Method for producing ceramic and glass ceramic dental prostheses

Abstract

A method for preparing a full ceramic dental restoration having an integral core and shell structure, in which a digital build model of the dental restoration is built and then the obtained CAD dataset is divided into at least two different CAD partial datasets, one of which defines the contour of the core structure and the second partial dataset defines the contour of the shell structure, a green body of the core structure is produced by means of the first CAD partial data set, and a green body of the shell structure of the prosthesis is produced by means of the second CAD partial data set. The core and shell structures are then joined together in the state of a green body, then the green body is subjected to a heat treatment to remove the binder, and then the assembly is sintered to obtain a finished dental restoration. The method enables the manufacture of dental prostheses with improved aesthetic properties without significant additional efforts compared to the manufacture of unitary prostheses.

Description

Technical Field

[0001] This invention relates to a method for preparing ceramic and glass-ceramic dental restorations, such as dental inlays, onlays, veneers, crowns, bridges, and frames. Background Technology

[0002] For aesthetic reasons, dental restorations are increasingly being made entirely of ceramic. In practice, frames made of oxide ceramics are often fitted with glass-ceramic veneers.

[0003] DE102005042091A1 discloses a method for manufacturing ceramic dental prostheses, wherein a frame is milled from an oxide ceramic preform, such as alumina or zirconium dioxide, and a veneer is milled from a glass-ceramic block, such as silicate ceramic. The frame and veneer are prepared using a CAD / CAM method. The frame and veneer are then joined and fired using a low-viscosity, low-melting-point ceramic material. After sintering, the occlusal surfaces are milled, and the restoration is completed during glaze firing.

[0004] WO2007 / 051447A1 discloses a method for fabricating multilayer dental prostheses, wherein a supporting frame structure is first fabricated from metal, ceramic, or polymer materials using CAD / CAM, and then a functional layer is applied as a veneer. The functional layer is preferably fabricated using additive methods such as hot pressing, die casting, or grouting.

[0005] Milling ceramic molded components is disadvantageous because ceramic materials are very hard, making machining time-consuming and associated with high wear on the grinding equipment and milling cutters used. To avoid these drawbacks, WO2010 / 010087A1 proposes using porous ceramic bodies to manufacture veneers, which are applied to metal or ceramic frames. Veneers can consist of several layers with interfaces corresponding to the dentin / enamel interface of natural or artificial teeth. They are prepared by pressing commercially available veneer ceramic powder into blocks and then pre-sintering them. CAD / CAM systems are used to mill the veneers from the blocks, which are then fired onto a zirconia base crown and densely sintered. In this process, the different shrinkage behaviors of the frame and veneer materials must be considered.

[0006] DE102010002484A1 discloses the manufacture of a dental crown having an oxide ceramic core and a plastic, oxide ceramic, or glass ceramic outer layer. The interface between the core and the outer layer mimics the dentin-enamel boundary of a natural tooth. In this way, an appearance similar to that of a natural tooth is said to be achieved. The core is prepared using computer-aided methods, such as CAD / CAM or generative processes, while the outer layer is prepared by manual layering, overpressing, or using computer-aided methods. The outer layer is bonded to the core by adhesive bonding, sintering, or polymerization.

[0007] DE102016115916A1 discloses a method for generating processing data for fabricating dental prostheses with ceramic veneers and carriers. This method takes into account the different shrinkage factors of the carrier and the veneer, and is said to be the first to enable veneers and carriers made of different materials to be sintered together. The problem is that the carrier and veneer shells only fully adapt to each other during the final sintering process, making it difficult to precisely position the shell onto the carrier before sintering and increasing the risk of errors.

[0008] In addition to traditional milling methods, generative processes such as stereolithography are increasingly being used in the manufacture of dental restorations. In stereolithography, molded components are constructed layer by layer from liquid and curable monomer resin using computer-aided design data (CAD data) (A. Beil, Fertigung von Mikro-Bauteilenmittels Stereolithographie [Production of micro-components using stereolithography], Düsseldorf 2002, VDI-Publisher 3 ff.). Stereolithography is advantageous in the fabrication of dental molds made of ceramic materials because it significantly simplifies manual molding and casting methods, as well as milling and grinding operations, and avoids the substantial material loss associated with non-generative processes. With the establishment of a complete digital process chain, classical steps in the fabrication of dental restorations can be replaced by the digitization of models, virtual design of dental molds, and generative stereolithography fabrication.

[0009] For the stereolithography preparation of ceramic molded parts, a ceramic green body is first prepared by layer-by-layer radiation hardening of a ceramic slip, and then sintered into a dense ceramic mold after debinding. The green body is also called the green part. Debinding refers to the removal of the binder. In this paper, the binder used is typically decomposed and removed by heating the green body to a temperature of approximately 80°C to 600°C, through thermal and thermochemical processes to form volatile components. It is crucial to avoid the formation of cracks and deformation as much as possible.

[0010] Degreasing is a critical step in the process. The gases generated and the pressure exerted during the decomposition of the organic matrix pose a high risk of damaging the component. During degreasing, even small defects between individual build layers can lead to component breakage or even complete failure. This risk can be reduced by increasing the degreasing time, but this significantly increases the process time.

[0011] The components are sintered and degreased during a high-temperature firing process in a sintering furnace. Through the action of a temperature lower than the melting temperature of the main components, the finely dispersed ceramic powder is compacted and solidified, making the porous components smaller and increasing their strength.

[0012] US5,496,682 discloses a photocurable composition for preparing three-dimensional objects by stereolithography, comprising 40 to 70 vol% ceramic or metal particles, 10 to 35 wt% monomers, 1 to 10 wt% photoinitiator, 1 to 10 wt% dispersant, and preferably further comprising a solvent, a plasticizer, and a coupling agent.

[0013] US6,117,612 describes resins prepared by stereocuring for sintering ceramic or metal parts. The viscosity of the resin is less than 3000 mPa·s. Monomers with low viscosity are used in their preparation, preferably in aqueous solutions. The use of dispersants aims to obtain high solids content and low viscosity.

[0014] DE102005058116A1 discloses a suspension for stereocuring to prepare ceramic implants in a manner described in US 6,117,612, which does not contain any diluents such as water or organic solvents. The viscosity of the suspension is adjusted to less than 20 Pa·s by varying the concentration of the dispersant. Alkyl ammonium salts of copolymers having acidic groups are used as dispersants, thereby allowing them to be layered onto the ceramic powder particles.

[0015] US2005 / 0090575A1 describes a method and composition for stereolithography preparation of ceramic components. It is claimed that molded parts prepared with liquid materials known from US5,496,682 are soft and therefore require an additional hardening step to prevent deformation during firing, while molded parts obtained from paste-like materials accumulate internal stress during debinding, leading to cracking during sintering. To avoid these problems, a plasticizer is used and the amount of ceramic powder is selected such that the viscosity of the composition is at least 10,000 Pa·s.

[0016] EP2233449A1 discloses a slurry for preparing ceramic molded parts using a thermal inkjet printing method, comprising ceramic particles, wax, and at least one free-radical polymerizable wax, which produces a degreased green body without cracking. A disadvantage of these slurries is that they tend to separate in a liquid state when left to stand for extended periods. This is not significant in thermal inkjet printing because the slurry exists in liquid form only during the printing process, i.e., for a relatively short period. However, in stereolithography, the slurry must remain stable in liquid form for a longer period, which in particular means that particles dispersed in the slurry must not settle prematurely. Summary of the Invention

[0017] The purpose of this invention is to provide a method and materials for manufacturing all-ceramic dental restorations with high strength, which do not have the disadvantages of the prior art and can simplify the manufacture of aesthetically pleasing restorations with a natural appearance.

[0018] According to the invention, this task is solved by a method in which a dental restoration having a monolithic frame structure and a matching veneer structure is prepared separately by using an additive manufacturing method and then joined together to form a dental restoration. The frame structure is also referred to herein as a core structure or core. The veneer structure may be monolithic or comprise several components that together form the veneer structure. The veneer structure and its components are also referred to as a shell structure or shell. If the veneer structure comprises several components, these components are preferably also manufactured separately from each other.

[0019] In the first step of the method according to the present invention, a CAD (Computer-Aided Design) program is used to construct a digital design model of a dental prosthesis according to anatomical and clinical requirements. The CAD data set of the prosthesis obtained in this way is then divided into at least two different but not mutually independent partial data sets (file splitting), with the first CAD partial data set defining the contour of the core structure (core) of the dental prosthesis and the second CAD partial data set defining the contour of the shell structure (shell) of the dental prosthesis. The second partial data set can in turn be subdivided into two or more partial data sets, each partial data set including a part of the contour of the shell structure. One or more joining gaps can be provided at defined points between the contours. As a result, at least two CAD data sets are obtained, where each data set is saved by the CAD software in a suitable file format, preferably in STL format. Then, using CAM (Computer-Aided Manufacturing) software, the CAD data sets are used to generate processing data for the additive manufacturing of the (multiple) core and shell structures. The final output format is at least two different output files. Then, in a computer-controlled process, the generated data sets are used to additively manufacture the (multiple) core and shell structures independently of each other, preferably by stereolithography.

