WO2014140105A1 - Materials and compositions for dental cements and filler materials - Google Patents

Materials and compositions for dental cements and filler materials Download PDF

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Publication number
WO2014140105A1
WO2014140105A1 PCT/EP2014/054846 EP2014054846W WO2014140105A1 WO 2014140105 A1 WO2014140105 A1 WO 2014140105A1 EP 2014054846 W EP2014054846 W EP 2014054846W WO 2014140105 A1 WO2014140105 A1 WO 2014140105A1
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filler material
graphene
cement
dental
vol
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PCT/EP2014/054846
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French (fr)
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Thomas Maria Bayerl
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D2 Bioscience Group Ltd.
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Publication of WO2014140105A1 publication Critical patent/WO2014140105A1/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K6/00—Preparations for dentistry
    • A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
    • A61K6/884—Preparations for artificial teeth, for filling teeth or for capping teeth comprising natural or synthetic resins
    • A61K6/887—Compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • A61K6/889—Polycarboxylate cements; Glass ionomer cements

Definitions

  • the field of the invention relates to dental cements or filler materials for direct or indirect dental restoration and/or prevention.
  • Dental cements and filler materials can be divided into 3 classes: i) Glass-ionomer cements (GIC), ii) resin modified glass ionomer cements (RMGIC) and iii) resin based cements (RBC). While GIC ' s (Naasan MA et al., Am J Dent 11 :36-45 , 1998) have advantages regarding their easy handling, continuing release of flouride ions for prevention of enamel demineralization and excellent binding to enamel and dentine, RBC ' s (Summers A et al., American Journal of Orthodontics and Dentofacial Orthopedics 126: 200-206, 2004) exhibit better mechanical parameters (mostly regarding surface hardness, bending stiffness and compressive strength as compared to GIC ' s) and RMGIC ' s (Sidhu SK et al., Am J Dent 8:59-67, 1995) represent the attempt to have the advantages of the other two classes unified in one dental cement or
  • RMGIC's and RBC ' s require a source of free radicals for initiation of the polymerization of the resin which is either provided by a chemical initiator (self-cure) or energy, preferably in the form of UV-light (light-cure). If both is used, they are called dual-cure RBC ' s and dual-cure RMGIC ' s, respectively.
  • the invention provides materials and compositions for the improvement of the mechanical parameters, in particular, without being restricted to these, tensile strength, surface hardness and compressive strength, of conventional dental cements and filler materials.
  • the invention uses graphene (strictly two dimensional single layer carbon sheets with material parameters which are in virtually all aspects superior to steel) and its chemically functionalized forms as a material to reinforce dental cements and filler materials by inclusion of graphene into the dental cement or filler material matrix, resulting in a composite of higher mechanical strength.
  • the invention uses deuterium oxide or deuterium to replace the water in conventional glass ionomer dental cement or filler material preprations to improve the mechanical parameters of glass ionomer dental cements or filler materials.
  • deuterium oxide or deuterium is used alone or in combination with graphene in the glass ionomer dental cement or filler material materials.
  • the invention provides composite glass ionomer dental cements or filler materials which include both graphene and deuterium oxide.
  • the invention provides glass ionomer dental cements (GIC) or filler materials which include either deuterium oxide alone (GIC) or graphene and deuterium oxide (composite GIC) in combination with one or more water soluble polymers.
  • GIC glass ionomer dental cements
  • filler materials which include either deuterium oxide alone (GIC) or graphene and deuterium oxide (composite GIC) in combination with one or more water soluble polymers.
  • the term “webgraphene” comprises all types of single layer sp 2 - bonded carbon sheets forming a honeycomb crystal lattice, without or with functional groups bound to it, in particular with -OH, -NH2 or -COOH groups or any other, hydrogen bond formation enabling functional groups bound to its edges.
  • the said honeycomb crystal lattice may have holes in it, resulting in a two-dimensional mesh.
  • the term graphene comprises both rod like and slab like structures which can be single or layered on top of each other.
  • the term "dental cement” as used in this invention comprises all materials which can be used as a cement in dentistry, in particular resin based cements, resin modified glass ionomer cements and glass ionomer cements.
  • filler material comprises all materials which can be used as a filler material in dentistry, in particular resin based filler materials, resin modified glass ionomer filler materials and glass ionomer filler materials.
  • direct dental restoration and/or prevention comprises all restoration and/or prevention works which are performed on site, i.e. directly in the mouth of the patient.
  • indirect dental restoration and/or prevention comprises all restoration and/or prevention works which are performed off site, i.e. outside the mouth of the patient, including, but not restricted to, all works to produce inlays, onlays, veneers, bridges and crowns by both reductive (e.g. milling) and/or additive (e.g. 3-dimensional printing) techniques.
  • reductive e.g. milling
  • additive e.g. 3-dimensional printing
  • shrinkage or “shrinking” as used in this invention comprises all physical, chemical and physico-chemical processes which lead to an effective volume reduction of a specimen made of dental cement or filler material during its curing, including the formation of fractures and fissures in the specimen.
  • bulk filling comprises all methods and/or techniques of direct dental restoration and/or prevention where a cavity is filled with a suitable filling material.
  • one-step bulk filling comprises all methods and/or techniques of direct dental restoration and/or prevention where the filling is performed in a way that the total volume of the cavity is filled up completely with the filling material in one step during the setting of the filling material.
  • deuterium oxide as used in this invention comprises deuterium oxide in all possible isotopic enrichments above the natural abundance of the deuterium isotope, it further comprises all semi-deuterated water molecules (H-O-D) where one hydrogen and one deuterium atom are bound to the oxygen atom.
  • H-O-D semi-deuterated water molecules
  • Deuterium is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in 6,420 of hydrogen. Thus deuterium accounts for approximately 0.0156% (or on a mass basis: 0.0312%) of all the naturally occurring hydrogen in the oceans, while the most common isotope (hydrogen-1 or protium) accounts for more than 99.98%.
  • deuterium comprises all deuterium atoms which originated from deuterium oxide.
  • carbon nanotubes as used in this invention is synonymous for single walled and multi walled carbon nanotubes.
  • fibers as used in this invention, comprises all types of fiber forming materials which can be included or embedded into a cement, such as a ortland cement or dental cement, with the aim of improving the the mechanical stability of said cements.
  • reinforcement as used in this invention is used synonymously for all suitable methods and techniques where a substance or material forms microscopic or macroscopic structures of its own inside a matrix (e.g. a dental cement or filler material) which improve the mechanical stability of the compound material (e.g. a composite of graphene and dental cement or filler material)
  • composite as used in the invention relates generally to all materials which are made of a combination of different substances, in the stricter sense of dental materials it relates to all kinds of mixtures of materials which can be used to fill a cavity or to glue dental parts and/or implants.
  • the term "setting” of a material mostly a dental cement or filler material, as used in this invention, relates to the sum of all physical and chemical processes which are initiated by the mixing of its components and which result in a change of the physical state of the dental cement or filler material, in most cases the transformation to the solid physical state.
  • the "setting time” is the time span from initial mixing until the material, preferably present in the form of a paste-like mixture, has become a solid.
  • curing as used in this invention comprises part ⁇ s) or all of the setting but includes all physical, chemical or physico-chemical changes the material undergoes post-setting, in particular, but not restricted to, the first 100 hours of a material after the initial mixing of its components with the initiation of a setting reaction.
  • matrix'' as used in this invention relates to all types of host materials (a substance or a mixtures of several substances) which allow the inclusion or embedding of another material which is enabled to form structures of its own within the host material and forms a quasi- continous fluid , semi-fluid or solid phase around the embedded material or structure.
  • mechanical strength as used in this invention relates to all physical parameters which can be measured by dedicated techniques to describe qualitatively and quantitatively the mechanical state and stability of a material, in particular, but not restricted to, tensile strength, bending stiffness, compressive strength and surface hardness.
  • improvement of mechanical strength or the term “improvement of mechanical parameters” as used in this invention relates to all methods and compositions which improves one or several of the physical parameters which describe the mechanical strength of a material in the sense that said parameters change by the improvement measurably to give the material additional mechanical stability and/or resilience.
  • glass-ionomer cement as used in this invention comprises conventional glass ionomer cements based on the reaction of silicate glass and polyalkenoic acid or other agents suitable for an acid-base reaction which results in a said cement as well as metal reinforced glass ionomer cements which additionally comprise a metal component to release metal ions.
  • resin based cement as used in this invention relates to all dental cements or filler materials based on a hardenable resin which self cures or light cures or dual cures and with the resin selected preferab ⁇ y , but not restricted to, from acrylic resin, methacrylic resin, epoxy resin, vinyl resin, urethane resin or mixtures of these resins.
  • resin modified glass ionomer cement comprises all glass- ionomer cements which contain additionally a resin (such as hydroxymethylmethacrylate) and a photoinitiator. It encompasses hybrid ionomer cements, dual-cured and tri-cured glass ionomer cements.
  • silane groups or “silane chains” as used in this invention relates to all silanating agents capable of chemically silanting graphene and include those having at least one polymerizable double bond and at least one group that easily hydrolyses with water, preferably 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropydimethoxy-monochlorosilane, 3-methacryloxypropldichlcromonomethoxysilane, methacryloxypropyltri-chlorosilane,
  • Figure 1 shows a table (Table A) presenting the results from the surface hardness measurements performed according to Example 10.
  • MH surface hardness measured according to DIN EN ISO 14577 of commercially available dental glass-ionomer cements (KC) and filler materials (KME), resin based dental cements (NX3), resin modified glass ionomer cement (KCP) and carbomer - modified glass ionomer cement (CMGIC).
