CA 02351154 2001-06-21
Low-temperature-sintering potassium-zinc-silicate glass
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
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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 mos~~~, 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 Zn0 at most and are characterized inter alia by a Kz0
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.
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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-walled veneers
or thin-walled crowns with a glass ceramic core is not possible
wi th- 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
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restorations in a wide temperature range.
This object is achieved by means of the potassium-zinc-silicate
glass according to claims 1 to 7.
The subject-matter of the present invention ~is also the dental
material according to claims 8 to 11, the use according to claims
12 to 16 as well as the shaped dental product according to claims
17 to 20.
The -potassium-zinc-silicate glass according to the invention
comprises the following components:
Component wt . - %
SiOz 60.0 to 72.0
LizO 1.0 to 5.0
Kz~ 10.0 to 23.0
Zn0 _ ~ ~ 8 . 5 to 20 . 0
The glass according to the invention can additionally comprise at
least one of the following components:
Component wt.-%
NazO 0 to 4.0
Mg0 0 to 4.0
Ca0 0 to 3.6
Sr0 0 to 3.0
A1z03 0 to 8.0
Bz~3 0 to 3.3
3 0 Laz03 0 to 3 . 0
ZrOz 0 to 6.0
TiOz 0 to 2.5
CeOz 0 to 2.0
SnOz 0 to 5.0
P20; 0. to 1.0
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Tb40, 0 to 1.8
F 0 to l.l.
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 . - %
_ Si02 62 . 0 to 70 . 0
LizO 2.0 to 5.0
Kz~ 10.0 to 20.0
Zn0 10.0 to 19.0
Na20 0 to 3.0
Mg0 0 to 3.0
Ca0 0 to 3.0
Sr0 -~ 0 to 3.0
A1z03 0 to 6.0
B203 0 to 3.0
La203 0 to 2.0
ZrOz 0 to 5.0
TiOz 0 to 2.0
Ce02 0 to 1.5
SnOz 0 to 4.0
Pads 0 to 0.8
Tb40, 0 to 1.0
F 0 to 1Ø
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:
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Component wt.-%
SiOz 63.0 to 69.0
LizO 3.0 to 5.0
Kz~ 11.0 to 19.0
Zn0 10.0 to 17.0
NazO 0 to 2.5
Mg0 0 to 2.5
Ca0 0 to 2.5
Sr0 0 to 2.5
A1z03 0 to 4.0
823 0 to 2 . 0
Laz03 0 to 1.8
ZrOz 0 to 4.0
TiOz 0 to 1.8
CeOz 0.1 to 1.5
Sn.Oz 0 to 3.5
pzOs 0 to 0.5
Tb40, _ - ~ 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
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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 disilicate glass ceramic. Glasses are particularly
preferred which have a sintering temperature of 760°C and below and
thus_ can be processed at this temperature. These low sintering
temperatures are presumably attributable to the special composition
of the glass according to the invention.
It is of quite particular advantage that the glass according to the
invention can also be processed by sintering even where there are
large deviations from the actual sintering temperature, i.e. the
temperature at which the dimensional stability as well as the
porosity of the glass are particularly satisfactory. Thus the glass
can even be processed in a sintering temperature range of ~ 20°C,
or more, such as e.g. ~ 40°C, above or below the actual sintering
temperature without cracks or faults occurring in the dental
restoration. When working in this temperature range, the sintered
glass has a very low porosity and a very good dimensional
stability. An indication of the excellent dimensional stability is
that even the very thin-walled incisor edge, which has been formed
by applying a mixture of glass powder and admixing liquid to a
framework as well as its shaping, retains its form after the
sintering process and thus lasts. Thus, the glass according to the
invention can also be sintered in furnaces which do not permit a
precise control of the firing temperature, which is particularly
advantageous. In contrast to this, conventional glasses permit only
deviations of ~ 10°C from the sintering temperature. With larger
deviations, satisfactory restorations cannot be prepared with them.
