Resin composition, printing method, dental product obtainable by the printing method and method of treating the dental product

Abstract

The present invention relates to a resin composition comprising at least one methacrylate compound having at least two methacryl functional groups, at least one thiol compound having at least two thiol functional groups and at least one methallyl compound having at least two methallyl functional groups. The present invention further relates to a printing method, a dental product obtainable by the printing method, and a method of treating a dental product.

Description

[0001] Resin composition, printing method, dental product obtainable by the printing method and method of treating the dental product

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of dental products, more specifically occlusal splints, night guards or dental aligners. In particular, the present invention relates to a resin composition suitable for forming the dental product by a printing method, the printing method, the dental product obtainable by the printing method, and a method of treating the dental product.

[0004] BACKGROUND

[0005] Dental products, such as occlusal splints, night guards or dental aligners, are widely-used for aligning or protecting teeth of a person, for instance for protecting the teeth from damage caused by grinding overnight. To fulfill these tasks, the dental products must be made from a material, which provides sufficient mechanical stability and robustness to protect or align the teeth, but also suitable tensile properties, such as a sufficient toughness or elongation at break to avoid brittling upon insertion and during application of the dental product in the mouth.

[0006] In recent years, dental products are more and more frequently manufactured by additive manufacturing methods, such as 3D printing. Among the known 3D printing methods, stereolithography (SLA) represents a very promising approach, since it attains a very high resolution that can hardly be attained with other techniques. This technique based on photopolymerization of liquid resins has a great potential for the manufacture of tailored shaped articles in the dental or orthodontic field where a high fitting accuracy is desired.

[0007] Previous attempts to provide orthodontic devices by 3D printing of photocurable compositions are disclosed in US 11,427,721 B2 and US 11,873,362 B2. The photocurable compositions provided by Graphy Inc. described therein are based on polyurethane oligomers. However, these orthodontic devices exhibit significant stress relaxation overtime resulting in significant decrease of the force that acts on the teeth, which may lead to insufficient or even inappropriate aligning properties thereof. The significant lower forceafter stress relaxation is determined by the shape memory effect of the material due to the fact that the shape memory effect generally occurs at temperatures below 40 °C, i.e. when the orthodontic device is worn in the mouth of a user, which is typically undesired.

[0008] Thus, there is room for improvements in the manufacture of tailor-made dental products by 3D printing methods. In particular, there is a need for such dental products having improved mechanical or tensile properties, in particular toughness and / or sufficient Young's modulus and reduced or decelerated stress relaxation.

[0009] OBJECT OF THE INVENTION

[0010] In light of the foregoing, the present invention aims at overcoming the above described problems and drawbacks of hitherto available dental products, more specifically occlusal splints, night guards or dental aligners, made by 3D printing methods.

[0011] Thus, an object of the present invention is to provide a resin composition suitable for use for 3D printing a dental product, more specifically a dental aligner, an occlusal splint or a night guard, having improved mechanical properties, in particular in terms of tensile properties, more specifically Young's modulus (E modulus) and elongation at break (tensile strength at break), toughness and reduced or decelerated stress relaxation.

[0012] SUMMARY OF THE INVENTION

[0013] The present inventors have made diligent studies for solving this object and have found that by using a thiol-ene resin composition comprising specific compounds, namely at least one methacrylate compound having at least two methacryl functional groups, at least one thiol compound having at least two thiol functional groups, and at least one methallyl compound having at least two methallyl functional groups, this object can be solved. Moreover, by appropriately selecting the ratios of the numbers of functional groups in the resin composition, the properties of a 3D printed dental product may be particularly tailored.

[0014] Without wishing to be bound to any theory, the present inventors currently assume the following:Methacrylate compound: If the resin composition only comprises a methacrylate compound, homopolymerisation of the methacrylate group occurs. With a monomer functionality of more than one (>1), a cross-linked polymer network is formed. During the polymerisation reaction, the free volume decreases, which leads to shrinkage of the material. Polymerisation begins in the liquid phase, whereby the monomer mixture initially becomes gel-like and later takes on a glass-like structure. Shrinkage in the gel and glass state leads to the formation of shrinkage stresses, which explain, among other things, the increased brittleness of photopolymers.

[0015] Thiol compound: The addition of a thiol compound shifts the gel point so that it is reached later. As a result, a larger part of the polymerisation takes place in the liquid phase, while less reaction takes place in the gel or glassy state. This leads to a reduction in shrinkage stress and thus to lower brittleness. In addition, the reaction of thiol with the methacrylate group causes a reduction in the network density. A lower network density leads to lower brittleness (higher toughness) as well as a reduction in the modulus of elasticity and the glass transition temperature. As the thiol concentration increases, the glass transition temperature decreases accordingly.

