CA 02351193 2001-06-21
Low-temperature-sintering apatite glass ceramic
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.-% Zn0 at
most, for which reason their chemical resistance is still not
CA 02351193 2001-06-21
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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 Si02-A1203-P205-K20-Na20-Ca0-
F. Additional components are possible but only in relatively small
amounts . So the Zn0 content is limited to 5 . 0 wt . -s at most and
that of K20 to 8.5 wt.-°s 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 800°C. 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
CA 02351193 2001-06-21
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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
l0 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:
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Component wt.-o
Si02 56.0 to 65.0
LizO 1.8 to 5.3
K20 9.0 to 17.5
Zn0 9.0 to 16.0
Ca0 3.5 to 10.5
pz~s 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,_g
NazO 0 to 5.0
Mg0 0 to 3.5
Sr0 , 0 to 3.5
A1203 0 to 6.0
Bz03 0 to 2.0
La203 0 to 3.0
Zr02 0 to 7.5
Ti02 0 to 7.5
Ce02 0 to 2.0
Sn02 0 to 5.0
Tb407 0 to 0.5.
If these additional components are present, they are used in
particular in amounts of at least 0.1 wt.-o.
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:
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Component wt.-o
Si02 56.0 to 64.0
Li20 2.0 to 5.0
K2~ 9.5 to 16.0
Zn0 9.0 to 15.0
Ca0 4.0 to 10.0
P2~s 2.0 to 5.0
0.5 to 0.9
Na20 0 to 4.0
Mg0 0 to 3.0
Sr0 0 to 3.0
A1z03 0 to 5.0
B2~3 0 to 1.8
Laz03 0 to 2.5
Zr02 0 to 6.0
Ti02 0 to 6.0
CeOz 0 to 1.8
Sn02 0 to 4.0
Tb40~ 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.-
Si02 56.0 to 63.0
LizO 2.5 to 5.0
3 0 K20 10 . 0 to 15 . 0
Zn0 9.0 to 14.0
Ca0 4.0 to 9.0
P2~s 2.5 to 5.0
0.5 to 0.8
3 5 Na20 0 to 3 . 0
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Mg0 0 to 2.5
Sr0 0 to 2.5
A1203 0 to 4.0
823 0 t0 1.5
LazO; 0 to 2.0
Zr02 0 to 5.0
Ti02 0 to 5.0
Ce02 0 to 1.5
SnOz _ 0 to 3.0
Tb40, 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 ~,m, in particular
smaller than 7 ~,m and particularly preferably smaller than 5 ~,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.
CA 02351193 2001-06-21
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 NaCaP04 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
particularly desired low sintering temperature.
The glass ceramic 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. Those glass ceramics according to
the invention are particularly preferred which have a sintering
temperature of 780°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 ceramic
according to the invention.
It is of particular advantage that the glass ceramic according to
the invention can also be worked 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
25~ porosity of the glass ceramic are particularly satisfactory. Thus
the glass ceramic 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 ceramic 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 ceramic 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
CA 02351193 2001-06-21
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ceramic 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 . On the other hand, conventional
glass ceramics permit only deviations of ~ 10°C from the sintering
temperature. With larger deviations, satisfactory restorations
cannot be prepared with them.
Furthermore, the apatite-glass ceramic normally has a low thermal
coefficient of expansion of 9.3 to 10.8 x 10-6K-1, measured in the
temperature range of 100°C to 400°C.
For the preparation of the apatite glass ceramic according to the
invention
a) a starting glass which contains the above stated components
is melted at temperatures of 1200°C to 1650°C,
b) the obtained glass melt is_pou.red into water accompanied by
formation of a glass granulate,
c) the glass granulate is optionally reduced to a glass powder
with an average particle size of 1 to 450 Vim, relative to the
number of particles, and
d) the glass granulate or the glass powder is subjected to a
thermal treatment at more than 500°C and up to 900°C for a
period of 30 minutes to 6 hours.