  • MH values are shown for the unmodified cements (KME, KC, NX3, RXU, CMGIC) and for cements modified by addition of graphene (-G) and/or deuterium oxide (D-).
  • the number in the sample name following the -G represents the graphene concentration in wt.%.
  • D-KME-G0.1 denotes deuterium enriched Ketac Molar Easymix containing 0.1 wt% (% w/w) graphene.
  • KC Ketac Cem ® (3M ESPE, Seefeld, Germany); KME: Ketac Molar Easymix® (3M ESPE, Seefeld, Germany); KCP: Ketac Cem Plus ® (3M ESPE, Seefeld, Germany ); NX3: NX3 ® dual cure resin cement (Kerr Corp. CA, USA).
  • Figure 2 shows a table (Table B) presenting the results from the bending stiffness measurements performed according to Example 11.
  • KC Ketac Cem ® (3M ESPE, Seefeld, Germany); KME: Ketac Molar Easymix ® (3M ESPE, Seefeld, Germany); KCP: Ketac Cem Plus ® (3M ESPE, Seefeld, Germany ); NX3: NX3 ® dual cure resin cement (Kerr Corp. CA, USA)
  • Figure 3 shows a table (Table C) presenting the results from the compressive strength measurements performed according to Example 12.
  • MH values are shown for the unmodified cements (KME, KC, NX3, RXU, CMGIC) and for cements modified by addition of graphene (-G) and/or deuterium oxide (D-).
  • the number in the sample name following the -G represents the graphene concentration in wt.% (% w/w).
  • D-KME-G0.1 denotes deuterium enriched Ketac Molar Easymix containing 0.1 wt% (% w/w) graphene.
  • KC Ketac Cem® (3M ESPE, Seefeld, Germany); KME: Ketac Molar Easymix® (3M ESPE, Seefeld, Germany); KCP: Ketac Cem Plus® (3M ESPE, Seefeld, Germany ); NX3: NX3® dual cure resin cement (Kerr Corp. CA, USA)
  • the present invention provides means and compositions to improve the essential mechanical stability parameters of GIC's , RMGIC ' s and RBC's by the formation of reinforcement structures within the dental cement or filler material resulting, among other things, in the prevention of microscopic fractures and fissures during the curing process and improvement of mechanical strength.
  • Preferred candidate material to successfully achieve the task of reinforcing dental cements or filler materials in accordance with the present invention would possess one or more of the following characteristics: (i) The material is one (like a rod) or two dimensional (like a sheet, slab or platelet) and its spatial extension is in the order of micrometers to millimeters in order to span a distance inside the dental cement or filler material which is in a reasonable relation to the external dimensions of the composite, (ii) The material has superior mechanical parameters which exceed those of the dental cement or filler material, (iii) The material exhibits superior resistance to acids, bases, metal ions and any other liquids and solids (organic and anorganic) which occur regularly or even temporary in the vicinity of dental cement or filler material constructs in the mouth.
  • the material forms tight bonds with the dental cement or filler material matrix in order to truly reinforce the composite rather than forming a (demixed or isolated) phase of its own which would destabilize the composite and to prevent the formation of miro-fissures or cracks during the curing of the dental cement.
  • the present invention provides materials with these characteristics by the first time introduction of graphene (strictly two dimensional single layer carbon sheets with material parameters which are in virtually all aspects superior to steel) and its chemically functionalized forms as a material to reinforce dental cements or filler materials.
  • Graphene is a single layer sp 2 -bonded carbon sheet forming a honeycomb crystal lattice, reported first by Mouras (Mouras.S.et al. , Revue de Chimie Minerale, 1987:24:572) as the two dimensional (2D) form of graphite.
  • Graphene is optically transparent and can be readily produced, amonog other preparation methods, from graphite by exfoliation techniques (Hernandez.Y. et al., Nature Nanotechnol. 3, 563-568 , 2008) , the resulting graphene platelets have a size of up to 100 ⁇
  • the edges of the graphene platelets can be modified by -OH, -COOH, -NH2 groups , by Flouride (F) atoms, or functionalized with silane groups, which allows to dissolve graphen in aqueous and nonaqueous solutions as well as the controlled modification of its solution properties.
  • graphene is used at a concentration of 0.00001 weight/weight (% w/w) to 90 % w/w, preferred 0.01 % w/w to 10 % w/w, more preferred 0.01 % w/w to 5 % w/w, most preferred 0.05 % w/w to 3 % w/w in terms of the dry phase.
  • the invention provides a dental cement or filler material, preferably a GIC, comprising of a substance (deuterium oxide or deuterium) to partly or totally replace the water in the fluid component of GIC preprations, to improve the mechanical parameters of dental cements/filler materials with or without graphene even further.
  • a dental cement or filler material preferably a GIC, comprising of a substance (deuterium oxide or deuterium) to partly or totally replace the water in the fluid component of GIC preprations, to improve the mechanical parameters of dental cements/filler materials with or without graphene even further.
  • Deuterium oxide (D20) or heavy water is a water-like molecule where the two hydrogens bound to the oxygen atom are replaced by a stable isotope of hydrogen called deuterium.
  • Deuterium contains an additional neutron in its nucleus and as a result D20 is about 10% heavier than normal water (H20). This in turn results in a higher density and different vapor pressure.
  • Heavy water occurs in natural water, roughly every 6000th molecule in natural water is a heavy water molecule. It is produced by very energy intensive destination procedures of natural water and can be obtained commercially at a very high degree of purity (degree of deuterium enrichment) of up to 99.9%.
  • Highly enriched deuterium oxide exhibits a approximately 10% higher viscosity than normal water at the same temperature.
  • the replacement of H20 by D20 in the fluid component of a GIC provides means of manipulation or modulation of the setting reaction. This may result in improvements of the mechanical stability of the cured GIC.
  • D20 A salient feature of D20 is its higher strength to bind to other atoms or molecules via so-called hydrogen bonds. This enables D20 or deuterons in general to bind significantly stronger to hydrogen bonding sites than hydrogen (or H20) itself.
  • any water soluble polymers to the GIC composition which are able to form hydrogen bonds can further improve the mechanical strength of a GIC under conditions where the H20 is replaced by D20.
  • examples for such polymers are all nonionic, cationic or anionic polymers , in particular acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
  • deuterium oxide or deuterium is used at a concentration of of 3 % vol. to 99,9 % vol., preferred at a concentration of 15 % vol. to 99 % vol., more preferred at a concentration of 50 % vol. to 99 % vol., even more preferred at a concentration of 70 % vol. to 99 % vol., most preferred at a concentration of 80 % vol. to 99 % vol., in terms of the fluid phase (in solution).
  • the water-soluble polymer is used at a concentration of 0.0001 % w/w to 50 % w/w, more preferred 0.001 % w/w to 25 % w/w and most preferred 0.05 % w/w to 5.0 % w/w.
  • the present invention further provides for a dual presence of graphene platelets (with -OH, -NH2 or -COOH groups or any other, hydrogen bond formation enabled functional groups bound to its edges) and of D20 replacing partially or totally the H20 in a dental cement or filler material, preferably a GIC.
  • this dual presence has an even stronger effect regarding the improvement of the resulting mechanical properties of the GIC. This is because the deuterons replace the hydrogen atoms at the hydrophilic functional groups attached to the graphene edges.
  • the higher (hydrogen) binding strength of the deuterons causes a tighter packing of the solid components including the graphene and its tighter binding to the GIC matrix, resulting in improved mechanical strength of the graphene-GIC composite beyond that of just graphene GIC composites or D20 enriched GIC ' s alone.
  • the effect of graphene on the mechanical properties of the composite dental cement filler material is different.
  • the embedding of the pristine or flouride -modified (hydrophobic) graphene patelets provides essentially a reinforcement of the composite structure over distances which correlates with the spatial extension of the graphene platelets.
  • the resin matrix will bind in the setting process to the graphene via the functional groups or directly to the pristine graphene, because the graphene surface can attract free radicals (induced by an initiator molecule (dual cure) of by shining UV light on the mixture (light-cure) which in turn are essential for a high degree of polymerization of the resin matrix.
  • the resin matrix in the vicinity of the graphene platelets exhibits a particularly high polymerization density reinforced by the underlying graphene platelet and surrounded by the cured resin matrix.
  • This composite structure inside the RMGIC ' s and RBC, respectively significantly improves the overall mechanical stability of the RMGIC's and RBC, respectively, and helps to prevent the formation of fissures during the curing of the RMGIC's and RBC owing to shrinking of the material.
  • the reinforcement of dental cements and filling materials by graphene has important ramifications for the prevention of shrinking of the materials.
  • the mechanical properties of graphene bound to the matrix of any dental cement or filling material stabilizes against volume loss during the curing of the material, thus preventing the formation of fractures and fissures. This enables one-step bulk filling techniques for all self curing dental filling materials.
  • the application of all dental cements or filler materials in patients requires that the color of the surrounding tooth is matched by the dental cements or filler materials to find acceptance with the users (dentists) and their patients.
  • the materials/substances used in the present invention are both optically transparent and thus do not interfere with the coloring scheme of the the dental cements/filler materials.
  • the invention relates in its first subject to a dental cement or filler material composition comprising graphene and/or deuterium oxide or deuterium.
  • a preferred embodiment relates to an inventive dental cement or filler material, whereby the dental cement or filler material is a glass ionomer cement or filler material or resin based cement or filler material or resin modified glass ionomer cement or filler material.
  • a further preferred embodiment relates to a dental cement or filler material, whereby the graphene is in its pristine form or with its reactive groups chemically modified, preferably modified with hydroxyl, carboxyl, amide or silane functional groups or with the graphene reactive groups bound to flouride atoms.
