Photocurable composition for producing dental components having a matte surface - Patent Application 20070122997

Abstract

The present invention relates to a photocurable composition for producing a dental part by a DLP method or an SLA method, the photocurable composition comprising: a liquid monomer composition having a mass proportion of 60% or more relative to the total mass of the photocurable composition, the liquid monomer composition containing one or more radically polymerizable monomers; one or more photoinitiators having a mixed mass proportion in the range of 0.001 to 10%; and solid polymer particles having a particle size in the range of 0.4 to 4 μm and a mixed mass proportion in the range of 0.1 to 30%, the solid polymer particles being dispersed in the liquid monomer composition.

Description

[Technical Field]

[0001] The present invention relates to a photocurable composition for producing dental parts in a DLP or SLA process, a method for producing the photocurable composition, the use of the corresponding photocurable composition in a DLP or SLA process to produce dental parts with a matte surface, and a kit for producing the corresponding photocurable composition. Additionally, the present invention discloses the use of solid polymer aggregates in producing photocurable compositions, the use of solid polymer particles in a photocurable composition to reduce the gloss characteristics of dental parts obtained by photocuring, uncoated dental parts with a matte surface, and a system for producing dental parts in a DLP or SLA process. The subject matter of the present invention is defined in the claims. [Background technology]

[0002] The technological advances and advanced 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 the past few decades, many types of dentures, such as crowns, bridges, partial and complete dentures, or inlays, as well as orthodontic treatment devices, such as splints, have been manufactured manually, especially by dental technicians. In this case, the techniques of taking dental and jaw impressions, as well as the production of cement models, were central work steps as the basis for subsequent dental work.

[0003] Traditional procedures are now being supported and increasingly replaced by the use of computer-aided manufacturing and fabrication methods, sometimes referred to by those skilled in the art as digital dentures.

[0004] Here, so-called CAD / CAM methods are often an essential element of computer-aided manufacturing. The term CAD stands for computer-aided design and, in some cases, for the generation of digital components that can be modified directly by the user on a computer. The term CAM stands for computer-aided manufacturing, i.e., the conversion of CAD-generated components into code that can be used to control machines, such as cutting machines or 3D printers. In the field of dental technology, the use of so-called intraoral scanners, which can transfer precise images of the patient's oral cavity to a computer without contact, is becoming increasingly established for the creation of CAD components.

[0005] Additive manufacturing methods, in particular, are of great importance in dental technology. In these methods, products made from formless materials are produced without special tools, based on computer data sets generated by CAD / CAM. These methods, also known in part as "rapid prototyping" based on the English expression, are currently replacing or complementing many work steps in the production of dental components in the field of dental technology.

[0006] A variety of additive manufacturing methods have been established in recent years. These methods differ not only in the structure of the equipment but also in the specific raw materials used. Many of these so-called 3D printers are capable of processing solid starting materials, for example in the form of granules or fibers. What most of these methods have in common is that they produce three-dimensional parts by constructing them from layers arranged one on top of the other.

[0007] Among additive manufacturing methods, the so-called stereolithography (SLA) and digital light processing (DLP) play a leading role. In these methods, a photocurable composition is deposited and cured layer by layer by spatially separated, targeted irradiation at the desired locations. The resulting component, for example, gradually sinks into the composition or gradually rises out of it, so that after each layer, a thin layer of photocurable composition is deposited on top of the previously deposited layer. This thin layer roughly corresponds to the thickness of the next layer to be polymerized. While SLA and DLP methods are similar in their basic principles, they are completely different in the equipment configuration. In SLA, for example, a laser is used to sequentially illuminate the structure to be produced, while in DLP, the entire surface is simultaneously exposed using a suitable projection technology.

[0008] The principles of the SLA and DLP processes are known from the prior art and are disclosed, for example, in U.S. Patent Application Publication No. 4,575,330 A. The use of additive manufacturing methods in dental technology is known, for example, from German Patent Application Publication Nos. 102016107935 A1 and 1020122011371 A1 and is also described in European Patent Application Publication No. 3,020,361 B1. These methods now make it possible to process part information obtained from a patient directly in a computer and convert it directly into a dental part by additive manufacturing. This makes it possible, for example, to eliminate the steps of taking impressions and cement casting when producing dental parts. Furthermore, partial or even complete dentures can be manufactured using the SLA and / or DLP processes.

[0009] The undisputed practicality of this method is evidenced by the rapid spread of this technology, but despite its practicality, there are still fundamental problems in the production of corresponding dental components, which have not yet been satisfactorily solved. Generally, components produced by the SLA or DLP method, i.e., after curing, have a surface with too high a gloss, i.e., they have the property of completely or partially specularly reflecting light.

[0010] While this characteristic is not a major problem in many other technical fields, or even desirable in some cases, in dental technology, this surface characteristic is usually found to be a drawback.Those skilled in the field of dental technology understand that for the intended use of dental components, a matte surface, or at most a surface with a silk-matt sheen, would be desirable.This is because, historically, most of the established processes for processing dental components have been adapted to the cements and their surface textures that have been used for decades, and this is reflected in the fact that shiny components have not been well received by users.Correspondingly, it is particularly desirable for dental components to resemble traditional cement models in terms of gloss, reflective behavior, and matteness.

[0011] In this case, the most important aspect in practice is the digital scannability of the part, which can be very limited in the case of a glossy surface. In practice, dental parts manufactured by additive manufacturing methods, for example, need to be manually processed in further steps and finally re-digitized with a suitable scanner. This re-digitization is very difficult if the surface of the dental part is glossy, unlike the case of a cement model, so the resulting CAD data is sometimes of insufficient quality or has defects. This requires multiple scanning processes, which is laborious and expensive.

[0012] This problem of often poor scannability of glossy structures is well known in the art. The inventors have now experienced that this undesirable tendency toward glossy surfaces is accentuated when certain monomers are used in photocurable compositions. Unfortunately, most of the corresponding high-boiling monomers in photocurable compositions are often important for imparting desired product properties, such as mechanical strength or temperature resistance, to dental parts obtained therefrom, and therefore cannot be easily replaced with monomers that have less gloss tendency.

