The present invention relates to self-adhesive dental materials featuring a high level of adhesion to hard tooth substances, simplicity in use, and good mechanical properties. The compositions of the invention can be used in the dental segment as fillings, cements, core buildups, fissure sealants and as dental engineering materials.
In accordance with the present-day state of the art essentially the following classes of substance are used for the abovementioned end applications:
glass ionomer cements (GICs)
resin-modified glass ionomer cements (RMGICs)
It is known that amalgams exhibit no self-adhesion to the hard tooth substances enamel and dentine. Amalgams are fixed solely by mechanical means, by way of what is known as an undercut preparation. Consequently there is a marginal gap between hard tooth substance and the amalgam, which is frequently the cause of unwanted development of secondary caries. These circumstances are described in detail, for example, in WO 93/12759.
In contrast to amalgam, the glass ionomer cements (GICs) exhibit weak adhesion to the hard tooth substances. The adhesion levels, however, are in the very low region of 1 MPa and are generally achieved only by a conditioning step beforehand. A further disadvantage of the GICs are the low mechanical values, in particular the low flexural strengths, which limit use in the area exposed to masticatory pressure.
Composites feature very good mechanical properties and excellent esthetics. In the cured form, composites are composed essentially of a crosslinked polymeric resin matrix based on (meth)acrylate monomers and a fraction of fillers. In order to protect the bond between resin matrix and filler against hydrolytic decomposition, composites are generally given an apolar, hydrophobic formulation. A consequence of this is that composites do not exhibit self-adhesion to the hard tooth substances and in particular not to dentine. Additionally, composites exhibit shrinkage in the course of curing, which allows marginal gaps to form and secondary caries to develop. In order to fix the composites adhesively to the hard tooth substances and to avoid the marginal gap, additional pretreatments and/or worksteps involving what is known as bonding are required. In accordance with the present state of the art it is necessary in this case for the practitioner to carry out the following worksteps:
incipient etching of the entire hard tooth substances by means of a suitable acid such as phosphoric acid (total etch technique);
application of a primer which penetrates the hard tooth substance superficially;
application of a bonding material which together with the primer forms a hybrid layer;
polymerization of the bonding material, for example, by irradiation with light; and/or redox reaction;
application of the actual composite.
In order to reduce the number of worksteps the following, individual new methods have been developed in the meantime:
Combination of the primer and bonding material to form one component.
Combination of the primer and etching agent to form one component, which is no longer rinsed off after application.
Combining of the etching agent, primer, and bonding material to form one solution, which now need only be applied and cured.
The processing of composites, therefore, is time-consuming and, moreover, is labor-intensive as a result of its sensitivity to moisture during the curing operation (placement of rubber dam). The problems referred to are documented, for example, in W. Geurtsen, Klinik der Kompositfüllung, Carl Hanser Verlag, Munich, Vienna 1989.
Compomers are chemically related to the composites. They are given a more hydrophilic formulation, however, through the use of acid-functional (meth)acrylates in the monomer mixture. With use of these materials, in contrast to the composites, there is no longer any need for absolute dryness (no placement of rubber dam). Nevertheless, these materials as well require the use of a bonding material in order to achieve an effective adhesive bond with the hard tooth substances.
The RMGICs are composed essentially of a basic filler, acids, water, (meth)acrylate-based monomers, and initiators for a free-radical polymerization. The RMGICs cure both by way of an acid/base reaction and by way of a free-radical polymerization. The esthetics of the RMGICs are improved as compared with those of the conventional GICs. Here again a conditioning step is generally necessary for adhesion—albeit minimal—to the hard tooth substances. Furthermore, the formulations of the products on the market include hydroxyethyl methacrylate (HEMA), which functions as a solubilizer for the water-soluble acids and remaining (meth)acrylates. HEMA is toxicologically objectionable and adversely affects the swelling characteristics and hence the mechanical properties, such as the flexural strength, of the RMGICs.