[0016] Methallyl compound: The inventors have surprisingly found that the addition of a methallyl compound compensates for the reduction in the modulus of elasticity and the glass transition temperature, while the toughness is maintained.

[0017] As result, a 3D printed dental product, more specifically a dental aligner, an occlusal splint or a night guard, can be obtained having improved mechanical properties, in particular in terms of tensile properties, more specifically Young's modulus (E modulus) and elongation at break (tensile strength at break), toughness and reduced or decelerated stress relaxation.

[0018] Accordingly, the present invention relates to a resin composition comprising at least one methacrylate compound having at least two methacryl functional groups, at least one thiol compound having at least two thiol functional groups and at least one methallyl compound having at least two methallyl functional groups.

[0019] Moreover, the present invention further relates to a (three-dimensional, 3D) printing method comprising the steps of providing a resin composition as described herein, and irradiating at least a part of the resin composition with an energy-carrying activation beamso as to cause polymerization of at least a part of the resin composition (so as to obtain a printed dental product).

[0020] The present invention further relates to a (three-dimensional) dental product obtainable (or obtained) by the method as described herein, wherein the dental product is selected from the group consisting of a dental aligner, an occlusal splint, and a night guard.

[0021] Furthermore, the present invention relates to method of treating (e.g. reactivating in terms of orthodontic force) the dental product as described herein, the method comprising the step of heating the dental product to a temperature of at least 40°C.

[0022] Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following detailed description of embodiments.

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, details of the present invention and other features and advantages thereof will be described. However, the present invention is not limited to the following specific descriptions, but they are rather for illustrative purposes only.

[0025] It should be noted that features described in connection with one exemplary embodiment or exemplary aspect may be combined with any other exemplary embodiment or exemplary aspect, in particular features described with any exemplary embodiment of a resin composition may be combined with any exemplary embodiment of a printing method, dental product, a method of treating, and vice versa, unless specifically stated otherwise.

[0026] Where an indefinite or definite article is used when referring to a singular term, such as “a”, “an” or “the”, a plural of that term is also included and vice versa, unless specifically stated otherwise, whereas the word “one” or the number “1”, as used herein, typically means “just one” or “exactly one”.

[0027] The expression “comprising”, as used herein, includes not only the meaning of “comprising”, “including” or “containing”, but may also encompass “consisting essentially of” and “consisting of’.Unless specifically stated otherwise, the expressions “at least partially”, “at least a partial” or “at least a part of’, as used herein, may mean at least 5 % thereof, in particular at least 10 % thereof, in particular at least 15 % thereof, in particular at least 20 % thereof, in particular at least 25 % thereof, in particular at least 30 % thereof, in particular at least 35 % thereof, in particular at least 40 % thereof, in particular at least 45 % thereof, in particular at least 50 % thereof, in particular at least 55 % thereof, in particular at least 60 % thereof, in particular at least 65 % thereof, in particular at least 70 % thereof, in particular at least 75 % thereof, in particular at least 80 % thereof, in particular at least 85 % thereof, in particular at least 90 % thereof, in particular at least 95 % thereof, in particular at least 98 % thereof, and may also mean 100 % thereof.

[0028] In a first aspect, the present invention relates to a resin composition.

[0029] The term “composition”, as used herein, may in particular mean that the components (ingredients) of the composition are in close proximity with each other and / or that the components are (intensely) mixed with each other, for instance by using a mixer, a stirrer and / or by shaking, to thereby form the composition. In particular, the components of the compositions may be uniformly distributed or dispersed throughout within the composition. The composition may be in particular solid, semi-solid (pasty) or liquid, in particular a liquid solution or a semi-solid or liquid suspension.

[0030] The resin composition may in particular be a photo-reactive resin composition. The term “photo-reactive”, as used herein, may in particular mean that the resin composition, in particular some or all of its components, undergo a (chemical) reaction upon irradiation with an energy-carrying activation beam, in particular with electromagnetic radiation.

[0031] The resin composition comprises at least three compounds: (i) at least one methacrylate compound; (ii) at least one thiol compound; and (iii) at least one methallyl compound. As it is evident, the resin composition may contain more than one methacrylate compound (such as a mixture of different methacrylate compounds), more than one thiol compound (such as a mixture of different thiol compounds) and / or more than one methallyl compound (such as a mixture of different methallyl compounds), as well as further ingredients or components, which will be described below.

[0032] The methacrylate compound has at least two methacryl functional groups. For instance, the methacrylate compound may have two methacryl functional groups, threemethacryl functional groups or more than three methacryl functional groups. Preferably, the methacrylate compound has two methacryl functional groups.

