Compositions: coating or plastic – Coating or plastic compositions – Dental
Reexamination Certificate
2001-06-22
2003-09-30
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Dental
C501S057000, C501S058000, C501S059000, C501S063000, C501S064000, C501S070000, C501S072000
Reexamination Certificate
active
06626986
ABSTRACT:
The invention relates to potassium-zinc-silicate glass and particularly that which can be processed at low temperatures by sintering and is particularly suitable for the desired establishment of the optical properties and the processing properties of coating and veneering material for ceramic dental restorations.
Apart from metalic dental restorations which, for aesthetic reasons, are veneered with ceramic layers, all-ceramic restorations, in which a ceramic veneering or coating material is also applied to a core made from ceramic material, are increasingly used in dentistry. Glass ceramics can be considered amongst others for use as core and also as coating material.
Above all, the optical properties as well as the working properties of glass ceramic coating material are however frequently unsatisfactory. Thus as a result of their high crystal content, the glass ceramics used show a pronounced turbidity, which is not acceptable especially in the case of dental restorations for the incisor region. Moreover, in many cases, the glass ceramics have a very high coefficient of expansion, which is why they are unsuitable as coating material for cores made from glass ceramic with a low coefficient of expansion, such as e.g. lithium disilicate glass ceramic. As a result of the inadequate matching of the coefficients of expansion, undesired separation of the coating material may result.
It is furthermore known that leucite-containing glass ceramics themselves have very high linear thermal coefficients of expansion. These are due to the level of leucite crystals, which are formed by the controlled crystallization of a corresponding starting glass.
Alkali-zinc-silicate glasses are known from EP-A-695 726, which are suitable for veneering mainly metal dental suprastructures, but can contain only 8.0 wt.-% ZnO at most, which is why their chemical resistance is still not satisfactory in every case. With thermal treatment in the range of 600° C. to 1000° C. and thus under processing conditions usual for the dental technician, the glasses furthermore form corresponding glass ceramics which are pronouncedly clouded as a result of their crystal content and are thus not suitable for establishing a high translucence in a glass ceramic coating material. The level of crystals, in particular leucite, also leads to undesirably high sintering temperatures and coefficients of expansion, so that they are not satisfactory for the veneering of ceramic substrates with low coefficients of expansion.
Alkali-silicate glasses are known from EP-A-885 606 which can be used as dental coating or veneering materials. However they contain 5.0 wt.-% of ZnO at most and are characterized inter alia by a K
2
O content of only 8.5 wt.-% at most. Consequently, the chemical resistance of these glasses is not sufficient in every case and they still have rather high sintering temperatures.
Even if the known glasses already show good results when used as components for veneering and coating materials, coatings on thin frameworks made from glass ceramics cannot however be manufactured with them without cracks forming. As a rule, the result in these thin layered composites is a build-up of stress and thus a cracking-off of the applied coating material or a fracture of the completed dental restoration. A further reason for this behaviour is the sintering temperatures of the known glasses which are still rather high. Thus the preparation of veneers, thin-valled veneers or thin-walled crowns with a glass ceramic core is not possible with them.
Furthermore, the satisfactory processing of the known glasses by sintering is possible only in a narrow temperature range. When there are larger deviations from the actual sintering temperature, these glasses show an unsatisfactory dimensional stability in the case of too high a temperature and an unacceptably high porosity in the case of too low a temperature after sintering. The satisfactory workability only in a narrow temperature range is very disadvantageous, as the furnaces used for the preparation of dental restorations are small, and it is thus generally difficult to constantly maintain a desired temperature in them over a certain period of time. Particularly in furnaces which operate at low temperatures, such as lower than 850° C., considerable fluctuations in temperature occur during a sintering process.
The object of the invention is therefore to provide a glass which has a low coefficient of expansion, a low sintering temperature, a high chemical resistance as well as a high translucence and the chemical composition of which is compatible in particular with that of apatite glass ceramics and lithium disilicate glass ceramics, so that a strong bond can be formed between the glass and the glass ceramic and the glass is thus suitable for the preparation of coatings or veneers for thin-walled dental restorations. Furthermore, the glass is to be processable into the desired restorations in a wide temperature range.
