measurement of the bending strength and modulus of elasticity are carried out in accordance with DIN EN ISO 10477:2020(7.5).

[0080] The preparation of the sample bodies and the determination of the work of fracture and fracture toughness are carried out in accordance with DIN EN ISO 20795-2:2013(8.4).

[0081] The results are summarized in Table 6. [Table 6]

[0082] The above data clearly show that excellent mechanical properties can be achieved with the radiation-curable compositions according to the invention, which are clearly superior to systems known from the prior art for directly comparable samples M1, Z1 and Z2. Measurements of Z7 and Z12 confirmed that the advantageous property profile can be maintained over a wide range of compositions.

Claims

1. 1. A radiation-curable composition for the production of dental components in the DLP or SLA process, comprising, with respect to the total weight of the radiation-curable composition: i) one or more radical polymerizable monomers having a total mass fraction of 60% or more; ii) one or more hexaarylbiimidazole compounds in a total mass fraction ranging from 0.1 to 5%; iii) one or more mercaptotetrazole compounds in a total mass fraction ranging from 0.1 to 5%, A radiation curable composition, wherein the total mass fraction of fillers in said radiation curable composition is less than 30%.

2. 2. The radiation-curable composition of claim 1, wherein the radiation-curable composition has a dynamic viscosity at 23° C. in the range of 0.001 to 10 Pa·s.

3. The radiation curable composition of claim 1 or 2, wherein the radiation curable composition comprises the one or more radically polymerizable monomers in a total mass fraction of 65% or more.

4. The radiation-curable composition according to any one of claims 1 to 3, wherein the total mass fraction of the filler in the radiation-curable composition is 25% or less.

5. The radiation curable composition is 4. The radiation curable composition of claim 1, further comprising iv) one or more fillers having a total mass fraction in the range of 0.05 to 29%.

6. 6. The radiation-curable composition according to claim 1, wherein the quotient obtained by dividing the total mole fraction of the one or more hexaarylbiimidazole compounds by the total mole fraction of the one or more mercaptotetrazole compounds is 1.0 or less.

7. The radiation curable composition of any one of claims 1 to 6, wherein the one or more hexaarylbiimidazole compounds are selected from the group consisting of hexaaryl-1,2'-biimidazole compounds.

8. The radiation-curable composition according to any one of claims 1 to 7, wherein the radiation-curable composition comprises two or more different hexaarylbiimidazole compounds.

9. The radiation-curable composition according to any one of claims 1 to 8, wherein the one or more mercaptotetrazole compounds are selected from the group consisting of mercaptotetrazole compounds having at least one substituent on the tetrazole ring.

10. 10. The radiation curable composition of claim 9, wherein the substituent is selected from the group consisting of substituents having a +M effect.

11. 11. The radiation curable composition of claim 9 or 10, wherein the one or more mercaptotetrazole compounds are selected from the group consisting of 5-mercapto-1-phenyl-1H-tetrazole (MPHTA), 1-(4-hydroxyphenyl)-5-mercapto-1H-tetrazole (HPMTA), 1-(4-ethoxyphenyl)-5-mercapto-1H-tetrazole (EPMATA), 1-(4-carboxyphenyl)-5-mercapto-1H-tetrazole, 4-(5-sulfanyl-1H-1,2,3,4-tetrazol-1yl)benzonitrile (STABN), and 1-[4-(5-mercapto-1H-tetrazol-1-yl)phenyl]ethanone (MTPE).

12. The radiation curable composition according to any one of claims 9 to 11, wherein the mercaptotetrazole compound is 1-(4-hydroxyphenyl)-5-mercapto-1H-tetrazole (HPMTA).

13. The radiation-curable composition according to any one of claims 9 to 12, comprising 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole as the hexaarylbiimidazole compound and 5-mercapto-1-phenyl-1H-tetrazole (MPHTA) as the mercaptotetrazole compound.

14. A dental component produced or producible by the DLP method or the SLA method by radiation curing the radiation-curable composition according to any one of claims 1 to 13.

15. 1. Use of an initiator system in a radiation-curable composition to improve the mechanical properties and reduce health concerns of dental components producible from said radiation-curable composition in a DLP or SLA process, comprising: The radiation curable composition comprises, with respect to the total weight of the radiation curable composition: i) containing one or more radical polymerizable monomers in a total mass fraction of 60% or more, the total mass fraction of fillers in the radiation-curable composition is less than 30%; The initiator system comprises, relative to the total weight of the radiation curable composition: x) one or more hexaarylbiimidazole compounds in a total mass fraction ranging from 0.1 to 5%; y) one or more mercaptotetrazole compounds in a total mass fraction ranging from 0.1 to 5%.

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