[0020] The (multiple) core and shell structures are designed according to desired requirements. The core structure is generally darker colored and less translucent compared to the lighter colored but more translucent shell structure. Their respective characteristics are suitable for the aesthetic requirements of the practitioner or patient or the condition of the remaining teeth.

[0021] To manufacture the dental prosthesis, preferably the first CAD partial data set is used to prepare a green body of the core structure of the prosthesis by locally applying radiation energy to cure a first slurry to form the geometry of the core structure.

[0022] In a further step, the second CAD partial data set is used to prepare a green body of the shell structure of the prosthesis by locally applying radiation energy to cure a second slurry to form the geometry of the shell structure.

[0023] If the shell structure includes more than one component, a separate green body is created for each part of the shell structure. To prepare a multi-component shell structure, the second CAD partial data set of the digital design model is divided into two or more additional CAD data sets (n 输出文件>2), where each dataset includes a portion of the shell structure's outline. Components are then manufactured using these CAD shell structure partial datasets through the following steps: using the first CAD shell structure partial dataset, a second ceramic slurry is hardened by locally applied radiation energy to form the geometry of a first component of the shell structure; separately, using the second CAD shell structure partial dataset, another ceramic slurry is hardened by locally introduced radiation energy to form the geometry of a second component of the shell structure; and this process is repeated as needed, depending on the number of CAD shell structure partial datasets, to produce a desired number of components. Each repetition produces a green body of one shell structure component.

[0024] To prepare shell-structured components, the same or different ceramic slurries can be used for each component. Preferably, the components are made of different, and particularly preferably different, colored slurries.

[0025] In subsequent steps, the core and shell structures, or core and shell structures, are joined together in the green state to obtain a green body of the joined dental restoration. Preferably, an additional slurry is used to improve the bonding of the individual components; this is referred to herein as a bonding ceramic slurry. The bonding ceramic slurry is preferably polymerizable, and particularly preferably free-radical polymerizable. Photoreactive bonding slurries are particularly preferred, i.e., slurries that can be cured by light irradiation, and the polymerization of the bonding ceramic slurry is preferably initiated by exposing the slurry to light. The polymerization of the bonding ceramic slurry enables a strong bond between the individual elements of the joined dental restoration in the green state.

[0026] Before component bonding and before applying the bonding ceramic slurry, the bonding surfaces of the core and / or shell structures can be individually characterized by applying a targeted, strongly stained slurry. Slurries with the same composition as those used to prepare the core and shell structures, but with a higher content of the color component, are particularly suitable for this purpose. These strongly stained slurries are preferably photoreactive and can be locally fixed by irradiation before applying the bonding ceramic slurry, and the various components of the dental restoration are ultimately bonded together.

[0027] The green dental restoration is then subjected to heat treatment in a further step to remove the binder (degreasing) and obtain a brown blank for the dental restoration. In a subsequent step, the brown blank of the dental restoration is sintered to obtain the final dental restoration.

[0028] The core-shell structured green body is preferably prepared by stereolithography. In this method, the core-shell structured ceramic green body is prepared by layer-by-layer radiation curing of a flowable ceramic slurry at a processing temperature, and then bonded together to form a green body for the dental restoration. Bonding can be done manually. Preferably, a bonding ceramic slurry is used to bond the green body. Photoreactive bonding ceramic slurry is particularly preferred, and it is hardened after bonding by irradiating it with light of a suitable wavelength. This increases the strength of the dental restoration green body, facilitates its processing, and reduces the risk of damage.

[0029] The raw dental restoration is then degreased, preferably by heating it to a temperature of 90°C to 600°C.

[0030] The resulting brown preform for the dental restoration is then sintered to form a dense ceramic molded body. Sintering is preferably carried out, for example, by heating to a temperature of 650 to 1800°C in a sintering furnace. The sintering conditions depend on the building material used. Brown preforms made of glass-ceramic are preferably sintered at 650 to 1100°C, particularly preferably 700 to 950°C; brown preforms made of zirconium dioxide are preferably sintered at 1100 to 1600°C, particularly preferably 1300 to 1500°C; and brown preforms made of alumina are preferably sintered at 1400 to 1800°C, particularly preferably 1600 to 1700°C.

[0031] The ceramic molded parts prepared according to the method of the present invention are characterized by high strength and high precision. For molded bodies made of glass-ceramic, the flexural strength according to ISO 6872 is preferably above 100 MPa, particularly in the range of 150 to 500 MPa. Molded bodies made of Al2O3 have a flexural strength preferably greater than 300 MPa, particularly 500 to 700 MPa, and molded bodies made of ZrO2 have a flexural strength greater than 500 MPa, particularly 800 to 1100 MPa.

[0032] According to the present invention, core and shell structures are prepared using slurries with similar coefficients of thermal expansion and similar sintering shrinkage rates, and, where applicable, as bonding ceramic slurries, this allows the green bodies of dental restorations to be degreased and sintered without any problems. The matching of the coefficients of thermal expansion and sintering shrinkage rates allows the green bodies of the core and shell structures to be prepared with a precise fit, as there is no need to consider different shrinkage behaviors. This greatly simplifies the bonding of the core and shell structures and reduces the risk of errors, such as those due to unintentional displacement of the shell structure on the core.

[0033] To facilitate the bonding of the core and shell structures, the core and shell structures can be provided with insertion slots, joints, ribs, or similar structures that ideally align the core and shell with each other, allowing the molded parts to be clearly and shape-fitted. Such structures can also exhibit optical functions after sintering. For example, they can mimic the natural mammary gland structure of teeth.

[0034] The dental prosthesis according to the invention comprises a supporting core structure and a shell structure. The shell structure is connected to the core structure. When the completed prosthesis is placed in the patient's mouth, the core structure is connected to one or more teeth to be restored, or to one or more implants. The shell structure may completely or preferably partially surround or cover the surface of the core. The shell structure of the dental prosthesis may include one or more, preferably one or two components that together form the shell structure. Preferably, the shell structure comprises only one component.

[0035] Using multiple components is more complex, but advantageous, because the concave core structure can be better encapsulated. Additionally, dividing the shell structure into several components is advantageous in terms of fabrication techniques. For example, it is easier to fabricate two separate components to cover the front and rear of the core structure than to fabricate a single shell structure covering both regions. Using a multi-component shell structure also reduces the risk of stress and cavitation during the joining process. Using multiple components also has aesthetic advantages. For example, several shell structures with different colors can be stacked on top of each other to achieve a particularly natural appearance.

[0036] For the preparation of core and shell structures and as a bonding ceramic slurry, a slurry containing the following is preferred:

[0037] (a) at least one monomer that can be polymerized by free radicals,

[0038] (b) at least one photoinitiator and

[0039] (c) Ceramic, glass and / or glass-ceramic particles.

[0040] The slurry according to the invention comprises at least one (meth)acrylate and / or (meth)acrylamide as monomer (a), preferably a monofunctional or polyfunctional (meth)acrylate, or a mixture thereof. Particularly preferred are materials containing at least one polyfunctional (meth)acrylate or a mixture of monofunctional and polyfunctional (meth)acrylates as radically polymerizable monomers. A monofunctional (meth)acrylate is a compound having one radically polymerizable group, and a polyfunctional (meth)acrylate is a compound having two or more, preferably two to six radically polymerizable groups.

[0041] Particularly preferred monofunctional or polyfunctional (meth)acrylates are methyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, butyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate or isobornyl (meth)acrylate, p-cumyl-phenoxyethylene glycol methacrylate (CMP-1E), bisphenol A di(meth)acrylate, bis-G(M)A (an addition product of (meth)acrylate and bisphenol A diglycidyl ether), ethoxy- or propoxylated bisphenol A di(meth)acrylate, such as bisphenol-A-di(meth)acrylate having 3 ethoxy groups (SR-348C = methacrylate; SR-349 = acrylate, Sartomer) or 2 ethoxy groups (SR-348L = methacrylate, Sartomer), 2,2-bis[4-(2-(methyl)methacrylate) Acryloyloxypropoxyphenyl]propane, UD(M)A (an addition product of 2-hydroxyethyl methacrylate and 2,2,4- or 2,4,4-trimethylhexamethylene-1,6-diisocyanate), di-, tri-, tetra-, penta-, hexa- or hepta-ethylene glycol di(meth)acrylate, di-, tri-, tetra-, penta-, hexa- or hepta-propane glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and glyceryl di(meth)acrylate and glyceryl tri(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate (D3MA), 1,12-dodecanediol di(meth)acrylate, oligomeric polyether-, polyester-, epoxy-, urethane- (meth)acrylate, tricyclodecanediethanol di(meth)acrylate, and mixtures thereof.

