Polymerizable composite material

Details Polymerizable composite material Polymerizable composite material

1998-12-11

2002-03-05

Medley, Margaret (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C523S116000, C523S115000, C524S404000, C524S433000, C524S443000, C524S494000, C524S779000

Reexamination Certificate

active

06353039

ABSTRACT:

The invention relates to polymerizable composite material which contains a special transparent glass having a high release of calcium ions and fluorine ions. Because of its advantageous properties, the composite material can be used in particular as dental material.
There continues to be a great need in dentistry to prevent the secondary caries which frequently occurs after the use of dental restoration material, such as a filling composite. For this reason, filling composites which can release ions, such as fluorine, calcium or hydroxyl ions, in the oral cavity have also been investigated in recent years. These ions are advantageous since they have a remineralizing, bioactive or cariostatic action.
Restorative dental materials which develop a caries-inhibiting action because they contain sources of fluoride, such as special chlorohexidine-fluoride compounds, are known e.g. from U. Salz, Phillip Journal 14 (1997) 296.
Further examples of ion-releasing filling materials are glass ionomer cements or compomers whose organic matrix is always made of monomers, oligomers or polymers with carboxyl groups (cf. inter alia: A. D. Wilson, J. W. McLean, Glass Ionomer Cement, Quintessence Publishers, Chicago 1988; J. Nicholson, M. Anstice, Trends Polym. Sci. 2 (1994) 272; R. Hickel, L. Kremers, C. Haffner, Quintessenz 47 (1996) 1581).
Although these filling materials display a high degree of ion release, a clear reduction in the mechanical properties, in particular in strength, occurs in them after prolonged contact with water.
Furthermore, there is known from EP-B-449 399 a dental composite material which is used as relining material or as cement. In addition to customary (meth)acrylates the composite material contains a special glass which releases calcium ions and hydroxyl ions. However, the glass has too high an opacity, so that it gives the composite material an unnaturally dead appearance and therefore cannot be used in the field of aesthetically demanding restorations. The low translucence also prevents a light-curing of the composite material, so that a high through-curing depth, which is precisely what is needed in the case of filling materials for deep cavities, cannot be achieved. Finally, the glass also contains only very small quantities of fluorine which may come from cryolite, NaF or KF which is optionally used as flux.
The object of the invention is accordingly to make available a polymerizable composite material which, in addition to a high release of calcium ions, also displays a high release of fluorine ions upon contact with water, is fully cured by light even in deep layers and displays a high translucence which makes possible its use as a material for aesthetically demanding dental restorations.
This object is surprisingly achieved by the polymerizable composite material according to claims 1 to 9. The invention also relates to the transparent glass according to claim 10 and to the use of the composite material according to claims 11 and 12.
The polymerizable composite material according to the invention is characterized in that it contains
(a) at least one polymerizable monomer and
b) at least one transparent glass having a high release of calcium ions and fluorine ions, which contains the following components:
Component
wt.-%
SiO
2
24.0 to 56.0
CaO
26.0 to 57.0
F
  4.0 to 14.0.
The glass used according to the invention preferably contains in addition at least one of the following components
Component
wt.-%
Na
2
O
1.0 to 9.0
B
2
O
3
 1.0 to 14.0
MgO
 1.0 to 14.0
SrO
 1.0 to 12.0
ZnO
1.0 to 7.0
Al
2
O
3
0.5 to 5.0
ZrO
2
 0.5 to 4.0.
Preferred quantity ranges exist for the individual components of the glass. These can be chosen independently of one another and are as follows
Component
wt.-%
SiO
2
30.0 to 54.0,
in particular 36.0 to 54.0
CaO
32.0 to 50.0
F
5.0 to 12.0
Na
2
O
1.0 to 8.0
B
2
O
3
1.0 to 12.0
MgO
1.0 to 10.0
SrO
1.0 to 10.0
ZnO
1.0 to 5.0
Al
2
O
3
0.5 to 4.0
ZrO
2
0.5 to 4.0.
Particularly preferred quantity ranges of the components of the glass, which can be chosen independently of one another, are as follows
Component
wt.-%
SiO
2
45.0 to 54.0
CaO
35.0 to 50.0
F
 6.0 to 12.0
Na
2
O
4.0 to 7.0
B
2
O
3
 1.0 to 12.0
MgO
 1.0 to 10.0
SrO
 1.0 to 10.0
ZnO
1.0 to 5.0
Al
2
O
3
0.5 to 4.0
ZrO
2
 0.5 to 4.0.
All the quantities that are given above and in the following in the description and in the claims of the components of the glass are to be understood as values which were obtained as follows: the quantities of the oxides were ascertained by quantitative analysis of the corresponding cations, i.e. Si, Ca, Na, B, Mg, Sr, Zn, Al and Zr, by means of X-ray fluorescence analysis and conversion of the obtained values into the quantities of the respective oxides. Thus the level of a cation serves to deduce the level of the corresponding oxide. In contrast to this, the quantity of F is determined directly by means of an electrode which is selective for fluoride ions after the glass had been subjected to a fusion with soda-potash dissolution.
As a result of the high F-contents of the glasses, they contain fluorides, such as CaF
2
, to a notable extent. Therefore, the oxide contents calculated from the cation contents and accordingly the absolute oxygen content of the glass are too high, and the sum of the components exceeds 100%. The portion going beyond 100% is therefore usually referred to as so-called “fluorine-equivalent oxygen”. This is customary for silicate glasses containing fluoride and is described at length e.g. in J. Lange “Rohstoffe der Glas-industrie”, Deutscher Verlag für Grundstoff-industrie, Leipzig, Stuttgart (1993), pp. 221-223.
It is generally customary in glass manufacture to add small quantities of fluorides as flux in order to improve the melting behaviour of the glass in question. This is also, as described at the outset, known in the case of glasses for conventional dental materials. However, the overall structure of the glasses is not substantially changed by these small portions of fluorine.
In contrast to this, a high fluorine portion of at least 4,0 wt.-% is built in in the transparent glass used according to the invention, which substantially changes the basic structure of the glass compared with corresponding glasses which are free from fluorine or have only small fluorine contents as a result of the use of flux. A marked degradation of the SiO
4
tetrahedron network structure of the glass occurs because of this high fluorine content and the simultaneous incorporation of other network modifying ions, such as Ca
2+
or Na
+
. A glass structure forms which can no longer be explained by the classical network theory. The glass structure comes close to a new glass structure which is called “inverted glass structure”. An inverted glass is understood to be a glass which has less than 50 mol.-% network-former material.
As a result of the changed structure, it is above all the refractive index of the glass which changes, and surprisingly a release of fluorine ions with a simultaneous release of calcium ions from the glass is also possible. When the composite material is used in the dental field, the desired alkaline action can thus be brought about in the oral cavity by the calcium ions together with carbonate in the saliva, and, through he fluorine ions, their known remineralizing action. Calcium ions also promote the remineralization process.
Furthermore, the high fluoride content of the glass brings about a marked reduction in its refractive index to values below 1.60 and preferably below 1.56. The organic matrix of the composite forming through curing of the polymerizable monomer has a very similar refractive index, for which reason the whole composite material can likewise be translucent or even transparent. This is of particular advantage if the composite material is to be used for the production of visible dental restorations, which naturally are to have similar optical properties to translucent natural dental material.
To produce the transparent glass used according to th

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