Alkali silicate glass

Details Alkali silicate glass Alkali silicate glass

2000-06-09

2001-10-23

Koslow, C. Melissa (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S067000, C501S068000, C501S069000, C501S070000, C501S072000, C501S066000, C501S003000, C501S016000, C501S021000, C501S024000, C501S025000, C501S026000, C106S035000, C433S206000, C433S212100, C433S202100, C427S002260, C427S002270, C427S002290

Reexamination Certificate

active

06306784

ABSTRACT:

The invention relates to alkali silicate glass and, in particular, to such a glass which is suitable for adjusting in a desired manner the optical properties and processing properties of coating and veneering material for ceramic dental restorations.
In addition to metallic dental restorations which are veneered with ceramic layers for aesthetic reasons, all-ceramic restorations are increasingly being used in dentistry wherein a ceramic veneering or coating material is applied to a core of ceramic material. Inter alia glass ceramics are suitable for use as both core and coating material.
The optical properties in particular, and the processing properties of glass ceramic coating material are, however, often unsatisfactory. The glass ceramics used exhibit considerable cloudiness due to their high crystal content which is not acceptable, particularly for dental restorations for the incisor region. Moreover, the glass ceramics have a very high expansion coefficient in many cases, for which reason they are unsuitable as a coating material for cores of glass ceramic with a low expansion coefficient, such as lithium disilicate glass ceramic. As a result of the unsatisfactory adjustment of the expansion coefficients, undesired detachment of the coating material may occur.
It is also known that leucite-containing glass ceramics in particular have very high thermal expansion coefficients. These are attributable to the content of leucite crystals which are formed by controlled crystallisation of an appropriate starting glass.
Alkali silicate glasses are known from EP-A-695 726 which are suitable for veneering primarily metallic dental frameworks and contain no B
2
O
3
. During heat treatment at temperatures of 600° C. to 1000° C. and hence under conventional conditions for further dental processing, the glasses, however, form corresponding glass ceramics which, as a result of their crystal content, are very cloudy and are therefore unsuitable for obtaining a high translucence in a glass ceramic coating material. The crystal content, particularly leucite, also leads to undesirably high expansion coefficients and sintering temperatures, so that they are unsatisfactory for veneering ceramic substrates with low expansion coefficients.
The object of the invention is, therefore, to provide a glass which does not crystallise under the conventional conditions of dental processing in the temperature range from 600° C. to 1000° C., has a low thermal expansion coefficient, a low sintering temperature, good chemical stability and high translucence, and consequently may be added in particular to dental glass ceramic coating material in order to improve the properties thereof.
The alkali silicate glass according to the invention is characterised in that it contains the following components:
Component
Wt. %
SiO
2
55.0
to
71.0
Al
2
O
3
5.0
to
16.0
B
2
O
3
0.2
to
10.0
K
2
O
4.5
to
10.0
Na
2
O
3.0
to
14.0
SiO
2
is preferably present in an amount of 55.0 to 65.0 wt. %. The glass according to the invention may additionally contain at least one of the following components:
Component
Wt. %
CaO
0
to
3.0
F
0
to
3.0
P
2
O
5
0
to
0.6
Li
2
O
0
to
4.0
BaO
0
to
5.0
ZnO
0
to
4.0
TiO
2
+ ZrO
2
0.2
to
5.0
CeO
2
0
to
2.0
With the exception of TiO
2
and ZrO
2
, the lower limits for these additional components are usually 0.05 wt. %.
Preferred quantity ranges exist for the individual components of the alkali silicate glass according to the invention. These may be chosen independently of one another and are as follows:
Component
Wt. %
SiO
2
60.0
to
65.0
Al
2
O
3
6.0
to
10.0
B
2
O
3
0.5
to
 8.1
K
2
O
5.5
to
 9.0
Na
2
O
3.5
to
10.0
CaO
0.5
to
 3.0
F
0.2
to
 2.0
Particularly preferred quantity ranges for the individual components of the glass according to the invention are as follows and these may be chosen independently of one another:
Component
Wt. %
SiO
2
61.0
to
64.0
Al
2
O
3
7.0
to
 9.0
B
2
O
3
0.5
to
 4.0
Na
2
O
7.0
to
 9.0
CaO
0.5
to
 1.5
F
1.0
to
 2.0
Li
2
O
0
to
 3.0
BaO
1.5
to
 3.5
ZnO
2.0
to
 3.5
All the above-mentioned quantities in wt. % relate to the glass.
For the production of the glass according to the invention, it is preferable to proceed in such a way that suitable starting materials, such as carbonates, oxides and fluorides, are melted at temperatures from 1350° C. to 1650° C., preferably 1400° C. to 1600° C. over a period of 30 minutes to 4 hours, preferably one hour to 2.5 hours, with the formation of a homogeneous melt. The molten glass is then usually quenched in water i.e. fritted and, after drying, ground to the desired particle size.
It was possible to ascertain by scanning electron microscope analyses that the glass according to the invention is free from crystals. Additionally, it became apparent that the glass also withstands the conditions prevailing during conventional further dental processing by sintering without the formation of crystals which occurs with known glasses. Crystallisation did not occur even during a heat treatment at temperatures of 600° C. to 1000° C. for one minute to 2 hours.
This behaviour is presumably attributable to the special composition of the glass according to the invention.
The glass according to the invention usually has a sintering temperature of 650° C. to 1150° C. Glasses having a sintering temperature of 700° C. to 1050° C. are particularly preferred. Glass which can be sintered at low temperatures of 750° C. to 880° C. and can thus be processed is quite particularly preferred.
A rate of heating of 3 to 100° C./min and preferably 30 to 80° C./min and a holding time at the sintering temperature of 10 seconds to 1 hour and preferably 30 seconds to 5 minutes is usually chosen for carrying out sintering. It is advantageous to carry out sintering under vacuum so that the sintered body has a few pores as possible.
The thermal expansion coefficient of the glass according to the invention is usually 5.5 to 12.5×10
−6
K
−1
, preferably 6.0 to 11.0×10
−6
K
−1
, measured in the temperature interval of 100° C. to 400° C.
The glass according to the invention is used by itself or together with other components preferably as dental material.
To this end it is generally used in the form of a powder with an average particle size of less than 90 &mgr;m. Further suitable components are glass ceramics and other glasses, but also dyes, particularly coloured pigments, oxides of the 3d elements or metal colloids, and fluorescent materials, particularly ytterbium silicate doped with d and f elements.
Dental material which contains at least one apatite glass ceramic as the further component is particularly advantageous.
A preferred apatite glass ceramic is one containing CaO, P
2
O
5
and F in a molar ratio of CaO:P
2
O
5
:F of 1:0.020 to 1.5:0.03 to 4.2 and contains apatite crystals as the main crystal phase. Such apatite glass ceramics are characterised by particularly good chemical stability, which is of great importance especially for use in dental restorations.
Moreover, the use of an apatite glass ceramic which contains at least one of the following components and contains apatite crystals as the main crystal phase is also preferred:
Component
Wt. %
SiO
2
45.0
to
70.0
Al
2
O
3
5.0
to
22.0
P
2
O
5
0.5
to
 6.5
K
2
O
3.0
to
 8.5
Na
2
O
4.0
to
13.0
CaO
1.5
to
11.0
F
0.1
to
 2.5
In particular preference, this apatite glass ceramic additionally contains at least one of the following components:
Component
Wt. %
B
2
O
3
0 to 8.0
La
2
O
3
0 to 5.0
Li
2
O
0 to 5.0
BaO
0 to 5.0
MgO
0 to 5.0
ZnO
0 to 5.0
SrO
0 to 7.0
TiO
2
0 to 4.0
ZrO
2
0 to 4.0
CeO
2
0 to 3.0
The above amounts given in wt. % relate to the apatite glass ceramic.
The apatite glass ceramics described above are produced by melting a starting glass composed of suitable starting materials, such as oxides, carbonates and fluorides, at temperatures of 1200° C. to 1650° C., pouring this into water and subjecting the glass granules formed, optionally after further comminution, to a heat treatment at temperatures

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