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In order to carry out the sintering of the glass according to the
invention, a heating-up rate of 3°C to 100°C/min and preferably
of
30°C to 80°C/min as well as a holding time at the sintering
temperature of 10 seconds to 1 hour and preferably 30 seconds to 5
minutes is selected as a rule. It is advantageous to carry out the
sintering in a vacuum so that the sintered body has as few a pores
as possible.
The linear thermal coefficient of expansion of the glass according
to the invention is normally less than 12.3 x 10-6K-1,- preferably 7.7
to -1-0.9 x 10-6K-1, measured in the temperature range from 100°C to
400°C.
The glass according to the invention is preferably used as dental
material either on its own or together with further components. To
this end, it is usually used in the form of a powder with an
average particle size of less than 90 ~Cm. Glass ceramics and other
glasses, but also dyestuffs, in .particular color pigments, oxides
of the 3d elements or metal colloids, as well as fluorescence
materials, in particular ytterbium silicate doped with d- and f-
elements, can also be considered as further components.
Dental material which contains at least one glass ceramic and
preferably an apatite glass ceramic as a further component is
particularly advantageous.
An apatite glass ceramic is preferred which comprises the following
components and in which the main crystal phase is formed by apatite
crystals:
component wt.-s
SiOz 56.0 to 65.0
Li20 1.8 to 5.3
Kz~ 9.0 to 17.5
ZnO 9.0 to 16.0
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Ca0 3.5 to 10.5
Pz~s 2.0 to 6.0
0.5 to 1.0
This apatite glass ceramic particularly preferably comprises in
addition at least one of the following components:
Component . wt.-%
NazO 0 to 5.0
-Mg0 0 to 3.5
Sr0 0 to 3.5
A1z03 0 to 6.0
$z~3 0 to 2.0
Laz03 0 to 3.0
ZrOz 0 to 7.5
TiOz 0 to 7.5
CeOz - ,~ 0 to 2.0
SnOz 0 to 5.0
Tb40., 0 to 0.5.
The above amounts in wt.-% relate to the apatite glass ceramic. If
these additional components are present, they are used in
particular in amounts of at least 0.1 wt.-%.
The apatite glass ceramics are prepared by melting a starting glass
from suitable starting materials, such as oxides, carbonates and
f luorides , at temperatures f rom 12 0 0 ° C to 165 0 ° C,
pouring this into
water and subjecting the formed glass granulate, optionally after
further reduction, to a thermal treatment at more than 500°C and up
to 900°C for a period of 30 minutes to 6 hours.
The obtained apatite glass ceramics are characterized by a high
translucence, high chemical resistance as well as a low coefficient
of expansion. They are moreover excellently matched in their
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chemical composition to the glasses according to the invention, so
that disadvantageous material transport reactions between both
materials and thus ensuing build-up of stress are avoided in
particular in thin layered composites.
The dental material according to the invention normally has a
linear thermal coefficient of expansion of 9.0 to 10.9 x 10-6K-1,
measured in the range of 100°C to 400°C. The respectively
desired
coefficient can be set by suitable choice of the type of potassium-
zinc-silicate glass and any further components, as well as their
amounts. Favourable dental materials contain 10 to 90 wt.-%
potassium-zinc-silicate glass and 90 to 10 wt.-~ further
components, relative to the dental material.
The dental material according to the invention is suitable for
coating substrates and in particular for coating or veneering
dental restorations. The coating takes place in particular by
applying the dental material -to~ the selected substrate and
subsequent sintering at less than 800°C and in particular 760°C
or
less.
Preferably a powder of the glass according to the invention is
firstly mixed with a powder of the optionally present further
components and processed to a paste by adding aqueous admixing
solutions. This paste is then applied to the substrate and after
desired shaping sintering takes place in order to obtain a firmly
adhering coating or veneer.
The dental material according to the invention can be used as
coating or veneering material for substrates such as dental
suprastructures e.g. based on ceramic or glass ceramic materials.