[0013] The prior art has established various solutions to address the problems of glossy surfaces and poor scannability. German Patent Application Publication No. 100038564 A1, for example, teaches the use of metal powders or powders with metallic effects in paste-like molding materials, such as cement, to improve their scannability. German Patent Application Publication No. 102006056451 A1, on the other hand, discloses the subsequent roughening of impression materials to improve scannability. The principles of these two solutions are not easily transferable to additive manufacturing methods and are therefore generally considered disadvantageous. In particular, subsequent mechanical roughening of the component is often not considered if, apart from the cost, this could alter the precise dimensions of the component or adversely affect surface adhesion.

[0014] The solution known from other industries, such as the paint industry, which often involves adding a matting agent to the coating, is usually not suitable for use in the SLA and DLP processes. This is because the matting agent is often a filler, which causes an uneven surface after the coating has dried and hardened, thereby leading to diffuse reflection. The conditions for this effect are, in particular, the high shrinkage of the corresponding coating composition, which leaves the surface undulations caused by the filler after drying. However, the monomers used in dental technology usually should not achieve a correspondingly strong shrinkage during hardening, because this is also undesirable when focusing on fine-tuning the undulations of the part. Furthermore, a significantly roughened surface to achieve a matte effect is often undesirable, especially when it is important to accurately configure the undulations of the part. This is because the increased adhesion of the roughened surface can cause, for example, paste-like impression or model materials to adhere too strongly, making it difficult to work with the dental part.

[0015] As an alternative to this approach, matting liquids have been established in the dental field, as disclosed, for example, in German Patent Application Publication No. DE 102013110549 A1. These matting liquids contain, in addition to an adhesive, a pigment, such as titanium dioxide. However, the use of such matting liquids on dental components manufactured by SLA or DLP processes is generally considered inconvenient. This is especially true because applying the matting liquid is an additional work step, significantly extending the manufacturing time and thus increasing costs. Furthermore, the accuracy of digitizing the surface shape of the dental component during a possible 3D scanning step can be adversely affected by an uneven layer thickness of the matting liquid. Furthermore, because the dental component being coated is usually a pharmaceutical product, the corresponding use of the matting liquid would inconveniently require corresponding approval as a pharmaceutical product. This increases the regulatory burden involved in commercialization.

[0016] U.S. Patent Application Publication Nos. 20140131908 A1 and 20190053883 A1 disclose compositions, which may be implemented as photocurable compositions, that utilize so-called "silicone-acrylic-based rubber impact modifiers" implemented as core-shell particles, preferably having diameters in the range of 0.01 to 100 μm, which contribute to improving the mechanical properties of the cured composition.

[0017] International Patent Application No. WO 2018 / 167213 discloses dental moldings having an opacity of 70-78% and containing organic fillers and / or powder composites. According to the disclosed embodiment, the composition for producing the moldings contains approximately 66% by weight of polymer particles having an average particle size in the range of 15-60 μm.

[0018] Up until now, no photocurable compositions for use in SLA or DLP processes have been known, specifically compositions that have been modified so that dental components produced therefrom directly have particularly advantageous gloss properties, and their surfaces exhibit at most a silk-matt gloss. Summary of the Invention

[0019] Therefore, the main object of the present invention was to provide a photocurable composition for producing dental parts in the DLP or SLA process, which allows the production of dental parts exhibiting effective gloss properties without further surface treatment, thereby eliminating or avoiding the above-mentioned drawbacks of solutions known from the prior art. The photocurable composition must have a relatively low viscosity, preferably easily adjustable, so that it can be handled without problems in the SLA or DLP process. In addition, the photocurable composition must be curable with typical photoinitiators. In this case, it is desirable that organic additives or fillers, particularly metals or metal oxides, are not required to achieve this effect, as these can undesirably increase the weight and / or surface strength and / or mechanical properties of the produced part, thereby reducing, for example, its processability. It is particularly desirable that dental parts made from the photocurable composition do not have a high surface roughness, as this could artificially modify the desired surface structure according to the CAD data and / or lead to undesirable strong adhesion of the applied paste-like molding material.

[0020] One objective of the present invention was to make it possible to produce a large proportion of photocurable compositions from materials already commonly used in dental technology. In this case, the photocurable compositions must be able to contain monomers that are particularly prone to having a glossy surface. In particular, due to the unresolved health assessment of nanoparticles, i.e., nanoparticles with a diameter of 300 nm or less, and also from health and regulatory standpoints, it is particularly desirable to provide photocurable compositions that do not contain small nanoparticles with a diameter of 300 nm or less.

[0021] A secondary object of the present invention is to provide a method for producing a photocurable composition, which can produce photocurable compositions cost-effectively and reproducibly, and can use SLA or DLP method to produce dental parts whose surface exhibits only a silk-matt gloss at best.In this regard, it is desirable that this method can be carried out using common equipment, and in particular that only starting products that can be easily handled and stored are used, and it is particularly desirable that workers do not come into contact with dry or dusty nanoparticles when carrying out this method.This is to ensure the highest possible work safety and avoid environmental pollution.

[0022] A further object of the present invention was to provide corresponding photocurable compositions and uses for the solid polymer aggregates and solid polymer particles.

[0023] A complementary object of the present invention can be seen to be the provision of a kit for producing the corresponding photocurable composition, a system for producing dental articles, and uncoated dental articles having a matte surface.

[0024] The inventors have now discovered that the above-mentioned problems can be solved by adding solid polymer particles having a particle size in the range of 0.4 to 4 μm and a mixed mass ratio in the range of 0.1 to 30% to a photocurable composition containing a high proportion of liquid monomer, and dispersing these solid polymer particles in the liquid monomer composition.