[0033] The term “methacryl functional group” as used herein and as commonly understood by a person skilled in the art, may be represented by the general formula “H2C=C(CH3)-C(=O)-O-”. The term “methacryl functional group” may also be designated “methacrylate functional group”. The methacryl functional group (in particular its carbon-carbon double bond) may undergo a thiol-ene reaction with a thiol group of a thiol compound, which type of reaction is particularly suitable for stereolithography.

[0034] Besides the at least two methacryl functional groups, the structure of the methacrylate compound is not particularly limited and may include branched or linear (carbon) moieties, which may include various functional groups, as well as oligomeric or polymeric chains. In particular, the at least one methacrylate compound may comprise at least one group or moiety selected from a linear or branched, saturated or unsaturated, substituted or unsubstituted alkyl group; a linear or branched, saturated or unsaturated, substituted or unsubstituted heteroalkyl group; a saturated or unsaturated, substituted or unsubstituted cycloalkyl group; a saturated or unsaturated, substituted or unsubstituted heterocycloalkyl group; a substituted or unsubstituted aryl group; a substituted or unsubstituted heteroaryl group; a linear or branched, substituted or unsubstituted aralkyl group; a linear or branched, substituted or unsubstituted alkaryl group; an oligomer or a polymer.

[0035] The meaning of the terms “linear”, “branched”, “saturated”, “unsaturated” and “unsubstituted”, as used herein, corresponds to the respective well-established meanings thereof, as known to a person skilled in the art. The term “substituted”, as used herein, means that one or more, in particular 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, hydrogen atom(s) of the respective groups are substituted by a substituent. Examples of suitable substituents, include halogen atoms, such as -F, -Cl, -Br, -I; -OH, hydroxyalkyl groups (ether), -SH, thioalkyl groups (thioether), =0, carboxyl groups (-COOH) and salts, esters and amides thereof, -NH2, secondary amine groups, tertiary amine groups, nitrile groups and nitro groups. If two or more substituents are present, they may be the same or different and they may be bound to each other to form a ring. The terms “heteroalkyl group”, “heterocycloalkyl group” or “heteroaryl group”, respectively, represents an alkyl group, a cycloalkyl group or an aryl group, respectively, wherein one or more, in particular 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, carbon atoms are replaced by a hetero atom, such as O, N or S, in particular O and / or N. Ifmore than one hetero atom is contained in a group, these hetero atoms may be the same or different.

[0036] Suitable examples of the alkyl group include Ci to C20 alkyl groups, in particular C2 to C10 alkyl groups, in particular C3 to Cs alkyl groups, in particular C4 to Ce alkyl groups.

[0037] Suitable examples of the cycloalkyl group include C3 to C20 cycloalkyl groups, in particular C4 to C15 cycloalkyl groups, in particular C5 to C10 cycloalkyl groups, in particular Ce to Cs cycloalkyl groups.

[0038] Suitable examples of the aryl group include Ce to C20 aryl groups, in particular Ce to C16 aryl groups, in particular Ce to C14 aryl groups, in particular Ce to C10 aryl groups. In particular, the aryl group may be a phenyl group.

[0039] An “aralkyl group”, as used herein, denotes a group having an aliphatic and an aromatic moiety, wherein the aliphatic moiety binds to the methacryl functional group or any other functional group, such as an ether, carbonate, carbamate or ester functional group, and wherein the aromatic moiety and / or the aliphatic moiety may optional comprise a hetero atom. In other words, an “aralkyl group” represents an alkyl or cycloalkyl group (or a heteroalkyl or heterocycloalkyl group) having an aryl group (or a heteroaryl group) as a substituent. Suitable aliphatic and aromatic moieties of the aralkyl group correspond to the alkyl, cycloalkyl and aryl groups (or heteroalkyl, heterocycloalkyl and heteroaryl groups, respectively), as defined above.

[0040] An “alkaryl group”, as used herein, denotes a group having an aliphatic and an aromatic moiety, wherein the aliphatic moiety binds to the methacryl functional group or any other functional group, such as an ether, carbonate, carbamate or ester functional group, and wherein the aliphatic moiety and / or the aromatic moiety may optional comprise a hetero atom. In other words, an “alkaryl group” represents an aryl group (or a heteroaryl group) having an alkyl or cycloalkyl group (or a heteroalkyl or heterocycloalkyl group) as a substituent. Suitable aliphatic and aromatic moieties of the alkaryl group correspond to the alkyl, cycloalkyl and aryl groups (or heteroalkyl, heterocycloalkyl and heteroaryl groups, respectively), as defined above.