One object of the present invention can therefore be seen as being to provide dental materials which do not have the described disadvantages of the state of the art and which in particular feature simple application, a high level of adhesion to hard tooth substances without pretreatment such as the use of a conditioner, bonding material, primer or etching agent, for example, and also good mechanical properties.
Surprisingly it has been found that the object of the invention can be achieved by means of formulations comprising the following components:
(A) from 5 to 75% by weight of one or more mono- or polyfunctional ethylenically unsaturated compounds which additionally possess at least one acid-functional group, at least one of the compounds containing at least one P—OH group, such as a phosphoric, phosphonic or phosphinic acid group, for example,
(B) from 2 to 50% by weight of one or more mono- or polyfunctional ethylenically unsaturated compounds without an acid-functional group,
(C) from 22.8 to 85% by weight of filler(s), including at least one filler capable of reacting with component (A) in an ion exchange, neutralization, acid-forming and/or chelate-forming reaction,
(D) from 0.1 to 8% by weight of one or more initiators and, if desired, activators,
(E) from 0.1 to 20% by weight of additional additives and/or modifiers, the weight ratio in % of component (A) to component (B) being in the range from 21 to 90:10 to 79, preferably in the range from 25 to 90:10 to 75, more preferably from 30 to 90:10 to 70 and very preferably from 40 to 80:20 to 60.
It has been found that formulations with the above composition exhibit an adhesion to bovine dental enamel or dentine of at least 2.0 MPa, preferably of at least 2.5 MPa, more preferably at least 3.0 MPa, measured in accordance with the adhesion determination method indicated below, “Determination of adhesion”, without the need for pretreatment of the hard tooth substance. The formulations of the invention, moreover, have good mechanical properties and are easy to handle.
The following properties are characteristic of the formulations of the invention:
adhesion of at least 2.0 MPa, preferably at least 2.5 MPa, more preferably at least 3.0 MPa
low water absorbency of <50 μg/mm3, preferably <40 μg/mm3, more preferably <30 μg/mm3
flexural strength of >30 MPa, preferably >40 MPa
The term “pretreatment” encompasses steps such as etching, priming, bonding, and conditioning, for example.
The terms “include”, “contain” or “comprise” introduce a nonexclusive enumeration of features. Similarly, the term “one” is to be understood in the sense of “at least one”.
At least one monomer of component (A) contains at least one P—OH group, such as a phosphoric, phosphonic or phosphinic acid group, for example. This monomer is present preferably in a concentration of at least about 5% by weight, more preferably at least about 10% by weight, based on constituents (A) to (E).
Based on the fraction within component (A), this monomer is present preferably in an amount of at least 30%, more preferably at least 50% by weight.
It has also been found that a formulation wherein the weight ratio (in %) of component (A) to component (B) is in the range from 21 to 90:10 to 79, preferably in the range from 25 to 90:10 to 75, more preferably from 30 to 90:10 to 70 and very preferably from 40 to 80:20 to 60 has particularly advantageous properties.
Component (A) comprises compounds which possess at least one ethylenically unsaturated group and also at least one acid-functional group. The polymerizable groups are acrylic, methacrylic, vinyl and/or styryl groups, with acrylic and methacrylic groups being particularly preferred.
Examples of suitable acid groups are carboxylic acid residues, acid residues of phosphorus (e.g., phosphoric, phosphonic, phosphinic acids), of sulfur (e.g., sulfuric, sulfonic, sulfinic acids) and of boron. A feature of the acid groups is that they are able to enter into ion exchange, neutralization, salt-forming and/or chelate-forming reactions with reactive inorganic fillers. It is also possible for the acid residues of component (A) to be present not completely in free form but also, in part, in derivatized form, for instance as a salt, acid halide, acid hydride or readily hydrolyzable esters.
Suitable components (A) and their preparation are described for example in DE 35 36 076 A1, EP 0 237 233 A, and WO 95/22956. By way of example mention may be made of the following: 4-(meth)acryloyloxyethyltrimellitic acid, butenetricarboxylic acid, bis-4,6- and/or bis-2,5-(meth)acryloyloxyethyltrimellitic acid, phosphoric esters of hydroxyethyl (meth)acrylate (HEMA), glyceryl di(meth)acrylate and/or pentaerythrityl tri(meth)acrylate, chloro- and bromophosphoric esters of bisphenol A glycidyl (meth)acrylate. The use of oligomers or polymeric derivatives of abovementioned compounds also leads to dental materials of the invention having good properties.