[0025] In experiments, the inventors have reliably demonstrated that the corresponding photocurable compositions in the SLA or DLP process produce dental parts with significantly reduced surface gloss, and that this principle holds true. Surprisingly, the resulting dental parts do not exhibit significantly higher surface roughness values ​​than dental parts to which solid polymer particles have not been added beforehand. This suggests that the effect discovered by the inventors is probably not due to a particularly uneven surface, as is known, for example, in paints. While not wishing to be bound by this theory, it appears that the solid polymer particles in the cured material exist as small, discrete domains dispersed throughout the material. In these domains, the resulting components have a different chemical composition and, consequently, different optical refractive or scattering properties than the polymerized monomer composition. The inventors believe that the distribution of these small domains across the surface of the dental part likely contributes to the extremely high matte effect observed in the experiments.

[0026] Furthermore, the inventors have developed a highly efficient process by which the corresponding photocurable composition can be obtained. The essential aspect of this method is based on adding solid polymer particles to a liquid monomer composition not alone but in the form of large polymer agglomerates, sometimes called agglomerated polymer beads. These polymer agglomerates are added to the liquid monomer composition to form a base mixture. The base mixture is then mechanically processed, specifically by a three-roll process, to separate the solid polymer agglomerates and disperse the polymer particles in the liquid monomer composition to form solid polymer particles. This results in a photocurable composition that can be further processed to produce the advantageous gloss characteristics described above.

[0027] Therefore, the above-mentioned problems are solved by the light-curable compositions, methods, uses, systems, kits, and uncoated dental parts as disclosed below.

[0028] Preferred configurations of the present invention are evident from the dependent claims and the following embodiments. Features that are expressed as preferred below are combined with other features that are expressed as preferred in particularly preferred embodiments. Most preferred are therefore combinations of two or more embodiments that are expressed as particularly preferred below. Features that are expressed as preferred below for the photocurable composition of the present invention are also preferred features of the corresponding methods and uses.

[0029] The present invention provides a photocurable composition for producing a dental article by a DLP method or an SLA method, comprising, relative to the total mass of the photocurable composition: a liquid monomer composition having a mass proportion of 60% or more, the liquid monomer composition comprising one or more radically polymerizable monomers, preferably consisting of one or more radically polymerizable monomers; One or more photoinitiators having a mixed mass proportion in the range of 0.001 to 10%; and solid polymer particles having a particle size in the range of 0.4 to 4 μm and a mixed mass ratio in the range of 0.1 to 30%, which are dispersed in the liquid monomer composition.

[0030] The term "photocurable" used above in connection with the properties of the composition corresponds to a common technical term in the art. This term is understood to mean the property of a composition that is cured by using electromagnetic radiation, specifically light. Here, polymerization of radically polymerizable monomers in the composition is induced via radiation using a photoinitiator. The wavelength of the radiation used for this purpose does not necessarily have to be in the visible light range, but may also include border wavelength regions in the infrared or UV range. Here, wavelengths in the 200-500 nm range, i.e., wavelengths in the blue light and ultraviolet range, are frequently used.

[0031] The expression dental part, within the meaning of the present invention, refers to any part and three-dimensional structure that is produced as an intermediate or final product, independently of the underlying dental representations in the field of dental technology, such as dental models, gingival masks, bite splints, CAD-to-cast moulds, impression trays or drilling jigs.

[0032] The terms DLP and SLA refer to the aforementioned digital light processing or stereolithography methods, both of which are known to those skilled in the art. The description of the suitability of photocurable compositions for producing dental components using these methods sets functional requirements for the viscosity of the material, particularly in cases where the viscosity must be sufficiently low. This excludes many photocurable compositions used elsewhere in the dental field, particularly those with a high filler content, such as ceramic slurries. Those skilled in the art can easily recognize whether a monomer composition is qualitatively liquid. Within the scope of the present invention, any monomer composition having a dynamic viscosity of 10 Pa·s or less, preferably 5 Pa·s or less, at 23°C can be considered liquid.

[0033] The weight percentages for the liquid monomer composition, photoinitiator, and solid polymer particles defined above are all percentages relative to the total weight of the photocurable composition. Those skilled in the art will understand that the weight percentages are defined with the proviso that the total weight percentages of the photocurable composition add up to 100%. This means that if, for example, 10% weight percentage of an additive is added to the composition, the combined weight percentage of the photoinitiator and solid polymer particles may only be 30% or less.

[0034] Radically polymerizable monomers are characterized by the property of crosslinking with each other in a chain reaction when contacted with a radical initiator. The radical initiator is usually provided by one or more photoinitiators in the photocurable composition. In principle, the present invention is not limited to a specific radically polymerizable monomer, but can be used with any radically polymerizable monomer, which usually has a terminal unsaturated double bond through which radical polymerization can occur. However, in the field of dental chemistry, (meth)acrylates are extremely important as monomers, and the term (meth)acrylate is understood by those skilled in the art to refer to not only acrylates but also methacrylates. These monomers frequently used in dental chemistry are known to those skilled in the art and are disclosed, for example, in EP 3020361 B1 or DE 3941629 C1. The monomers, which may be monofunctional or polyfunctional, are selected by those skilled in the art based on the desired physicochemical and application-technical properties of the dental part to be produced.

[0035] The photoinitiator is selected by those skilled in the art based on the radically polymerizable monomer used and the desired wavelength range for polymerization. Here, those skilled in the art can freely use the information summarized in the table and / or the information provided by the manufacturer. In the scope of the present invention, the term photoinitiator also includes co-initiators, coinitiators, or accelerators. Suitable photoinitiators are disclosed, for example, in EP 3020361 B1 or WO 95 / 13565 A1.

[0036] The solid polymer particles added to the photocurable composition according to the present invention have a particle size in the range of 0.4 to 4 μm. Experiments have shown that even a small amount of this additive can significantly improve the gloss properties of dental parts manufactured from the photocurable composition. According to the present invention, the polymer particles are solid, i.e., nearly completely polymerized, i.e., at least 80%, preferably at least 90%, and particularly preferably at least 98% polymerized.