[0042] Particularly preferred are monofunctional, difunctional, and trifunctional acrylates and methacrylates with a molecular weight <1000 g / mol, such as aliphatic carbamate diacrylates and phthalate HEA esters (Photomer). 4173), pyromellitic ester diHEA (HEA = 2-hydroxyethyl acrylate), bisphenol A di(meth)acrylate, bis-G(M)A (an addition product of (meth)acrylate and bisphenol A diglycidyl ether), ethoxylated or propoxylated bisphenol A di(meth)acrylate, such as bisphenol A di(meth)acrylate (SR-348C, SR-349, SR-348L), 2,2-bis[4-(2-(meth)acryloyloxypropoxy)phenyl]propane, UD(M)A, triethylene glycol di(meth)acrylate (TEGD(M)A), tricyclodecanediethanol di(meth)acrylate, ethoxylated or propoxylated trimethylolpropane tri(meth)acrylate, such as 3-propoxylated trimethylolpropane triacrylate (Sartomer SR-492), tripropylene glycol diacrylate and mixtures thereof. These monomers are characterized by high reactivity / high double bond conversion, good mechanical properties, low polymerization shrinkage, and relatively low viscosity.

[0043] Other suitable monomers are acrylamides, such as N-ethylacrylamide, N,N-dimethylacrylamide, N-(2-hydroxyethyl)acrylamide, N,N'-diethyl-1,3-bis(acrylamido)-propane, and 1,4-bis(acrylamido)butane. Bisacrylamides are preferred for use in organic binders in excess compared to monoacrylamides.

[0044] The properties of the slurry before and after UV curing are influenced by the specific combination of monomers. Mixtures of monofunctional and difunctional monomers are characterized by relatively low viscosity and reactivity of the resin mixture, with viscosity and reactivity decreasing as the content of the monofunctional monomer decreases. The content of monofunctional monomers ensures lower brittleness and faster debinding of the green body obtained from the UV-cured slurry. Mixtures of difunctional and trifunctional monomers exhibit higher reactivity, with reactivity increasing as the content of the trifunctional monomer increases. The content of trifunctional monomers leads to higher brittleness and slower debinding of the green body.

[0045] The reactivity, viscosity, and polymerization shrinkage of the resin mixture are also determined by the molar mass of the monomers; thus, polymerization shrinkage decreases with increasing molar mass, while viscosity increases. Finally, the interaction with the materials in the stereocuring bath, such as the swelling of the polymerization bath material, is affected by the polarity of the monomers.

[0046] Preferred photoinitiators (b) for initiating free radical photopolymerization are benzophenone, benzoin and its derivatives, or diketones or their derivatives, such as 9,10-phenanthroquinone, 1-phenylpropane-1,2-dione, butanedione or 4,4'-dichlorobenzoyl. Particularly preferred are camphorquinone (CQ) and 2,2-dimethoxy-2-phenylacetophenone, and particularly preferred are combinations of α-diketones with amines as reducing agents, such as 4-(dimethylamino)benzoate (EDMAB), N,N-dimethylaminoethyl methacrylate, N,N-dimethyl-symmetric-dimethylamine or triethanolamine.

[0047] Particularly preferred photoinitiators are Norrish type I photoinitiators, especially monoacyl or diacylphosphine oxides, particularly monoacyltrialkylgermanium compounds or diacyldialkylgermanium compounds, such as benzoyltrimethylgermanium, dibenzoyldiethylgermanium, or bis(4-methoxybenzoyl)diethylgermanium (MBDEGe). Advantageously, mixtures of various photoinitiators, such as combinations of bis(4-methoxybenzoyl)diethylgermanium with camphorquinone and ethyl 4-dimethylaminobenzoate, can also be used.

[0048] Of particular preference are camphorquinone (CAS No. 10373-78-1) and ethyl 4-(dimethylamino)benzoate (EMBO, CAS No. 10287-53-3), as well as Norrish type I photoinitiators, especially 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO, CAS No. 75980-60-8), ethyl(2,4,6-trimethylbenzoyl)phenylphosphine ester (TPO-L, CAS No. 84434-11-7), phenyl-bis(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure 819, CAS 162881-26-7), and bis(2,6-difluoro-3-(1-hydropyrrolo-1-yl)phenyl)dicenoctanetane (Irgacure 784, CAS no.). Combinations of 125051-32-3), 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone (Irgacure 369, CAS no. 119313-12-1), 1-butanone-2-(dimethylamino)-2-(4-methylphenyl)methyl-1-4-(4-morpholino)phenyl (Irgacure 379, CAS No. 119344-86-4), and especially bis(4-methoxybenzoyl)diethylgermanium (MBDEGe; Ivocerin).

[0049] As component (c), the slurry according to the invention comprises ceramic and / or glass particles and / or glass-ceramic particles. Ceramics are understood as inorganic materials having a crystalline structure and are typically prepared from corresponding powders. Preferably, the ceramic is prepared by sintering (sintered ceramic). Oxide ceramics are preferably obtained by sintering metal oxide powders such as ZrO2 or Al2O3.

[0050] According to the invention, a slurry comprising glass and / or glass-ceramic particles as component (c) is preferred. Glass-ceramics are materials typically prepared from amorphous glass, particularly silicate glass, through controlled crystallization, wherein a glassy phase and one or more crystalline phases exist side-by-side in a solid. Glass or glass-ceramic particles comprising leucite, apatite, and most preferably lithium pyrosilicate crystals are particularly preferred. Glass-ceramics can be prepared from glass powder of a suitable composition that does not contain any microcrystals by heat treatment (crystallization and sintering). According to one embodiment, the slurry according to the invention can therefore contain glass powder that transforms into the corresponding glass-ceramic only after sintering of the dental restoration.

[0051] According to other preferred embodiments, in addition to pure glass or glass-ceramic powders, mixtures of glass and glass-ceramic powders can also be used. Based on the total mass of the glass and glass-ceramic powders, the preferred mixture contains 0.5 to 99.99% by weight of glass-ceramic powder, with the proportion of glass powder preferably corresponding to a difference of 100% by weight. In this way, sintering activity and dimensional stability can be adjusted. Glass has higher sintering activity (fewer pores, smoother surface), while glass-ceramic powder has higher dimensional stability (no deformation). Furthermore, the glass-ceramic powder in the slurry is chemically more stable, resisting ionic dissolution and the formation of carbonates and other undesirable products, resulting in more stable slurry properties.

[0052] Preferred glass-ceramics according to the present invention are described in detail in EP1505041A1, EP2261184A1, EP2377830A1 and EP2377831A1. Lithium silicate materials described in DE10336913A1 are particularly preferred, and lithium pyrosilicate glass-ceramics described in EP0827941A1 are particularly preferred.

[0053] The ceramic, glass, or glass-ceramic particles used as component (c) are preferably colored, and particularly preferably, different colored pastes are used to prepare the core and shell structures. To obtain a natural appearance for the dental restoration, which mimics the core-shell imprint of the tooth formed by dentin and enamel, the paste used to prepare the core is stained darker and more opaque, while the paste used to prepare the shell structure is stained lighter and more transparent to match natural tooth enamel.

[0054] For this purpose, ceramic, glass, and / or glass-ceramic particles are preferably mixed with one or more pigments. Inorganic pigments, such as oxides of Pr, Tb, Ce, Co, Ni, Cu, Bi, La, Nd, Sm, Eu, and Gd, and especially oxides of Fe, Mn, Cr, and Er, are particularly preferred. AB₂O₄ type coloring spinel compounds can also be advantageously used for coloring ceramic or glass-ceramic powders, wherein A is preferably an alkali metal or alkaline earth metal ion, and B is a transition metal ion with an oxidation state higher than A. Spinels are particularly suitable for coloring glass-ceramics, especially lithium pyrosilicate glass-ceramics. The coloring components are added in the amount required to achieve the desired color. Preferably, the type and amount of (multiple) coloring components are selected such that a tooth-colored ceramic mold is obtained after debinding and sintering. The color imprint is ultimately formed only during sintering. Typically, the amount of each coloring component is 0.01 to 1% by weight, preferably 0.05 to 0.5% by weight, based on the total mass of component (c). Alternatively, ceramic, glass, or glass-ceramic powders can also be colored by adding glass coloring oxides (so-called ion coloring) according to EP0827941A1. Preferred glass coloring oxides are TiO2, CeO2, and / or Fe2O3.

[0055] To obtain the desired color imprint, mixtures of ceramic, glass, or glass-ceramic powders with different colors can also be used.

[0056] The particle size of component (c) is preferably in the range of 10 nm to 100 µm, more preferably in the range of 100 nm to 10 µm. This depends on the ceramic used. For Al2O3, the particle size used as component (c) is preferably in the range of 50 to 500 nm, particularly preferably 75 to 200 nm; for glass powder and / or glass-ceramic powder, it is in the range of 500 nm to 50 µm, most preferably 1 to 15 µm; for TZP-3Y zirconium dioxide, it is in the range of 50 to 500 nm, most preferably 50 to 350 nm. The particle size is preferably selected in a manner that yields a sedimentation-stable slurry. The specified lower and upper limits of the particle size range are the D10 and D90 values, respectively. Therefore, a range of 500 nm to 50 µm means a D10 value of 500 nm and a D90 value of 50 µm, i.e., 10 vol% of the particles are less than 500 nm and 90 vol% of the particles are less than 50 µm.

