Adhesive systems

Details Adhesive systems Adhesive systems

2002-04-05

2004-12-28

Copenheaver, Blaine (Department: 1733)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C156S327000, C523S116000, C523S118000

Reexamination Certificate

active

06835271

ABSTRACT:

The present invention relates to adhesive systems for the attachment of materials which are only or also cationically polymerizable.
To date, predominantly methacrylate and acrylate monomers have been used in polymerizable dental compositions. The 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]-propane (bis-GMA) [U.S. Pat. No. 3,066,112] described by Bowen deserves particular attention. Mixtures of this methacrylate with triethylene glycol dimethacrylate also still serve today as the standard formulation for dental plastic direct filling materials. Methacryl derivatives of twice-formylated bis-(hydroxymethyl)tricyclo[5.2.1.0
2,6
]decane have also proved successful as monomers for dental composites [W. Gruber et al., DE-A-27 14 538; W. Schmitt et al., DE-A-28 16 823; J. Reiners et al., EP 0 261 520]. A major disadvantage of these dental compositions is however the high volume shrinkage which occurs through the polymerization. This can be minimized for example through the use of ring-opening monomers, such as the cationically curing epoxides.
Only a little is known about cationically curable epoxide compositions for dental applications. U.S. Pat. No. 5,556,896 describes epoxide-containing compositions which must necessarily contain spiroorthocarbonates as shrinkage-compensating monomers. Bowen describes a composition containing quartz sand and an aliphatic diepoxide (bisphenol-A-diglycidyl ether) which in the cured state allegedly displays good stability in the mouth environment [J. Dent. Res. 35, 1956, 360-379]. AT-A-204 687 describes epoxide dental compositions based on bisphenol-A which are cured by means of Lewis acid catalysts. The specifications DE-A-196 48 283, WO-96/13538 and WO-95/30402 likewise describe polymerizable dental compositions based on epoxides and their use.
Although there are extensive experiences with epoxides and cycloaliphatic epoxides (U.S. Pat. No. 2,716,123, U.S. Pat. No. 2,750,395, U.S. Pat. No. 2 863 881, U.S. Pat. No. 3,187,018), such monomers and cationically polymerizable compositions formulated therefrom with the properties necessary for dental applications have not been commercially available at any point in time.
This is because the curing of these cationically polymerizable compositions is inhibited by water and the hard tooth substance, for example in dentine, contains approx. 11 to 16 weight per cent water (G.-H. Schumacher et. al., Anatomie und Biochemie der Zähne, Gustav Fischer Verlag, 1990, 4
th
edition).
Thus it is readily explicable that for example formulations of dental filling materials on an epoxides basis, in contrast to formulations on a (meth)acrylate basis, cannot show any inherent adhesion to dentine and the use of such materials was thus not possible.
For improved attachment of (meth)acrylate-based dental filling materials—i.e. radically curing systems—so-called adhesive systems are used.
The quality of these adhesive systems is reflected in the following criteria:
Complete bonding to the hard tooth substance without flaws (“sealing”),
Complete bonding to the filling material,
Permanent bond.
However, as the polymerization of (meth)acrylate systems takes place via a radical mechanism, a bonding of cationically polymerizing tooth materials to such adhesive systems is not to be expected. A dental adhesive system for (also) cationically cross-linking materials has not been commercially available on the market at any point in time.
Although DE-A-197 43 564 describes compositions based on solvent-free, cationically and/or radically curable cross-linking systems as radiation-curable adhesion promoters—so-called primers—these are used only for the coating of anhydrous materials, for example plastics such as polyvinylidene chloride (PVDC) or silicon.
WO-98/47046 describes photopolymerizable epoxide-based mixtures containing an epoxide resin, an iodonium salt, a transfer molecule sensitive in visible light and an electron donor, and their use as a dental adhesive system. However, it has been shown that with such mixtures, no bonding to cationically curing mixtures is to be achieved on the hard tooth substance (see comparison mixtures 1 to 3).
WO-99/34766 states that compositions with a high proportion of cationically curable groups do not bond at all, or only very poorly, to hard tooth tissue. To solve the problem, it is proposed to provide either a hybrid composition containing constituents with radically and cationically polymerizable groups or a composition which is largely free from cationically polymerizable groups.
The object of the present invention is to provide methods of bringing either materials which are only cationically cross-linking or materials which are radically and cationically cross-linking to bond to hard tissue containing water, such as a tooth, the bonding preferably being intended to take place essentially uniformly over the entire surface available for the bonding.
This object is achieved according to the invention by the use of adhesive systems which are radically polymerizable and contain 1 to 30 wt.-%, preferably not more than 20 wt.-% and in a particularly preferred manner not more than 15 wt.-% of a reactive solvent with a pKS value less than or equal to that of acetone, for the attachment of materials which are only or also cationically polymerizable to hard tissue containing water, the adhesive system containing at least one component i) which is capable of starting a radical reaction, and one component ii) which contains radically polymerizable monomers which are acid-functional or contain groups which can form acids.
Surprisingly, it was found that in the case of the use of radically polymerizable adhesive systems and cationically polymerizable dental materials, a good bonding to hard tissue containing water, such as hard tooth substance, can be achieved, although there are two completely different polymerization forms.
As the cationic polymerization takes place via an ionic chain propagation mechanism, there are theoretically no possibilities of polymerizing non-radically polymerizing monomers with radically growing chains.
In addition, the water contained in the hard tissue or the reactive solvent added to the adhesive system should disturb the cationic polymerization, as it acts as a chain-breaking agent. Through the continuous chain breaking, many short chains should thus form which prevent the construction of a polymer network.
It is completely surprising that, despite what has been said above, cationically polymerizable materials can be brought to bond to the hard tooth substance containing water or also to radically polymerizing adhesive systems containing reactive solvents. Further advantages are the lower toxicity compared with customary solvents such as CH
2
Cl
2
or acetonitrile, and the reduced volatility which allows the adhesive mixture to be applied uniformly before the solvent evaporates. Improved solution properties which allow the use of a large number of different monomers are also advantageous.
The invention is described in more detail in the following.
The adhesive mixture which displays the described advantages when used according to the invention contains as constituent i) preferably 0.01 to 10 wt.-%, in particular 0.1 to 7 wt.-%, and particularly preferably 0.1 to 5 wt.-% of an initiator system which is capable of starting a radical polymerization and as constituent ii) preferably 90 to 99.99 wt.-%, in particular 93 to 99.90 wt.-% and particularly preferably 95 to 99.90 wt.-% of the radically polymerizable material.
The proportion of reactive solvent lies in the range from 1 to 30 wt.-%, preferably in the range from 5 to 25 wt.-% and quite particularly preferably in the range from 8 to 20 wt.-%.
Reactive solvents are those with acid protons and a pKS value of less than or equal to that of acetone, such as water, methanol, ethanol, n- and i-propanol. In tests, it has been shown that such solvents, in particular those which carry hydroxyl groups, contrary to what was said above, improve the bond between cationic materia

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