Infiltrant for dental ceramics

Abstract

Infiltrant comprising 90 to 99.9 wt.% of at least one polymerizable monomer, oligomer or prepolymer and 0.05 to 10 wt.% of a polymerization initiator, wherein the infiltrant has a dynamic viscosity of 0.3 to 100 mPa·s (23°C); for use in a method for solidifying a fixed ceramic dental prosthesis in the oral cavity.

Description

[0001] Dental prostheses are subject to high stress during use. Damage is typically caused by wear and tear, but sometimes also by the dentist, for example, during occlusion adjustment, such as by using a drill immediately after the prosthesis has been fixed. This leads to the formation of damaged areas, particularly in permanently fixed ceramic prosthesis components. A damaged area can be identified by its rougher surface compared to the surrounding ceramic surface. A damaged area is specifically defined as a surface layer with microcracks and / or micro-holes. Damaged areas are characterized by a propagating weakened layer of the ceramic material. A damaged area reduces the lifespan of a ceramic dental prosthesis, for example, by accelerating crack growth and fracture.Currently, dentists lack the means or methods to improve the strength and durability of a fixed prosthesis or to restore a damaged area of ​​a fixed prosthesis in the oral cavity. The object of the present invention was therefore to provide means and methods for improving the strength and durability and / or restoring surface areas of intraorally fixed ceramic prosthesis components. Surprisingly, it was found that the means and methods provided according to the invention are suitable for completely or almost completely restoring the tensile strength of a ceramic component. The provided means and methods are effective, convenient, and time-saving for both the patient and the dentist.

[0002] Progressive weakening of layers is a particular problem when using silicate-based ceramics, such as feldspar ceramics or glass ceramics.

[0003] In dentistry, the best but currently insufficient method for treating roughened surfaces of ceramic prosthetic restorations is to polish the affected areas. However, polishing a damaged or weakened area of ​​ceramic may not restore its original strength.

[0004] European patent application EP 2145613 A1 relates to infiltrants with high penetration coefficients for the treatment or prevention of carious enamel lesions, comprising crosslinking monomers, wherein at least 5 wt% of the crosslinking monomers comprise at least three polymerizable groups. European patent application EP 2145613 A1 further teaches that the proportion of the crosslinking monomers with at least three polymerizable groups and a distance between the crosslinking points of less than 10 bond lengths, based on the total mass of the monomers, is preferably less than 20 wt%, more preferably less than 10 wt%, and more preferably less than 5 wt%.

[0005] European patent EP 2226061 B1 describes infiltrants with high penetration coefficients for the treatment or prevention of carious enamel lesions, comprising crosslinking monomers and acidic monomers with phosphoric and / or phosphonic acid groups.

[0006] US 2013 / 0116384 A1, US 2006 / 0264532 A1 and DE 202012011045 U1 concern infiltrants for the treatment or prevention of carious enamel lesions.

[0007] The object of the present invention was to provide compositions, kits and methods for restoring damaged or weakened intraoral fixed ceramic prosthesis components to restore at least their original strength and / or at least to increase their durability.

[0008] A further object of the present invention was to provide compositions, kits and methods for increasing the strength and / or durability of intraoral fixed ceramic prosthesis components, in particular damaged or weakened intraoral fixed ceramic prosthesis components.

[0009] The present invention is defined in the claims.

[0010] Surprisingly, it was found that the provided compositions, kits and methods are suitable for restoring at least the original tensile strength or flexural strength of a ceramic body.

[0011] Furthermore, it was surprisingly found that the provided compositions, kits and procedures are suitable for improving the tensile or flexural strength of a ceramic body, especially damaged or weakened intraoral fixed ceramic prosthesis components.

[0012] The provided compositions, kits and processes are particularly suitable for the strengthening of silicate-based ceramics after deterioration of the ceramic surface by mechanical processes, e.g. abrasive wear.

[0013] The invention provides an infiltrant comprising 90 to 99.9 wt.% of at least one polymerizable monomer, oligomer or prepolymer and 0.05 to 10 wt.% of a polymerization initiator, wherein the infiltrant has a dynamic viscosity of 0.3 to 100 mPa·s (23°C); for use in a method for solidifying a fixed ceramic dental prosthesis in the oral cavity.

[0014] The procedure preferably includes the following steps: a. if necessary, cleaning a ceramic surface layer of the fixed prosthesis, b. if necessary, rinsing the ceramic surface layer, c. Drying of the ceramic surface layer, d. Application of the infiltrant to the dried ceramic surface layer, e. if necessary, removal of adhering infiltrant from the surface of the ceramic surface layer, f. Hardening of the infiltrant in the ceramic surface layer, g. if necessary, cleaning and / or polishing the surface of the ceramic surface layer.

[0015] Preferably, one of the first process steps is the identification of a damaged or degraded ceramic surface. This identification can be carried out by visual and / or tactile inspection or by OCT (Optical Coherence Tomography). Optical coherence tomography (OCT) is preferred because it provides an exact three-dimensional image of a damaged ceramic layer.

[0016] Another embodiment of the invention is the provision of a kit comprising: a. an organic solvent with an evaporation number of 1 to 35, preferably 1 to 15, b. an infiltrant according to any one of claims 1 to 7.

[0017] The first kit component comprises a desiccant, which essentially consists of an organic liquid with an evaporation rate of 1 to 35. The kit component container preferably includes an application device, in particular a brush, a cannula, or a tip.

[0018] The second kit component comprises an infiltrant according to the invention. The kit component container preferably comprises an application device, in particular a brush, a cannula or a tip.

[0019] Within the scope of the present invention, it was assumed that penetrating oral fluids promote the progression of a damaged layer. Therefore, an attempt was made to prevent this progression by permanently sealing the damaged layer.

[0020] The procedure consisted of completely infiltrating existing microcracks and / or microholes with infiltrants having excellent penetration properties and, after the infiltrant had hardened, sealing the microcracks and microholes below the surface.

[0021] Surprisingly, the experiments showed that not only was the progression of the weakening prevented, but the weakened structure itself could also be restored.

[0022] In particular, the strength (especially the fracture strength) of the ceramic was improved, restored or even enhanced compared to the initial strength or the strength after polishing away a weakened layer area.

[0023] In one embodiment, the infiltrant essentially consists of a mixture of monomers, oligomers or prepolymers having more than one polymerizable grouping and additives for curing.

[0024] Preferably, the infiltrant can be cured by radical polymerization.