  • Another preferred embodiment relates to a dental cement of filler material composition, whereby graphene is comprised at a concentration of 0.00001 % w/w to 90 % w/w, preferred 0.01 % w w to 10 % w/w, more preferred 0.01 % w/w to 5 % w/w, most preferred 0.05 % w/w to 3 % w/w in terms of the dry phase.
  • Another preferred embodiment relates to a dental cement of filler material composition, whereby deuterium oxide or deuterium is comprised at a concentration of of 3 % vol. to 99,9 % vol., preferred at a concentration of 15 % vol. to 99 % vol., more preferred at a concentration of 50 % vol. to 99 % vol., even more preferred at a concentration of 70 % vol. to 99 % vol., most preferred at a concentration of 80 % vol. to 99 % vol., in terms of the fluid phase (in solution).
  • the dental cement or filler material whereby the glass ionomer cement composition comprises additionally a water soluble polymer, which can form hydrogen bonds, selected from the group consisting of synthetic or natural polymers being either nonionic, cationic or anionic, preferably at neutral pH value, preferably acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
  • a water soluble polymer which can form hydrogen bonds, selected from the group consisting of synthetic or natural polymers being either nonionic, cationic or anionic, preferably at neutral pH value, preferably acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
  • a preferred embodiment relates to a dental cement or filler material for direct or indirect dental restoration and/or prevention.
  • Another preferred embodiment relates to a dental cement or filler material for the use in direct or indirect dental restoration and/or prevention.
  • All conventional state of the art dental cements and filler materials can be improved according to the invention regarding their mechanical strength and parameters by the inclusion of graphene and/or deuterium oxide or deuterium into their matrix prior to the setting/curing process.
  • All conventional state of the art dental cements and filler materials in well-known compositions and concentrations can be used to carry out the invention
  • a preferred embodiment of the invention relates to the inclusion of graphene into dental cements or filler materials.
  • the preferred properties of the graphene platelets used for inclusion are single layer graphene with the carbons at the edges of the platelets functionalized with chemical groups which provide for a optimum binding of the graphene platelets with the matrix.
  • the most preferred functional groups bound to graphene are hydrophilic and can for hydrogen bonds.
  • the graphene preferably used is either pristine or functionalized with groups which render it hydrophobic like flouride atoms (giving partially or perflourated graphene) or silane groups/chains.
  • the invention is not restricted to the above functional modifications, in general all modifications which improve further the binding between the graphene and the matrix and/or the spatial distribution of the graphene within the matrix are preferred.
  • Multi-layer graphene platelets or graphene obtained from processing carbon nanotubes (both single walled and multi walled) as well as mixtures of all types of graphene represent further preferred embodiments of the invention regarding their inclusion in the matrix.
  • the amount of graphene used for the inclusion into the matrix is 0.00001 % to 90 %, preferred 0.01 % to 10 % , more preferred 0.01 % to 5 %, most preferred 0.05 % to 3 %. All percentages given for the graphene inclusion are by weight.
  • deuterium oxide in glass ionomer dental cements/filler materials, either with graphene included or without graphene, is a further especially preferred embodiment of the invention.
  • the deuterium oxide can be partially deuterium enriched or highly deuterium enriched with a degree of enrichment of up to 90 % and even 99.999 %.
  • the D20 is preferably added to the fluid phase of a GIC prior to the mixing with the solid phase in order to allow for a replacement of part or all of the hydrogen atoms in the fluid phase by deuterium atoms. All known physical and chemical methods to replace the hydrogen atoms in the fluid phase by deuterium atoms represent embodiments of the invention.
  • the preferred final deuterium enrichment in the fluid phase i.e.
  • the percentage of hydrogen atoms in the fluid phase exchanged by deuterium atoms) prior to the mixing with the solid phase of a GIC is 3 % to 99,9 %, more preferred 50 % to 99%, most preferred 80 % to 99%.
  • the solid phase of a GIC can also contain hydrogen atoms which can be exchanged by deuterium atoms prior to the mixture with the fluid phase. All known physical or chemical methods to achieve such an exchange in said solid phase prior to the mixing with the said fluid phase represent embodiments of the invention.
  • the preferred final deuterium enrichment in the solid phase i.e.
  • the percentage of hydrogen atoms in the solid phase exchanged by deuterium atoms) prior to the mixing with the fluid phase of a GIC is 1 % to 99,9 %, more preferred 50 % to 99 %, most preferred 80 % to 99 %. All percentages given for the deuterium oxide or deuterium inclusion are by volume.
  • the dual use of deuterium oxide and graphene in a glass ionomer dental cement or filler material represents another especially preferred embodiment of the invention.
  • This embodiment improves the reinforcement and mechanical parameters of dental cements or filler materials even further.
  • the graphene is added to either the solid or the fluid phase prior to the mixing of the two phases but the addition of graphene during the mixing is possible as well.
  • the graphene addition happens before the commencement of the setting/curing of the GIC.
  • the deuterium oxide addition to the GIC phases with the aim of the exchange of part or all of the hydrogen atoms or the use of other hydrogen-deuterium exchange techniques to achieve such an exchange are analogous to the case described above for the sole use of deuterium oxide in GIC ' s.
  • deuterium oxide to the GIC is prior to the mixing of the two phases, preferred is the partial replacement of the water component of the fluid phase of the GIC by deuterium oxide, most preferred is the replacement of the complete water component of the fluid phase of the GIC by deuterium oxide.
  • the additional introduction of water soluble polymers which provides additional hydrogen bonding sites to the glass ionomer dental cement/filler material and with the H20 replaced partially or in full by D20, either with or without graphene represents a further embodiment of the invention.
  • the at least one polymer is added to a dental cement or filler material, preferably a GIC composition, either to its solid or liquid phase prior to mixing but the addition of said polymer during the mixing of the two phases is equally possible, provided the addition is concluded before the conclusion of the setting of the GIC.
  • the amount of polymers added to the GIC composition is in the range 0.0001 % w/w to 50 % w/w, more preferred 0.001 % w/w to 25 % w/w and most preferred 0.05 % w/w to 5.0 % w/w.
  • the at least one polymer is preferably added to an inventive dental cement or filler material comprising deuterium oxide or a combination of deuterium oxide and graphene.
  • the dental cement or filler material comprises graphene.
  • the dental cement/filler material is a glass ionomer cement/filler material or resin based cement or filler material or resin modified glass ionomer cement/filler material.
  • the graphene comprised by the dental cement or filler material is in its pristine form or with its reactive groups chemically modified, preferably modified with hydroxyl, carboxyl, amide or silane functional groups or with the graphene reactive groups bound to flouride atoms.
  • a dental cement or filler material composition for direct or indirect dental restoration and/or prevention, where the dental cement or filler material comprises deuterium oxide or deuterium.
  • the dental cement or filler material is a glass ionomer cement/filler material or resin based cement/filler material or resin modified glass ionomer cement/filler material.
  • the glass ionomer cement composition comprises additionally a water soluble polymer which can form hydrogen bonds, whereby the water soluble polymer is selected from the group consisting of synthetic or natural polymers being either nonionic, cationic or anionic, preferably acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
  • the water soluble polymer is selected from the group consisting of synthetic or natural polymers being either nonionic, cationic or anionic, preferably acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
  • a yet another embodiment relates to a dental cement or filler material composition for direct or indirect dental restoration and/or prevention, where the dental cement comprises graphene and deuterium oxide or deuterium.
  • the cement is a glass ionomer cement filler material or resin based cement/filler material or resin modified glass ionomer cement/filler material.
  • the glass ionomer cement composition comprises additionally a water soluble polymer which can form hydrogen bonds, selected from the goups synthetic or natural polymers being either nonionic, cationic or anionic at neutral pH value, in particular acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
  • Example 1 Graphene preparation
  • Hydophobic pristine graphene in organic solution was prepared by liquid-phase exfoliation of graphite (Hernandez, Y et al., High-yield production of graphene by liquid phase exfoliation of graphite. Nature Nanotechnol. 3, 563-568, 2008).
  • a Branson W-250 titanium-rod sonifier was employed in pulsed mode (2s pulses with 1 s interval) at highest power (200W) for 20 min. for the sonication of the graphite solution in a thermostated water bath ( 40°C).
  • the graphite powder was from Sigma-Aldrich (Cat. No. 332461) and the solvent used was N- methtylpyrrolidone (N P).
  • the final solution (after concentration of the centrifugation pellets) contained 1.5% (wt.) of non-oxidized graphene monolayer platelets with a size distribution of less than 30 nm - 5 pm as determined by electron microscopy (TEM).
  • the solution was freeze- dried in a freeze-drying flask after rotating the flask in liquid nitrogen until all liquid was homogeneously frozen at the wall of the flask. After this, the freeze drying was performed for 2 h using a benchtop manifold freeze dryer (BT85 from Millrock Technology, guitarist, NY, USA) operating at a pressure of 10 '3 mbar. The freeze-dried graphene flakes were mechanically removed from the flask and stored under vacuum.
  • Hydrophrlic (water soluble) graphene monolayer platelets tn aqueous solution were prepared from graphite oxide according to procedures of liquid phase exfoliation and and were further concentrated by centrifugation (Dreyer, D R et al., From conception to realization: an historical account of graphene and some perspectives for ist future. Angew. Chem. Int. Ed. 49, 9336-9344 , 2010).
  • a Branson W-250 titanium-rod sonifier was employed in pulsed mode (2s pulses with 1 s interval) at 100W output power for 15 min. for the sonication of the graphite oxide solution in a thermostated water bath ( 60°C).
  • the final aqueous solution comprised a liquid.graphene (exfoliated graphene nano platelets) ratio of 3:1 (wt.) where the individual platelets ranged in size from less than 20 nm up to 50 pm with a thickness of less than 5 nm to 50nm, as determined by electron microscopy.
