Dental ceramic material with a relatively low processing temperature

A dental ceramic material is disclosed for the preparation and repair of metal ceramic and fully ceramic dentures, which has a processing temperature of 660.+-.30.degree. C., and has the following composition: 60 to 65% by weight of SiO.sub.2, 8.5 to 11% by weight of Al.sub.2 O.sub.3, 8 to 12% by weight of K.sub.2 O, 10.5 to 12% by weight of Na.sub.2 O, 0.7 to 2% by weight of CaO, 0.6 to 2% by weight of BaO, 0.5 to 2.5% by weight of B.sub.2 O.sub.3, 0.1 to 0.6% by weight of Sb.sub.2 O.sub.3, 0 to 0.5% by weight of CeO.sub.2, 1.2 to 3.8% by weight of TiO.sub.2, 0.8 to 1.4% by weight of Li.sub.2 O, and 1.2 to 3.8% by weight of F.sub.2.

INTRODUCTION AND BACKGROUND 
The present invention relates to a dental ceramic material for the 
preparation and repair of metal ceramic and fully ceramic dentures with a 
processing temperature below 700.degree. C. and a coefficient of thermal 
expansion .alpha. of 13-14.multidot.10.sup.-6 .multidot.K.sup.-1 between 
20.degree. and 500.degree. C. 
Using dental ceramic materials, it is possible to prepare fully ceramic 
dentures, to carry out modifications to change the shape of metal ceramic 
and fully ceramic dentures, to repair damaged sections or to line metallic 
dentures with a ceramic layer. 
For many years ceramic layers have been used in dentistry for lining 
metallic frameworks (crowns, bridges), using a type of enamelling, in 
order to give the denture a natural appearance. In this case, ceramic 
powders are applied to the metallic framework as an aqueous slurry and 
fired at elevated temperatures. It is important here that the firing 
temperature (processing temperature) of the ceramic body is at least 
100.degree. C. below the solidus temperature of the material in the 
metallic framework and that the coefficient of thermal expansion of the 
ceramic body in the range 20.degree. to 500.degree. C. is only very 
slightly less than that of the metallic material, so that no cracks are 
produced in the lining layer during firing and cooling down. 
In the same way as these so-called metal ceramic dentures, fully ceramic 
dental items such as full crowns, part crowns, temporary fillings and 
lining shells may be prepared in sinter processes, using the same ceramic 
materials on refractory ceramic molding materials. 
Dental ceramics of this type, for lining, generally require high 
coefficients of thermal expansion, which should be 13 to 
14.multidot.10.sup.-6 .multidot.K.sup.-1 between 20.degree. and 500 
.degree. C., due to the material in the metallic framework. Normally, 
these ceramics are processed at 950.degree..+-.30.degree. C., but this is 
too high for some dental alloys. It is very difficult to lower the 
processing temperature significantly by altering the composition of the 
dental ceramics without adversely altering the coefficients of thermal 
expansion and resistance to corrosion. Furthermore, biologically suspect 
components, such as e.g. lead oxide, must be avoided. 
Coefficients of thermal expansion of 13-14.multidot.10.sup.-6 
.multidot.K.sup.-1 between 20.degree. and 500.degree. C. are generally 
only achieved if the dental ceramic materials contain 25 to 30% by weight 
of alkali metal oxides. However, in an acid environment, such as e.g. in 
oral cavities under plaque, this means that the limit of resistance to 
corrosion of these ceramics is reached. 
DE-OS 39 11 460 discloses dental ceramic materials for the preparation, 
correction and repair of metal ceramic and fully ceramic dentures, which 
contain, apart from SiO.sub.2 as the balance, 5-15% Al.sub.2 O.sub.3, 
0.5-2.5% B.sub.2 O.sub.3 0.5-2.5% Sb.sub.2 O.sub.3, 0.1-0.5% CaO, 0.5 
-2.5% BaO, 5-10% Na.sub.2 O, 10-15% K.sub.2 O, 0.1-0.5% Li.sub.2 O and 
0.1-0.5% F.sub.2. These actually have coefficients of thermal expansion of 
13.5 (.+-.1).multidot.10.sup.-6 .multidot.K.sup.-1 between 20.degree. and 
500.degree. C., but their processing temperatures of 
730.degree..+-.30.degree. C. are still too high for some dental alloys 
during lining. 
In German Patent Application p 40 31 168.6, which has not been published 
previously, ceramic materials for lining metallic dentures, which have a 
coefficient of thermal expansion of 
16-17.5.multidot.10.sup.-6.multidot.K.sup.-1 and a processing temperature 
of 770.degree..+-.70.degree. C., are described. They consist of 60 to 68% 
SiO.sub.2, 10 to 15% Al.sub.2 O.sub.3, 0.7 to 1.5% B.sub.2 O.sub.3, 0 to 
0.5% Sb.sub.2 O.sub.3, 0 to 0.5% CeO.sub.2, 0 to 0.5% BaO, 0.1 to 0.5% 
CaO, 9 to 12% K.sub.2 O, 9 to 11% Na.sub.2 O, 0.8 to 1.4% Li.sub.2 O and 
0.2 to 0.4% F.sub.2. 
SUMMARY OF THE INVENTION 
An object of the present invention was to develop a dental ceramic material 
for the preparation and repair of metal ceramic and fully ceramic 
dentures, which has a coefficient of thermal expansion of 13 to 
14.multidot.10.sup.-6 .multidot.K.sup.-1 between 20.degree. and 
500.degree. C. and a processing temperature below 700.degree. C. In 
addition, it should contain no biologically suspect components and be 
resistant to corrosion in the mouth. 
The present invention discloses a material which consists of 60 to 65% by 
weight of SiO.sub.2, 8.5 to 11% by weight of Al.sub.2 O.sub.3, 8 to 12% by 
weight of K.sub.2 O, 10.5 to 12% by weight of Na.sub.2 O, 0.7 to 2% by 
weight of CaO, 0.6 to 2% by weight of BaO, 0.5 to 2.5% by weight of 
B.sub.2 O.sub.3, 0.1 to 0.6% by weight of Sb.sub.2 O.sub.3, to 0.5% by 
weight of CeO.sub.2, 1.2 to 3.8% by weight of TiO.sub.2, 0.8 to 1.4% by 
weight of Li.sub.2 O and 1.2 to 3.8% by weight of F.sub.2. 
The present invention also discloses a method of using the dental ceramic 
material described herein and to a dental prosthesis comprising a metal 
ceramic denture or ceramic denture and the dental ceramic material 
described herein.

