Compositions: ceramic – Ceramic compositions – Devitrified glass-ceramics
Reexamination Certificate
2001-06-22
2003-09-16
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Devitrified glass-ceramics
C501S003000, C428S428000, C428S701000, C433S212100, C433S228100
Reexamination Certificate
active
06620747
ABSTRACT:
The invention relates to a low-temperature-sintering apatite glass ceramic which is suitable in particular for use in restorative dentistry and above all for coating or veneering dental restorations, such as ligaments, veneers, bridges or crowns.
Glass ceramics for use in dentistry are known from the state of the art.
EP-A-0 690 030 discloses leucite-containing phosphosilicate glass ceramics which can be used in dental technology. However, they have very high linear thermal coefficients of expansion because of their leucite content, so that they are not suitable for coating materials with low coefficients of expansion, such as e.g. lithium disilicate glass ceramics.
Furthermore, alkali-zinc-silicate glass ceramics are disclosed in EP-A-0 695 726 which can however contain only 8.0 wt.-% ZnO at most, for which reason their chemical resistance is still not satisfactory in every case. These glass ceramics have moreover the disadvantage that they contain no apatite but leucite as crystal phase. Due to the high coefficient of expansion of leucite, the glass ceramics are therefore as a rule likewise not suitable as coatings for lithium disilicate glass ceramics.
Apatite glass ceramics have also already been used in restorative dentistry.
EP-A-885 855 and EP-A-885 856 describe apatite glass ceramics with optical properties which come close to those of natural teeth. They show a good resistance under the conditions of the oral environment and are derived from the chemical system SiO
2
—Al
2
O
3
—P
2
O
5
—K
2
O—Na
2
O—CaO—F. Additional components are possible but only in relatively small amounts. So the ZnO content is limited to 5.0 wt.-% at most and that of K
2
O to 8.5 wt.-% at most. Due to these restrictions, a combination of good chemical resistance and low sintering temperature can still not be achieved in every case with these materials.
A further disadvantage of these glass ceramics is that, as a rule, they cannot be sintered onto a ceramic or glass ceramic dental framework, such as a lithium disilicate glass ceramic at low temperatures of less than 800C. However, it is precisely when preparing thin-walled dental restorations, such as thin-walled veneers, also sometimes referred to as ligaments, that stresses and fractures of the dental restoration occur, because of the necessary high temperatures. Thus, in particular dental veneers with a core made from lithium disilicate glass ceramic and apatite glass ceramic sintered onto it cannot be prepared in a satisfactory way according to the state of the art.
Furthermore, the satisfactory processing of the known glass ceramics by sintering is possible only in a narrow temperature range. When there are larger deviations from the actual sintering temperature, these glass ceramics 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 accordingly to prepare an apatite glass ceramic which is similar in its optical properties and in particular in its high translucency to natural tooth material and has an excellent chemical resistance and a low thermal coefficient of expansion. Furthermore, the apatite glass ceramic is to have a low sintering temperature so that it is above all suitable as coating or veneering material for preparing stable thin-walled dental restorations, such as dental veneers. Finally, the glass ceramic is to be able to be processed to produce the desired restorations in a wide temperature range.
This object is surprisingly achieved by the low-temperature-sintering apatite glass ceramic according to claims
1
to
9
.
The subject-matter of the invention are also the process for preparing the apatite glass ceramic according to claim
10
, the dental material according to claims
11
to
14
, the use according to claims
15
to
18
as well as the shaped dental products according to claims
19
to
22
.
The apatite glass ceramic according to the invention is characterized in that it comprises the following components:
Component
wt.- %
SiO
2
56.0 to 65.0
Li
2
O
1.8 to 5.3
K
2
O
9.0 to 17.5
ZnO
9.0 to 16.0
CaO
3.5 to 10.5
P
2
O
5
2.0 to 6.0
F
0.5 to 1.0
and the main crystalline phase is formed by apatite crystals.
The glass ceramic according to the invention can additionally comprise at least one of the following components:
Component
wt. - %
Na
2
O
0 to 5.0
MgO
0 to 3.5
SrO
0 to 3.5
Al
2
O
3
0 to 6.0
B
2
O
3
0 to 2.0
La
2
O
3
0 to 3.0
ZrO
2
0 to 7.5
TiO
2
0 to 7.5
CeO
2
0 to 2.0
SnO
2
0 to 5.0
Tb
4
O
7
0 to 0.5.
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 apatite glass ceramic according to the invention, there are preferred quantity ranges. These can be selected, unless otherwise stated, independently of each other and are as follows:
Component
wt. - %
SiO
2
56.0 to 64.0
Li
2
O
2.0 to 5.0
K
2
O
9.5 to 16.0
ZnO
9.0 to 15.0
CaO
4.0 to 10.0
P
2
O
5
2.0 to 5.0
F
0.5 to 0.9
Na
2
O
0 to 4.0
MgO
0 to 3.0
SrO
0 to 3.0
Al
2
O
3
0 to 5.0
B
2
O
3
0 to 1.8
La
2
O
3
0 to 2.5
ZrO
2
0 to 6.0
TiO
2
0 to 6.0
CeO
2
0 to 1.8
SnO
2
0 to 4.0
Tb
4
O
7
0 to 0.4.
Particularly preferred quantity ranges for the individual components of the apatite glass ceramic according to the invention are as follows and these can be selected independently of each other:
Component
wt. - %
SiO
2
56.0 to 63.0
Li
2
O
2.5 to 5.0
K
2
O
10.0 to 15.0
ZnO
9.0 to 14.0
CaO
4.0 to 9.0
P
2
O
5
2.5 to 5.0
F
0.5 to 0.8
Na
2
O
0 to 3.0
MgO
0 to 2.5
SrO
0 to 2.5
Al
2
O
3
0 to 4.0
B
2
O
3
0 to 1.5
La
2
O
3
0 to 2.0
ZrO
2
0 to 5.0
TiO
2
0 to 5.0
CeO
2
0 to 1.5
SnO
2
0 to 3.0
Tb
4
O
7
0 to 0.3
All the above quantity amounts in wt.-% relate to the glass ceramic.
The glass ceramic according to the invention can furthermore contain e.g. usual color components for matching to the colour of the natural tooth material of a patient.
It was ascertained by scanning electron microscope and x-ray diffraction studies that apatite, such as hydroxy apatite, and/or fluoroapatite, forms the main crystal phase in the glass ceramic. The apatite crystals have grown hexagonally for preference, and in particular in a needle-shaped manner. At their greatest extension, the apatite crystals are preferably than 10 &mgr;m, in particular smaller than 7 &mgr;m and particularly preferably smaller than 5 &mgr;m.
The optical properties of the glass ceramic are controlled by the separated apatite crystals, which are similar in appearance to the carbonate-apatite crystals of natural tooth material. Thus it is possible that a glass ceramic is produced with an appearance which corresponds to that of dentine or enamel of a tooth. Simultaneously, an optical depth effect is achieved in the glass ceramic, such as is not possible with other types of crystals.
Leucite crystals are not radiographically detectable in the glass ceramic according to the invention, but secondary crystal phases such as e.g. sodium-calcium orthophosphate of the NaCaPO
4
type may be present.
A further particular advantage of the glass ceramic according to the invention is that, due to its particular composition, it has not only a high chemical resistance and translucency, but also a p
Höland Wolfram
Rheinberger Volker
Schweiger Marcel
Group Karl
Ivoclar Vivadent AG
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