  • the graphene platelets obtained this way are covered at their edges by hydroxide groups and hydrogen caps, rendering them water soluble. Further analysis showed that less than 50% of the graphene platelets were thicker than one monolayer.
  • a GIC dental filling material etac Molar Easymix (KME), 3M ESPE, Seefeld, Germany) and and GIC dental cement (Ketac Cem (KC), 3M ESPE, Seefeld, Germany), both comprising of a solid and a liquid phase to be mixed on application with a setting time of less than 5 min.
  • the cement specimens KME and KC were prepared according to the user manual instructions by mixing the two phases at a solid : liquid phase ratio of 3.5 (wt.) , and filling the mixtures into cylindrical cast moulds, capped on each open side by a foil of cellulose acetate supported by a glass slide.
  • the size of the cylindrical cast moulds was 4 mm diameter and 6 mm height (for compression and flexural strength measurements) and 18.7 mm diameter and 3.0 mm height (for surface hardness measurements).
  • the specimens were then stored at 37 ° C and 30% rel. humidity for 60 min. , after this the cast moulds were removed and the specimen samples were cured in destilled water for at least 48 h at 37°C.
  • Example 3 Deuterium oxide-substituted glass-ionomer cement (D-GIC) specimen preparation
  • the liquid phase of the commercial GIC's from example 1 was freeze dried (lyophilized) in a freeze-drying flask after rotating the flask in liquid nitrogen until all GIC liquid phase was homogeneously frozen at the wall of the flask. After this, the freeze drying was performed for 3 h using a benchtop manifold freeze dryer (BT85 from Millrock Technology, Springfield, NY, USA) operating at a pressure of 10 '3 mbar.
  • the freeze dried flakes in the flask were resuspended with Deuterium oxide (D20) of 98% enrichment (CU Chemie Uetikon AG. CH) at the original volume of the liquid phase.
  • the resulting deuterated liquid phase was -like the original liquid phase- optically clear and featured a 6% higher viscosity owing to the higher density of deuterium oxide compared to water.
  • the D-GIC specimen preparation was analogous to example 2 except that the liquid phase was replaced by the deuterated liquid phase, giving D-KME and D-KC.
  • Specimen were prepared analogous to example 2) but with the liquid phase of the said commercial dental cements now containing either 0.1 % or 0.3% (wt.) graphene platelets prepared according to example 1 , giving KME-G0.1 , KC-G0.1 and KME-G0.3 , KC-G0.3 specimens, respectively .
  • the volume of the liquid phase was preserved during the addition of the graphene platelet aqueous solution by slow evaporation (at 40°C and ambient pressure under an nitrogen atmosphere) of an equal amount of water from the liquid GIC phase prior to the addition of the platelet solution at the same volume as previously extracted.
  • Specimen were prepared analogous to example 4 but with the liquid phase now replaced by the deuterated liquid phase (example 3) now containing either 0.1 % or 0.3% (wt.) graphene platelets prepared according to example 1 , giving D-K E-G0.1 , D-KC-G0.1 and D-KME-G0.3 , D-KC- G0.3 specimens, respectively .
  • the addition of the graphene platelets to the liquid phase was performed as described in example 4 with the exception that the deuterium substituted graphene solution prepared according to example 1 has been used.
  • Ketac Cem Plus (3M ESPE, Seefeld, Germany ) is a self-curing resin modified glass ionomer luting cement.
  • the control specimens (KCP) were prepared by filling the cement from the mixing dispenser directly into the cylindrical cast moulds and further processed as described below (self-cure only) .
  • the graphene modified specimens were prepared by adding to the cement from the mix-dispenser oxidized graphene platelets (obtained as solid flakes after freeze-drying the aqueous solution as described in example 1) .
  • the platelets were mechanically mixed into the paste (final graphene concentration 0.08 wt%) for 1 min. using a rotating mixing plate (rotation speed 50 rev./min).
  • the specimens were produced by filling the graphene-Ketac Cem Plus mixture (KCP-G) mixture into cylindrical cast moulds, capped on each open side by a foil of cellulose acetate supported by a glass slide.
  • the size of the cylindrical cast moulds was 4 mm diameter and 6 mm height (for compression and flexural strength measurements) and 18.7 mm diameter and 3.0 mm height (for surface hardness measurements).
  • the mixture was allowed to self-cure in the casting moulds for 1 h and after this the specimens were removed from the moulds and stored until further use at 37"C at 30% rel. humidity.
  • Example 7 Resin based cement (RBC) specimen preparation
  • NX3 dual cure resin cement (Kerr Corp. CA, USA) was used right from the self-mix dispenser unit to obtain the control specimen (NX3) by filling them into cast moulds and allowing self-cure as in example 6.
  • the graphene modified specimen (NX3-G) were obtained by adding pristine graphene platelets prepared according to example 1 to the original NX3 cement from the self- mix dispenser unit and mixing both for 1 min as described in example 6.
  • the final pristine graphene platelets content was 0.08% (wt.).
  • the further specimen preparation (self-cure only) was analogous to example 6.
  • Example 8 Carbomer modified GIC specimen preparation (CMGIC)
  • CMGIC specimen were prepared from Ketac Molar Easymix ( 3M ESPE, Seefeld, Germany) according to Example 2 with the exception that 0,5 % (wt.) of Carbopol®980 (Lubrizol, Cleveland, USA) was added to the solid phase prior to the mixing with the liquid phase.
  • Example 9 Deuterium oxide-substituted Carbomer modified GIC specimen preparation (D-CMGIC)
  • D-CMGIC specimen were prepared according to Example 3 with the exception that 0,5 % (wt.) of Carbopol®980 (Lubrizol, Cleveland, USA) was added to the solid phase prior to the mixing with the (deuterium oxide-substituted) liquid phase.
  • Bending stiffness measurements were performed according to DIN EN ISO 4049:2009(E) using a Zwick materials testing machine ⁇ 0507 ⁇ 3 (Zwick/Roell, Ulm, Germany).
  • the test speed of the normal force i.e. the force applied perpendicular to the specimen long axis halfway between the two holding points of the specimen was 0.75mm/min.
  • Compressive strength measurements were performed according to DIN EN ISO 9917 using a Zwick materials testing machine Z050 THA3 (Zwick/Roell, Ulm, Germany). The test speed of the force applied along the long axis of the test specimen was 0.75mm/min. Compressive strength C was calculated as

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Abstract

The invention relates to dental cement or filler material composition comprising graphene and/or deuterium oxide or deuterium and their uses in direct or indirect dental restoration and/or prevention.

Description

Materials and compositions for dental cements and filler materials
Field of the invention
The field of the invention relates to dental cements or filler materials for direct or indirect dental restoration and/or prevention.
Background of the invention
Dental cements and filler materials can be divided into 3 classes: i) Glass-ionomer cements (GIC), ii) resin modified glass ionomer cements (RMGIC) and iii) resin based cements (RBC). While GIC's (Naasan MA et al., Am J Dent 11 :36-45 , 1998) have advantages regarding their easy handling, continuing release of flouride ions for prevention of enamel demineralization and excellent binding to enamel and dentine, RBC's (Summers A et al., American Journal of Orthodontics and Dentofacial Orthopedics 126: 200-206, 2004) exhibit better mechanical parameters (mostly regarding surface hardness, bending stiffness and compressive strength as compared to GIC's) and RMGIC's (Sidhu SK et al., Am J Dent 8:59-67, 1995) represent the attempt to have the advantages of the other two classes unified in one dental cement or filler for better long term wear and strength. All three classes expose, to a different degree, the feature of shrinkage during the hardening (curing) process which poses a general problem because of the possible formation of tiny fissures and mico fractures. Although GIC's exhibit, because of their inorganic nature, several advantages particularly as dental filling materials, (flouride release, dentine binding, colour retention, acid and base resistance), their use is limited because of inferior mechanical parameters (Zhen Chun Lia et al., Journal of Prosthetic Dentistry 81 : 597- 609, 1999). While GIC's cure in a chemical acid-base reaction without the addition of further components, RMGIC's and RBC's require a source of free radicals for initiation of the polymerization of the resin which is either provided by a chemical initiator (self-cure) or energy, preferably in the form of UV-light (light-cure). If both is used, they are called dual-cure RBC's and dual-cure RMGIC's, respectively.
In the field of dental cements and filler materials, no material has been devised in the state of the
l art which achieve adeqaute reinforcement. The presence of such a material would reduce the probability of the progression of micro fractures and fissures through the dental cement or filler material during its curing owing to plastic shrinkage and thus contribute to the prevention of faults formation and the improvement of mechanical strength.
Summary of the invention
The invention provides materials and compositions for the improvement of the mechanical parameters, in particular, without being restricted to these, tensile strength, surface hardness and compressive strength, of conventional dental cements and filler materials.
In one aspect, the invention uses graphene (strictly two dimensional single layer carbon sheets with material parameters which are in virtually all aspects superior to steel) and its chemically functionalized forms as a material to reinforce dental cements and filler materials by inclusion of graphene into the dental cement or filler material matrix, resulting in a composite of higher mechanical strength.
In another aspect, the invention uses deuterium oxide or deuterium to replace the water in conventional glass ionomer dental cement or filler material preprations to improve the mechanical parameters of glass ionomer dental cements or filler materials. According to the invention, deuterium oxide or deuterium is used alone or in combination with graphene in the glass ionomer dental cement or filler material materials.
Consequently, in a further aspect, the invention provides composite glass ionomer dental cements or filler materials which include both graphene and deuterium oxide.