Due to its low coefficient of expansion, it is preferably used for
substrate materials with a thermal coefficient of expansion of 7.0
to 12.0, in particular 8.0 to 11.0 x 10-6K-1. It is preferably used
for coating or veneering Zr02 ceramics, A1203 ceramics, ZrOz/A1203
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ceramics, ceramic or glass ceramic composite materials and
titanium.
It is particularly advantageously used however to veneer substrates
based on lithium disilicate glass ceramic in order to in this way
prepare aesthetically very attractive all-ceramic dental products
which have a very high strength as well as an excellent chemical
resistance.
Lithium disilicate glass ceramics which contain ,the components
listed below and which can be obtained e.g. by melting of suitable
starting glasses, fritting and thermal treatment at 400°C to
1100°C, have proved particularly suitable:
Component wt,_%
SiOz 57.0 to 80.0
A1z03 0 to 5.0
Laz03 - ~~~ 0 . 1 to 6 . 0
Mg0 0 to 5.0
Zn0 0 to 8.0
LizO 11.0 to 19.0
Pz~s 0 to 11.0
where
(a) A1z03 + Laz03 account for 0. 1 to 7.0 wt. -
and
(b) Mg0 + Zn0 account for 0.1 to 9.0 wt.-%.
The amounts in wt.-% relate to the lithium disilicate glass
ceramic.
The potassium-zinc-silicate glass according to the invention and
the dental material according to the invention can be processed
into shaped dental products in the usual way together with the
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optionally present additives. Dental restorations such as e.g. an
inlay, an onlay, a bridge, a stump reconstruction, a veneer, also
referred to as ligament, a facette, a filling or a connector can be
considered in particular as shaped dental products according to the
invention which contain potassium-zinc-silicate glass or the dental
material. Veneers, bridges, crowns and part-crowns are particularly
preferred dental restorations.
The dental products preferably have a core based on ceramic or
glass ceramic material, in particular lithium disilicate glass
ceramic, to which the glass according to the invention 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, the glass according to the
invention is even better suited in its chemical composition to
apatite glass ceramics and lithium-t~isilicate glass ceramics which
are preferably used as further components of a coating material and
as a substrate, respectively. The consequence of this is that
precisely with thin layered composites, such as e.g. thin-walled
veneers, with lithium disilicate glass ceramic as substrate to
which a mixture of glass according to the invention and apatite
glass ceramic has been applied, there are no signs of separation of
the coating or a fracture of the finished product. The low
sintering temperature of the glass according to the invention is
also responsible for this advantageous behaviour.
Furthermore, the conditions prevailing during the sintering of the
glass do not lead to a crystallization which would reduce its
translucence in an undesired manner. Thus it essentially reproduces
the colouring of the coated substrate which is advantageous in
particular in case of the preparation of all-ceramic dental
restorations.
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In addition, the glass according to the invention shows an
excellent chemical resistance which is imperative for its use as
dental material around which acid liquids wash permanently in the
oral cavity. It is surprising that the glass has both a good
chemical resistance and a low sintering temperature. This
favourable combination of properties is possibly attributable to
the fact that the glass simultaneously contains several types of
alkali metal ions.
The invention is explained in more detail below using examples.
Examples
Examples 1 to 34
In total, 34 different glasses _acCOrding to the invention were
prepared with the chemical compositions listed in Table I.