[0041] In an embodiment, the at least one methacrylate compound further comprises at least one urethane (functional) group. For instance the at least one methacrylate compound maycomprise a urethane dimethacrylate. The additional presence of a urethane functional group involves the capability of forming a hydrogen bond with water and / or an alcohol, which may further improve the tensile properties of the polymer and eventually the dental product obtained.

[0042] In an embodiment, the at least one methacrylate compound comprises diurethane dimethacrylate (7,7,9-trimethyl-4, 13-dioxo-3, 14-dioxa-5, 12-diazahexadecane- 1 , 16-diyl bis(2-methylacrylate, LIDMA, CAS: 72869-86-4), which has proven particularly suitable for solving the object underlying the present invention.

[0043] The thiol compound has at least two thiol functional groups. For instance, the thiol compound may have two thiol functional groups, three thiol functional groups, four thiol functional groups or more than four thiol functional groups. Preferably, the thiol compound has at least three thiol functional groups, in particular three or four thiol functional groups.

[0044] The term “thiol functional group”, as used herein and as commonly understood by a person skilled in the art, represents a functional group represented by the general formula “-SH” which may also be present in protected form represented for instance by the general formula “-SZ”, wherein “Z” represents a protection group for “-SH”, i.e. a thiol protection group, as described in further detail in WO 2020 / 016343 A2, the entire content of which is incorporated herein by reference.

[0045] Besides the at least two thiol functional groups, the structure of the thiol compound is not particularly limited and may include branched or linear (carbon) moieties, which may include various functional groups, as well as oligomeric or polymeric chains. In particular, the at least one thiol compound may comprise at least one group or moiety selected from a linear or branched, saturated or unsaturated, substituted or unsubstituted alkyl group; a linear or branched, saturated or unsaturated, substituted or unsubstituted heteroalkyl group; a saturated or unsaturated, substituted or unsubstituted cycloalkyl group; a saturated or unsaturated, substituted or unsubstituted heterocycloalkyl group; a substituted or unsubstituted aryl group; a substituted or unsubstituted heteroaryl group; a linear or branched, substituted or unsubstituted aralkyl group; a linear or branched, substituted or unsubstituted alkaryl group; an oligomer or a polymer. The definitions of the terms “linear”, “branched”, “saturated”, “unsaturated”, “unsubstituted” and “substituted” may in particular correspond to the above given definitions. Likewise, the definitions and / or suitable examples of the terms “alkyl group”, “heteroalkyl group”, “cycloalkyl group”,“heterocycloalkyl group”, “aryl group”, “heteroaryl group”, “aralkyl group” and “alkaryl group” may in particular correspond to the above given definitions and / or examples. Moreover, reference is again made to WO 2020 / 016343 A2 disclosing various suitable examples of thiol compounds, which disclosure is incorporated herein by reference.

[0046] In an embodiment, the at least one thiol compound is selected from the group consisting of trimethylolpropane tris(3-mercaptopropionate) (TMPMP, CAS: 33007-83-9), and pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). In particular. TMPMP has proven particularly suitable for solving the object underlying the present invention.

[0047] The at least one methallyl compound has at least two methallyl functional groups. For instance, the methallyl compound may have two methallyl functional groups, three methallyl functional groups or more than three methallyl thiol functional groups. Preferably, the methallyl compound has at least three methallyl functional groups, in particular three methallyl functional groups.

[0048] The term “methallyl functional group”, as used herein and as commonly understood by a person skilled in the art, may be represented by the general formula „H2C=C(CH3)-CH2-“. The methallyl functional group (in particular its carbon-carbon double bond) may undergo a thiol-ene reaction with a thiol group of a thiol compound, which type of reaction is particularly suitable for stereolithography.

[0049] Besides the at least two methallyl functional groups, the structure of the methallyl compound is not particularly limited and may include branched or linear (carbon) moieties, which may include various functional groups, as well as oligomeric or polymeric chains. In particular, the at least one methallyl compound may comprise at least one group or moiety selected from a linear or branched, saturated or unsaturated, substituted or unsubstituted alkyl group; a linear or branched, saturated or unsaturated, substituted or unsubstituted heteroalkyl group; a saturated or unsaturated, substituted or unsubstituted cycloalkyl group; a saturated or unsaturated, substituted or unsubstituted heterocycloalkyl group; a substituted or unsubstituted aryl group; a substituted or unsubstituted heteroaryl group; a linear or branched, substituted or unsubstituted aralkyl group; a linear or branched, substituted or unsubstituted alkaryl group; an oligomer or a polymer. The definitions of the terms “linear”, “branched”, “saturated”, “unsaturated”, “unsubstituted” and “substituted” may in particular correspond to the above given definitions. Likewise, the definitions and / or suitable examples of the terms “alkyl group”, “heteroalkyl group”, “cycloalkyl group”,“heterocycloalkyl group”, “aryl group”, “heteroaryl group”, “aralkyl group” and “alkaryl group’ may in particular correspond to the above given definitions and / or examples.