In yet another aspect, the invention provides glass ionomer dental cements (GIC) or filler materials which include either deuterium oxide alone (GIC) or graphene and deuterium oxide (composite GIC) in combination with one or more water soluble polymers.
Within the scope of this invention, the term„graphene" comprises all types of single layer sp2- bonded carbon sheets forming a honeycomb crystal lattice, without or with functional groups bound to it, in particular with -OH, -NH2 or -COOH groups or any other, hydrogen bond formation enabling functional groups bound to its edges. The said honeycomb crystal lattice may have holes in it, resulting in a two-dimensional mesh. Furthermore, the term graphene comprises both rod like and slab like structures which can be single or layered on top of each other.
The term "dental cement" as used in this invention comprises all materials which can be used as a cement in dentistry, in particular resin based cements, resin modified glass ionomer cements and glass ionomer cements.
The term "filler material" as used in this invention comprises all materials which can be used as a filler material in dentistry, in particular resin based filler materials, resin modified glass ionomer filler materials and glass ionomer filler materials.
The term "direct" dental restoration and/or prevention as used in this invention, comprises all restoration and/or prevention works which are performed on site, i.e. directly in the mouth of the patient.
The term "indirect" dental restoration and/or prevention as used in this invention comprises all restoration and/or prevention works which are performed off site, i.e. outside the mouth of the patient, including, but not restricted to, all works to produce inlays, onlays, veneers, bridges and crowns by both reductive (e.g. milling) and/or additive (e.g. 3-dimensional printing) techniques.
According to the present invention, the terms "dental cement", "cement", "filler material", "filler" and "filler material matrix" and "filler matrix" are used synonymously.
The term "shrinkage" or "shrinking" as used in this invention comprises all physical, chemical and physico-chemical processes which lead to an effective volume reduction of a specimen made of dental cement or filler material during its curing, including the formation of fractures and fissures in the specimen.
The term "bulk filling" as used in this invention comprises all methods and/or techniques of direct dental restoration and/or prevention where a cavity is filled with a suitable filling material.
The term "one-step bulk filling" as used in this invention comprises all methods and/or techniques of direct dental restoration and/or prevention where the filling is performed in a way that the total volume of the cavity is filled up completely with the filling material in one step during the setting of the filling material.
The term "deuterium oxide" as used in this invention comprises deuterium oxide in all possible isotopic enrichments above the natural abundance of the deuterium isotope, it further comprises all semi-deuterated water molecules (H-O-D) where one hydrogen and one deuterium atom are bound to the oxygen atom.
Deuterium is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in 6,420 of hydrogen. Thus deuterium accounts for approximately 0.0156% (or on a mass basis: 0.0312%) of all the naturally occurring hydrogen in the oceans, while the most common isotope (hydrogen-1 or protium) accounts for more than 99.98%.
The term "deuterium" comprises all deuterium atoms which originated from deuterium oxide.
According to the invention, the terms "deuterium oxide", "D20", "deuterium" and "heavy water", are used synonymously and can be replaced by each other.
The term "carbon nanotubes" as used in this invention is synonymous for single walled and multi walled carbon nanotubes.
The term "fibers" as used in this invention, comprises all types of fiber forming materials which can be included or embedded into a cement, such as a ortland cement or dental cement, with the aim of improving the the mechanical stability of said cements.
The term "reinforcement" as used in this invention is used synonymously for all suitable methods and techniques where a substance or material forms microscopic or macroscopic structures of its own inside a matrix (e.g. a dental cement or filler material) which improve the mechanical stability of the compound material (e.g. a composite of graphene and dental cement or filler material)
The term "composite" as used in the invention relates generally to all materials which are made of a combination of different substances, in the stricter sense of dental materials it relates to all kinds of mixtures of materials which can be used to fill a cavity or to glue dental parts and/or implants. The term "setting" of a material, mostly a dental cement or filler material, as used in this invention, relates to the sum of all physical and chemical processes which are initiated by the mixing of its components and which result in a change of the physical state of the dental cement or filler material, in most cases the transformation to the solid physical state. The "setting time" is the time span from initial mixing until the material, preferably present in the form of a paste-like mixture, has become a solid.
The term "curing" as used in this invention comprises part{s) or all of the setting but includes all physical, chemical or physico-chemical changes the material undergoes post-setting, in particular, but not restricted to, the first 100 hours of a material after the initial mixing of its components with the initiation of a setting reaction.
The term "matrix'' as used in this invention relates to all types of host materials (a substance or a mixtures of several substances) which allow the inclusion or embedding of another material which is enabled to form structures of its own within the host material and forms a quasi- continous fluid , semi-fluid or solid phase around the embedded material or structure.
The term "mechanical strength" as used in this invention relates to all physical parameters which can be measured by dedicated techniques to describe qualitatively and quantitatively the mechanical state and stability of a material, in particular, but not restricted to, tensile strength, bending stiffness, compressive strength and surface hardness.
The term "improvement of mechanical strength" or the term "improvement of mechanical parameters" as used in this invention relates to all methods and compositions which improves one or several of the physical parameters which describe the mechanical strength of a material in the sense that said parameters change by the improvement measurably to give the material additional mechanical stability and/or resilience.
The term "glass-ionomer cement" as used in this invention comprises conventional glass ionomer cements based on the reaction of silicate glass and polyalkenoic acid or other agents suitable for an acid-base reaction which results in a said cement as well as metal reinforced glass ionomer cements which additionally comprise a metal component to release metal ions. The term "resin based cement" as used in this invention relates to all dental cements or filler materials based on a hardenable resin which self cures or light cures or dual cures and with the resin selected preferab\y , but not restricted to, from acrylic resin, methacrylic resin, epoxy resin, vinyl resin, urethane resin or mixtures of these resins.
The term "resin modified glass ionomer cement" as used in this invention comprises all glass- ionomer cements which contain additionally a resin (such as hydroxymethylmethacrylate) and a photoinitiator. It encompasses hybrid ionomer cements, dual-cured and tri-cured glass ionomer cements.
The term "silane groups" or "silane chains" as used in this invention relates to all silanating agents capable of chemically silanting graphene and include those having at least one polymerizable double bond and at least one group that easily hydrolyses with water, preferably 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropydimethoxy-monochlorosilane, 3-methacryloxypropldichlcromonomethoxysilane, methacryloxypropyltri-chlorosilane,
3-methacryloxypropyldichloromonomethyl-silane,
3-methacryloxypropylmonochlorodimethylsliane, and mixtures thereof.
Brief description of the drawings
The present invention is illustrated on the basis of Fig. 1 to 3, although, these do not restrict the scope and subject-matters of the invention.
Figure 1 shows a table (Table A) presenting the results from the surface hardness measurements performed according to Example 10.
Surface hardness (Martens-hardness, MH) measured according to DIN EN ISO 14577 of commercially available dental glass-ionomer cements (KC) and filler materials (KME), resin based dental cements (NX3), resin modified glass ionomer cement (KCP) and carbomer - modified glass ionomer cement (CMGIC). MH values are shown for the unmodified cements (KME, KC, NX3, RXU, CMGIC) and for cements modified by addition of graphene (-G) and/or deuterium oxide (D-). The number in the sample name following the -G represents the graphene concentration in wt.%. For example, D-KME-G0.1 denotes deuterium enriched Ketac Molar Easymix containing 0.1 wt% (% w/w) graphene.
KC: Ketac Cem® (3M ESPE, Seefeld, Germany); KME: Ketac Molar Easymix® (3M ESPE, Seefeld, Germany); KCP: Ketac Cem Plus® (3M ESPE, Seefeld, Germany ); NX3: NX3® dual cure resin cement (Kerr Corp. CA, USA). Figure 2 shows a table (Table B) presenting the results from the bending stiffness measurements performed according to Example 11.
Bending stiffness measured according to DIN EN ISO 4049:2009(E) of commercially available dental glass-ionomer cements (KC) and filler materials (KME), resin based dental cements (NX3), resin modified glass ionomer cement (KCP) and carbomer -modified glass ionomer cement (CMGIC). MH values are shown for the unmodified cements (KME, KC, NX3, RXU, CMGIC) and for cements modified by addition of graphene (-G) and/or deuterium oxide (D-). The number in the sample name following the -G represents the graphene concentration in wt.% (% w/w). For example, D-KME-G0.1 denotes deuterium enriched Ketac Molar Easymix containing 0.1 wt% (% w/w) graphene.
KC: Ketac Cem® (3M ESPE, Seefeld, Germany); KME: Ketac Molar Easymix® (3M ESPE, Seefeld, Germany); KCP: Ketac Cem Plus® (3M ESPE, Seefeld, Germany ); NX3: NX3® dual cure resin cement (Kerr Corp. CA, USA)
Figure 3 shows a table (Table C) presenting the results from the compressive strength measurements performed according to Example 12.
Compressive strength measured according to DIN EN ISO 9917 of commercially available dental glass-ionomer cements (KC) and filler materials (KME), resin based dental cements (NX3), resin modified glass ionomer cement (KCP) and carbomer -modified glass ionomer cement (CMGIC). MH values are shown for the unmodified cements (KME, KC, NX3, RXU, CMGIC) and for cements modified by addition of graphene (-G) and/or deuterium oxide (D-). The number in the sample name following the -G represents the graphene concentration in wt.% (% w/w). For example, D-KME-G0.1 denotes deuterium enriched Ketac Molar Easymix containing 0.1 wt% (% w/w) graphene.
KC: Ketac Cem® (3M ESPE, Seefeld, Germany); KME: Ketac Molar Easymix® (3M ESPE, Seefeld, Germany); KCP: Ketac Cem Plus® (3M ESPE, Seefeld, Germany ); NX3: NX3® dual cure resin cement (Kerr Corp. CA, USA)
Detailed description of the invention
The present invention provides means and compositions to improve the essential mechanical stability parameters of GIC's , RMGIC's and RBC's by the formation of reinforcement structures within the dental cement or filler material resulting, among other things, in the prevention of microscopic fractures and fissures during the curing process and improvement of mechanical strength.
