Note: Descriptions are shown in the official language in which they were submitted.
CA 02239861 1998-06-08
Alkali silicate ~lass
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 B2O3. During heat treatment at temperatures of 600~C
to lOOO~C and hence under conventional conditions for further
CA 02239861 1998-06-08
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
5 expansion coefficients and sintering temperatures, so that they are
unsatisfactory for veneering ceramic substrates with low expansion
coefficients.
The glass described herein does not crystallise under the conventional
10 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 contains the following
components:
Component Wt.%
SiO2 55.0 to 71.0
Al2O2 5.0 to 16.0
B2O3 0.2 to 10.0
K2O 4.5 to 10.0
Na2O 3.0 to 14.0
SiO2 is preferably present in an amount of 55.0 to 65.0 wt.%.
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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
P2O5 0 to 0.6
Li2O 0 to 4.0
BaO 0 to 5.0
ZnO 0 to 4.0
TiO2 + ZrO2 0.2 to 5.0 -
CeO2 0 to 2.0
With the exception of TiO2 and ZrO2, 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. %
SiO2 60.0 to 65.0
Al2O3 6.0 to 10.0
Bz03 0.5 to 8.1
K2O 5.5 to 9.0
NazO 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 61.0 to 64.0
Al2O3 7.0 to 9.0
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s2O30.5 to 4.0
Na2G7.0 to 9.0
CaO 0.5 to 1.5
F 1.0 to 2.0
Li2O 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 att.ibutable 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.
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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 as few pores
as possible.
The thermal expansion coefficient of the glass according to the
invention is usually 5.5 to 12.5 x 10 K , preferably 6.0 to 11.0
x 10-6K-l, 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 ~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 ~ 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, P2O5 and
F in a molar ratio of CaO : P2O5 : 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:
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Component Wt. %
SiO2 45.0 to 70.0
Al2O3 5.0 to 22.0
P2O5 0.5 to 6.5
R2O 3.0 to 8.5
Na2O 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.%
B2O3 0 to 8.0
La2O3 ~ to 5.0
Li2O 0 to 5.0
BaO 0 to 5.0
MgO 0 to 5.0
ZnO 0 to 5.0
SrO 0 to 7.0
TiO2 0 to 4.0
ZrO2 0 to 4.0
CeO2 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 of more than 900~C and up to
1200~C for a period of 30 minutes to 6 hours.
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The apatite glass ceramics obtained are characterised by high
translucence, good chemical stability and a low expansion
coefficient. These properties are presumably attributabie to
their special composition and to the apatite crystals produced
during their manufacture, which crystals have in particular a
needle-shaped morphology and hence resemble the apatite crystals
of natural tooth material.
The dental material according to the invention normally has a
thermal expansion coefficient of 5.5 to 12.5 x 106Kl, measured
in the temperature range of from 100 to 400~C. The coefficient
required in each case can be adjusted by a suitable choice of the
type of alkali silicate glass and any other components and the
quantities thereof. Favourable dental materials contain 10 to 90
wt.% of alkali silicate glass and 90 to 10 wt.~ of other
components, based on the dental material.
The dental material is suitable for coating substrates and in
particular for coating or veneering dental restorations. Coating
is effected in particular by applying the dental material to the
chosen substrate and then sintering it at temperatures of ~50 to
1150~C.
In preference, a powder of the glass according to the invention
is mixed with a powder of the other components optionally present
and processed to a paste by adding aqueous mixing solutions. This
paste is then applied to a substrate and, after the desired
shaping, sintering takes place to obtain a firmly adhering
coating or veneer.
The dental material according to the invention may be used as a
coating or veneering material for substrates such as dental
framewor~s, based on ceramic or glass ceramic materials. In view
of its low expansion coefficient, it is used preferably with
substrate materials with a thermal expansion coefficient of 7.0
to 12.0, particularly 8.0 to 11.0 x 10-6K-l. It is used preferably
CA 02239861 1998-06-08
for coating or veneering ZrO2 ceramics, Al2O3 ceramics, ZrO2/Al2O3
ceramics, ceramic or glass ceramic composite mate~ials and
titanium.
It is used particularly advantageously, however, for veneering
substrates based on lithium disilicate glass ceramic in order to
produce in this way aesthetically very attractive fully ceramic
dental products which have very high strength and excellent
chemical stability.