[0025] In another embodiment, the infiltrant essentially consists of a mixture of monomers, oligomers or prepolymers having more than one polymerizable grouping, and a small percentage of monomers, oligomers or prepolymers having a silanol grouping, and additives for curing.

[0026] An infiltrant is understood to be a composition that flows into micropores and / or microcracks of a solid body and fills thepores and cracks within a few seconds, where it can be cured. Thepores and cracks have sizes ranging from a few microns to a few nanometers. Furthermore, an infiltrant is understood to be a curable, or more precisely, polymerizable liquid or solution comprising polymerizable monomers or a mixture of various polymerizable monomers, oligomers, or prepolymers, and additives dissolved in the monomers or monomer mixture. Within the scope of the invention, the term infiltrant is defined as a liquid mixture at room temperature (23°C) containing monomers, polymerization initiators and / or inhibitors, and / or other additives necessary to keep the infiltrant manageable, at least for the duration of its shelf life.A monomer, oligomer, or prepolymer is defined as a molecule possessing at least one polymerizable group, such as a vinyl group. Monomers, oligomers, or prepolymers with more than one polymerizable group can act as crosslinkers. The infiltrants are Newtonian fluids. The infiltrant preferably has a dynamic viscosity at room temperature (RT) of 0.3 to 30 mPa·s. In another embodiment, the infiltrant has a dynamic viscosity at room temperature (RT, 23°C) of 30 to 100 mPa·s.

[0027] Ceramic refers to a solid, predominantly inorganic material produced by sintering at a specific temperature over a given period. A fixed ceramic prosthesis (or part thereof) is permanently fixed, in particular bonded or cemented and / or screwed to dental hard tissue or a synthetic substrate.

[0028] A silicate-based ceramic is understood to be a ceramic that is based on silicates or contains significant amounts of silicates. Silicate ceramics used in dental technology are ceramics with a high glass content based on aluminosilicate glass [JR Kelly, JADA 2008, 139, Suppl. 4, 4S-7S], e.g., feldspathic ceramics, leucite and mica-based ceramics, or high-fusing glass ceramics.

[0029] Another class of silicate-based ceramics is structural ceramics with low glass content, such as lithium disilicate ceramics, glass-infused metal oxides or glass-infused spinels, and the like.

[0030] The present invention is particularly suitable for treating the surface of a ceramic that is permanently fixed to a tooth or permanently mounted in the oral cavity, such as a dental implant. Such a ceramic component can be an inlay, an onlay, a veneer, a partial crown, a crown, a bridge, a larger fixed prosthesis, or the like. The prosthesis consists wholly or partially of ceramic material. The ceramic component has at least one surface facing the oral cavity, which may be an oral, vestibular, occlusal, incisal, or proximal surface.

[0031] The present invention can be applied in particular to all types of silicate ceramic surfaces, especially to all types of silicate ceramics that are fixed in the mammalian body for medical and especially dental reasons.

[0032] The cleaning in step a. of the method according to the invention means at least the cleaning of the damaged area of ​​the ceramic prosthesis. Cleaning means the removal of, for example, plaque and other adhering contaminants and can be carried out by conventional dental treatment, e.g. polishing with abrasive pastes or air abrasion, or using dental instruments or machines.

[0033] The rinsing in step b. of the method according to the invention can be carried out by conventional dental treatment, e.g. with air-water spray or water alone.

[0034] The drying in step c. of the method according to the invention can be carried out by applying a stream of dried air over a specific period of time – until it can be assumed that water or aqueous residues have largely evaporated from existing holes and cracks. Preferably, the drying is carried out by rinsing with an organic liquid. A suitable organic liquid is completely volatile; it preferably has an evaporation number of 1 to 35, more preferably 1 to 15, where evaporation number is understood to be the evaporation time of the organic liquid divided by the evaporation time of acetone under the same conditions. The evaporation number can be determined according to German Industrial Standard (DIN) 53170:2009. Such a volatile organic liquid evaporates rapidly in the oral cavity and thereby removes residual water molecules.This drying process can be achieved by simply injecting the liquid once or several times from a syringe onto the ceramic surface. The liquid is then allowed to evaporate. Preferably, the evaporation of the solvent is further accelerated by applying a stream of dry air and / or the evaporation of the solvent is followed by the application of a stream of dry air. The volatile organic liquid preferably has an initial boiling point between 35°C and 100°C, more preferably between 50°C and 80°C. The organic liquid is preferably completely miscible with water. The organic liquid preferably contains no water or less than 5% water by weight. Ethanol or a mixture of ethanol with other organic solvents is particularly preferred as the organic liquid.

[0035] The application of an infiltrant in step d. of the method according to the invention can be carried out simply by bringing the infiltrant into contact with the ceramic surface, e.g. by using a cannula tip, a syringe, a brush or other suitable application systems, e.g. a sandwich composite film with channels in it with a proximal opening towards the ceramic surface.

[0036] The hardening of the infiltrant in step f. of the inventive process can be carried out by applying actinic radiation to the area using conventional dental polymerization lamps, most preferably with an emission maximum of 350 to 500 nm.

[0037] The infiltrant may contain adjuvants that can potentially infiltrate holes and cracks. For specific reasons, the infiltrant may also contain known dental fillers ranging in size from 1 nanometer to 100 microns, which can potentially infiltrate holes and cracks.

[0038] The infiltrant preferably has a contact angle at room temperature (23°C) and atmospheric pressure of less than about 60°, more preferably 0 to about 35°, on any flat ceramic or soda-lime glass surface, or more preferably, soda-lime silicate glass surface, finished with a mirror polish of 4000 grit. The surface tension of the infiltrant, measured at room temperature (23°C) and atmospheric pressure, is preferably higher than about 5 mN / m, more preferably higher than about 10 mN / m, and most preferably higher than about 20 mN / m or between about 20 and 50 mN / m.

[0039] The surface tensions of the infiltrants can be determined, for example, with an optical drop shape analyzer of the type KRÜSS DSA 10 (KRÜSS GmbH, Germany), e.g., using the pendant drop method.

[0040] Contact angles of infiltrants can be measured, for example, on soda-lime glass slides (e.g., Menzel glasses, Thermo Scientific, Gerhard Menzel GmbH, Germany) or polished ceramic discs, e.g., with an optical drop shape analyzer of the KRÜSS DSA 10 type (KRÜSS GmbH, Germany), e.g., using the sessile drop method.