Particular preference is given to the reaction products of nucleophilic acrylates and methacrylates such as 2-hydroxyethyl methacrylate (HEMA) or glycerol methacrylate esters, for example, with reactive phosphonic or phosphinic or phosphoric acid derivatives such as POCl3, P2O5 or PCl3, for example.
More preferably the abovementioned ethylenically unsaturated acids and/or derivatives thereof have a molecular weight in the range from 70 to 5 000, preferably in the range from 90 to 2 500, more preferably in the range from 100 to 1 000 g/mol.
Compounds suitable as component (B) are those which possess at least one ethylenically unsaturated group. The polymerizable groups are acrylic, methacrylic, vinyl and/or styryl groups, with acrylic and methacrylic groups being particularly preferred.
Suitable mono- and polyfunctional (meth)acrylates and also further ethylenically unsaturated compounds are described for example in EP 0 480 472 A, DE 39 41 629 C2 and in G. Webster (Ed.), Chemistry & Technology of UV & EB Formulation for Coatings, Inks and Paints, Vol. II Prepolymers & Reactive Diluents, J. Wiley and Sons, Chichester, N.Y., Weinheim, Brisbane, Toronto, Singapore, 1997. The ethylenically unsaturated compounds can be used in solitary form or in mixtures in the formulations.
Examples of suitable monomers are the acrylic and methacrylic esters of mono-, di- or higher polyfunctional alcohols. By way of example mention may be made of the following: methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, glyceryl 1,3-di(meth)acrylate (GDMA), glyceryl 1,2-di(meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, isobornyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, triethylene glycol di(meth)acrylate (TEGDMA), 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythrityl tetra(meth)acrylate, and dipentaerythrityl hexa(meth)acrylate.
With advantage it is also possible to use bisphenol A di(meth)acrylate and also the ethoxylated and/or propoxylated di(meth)acrylates derived therefrom. Also suitable are the monomers described in U.S. Pat. No. 3,066,112 A based on bisphenol A and glycidyl (meth)acrylate, or their derivatives formed by addition reaction with isocyanates.
Also highly suitable are the diacrylic and dimethacrylic esters of bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane specified in DE 28 168 23 C and the diacrylic and dimethacrylic esters of the compounds of bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane extended with from 1 to 3 ethylene oxide and/or propylene oxide units.
Additionally urethane (meth)acrylates such as 7,7,9-trimethyl-4,13-dioxo-5,12-diazahexadecane-1,16-dioxydi(meth)acrylate (UDMA, Plex 6661) can be a constituent of component (B). The stated compounds and their derivatives preferably have a molecular weight in the range from 70 to 5 000, preferably in the range from 90 to 2 500, more preferably in the range from 100 to 1 000 g/mol.
As component (C) it is possible to use inorganic fillers such as glasses or ceramics and/or organic fillers. The fillers can be used in solitary form or in mixtures. Furthermore, in order to optimize the product properties, the fillers can be incorporated in different particle sizes into the formulas, i.e., the fillers can have a unimodal or polymodal distribution, bimodal for example.
At least one filler must be used which is able to react with component (A) in an ion exchange, neutralization, salt-forming and/or chelate-forming reaction (reactive filler). In addition it is possible to use those fillers which are inert toward the acid functions of component (A) (nonreactive fillers). Furthermore, reinforcing materials, such as fibers or fibrous compounds, can also be added.
Fillers capable of reacting with the acid groups of component (A) are used, for example, to produce polycarboxylate cements and glass-ionomer cements and are described, for example, in D. C. Smith, Biomaterials 19, 467-478 (1998), DE 20 61 513 A, and WO 95/22956.