[0037] According to the present invention, the solid polymer particles are dispersed in the liquid monomer composition. This means that there is almost no concentration gradient of the solid polymer particles in the photocurable composition between two macroscopic volume portions of the photocurable composition. This preferably means that the concentration difference between two separate macroscopic volume portions of the photocurable composition, each of which is 1 millimeter, shows a deviation in the concentration of the solid polymer particles of less than 10%, preferably less than 5%, and particularly preferably less than 2%. Within the meaning of the present invention, the solid polymer particles are not dispersed in the liquid monomer composition, especially if they float to the surface of the liquid monomer composition. For example, when the solid polymer particles float to the surface of the liquid monomer composition, as occurs in agglomerated particles in polymer agglomerates, the effective effect of the present invention is not exhibited.

[0038] Correspondingly, photocurable compositions in which solid polymer particles are present in almost no agglomeration are preferred.This means that polymer particles are present in an agglomerated state of preferably less than 50%, particularly preferably less than 20%, and most preferably less than 10%.However, those skilled in the art will understand that in the case of corresponding small polymer particles, local formation of small agglomerates may always occur, and it is not necessary to completely eliminate this.This agglomerate preferably contains at most 10 solid polymer particles.

[0039] In the photocurable composition according to the present invention, it is preferred that the photocurable composition does not contain metal particles or metal oxides.

[0040] The photocurable composition of the present invention allows dental articles to be produced using the SLA or DLP process. The dental articles exhibit advantageous gloss characteristics, i.e., low gloss, on their surfaces without further processing. Due to the high proportion of liquid monomer components, the photocurable composition of the present invention has a relatively low viscosity, which can be easily set using polymer particles. The photocurable composition of the present invention can be cured using typical photoinitiators, and most of the compositions can be produced from materials already commonly used in dental chemistry, or even monomers with a high gloss tendency. Advantageously, no organic additives or nanoparticles with a diameter of 300 nm or less are required to achieve this effect, and dental articles produced from the photocurable composition do not have a high degree of roughness on their surfaces.

[0041] In the photocurable composition according to the present invention, the solid polymer particles are preferably made of a polymer of a monomer selected from the group consisting of monofunctional (meth)acrylates and polyfunctional (meth)acrylates, preferably polymethyl methacrylate, and the solid polymer particles are preferably made of a polymer of a monomer that is not a constituent material of the liquid monomer composition.

[0042] The above-mentioned photocurable composition is preferred because the above-mentioned polymer particles, when used in the photocurable composition, are particularly advantageous in that they reduce the surface gloss of the dental article produced therefrom. This is particularly advantageous when the polymer particles are composed of a polymer of a monomer that is not itself a component of the liquid monomer composition, or a monomer that has a mass percentage of less than 10% in the liquid monomer composition and therefore has relatively little effect on the physicochemical properties of the polymerized monomer composition. Without wishing to be bound by this theory, it is assumed that in the corresponding preferred photocurable composition, the chemical composition gradient between the solid polymer particles and the dental article material obtained by polymerization from the liquid monomer composition is particularly pronounced. Here, the optical properties in the small regions introduced by the solid polymer particles are particularly different from the optical properties that occur when the liquid monomer composition is cured.

[0043] For this reason, photocurable compositions in which the solid polymer particles are at least partially transparent polymer particles, the refractive index of which differs from the refractive index of the liquid monomer composition upon polymerization, are also preferred.

[0044] In the photocurable composition according to the present invention, the solid polymer particles preferably have an approximately spherical particle shape and are preferably produced by spray drying.

[0045] The corresponding photocurable compositions are considered preferred because, upon testing of the polymer particles used in the experiments, they typically exhibit a corresponding spherical, i.e., ball-like, particle shape. Specifically, in light of the presumed effect of solid polymer particles in the cured photocurable compositions, it is believed that the relatively uniform spatial extension of spherical polymer particles contributes to the altered scattering properties of the surface compared to, for example, flat, plate-like polymer particles.

[0046] In the photocurable composition according to the present invention, the radically polymerizable monomer is selected from the group consisting of monofunctional (meth)acrylates and polyfunctional (meth)acrylates, preferably polymethyl methacrylate, and preferably diurethane dimethacrylate, tris(2-acryloyloxyethyl)isocyanurate, alkoxylated bisphenol A dimethacrylate, tricyclo[5.2.1.0] 2.6 ] A photocurable composition is preferred in which the radical polymerizable monomer is selected from the group consisting of decanedimethanol diacrylate and dicyclopentanyl methyl acrylate, and / or the radical polymerizable monomer does not contain a silicon element.

[0047] The corresponding photocurable compositions are preferred because the corresponding radically polymerizable monomers provide particularly good results in practice. These radically polymerizable monomers are also established components in the field of dental chemistry, with comprehensive approvals and well-investigated risks. Furthermore, these (meth)acrylates can be photopolymerized with extremely high efficiency, and the large bandwidth of possible components allows for particularly flexible configuration of physicochemical properties. Most preferred are photocurable compositions containing diurethane dimethacrylate, tris(2-acryloyloxyethyl)isocyanurate, alkoxylated bisphenol A dimethacrylate, tricyclo[5.2.1.0]isocyanurate, hydroxypropyl methyl acrylate, methyl meth ... 2.6 ] photocurable compositions containing decanedimethanol diacrylate and dicyclopentanyl methyl acrylate, because these have been identified in independent tests as suitable starting materials for the production of dental components, having particularly advantageous mechanical properties.

[0048] In the photocurable composition according to the present invention, it is preferred that the liquid monomer composition contains a radically polymerizable monomer, and that its boiling point at a pressure of 101.3 kPa is higher than 100°C, preferably higher than 120°C, and particularly preferably higher than 140°C.

[0049] The reason why the corresponding photocurable composition is most preferred is that the inventors have found that the problem of gloss on the surface of dental articles occurs particularly when using radically polymerizable monomers with low vapor pressure, i.e., boiling points at ambient pressure higher than a certain temperature. However, at the same time, corresponding high-boiling point monomers are usually essential for setting the physicochemical properties of dental articles. Although undesirable gloss effects can also occur when using other radically polymerizable monomers, the reduction in gloss that can be achieved by the photocurable composition of the present invention is significant in the case of the monomers specified here.