, ,
Lithium disilicate glass ceramics having the following
composition which may be obtained e.g. by melting appropriate
starting glasses, fritting and heat treatment at 400~C to 1100~C
have proved to be particularly suitable:
ComPonent Wt.%
SiOz57.0 to 80.0
Al2O3 0 to 5.0
La2O30.1 to 6.0
MgO 0 to 5.0
ZnO 0 to 8.0
K2O 0 to 13.5
Li2O11.0 to 19.0
P2O5 0 to 11.0
with the proviso that
(a) Al2O3 + La2O3is 0.1 to 7.0 wt.% and
(b) MgO + ZnO is 0.1 to 9.0 wt.%.
The amounts given in wt.% are based on the lithium disilicate
glass ceramic.
For the production of coatings, dental material according to the
invention that has a thermal expansion coefficient that is
smaller than that of the substrate to be coated is advantageous.
CA 02239861 1998-06-08
Dental material whose expansion coefficient is not more than 3.0
x 10-6K-l smaller than t~lat of the substrate is particularly
advantageous.
The alkali silicate glass according to the invention and the
dental material according to the invention may be processed in
the usual way together with the additives optionally present to
obtain shaped dental products. Suitable shaped dental products
according to the invention cont~i n ing the alkali silicate glass
or the dental material are, in particular, dental restorations
such as an inlay, an onlay, a bridge, an abutment, a jacket, a
veneer, a facet, a filling, or a connector. Particularly
preferred dental restorations are bridges, crowns and partial
crowns.
The dental products preferably have a core based on ceramic or
glass ceramic material, particularly lithium disilicate glass
ceramic, onto which the glass according to the in~ention or the
dental material according to the invention is applied.
Preferred lithium disilicate glass ceramics have already been
described above.
In contrast to conventional glass, crystallisation which would
undesirably lower its translucence does not occur with the glass
according to the invention under the conditions prevailing during
the sintering thereof. It therefore reproduces essentially the
colour of the coated substrate which is very desirable,
particularly during the production of all-ceramic dental
restorations.
The lack of crystal formation and in particular the lack of
formation of leucite crystals ascertained in the case of known
glasses is a particular advantage since the high expansion
coefficient of leucite would confer a high thermal expansion
coefficient on the glass. The glass would therefore be unsuitable
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for coating substrates with low expansion coefficients, such as
ZrO~ or lithium disilicate glass ceramic. The lack of adjustment
of the expansion coefficients would lead to high stresses which
regularly manifest themselves in cracks and chippings. These
disadvantages are not exhibited by the glass according to the
invention due to its low expansion coefficient, so it is very
suitable for coating substrates with low expansion coefficients.
- Moreover, despite its B2O3 content, the glass exhibits excellent chemical stability which is vital for its use as a dental
~ - . .
material, which is permanently flushed by acid fluids in ~he oral
cavity.
Finally, the glass may be sintered onto a substrate within a
short sintering time even at low temperatures in order to produce
a firmly adhering coating or veneer in this way.
A~mi x; ng the glass with apatite glass ceramics in particular
leads to dental materials which have increased translucence, a
shorter sintering time and lower sintering temperature and a
lower thermal expansion coefficient compared with the pure
apatite glass ceramic.
The invention will be explained in more detail below on the basis
of examples.
Examples
Examples 1 to 8
A total of 8 different glasses according to the invention with
the chemical compositions given in Table I were produced.
Table 1: Compositions of glasses according to the invention (quantitiès in wt.%)
Ex. SjO2 Al2O3 P205 CaO F K:2O Na20 Li20 B203 TiO2 ZrO2 CeO2 BaO ZnO
No.