Suitable in principle are finely divided metals such as finely divided zinc, metal compounds such as the oxides and/or hydroxides of calcium, magnesium, strontium, and zinc. Also suitable are basic glass powders having a high fraction of divalent and trivalent ions, and also silicates which release metal cations, such as phyllosilicates, bentonites or calcium silicates, sodium aluminum silicates, and zeolites, including the molecular sieves, and also apatite. Likewise suitable as glasses reactive toward component (A) are the borate, phosphate, and fluoroaluminosilicate glasses specified in WO 93/12759. Particularly preferred reactive fillers are the fluoroaluminosilicate glasses and also hydroxides of the alkaline earth metals.
Suitable inert inorganic fillers are, for example, quartz, zirconium silicates, precipitated silicates (HDKH) and low-solubility metal salts such as barium sulfate or calcium fluoride. Further inert inorganic fillers are described in WO 95/22956. Particularly preferred inert inorganic fillers are quartz and zirconium silicates. Component (C) here does not include, in the sense of the invention, any pyrogenic silicas.
Examples of organic fillers include bead polymers and copolymers based on methyl methacrylate, which are available commercially under the designation “Plexidon” or “Plex” from the company Röhm. Also particularly suitable are the polyurethane-based organic fillers described in DE 19 941 738.
For better incorporation into the polymer matrix it can be of advantage to surface-treat or surface-coat the stated fillers and also, if appropriate, X-ray-opaque additives using methods known for the skilled person. An example that may be mentioned is surface treatment with a silane such as methacryloxypropyltrimethoxysilane. The amount of coating agent used is normally between 0.05 and 10% by weight, preferably between 0.1 and 5% by weight, based on the filler.
By initiators in accordance with component (D) are meant initiator systems which effect the free-radical polymerization of the monomers, examples being photoinitiators and/or what are called redox initiatory systems and/or thermal initiators.
Suitable photoinitiators are described for example in J. -P. Fouassier, Photoinitiation, Photopolymerization and Photocuring, Hanser Publishers, Munich, Vienna, N.Y. 1995 or else J. F. Rabek (ed.), Radiation Curing in Polymer Science and Technology, Vol. II, Elsevier Applied Science, London, N.Y., 1993 and also in the patent publications EP 0 073 413 A, EP 0 007 508 A, EP 0 047 902 A, EP 0 057 474 A, and EP 0 184 095 A. Examples that may be mentioned include benzoin alkyl ethers, benzil ketals, and acylphosphine oxides. Particularly suitable are aliphatic and aromatic 1,2-diketone compounds such as camphorquinone in combination with activators such as tertiary amines.
Examples of suitable redox initiator systems include organic compounds with an oxidative action, such as peroxide compounds, together with what are termed activators. Suitable organic peroxide compounds include, in particular, compounds such as lauroyl peroxide, benzoyl peroxide, and also p-chlorobenzoyl and p-methylbenzoyl peroxide.
Examples of suitable activators include tertiary aromatic amines, such as the N,N-bis(hydroxyalkyl)-3,5-xylidines known from U.S. Pat. No. 3,541,068 A and the N,N-bis(hydroxyalkyl)-3,5-di-t-butylanilines known from DE 26 58 538 A, especially N,N-bis(β-oxybutyl)-3,5-di-t-butylaniline, and also N,N-bis(hydroxyalkyl)-3,4,5-trimethylaniline. Further highly suitable activators are compounds of sulfur in oxidation state +2 or +4 such as sodium benzenesulfinate or sodium para-toluenesulfinate or the barbituric acids or barbituric acid derivatives described in DE 14 955 20 B and also the malonylsulfamides described in EP 0 059 451 A. Preferred malonylsulfamides are 2,6-dimethyl-4-iso-butylmalonylsulfamide, 2,6-diisobutyl-4-propylmalonylsulfamide, 2,6-dibutyl-4-propylmalonylsulfamide, 2,6-dimethyl-4-ethylmalonylsulfamide and 2,6-dioctyl-4-isobutylmalonylsulfamide.