[0050] Preferably, the liquid monomer composition contains at least 20%, preferably at least 40%, and most preferably at least 60% by weight of a radically polymerizable monomer having a boiling point as defined above. While not wishing to be bound by this theory, the inventors believe that the tendency for high-boiling-point monomers to have high gloss is related to the process temperature at the moment when photoinduced polymerization occurs locally, for example, in the SLA process. The tendency for high gloss appears to be more pronounced the further the boiling point of the radically polymerizable monomer is from the temperature of about 70-80°C that occurs during polymerization.

[0051] In the photocurable composition according to the present invention, it is preferred that the mass proportion of the liquid monomer composition is 70% or more, preferably 80% or more, and particularly preferably 85% or more, and / or the mixed mass proportion of the photoinitiator is in the range of 0.01 to 5%, preferably 0.1 to 2%, and particularly preferably 0.2 to 1%, and / or the mixed mass proportion of the solid polymer particles is in the range of 0.2 to 20%, preferably 0.5 to 15%, and particularly preferably 1 to 10%.

[0052] The corresponding photocurable compositions are preferred because they have a high mass fraction of liquid monomer composition and a relatively low mass fraction of solid polymer particles, which exhibit particularly good processability and are particularly easy and cost-effective to produce. Furthermore, using as little photoinitiator as possible is particularly cost-effective, and the storage stability of the resulting material is also very beneficial. Generally, the photocurable compositions according to the present invention advantageously achieve satisfactory results even with low amounts of photoinitiator. The inventors have now discovered that even small amounts of solid polymer particles added to the photocurable composition, i.e., even in the case of compositions containing a high amount of monomer, have a particularly pronounced effect on gloss properties.

[0053] In the photocurable composition according to the present invention, the solid polymer particles preferably have a particle size in the range of 0.5 to 2.5 μm, preferably in the range of 0.7 to 2 μm, and / or a d50 value in the range of 0.7 to 2 μm, preferably in the range of 0.8 to 1.6 μm, particularly preferably in the range of 0.9 to 1.2 μm.

[0054] By selecting a suitable particle size for the solid polymer particles, it is possible to advantageously set the rheological properties of the photocurable composition in the liquid state, particularly the dynamic viscosity at 23°C, to the desired values. In addition, for the same mass proportion of solid polymer particles, a smaller particle size is usually associated with a more uniform dispersion in the material. In this regard, the inventors have confirmed that particularly small particles can achieve a particularly significant reduction in gloss value, which is due to their particularly uniform dispersion in the photocurable composition.

[0055] The photocurable composition according to the present invention preferably has a dynamic viscosity at 23°C in the range of 0.1 to 10 Pa·s, preferably 0.5 to 5 Pa·s, and particularly preferably 0.7 to 2.5 Pa·s.

[0056] The photocurable compositions described above are particularly advantageous because they can be processed with high efficiency and at the same time have a sufficiently high stability of the solid polymer particles in the photocurable compositions. By avoiding premature precipitation of the solid polymer particles, the viscosity defined above contributes to an improved shelf life, which is particularly advantageous in the case of the photocurable compositions according to the present invention. In the context of the present invention, the dynamic viscosity at 23°C is measured by a rheometer (Anton Paar, Physiker NCR 301) in accordance with DIN 1342-2; 2003-11 for Newtonian fluids and DIN 1342-3; 2003-11 for non-Newtonian fluids.

[0057] In the photocurable composition according to the present invention, it is preferred that the photoinitiator be capable of initiating a polymerization reaction when irradiated with electromagnetic radiation in the wavelength region of 200 to 500 nm, preferably in the wavelength region of 350 to 450 nm, and particularly preferably in the wavelength region of 380 to 420 nm.

[0058] Corresponding photoinitiators usually have particularly high compatibility with commonly used (meth)acrylates.In addition, the use of radiation in the wavelength range between ultraviolet and blue light is particularly preferred, because this radiation has higher energy than, for example, infrared light, and therefore can usually initiate photocrosslinking curing more cleanly and quickly.

[0059] The photocurable composition according to the present invention further contains one or more additives in a mixed mass ratio of 0.01 to 10%, preferably 0.1 to 5%, and particularly preferably 0.2 to 2%, and the additives are preferably selected from the group consisting of fillers, pigments, colorants, drag reducers, thixotropic agents, thickeners, and stabilizers.

[0060] A particular advantage of the photocurable compositions according to the invention is that further additives may be added without adversely affecting the positive effect on the gloss properties of the dental parts produced.

[0061] The present invention further relates to a method for producing a photocurable composition for producing dental components in the DLP or SLA process, preferably a photocurable composition according to the invention, which method comprises: A) preparing or providing a liquid monomer composition comprising one or more radically polymerizable monomers; B) producing or providing a solid polymer agglomerate comprising agglomerated solid polymer particles having a particle size in the range of 0.4 to 4 μm; C) mixing the components produced or prepared in step A and step B to obtain a basic mixture, wherein the basic mixture contains the liquid monomer composition in a mass ratio of 60% or more and the solid polymer aggregate in a mixed mass ratio of 0.1 to 30% based on the total mass of the basic mixture; D) mechanically treating the base mixture to separate the solid polymer agglomerates and to disperse the polymer particles in the liquid monomer composition.

[0062] The liquid monomer composition in step A) and the solid polymer agglomerates in step B) can be produced in accordance with the method procedure of the present invention or can be prepared separately, for example by purchasing them from a supplier. What is important for the method of the present invention is that the solid polymer particles are not used in their sole form, i.e., not introduced into the liquid monomer composition, but in the form of solid polymer agglomerates, sometimes called agglomerated polymer beads. These solid polymer agglomerates contain a large number of solid polymer particles as primary particles and are mixed with the monomer composition in step C), thereby obtaining a base mixture.