[0050] In an embodiment, the at least one methallyl compound further comprises at least one isocyanurate (functional) group. The additional presence of an isocyanurate ring structure may involve the capability of forming a hydrogen bond with water and / or an alcohol, which may further improve the tensile properties of the polymer and eventually the dental product obtained.

[0051] In an embodiment, the at least one methallyl compound comprises trimethallyl isocyanurate (1 ,3,5-tris(2-methyl-2-propenyl)-1 , 3, 5-triazinane-2, 4, 6-trione, 1 ,3,5-T ris(2-methylallyl)-1 , 3, 5-triazinane-2, 4, 6-trione, CAS: 6291-95-8), which has proven particularly suitable for solving the object underlying the present invention.

[0052] In an embodiment, the amounts of the at least one methacrylate compound, the at least one thiol compound and the at least one methallyl compound are such that the ratio of the number of methacryl functional groups : thiol functional groups : methallyl functional groups is (15 to 80) : (5 to 20) : (5 to 20), in particular (30 to 80) : (10 to 15) : (10 to 15). In other words, the at least one methacrylate compound, the at least one thiol compound and the at least one methallyl compound may be contained in amounts such that the ratio of the number of methacryl functional groups : thiol functional groups : methallyl functional groups is (15 to 80) : (5 to 20) : (5 to 20), in particular (30 to 80) : (10 to 15) : (10 to 15). The inventors have surprisingly found that by changing the ratio of the number of methacryl functional groups to the number of thiol functional groups to the number of methallyl functional groups, several relevant mechanical properties, among them the glass transition temperature (range) and thus the temperature, at which a shape-memory effect may be triggered, of the polymer and eventually the dental product obtained may be varied and appropriately adjusted. In particular, within the above defined ranges, particularly advantageous mechanical properties may be achieved. In particular, it may be possible to adjust the glass transition temperature (range) of the polymer and eventually the dental product obtained to above 40 °C, which not only allows that a shape-memory effect does not occur when the dental product is worn in the mouth of a user, but can be deliberately triggered (e.g. by heating above the glass transition temperature), but also that the stress relaxation of the dental product when worn in the mouth of a user is significantly decelerated and reduced enabling an appropriate orthodontic force over longer time and thus an improved aligning performance.In an embodiment, the amounts of the at least one thiol compound and the at least one methallyl compound are such that the ratio of the number of thiol functional groups to the number of methallyl functional groups is from 1 : 0.8 to 1 : 1.25, in particular from 1 : 0.9 to 1 : 1.1. In other words, the at least one thiol compound and the at least one methallyl compound may be contained in amounts such that the ratio of the number of thiol functional groups to the number of methallyl functional groups is from 1 : 0.8 to 1 : 1.25, in particular from 1 : 0.9 to 1 : 1.1. The inventors have surprisingly found that highly advantageous mechanical properties in terms of modulus of elasticity, the glass transition temperature, toughness can be achieved within the above defined ranges of the ratio of the number of thiol functional groups to the number of methallyl functional groups.

[0053] In an embodiment, the resin composition comprises diurethane dimethacrylate, trimethylolpropane tris(3-mercaptopropionate) and trimethallyl isocyanurate, which combination of methacrylate compound, thiol compound and methallyl compound has proven particularly suitable for solving the object underlying the present invention.

[0054] In an embodiment, the resin composition further comprises at least one of the group consisting of a photoinitiator, a light absorber (in particular a UV absorber), a reactive diluent, and a stabilizer (e.g. a phosphorous containing compound and / or a radical scavenger). Reference is again made to WO 2020 / 016343 A2 disclosing various details and suitable examples of these optional components, which disclosure is incorporated herein by reference.

[0055] The resin composition may be in particular suitable for printing (in particular by means of stereolithography), for instance in a printing method as described in further detail below.

[0056] In a second aspect, the present invention relates to a printing method, in particular to a method of preparing a dental product. The dental product may in particular be a three-dimensional dental product, such as a 3D-printed dental product, as described in further detail below.

[0057] In an embodiment, the printing method is a three-dimensional printing (3D) method. The term “three-dimensional printing method”, as used herein, in particular denotes that the (dental) product of the printing method extends in three directions (for example, length, width and height). Thus, the product of a three-dimensional printing method may be inparticular a three-dimensional object. The three-dimensional printing method may be in particular any one selected from the group consisting of stereolithography (SLA), two-photon absorption (TPA) polymerization, digital light processing (DLP), masked stereolithography, reactive laser sintering (RLS), solid ground curing (SGC), multi jet modeling (MJM) or a combination thereof. In view of its high resolution, stereolithography (SLA) may be preferred.