[0057] In addition, ceramic, glass, or glass-ceramic particles with a particle size range of 10 to 200 nm can also be used as nanosols or organosols, i.e., dispersions of nanoparticles in a solvent, a suitable monomer of component (a), or a mixture thereof. This is also the D10 or D90 value.

[0058] Static light scattering (SLS) is preferred, for example, using a static laser scattering particle size analyzer LA-960 (Horiba, Japan) or a Microtrac S100 particle size analyzer (Microtrac, USA) for particle size determination in the range of 0.1 µm to 1000 µm. The light sources used are a laser diode with a wavelength of 655 nm and an LED with a wavelength of 405 nm. Using two light sources with different wavelengths allows the entire particle size distribution of the sample to be measured in a single measurement operation, thus the measurement is performed as a wet measurement. For this purpose, an aqueous dispersion of the packing material is prepared, and its scattered light is measured in a flow cell. The scattered light analysis used to calculate particle size and particle size distribution is performed according to DIN / ISO 13320 based on Mie theory. Particle size measurements in the range of 1 nm to 0.1 µm are preferably performed by dynamic light scattering (DLS) of the aqueous particulate dispersion, preferably using a He-Ne laser with a wavelength of 633 nm, at a scattering angle of 90° and at 25°C, for example using a Malvern Zetasizer Nano ZS (Malvern Instruments, Malvern UK).

[0059] In the case of aggregated and clustered particles, the major particle size can be determined using TEM imaging. Transmission electron microscopy (TEM) is preferably performed using a Philips CM30 TEM at an accelerating voltage of 300 kV. For sample preparation, droplets of the particle dispersion are applied to a 50 Å thick copper mesh (300 mesh size) coated with carbon, and then the solvent is evaporated. The particles are counted, and the arithmetic mean is calculated.

[0060] According to the present invention, glass and lithium pyrosilicate glass-ceramics having the following composition are particularly preferred:

[0061] SiO2 57.0 to 80.0% by weight

[0062] Al2O3 0 to 5.0% by weight

[0063] La2O3 0.1 to 6.0 wt%

[0064] MgO 0 to 5.0 wt%, particularly 0.1 to 5.0 wt%.

[0065] ZnO 0 to 8.0% by weight

[0066] K2O 0 to 13.5% by weight

[0067] Li2O 11.0 to 19.0% by weight

[0068] P2O5 0 to 11.0% by weight

[0069] Color component 0 to 8.0% by weight

[0070] The other components are 0 to 6.0% by weight.

[0071] thus

[0072] Al2O3 + La2O3 is 0.1 to 7.0% by weight and

[0073] The concentration of MgO + ZnO ranges from 0.1% to 9.0% by weight.

[0074] Furthermore, the color components are formed from glass-colored oxides and / or color bodies in the following amounts:

[0075] Glass-colored oxides 0 to 5.0% by weight and

[0076] Chromogens 0 to 5.0% by weight.

[0077] Preferred glass-coloring oxides are TiO2, CeO2, and / or Fe2O3. Preferred chromophores are metal oxides commonly used in dental glass ceramics, such as the aforementioned inorganic pigments, particularly commercially available isochromatic chromophores, such as colored or doped spinel and / or doped ZrO2. Chromophores can be non-fluorescent or fluorescent materials. Unless otherwise stated, all percentages herein refer to the total mass of the glass ceramic.

[0078] According to the present invention, the individual components of the preferred glass or lithium pyrosilicate glass-ceramic have preferred quantity ranges. These quantity ranges can be selected independently of each other, and are as follows:

[0079] SiO2 57.0 to 75.0% by weight

[0080] Al2O3 0 to 2.5% by weight

[0081] La2O3 0.1 to 4.0 wt%

[0082] MgO 0.1 to 4.0 wt%

[0083] ZnO 0 to 6.0 wt%, particularly 0.1 to 5.0 wt%.

[0084] K2O 0 to 9.0% by weight, particularly 0.5 to 7.0% by weight.

[0085] Li2O 13.0 to 19.0% by weight

[0086] P2O5 0 to 8.0 wt%, particularly 0.5 to 8.0 wt%.

[0087] Color component 0.05 to 6.0% by weight

[0088] The other components are 0 to 3.0 by weight.

[0089] In addition to the components mentioned, glass or lithium pyrosilicate glass ceramics may contain other additional components, particularly B₂O₃, F, Na₂O, ZrO₂, BaO, and / or SrO. The viscosity of the residual glass phase in glass ceramics is affected by B₂O₃ and F, which are believed to alter the ratio of surface crystallization to volumetric crystallization, favoring surface crystallization.

[0090] Preferably, the glass or lithium pyrosilicate glass-ceramic is essentially composed of the above-mentioned components.

[0091] To prepare glass or lithium pyrosilicate glass-ceramics, a starting glass containing the aforementioned components, excluding the chromophore, is melted at a temperature of 1200 to 1650 °C. For this purpose, suitable starting materials such as carbonates, oxides, and fluorides are tightly mixed together and heated to a specified temperature. If coloring oxides are to be used, these are added to the mixture. The resulting molten glass is poured into water to form glass particles, which are then pulverized into powder with the desired particle size. Any present chromophores are then added to the powder. This glass powder can then be used to prepare the desired slurry. In this case, the glass-ceramic is formed during sintering. Preferably, the glass powder is subjected to heat treatment at a temperature range of 400 to 1100 °C. The heat treatment is used to initiate the crystallization of the initial glass, thus forming the glass-ceramic, which exists after the heat treatment and can then be used to prepare the ceramic slurry. As described above, a mixture of glass and glass-ceramic powders can also be used to prepare the ceramic slurry.

[0092] Preferred glass and lithium pyrosilicate glass ceramics according to the present invention are described in detail in EP0827941A1, whereby the glass ceramics specifically described therein are particularly preferred.

[0093] According to a preferred embodiment of the invention, the particles of component (c) are surface-modified with a suitable substance. For surface modification, chemical bonding is preferred, i.e., compounds chemically bonded to the surface of ceramic, glass, and / or glass-ceramic particles via ionic or covalent bonds. Preferably, the compound contains an acidic group, preferably a carboxylic acid, phosphonic acid, hydrogen phosphate group, or acidic phosphate ester group, or a silyl group, preferably an alkoxysilyl group. The particle surface may be partially or preferably completely covered by the modifier. The modifier used according to the invention is a monomeric compound.

[0094] According to the invention, such compounds are particularly suitable, as opposed to so-called adhesion promoters or coupling agents, containing only groups that react with the particle surface, but not groups that can be free-radicalized to form covalent bonds with the resin matrix (a). Such compounds are referred to herein as non-polymerizable surface modifiers. The advantage of these compounds is that no stable bond appears between the particle surface and the polymer matrix in the cured green body, which simplifies the complete removal of the polymer components during degreasing.

[0095] Suitable nonpolymerizable surface modifiers are particularly linear or branched carboxylic acids, such as formic acid, acetic acid, propionic acid, octanoic acid, isobutyric acid, isovaleric acid, neopentanoic acid, or phosphonic acids, such as methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, hexylphosphonic acid, octylphosphonic acid, or phenylphosphonic acid. Suitable silanes as nonpolymerizable surface modifiers are, for example, propyltrimethoxysilane, phenyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, trimethylchlorosilane, trimethylbromosilane, trimethylmethoxysilane, or hexamethyldisilazane. Particularly preferred are acidic phosphate esters, such as dimethyl phosphate, diethyl phosphate, dipropyl phosphate, dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, dioctyl phosphate, or di(2-ethylhexyl) phosphate.

[0096] Polymers, particularly polyelectrolytes such as polycarboxylic acids or polycarboxylate salts, or nonionic polymers such as polyethylene glycol or carboxymethyl cellulose, are also suitable as surface modifiers for aqueous slurries. Polyelectrolytes carrying ionic groups, such as ammonium polycarboxylate, can be adsorbed relatively readily onto solid surfaces, thereby imparting a charge to the particles. In the case of organic, non-aqueous slurries, polymers soluble in the polymerizing resin are suitable. Modifiers with molecular weights in the range of 50 to 5000 g / mol are preferred.

[0097] Depending on the quality of the slurry, the surface modifier may optionally be used in an amount preferably from 0.1 to 5% by weight, particularly preferably from 0.2 to 2% by weight, and most preferably from 0.5 to 1.5% by weight.

[0098] The slurry according to the invention may contain one or more nonionic surfactants as component (d). Nonionic surfactants are substances with surface-active properties that do not form ions in aqueous media. They are molecules with hydrophobic and hydrophilic portions. The overall hydrophobicity of the molecule can be tuned by selecting the length and type of the hydrophobic and hydrophilic portions.