[0063] In this base mixture, the solid polymer aggregates tend to float in the liquid monomer composition, rather than being uniformly dispersed in the base mixture. In this state, the base mixture is not suitable for use in the SLA or DLP process, and the resulting dental part does not show any improvement in gloss properties. Only by mechanically processing the base mixture in step D) can the photocurable composition exhibiting the positive effects of the present invention be obtained.

[0064] Mechanical treatment of the base mixture is carried out to break up the solid polymer agglomerates and to disperse the polymer particles in the liquid monomer composition, which separates the polymer agglomerates into primary particles, i.e., solid polymer particles, and achieves a substantially uniform dispersion of the solid polymer particles in the photocurable composition.

[0065] In the method according to the present invention, a photoinitiator required for photocuring must also be added to the basic mixture to produce a photocurable composition. The timing of mixing the photoinitiator is not critical. This can be done, for example, after the mechanical treatment or before mixing the two components, for example by adding it to the liquid monomer mixture. In either case, however, it is useful to ensure thorough mixing.

[0066] The method according to the invention allows for the cost-effective and reproducible production of the photocurable compositions according to the invention, in which the method can be carried out using relatively common equipment, the required starting products are relatively easy to handle and store, and high work safety is guaranteed, since workers do not come into contact with small nanoparticles in dry or dusty form when carrying out the method.

[0067] In the method according to the present invention, the polymer aggregates preferably have a particle size in the range of 5 to 200 μm, preferably in the range of 10 to 150 μm, and particularly preferably in the range of 15 to 75 μm.

[0068] When sufficiently small polymer aggregates are used, they are already well and uniformly dispersed in the base mixture before mechanical processing and can be easily separated by mechanical processing. This advantageously results in a more homogeneous photocurable composition. However, it is recognized that larger polymer aggregates may have significant advantages, particularly in terms of ease of handling and from a health standpoint, particularly in the case of dust formation during processing.

[0069] In the method according to the invention, it is preferred that the polymer aggregates have an approximately spherical shape.

[0070] In the method according to the invention, the mechanical treatment step is carried out by a grinding process and / or a stirring process and / or a rolling process, in particular using a ball mill and / or a dissolver and / or a three-roll mill, preferably by a rolling process, in particular using a three-roll mill.

[0071] The mechanical treatment of the base mixture can be carried out by any suitable method suitable for separating solid polymer agglomerates. In practice, grinding, stirring, and rolling processes have proven particularly effective for this purpose, with the use of a three-roll process, i.e., a three-roll mill, being particularly preferred, since the three-roll mill allows for particularly efficient and targeted separation of the agglomerates after addition to the base mixture by setting the roller gap as narrow as possible. In particular, the use of a three-roll mill allows for sufficient separation of the polymer agglomerates, which can be difficult to achieve for the entire amount of the base mixture, especially in a stirring process.

[0072] Those skilled in the art will adjust the strength of the mechanical treatment based on routine experiments to determine the optimal load factor for the material used. If a sufficiently large mechanical load is not selected, a large portion of the polymer aggregates may remain, thereby reducing the technical effect of the photocurable composition according to the present invention. Furthermore, it has been found that if the mechanical load of the basic mixture is too strong, the overall properties of the produced photocurable composition may be impaired, resulting in poor quality of the dental part obtained.

[0073] Photocurable compositions prepared according to the above-described method are particularly preferred.

[0074] The present invention relates to the use of the photocurable composition according to the invention for producing dental components with a matte surface in a DLP or SLA process, wherein the surface of the dental component has a gloss value of 10 GU or less, preferably 5 GU or less, particularly preferably 2 GU or less.

[0075] It has surprisingly been found that by using the photocurable composition according to the invention in the DLP or SLA process, dental parts can be obtained that have particularly effective gloss properties and a matte surface. In the context of the present invention, gloss properties are expressed in GU, i.e., Gloss Units, which are well known to those skilled in the art.

[0076] Within the scope of the present invention, gloss values ​​are determined by the gloss measurement method using an instrument from BYK (type micro-TRI gloss) at an angle of 60 degrees.

[0077] Additionally, the use of a solid polymer agglomerate comprising agglomerated solid polymer particles having a particle size in the range of 0.4 to 4 μm is disclosed in the preparation of a photocurable composition for producing a dental part in a DLP or SLA process, preferably for the preparation of a photocurable composition according to the present invention.

[0078] It has surprisingly been found that the use of solid polymer agglomerates in preparing the photocurable composition makes it possible to obtain photocurable compositions according to the invention with particularly high efficiency, without the formation of undesirable dust when handling the solid polymer particles.

[0079] Also disclosed is the use of solid polymer particles having a particle size in the range of 0.4 to 4 μm in a photocurable composition for producing a dental part by the DLP method or SLA method, in order to reduce the gloss characteristics of the dental part obtained by photocuring.

[0080] Further disclosed is an uncoated dental component produced from the composition according to the invention in a DLP or SLA process, wherein the surface of the dental component has a gloss value of 10 GU or less, preferably 5 GU or less, particularly preferably 2 GU or less, and an average surface roughness Ra of 2.5 μm or less, preferably 2.0 μm or less, where Ra is measured according to the standard DIN EN ISO 4287:2010.

[0081] This uncoated dental article is produced by the photocurable composition of the present invention by the DLP method or the SLA method, and has particularly advantageous gloss properties on its surface, and has a moderate surface roughness, as indicated by an average surface roughness Ra of 2.5 μm or less.This advantageously provides a particularly smooth surface, on which, for example, a paste-like molding material can be applied, and then removed again without leaving any residue.This advantageously allows the corresponding uncoated dental article to have a large contact area with water.As a result, it can be particularly efficiently cleaned.

[0082] Further disclosed is a system for producing dental components in a DLP or SLA process, the system comprising a DLP or SLA printer with a liquid reservoir for containing a photocurable composition, the liquid reservoir containing the photocurable composition according to the present invention.