[0058] The printing method comprises the step of providing a resin composition as described in the first aspect above. The resin composition may be prepared (such as the individual components thereof may be mixed) in advance and stored until used in the printing method. However, it is of course also possible to prepare the resin composition immediately before its use in the printing method, which is advantageous in case stability of the resin composition might be an issue. Moreover, the step of providing in particular includes a step of printing the resin composition.

[0059] The printing method comprises the step of irradiating at least a part of the resin composition with an energy-carrying activation beam (which may also be referred to as an irradiation step or a curing step) so as to cause polymerization of the at least a part of the resin composition. By irradiating at least a part of the resin composition with an energycarrying activation beam, a chemical reaction may be caused at the irradiated part of the resin composition (more specifically, a thiol-ene reaction) with the result that the monomers (i.e. the compounds) undergo a cross-linking or polymerization reaction at the irradiated part and consequently a polymer is formed at the irradiated part of the resin composition. The polymer thus formed may also be referred to as a photopolymer. The energy-carrying activation beam may in particular comprise electromagnetic radiation (in particular actinic radiation). In particular, the energy-carrying activation beam may be at least one selected from the group consisting of ultraviolet radiation (such as having a wavelength of from 10 to 380 nm, in particular from 200 to 380 nm, in particular from 250 to 380 nm) and visible light radiation (such as having a wavelength of from 380 to 780 nm).

[0060] In an embodiment, the printing method further comprises a step of heating the resin composition. This might be advantageous for instance if the viscosity of the resin composition is high, so that the viscosity of the resin composition may be lowered by heating, which may facilitate the printing process. For instance, the resin composition may be heated to a temperature within the range of from 40 °C to 120 °C, such as 50 °C to 100 o / ^In an embodiment, the printing method further comprises a step of rinsing the polymer, in particular during and / or after irradiating the at least part of the resin composition. For instance, the polymer may be rinsed by means of an alcohol, such as isopropanol. By taking this measure, the amount of residual monomers in the printed polymer may be lowered.

[0061] In an embodiment, the printing method further comprises a step of post-curing the polymer, in particular after irradiating the at least part of the resin composition and / or after a step of rinsing. Thus, the printing step may comprise, in particular after an irradiation step and / or a rinsing step, a step of post-curing, wherein the initially formed polymer is further or again provided with actinic energy. For instance, in case of stereolithography, the (initially) formed polymer may be further or again irradiated with ultraviolet radiation in a post-curing step. The post-curing may in particular carried out at an elevated temperature, for instance in a range of from 30 to 80 °C.

[0062] In a third aspect, the present invention relates to a (three-dimensional) dental product obtainable (or obtained) by the method of the second aspect. The dental product obtainable by a printing method using a resin composition of the first aspect may in particular have improved mechanical properties, in particular in terms of tensile properties, more specifically Young's modulus (E modulus) and elongation at break (tensile strength at break), toughness and reduced or decelerated stress relaxation, which render it particular suitable for use as a dental aligner, an occlusal splint, and a night guard.

[0063] The term “dental product”, as used herein, may in particular mean a product that is intended to put into the mouth of a human or animal being, but without being swallowed. Thus, a dental product does not represent a food or a medicament. Rather, a dental product within the meaning of the present application is selected from the group consisting of a dental aligner, an occlusal splint, and a night guard. The dental product is in particular intended to be placed in the mouth of a person for a certain period of time (for instance overnight) and basically serves to protect and / or align the teeth of the wearer, for instance a protection against damages caused by grinding or gnashing. More specifically, the dental product within the meaning of the present invention may serve for orthodontic appliances and may thus also be referred to as orthodontic device.In an embodiment, the dental product is a dental aligner. In particular, a dental aligner within the meaning of the present invention is an orthodontic device that is suitable to help an alignment and / or straightening of teeth.

[0064] In an embodiment, the dental product exhibits a shape memory effect at a temperature above 40°C, in particular above 45°C, in particular above 50°C. Thus, a shape-memory effect does not occur when the dental product is worn in the mouth of a user, but can be deliberately triggered (e.g. by heating above the glass transition temperature).

[0065] In a fourth aspect, the present invention relates to a method of treating the dental product of the third aspect. The method of treating may in particular result in triggering a shape memory effect so that the dental product may adopt again its initial shape and clamping force. The method of treating of the fourth aspect may therefore also be referred to as a method of reactivating the dental product in terms of clamping force.

[0066] The method of treating the dental product comprises the step of heating the dental product to a temperature of at least 40°C and / or to a temperature above the glass transition temperature of the material (in particular the polymer) constituting the dental product.