[0041] The infiltrant comprises 90 to 99.9, preferably 95 to 99.9, wt. percent of polymerizable monomers or a mixture of polymerizable monomers, oligomers, or prepolymers. A particularly preferred infiltrant comprises 95 to 99.8 percent of a mixture of monomers with at least two polymerizable groups.

[0042] Suitable monomers, oligomers, and prepolymers are acrylates and methacrylates or acrylamides and methacrylamides. Preferred polymerizable monomers, oligomers, or prepolymers are crosslinkable monomers, oligomers, or prepolymers. Preferred crosslinkable monomers, oligomers, or prepolymers are diacrylates, triacrylates, or polyacrylates; or dimethacrylates, trimethacrylates, or polymethacrylates; or diacrylamides, triacrylamides, or polyacrylamides; or dimethacrylamides, trimethacrylamides, or polymethacrylamides.

[0043] Other suitable monomers, oligomers or prepolymers contain one or more polymerizable groups selected from the group consisting of a polymerizable double bond, a ring-opening polymerizable group, a thiol group, an epoxy group, and a vinyl group.

[0044] A preferred composition of an infiltrant for the treatment of a degraded dental ceramic surface in the oral cavity comprises the components (a)-(g) defined below, wherein the parts of components (a)-(g) sum to 100. The proportions of the components are given in parts by weight.

[0045] Component (a) is a monomer or a mixture of monomers with exactly two polymerizable groups per molecule. Preferably, the infiltrant composition comprises component (a) in an amount of 30 to 99.5 wt.%. More preferably, component (a) is present in an amount of 30 to 79 wt.%, and most preferably, component (a) is present in an amount of 40 to 74 wt.%.

[0046] They may preferably be selected from the group consisting of allyl methacrylate; allyl acrylate; PRDMA, 1,3-propanediol dimethacrylate; BDMA, 1,3-butanediol dimethacrylate; BDDMA, 1,4-butanediol dimethacrylate; PDDMA, 1,5-pentanediol dimethacrylate; NPGDMA, neopentyl glycol dimethacrylate; HDDMA, 1,6-hexanediol dimethacrylate; NDDMA, 1,9-nonanediol dimethacrylate; DDDMA, 1,10-decanediol dimethacrylate; DDDDMA, 1,12-dodecanediol dimethacrylate; PRDA, 1,3-propanediol diacrylate; BDA, 1,3-butanediol diacrylate; BDDA, 1,4-butanediol diacrylate; PDDA, 1,5-pentanediol diacrylate; NPGDA, neopentyl glycol diacrylate; HDDA, 1,6-hexanediol diacrylate; NDDA, 1,9-nonanediol diacrylate; DDDA, 1,10-decanediol diacrylate; DDDDA, 1,12-dodecanediol dimethacrylate; EGDMA, ethylene glycol dimethacrylate; DEGDMA, diethylene glycol dimethacrylate; TEDMA, triethylene glycol dimethacrylate; TEGDMA, tetraethylene glycol dimethacrylate; EGDA, ethylene glycol diacrylate; DEGDA, diethylene glycol diacrylate; TEDA, triethylene glycol diacrylate; TEGDA, tetraethylene glycol diacrylate;PEG200DMA, Polyethylenglykol-200-dimethacrylat; PEG300DMA, Polyethylenglykol-300-dimethacrylat; PEG400DMA, Polyethylenglykol-400-dimethacrylat; PEG600DMA, Polyethylenglykol-600-dimethacrylat; PEG200DA, Polyethylenglykol-200-diacrylat; PEG300DA, Polyethylenglykol-300-diacrylat; PEG400DA, Polyethylenglykol-400-diacrylat; PEG600DA, Polyethylenglykol-600-diacrylat; PPGDMA, Polypropylenglykoldimethacrylat; PPGDA, Polypropylenglykoldiacrylat; NPG(PO)2DMA, propoxyliertes (2) Neopentylglykoldimethacrylat; NPG(PO)2DA, propoxyliertes (2) Neopentylglykoldiacrylat; Bis-MA, Bisphenol-A-dimethacrylat; Bis-GMA, Bisphenol-A-glycerindimethacrylat; BPA(EO)DMA, ethoxyliertes Bisphenol-A-dimethacrylat (EO=1-30); BPA(PO)DMA, propoxyliertes Bisphenol-A-dimethacrylat (PO=1-30); BPA(EO)DA, ethoxyliertes Bisphenol-A-diacrylat (EO=1-30); BPA(PO)DA, propoxyliertes Bisphenol-A-diacrylat (PO=1-30); BPA(PO)GDA, propoxyliertes Bisphenol-A-glycerindiacrylat; UDMA, Diurethandimethacrylat;TCDDMA, Tricyclo[5.2.1.0]decandimethanol dimethacrylate; TCDDA, Tricyclo[5.2.1.0]decandimethanol diacrylate; EBA, N,N'-Ethylene bisacrylamide; DHEBA, N,N'-(1,2-Dihydroxyethylene)bisacrylamide; DEPBA, N,N'-Diethyl(1,3-propylene)bisacrylamide; TMHMBMA, N,N'-(2,2,4-Trimethylhexamethylene)bismethacrylamide; and Bis[2-(2-methylacrylamino)ethoxy-carbonyl]hexamethylenediamine.;

[0047] Component (b) is a monomer or a mixture of monomers with at least 3 polymerizable groups in one molecule.

[0048] The proportion of crosslinking monomers with at least three polymerizable groups can be between 0 and 60 wt.%, preferably 10 and 60 wt.%, even more preferably between 20 and 60 wt.% and most preferably between 25 and 50 wt.%.

[0049] Suitable low-viscosity monomers with at least three polymerizable groups include, for example, glycerol triacrylate, TMPTMA; trimethylolpropane trimethacrylate, TMPTA; trimethylolpropane tri(meth)acrylate, DTMPTA; ditrimethylolpropane tetra(meth)acrylate; DiPENTA, dipentaerythritol penta(meth)acrylate; or DPEHA, dipentaerythritol hexa(meth)acrylate.

[0050] Preferred low-viscosity monomers with at least three polymerizable groups are based, for example, on alkoxylated multiple alcohols (tri-, tetra-, penta-, hexa-, polyols) such as trimethylolpropane, ditrimethylolpropane, glycerol, pentaerythritol or dipentaerythritol.