CA 02351154 2001-06-21
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o\o
3
O
00 b
0
N
0
~
N
.1"I 'V ~I
~N
G,' M O
O V 'r N
ON
U V'O
N V1
N
O O~ op
N N ; n-;
~
t
pN
N
r~
N
a
0
ni
U
U
O
...N N N O
M ~''i op
N
N
a7 O
~
1~
U
O
U
U
~ ~
-r ~OO o0
-i
cV~ C
O
-ri cs O t
z ~ a
O n Oh O M N h hN O h O OWE O O b OerO M h h O
~ ~ ~
N MV V M '1~ OM 'r1O O N ~1NN O M M hN M N N N M
N r ct w ~ ~ ~ op o ~
~ w o ~
r ~ ~ , w~ w ~ ~ ww N ~ w ww w ~ ~ w w
O
O O o ~h ~ h OvN N1 nt w w p hn O O M OO N O O O O
o < e t o ~
0 0 hh h M ~ N hM hh h h r ~,r h N v ON M h M M N
~ ~~ < ~ ~ t
J-J C r rW r W tee~ w1 .,W . r W W~ W ~ ~ ~r W ~ N N W
' '~ ' ' ' '. ~ ' ' ~ ~ ~ ' '
'
~ OO ~ M 0 0 0M NO 0 h h ~h O 0 O MO N , ~ ~ 0
~ ~ a a 0 o t o ~ ~ 0
J M hh 1 t M t 1h Mh f ~ i i~ v M M M~ h M M M ri
r ~~ e r r ~ r n n ~ ~'
QO O v ~ h w ~O . p N ~ O O h O r O 0 ! f
O h ~ o l M ~ O ~ ~ ~ O
b ~ ~ ~ ~ ~ ~ ~ ~
O ~O ~ O O CC ~O O b ~ Ob ~ O ~ O O O O
~ ~ ~ ~ ~ ' ~ ~
ri C ~. ~7' T 'a \ p v ~, M ~ t ' O
~ c 7' T ' O ~ Cv c M h l G O C N h
M h l c O.
I ~ ,, w.. ~ ~ r ... Nt~~ N N c V
(~ ~ w ....N N
H
<IMG>
CA 02351154 2001-06-21
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For their preparation, a corresponding amount of suitable oxides,
carbonates and fluorides was melted each time in a
platinum/rhodium crucible at a temperature of 1550°C to 1600°C
for a homogenization time of 1 to 1.5 hours. The glass melt was
quenched in water, and the granulate formed from the glass was
dried and ground to an average particle size of less than 90 Vim,
relative to the number of particles.
For some of the prepared glasses, selected properties are listed
in Table II which have been measured in test pieces ,made from the
respective glass. The examples illustrate how glasses with
different properties can be obtained by changing the chemical
composition.
CA 02351154 2001-06-21
_ 17
O
a
O '
U
.rl N N ri
~.1 0
a
G: ~ l~ Id O D O OO O O O
O
U ~1 1.1 C~001O ~O N 0001
5 GO I
~ S.i td ~ ~ o mm coc~~
N
W ~'~
W N O N
ar G I
1J
O
bi 'd Id
r1 ~ ~ Lll t~'1 ('~l0t~
W ~~
U 00 ~ In -1 rlcY1d'
O
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GU
u1 b1 O o
0 0 0 00 0 0 0
O N N l0N dlO rl
W
O 1~ H
U
U
J..1JJJ..1.4.~1~.J..~1J
~ N ~ N
ri N Al'U ~ N
rdrartS~~ rtiy d
vd
~
O (drtfc~(d~ aSfdrti
.1.~1J1~~..1111~J..1.7..1
r~
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0000O 00L~cr dl
l~00O i-IQ1O 00
O
~O _
U
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O ~ ao0 d~01crD d1h
l l
1 1I~ 01~l0fll0
L L l
01O O ~0041C31
C O l
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1
a
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Ql ri
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(
'~ NN ~7~
' "'~, t
N
W
CA 02351154 2001-06-21
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Measurement of the coefficient of expansion a
To measure the linear thermal coefficient of expansion a, a rod-
shaped green body was prepared from the powder of the respective
glass, and was sintered in a vacuum firing furnace at a heating-
up rate of 60°C/min and with a holding time of 1 minute at the
respective firing temperature for the preparation of the test
pieces. Subsequently a glaze firing was carried out without
vacuum at a final temperature which was 20°C higher and with a
holding time of 1 minute. The linear thermal coefficient of
expansion was measured with the obtained test piece in the
temperature range of 100 to 400°C.
Measurement of the acid resistance
The acid resistance is a measure of the chemical resistance
especially of glasses and glass ceramics used in the dental
field, as these are permanently e5cposed to the action of acid
substances in the oral cavity.