[0067] In an embodiment, the method of treating comprises heating the dental product to a temperature of at least 45°C, in particular at least 50°C. The upper limit of the temperature is not particularly limited, as long as the dental product is not damaged, and typically is up to 120°C, such as up to 100 °C, such as up to 70 °C,

[0068] In an embodiment, the step of heating the dental product to a temperature of at least 40°C comprises placing the dental product in a liquid, such as water, having a temperature of at least 40°C, in particular at least 45°C, in particular at least 50°C.

[0069] In an embodiment, the method of treating further comprises maintaining the dental product (at the elevated or heating temperature) for at least 2 seconds, in particular at least 10 seconds. The upper limit of the duration is not particularly limited, and typically is less than 24 hours, such as less than 12 hours.The present invention is further described by the following examples, which are solely for the purpose of illustrating specific embodiments, and are not construed as limiting the scope of the invention in any way.

[0070] Examples

[0071] Resin compositions comprising the following components have been prepared: UDMA CAS: 72869-86-4

[0072] TPO-L CAS: 84434-11-7

[0073] IBOMA CAS: 7534-94-3

[0074] TMPMP CAS: 33007-83-9

[0075] TAICROS-M CAS: 6291-95-8

[0076] The resin compositions have been subjected to a printing method involving curing of the resin composition by irradiation with light.

[0077] The tensile properties, more specifically the Young's modulus (E modulus) and the elongation at break of the photopolymer have been determined in accordance with DIN EN ISO 527-1 and the stress prior and after stress relaxation of the photopolymer has been determined in accordance with DIN 53441 at 1,5 % elongation for 30 min. The results are summarized in the following Table 1.

[0078] [Table 1]

[0079] Elongation Stress

[0080] E-modulus at at break at at Stress at 40°C 40°C start at end of test at 40°C 40°C

[0081] TMPMP / Taicros M Mpa % MPa MPa 11.25 1450 23 12.7 3.4 13.25 1337 26 11.8 2.9 15.25 866 40 7.01 0.95 17.25 853 44 6.94 0.95 18.25 905 34 7.3 0.9 19.25 767 42 6.1 0.7 21.25 782 46 6.2 0.7 Foils Scheu CA-Pro 1561 200 17 13.5

[0082]

[0083] TC-85 110 70 0.9 0The samples “TMPMP / Taicros M” concern resin composition comprising 30 wt.-% IBOMA, 70 wt.-% LIDMA and the indicated value (such as 11.25, 13.25, etc.) wt.-% of a mixture of TM PM P and Taicros M (in a ratio of 1:1 functional groups) and 5% IBOMA.

[0084] The sample “Foils Scheu CA-Pro” is a deep-drawn (thermoformed) film representing the prior art.

[0085] The sample “TC-85” is polyurethane-based composition provided by Graphy Inc.

[0086] As evident from the tensile test shown in Table 1 , the addition of a mixture of TMPMP and Taicros M (in a ratio of 1:1 functional groups) leads to a decrease in the modulus of elasticity and to a higher elongation at break. This is due to the fact that the glass transition is shifted to lower temperatures.

[0087] A stress relaxation experiment was also carried out. Each sample was stretched by 1.5 % in water at 40°C and the stress was measured both immediately after stretching and after 30 minutes. The results show that the concentration of TMPMP / Taicros M has an influence on the final stress.

[0088] It is clear that deep-drawn splints exhibit significantly lower stress relaxation than 3D-printed splints, which has a direct effect on the treatment. Furthermore, it can be seen that the stress after 30 min is significantly higher (0.7 MPa) with the splints according to the present invention than with the Graphy splint (not measurable with the set-up).

[0089] However, the major advantage of 3D-printed splints over deep-drawn versions is the shape memory effect. The original shape and therefore stress can be restored by heating with warm water.

[0090] In a further experiment, a regeneration by the shape memory effect was demonstrated. After heating to 55°C and subsequent cooling, the dental splints achieved almost the same strength values as before the treatment, which proves that their original mechanical properties were restored, as shown in Table 2 below.

[0091] [Table 2]

[0092] After 0 h at jaw model After 18 h at jaw model After reactivation at 55°C Forces [N] 12.9 2.2 11.9

[0093]

[0094] Moreover, it could be confirmed that the regeneration of the dental splints could be repeated several times with substantially restored mechanical properties.