DETAILED DESCRIPTION OF THE INVENTION 
Preferably the dental ceramic materials contain 60 to 63% by weight of 
SiO.sub.2, 8.5 to 9.5% by weight of Al.sub.2 O.sub.3, 10 to 11.5% by 
weight of K.sub.2 O, 10.5 to 11.5% by weight of Na.sub.2 O, 0.7 to 1.5% by 
weight of CaO, 0.6 to 1.2% by weight of BaO, 0.7 to 1.5% by weight of 
B.sub.2 O.sub.3, 0.2 to 0.4% by weight of Sb.sub.2 O.sub.3, 0.1 to 0.4% by 
weight of CeO.sub.2, 1.5 to 3% by weight of TiO.sub.2, 0.8 to 1.2% by 
weight of Li.sub.2 O and 1.2 to 2.4% by Weight of F.sub.2. 
The dental ceramic materials according to the present invention have 
processing temperatures of 660.degree..+-.30.degree. C. The glass point is 
about 450.degree. C. and the softening point is about 510.degree. C. They 
possess very high material homogeneity and a very high transparency (more 
than 70% light transmission). The resistance to bending according to DIN 
13925 is 110 N.multidot.mm.sup.-2 and is therefore far above their minimum 
requirement of 50 N.multidot.mm.sup.-2. 
The loss in mass during resistance to corrosion testing according to DIN 
13925 (16 hours in 4% acetic acid) is about 0.028% by weight. 
Surprisingly, the resistance to bending is then increased by up to 50%, 
whereas it decreases by up to 30% with known dental ceramics. 
The following Table reproduces the composition of some particularly 
advantageous materials: 
______________________________________ 
Material 1 2 3 
______________________________________ 
SiO.sub.2 61.3% 60.9 62.3 
Al.sub.2 O.sub.3 
9.0% 8.6 9.3 
K.sub.2 O 10.7% 11.2 10.2 
Na.sub.2 O 
10.9% 10.7 12.0 
CaO 1.0% 0.9 0.8 
BaO 0.9% 0.7 0.8 
B.sub.2 O.sub.3 
1.0% 1.8 0.5 
Sb.sub.2 O.sub.3 
0.3% 0.2 0.1 
CeO.sub.2 0.2% 0.3 0.1 
TiO.sub.2 2.1% 1.2 1.3 
Li.sub.2 O 
1.0% 0.8 1.4 
F.sub.2 1.6% 2.7 1.2 
______________________________________ 
The present invention also concerns a method of making dental prosthesis 
using the dental material described above and utilizing methods known in 
the art to form dental prosthesis. The present invention further concerns 
a dental prothesis, dental bridge, dental crown or other dental items 
formed from the material described above by methods known in the art. U.S. 
Pat. No. 4,562,882 is incorporated by reference in its entirety. 
Further variations and modifications of the invention will become apparent 
to those skilled in the art from the foregoing and are intended to be 
encompassed by the claims appended hereto.