S-).S 6.7 0.3 3.0 0.9 8.6 6.6 1.4 4.() .. 2.5 1.0 4.7 3.8 - a'
2 61.5 8.7 .. 1.0 1.7 7.0 8.8 .. 2.4 1.5 1.0 0.5 2.9 3.0 1 1-
3 60.4 11.9 .. .. 0.3 6.4 7.0 1.8 0.3 1.5 3.5 .. 3.2 3.7
4 61.4 8.5 .. 1.1 1.7 7.8 8.7 0.6 1.9 1.5 1.0 0.5 2.1 3.2 O62.3 R.7 .. 1.3 1.6 7 0 7.0 2.0 1.1 1.4 1.0 0.6 3.0 3.0
6 70.R 8.6 .. 2.1 ().9 6.9 8.3 1.5 0.2 0.7 .. ~ ~- -
7 63.4 6.2 0.4 1.7 ~- 6.4 9.6 .. 3.7 1.7 1.1 0.5 2.3 3.0
8 61.9 9.9 .. 1.1 1.5 5.8 3.7 0.2 8.0 1.4 1.1 0.5 2.8 2.1
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For the production of said glasses, an appropriate batch of
suitable oxides, carbonates and fluorides in each case was melted
in a platinum/rhodium crucible at a temperature of 1550~C to
1600~C for a homogenisation period of 1 to 1.5 hours. The glass
melt was quenched in water, and the granules of the glass formed
were dried and ground to an average particle size of less than
90 ~m.
Selected properties that were determined on specimens composed
of the respective glass are given in Table II. The examples
illustrate how glasses with different properties may be obtained
by altering the chemical composition.
Table II
LS
Ex. Firing Tg [ C] a-value Optical Acid
tempe- x 10oK appearance resist2ance
rature '100 C- [~g/cm ]
[ C]* ~0~ C)
1 760 500 c.~ translucent 26
2 810 522 9._ very 17.2
translucent
3 880 528 9.5 translucent 17
4 770 494 9.4 very 26.3
translucent
750 468 9.4 very 17.9
translucent
7 840 565 8.9 very 30
translucent
8 880 543 6.6 very <100
translucent
* Firing temperature = temperature which was used for
production of the specimens by sintering onto quartz
(vacuum, 1 minute holding time)
Determination of the expansion coefficient a
In order to measure the thermal expansion coefficient a, a rod-
shaped green compact was prepared from powder of the glass in
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question, and said compact was sintered in a vacuum furnace at
a rate of heating of 60~C/min and with a holding time of 1 minute
at the respective firing temperature. A glaze bake was then
carried out without vacuum at a 20~C higher final temperature and
with a holding time of 1 minute. The thermal expansion
coefficient was determined on the specimen obtained.
Determination of acid resistance
The acid resistance is a measure of the chemical stability of
glasses and glass ceramics used in dentistry in particular, since
these are permanently exposed to the action of acid substances
in the oral cavity.
The acid resistance was determined according to the ISO
specification 6872:1995. To this end, small sample plates 12 mm
in diameter and 1 mm thick were prepared initially by sintering
together glass granules with an average particle size of 90 ~m.
The granules were kept at the sintering temperature for 1 minute.
The sample plates were then treated for 16 hours in a Soxhlet
apparatus with 4 vol.% of aqueous acetic acid and finally the
loss of mass occurring was determined as a measure of the acid
resistance.
Example 9
This Example describes the use of glasses according to the
in~ention according to Example 2 and 4 together with an apatite
glass ceramic (A) as a coating material for ceramic frameworks
and thus for the production of fully ceramic dental products.
The apatite glass ceramic (A) had the composition SiO2 55.5 wt.%,
Al2O. 19.2 wt.%, P2O5 1.2 wt.%, CaO 2.7 wt.%, F 0.6 wt.%, K2O 6.7
wt.%, Na2O 9.7 wt.%, B2O3 0.3 wt.%, TiO2 1.4 wt.%, ZrO2 2.2 wt.%
and CeO~ 0.5 wt.%. For the preparation thereof, a starting glass
of the appropriate composition was melted, fritted and ground to
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a powder. This powder was then heat treated for one hour at
1020~C. The crystals present in the glass ceramic formed could
be identified as needle-shaped apatite crystals by X-ray
diffractometry.
S
In order to obtain a suitable expansion coefficient and sintering
temperature, this apatite glass ceramic (A) was mixed with the
alkali silicate glasses 2 and 4 according to the invention in the
form of powders with an average particle size of less than 90 ~m
and in a weight ratio of 30% apatite glass ceramic (A), 35%
alkali silicate glass according to Example 2 and 35~ alkali
silicate glass according to Example 4.
This mixture was sintered at 880~C to a rod-shaped green compact
in a vacuum furnace at a rate of heating of 60~C/min and with a
holding time of 1 min. A thermal expansion coefficient of 9.5 x
10-6K-l, measured in the temperature range of from lO0 to 400~C,
was determined for the sample obtained.