Preferred candidate material to successfully achieve the task of reinforcing dental cements or filler materials in accordance with the present invention would possess one or more of the following characteristics: (i) The material is one (like a rod) or two dimensional (like a sheet, slab or platelet) and its spatial extension is in the order of micrometers to millimeters in order to span a distance inside the dental cement or filler material which is in a reasonable relation to the external dimensions of the composite, (ii) The material has superior mechanical parameters which exceed those of the dental cement or filler material, (iii) The material exhibits superior resistance to acids, bases, metal ions and any other liquids and solids (organic and anorganic) which occur regularly or even temporary in the vicinity of dental cement or filler material constructs in the mouth. Finally, (iv) the material forms tight bonds with the dental cement or filler material matrix in order to truly reinforce the composite rather than forming a (demixed or isolated) phase of its own which would destabilize the composite and to prevent the formation of miro-fissures or cracks during the curing of the dental cement.
In a first aspect, the present invention provides materials with these characteristics by the first time introduction of graphene (strictly two dimensional single layer carbon sheets with material parameters which are in virtually all aspects superior to steel) and its chemically functionalized forms as a material to reinforce dental cements or filler materials.
Graphene is a single layer sp2-bonded carbon sheet forming a honeycomb crystal lattice, reported first by Mouras (Mouras.S.et al. , Revue de Chimie Minerale, 1987:24:572) as the two dimensional (2D) form of graphite.
Graphene is optically transparent and can be readily produced, amonog other preparation methods, from graphite by exfoliation techniques (Hernandez.Y. et al., Nature Nanotechnol. 3, 563-568 , 2008) , the resulting graphene platelets have a size of up to 100 μπν The edges of the graphene platelets can be modified by -OH, -COOH, -NH2 groups , by Flouride (F) atoms, or functionalized with silane groups, which allows to dissolve graphen in aqueous and nonaqueous solutions as well as the controlled modification of its solution properties. This enables the use of graphene in GIC's where a hydrophilic graphene is required for the formation of a composite , but also in R GIC's and RBC's where a hydrophobic graphen is the prerequisite for its dissolution and binding to the resin matrix. According to the present invention, graphene is used at a concentration of 0.00001 weight/weight (% w/w) to 90 % w/w, preferred 0.01 % w/w to 10 % w/w, more preferred 0.01 % w/w to 5 % w/w, most preferred 0.05 % w/w to 3 % w/w in terms of the dry phase.
In a second aspect, the invention provides a dental cement or filler material, preferably a GIC, comprising of a substance (deuterium oxide or deuterium) to partly or totally replace the water in the fluid component of GIC preprations, to improve the mechanical parameters of dental cements/filler materials with or without graphene even further.
Deuterium oxide (D20) or heavy water is a water-like molecule where the two hydrogens bound to the oxygen atom are replaced by a stable isotope of hydrogen called deuterium. Deuterium contains an additional neutron in its nucleus and as a result D20 is about 10% heavier than normal water (H20). This in turn results in a higher density and different vapor pressure. Heavy water occurs in natural water, roughly every 6000th molecule in natural water is a heavy water molecule. It is produced by very energy intensive destination procedures of natural water and can be obtained commercially at a very high degree of purity (degree of deuterium enrichment) of up to 99.9%. Highly enriched deuterium oxide exhibits a approximately 10% higher viscosity than normal water at the same temperature. Because the setting reaction of a GIC depends, among other factors, on the viscosity of the fluid phase, the replacement of H20 by D20 in the fluid component of a GIC provides means of manipulation or modulation of the setting reaction. This may result in improvements of the mechanical stability of the cured GIC.
A salient feature of D20 is its higher strength to bind to other atoms or molecules via so-called hydrogen bonds. This enables D20 or deuterons in general to bind significantly stronger to hydrogen bonding sites than hydrogen (or H20) itself.
For example, in GIC formation starting from its two components (an acidic liquid phase containing water and a solid phase of essentially silicate containing metal ions), hydrogen bonds play an essential role because water is the medium where the acid base reaction in the setting process of the dental cement/filler material takes place. Hence all water soluble GIC components (silicate, ions, acid polymers) will be surrounded by a hydration shell of water (H20). If H20 is replaced by D20, the increase in (hydrogen) binding strength translates into a tighter packing of the components during the settlement process while the higher viscosity of D20 modulates the diffusion of the components during the setting time. Both processes give rise to a higher mechanical stability of the settled GIC. Since hydrogen bonds are essential in the setting reaction of GIC's and their curing, the addition of any water soluble polymers to the GIC composition which are able to form hydrogen bonds can further improve the mechanical strength of a GIC under conditions where the H20 is replaced by D20. Examples for such polymers are all nonionic, cationic or anionic polymers , in particular acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
According to the present invention, deuterium oxide or deuterium is used at a concentration of of 3 % vol. to 99,9 % vol., preferred at a concentration of 15 % vol. to 99 % vol., more preferred at a concentration of 50 % vol. to 99 % vol., even more preferred at a concentration of 70 % vol. to 99 % vol., most preferred at a concentration of 80 % vol. to 99 % vol., in terms of the fluid phase (in solution).
According to the present invention, the water-soluble polymer is used at a concentration of 0.0001 % w/w to 50 % w/w, more preferred 0.001 % w/w to 25 % w/w and most preferred 0.05 % w/w to 5.0 % w/w.
In a third aspect, the present invention further provides for a dual presence of graphene platelets (with -OH, -NH2 or -COOH groups or any other, hydrogen bond formation enabled functional groups bound to its edges) and of D20 replacing partially or totally the H20 in a dental cement or filler material, preferably a GIC. During curing, this dual presence has an even stronger effect regarding the improvement of the resulting mechanical properties of the GIC. This is because the deuterons replace the hydrogen atoms at the hydrophilic functional groups attached to the graphene edges. The higher (hydrogen) binding strength of the deuterons causes a tighter packing of the solid components including the graphene and its tighter binding to the GIC matrix, resulting in improved mechanical strength of the graphene-GIC composite beyond that of just graphene GIC composites or D20 enriched GIC's alone.
In R GIC's and RBC's the effect of graphene on the mechanical properties of the composite dental cement filler material is different. Here the embedding of the pristine or flouride -modified (hydrophobic) graphene patelets provides essentially a reinforcement of the composite structure over distances which correlates with the spatial extension of the graphene platelets. The resin matrix will bind in the setting process to the graphene via the functional groups or directly to the pristine graphene, because the graphene surface can attract free radicals (induced by an initiator molecule (dual cure) of by shining UV light on the mixture (light-cure) which in turn are essential for a high degree of polymerization of the resin matrix. As a result, the resin matrix in the vicinity of the graphene platelets exhibits a particularly high polymerization density reinforced by the underlying graphene platelet and surrounded by the cured resin matrix. This composite structure inside the RMGIC's and RBC, respectively, significantly improves the overall mechanical stability of the RMGIC's and RBC, respectively, and helps to prevent the formation of fissures during the curing of the RMGIC's and RBC owing to shrinking of the material.
In general, the reinforcement of dental cements and filling materials by graphene has important ramifications for the prevention of shrinking of the materials. The mechanical properties of graphene bound to the matrix of any dental cement or filling material stabilizes against volume loss during the curing of the material, thus preventing the formation of fractures and fissures. This enables one-step bulk filling techniques for all self curing dental filling materials.
The application of all dental cements or filler materials in patients requires that the color of the surrounding tooth is matched by the dental cements or filler materials to find acceptance with the users (dentists) and their patients. The materials/substances used in the present invention (graphene and D20) are both optically transparent and thus do not interfere with the coloring scheme of the the dental cements/filler materials.
The invention relates in its first subject to a dental cement or filler material composition comprising graphene and/or deuterium oxide or deuterium.
A preferred embodiment relates to an inventive dental cement or filler material, whereby the dental cement or filler material is a glass ionomer cement or filler material or resin based cement or filler material or resin modified glass ionomer cement or filler material.
A further preferred embodiment relates to a dental cement or filler material, whereby the graphene is in its pristine form or with its reactive groups chemically modified, preferably modified with hydroxyl, carboxyl, amide or silane functional groups or with the graphene reactive groups bound to flouride atoms.
Another preferred embodiment relates to a dental cement of filler material composition, whereby graphene is comprised at a concentration of 0.00001 % w/w to 90 % w/w, preferred 0.01 % w w to 10 % w/w, more preferred 0.01 % w/w to 5 % w/w, most preferred 0.05 % w/w to 3 % w/w in terms of the dry phase. Another preferred embodiment relates to a dental cement of filler material composition, whereby deuterium oxide or deuterium is comprised at a concentration of of 3 % vol. to 99,9 % vol., preferred at a concentration of 15 % vol. to 99 % vol., more preferred at a concentration of 50 % vol. to 99 % vol., even more preferred at a concentration of 70 % vol. to 99 % vol., most preferred at a concentration of 80 % vol. to 99 % vol., in terms of the fluid phase (in solution).
A further preferred embodiment, the dental cement or filler material, whereby the glass ionomer cement composition comprises additionally a water soluble polymer, which can form hydrogen bonds, selected from the group consisting of synthetic or natural polymers being either nonionic, cationic or anionic, preferably at neutral pH value, preferably acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
A preferred embodiment relates to a dental cement or filler material for direct or indirect dental restoration and/or prevention. Another preferred embodiment relates to a dental cement or filler material for the use in direct or indirect dental restoration and/or prevention.