The acid resistance was measured according to ISO-specification
6872:1995. To this end, small test plates with a diameter of 12
mm and a thickness of 1 mm were firstly prepared by sintering
together glass powder with an average particle size of less than
90 ~,m. The powder was maintained for 1 minute at the relevant
firing temperature for the preparation of the test pieces. Then
the small test plates were treated for 16 hours with 4 vol.-
aqueous acetic acid at 80°C, and finally the loss of weight which
had occurred, relative to the surface of the small plates, was
determined as a measure of the acid resistance.
Example 35
This example describes the preparation of a glass according to
the invention which can be used as a low-temperature-melting
glazing or correcting material.
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The application of a glaze layer containing glass according to
the invention to a translucent lithium disilicate basic framework
is particularly advantageous, as aesthetically pleasing dental
restorations, e.g. in the form of inlays, onlays, part-crowns,
veneers, crowns or bridges can thus be prepared. The application
of a thick, multi-layered glass ceramic layer is not necessary
as a result of the use of a glaze layer.
Firstly, glass powder with the composition given in Table I for
example 34 was prepared analogously to the method given above for
examples 1 to 34. This powder was sintered to produce a rod-
shaped green body in a vacuum furnace at a heating-up rate of
60°C/minute and with a holding time of 1 minute at 780°C.
Subsequently a glaze firing was carried out without a vacuum at
760°C and with a holding time of 1 minute.
For the specimen obtained in this way, a thermal coefficient of
expansion of 9.69 x 106K1 wasdetermined, measured in the
temperature range of 100 to 400°C.
This glass was therefore able to be used for sintering onto a
substrate with a low coefficient of expansion of 10.6 x 10-6K-1,
such as a crown or bridge framework based on lithium disilicate
glass ceramic. It is shown that the sintering of the glass onto
the framework was already possible at a temperature of only
700°C.
Because the coefficient of expansion is matched to lithium
disilicate glass ceramics, the very good chemical resistance and
the low processing temperature, this glass according to the
invention is particularly suitable for glazing very translucent
frameworks based on lithium disilicate glass ceramic and also as
correction material for sintering materials coated onto such
frameworks.
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Example 36
This example describes the use of a mixture of the glass
according to the invention according to example 30 together with
an apatite glass ceramic as a coating material for ceramic
suprastructures and thus its usability for the preparation of
all-ceramic dental products.
The apatite glass ceramic used had the-composition (in wt.-%):
S i.02 5 9 . 6 ; Li20 4 . 2 ; K20 13 . 4 ; Zn0 10 . 4 ; P205 3 . 5 ; Ca0 6 . 0
; F 0 . 5 ;
Zr02 1. 9 ; Ce02 0 . 5 .
For the preparation of this apatite glass ceramic, a starting
glass of a corresponding composition was melted, fritted and
ground into a powder. This powder was then thermally-treated for
4 hours at 520°C and.subsequently for 1 hour at 800°C.
To obtain a coating material in which sintering temperature and
coefficients of expansion are suitably set, 50 wt.-% of the
apatite glass ceramic was mixed with 50 wt.-% of the glass
according to the invention in the form of powders with an average
particle size of less than 90 ~,m.
This mixture was sintered to produce a rod-shaped green body in
a vacuum furnace at a heating-up rate of 60°C/min and with a
holding time of 1 minute at 840°C. Subsequently, a glaze firing
was carried out without vacuum at 820°C and with a holding time
of 1 minute. For the test piece thus obtained, a thermal
coefficient of expansion of 9.96 x 106K1 was determined,
measured in the temperature range of 100°C to 400°C.
Thus this mixture was able to be used for sintering onto a very
translucent lithium disilicate glass ceramic with a thermal
coefficient of expansion of 10.6 x 106K1. It was shown that the
sintering-on of the mixture was already possible at a temperature
of only 730°C. Consequently, all-ceramic dental products such as
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crowns or bridges, were thus able to be prepared which are
characterized by an excellent bonding of the individual layers,
an aesthetically pleasing appearance and good chemical
resistance.
ExamEle 37
Preparation of a thin-walled veneer.