[0083] Finally, there is provided a kit for preparing a photocurable composition according to the present invention, comprising, as separate components in separate containers: U a solid polymer agglomerate comprising agglomerated solid polymer particles having a particle size in the range of 0.4 to 4 μm; V a liquid monomer composition comprising one or more radically polymerizable monomers.

[0084] As mentioned above, particularly good results are obtained with the photocurable composition of the present invention when the solid polymer particles are dispersed as uniformly as possible in the photocurable composition. Specifically, if the photocurable composition has a low dynamic viscosity, this property may deteriorate during prolonged continuous storage because the solid polymer particles in the liquid monomer composition slowly settle. Accordingly, it is particularly convenient to provide the components for the photocurable composition of the present invention to the end user, e.g., a dentist or dental laboratory technician, as separate components. From these components, the photocurable composition of the present invention can be produced using the method of the present invention. Advantageously, the solid polymer aggregates are sufficiently large to be relatively safe to handle in the laboratory. The dentist or dental technician simply mixes the two components together and ensures that the solid polymer aggregates are separated into solid polymer particles by mechanical processing. The solid polymer particles are then dispersed in the photocurable composition.

[0085] Optionally, the kit may further comprise one or more photoinitiators as a further component W. Alternatively, these photoinitiators may be added in advance to the liquid monomer composition. The advantage of preparing components U, V and W separately and finally mixing them is that premature polymerization of the monomer composition due to undesired radiation cannot occur, thereby further increasing storage stability. [Brief explanation of the drawings]

[0086] [Figure 1] 200x magnification micrograph of spray-dried polymer aggregates made of polymethyl methacrylate. [Figure 2] 8000x magnification micrograph of spray-dried primary particles of polymer aggregates made of polymethyl methacrylate. [Figure 3] 1 is a microscopic image of spray-dried primary particles of polymer aggregates made of polymethyl methacrylate at 10,000x magnification. [Figure 4]FIG. 1 is a plot of the gloss value (Y) calculated by experiments using test specimens prepared from the photocurable composition and the corresponding dynamic viscosity (Z) of the photocurable composition against the mass fraction of solid polymer particles (X) in the photocurable composition. DETAILED DESCRIPTION OF THE INVENTION

[0087] In the following, the present invention and preferred embodiments thereof will be explained and described in more detail with reference to experiments.

[0088] To illustrate the surprising technical effects of the photocurable composition according to the present invention, we consider below a reference system that the inventors typically use, for example, to test the effects of additives. Here, the reference system includes five radically polymerizable monomers with very different chemical structures. These represent the wide range of (meth)acrylates that are most frequently used in practice. For the reference system, PMMA particles were chosen as the solid polymer particles because they are available as sufficiently small particles and, based on experience, solid PMMA is a relatively representative material for polymerized (meth)acrylates. Neither the experiments presented here nor the accompanying tests performed by the inventors have been observed to support the assumption that the results can be transferred to other systems.

[0089] In the frame of reference, the following is used: A liquid monomer composition comprising a first monomer mixture and a second monomer mixture in a weight-related mixing ratio of 1 to 1.67, wherein the first monomer mixture contains equal weight proportions of tris(2-acryloyloxyethyl)isocyanurate, dicyclopentanylmethyl acrylate, and tricyclo[5.2.1.0 2.6 a liquid monomer composition comprising bisphenol A ethoxylate dimethacrylate and diurethane dimethacrylate in a weight ratio of 2:1; phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide as a photoinitiator; an additive composition consisting of 2-hydroxy-4-methoxybenzophenone (additive 1), titanium (IV) oxide (additive 2), lamp black (additive 3), and 5% PV FAST BLUE A2R in diurethane dimethacrylate (additive 4); and polymer particles made of polymethyl methacrylate, i.e., a polymer of methyl ester of methacrylic acid.

[0090] Photocurable compositions were prepared from these materials as described in Table 1, where values ​​are reported in percent as mass proportions. Of these compositions, Examples 1 to 5 are photocurable compositions according to the present invention, while Comparative Composition Example 1 is a comparative composition that does not contain solid polymer particles.

[0091] Table 1. Compositions of tested photocurable compositions with different solid polymer particle contents TIFF0007742846000001.tif69170

[0092] The minimum deviation from the total of all components being 100% was calculated by rounding down, but it is understood by those skilled in the art that the agreement does not affect the significance of the experiment, since, specifically, from the perspective of those skilled in the art, it is meaningless to state the mass percentages more precisely than the manufacturing procedure allows.

[0093] The liquid monomer composition contains five radically polymerizable monomers and is prepared by mixing these components. The photoinitiator is suitable for inducing polymerization of the liquid monomer composition by irradiating the composition with light. The polymer particles are solid, spherical polymer particles having diameters ranging from 0.7 to 2.0 μm. The above-described composition was prepared by the method of the present invention. Here, the polymer particles were introduced into the composition by adding spherical polymer aggregates having diameters of approximately 15 to 75 μm. The additives and photoinitiator were added to the liquid monomer composition before mixing with the polymer aggregates. Mechanical treatment of the base mixture to separate the solid polymer aggregates was carried out using a three-roll process using a three-roll mill. The mixture was homogenized twice with a roll gap of 5 μm. As a result of the mechanical treatment, the polymer particles were present in the composition of the present invention as dispersed, non-agglomerated particles, and no concentration gradient of the solid polymer particles was observed throughout the volume of the photocurable composition.

[0094] Figures 1 to 3 are microscopic images showing the polymer aggregates used at different magnifications (200x, 8000x, and 10000x), where the solid polymer particles are clearly recognizable as primary particles of the polymer aggregates.

[0095] The dynamic viscosity (Z) of the prepared samples at 23 °C was measured using a flowmeter (Anton Paar, Physiker NCR 301, 100 / s, viscosity range 200–3000 mPa·s at 23 °C) in accordance with DIN 1342-2;2003-11 for Newtonian fluids and DIN 1342-3;2003-11 for non-Newtonian fluids. The results are summarized in Table 2.