In stage (a) , a startir~g glass is firstly melted, by intimately
mixing suitable starting materials, such as for example carbonates,
oxides and fluorides, with each other and heating to the stated
temperatures.
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Then in stage (b) , the obtained glass melt is quenched by being
poured into water and thereby transformed into a glass granulate.
This procedure is customarily also called fritting.
The glass granulate is optionally then reduced in stage (c) and is
ground to the desired part,_'cle size in particular with customary
mills . The obtained glass powder preferably has an average particle
size of 1 to 450 Vim, relative to the number of particles.
In stage (d), the glass granulate or optionally the.glass powder is
subjected to a thermal treatment at a temperature in the range of
more than 500°C and up to 900°C for a period of 30 minutes to 6
hours, preferably 30 minutes to 3 hours. Contrary to the
conventional apatite-glass ceramics, it is possible to carry out
the temperature treatment and thus the production of the apatite
crystals at temperatures of less than 900°C, which is without
question an advantage.
A volume crystallisation takes place during the thermal treatment.
This leads to a homogenous distribution of the apatite crystals
inside the entire glass ceramic, in contrast to the leucite
crystallisation, which can take place only on the inner surfaces of
a glass powder.
It was ascertained by scanning electron microscope and x-ray
diffraction studies that apatite, preferably fluoroapatite., forms
the main crystal phase. The size of the obtained crystals can be
controlled by the selected temperature and the period of thermal
treatment. In addition to the apatite crystals, further crystals
3C phases can be formed depending on the chemical composition of the
starting glass used.
Alongside the different crystal phases, microheterogenous
separation areas, i.e. different glass phases, may also be present.
These areas can be recognised in the scanning electron microscope
CA 02351193 2001-06-21
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as small microheterogenous glass drop phases with a size of approx.
20 to 400 nm. Together with the crystals, the glass drop phases
occurring influence the optical properties of the glass ceramics
according to the invention, such as e.g. opalescence and
translucency.
Surprisingly, the optical properties of the apatite glass ceramic
according to the invention can be adjusted from glassy-transparent
to cloudy white . This is absolutely necessary for the use as dental
material or component thereof in order to be able to reproducibly
prepare all the different variations of natural teeth. The fine
apatite crystals in the structure of the glass ceramic according to
the invention have a very great similarity to natural teeth in
terms of optics and structure.
The apatite glass ceramic according to the invention is therefore
preferably used as dental material either on its own or together
with further components. To this eiid, it is normally used in the
form of a powder with an average particle size of less than 90 ~,m.
Glasses and other glass ceramics, but also color components, in
particular colored 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. It is preferred that the dental
material contains 10 to 90 wt.-o of the apatite glass ceramic.
When using the apatite glass ceramic as a component of dental
material, dental materials can by obtained by suitable selection of
their composition as well as the type of the further components in
which important properties, such as e.g. working temperature,
optical properties, thermal coefficient of expansion and chemical
resistance, are matched exactly to the respective demands. This is
often not possible with pure glass ceramics.
CA 02351193 2001-06-21
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Dental material is particularly advantageous which contains as
further component at least a glass and preferably a potassium-zinc-
silicate glass.
A potassium-zinc-silicate glass is preferred which comprises the
following components:
Component wt.-
Si02 - 60.0 to 72.0
Li20 1.0 to 5.0
Kz0 10.0 to 23.0
Zn0 8.5 to 20.0
This glass can additionally comprise at least one of the following
components:
Component wt . - %
Na20 - ~ 0 to 4.0
Mg0 0 to 4.0
Ca0 0 to 3.6
Sr0 0 to 3.0
A1203 0 t0 8.0
Bz03 0 to 3.3
Laz03 0 to 3.0
Zr02 0 to 6.0
Ti02 0 to 2.5 -
CeOz 0 to 2.0
Sn02 0 to 5.0
pz05 0 to 1.0
3 0 Tb40~ 0 to 1 . 8
0 to 1.1.
If these additional components are present, they are used in
particular in amounts of at least 0.1 wt.-%.