For further acceleration of curing the polymerization can be conducted in the presence of heavy metal compounds based on, for example, Ce, Fe, Cu, Mn, Co, Sn or Zn, with copper compounds being particularly suitable. The heavy metal compounds are used preferably in the form of soluble organic compounds.
One particularly suitable redox system comprises the following components:
I. from 14.9 to 50% by weight, preferably from 20 to 45% by weight, of a barbituric acid or thiobarbituric acid or of a barbituric or thiobarbituric acid derivative,
II. from 30 to 75% by weight, preferably from 35 to 67.8% by weight, of a peroxodisulfate compound and/or peroxodiphosphate compound,
III. from 10 to 35% by weight, preferably from 12 to 30% by weight, of a sulfinic acid compound, and
IV. from 0.1 to 5% by weight, preferably from 0.2 to 4% by weight, of a copper compound.
Where the dental compositions of the invention are cured by photopolymerization it is possible to formulate one-component systems. Where the dental compositions of the invention comprise a redox initiator system, comprising for example organic peroxide and activator, then for reasons of storage stability peroxide and activator are present in spatially separate parts of the dental composition of the invention, which are not mixed with one another until immediately prior to application. These, in other words, are at least two-component formulations in the form, for example, of powder/liquid or paste/paste.
For reasons of storage stability the constituents of the initiator system of the invention may be microencapsulated. Methods of microencapsulation are described for example in U.S. Pat. No. 5,154,762 and EP 0 588 878 B1.
In order to set specific properties it is possible as component (E) to introduce additional additives or modifiers into the formulations. Possible additives and their functions are described in U. Zorll (ed.), Lehrbuch der Lacktechnologie, Vincentz Verlag, Hanover 1998 and P. Nanetti, Lackrohstoffkunde, Vincentz Verlag, Hanover 1997. With no claim to completeness, representative mention may be made of some additives and/or modifiers:
plasticizers such as phthalates, adipates, sebacates, phosphates or citrates, for example to increase the flexibility of the compositions;
organic and inorganic pigments and/or dyes such as white pigments based on titanium dioxide or zinc sulfide (lithopones), red iron oxide 3395, Bayferrox 920 Z Yellow, Neozapon Blue 807 (copper phthalocyanine-based dye) or Helio Fast Yellow ER, for individual coloring of the dental compositions;
stabilizers, especially free-radical scavengers, such as substituted and unsubstituted hydroxyaromatics (e.g., para-methoxyphenol), phenothiazine, HALS (hindered amine light stabilizers) and/or heavy metal scavengers such as EDTA;
thixotropic assistants such as pyrogenic silicas (Aerosil) or else modified phyllosilicates;
ion donor substances, particularly those which release fluoride ions, such as the fluoride salts of metals from main groups one and/or two such as sodium fluoride. Particularly suitable are complex inorganic fluorides of the general formula AnMFm as described in EP 0 717977 A. In this formula A is a mono- or polyvalent cation, M is a metal from main or transition group III, IV, V, n is an integer from 1 to 3, and m is an integer from 3 to 6. As representatives mention may be made of calcium zinc fluoride and potassium hexafluorotitanate.
Bactericidal or antibiotic substances such as chlorhexidine, pyridinium salts or the customary pharmaceutical substances such as β-lactam antibiotics (penicillins), cephalosporins, tetracyclines, chloramphenicol, fosfomycin, antibacterial macrolides or polypeptide antibiotics, for example, may likewise be used.
It is also possible to use solvents as flow improvers and to improve the mixing characteristics. Particularly preferred in this context are water, acetone, methyl ethyl ketone and/or short-chain alcohols having less than 10 carbon atoms such as ethanol or isopropanol, for example.
Furthermore, in order to set specific properties, it is also possible as component (E) to use soluble organic polymers such as polyvinyl acetate, polyacrylic acid and/or polyvinyl ethers.
The compositions of the invention can be used in the dental segment, for example, as filling materials, fissure sealants, cements, core buildups and as dental engineering materials and/or bone substitute compositions.
The invention is described in more detail below with reference to examples, which should not be understood as limiting the invention in any way whatsoever.