A thin-walled veneer for a middle upper incisor with a layer
thickness of max. 0.5 mm was prepared from a lithium disilicate
glass ceramic by compression in the viscous state. After the hot
pressing, the layer thickness was reduced to max 0.25 mm by
mechanical reworking with a diamond tool. The surface of the
veneer was then cleaned in an aqueous solution of 0.5 vol.-% HF
and 3 vol.-% HZS04 for 10 minutes in an ultrasound bath and then
sand-blasted with A1203 at a jet pressure of 1.5 bar. A dental
material was then sintered on, this being a mixture of the glass
21 according to the invention and an apatite glass ceramic. The
apatite glass ceramic used had the composition (in wt.-%):
S i0z : 61. 4 ; Li20 : 4 . 3 ; Kz0 : 13 . 6 ; Zn0 : 10 . 6 ; Pz05 : 3 . 5 ;
Ca0 : 6 . 1;
F: 0.5.
To prepare this glass ceramic, a starting glass of suitable
composition was melted, fritted and ground to a powder. This
powder was then thermally-treated for 1 hour at 800°C. To obtain
a ,coating material in which sintering temperature and coefficient
of expansion are suitably set, 50 wt.-% of the apatite glass
ceramic were mixed with 50 wt.-% of the glass according to the
invention in the form of powders with an average particle size
of less than 90 ~.m. The thermal coefficient of expansion of this
dental material was 9.4 x 10-6K1. The sintering temperature was
750°C and was maintained for 1 minute during the coating of the
veneer. A total of 5 firings were carried out with material
application at 750°C until the veneer was completed. The final
glaze firing was carried out at 740°C without vacuum in order to
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achieve a superficial inherent shine. The veneer representing a
dental restoration showed a very homogenous Layer bonding. No
cracks or faults formed, which is not usual with such thin-walled
thicknesses. The veneer furthermore showed a very good
translucence, which is an extremely important property for such
a type of dental restoration.
Example 38
Preparation of a 3-membered front tooth bridge
A front tooth bridge framework with an intermediate member was
prepared from a lithium disilicate glass ceramic by compression
in the viscous state. The smallest wall thickness was approx. 0.5
mm. After the hot pressing, the framework was cleaned with an
aqueous solution of 0.5 vol.-% HF and 3 vol.-% HzS04 in an
ultrasound bath for 10 minutes and subsequently sand-blasted with
A1203 at a j et pressure of 1. 5 far.. Then a dental material was
sintered on which consisted of the glass 30 according to the
invention and an apatite glass ceramic . The apatite glass ceramic
used had the composition (in wt.-%):
SiOz : 57 . 8 ; LizO : 4 . 3 ; Kz0 : 13 . 5 ; Zn0 : 10 . 5 ; Pz05 : 3 . 5 ;
Ca0 : 6 . 0 ;
F : 0 . 5 ; Mg0 : 1. 3 ; Zr02 : 2 . 0 ; CeOz~: 0 . 6 .
To prepare this glass ceramic, a starting glass of suitable
composition was melted, fritted and ground to a powder. This
powder was then thermally-treated for 4 hours at 520°C and
subsequently for 1 hour at 800°C. To obtain a coating material
in which sintering temperature and coefficient of expansion are
suitably set, 50 wt.-% of the apatite glass ceramic were mixed
with 50 wt.-% of the glass according to the invention in the form
of powders with an average particle size of less than 90 ~.m. The
thermal coefficient of expansion of this dental material was 10.0
x 105Kj. The sintering temperature was 730°C and was maintained
for 1 minute in each case during the coating of the framework.
A total of 5 firings were carried out with material application
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at 730~C until the front tooth bridge was completed. The final
glaze firing was carried out at 720°C without vacuum, in order
to achieve a superficial inherent shine. The obtained three-
membered tooth bridge showed a homogenous bond between lithium
disilicate framework and sintering material. No cracks or faults
formed in the bridge as a result of the matched coefficient of
thermal expansion, the low sintering temperature and the chemical
compatibility between the individual components.