[0099] According to the invention, nonionic surfactants with HLB values ​​preferably in the range of 3 to 16, particularly 4 to 13, and especially 4 to 10 are preferred. The HLB value is determined according to the Griffin method.

[0100] Preferred nonionic surfactants (d) are fatty alcohols, carbonyl synthetic alcohols or ethoxylated fatty acids, fatty acid esters of sugars and hydrogenated sugars, alkyl glycosides, and block polymers of ethylene oxide and propylene oxide, especially short-chain block co-oligomers.

[0101] Particularly preferred are fatty acid esters of hydrogenated sugars, especially those having the formula R'-CO-O-sugar, where R' is a branched or preferably straight-chain alkyl group having 10 to 25 carbon atoms, preferably 12 to 22 carbon atoms. Straight-chain alkyl groups having 16 to 22 carbon atoms are particularly preferred. "Sugar" refers to a hydrogenated sugar residue, which is preferably ethoxylated 1 to 5 times. Particularly preferred are fatty acid esters of sorbitol, especially sorbitan stearates, such as sorbitan monostearate (CAS 1338-41-6).

[0102] Other groups particularly favor surfactants that are ethoxylated fatty acids, especially those with the general formula R''-(CO)-(OCH2CH2). m Those with -OH, wherein R'' is a branched or preferably straight-chain alkyl group having 10 to 25 carbon atoms, preferably 12 to 22 carbon atoms. Straight-chain alkyl groups having 16 to 22 carbon atoms are particularly preferred. m is an integer from 2 to 20, preferably 2 to 10, and particularly preferably 2 to 6.

[0103] According to the present invention, the particularly preferred surfactant (d) is an ethoxylated fatty alcohol, especially having the general formula R-(OCH2CH2). n -OH polyalkylene glycol ethers, wherein R is an alkyl group having 10 to 20 carbon atoms, and n is an integer from 2 to 25. R can be a branched or preferably straight-chain alkyl group having 12 to 22 carbon atoms, particularly a straight-chain alkyl group having 12 to 22 carbon atoms. Particularly preferred alkyl groups are lauryl, cetyl, cetearyl, and stearyl.

[0104] Polyalkylene glycol ethers are obtained by reacting the corresponding fatty alcohol with ethylene oxide (EO). The index n represents the number of ethylene oxide residues. Preferred polyalkylene glycol ethers have 2 to 21 (n = 2-21), particularly 2 to 12 (n = 2-12), and especially 2 to 5 (n = 2-5) ethylene oxide groups.

[0105] According to the present invention, a preferred example of a polyalkylene glycol ether is one in which R is a cetyl group (C 16Compounds with n being 20, especially 2, are designated as Ceteth-2 and Ceteth-20 by their INCI names. For example, Ceteth-2 has the molecular formula C2. 16 H 33 -(OCH2CH2)2-OH.

[0106] A further preferred embodiment is where R is a stearyl group (C 18 Compounds in which n is 2, 10, 20, or 21 (groups). These compounds are designated by INCI as steareth-2, steareth-10, steareth-20, and steareth-21. For example, steareth-2 has the molecular formula C2. 18 H 37 -(OCH2CH2)-OH.

[0107] Particularly preferred nonionic surfactants are stearyl alcohol polyether-20 (HLB=15.3), stearyl alcohol polyether-10 (HLB=12.4), cetyl alcohol polyether-20 (HLB=12.9), especially stearyl alcohol polyether-2 (HLB=4.9) and cetyl alcohol polyether-2 (HLB=5.3).

[0108] Mixtures of different nonionic surfactants, especially mixtures of different polyalkylene glycol ethers, can also be used.

[0109] INCI stands for International Nomenclature of Cosmetic Ingredients. It is an international guide for the correct disclosure of cosmetic ingredients. According to the present invention, it has been surprisingly found that the use of nonionic surfactants, commonly used in the manufacture of cosmetic and pharmaceutical products, significantly improves the properties of slurries used in the stereolithography preparation of ceramic and glass-ceramic bodies.

[0110] It has been found that the nonionic surfactant used according to the invention is homolytically miscible with free-radical polymerizable monomers, particularly acrylates and methacrylates, without impairing the polymerization of these monomers. Therefore, high reactivity and short exposure and processing times can be ensured in the stereolithography of the liquid slurry according to the invention. Advantageously, the nonionic surfactant is also readily miscible with short-chain polar and highly reactive monomers.

[0111] The nonionic surfactants according to the invention are preferably solid at temperatures <20°C, particularly preferably <30°C. As a result, they cause the slurry to solidify, i.e., the slurry has a paste-to-solid consistency at temperatures <20°C, preferably <30°C. One advantage of this is that uniform solidification prevents particle settling, thus significantly improving storage stability when stored in a solid state at room temperature. In addition, compared to green bodies made from slurries without component (d), the nonionic surfactants improve the strength of the polymerized material (green body) at room temperature.

[0112] The slurry preferably contains a nonionic surfactant with a melting point of 20°C to 120°C, more preferably 20°C to 100°C, and particularly preferably 20°C to 60°C. The slurry components are uniformly miscible above the melting point of component (d) and uniformly solidify below the melting point of component (d). This effectively prevents the sedimentation of particles below the melting point of component (d). This ensures the stability of the mixture over a long period of time.

[0113] Of particular advantage is that the nonionic surfactant used according to the present invention can effectively prevent premature sedimentation of particles even in the liquid state, thus giving the slurry high stability during processing.

[0114] Due to the excellent dispersibility of particles by nonionic surfactants, slurries can also be filled with ceramic, glass and / or glass-ceramic powders to a significantly higher degree, resulting in greater green density.

[0115] Another advantage of the preferred nonionic surfactants (d) according to the invention is that, due to their relatively low molecular weight, they melt during degreasing and flow out or evaporate from the matrix. They do not impede the degreasing process but rather create channels that facilitate the release of organic matrix decomposition products, thus promoting degreasing. During heating in the oven, the molecules of the nonionic surfactant (d) located between the polymer chains in the matrix flow out of the preform in liquid form before the partial depolymerization and subsequent pyrolysis of the mixture. Therefore, the risk of defects such as cracks or even mold body failure is at least significantly reduced during degreasing, and often completely eliminated. Furthermore, the outflow / evaporation of component (d) has already removed some organic matter at a relatively low temperature, and further heating can be carried out rapidly until all organic components have been completely removed, whereas previously only relatively low heating rates were possible.

[0116] In addition to the above-mentioned components, the slurry according to the present invention preferably contains at least one additive selected from colorants, ultraviolet absorbers, optical brighteners, solvents, inhibitors, degreasing accelerators, defoamers and / or skin formation inhibitors.

[0117] Organic dyes are preferred as colorants, particularly azo dyes, carbonyl dyes, cyanide dyes, azomethines and methines, phthalocyanines, and dioxazines. Dyes soluble in slurries, especially azo dyes, are particularly preferred. A particularly preferred dye is 4-(4-nitrophenylazo)aniline (Disperse Orange 3, CAS No. 730-40-5). Furthermore, dyes that absorb in the same wavelength range as the polymerization initiator are particularly preferred. Dyes with maximum absorption corresponding to the wavelength of light used for curing are particularly preferred. Dyes with maximum absorption in the range of 350 to 550 nm, preferably 380 to 480 nm, are highly advantageous.

[0118] Unlike coloring components used to color ceramic or glass-ceramic powders, colorants here are understood as substances that completely burn during debinding and sintering. These colorants are used only to color the paste, thus facilitating its processing. They are not used to color the ceramic itself. Coloring can help in making it easier to distinguish different ceramic pastes. Additionally, dyes absorb transmitted light during stereolithography printing and reduce their penetration depth into the material, making more precise printing of objects possible, which is particularly advantageous for very transparent ceramic pastes.

[0119] Preferred UV absorbers are 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol], 2,2',4,4'-tetrahydroxybenzophenone, 2-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl)-4-methylphenol, 2,2'-benzyl-1,4-diylbis(4h-3,1-benzoxazin-4-one), and 2-(4,6-bis(2,4-dimethylbenzyl) The preferred optical brighteners are 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene, 2-(2-hydroxy-5-methylphenyl)-benzotriazole, and 2-(2H-benzotriazole-2-yl)-6-dodecyl-4-methylphenol. According to the invention, a preferred optical brightener is 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene. Particularly preferred are ultraviolet absorbers and optical brighteners whose maximum absorption corresponds to the wavelength of light used for curing.

[0120] Organic solvents are preferred as solvents, especially those with a boiling point of at least about 120°C, preferably 150 to 250°C, to prevent premature evaporation during the stereolithography process of the slurry. Solvent mixtures that can gradually evaporate within a temperature range of 150 to 250°C are particularly suitable. Particularly suitable solvents include n-octanol, triethylene glycol divinyl ether, 2-amino-2-methyl-1-propanol, 2-methyl-2,4-pentanediol, tripropylene glycol, tetraethylene glycol, triethylene glycol, triethyl citrate, ethyl acetoacetate, cyclohexanol, cyclohexanone, diethylene glycol monomethyl ether, dibutyl oxalate, 2,5-dimethoxytetrahydrofuran, polyethylene glycol 300, 1- or 2-nonanol, diethylene glycol diethyl ether, and mixtures thereof.