[0051] Another preferred group of monomers are (meth)acrylic esters of alkoxylated polyalcohols such as ethoxylated glycerol triacrylate, propoxylated glycerol triacrylate, ethoxylated trimethylol propane trimethacrylate, ethoxylated trimethylol propane triacrylate, propoxylated trimethylol propane trimethacrylate, propoxylated trimethylol propane triacrylate, ethoxylated pentaerythritol trimethacrylate, ethoxylated pentaerythritol triacrylate, ethoxylated pentaerythritol tetramethacrylate, ethoxylated pentaerythritol tetraacrylate, ethoxylated dipentaerythritol trimethacrylate, ethoxylated dipentaerythritol tetramethacrylate, ethoxylated dipentaerythritol pentamethacrylate, ethoxylated dipentaerythritol hexamethacrylate, ethoxylated Dipentaerythritol triacrylate, ethoxylated dipentaerythritol tetraacrylate, ethoxylated dipentaerythritol pentaacrylate, ethoxylated dipentaerythritol hexaacrylate, propoxylated pentaerythritol trimethacrylate,Propoxylated pentaerythritol triacrylate, propoxylated pentaerythritol tetramethacrylate, propoxylated pentaerythritol tetraacrylate, propoxylated dipentaerythritol trimethacrylate, propoxylated dipentaerythritol tetramethacrylate, propoxylated dipentaerythritol pentamethacrylate, propoxylated dipentaerythritol hexamethacrylate, propoxylated dipentaerythritol triacrylate, propoxylated dipentaerythritol tetraacrylate, propoxylated dipentaerythritol pentaacrylate and propoxylated dipentaerythritol hexaacrylate.

[0052] These alkoxy groups bonded to the alcohols act as (molecular) chain extenders. Chain elongation can preferably be achieved by ethoxylation or propoxylation. Other linkages are also possible for chain elongation, such as ether bonds, ester bonds, amide bonds, urethane bonds, and the like, to which ethylene glycol or propylene glycol groups can preferably be attached.

[0053] The chain-extending group is preferably functionalized terminally with the crosslinking groups, preferably with a methacrylate or acrylate group, a methacrylamide or acrylamide group.

[0054] The crosslinking point is considered to be the position of the crosslinking polymerizable group, for example the position of a C=C double bond in the monomer.

[0055] The chain length is preferably such that the distance between the crosslinking points is at least 3, preferably at least 6, more preferably 6 to 30, particularly preferably 6 to 26 bond lengths, with 6 to 12 bond lengths being particularly preferred.

[0056] The distance between crosslinking points refers to the shortest distance between the crosslinking groups, such as two C=C double bonds, along the molecule. It therefore refers only to the constitution of the molecule, not the actual spatial arrangement of the groups relative to each other, as determined by configuration or conformation.

[0057] Bond length refers to the distance between two atoms in the molecule, regardless of the type of covalent bond and the exact bond length of each individual covalent bond.

[0058] The proportion of crosslinking monomers with at least three polymerizable groups and a distance between the crosslinking points of less than 30 bond lengths, preferably less than 12 bond lengths, based on the total mass of the monomers, is preferably less than more than 10 wt.%, further preferably more than 20 wt.%, further preferably more than 25 wt.%.

[0059] Component (c) is a monomer or a mixture of monomers with one or more additional functional groups in a molecule.

[0060] Preferably, the infiltrant comprises polymerizable monomers selected from the above-mentioned polymerizable monomers, oligomers, and prepolymers with one or more additional functional groups. These additional functional groups are selected from hydroxyl groups (-OH) or groups containing a hydroxyl group. Suitable groups are carboxylic acid groups (-CO-OH), phosphoric acid ester groups (-O-PO(OH)₂), or phosphonic acid groups (-PO(-OH)₃), and / or silanol groups (Si-OH) or groups that can be hydrolyzed to silanol groups. Silanol groups (Si-OH) and groups that can be hydrolyzed to silane groups (Si-OR) are particularly preferred. The silanol groups can be the -SiR₂-OH-, -SiR(OH)₂-, or -Si(OH)₃- group, where R preferably represents alkyl and more preferably methyl.Groups that can be hydrolyzed to a silanol group are preferably SiR3-n(X)n groups with n = 1-3 and R = alkyl, preferably methyl, where X represents a hydrolyzable group. Polymerizable monomers with silanol groups or groups that can be hydrolyzed to silanol groups are preferably present in their non-hydrolyzed or partially hydrolyzed form. The polymerizable silicon-containing monomer is most preferably methacryloxypropyltrimethoxysilane (MEMO). Preferably, the infiltrant comprises 0.1 to 50 wt% polymerizable monomers selected from the above polymerizable monomers, oligomers, and prepolymers with one or more further functional groups, more preferably 1 to 40 wt%, more preferably 3 to 30 wt%, and most preferably 20 to 30 wt%.

[0061] In a further embodiment of the invention, the infiltrant preferably comprises 3 to 30 percent by weight, preferably 3 to 10 percent by weight, of polymerizable monomers selected from the above polymerizable monomers, oligomers and prepolymers with one or more further functional groups.

[0062] Preferred acid groups are phosphono and phosphonic acid groups. Examples include corresponding organic hydrogen phosphates or dihydrogen phosphates.

[0063] The acid-containing monomers can be cross-linked, i.e., the monomer molecule contains two or more polymerizable groups in addition to the acid group.

[0064] In selected applications, it can be advantageous if the polymerizable monomers, oligomers, and prepolymers with one or more functional groups contain only one polymerizable group. In particular, the acid-group-containing monomers can be acrylates or methacrylates, acrylamides, or methacrylamides.

[0065] For example, these may be acrylates or methacrylates, which are listed below as preferred additional monomers with a polymerizable group and also a corresponding acid group.

[0066] According to the invention, the acid-containing monomers preferably have a molecular weight (average weight) of 100-1000 g / mol. Preferably, the acid-containing monomers are soluble in the infiltrant. The term "non-aqueous" preferably refers to infiltrants containing less than 5 wt%, preferably less than 2 wt%, water.