[0095] In a still further experiment, resin compositions were evaluated which only differ in the presence of trimethylallyl isocyanurate (TAICROS-M; CAS: 6291-95-8) vs. its allyl analogue, triallyl isocyanurate (TATO; CAS: 1025-15-6)

[0096] Test specimens were prepared from the respective formulations by means of additive manufacturing and then cleaned for 2 minutes in isopropanol in an ultrasonic bath, followed by post-curing under irradiation with light of 405 nm for 2 x 5 minutes at 60 °C. The samples were then stored in distilled water at 100 °C for 15 minutes. For conditioning, the samples were stored in water at 37 °C for 7 days and then in water at room temperature for 24 hours.

[0097] The mechanical test was finally carried out at room temperature in accordance with ISO 527-1 and ISO 527-2. The results are summarized in the following Table 3.

[0098] [Table 3]

[0099] Fracture energy [N mm] Standard deviation Inventive resin composition

[0100] 975.3 157.8 containing TAICROS-M

[0101] Comparative resin composition

[0102] 707.7 143.7 containing TATO

[0103]

[0104] As can be seen from the above results, cured resin compositions containing TAICROS-M are characterized by a significantly increased fracture energy. A high fracture energy is of utmost relevance for aligners, as they are permanently exposed to mechanical stress when used in the oral cavity and must not fail or break under any circumstances.

[0105] While the present invention has been described in detail by way of specific embodiments and examples, the invention is not limited thereto and various alterations and modifications are possible, without departing from the scope of the invention.

Claims

CLAIMS1. A resin composition comprising:at least one methacrylate compound having at least two methacryl functional groups; at least one thiol compound having at least two thiol functional groups; and at least one methallyl compound having at least two methallyl functional groups.

2. The resin composition according to claim 1 , wherein the amounts of the at least one methacrylate compound, the at least one thiol compound and the at least one methallyl compound are such that the ratio of the number of methacryl functional groups : thiol functional groups : methallyl functional groups is (15 to 80) : (5 to 20) : (5 to 20), in particular (30 to 80) : (10 to 15) : (10 to 15).

3. The resin composition according to claim 1 or 2, wherein the amounts of the at least one thiol compound and the at least one methallyl compound are such that the ratio of the number of thiol functional groups to the number of methallyl functional groups is from 1 : 0.8 to 1 : 1.25, in particular from 1 : 0.9 to 1 : 1.1.

4. The resin composition according to any one of the preceding claims, wherein the at least one thiol compound has at least three thiol functional groups; and / or the at least one methallyl compound has at least three methallyl functional groups.

5. The resin composition according to any one of the preceding claims, wherein the at least one methacrylate compound further comprises at least one urethane group, in particular wherein the at least one methacrylate compound comprises diurethane dimethacrylate.

6. The resin composition according to any one of the preceding claims, wherein the at least one thiol compound is selected from the group consisting of trimethylolpropane tris(3-mercaptopropionate) and pentaerythritol tetrakis(3-mercaptopropionate).

7. The resin composition according to any one of the preceding claims, wherein the at least one methallyl compound further comprises at least one isocyanurate group, in particular wherein the at least one methallyl compound comprises trimethallyl isocyanurate.

8. The resin composition according to any one of the preceding claims, comprising diurethane dimethacrylate, trimethylolpropane tris(3-mercaptopropionate) and trimethallyl isocyanurate.

9. The resin composition according to any one of the preceding claims, further comprising at least one of the group consisting of a photoinitiator, a light absorber, a reactive diluent, and a stabilizer.

10. A printing method comprising the steps of:providing a resin composition as defined in any one claims 1 to 9; and irradiating at least a part of the resin composition with an energy-carrying activation beam so as to cause polymerization of the at least a part of the resin composition.

11. The printing method according to claim 10, further comprising a step of heating the resin composition.

12. The printing method according to claim 10 or 11, further comprising a step of postcuring the polymer, in particular during and / or after irradiating the at least part of the resin composition.

13. A dental product obtainable by the printing method according to any one of claims 10 to 12, wherein the dental product is selected from the group consisting of a dental aligner, an occlusal splint, and a night guard.

14. The dental product according to claim 13, wherein the dental product is a dental aligner.

15. The dental product according to claim 13 or 14, exhibiting a shape memory effect at a temperature above 40°C, in particular above 45°C, in particular above 50°C.

16. A method of treating the dental product according to any one of claims 13 to 15, the method comprising the step of heating the dental product to a temperature of at least 40°C.

17. The method according to claim 16, wherein the method comprises heating the dental product to a temperature of at least 45°C, in particular at least 50°C.

18. The method according to claim 16 or 17, wherein the step of heating the dental product to a temperature of at least 40°C comprises placing the dental product in a liquid, such as water, having a temperature of at least 40°C.19 The method according to any one of claims 16 to 18, wherein the method further comprises maintaining the dental product for at least 2 seconds, in particular at least 10 seconds.

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