[0121] Preferred solvents also include polyethylene glycol (PEG), polypropylene glycol (PPG), PEG-PPG copolymers, glycerol and glycerol derivatives, especially ethoxylated and / or propoxylated glycerol, as well as phthalates, benzoates and alicyclic esters. Particularly preferred solvents have a Mw of less than 5000 g / mol, preferably less than 1000 g / mol. Suitable solvents are compounds that are liquid at room temperature and do not react with other components of the slurry under storage and application conditions. Particularly preferred solvents are PEG 200-600 g / mol, PPG 200-800 g / mol, co-PEG-PPG 200-800 g / mol, especially polypropylene glycol about 400 g / mol, diethyl phthalate, dimethyl phthalate, ethyl benzoate, butyl benzoate, benzyl benzoate, diethylene glycol dibenzoate, and diisononyl 1,2-cyclohexanedicarboxylate. Advantageously, mixtures of these solvents can also be used.

[0122] Depending on the quality of the slurry, one or more solvents are preferably used in a total amount of 0 to 50% by weight, particularly preferably 3 to 20% by weight.

[0123] The evaporation of the aforementioned solvents was found to further promote the formation of micropores in the green body. These pores close in the same manner as the channels formed by the outflow or evaporation of nonionic surfactants during sintering. They facilitate the escape of gases during degreasing, thus preventing stress and crack formation. Furthermore, the risk of delamination due to stereocuring is reduced, and complete removal of all organic components is facilitated.

[0124] Alternatively, the porosity of the green body can also be increased by removing the leaching components before heat treatment. A suitable extractable component must be matched with the extractant. Water can be used as the extractant for oxide ceramic particles. In this case, water-soluble polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene glycol are suitable. For water-sensitive ceramic, glass, and glass-ceramic particles, extraction can be performed using organic solvents, especially non-polar solvents. In this case, for example, substances soluble in gasoline such as long-chain fatty acid esters are suitable as extractable components. Based on the mass of the slurry, the preferred amount of the extractable component is 0 to 30% by weight, particularly preferably 1 to 20% by weight.

[0125] The slurry according to the invention can advantageously contain inhibitors as stabilizers, as other additives to prevent spontaneous polymerization. Inhibitors or stabilizers improve the storage stability of the slurry and also prevent uncontrolled polymerization in the stereochemical curing tank. The inhibitors are preferably added in an amount such that the slurry is stable during storage for approximately 2 to 3 years. Particularly preferably, in each case, the amount of inhibitor is 0.001 to 1.0% by weight, most preferably 0.001 to 0.50% by weight, based on the total mass of the slurry.

[0126] Preferred inhibitors are so-called aerobic inhibitors, particularly phenols such as hydroquinone monomethyl ether (MEHQ) or 2,6-di-tert-butyl-4-methylphenol (BHT), which are effective only in the presence of oxygen and are preferably used at concentrations in the range of 100 to 2000 ppmw. Suitable anaerobic inhibitors are phenothiazines, 2,2,6,6-tetramethylpiperidin-1-oxygen radicals (TEMPO), iodine, and cuprous iodide (I). These are effective even at low concentrations, preferably 10 to 50 ppm, and even in the absence of oxygen. Polymerization only occurs when these additives have been used up. The use of a mixture of aerobic and anaerobic inhibitors is advantageous.

[0127] In each case, based on the total mass of the slurry, the amount of aerobic inhibitor is preferably 0.001 to 0.50% by weight, and the amount of anaerobic inhibitor is preferably 0.001 to 0.02% by weight. Also based on the total mass of the slurry, a preferred mixture contains 0.005 to 0.10% by weight of aerobic inhibitor and 0.001 to 0.01% by weight of anaerobic inhibitor.

[0128] According to other embodiments of the invention, the slurry contains a so-called degreasing accelerator as an additional additive. In each case, it is used in an amount of 0 to 20% by weight, particularly preferably 0.01 to 10% by weight, based on the total mass of the slurry. The degreasing accelerator is a substance that promotes the removal of binder during the degreasing process.

[0129] For example, the degreasing of green bodies can be promoted or specifically influenced by polymerization reactive substances in polymerizable resins. On one hand, these are additives that affect network formation, such as chain transfer active substances, so-called chain regulators, which lead to a decrease in polymer network density and thus better thermal degradability. Known chain regulators, such as those used in free radical polymerization, are primarily thiols, such as lauryl thiols and disulfides. Disulfides, especially dithiocarbamate disulfides, such as tetramethylthiuram disulfide or isopropyl xanthate disulfide, act as so-called photoinitiator-transfer terminators in free radical photopolymerization. These are compounds that act as both photoinitiators (photoinitiator-) and participants in both transfer reactions (-transfer-) and termination reactions (-termination) (see T. Ostsu, M. Yoshida, Makromol. Chem., Rapid. Commun. 3 (1982) 127-132: Role of Initiator-Transfer Agent-Terminator (Iniferter) in Radical Polymerizations: Polymer Design by Organic Disulfidesas Iniferters). The addition of chain transfer active substances, i.e., chain regulators or photoinitiator-transfer terminators, results in a decrease in the network density of the polymerization network, while the reactivity of the polymerization resin mixture remains almost unchanged. The amounts of the chain regulator and the photoinitiator-transfer terminator relative to component (a) are preferably 0.005 to 25% by weight, particularly preferably 0.01 to 10% by weight.

[0130] Comonomers that reduce the thermal stability of polymer networks can also be used as degreasing accelerators. Comonomers containing thermally unstable groups, such as peroxide, azo, or urethane groups, are suitable for this purpose. These comonomers are introduced into the polymer network during stereocuring and then accelerate the degradation of the polymer network during thermal degreasing. A preferred example of a polymerizable peroxide is 4,4'-divinylbenzoyl peroxide, which can be obtained by reacting 4-vinylbenzoyl chloride with sodium peroxide. A preferred example of a polymerizable azo compound is an ester of 2-hydroxyethyl methacrylate and 4,4'-azobis(4-cyanovalerate). Preferred thermally unstable polyurethanes can be obtained from diisocyanates, for example, by reacting 2,2,4-trimethylhexamethylene diisocyanate (TMDI) or toluene diisocyanate (TDI) with hydroxypropyl acrylate (HPA) or 2-hydroxyethyl acrylate (HEA). Another example of a thermally unstable monomeric structural unit is α,α,α',α'-tetramethyl-1,4-phenylenedimethyl acrylate, which binds to Michael addition networks, such as the Michael addition networks of diacrylates and diacetoacetates, leading to accelerated degradation of the polymer network in the presence of catalytic amounts of acid.

[0131] The comonomers of α-methylstyrene, whose polymerization products are easily thermally degradable, are also suitable as degreasing accelerators. For example, α-methylstyrene has a low upper temperature limit (T0). c The preferred comonomer is the one used in free radical polymerization resins. The upper limit temperature is the limiting temperature at which polymerization and depolymerization reach equilibrium, and can be calculated from the quotient of the polymerization enthalpy and the polymerization entropy (see H.-G. Elias, Makromoleküle [Macromolecules], Vol. 1, 6). th (ed., Wiley-VCH, Weinheim et al. 1999, 193 ff.). For example, the T of α-methylstyrene. c The upper limit temperature T for polytetrahydrofuran (PTHF) is 61℃. c The temperature is 80°C. Therefore, the degradability of the poly(meth)acrylate network can be accelerated, for example, by using a telechelic polymer, particularly a PTHF di(meth)acrylate telechelic polymer, as a comonomer. According to the invention, comonomers with an upper limit temperature of -10 to 150°C, preferably 10 to 150°C, and particularly preferably 20 to 130°C, are particularly suitable. Based on component (a), the amount of comonomer is preferably 0.1 to 30% by weight, particularly preferably 0.5 to 20% by weight.

[0132] Furthermore, the slurry according to the invention may contain additives that promote the oxidative degradation of the polymer matrix during the degreasing process, such as peroxides stable at room temperature, or may also contain catalytically active components capable of catalyzing degreasing. In addition to peroxides, other oxidizing substances, such as nitric acid, or other substances that decompose or form oxidants, are also suitable.

[0133] Additionally, the slurry according to the invention may contain defoamers and / or anti-skinning agents, which prevent foam formation during slurry preparation or skin formation during slurry processing. Based on the mass of component (a), the preferred amount of the defoamer and / or skin formation inhibitor in the organic matrix is ​​0 to 5% by weight, particularly preferably 0.1 to 2% by weight.