[0096] Table 2. Dynamic viscosity (Z) of tested photocurable compositions with different solid polymer particle contents. TIFF0007742846000002.tif54170

[0097] The measurements reveal that the viscosity of the photocurable compositions according to the invention is still low enough to allow their use in SLA or DLP processes, even at a weight fraction of 10% solid polymer particles. By extrapolating the increase in viscosity as a function of the weight fraction of polymer particles, it can be assumed that weight fractions of up to 30% are feasible, without examining the fundamental suitability of the compositions according to the invention for use in SLA or DLP processes.

[0098] At the same time, it proves advantageous that the viscosity of the photocurable composition can be set particularly easily by adding solid polymer particles to the photocurable composition according to the invention and can be adapted to the respective requirements, without the need for, for example, organic additives.

[0099] To test the gloss properties of dental parts made from the photocurable compositions according to the present invention, specimens measuring 60 mm x 10 mm x 3.3 mm were prepared by the DLP method. A Kulzer DLP printer (model Cara Print 4.0) was used. The specimens were prepared in either a horizontal or vertical position, i.e., the material layer produced in the DLP method was prepared parallel or perpendicular to the surface to be measured during the gloss measurement.

[0100] The gloss values ​​were measured using a gloss measurement method using a BYK device (type micro-TRI gloss) at an angle of 60 degrees. The values ​​obtained are summarized in Table 3.

[0101] Table 3: Gloss values ​​(Y) of tested specimens made from photocurable compositions with different solid polymer particle contents (including standard deviations) TIFF0007742846000003.tif61170

[0102] The gloss values ​​(Y) in the above table of laid-out products are plotted in FIG. 4 along with the dynamic viscosity (Z) against the weight fraction of solid polymer particles in the corresponding photocurable composition (X).

[0103] Experimental data clearly show that adding even small amounts of solid polymer particles with particle sizes in the range of 0.4 to 4 μm results in a favorable reduction in the gloss characteristics of test specimens. The observed effect is particularly pronounced in test specimens fabricated in a vertical configuration, i.e., when measuring the surface gloss of the surface parallel to the layer structure. Adding only 1.25% by weight of solid polymer particles results in a reduction in gloss characteristics of more than 75%. The data obtained here suggest that the effect increases with the amount of solid polymer particles. Therefore, there is no indication that there may be a threshold at which the effect is first observed. By selecting a suitable amount of solid polymer particles, the photocurable composition according to the present invention can be used to obtain a particularly matte surface of the dental part fabricated therefrom, which results in a corresponding surface with improved scannability.

[0104] Additionally, the average surface roughness Ra of selected specimens was measured and the obtained values ​​are summarized in Table 4.

[0105] Table 4. Average surface roughness (Ra) of tested specimens made from photocurable compositions with different solid polymer particle contents. TIFF0007742846000004.tif53170

[0106] Advantageously, the average surface roughness of the test specimens made with the photocurable composition according to the present invention is not too high compared to the comparative samples. Correspondingly, it is advantageously possible to produce dental parts that provide a smooth surface. Such dental parts are particularly easy to clean, allowing the applied paste-like molding material to be removed without leaving any residue.

Claims

1. A photocurable composition for producing a dental component by a DLP method or an SLA method, comprising, relative to the total mass of the photocurable composition: a liquid monomer composition having a mass proportion of 80% or more, the liquid monomer composition including one or more radically polymerizable monomers; one or more photoinitiators having a mixed mass proportion in the range of 0.001 to 10%; and solid polymer particles having a particle size in the range of 0.4 to 4 μm and a mixed mass ratio in the range of 0.5 to 15% dispersed in the liquid monomer composition.

2. 10. The photocurable composition of claim 1, wherein the solid polymer particles comprise a polymer of a monomer comprising a monofunctional (meth)acrylate.

3. 3. The photocurable composition of claim 1, wherein the solid polymer particles are present in the photocurable composition as non-agglomerated particles.

4. The photocurable composition according to any one of claims 1 to 3, wherein the liquid monomer composition contains a radically polymerizable monomer, and the boiling point of the radically polymerizable monomer at a pressure of 101.3 kPa is higher than 100°C.

5. 5. The photocurable composition according to claim 1, wherein the solid polymer particles have a particle size in the range of 0.5 to 2.5 μm.

6. 6. The photocurable composition according to claim 1, wherein the photocurable composition has a dynamic viscosity at 23° C. in the range of 0.1 to 10 Pa·s.

7. The photocurable composition according to any one of claims 1 to 6, wherein the solid polymer particles have an approximately spherical particle shape.

8. A method for producing a photocurable composition for producing a dental part by a DLP method or an SLA method, comprising: A) preparing or providing a liquid monomer composition comprising one or more radically polymerizable monomers; B) producing or providing a solid polymer agglomerate comprising agglomerated solid polymer particles having a particle size in the range of 0.4 to 4 μm; C) mixing the components produced or prepared in step A and step B to obtain a basic mixture, wherein the basic mixture contains the liquid monomer composition in a mass proportion of 80% or more and the solid polymer aggregate in a mixed mass proportion of 0.5 to 15% based on the total mass of the basic mixture; D) mechanically treating said base mixture to separate said solid polymer agglomerates and to disperse said solid polymer particles in said liquid monomer composition.

9. 9. The method according to claim 8, wherein the mechanically treating step is performed by a grinding process and / or a stirring process and / or a rolling process.

10. 8. Use of the photocurable composition according to any one of claims 1 to 7 for producing a dental part having a matte surface in a DLP or SLA process, wherein the surface of the dental part has a gloss value of 10 GU or less.

11. Use of solid polymer particles having a particle size in the range of 0.4 to 4 μm in a photocurable composition for producing a dental part by a DLP method or an SLA method, the use being for reducing the gloss characteristics of the dental part obtained by photocuring.

12. A kit for producing the photocurable composition of any one of claims 1 to 7, comprising, as separate components in separate containers: U solid polymer agglomerates comprising agglomerated solid polymer particles having a particle size in the range of 0.4 to 4 μm; V. a liquid monomer composition comprising one or more radically polymerizable monomers.

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