This object is achieved by means of the potassium-zinc-silicate glass according to the present invention.
The subject-matter of the present invention is also the dental material, the use as well as the shaped dental product according to the invention.
The potassium-zinc-silicate glass according to the invention comprises the following components:
Component
wt.-%
SiO
2
60.0 to 72.0
Li
2
O
1.0 to 5.0
K
2
O
10.0 to 23.0
ZnO
8.5 to 20.0
The glass according to the invention can additionally comprise at least one of the following components:
Component
wt.-%
Na
2
O
0 to 4.0
MgO
0 to 4.0
CaO
0 to 3.6
SrO
0 to 3.0
Al
2
O
3
0 to 8.0
B
2
O
3
0 to 3.3
La
2
O
3
0 to 3.0
ZrO
2
0 to 6.0
TiO
2
0 to 2.5
CeO
2
0 to 2.0
SnO
2
0 to 5.0
P
2
O
5
0 to 1.0
Tb
4
O
7
0 to 1.8
F
0 to 1.1.
If these additional components are present, they are used in particular in amounts of at least 0.1 wt.-%. For the individual components of the potassium-zinc-silicate glass according to the invention, there are preferred quantity ranges. These can be selected independently of each other and are as follows:
Component
wt.-%
SiO
2
62.0 to 70.0
Li
2
O
2.0 to 5.0
K
2
O
10.0 to 20.0
ZnO
10.0 to 19.0
Na
2
O
0 to 3.0
MgO
0 to 3.0
CaO
0 to 3.0
SrO
0 to 3.0
Al
2
O
3
0 to 6.0
B
2
O
3
0 to 3.0
La
2
O
3
0 to 2.0
ZrO
2
0 to 5.0
TiO
2
0 to 2.0
CeO
2
0 to 1.5
SnO
2
0 to 4.0
P
2
O
5
0 to 0.8
Tb
4
O
7
0 to 1.0
F
0 to 1.0.
Particularly preferred quantity ranges for the individual components of the glass according to the invention are as follows, and these can also be selected independently of each other:
Component
wt.-%
SiO
2
63.0 to 69.0
Li
2
O
3.0 to 5.0
K
2
O
11.0 to 19.0
ZnO
10.0 to 17.0
Na
2
O
0 to 2.5
MgO
0 to 2.5
CaO
0 to 2.5
SrO
0 to 2.5
Al
2
O
3
0 to 4.0
B
2
O
3
0 to 2.0
La
2
O
3
0 to 1.8
ZrO
2
0 to 4.0
TiO
2
0 to 1.8
CeO
2
0.1 to 1.5
SnO
2
0 to 3.5
P
2
O
5
0 to 0.5
Tb
4
O
7
0 to 0.8
F
0 to 0.8.
All the above quantity amounts in wt.-% relate to the glass.
For the preparation of the glass according to the invention the preferable procedure is to melt suitable starting materials, such as e.g. carbonates, oxides and fluorides, at a temperature in the range of 1350° C. to 1650° C., preferably 1400° C. to 1600° C., over a period of time of 30 minutes to 4 hours, preferably 1 hour to 2.5 hours, with formation of a homogenous melt. The melted glass is then normally quenched in water, i.e. fritted, and after being dried is ground to the desired particle size.
By means of scanning electron microscopic studies, it was established that the glass according to the invention is free from crystals. It was further shown that the glass also survives the conditions which prevail in the case of a customary additional dental processing by sintering, without there resulting a formation of crystals such as occurs with known glasses. Even with a thermal treatment in the range of 600° C. to 800° C. for 1 minute to 1 hour, there was no crystallization.
The glass according to the invention normally has a very advantageous sintering temperature of less than 800° C. during sintering onto a ceramic or glass-ceramic substrate, such as a lithium disilicat
Höland Wolfram
Rheinberger Volker
Schweiger Marcel
Ivoclar Vivadent AG
Koslow C. Melissa
Nixon & Peabody LLP
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