[0067] Preferred acid-containing monomers include, for example, 4-methacryloxyethyltrimellitic acid (4-MET), methacryloyloxydecylmalonic acid (MAC-10), maleic acid mono-HEMA esters, N-methacryloyl-N',N'-dicarboxymethyl-1,4-diaminobenzene, N-2-hydroxy-3-methacryloyloxypropyl-N-phenylglycine, O-methacryloyltyrosinamide, 4-methacryloylaminosalicylic acid, phenylmethacryloyloxyalkyl phosphates, e.g., phenylmethacryloyloxyethyl phosphate (Phenyl-P), and methacryloyloxyalkyl dihydrogen phosphates.Methacryloyl-oxyethyl dihydrogen phosphate (HEMA-P), Methacryloyloxypropyl dihydrogen phosphate (MPP), Methacryloyloxyhexyl dihydrogen phosphate (MHP), Methacryloyl-oxydecyl dihydrogen phosphate (MDP), Glyceryl dimethacrylate phosphate (GPDM), Pentaerythritol triacrylate phosphate (PENTA-P), Bis(hydroxyethyl methacrylate) phosphate, (Meth)acrylamidophosphates, (Meth)acrylamidoalkyl diphosphates, (meth)acrylamidoalkylphosphonates, (meth)acrylamidoalkyldiphosphonates, bismethacrylamidoalkyldihydrogen phosphates, vinylbenzylphosphonic acid and vinylbenzoic acid.

[0068] Among the methacryloyloxyalkyldihydrogen phosphates mentioned, methacryloyl-oxydecyldihydrogen phosphate (MDP) is particularly preferred.

[0069] The acid component (c1) is preferably present in an amount of 0.5-10 wt.% and further preferably in an amount of 0.5 to 5 wt.%, based on the total infiltrant.

[0070] Preferred polymerizable monomers, oligomers, or prepolymers with one or more additional functional groups are listed above. Component (c2) of the infiltrant preferably comprises polymerizable monomers selected from monomers with silanol groups (Si-OH) or groups that can be hydrolyzed to silanol groups, the definitions given above. Component (c2) is preferably present in an amount of 0.5 to 25 wt.%, more preferably in an amount of 0.5 to 20 wt.%, and most preferably in an amount of 1 to 10 wt.%.

[0071] Component (d) is an initiator.

[0072] The infiltrant comprises 0.05 to 10 wt% infiltrant-soluble initiators for light-induced radical polymerization (photoinitiators). The infiltrant may also comprise 0.05 to 9.9 wt% infiltrant-soluble accelerators for light-induced radical polymerization. Suitable initiators preferably operate in the wavelength range of 300 to 600 nm, more preferably in the range of 350 to 500 nm, and most preferably in the range of 400 to 500 nm. Preferred initiators are camphorquinone (CQ), bisacylphosphine oxide (BAPO), trimethylbenzoyldiphenylphosphine oxide (TPO), and thioxanthone derivatives. The choice of suitable accelerators depends on the chosen initiator, which is not a problem for a person skilled in the art.

[0073] The term initiator system is to be understood as a combination of a photoinitiator and a suitable accelerator or a suitable group of accelerators. Component (e)

[0074] The infiltrant may optionally comprise up to 10 wt% infiltrant-soluble additives. Suitable additives are common additives for polymerizable dental materials known in the industry, such as stabilizers, infiltrant-soluble fluorescent dyes, and other colorants, etc. Other suitable additives include polymers such as poly(meth)acrylates. Component (f)

[0075] The infiltrant may comprise up to 10% by weight of known solvents that do not contain a polymerizable group. The solvent may help to dilute higher molecular weight monomers or oligomers, such as UDMA and BisGMA, in the infiltrant. Lower molecular weight alcohols, ethers, and ketones, or mixtures thereof, are preferred. Preferably, however, the infiltrant does not contain any such organic solvent that does not contain a polymerizable group. The infiltrant contains less than 1% by weight of water, or preferably no water, or only unavoidable traces of water.

[0076] In a preferred embodiment, the infiltrant comprises at least components (a) to (d). In another embodiment, the infiltrant comprises (a), (b), (c2) and (d). In a further embodiment, the infiltrant comprises (a), (b), (c1) and (d). In a preferred embodiment, the infiltrant comprises components (a), (b), (c1, c2) and (d).

[0077] The infiltrant components (a)-(d) carry (meth)acrylate or (meth)acrylamide groups as polymerizable groups, with (meth)acrylate groups being particularly preferred.

[0078] Preferably, the composition of the present invention, in addition to monomers containing functional groups, does not comprise significant concentrations of polymerizable monomers with only one polymerizable group in the molecule. The amount of such monomers should be less than 20 wt% and, more preferably, less than 5 wt%. It is particularly preferred that the composition of the present invention does not contain any such monomers. Method viscosity

[0079] The dynamic viscosity of the infiltrants can be measured using any suitable method. Suitable measurement methods for the dynamic viscosity of the infiltrants are described further in the examples. Surface roughness

[0080] Surface roughness can be measured using any suitable method. The surface roughness (Ra) was evaluated using an optical confocal profilometer (high-resolution, non-contact confocal white-light profilometer; CyberSCAN CT 100, Cyber ​​Technologies GmbH, Germany). The surface of the test specimens was scanned with a sensor head with a resolution of 0.02 mm in 10 µm increments for an illumination time of 0.5 ms. This technique detects height levels over a measurement range defined by different wavelengths in the projected white-light spectrum. Changes in intensity and wavelength are analyzed by the spectrometer, which defines height levels when they reach the maximum intensity level for a specific wavelength.To prevent interference from signals originating below the surface, reflection intensities were chosen to ensure a clean reading of light reflections coming only from the surface. Liability

[0081] Ceramic rods were cut from Vitablocs Mark II using a diamond saw (Bühler) and ground to the test dimensions (3 x 3 x 13 mm and 3 x 6 x 13 mm) using a diamond wheel. The infiltrants were applied to both opposing surfaces, which were then joined and polymerized from two different sides using a light-curing unit (Elipar Trilight, 3M ESPE) with a light intensity of 800 mW / cm² for 20 s. The samples were stored dry at room temperature. The tensile test was performed in air using a universal testing machine (Z 2.5, Zwick, Ulm, Germany) at a crosshead speed of 1 mm / min by pulling the upper rod with a low-yield rope (Dyneema SK75, DSM Dyneema, Stanley, USA) until detachment.The tensile bond strengths were calculated by dividing the maximum applied load (N) by the rectangular area of ​​the adhesive interface measured after testing with a digital caliper. Biaxial flexural strength

[0082] The biaxial bending strength can be measured according to any suitable method. Method 1