This mixture could thus be used for sintering onto a substrate
with a thermal expansion coefficient of 10.6 x 106Kl, such as
lithium disilicate glass ceramic, at an advantageous processing
temperature of 830~C.
Processing on a tooth substrate can usually take place at
temperatures that are 50 to 100~C lower than the sintering
temperature on quartz.
E~ample lO
In the same way as Example 9, different glasses according to the
invention may be mixed together or with other glass ceramics to
obtain desired expansion coefficients and sintering temperatures.
A powder mixture of 25 wt.% of alkali silicate glass according
to Example 4 with 50 wt.% of apatite glass ceramic (B) (heat
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treatment at 1100~C), and 25 wt.% of apatite glass ceramic (A)
according to Example 9 (heat treatment 1020~C) was prepared in
order to obtain a dental material according to the invention with
a low sintering temperature of 830~C and an expansion coefficient
of 9.5 x 10-6R-l. Such a material had outstanding optical
properties and was highly suitable as a sintering ceramic for an
all-ceramic framework structure with a low thermal expansion
coefficient.
The apatite glass ceramic (B) used in this case had the
composition SiO2 59.2 wt.%, Al2O3 7.9 wt.%, P2O5 3.0 wt.%,,CaO 5.1
wt.%, F 0.6 wt.%, KzO 6.8 wt.%, Na2O 9.6 wt.%, Li2O 0.3 wt.%,
B2O3 1.0 wt.%, TiO2 1.5 wt.%, ZrO2 2.5 wt.%, CeO2 0.5 wt.% and
ZnO2 2.0 wt.%. For the preparation thereof, a starting glass of
the appropriate composition was melted, fritted and ground to a
powder. This powder was then heat treated at 1100~C in order to
form the glass ceramic.
E~amples 11 to 14
In these Examples, other mixtures of alkali silicate glasses
according to the invention with apatite glass ceramics were
examined, which are highly suitable as coating or veneering
materials that can be sintered onto substrates with low thermal
expansion coefficients.
The following apatite glass ceramics were used:
1. Apatite glass ceramic (B) according to Example 10
2. Apatite glass ceramic (C) having the composition:
SiOz 62.8 wt.~, Al2O3 13.1 wt.%, P2O5 1.2 wt.%, CaO 2.7 wt.%,
F 0.6 wt.%, K2O 6.3 wt.%, Na2O 5.9 wt.%, ZrO2 1.7 wt.% ,
CeO2 0.5 wt.%, BaO 1.8 wt.% and ZnO 3.4 wt.%.
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3. Apatite glass ceramic (D) having the composition:
SiO2 64.5 wt.%, Al203 8.4 wt.%, P205 1.1 wt.%, CaO 2.8 wt.%,
F 0.7 wt.%, K20 6.6 wt.%, Na20 9.6 wt.%, Bz03 2.2 wt.%,
TiO2 1.2 wt.%, ZrO2 0.4 wt.%, and ZnO 2.5 wt.%.
The compositions of the individual mixtures and the heat
treatment carried out for the production of the apatite glass
ceramic used in each case are given in Table III.
The properties determined for these mixtures are also stated in
Table III and they show that, by means of a suitable choice of
components, it is possible to obtain dental materials with
properties adjusted to the application in question.
LS
~a~le III: Properties of mixtures of glasses according to the invention and
apatite glass ceramics
Ex. Composition llcal Mixing ratio Sintering Tg a~-value Optical Acid _
treatmenl [in wt.~] temp. [~Cl x 10-6Kl appedlance rÇsic~nre
[~C/hl [~Cl ( 1 0 0 ~ C - [,ug/cm2l 1 a~
400~C) ,_
11 Apatite glass ceramic 1050/1 50 850 530 9.3 milky, cloudy, <100
(B) ~- 50 tr:-nclllcen~
Alkali silicate glass 2 ~
12 Apalitc glass ceramic 1020/1 50 870 542 8.0 milky, < 100 ~
(13) .. 50 translucent
Alkali silicate glass 8
3 Apalite glass ceramic Illû()/1 40 910 552 8.8 very < 100
(C) .. 60 translucent
Alkali silicate glass S
14 Apalite glass ceramic 1050/1 70 850 539 8.7 slightly milky, < 100
(D) ~ 30 slightly opal,
Alkali silicate glass 6 Ir,~ r"~