All conventional state of the art dental cements and filler materials can be improved according to the invention regarding their mechanical strength and parameters by the inclusion of graphene and/or deuterium oxide or deuterium into their matrix prior to the setting/curing process. All conventional state of the art dental cements and filler materials in well-known compositions and concentrations can be used to carry out the invention
A preferred embodiment of the invention relates to the inclusion of graphene into dental cements or filler materials. The preferred properties of the graphene platelets used for inclusion are single layer graphene with the carbons at the edges of the platelets functionalized with chemical groups which provide for a optimum binding of the graphene platelets with the matrix. For GIC's the most preferred functional groups bound to graphene are hydrophilic and can for hydrogen bonds. For RMGIC's and RBC*s the graphene preferably used is either pristine or functionalized with groups which render it hydrophobic like flouride atoms (giving partially or perflourated graphene) or silane groups/chains. The invention is not restricted to the above functional modifications, in general all modifications which improve further the binding between the graphene and the matrix and/or the spatial distribution of the graphene within the matrix are preferred. Multi-layer graphene platelets or graphene obtained from processing carbon nanotubes (both single walled and multi walled) as well as mixtures of all types of graphene represent further preferred embodiments of the invention regarding their inclusion in the matrix.
The amount of graphene used for the inclusion into the matrix is 0.00001 % to 90 %, preferred 0.01 % to 10 % , more preferred 0.01 % to 5 %, most preferred 0.05 % to 3 %. All percentages given for the graphene inclusion are by weight.
The use of deuterium oxide (D20) in glass ionomer dental cements/filler materials, either with graphene included or without graphene, is a further especially preferred embodiment of the invention. The deuterium oxide can be partially deuterium enriched or highly deuterium enriched with a degree of enrichment of up to 90 % and even 99.999 %. The D20 is preferably added to the fluid phase of a GIC prior to the mixing with the solid phase in order to allow for a replacement of part or all of the hydrogen atoms in the fluid phase by deuterium atoms. All known physical and chemical methods to replace the hydrogen atoms in the fluid phase by deuterium atoms represent embodiments of the invention. The preferred final deuterium enrichment in the fluid phase (i.e. the percentage of hydrogen atoms in the fluid phase exchanged by deuterium atoms) prior to the mixing with the solid phase of a GIC is 3 % to 99,9 %, more preferred 50 % to 99%, most preferred 80 % to 99%. The solid phase of a GIC can also contain hydrogen atoms which can be exchanged by deuterium atoms prior to the mixture with the fluid phase. All known physical or chemical methods to achieve such an exchange in said solid phase prior to the mixing with the said fluid phase represent embodiments of the invention. The preferred final deuterium enrichment in the solid phase (i.e. the percentage of hydrogen atoms in the solid phase exchanged by deuterium atoms) prior to the mixing with the fluid phase of a GIC is 1 % to 99,9 %, more preferred 50 % to 99 %, most preferred 80 % to 99 %. All percentages given for the deuterium oxide or deuterium inclusion are by volume.
The dual use of deuterium oxide and graphene in a glass ionomer dental cement or filler material represents another especially preferred embodiment of the invention. This embodiment improves the reinforcement and mechanical parameters of dental cements or filler materials even further. Preferably, the graphene is added to either the solid or the fluid phase prior to the mixing of the two phases but the addition of graphene during the mixing is possible as well. Generally, the graphene addition happens before the commencement of the setting/curing of the GIC. The deuterium oxide addition to the GIC phases with the aim of the exchange of part or all of the hydrogen atoms or the use of other hydrogen-deuterium exchange techniques to achieve such an exchange are analogous to the case described above for the sole use of deuterium oxide in GIC's. The preferred introduction of deuterium oxide to the GIC is prior to the mixing of the two phases, preferred is the partial replacement of the water component of the fluid phase of the GIC by deuterium oxide, most preferred is the replacement of the complete water component of the fluid phase of the GIC by deuterium oxide.
The additional introduction of water soluble polymers which provides additional hydrogen bonding sites to the glass ionomer dental cement/filler material and with the H20 replaced partially or in full by D20, either with or without graphene, represents a further embodiment of the invention. Preferably, the at least one polymer is added to a dental cement or filler material, preferably a GIC composition, either to its solid or liquid phase prior to mixing but the addition of said polymer during the mixing of the two phases is equally possible, provided the addition is concluded before the conclusion of the setting of the GIC. The amount of polymers added to the GIC composition is in the range 0.0001 % w/w to 50 % w/w, more preferred 0.001 % w/w to 25 % w/w and most preferred 0.05 % w/w to 5.0 % w/w. The at least one polymer is preferably added to an inventive dental cement or filler material comprising deuterium oxide or a combination of deuterium oxide and graphene.
Further embodiments of the invention relate to a dental cement or filler material composition for direct or indirect dental restoration and/or prevention, where the dental cement or filler material comprises graphene. In a preferred embodiment, the dental cement/filler material is a glass ionomer cement/filler material or resin based cement or filler material or resin modified glass ionomer cement/filler material. Preferably, the graphene comprised by the dental cement or filler material is in its pristine form or with its reactive groups chemically modified, preferably modified with hydroxyl, carboxyl, amide or silane functional groups or with the graphene reactive groups bound to flouride atoms.
Another embodiment relates to a dental cement or filler material composition for direct or indirect dental restoration and/or prevention, where the dental cement or filler material comprises deuterium oxide or deuterium. In a preferred embodiment, the dental cement or filler material is a glass ionomer cement/filler material or resin based cement/filler material or resin modified glass ionomer cement/filler material. Preferably, the glass ionomer cement composition comprises additionally a water soluble polymer which can form hydrogen bonds, whereby the water soluble polymer is selected from the group consisting of synthetic or natural polymers being either nonionic, cationic or anionic, preferably acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
A yet another embodiment relates to a dental cement or filler material composition for direct or indirect dental restoration and/or prevention, where the dental cement comprises graphene and deuterium oxide or deuterium. Preferably, the cement is a glass ionomer cement filler material or resin based cement/filler material or resin modified glass ionomer cement/filler material. Preferably, the glass ionomer cement composition comprises additionally a water soluble polymer which can form hydrogen bonds, selected from the goups synthetic or natural polymers being either nonionic, cationic or anionic at neutral pH value, in particular acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers.
References
Hernandez, Y.et al. High-yield production of graphene by liquid-phase exfoliation of graphite. Nature Nanotechnol. 3, 563-568 , 2008;
Mouras.S.et al. Synthesis of First Stage Graphite Intercalation Compounds With Fluorides, Revue de Chimie Minerale, 1987:24:572;
Naasan MA, Watson TF. Conventional glass ionomers as pos- tenor restorations. A status report for the American Journal of Dentistry. Am J Dent 1 1 : 36-45 , 1998;
Sidhu SK, Watson TF. Resin-modified glass ionomer materials. A status report for the American Journal of Dentistry. Am J Dent 8:59-67, 1995;
Summers A, Kao E, Gilmore J, Gunel E, Ngan P Comparison of bond strength between a conventional resin adhesive and a resin-modified glass ionomer adhesive: an in vitro and in vivo study. American Journal of Orthodontics and Dentofacial Orthopedics 126: 200-206, 2004;
Zhen Chun Lia, Shane N. White, Mechanical properties of dental luting cements. Journal of Prosthetic Dentistry 81 : 597-609, 1999 Examples
Example 1 : Graphene preparation
Hydophobic pristine graphene in organic solution was prepared by liquid-phase exfoliation of graphite (Hernandez, Y et al., High-yield production of graphene by liquid phase exfoliation of graphite. Nature Nanotechnol. 3, 563-568, 2008). A Branson W-250 titanium-rod sonifier was employed in pulsed mode (2s pulses with 1 s interval) at highest power (200W) for 20 min. for the sonication of the graphite solution in a thermostated water bath ( 40°C). The graphite powder was from Sigma-Aldrich (Cat. No. 332461) and the solvent used was N- methtylpyrrolidone (N P). The final solution (after concentration of the centrifugation pellets) contained 1.5% (wt.) of non-oxidized graphene monolayer platelets with a size distribution of less than 30 nm - 5 pm as determined by electron microscopy (TEM). The solution was freeze- dried in a freeze-drying flask after rotating the flask in liquid nitrogen until all liquid was homogeneously frozen at the wall of the flask. After this, the freeze drying was performed for 2 h using a benchtop manifold freeze dryer (BT85 from Millrock Technology, Kingston, NY, USA) operating at a pressure of 10'3 mbar. The freeze-dried graphene flakes were mechanically removed from the flask and stored under vacuum.
Hydrophrlic (water soluble) graphene monolayer platelets tn aqueous solution were prepared from graphite oxide according to procedures of liquid phase exfoliation and and were further concentrated by centrifugation (Dreyer, D R et al., From conception to realization: an historical account of graphene and some perspectives for ist future. Angew. Chem. Int. Ed. 49, 9336-9344 , 2010). A Branson W-250 titanium-rod sonifier was employed in pulsed mode (2s pulses with 1 s interval) at 100W output power for 15 min. for the sonication of the graphite oxide solution in a thermostated water bath ( 60°C). The final aqueous solution comprised a liquid.graphene (exfoliated graphene nano platelets) ratio of 3:1 (wt.) where the individual platelets ranged in size from less than 20 nm up to 50 pm with a thickness of less than 5 nm to 50nm, as determined by electron microscopy. The graphene platelets obtained this way are covered at their edges by hydroxide groups and hydrogen caps, rendering them water soluble. Further analysis showed that less than 50% of the graphene platelets were thicker than one monolayer. In order to obtain modified graphene platelets with the hydrogen atoms covering the edges replaced by deuterium atoms, the above preparation procedure was performed in deuterium oxide (D20) of 98% enrichment (CU Chemie Uetikon AG, CH) under a nitrogen atmosphere. The final D20 -graphene solution was adjusted to contain graphene nano platelets at the ratio of 3:1 (wt) and electron microscopic analysis showed a similar size distribution of the platelets.