[0083] After 24 hours of water immersion, the test specimens were subjected to bending tests by the control group (polished, n = 15) and the experimental groups (ground / polished, indented, and sandblasted, n = 15) using the piston-on-three-ball setup according to ASTM standard F 394-78. The test was performed in a universal testing machine (Zwick 2.5, Zwick, Germany) at a crosshead speed of 0.75 mm / min until fracture in air. Method 2

[0084] After storage in a dry environment at room temperature, the test specimens were subjected to bending tests by the control group (polished, n = 15) and the experimental group (sandblasted, n = 15) using the piston-on-three-ball setup according to ASTM standard F 394-78. The test was performed in a universal testing machine (Zwick 2.5, Zwick, Germany) at a crosshead speed of 1 mm / min until fracture in air. Examples

[0085] The following substances were used in the examples. substance abbreviation Triethylene glycol dimethacrylate (Evonik, Germany; η ~10 mPa·s at RT) TEDMA 1,6-Hexanediol dimethacrylate (Esstech, US) HDDMA Diurethane dimethacrylate, isomer mixture, CAS72869-86-4 (Genomer® 4297, Rahn, Switzerland) UDMA Bisphenol A glycerol dimethacrylate, CAS 1565-94-2 (CCP Composites, US) BisGMA Ethoxylated (EO)3 trimethylolpropane triacrylate (Miramer® 3130, Rahn, Switzerland, η ~60 mPa·s at RT) ETMPTA Trimethylolpropane trimethacrylate (Visiomer®TMPTMA, Evonik, Germany) TMPTMA 3-(Trimethoxysilyl)propyl methacrylate (Dynasylan® MEMO, Evonik, Germany, η ~3 mPa·s at RT) MEMO 10-Methacryloyloxydecyl dihydrogen phosphate MDP Camphorquinone (Rahn, Switzerland) CQ 2-Ethylhexyl-p-dimethylaminobenzoate (Genocure®EHA, Rahn, Switzerland) EHA Butylhydroxytoluene BHT Ethyl p-dimethylaminobenzoate, 99% pure, AlfaAesar EDAB Poly(methyl methacrylate), Degacryl MW 332, Evonik Industries PMMA Production example 1:

[0086] In a light-protected glass container, 59.2 parts by weight of TEDMA, 14.8 parts by weight of ETMPTA, 0.5 parts by weight of CQ, 0.8 parts by weight of EHA, and 0.0015 parts by weight of BHT were mixed. The mixture was then stirred at ambient temperature using a magnetic stirrer until a homogeneous, clear solution was obtained. This solution was kept at room temperature, protected from light (which can cause hardening). In an unprotected glass container, 75 parts by weight of this solution were mixed with 25 parts by weight of MEMO using a magnetic stirrer until a clear and homogeneous solution was obtained. This infiltrant was then used to treat damaged ceramic surfaces.

[0087] The viscosity of the infiltrant was measured using a Malvern Kinexus rheometer (Malvern Instruments GmbH, Germany) with a coaxial cylinder device for measuring liquids according to DIN 53019, featuring a 25 mm diameter cone within a 27 mm diameter cylinder, at a temperature of 23°C. Approximately 18 ml of the infiltrant was used in the cylinder. The measurement was performed in the absence of ambient light to prevent polymerization. The following parameters were applied: a table of shear stresses from 0.1 Pa to 1 Pa. The viscosity value was recorded at a shear stress of 0.126 Pa. The viscosity of the infiltrant was 6.2 mPa·s. Production examples 2 to 7

[0088] In a light-protected glass container, substances were mixed under yellow light conditions for each preparation example according to the specifications in Table 2. The mixtures were then stirred at ambient temperature using a magnetic stirrer until homogeneous, clear solutions were obtained. The solutions were kept at room temperature, protected from light, until the infiltrants were used to treat damaged ceramic surfaces.

[0089] The viscosity of the infiltrants was measured using a dynamic plate-plate viscometer (DSR, Dynamic Stress Rheometer, Rheometric Scientific Inc., US). Measurements were taken in "steady stress sweep" mode with gap sizes of 0.1 to 0.5 mm and shear stresses ranging from 0 to 50 Pa, without pre-shearing of the infiltrants. The viscosity of the infiltrants is given in Table 1.

[0090] Table 1: Compositions produced in the manufacturing examples; values ​​are given in parts by weight; viscosity of the samples according to the described method. Production example substance 1 2 3 4 5 6 7 TEDMA 59,2 32,0 28,8 30,4 28,83 22,4 22,4 HDDMA - 57,5 51,34 54,5 51,69 40,1 40,1 UDMA - - - - - - - BisGMA - - - - - - - ETMPTA 14 8 8,0 7,2 7,6 7,21 30,0 - TMPTMA - - - - - - 30,0 MDP - - 5,1 5,0 5,0 5,0 5,0 MEMO 25 - 5, 0 - - - - CQ 0,5 0,5 0,5 0,5 0,5 0,5 0,5 EHA 0, 8 - - - - - - EDAB - 2, 0 2, 0 2, 0 2,0 2,0 2,0 BHT 0,0015 0,002 0,003 0,003 0,002 0,002 0,002 PMMA - - - - 4,76 - - Viscosity / mPa·s 6,2 7,1 8,9 9,1 56,4 13,7 11,8 Example 1 - Healing of a damaged dental ceramic surface with an infiltrant

[0091] Using a glass-ceramic powder material (VM9, Vita Zahnfabrik), ceramic test specimens (discs, Ø = 12.5 mm and thickness 1.2 mm) were produced by condensation and sintering. Sintering was carried out in a furnace (Vacumat 4000, Vita Zahnfabrik) according to the following program: heating rate 55°C / min, 1 min holding time at 940°C under vacuum, and cooling rate 30°C / min. The sintered discs were ground to their final thickness with a diamond wheel and then mirror-polished on the stressed side with SiC papers (Bühler) in grits of 320, 600, 100, 1200, 2500 down to 4000.

[0092] Furthermore, test specimens from the experimental groups were prepared according to two surface treatments: (i) drilling with a coarse diamond drill bit (Komet drill bit no. 220) at 2500 rpm for 10 s with air cooling; (ii) sandblasting with aluminum oxide particles with a size of 35 µm at a pressure of 2 bar for 10 s at an angle of 45°. An optical confocal profilometer was used to measure the mean roughness (Ra) of the treated specimens, yielding Ra = 30 µm for the ground specimens and Ra = 5 µm for the sandblasted specimens. The damaged surfaces were subsequently infiltrated.