[0134] The rheological properties of the slurries according to the invention are preferably adjusted such that their viscosity is in the range of 200 to 200,000 mPa·s, particularly preferably 500 to 100,000 mPa·s. The viscosity is measured using a plate-to-plate viscometer at a shear rate of 20 / s at the desired processing temperature of the slurry. The processing temperature is preferably in the range of 10 to 100°C, more preferably 15 to 60°C, and most preferably 20 to 50°C.

[0135] The slurry according to the present invention preferably has the following composition:

[0136] - 5 to 65% by weight, preferably 9 to 57% by weight, particularly preferably 10 to 40% by weight of monomer (a);

[0137] - 0.001 to 1.0 wt%, preferably 0.01 to 1.0 wt%, particularly preferably 0.05 to 1.0 wt% of photoinitiator (b);

[0138] - 33 to 90% by weight, preferably 40 to 88% by weight, particularly preferably 56 to 86% by weight of ceramic, glass and / or glass-ceramic particles (c).

[0139] - Optional 1 to 30% by weight, preferably 2 to 15% by weight, particularly preferably 3 to 10% by weight of nonionic surfactant (d).

[0140] Ceramic, glass and / or glass-ceramic particles (c) are preferably colored in the manner described above, for example, by mixing with coloring pigments.

[0141] In addition, the slurry preferably contains:

[0142] - 0 to 0.2% by weight, preferably 0 to 0.05% by weight, particularly preferably 0 to 0.02% by weight of (various) colorants for coloring the paste; and / or

[0143] - 0.1 to 5% by weight, preferably 0.2 to 2% by weight, particularly preferably 0.5 to 1.5% by weight of surface modifier; and / or

[0144] - 0 to 50% by weight, preferably 5 to 20% by weight, particularly preferably 5 to 10% by weight of solvent.

[0145] Unless otherwise stated, all figures refer to the total weight of the slurry. The amount described with respect to component (c) contains the coloring component for coloring ceramic, glass, and / or glass-ceramic particles.

[0146] According to the invention, the same type of slurry is used to prepare the core and shell structures, i.e., glass, glass-ceramic, or ceramic slurry, whereby the slurry can be colored differently. According to a particularly preferred embodiment of the invention, glass-ceramic and, more preferably, lithium pyrosilicate glass-ceramic slurries are used to prepare the core and shell structures, which differ only in color and opacity after sintering, while having the same composition in other respects. In this way, a particularly good match is achieved between the coefficient of thermal expansion and the sintering shrinkage of the ceramic slurry. If aesthetics are less important, the core and shell structures can also be prepared from the same ceramic slurry.

[0147] It can be advantageous to prepare the shell structure using a slurry containing a slightly lower or slightly higher content of ceramic, glass, and / or glass-ceramic particles (c) than the slurry used to prepare the core structure. Preferably, the deviation is no more than ±1% by weight. This results in a slightly larger sintering shrinkage rate for the shell structure. The resulting tension stabilizes the dental restoration. This is especially true for monolithic shell structures that completely surround the core and form a closed shell. Slightly different sintering shrinkage rates are particularly advantageous if a bonding ceramic slurry is used.

[0148] It can also be advantageous to prepare the shell structure using a slurry containing ceramic, glass, and / or glass-ceramic particles with a softening temperature (glass transition temperature) lower than that of the slurry used to prepare the core. The difference in softening temperature is preferably ≤50°C. This can improve the gloss of the dental restoration. Additionally, if the core and shell materials have different softening temperatures, sintering can be controlled in a way that makes the core porosity higher than that of the shell structure. Generally, the goal of sintering is to achieve the highest possible density of the shell structure. If the density of the core is lower than that of the shell structure, it appears less transparent compared to the shell structure, giving the restoration a more natural appearance.

[0149] It is also preferable to use a slurry having the above-described composition to join the green bodies of the core and shell structures. The color and transparency of this joining ceramic slurry are preferably selected such that they fall between the color and translucency of the core and shell structures. If a joining ceramic slurry is used, it is preferable to provide a joining gap, preferably 10-300 μm wide, in at least some areas between the core and shell structures. The green bodies of the core and shell can be joined together, for example, by applying the joining ceramic slurry to the green body of the core and then placing the green bodies(s) of the shell structure(s) on top of the core green body under slight pressure. Any excess joining ceramic slurry is then removed.

[0150] The advantage of using bonding ceramic paste and bonding gaps is that so-called fastening meshes, support structures, etc., formed during the printing of molded parts only need to be removed to a extent exceeding the size of the bonding gap before bonding. Less residue and inaccuracy are compensated for by the bonding gap and bonding ceramic paste.

[0151] Bonding ceramic slurries are primarily used to fix parts after bonding. They should be stable, preventing loss during application and forming a stable slurry layer, and possessing sufficient strength and adhesion after bonding. During bonding, the parts to be bonded come together in a form-fitting manner. For example, bonding can be facilitated by a vibration table if desired. The fixation of the parts resulting from the bonding ceramic slurry is usually sufficient for further processing of the green body, making light curing of the bonding ceramic slurry not absolutely necessary, but may be advantageous.

[0152] The slurries according to the invention are sediment-stable in the liquid state. After degreasing, sintering, and cleaning, they provide good green strength and high dimensional stability, accuracy, and precision. The green body has a high green density and can be degreased without deformation, cracking, or stress formation. During sintering, they produce high-strength ceramics suitable for dental purposes. During sintering, a density greater than 98% of the theoretical density can be easily achieved. Ceramic slurries are particularly suitable for preparing ceramic or glass-ceramic compacts, especially for preparing dental restorations such as inlays, onlays, veneers, crowns, bridges, or frames.

[0153] Stereopolymerization is preferred for green body preparation. Stereopolymer printing is computer-aided based on CAD data. The required data is obtained in a conventional manner through optical or mechanical digitization in the patient's mouth (intraoral) or based on a model (extraoral). The core and shell structure of the dental restoration is then designed on a computer based on this dataset. Tooth shapes stored in a database can be used for this. Two datasets are then created under software control for printing the core and shell structures independently of each other. Material-related shrinkage behavior is taken into account accordingly when designing the restoration.

[0154] Green bodies prepared by printing methods already possess relatively high strength and can be handled without problems. The core and shell green bodies are preferably cleaned and then assembled to form the green body of the dental restoration. Because the sintering shrinkage and coefficients of thermal expansion are largely matched, green bodies can be prepared with precise matching, allowing them to remain together after bonding by shape fit and / or force compression, even without a bonding ceramic slurry, and can be degreased and sintered. However, preferably, a bonding ceramic slurry is used for bonding components, especially if the shell structure does not completely surround the core structure and / or is a multi-part assembly.

[0155] The advantages of stereolithography for core-shell structures include the ability to fabricate molded parts with great precision, without revealing any milling marks. Another advantage is that only one degreasing and sintering process is required, which significantly reduces the time needed to fabricate dental restorations.

[0156] After sintering, dental restorations can be glazed and personalized with dental ceramic stains.

[0157] The method and materials used according to the invention are suitable for preparing dental restorations for repairing several teeth, such as bridges, and particularly suitable for preparing dental restorations for repairing a single tooth, such as inlays, high inlays, veneers, and especially crowns. The multi-layered structure of the restoration enables the achievement of improved aesthetic properties. However, by joining the core and shell structures in the green state and then sintering the components together, the multi-layered structure requires no significant additional effort compared to preparing a monolithic restoration. The preferred slurry according to the invention also results in high green strength, which allows for safe handling of the green body and ensures high stability during the degreasing process. Furthermore, the green body can be well degreased after joining. Attached Figure Description

[0158] The present invention will now be explained in more detail with reference to the accompanying drawings and embodiments.

[0159] Figure 1 A front view showing the core structure of an anterior crown with a dental arch, designed by computer.

[0160] Figure 2 Showing with Figure 1 Rear view of the shell structure that matches the core structure shown.

[0161] Figure 3 The image shows the shell structure (left) and core structure (right) after printing, degreasing, and separate sintering. The shell and core structures were sintered separately to more clearly show the color differences.

[0162] Figure 4 Show Figure 3 Another view of the shell (left) and core (right) structure shown.

[0163] Figure 5 This shows an anterior crown composed of separately printed core (dentin) and shell (incisor) structures. The printed parts were joined together in the green state, then degreased and sintered together.

[0164] Figure 6 Showing the results after polishing and glazing Figure 5 The anterior crown shown. Detailed Implementation

[0165] Example

[0166] Example 1

[0167] Manufacturing of the core and shell structure of anterior crowns

[0168] Using standard CAD software (EXOCAD v3.2; exocad GmbH, Rosa-Parks-Str. 2, D-64295Darmstadt, Germany), crowns for incisors were designed on a computer. The dataset was then divided into two parts. The first part of the dataset was defined... Figure 1 The core structure of the tooth crown shown, the second part of the dataset definition Figure 2 The diagram shows a single, integrated shell structure. A 35 µm wide engagement gap is provided between the core and shell structures. Both the core and shell structures have cusps that mimic natural dental taper. These structures facilitate the engagement of the core and shell structures and give the dental restoration a natural appearance after engagement.