Example 2: Glass-lonomer cement (GIC) specimen preparation
The following commercially available dental cements were used: A GIC dental filling material ( etac Molar Easymix (KME), 3M ESPE, Seefeld, Germany) and and GIC dental cement (Ketac Cem (KC), 3M ESPE, Seefeld, Germany), both comprising of a solid and a liquid phase to be mixed on application with a setting time of less than 5 min. The cement specimens KME and KC were prepared according to the user manual instructions by mixing the two phases at a solid : liquid phase ratio of 3.5 (wt.) , and filling the mixtures into cylindrical cast moulds, capped on each open side by a foil of cellulose acetate supported by a glass slide. The size of the cylindrical cast moulds was 4 mm diameter and 6 mm height (for compression and flexural strength measurements) and 18.7 mm diameter and 3.0 mm height (for surface hardness measurements). The specimens were then stored at 37 ° C and 30% rel. humidity for 60 min. , after this the cast moulds were removed and the specimen samples were cured in destilled water for at least 48 h at 37°C.
Example 3: Deuterium oxide-substituted glass-ionomer cement (D-GIC) specimen preparation
The liquid phase of the commercial GIC's from example 1 was freeze dried (lyophilized) in a freeze-drying flask after rotating the flask in liquid nitrogen until all GIC liquid phase was homogeneously frozen at the wall of the flask. After this, the freeze drying was performed for 3 h using a benchtop manifold freeze dryer (BT85 from Millrock Technology, Kingston, NY, USA) operating at a pressure of 10'3 mbar. The freeze dried flakes in the flask were resuspended with Deuterium oxide (D20) of 98% enrichment (CU Chemie Uetikon AG. CH) at the original volume of the liquid phase. The resulting deuterated liquid phase was -like the original liquid phase- optically clear and featured a 6% higher viscosity owing to the higher density of deuterium oxide compared to water. The D-GIC specimen preparation was analogous to example 2 except that the liquid phase was replaced by the deuterated liquid phase, giving D-KME and D-KC.
Example 4: Composite GlC-graphene oxide cement (GIC-G) specimen preparation
Specimen were prepared analogous to example 2) but with the liquid phase of the said commercial dental cements now containing either 0.1 % or 0.3% (wt.) graphene platelets prepared according to example 1 , giving KME-G0.1 , KC-G0.1 and KME-G0.3 , KC-G0.3 specimens, respectively . The volume of the liquid phase was preserved during the addition of the graphene platelet aqueous solution by slow evaporation (at 40°C and ambient pressure under an nitrogen atmosphere) of an equal amount of water from the liquid GIC phase prior to the addition of the platelet solution at the same volume as previously extracted.
Example 5: Composite D-GIC-graphene oxide cement (D-GIC-G) specimen preparation
Specimen were prepared analogous to example 4 but with the liquid phase now replaced by the deuterated liquid phase (example 3) now containing either 0.1 % or 0.3% (wt.) graphene platelets prepared according to example 1 , giving D-K E-G0.1 , D-KC-G0.1 and D-KME-G0.3 , D-KC- G0.3 specimens, respectively . The addition of the graphene platelets to the liquid phase was performed as described in example 4 with the exception that the deuterium substituted graphene solution prepared according to example 1 has been used.
Example 6: Resin modified glass ionomer cement (RMGIC) specimen prepartion
Ketac Cem Plus (3M ESPE, Seefeld, Germany ) is a self-curing resin modified glass ionomer luting cement. The control specimens (KCP) were prepared by filling the cement from the mixing dispenser directly into the cylindrical cast moulds and further processed as described below (self-cure only) . The graphene modified specimens were prepared by adding to the cement from the mix-dispenser oxidized graphene platelets (obtained as solid flakes after freeze-drying the aqueous solution as described in example 1) . The platelets were mechanically mixed into the paste (final graphene concentration 0.08 wt%) for 1 min. using a rotating mixing plate (rotation speed 50 rev./min). After this the specimens were produced by filling the graphene-Ketac Cem Plus mixture (KCP-G) mixture into cylindrical cast moulds, capped on each open side by a foil of cellulose acetate supported by a glass slide. The size of the cylindrical cast moulds was 4 mm diameter and 6 mm height (for compression and flexural strength measurements) and 18.7 mm diameter and 3.0 mm height (for surface hardness measurements). The mixture was allowed to self-cure in the casting moulds for 1 h and after this the specimens were removed from the moulds and stored until further use at 37"C at 30% rel. humidity. Example 7: Resin based cement (RBC) specimen preparation
NX3 dual cure resin cement (Kerr Corp. CA, USA) was used right from the self-mix dispenser unit to obtain the control specimen (NX3) by filling them into cast moulds and allowing self-cure as in example 6. The graphene modified specimen (NX3-G) were obtained by adding pristine graphene platelets prepared according to example 1 to the original NX3 cement from the self- mix dispenser unit and mixing both for 1 min as described in example 6. The final pristine graphene platelets content was 0.08% (wt.). The further specimen preparation (self-cure only) was analogous to example 6.
Example 8: Carbomer modified GIC specimen preparation (CMGIC)
CMGIC specimen were prepared from Ketac Molar Easymix ( 3M ESPE, Seefeld, Germany) according to Example 2 with the exception that 0,5 % (wt.) of Carbopol®980 (Lubrizol, Cleveland, USA) was added to the solid phase prior to the mixing with the liquid phase.
Example 9: Deuterium oxide-substituted Carbomer modified GIC specimen preparation (D-CMGIC)
D-CMGIC specimen were prepared according to Example 3 with the exception that 0,5 % (wt.) of Carbopol®980 (Lubrizol, Cleveland, USA) was added to the solid phase prior to the mixing with the (deuterium oxide-substituted) liquid phase.
Example 10: Surface hardness measurements
Measurements were performed according to DIN EN ISO 14577 using a ZHU 2.5 universal hardness measurement device from Zwick Roell (Ulm, Germany) and the Martens-hardness (MH) was calculated from the penetration depth of a sphere into the specimen surface at a maximum load of 10N and a forward speed of 0.1 mm/s. For each data point four measurements using four different specimen were performed. The results for all specimens are listed in Figure 1 as Marten-hardness (MH). Example 11 : Bending stiffness measurements
Bending stiffness measurements were performed according to DIN EN ISO 4049:2009(E) using a Zwick materials testing machine Ζ0507ΤΉΑ3 (Zwick/Roell, Ulm, Germany). The test speed of the normal force (i.e. the force applied perpendicular to the specimen long axis halfway between the two holding points of the specimen) was 0.75mm/min.
The bending stiffness σ [ Pa] was calculated as
o = 3fmax L (2BH2)
where 1max is the maximum normal force (break down force in [N]) , L is the distance between the holding points [mm], B and H are specimen width and length [mm], respectively. Each value σ is the mean average over four measurements using four different specimen of identical composition.
The results for all specimens are presented in Figure 2
Example 12: Compressive strength measurements
Compressive strength measurements were performed according to DIN EN ISO 9917 using a Zwick materials testing machine Z050 THA3 (Zwick/Roell, Ulm, Germany). The test speed of the force applied along the long axis of the test specimen was 0.75mm/min. Compressive strength C was calculated as
C = 4 ( d2)
where fmax [N] is the force at which the specimen collapses and d [mm] is the diameter of the test specimen. Each value C is the mean average over four measurements using four different specimen of identical composition.
The results for all specimens are presented in Figure 3.

Claims

Claims
1. A dental cement or filler material composition comprising graphene and/or deuterium oxide or deuterium.
2. A dental cement or filler material according to claim 1 , whereby the dental cement or filler material is a glass ionomer cement or filler material or resin based cement or filler material or resin modified glass ionomer cement or filler material.
3. A dental cement or filler material according to claim 1 or 2, whereby the graphene is in its pristine form or with its reactive groups chemically modified, preferably modified with hydroxyl, carboxyl, amide or silane functional groups or with the graphene reactive groups bound to flouride atoms.
4. A dental cement of filler material composition according to any one of claims 1 to
3, whereby graphene is comprised at a concentration of 0.00001 % w/w to 90 % w w, preferred 0.01 % w w to 10 % w/w, more preferred 0.01 % w/w to 5 % w/w, most preferred 0.05 % w/w to 3 % w/w in terms of the dry phase.
5. A dental cement of filler material composition according to any one of claims 1 to
4, whereby deuterium oxide or deuterium is comprised at a concentration of 3 % vol. to 99,9 % vol., preferred at a concentration of 15 % vol. to 99 % vol., more preferred at a concentration of 50 % vol. to 99 % vol., even more preferred at a concentration of 70 % vol. to 99 % vol., most preferred at a concentration of 80 % vol. to 99 % vol., in terms of the fluid phase.
6. A dental cement or filler material according to any one of claims 1 to 5, whereby the glass ionomer cement composition comprises additionally a water soluble polymer, which can form hydrogen bonds, selected from the group consisting of synthetic or natural polymers being either nonionic, cationic or anionic, preferably at neutral pH value, preferably acrylic acid based polymers (carbomers), polyvinyl alcohol based polymers, poly-ethylene oxide polymers and sugar based polymers. A dental cement or filler material according to any one of claims 1 to 6 for direct or indirect dental restoration and/or prevention.
A dental cement or filler material according to any one of claims 1 to 6 for the use in direct or indirect dental restoration and/or prevention.
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