[0093] The infiltrant was applied twice to the ceramic surface using a microbrush and left undisturbed for 30 seconds. The infiltrant was then removed from the surface with a cotton pellet, leaving the surface glossy. The infiltrated ceramic surface was subsequently light-cured for 2 x 40 seconds using a halogen blue light lamp (Elipar Trilight, 3M ESPE) at a light intensity of 800 mW / cm². The light intensity was checked periodically with a radiometer. After light-curing, the ceramic discs were stored in vials of distilled water, sealed, and kept at 37°C in a heating module.

[0094] After 24 hours of water immersion, the test specimens from the control group (polished, n = 15) and the experimental groups (ground and sandblasted, n = 15) were tested under bending using the piston-on-three-ball setup according to ASTM standard F 394-78. The test was performed in a universal testing machine (Zwick 2.5, Zwick, Germany) at a crosshead speed of 0.75 mm / min until fracture in air.

[0095] The mean roughness (Ra) values ​​for drilled and sandblasted samples were 30 µm and 5 µm, respectively. Shape and scale parameters for the polished samples were as follows: m = 10.3 and □0 = 101.2 MPa. For drilled samples: m = 7.6 and □0 = 66.4 MPa for drill control; m = 9.0 and □0 = 84.2 MPa for infiltrated drill samples. For sandblasted samples: m = 12.6 and □0 = 78.2 MPa for sandblasted control; m = 8.8 and □0 = 99.98 MPa for sandblasted infiltrated samples. The increase in □0 after infiltration was significant at the 95% level for both drilled and sandblasted samples. Infiltration of smaller defects (sandblasted samples) restored the strength to the level of the polished control and was more efficient than infiltration of larger defects (drilled samples).

[0096] It has been shown that infiltration of defects created by a coarse drill or sandblasting increases the strength of dental ceramics compared to uninfiltrated damaged ceramic samples. Infiltration of small defects may restore the strength of dental ceramics to their initial values. Infiltration of damaged areas, whether caused by the dentist during intraoral adjustments or during function, has the potential to extend the lifespan of dental ceramic prostheses by delaying crack propagation and fracture. Example 2 - Surface crack healing with infiltrants: Glass versus feldspar ceramics

[0097] Soda-lime glass discs (Ø = 15 mm and thickness 1.9 mm; Schott, Germany) were used as reference test specimens. A Vickers indentation (Zwick, Germany) was created on the tensile side of the ceramic discs from Example 1 and the soda-lime glass discs (1 kg over a period of 15 s for VM9 and 500 g over a period of 15 s for glass). The infiltration was carried out as described in Example 1.

[0098] After 24 hours of water storage, the discs were tested under bending using the piston-on-three-ball setup. The Weibull parameters m and □0 were calculated (n = 15 for VM9 and n = 10 for glass) and mathematically corrected according to the number of n. The infiltration depth into the Vickers indentation was measured in samples infiltrated with a fluorescently stained infiltrant using a confocal laser scanning microscope (TCS SL, Leica, Germany).

[0099] Shape and scale parameters for the glass samples were as follows: m = 7.0 and □0 = 335.9 MPa for polished samples; m = 5.9 and □0 = 106.8 MPa for indented samples; m = 8.2 and □0 = 223.2 MPa for infiltrated samples. Shape and scale parameters for the ceramic VM9 samples were as follows: m = 10.3 and □0 = 101.2 MPa for polished samples; m = 11.4 and □0 = 63.52 MPa for indented samples; m = 5.1 and □0 = 83.9 MPa for infiltrated samples. The increase in □0 after infiltration was significant at the 95% level for both glass and ceramic. The infiltration depth in glass samples was recorded to a depth of up to 18 µm, while the infiltration depth in ceramics was 2 to 4 µm deep (subsurface layer).

[0100] As with glass, veneer ceramics can be strengthened and chipping potentially prevented by infiltrating surface cracks with low-viscosity infiltrants and subsequently hardening them. The infiltration depth in ceramics is limited, but this does not appear to impair their strengthening effect.

[0101] The results of Example 1 and Example 2 are summarized in Table 2.

[0102] Table 2: Biaxial flexural strength of sintered ceramic and soda-lime glass wafers of Examples 1 and 2 with different pretreatments of the glass / ceramic surface. Surface infiltration was carried out using the infiltrant from production example 1. Example 1 Example 2 Feldspar glass ceramic discs Soda-lime glass panes P S SI B BI E EGG O E EGG Average roughness [µm] 5 30 Weibull- m 10,3 12,6 8,8 7,6 9,0 11,4 5,1 7,0 5,90 8,20 Weibull σ0[MPa] 101,2 78,2 100,0 66, 4 84,2 63,5 83,9 335,9 106,8 223,2 P - polished grit 4000, S - sandblasted, SI - sandblasted and infiltrated, B - drill-treated, BI - drill-treated and infiltrated, E - depressed, EI - depressed and infiltrated, O - without treatment

[0103] Example 3 - Healing of dental ceramic surfaces damaged by sandblasting with the infiltrants from manufacturing examples 2-7

[0104] Ceramic plates (12 × 12 mm) were cut from finely structured feldspar ceramic blocks (Vitablocs® Mark II, Vita, Germany) and ground to the final thickness (1.3 ± 0.05 mm) by grinding with a diamond wheel as described in Example 1.

[0105] The ceramic slabs were subjected to two different surface treatments: (i) mirror polished with SiC papers (Bühler) with a grit size down to 4000 on the stressed side and (ii) sandblasted with aluminium oxide particles with a size of 35 µm at a pressure of 2 bar for a period of 5 s at an angle of 45°.

[0106] Each infiltrant was applied once to the ceramic surface using a microbrush and left undisturbed for 30 seconds. The infiltrant was then removed from the surface with a cotton pellet, leaving the surface glossy. The infiltrated ceramic surface was subsequently light-cured for 60 seconds using a halogen blue light lamp (Unilux AC Kulzer) at a light intensity of 800 mW / cm². After light-curing, the infiltrated samples were stored dry at room temperature. The specimens from the control group (polished, n = 15) and the experimental group (sandblasted, n = 15) were tested under bending using the piston-on-three-ball setup according to Method 2 described above. The results of Example 3 are summarized in Table 3.