[0169] Using standard CAM software (PrograPrint CAM software V1.2, Ivoclar Vivadent AG, Bendererstr. 2, 9494 Schaan, Liechtenstein), partial datasets were converted into processing data for a stereolithography printer (Prograprint PR5; Ivoclar Vivadent AG). The printer operated in a 40°C climate chamber to ensure the fluidity of the paste. Core and shell structures were then printed separately under computer control. The paste used had the following composition:

[0170]

[0171] 1) According to EP0827941A1

[0172] 2) Particle size range: 500 nm to 50 µm

[0173] The printed green compact was cleaned by rinsing with water and drying with compressed air. The resulting green compact was then degreased by heating to 500°C for 30 minutes at a heating rate of 0.2 K / min in a furnace (Naberther mL9 / 11 BO; Lilienthal Bremen, Germany), followed by sintering by heating to 890°C for 5 minutes at a heating rate of 10 K / min in a sintering furnace (Programat P510; Ivoclar Vivadent AG; Schaan, Liechtenstein). The sintered structure is as follows... Figure 3 and 4 As shown.

[0174] Example 2

[0175] Manufacturing of anterior crowns

[0176] Crowns for anterior teeth were designed in the manner described in Example 1 and manufactured using the ceramic slurry described in the table below.

[0177]

[0178] 1) According to EP0827941A1

[0179] 2) Particle size range: 500 nm to 50 µm

[0180] The printed green body is cleaned by rinsing with water and drying with compressed air. The support structure at the cut edges is removed using a rotating cutting disc (a standard dental tool). A bonding ceramic slurry is then applied to the bonding surfaces of the core and shell, pressing the two molds together in a form-fit manner, and then excess bonding slurry is removed.

[0181] The bonded green body was then light-cured using a dental light-curing unit (PrograPrint Cure, Program Wax, Ivoclar Vivadent AG) to increase the degree of polymerization. The bonding slurry was also cured.

[0182] The green body was then degreased by heating to 500°C for 30 minutes at a heating rate of 0.2 K / min in a furnace (Nabertherm L9 / 11 BO, Lilienthal Bremen, Germany), and then sintered by heating to 890°C for 5 minutes at a heating rate of 10 K / min in a sintering furnace (Programat P510; Ivoclar Vivadent AG; Schaan, Liechtenstein). The resulting crown is shown below. Figure 5 As shown. Figure 5 The crown shown was then polished. The completed crown is as follows: Figure 6As shown.

[0183] The slurry used to prepare the shell structure is filled slightly less than that used to prepare the core. Therefore, it exhibits a slightly larger sintering shrinkage than the core slurry, which leads to improved bonding between the core and shell structures during sintering. The filling level of the bonding ceramic slurry lies between that of the core and shell slurries, resulting in a smooth transition between the core and shell.

Claims

1. A method for producing a full ceramic dental restoration with an integral core structure and a single- or multi-part shell structure, wherein a digital build model of the dental restoration is constructed in a first step, and the CAD data set of the restoration obtained in this way is then divided into at least two different CAD partial data sets, a first partial data set defining the contour of the core structure and a second partial data set defining the contour of the shell structure, and the dental restoration is then produced using the data records created, characterized in that in a subsequent step, using the first CAD partial data set, a first slurry is solidified by local application of radiation energy to form the geometry of the core structure, a green body of the core structure of the restoration being produced, in a further step, using the second CAD partial data set, a second slurry is solidified by local application of radiation energy to form the geometry of the shell structure, a green body of the shell structure of the restoration being produced, in a subsequent step, the core and shell structure are combined in the green body state, to obtain a green body of the dental restoration, in a further step, the green body of the dental restoration is subjected to a heat treatment to remove the binder (debinding), to obtain a brown body of the dental restoration, and the brown body of the dental restoration is then sintered, to obtain the finished dental restoration.

2. The method according to claim 1, wherein the CAD partial data set of the shell structure is divided into two or more CAD shell structure partial data sets, each comprising a part of the contour of the shell structure, a second ceramic slurry is solidified by local introduction of radiation energy to form the geometry of a first component of the shell structure by means of the first CAD shell structure partial data set, separately, another ceramic slurry is solidified by local application of radiation energy to form the geometry of a second component of the shell structure by means of a second CAD shell structure partial data set, and this step is repeated according to the number of CAD shell structure partial data sets, and each repetition produces a green body of another component of the shell structure, and the core structure and the components of the shell structure are then joined together in the green body state, to obtain a green body of the dental restoration.

3. The method according to claim 2, wherein the components of the shell structure are produced using the same slurry, or preferably using different slurries, particularly preferably different pigmented slurries.

4. The method according to any one of claims 1 to 3, wherein the core structure and the shell structure are produced using slurries which differ in color and opacity but are otherwise of identical composition.

5. The method according to any one of claims 1 to 4, wherein the shell structure is produced using a slurry which contains slightly lower or slightly higher contents of ceramic, glass and / or glass-ceramic particles (c) than the slurry used to produce the core structure.

6. The method according to any one of claims 1 to 5, wherein the green bodies of the core structure and the shell structure are joined together using a joining ceramic slurry, and the joining ceramic slurry is solidified by polymerization after joining.

7. The method according to any one of claims 1 to 6, wherein the green bodies of the dental restorations are debound by heating the green bodies to a temperature of 90 °C to 600 °C.

8. The method according to any one of claims 1 to 7, wherein the brown bodies are sintered at a temperature of 650 to 1800 °C.

9. The method according to any one of claims 1 to 8, wherein each green body is prepared using a slurry which in each case comprises (a) 5 to 65 % by weight of at least one radically polymerizable monomer, (b) 0.001 to 1.0 % by weight of at least one photoinitiator, and (c) 33 to 90 % by weight of ceramic particles and / or glass particles and / or glass-ceramic particles.

10. The method according to claim 9, wherein each green body is prepared using a slurry which contains glass-ceramic particles of lithium metasilicate and / or glass particles for lithium metasilicate glass-ceramic.

11. The method according to claim 10, wherein each green body is prepared using a slurry which contains a glass or glass-ceramic powder having the following composition: SiO2 57.0 to 80.0 % by weight Al2O3 0 to 5.0 % by weight La2O3 0.1 to 6.0 % by weight MgO 0 to 5.0 % by weight, in particular 0.1 to 5.0 % by weight ZnO 0 to 8.0 % by weight K2O 0 to 13.5 % by weight Li2O 11.0 to 19.0 % by weight P2O5 0 to 11.0 % by weight color component 0 to 8.0 % by weight further component 0 to 6.0 % by weight whereby Al2O3 + La2O3 is 0.1 to 7.0 % by weight and MgO + ZnO is 0.1 to 9.0 % by weight and wherein the color component is formed from glass-coloring oxides and / or color bodies in the following amounts: glass-coloring oxides 0 to 5.0 % by weight and color bodies 0 to 5.0 % by weight.

12. The method according to claim 11, wherein the glass-coloring oxide(s) are selected from TiO2, CeO2 and / or Fe2O3 and / or the one or more color bodies are selected from doped spinels and / or doped ZrO2 and / or the further component is selected from B2O3, F, Na2O, ZrO2, BaO and / or SrO.

13. The method according to any one of claims 1 to 12, wherein a slurry comprising a mixture of glass and glass-ceramic powder is used.

14. The method according to any one of claims 9 to 13, comprising using a syrup comprising as radically polymerizable monomers (a) aliphatic urethane diacrylate, HEA phthalate, diHEA pyromellitate, bisphenol A di(meth)acrylate, bis-G(M)A (addition product of (meth)acrylic acid and bisphenol A diglycidyl ether), ethoxylated or propoxylated bisphenol A di(meth)acrylate, UD(M)A, triethylene glycol di(meth)acrylate (TEGD(M)A), tricyclodecane dimethanol di(meth)acrylate, ethoxylated or propoxylated trimethylolpropane tri(meth)acrylate, tripropylene glycol diacrylate or mixtures thereof.

15. The method according to any one of claims 9 to 14, comprising using a syrup comprising as photoinitiator (b) a combination of camphorquinone (CAS No. 10373-78-1) with ethyl 4-(dimethylamino)benzoate (CAS No. 10287-53-3), 2,4,6-trimethylbenzoyldiphenylphosphine oxide (CAS No. 75980-60-8), ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate (CAS No. 84434-11-7), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (CAS No. 162881-26-7), bis(2,6-difluoro-3-(1 -hydroxypyridin-1 -yl)phenyl)titanium difluoride (CAS No. 125051-32-3), 2-benzyl-2-(dimethylamino)-4'-morpholinophenylbutanone (CAS No. 119313-12-1), 1-butanone-2-(dimethylamino)-2-(4-methylphenyl)methyl-1-4-(4-morpholinyl)phenyl (CAS No. 119344-86-4), bis(4-methoxybenzoyl)diethyl germanium or mixtures thereof.

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