[0107] Table 3: Biaxial flexural strengths of sandblasted ceramic discs from Example 3 treated with infiltrants from the respective manufacturing examples; comparison with polished discs and sandblasted discs not treated with an infiltrant. Example 3 Feldspar glass ceramic discs polished sandblasted Sandblasted and infiltrated Production example no. 2 4 3 5 6 MDP MEMO PMMA TA TM Biaxial flexural strength [MPa] 113, 6 104,7 128,3 123,4 127,4 125,7 137,4 14 Example 4: Adhesion test of infiltrate on ceramic

[0108] The adhesion test described above was used to examine the adhesion of infiltrants to feldspar porcelain. The results are summarized in Table 4.

[0109] Table 4: Adhesion of infiltrants to feldspar ceramic rods during tensile testing Production example no. 3 4 7 Liability / MPa 6, 8 4, 7 4, 4

[0110] Examples show that surface degradation, whether by sandblasting or by indentation of the ceramic surface, leads to significant deterioration of the mechanical properties of the ceramic restorations (derived from biaxial flexural strength). The surface degradation methods used serve as models for the intraoral degradation of ceramic restorations.

[0111] The infiltration of the surface-degraded test specimens in examples 1 and 2 leads to improved mechanical properties up to the mechanical properties of the mirror-polished original test specimens.

[0112] When using the infiltrants from Example 3 (Manufacturing Examples Nos. 2-7), mechanical properties are obtained that are even superior to those of the polished control.

[0113] In particular, compositions used as infiltrants for the ceramic surface that contain extremely high amounts of monomers with two or three polymerizable groups in the molecule (production examples No. 6 and 7) show the greatest reinforcing effect.

[0114] The data from Example 4 indicate that the addition of a silane and an acid is preferred. The addition of only small amounts of silanes such as MEMO and acids such as MDP is preferred to avoid undesirably reducing the amount of monomers with two or, in particular, three polymerizable groups in the molecule. Ceramic infiltrants containing high amounts of crosslinkable monomers with at least three polymerizable groups and lower amounts of monomers with a silanol group are expected to exhibit greater durability and a higher potential for stabilizing roughened dental ceramic surfaces.

Claims

[1] Infiltrant comprising 90 to 99.9 wt% of at least one polymerizable monomer, oligomer or prepolymer and 0.05 to 10 wt% of a polymerization initiator, wherein the infiltrant has a dynamic viscosity of 0.3 to 100 mPa·s (23°C); for use in a process for solidifying a fixed ceramic dental prosthesis in the oral cavity. [2] Infiltrant according to claim 1, characterized by that the procedure includes the following steps: a. if necessary, cleaning a ceramic surface layer of the fixed prosthesis, b. if necessary, rinsing the ceramic surface layer, c. Drying of the ceramic surface layer, d. Application of the infiltrant to the dried ceramic surface layer, e. if necessary, removal of adhering infiltrant from the surface of the ceramic surface layer, f. Hardening of the infiltrant in the ceramic surface layer, g. if necessary, cleaning and / or polishing the surface of the ceramic surface layer. [3] Infiltrant according to claim 1 or 2, characterized by that it has a dynamic viscosity of 0.3 to 60 mPa·s (23°C), preferably 0.3 to 30 mPa·s (23°C), more preferably 2 to 15 mPa·s (23°C). [4] Infiltrant according to any one of claims 1 to 3, characterized by that it contains 3-30 wt% polymerizable monomers, oligomers or prepolymers with one or more functional groups consisting of: a. Hydroxy groups (-OH), b. Groups with a hydroxy group, preferably carboxylic acid groups (-CO-OH), phosphoric acid ester groups (-O-PO(OH)2) or phosphonic acid groups (-PO(-OH)3), c. Silanol groups (Si-OH), d. groups that can be hydrolyzed to silanol groups are selected. [5] Infiltrant according to claim 4, characterized bythat it comprises at least 65 wt% polymerizable monomers, oligomers or prepolymers with 2 or more polymerizable groups. [6] Infiltrant according to claim 5, characterized by that he: a. 45 to 75 wt.% polymerizable monomers, oligomers or prepolymers with 2 polymerizable groups, b. 20 to 50 wt.% polymerizable monomers, oligomers or prepolymers with 3 or more polymerizable groups, c. 3-30 wt% polymerizable monomers, oligomers or prepolymers with one or more further functional groups consisting of: i. Hydroxy groups (-OH), ii. Groups with a hydroxy group, preferably carboxylic acid groups (-CO-OH), phosphoric acid ester groups (-O-PO(OH)2) or phosphonic acid groups (-PO(-OH)3), iii. Silanol groups (Si-OH), iv. groups that can be hydrolyzed to silanol groups are selected. [7] Infiltrant according to claim 6, characterized by that he: a. 2.5-9.5 wt% polymerizable monomers, oligomers or prepolymers with one or more silanol groups (Si-OH) or groups that can be hydrolyzed to silanol groups, b. 0.5-7.5 wt% polymerizable monomers, oligomers or prepolymers with one or more carboxylic acid groups (-CO-OH), phosphoric acid ester groups (-O-PO(OH)2) or phosphonic acid groups (-PO(-OH)3). [8] Kit, comprising: a. an organic solvent with an evaporation number of 1 to 35, preferably 1 to 15, b. an infiltrant according to any one of claims 1 to 7. [9] Kit according to claim 8, characterized by that the solvent is an organic liquid with a water content of 5 wt.% or less, preferably an organic liquid that is completely miscible with water. [10] Kit according to claim 8 or 9, characterized bythat the solvent has a boiling point of 35 to 100°C, preferably 50 to 80°C. [11] Kit according to claim 10, characterized by that the solvent comprises an alcohol, preferably ethanol. [12] Method for solidifying a fixed ceramic dental prosthesis in the oral cavity, comprising the following steps: a. if necessary, cleaning a ceramic surface layer of the fixed prosthesis, b. if necessary, rinsing the ceramic surface layer, c. Drying of the ceramic surface layer, d. Application of an infiltrant according to one of claims 1 to 7 to the dried ceramic surface layer, e. if necessary, removal of adhering infiltrant from the surface of the ceramic surface layer, f. Hardening of the infiltrant in the ceramic surface layer, g. if necessary, cleaning and / or polishing the surface of the ceramic surface layer. [13] Method according to claim 12, characterized by that the drying of the ceramic surface layer is carried out by rinsing with an organic solvent with an evaporation rate of 1 to 35, preferably 1 to 15.