CA 02351193 2001-06-21
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The above amounts in wt.-% relate to the potassium-zinc-silicate
glass.
The potassium-zinc-silicate glass can be prepared in the customary
way, e.g. by melting a corresponding amount of suitable oxides,
carbonates and fluorides in a platinum/rhodium crucible at a
temperature of 1550°C to 1600°C for a homogenization time of 1
to
1.5 hours. If desired, the glass melt can then be quenched in
water, and the formed granulate dried and ground to a desired
particle size.
The obtained potassium-zinc-silicate glass is characterized by a
high translucency, high chemical resistance as well as a low
coefficient of expansion. It is moreover excellently matched in its
chemical composition to the apatite glass ceramic according to the
invention, so that disadvantageous material transport reactions
between both materials and an ensuing build-up of stress are
avoided in particular in case of 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-i,
measured in the range of 100°C to 400°C. The respectively
desired
coefficient can be set by suitable choice of the type of apatite
glass ceramic and any further components, as well as their amounts.
Favourable dental materials contain 10 to 90 wt.-o apatite glass
ceramic 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.
CA 02351193 2001-06-21
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Preferably a powder of the apatite glass ceramic according to the
inventicn is firstly mixed with a powder of the optionally present
further components and worked 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 in
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, Zr02/A1~03
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 following
components and which can be obtained e.g. by melting of suitable
starting glasses, fritting and thermal treatment at 4(10°C to
1100°C, have proved particularly suitable:
Component wt.-o
Si02 57.0 to 80.0
A120, 0 to 5.0
La203 0.1 to 6.0
Mg0 0 to 5.0
zn0 o to 8.0
i~i~0 11.0 to 19.0
CA 02351193 2001-06-21
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Pz~s 0 to 11.0
where
(a) A1203 + 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 apatite glass ceramic according to the invention and the dental
material according to the invention can be worked into shaped
dental products in the usual way together with the optionally
present additives. Dental restorations such as e.g. an inlay, an
onlay, a bridge, a stump reconstruction, a veneer, a facette, a
filling or a connector can be considered in particular as dental
products shaped according to the invention which contain apatite
glass ceramic or the dental material. Ligaments, 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 ceramic 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 ceramics, the glass ceramic
according to the invention is even better suited in its chemical
composition to glasses, such as potassium-zinc-silicate glasses,
and lithium disilicate glass ceramics which are preferably used as
further components of a coating material or as a substrate. The
consequence of this is that precisely with thin layered composites,
CA 02351193 2001-06-21
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such as e.g. thin-walled veneers, with lithium disilicate glass
ceramic as substrate to which a mixture of apatite glass ceramic
according to the invention and potassium-zinc-silicate glass 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 ceramic according to the invention is also responsible
for this advantageous behaviour.
In addition, the glass ceramic 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 suz-prising that the glass ceramic 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 ceramic simultaneously contains several
types of alkali metal ions.
The invention is explained in more~detail below using examples.
Examples
Examples 1 to 31
In total, 31 different glass ceramics according to the invention
were prepared. They had the chemical compositions listed in Table
I.
CA 02351193 2001-06-21
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h
'
, ~ o
3 N
O
o 00~o
-,i V N O O
N
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h
.
... O
~o h O O
L
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O
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l~ O h M
v 't: ~ o
-~ o
,~ M
.~
l~
d ~ N O
''C M ~C
bl
Om
-~ o
N
O
O O
h
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(a M
O
U QO h M M
M w w
O
a N O a
h O
W
U7 ~Oh h h thhh ~trt<th O ah V h h hh h h h ha h ~Oh h
~L OO O O O CC 00 O O ~ OO O O O OO O O O OO O O O O
r1
O ~ ~~ O ~ CWOoon~o~OO N N~ a O O OO O h M ~r~ W o ~-.O
V ~D~O~O~Oh !fh hh h ~Da Cs~Dh ~C~O~O~ON M h ~~ ~O<t~O~O
N
O ~Oh h h rh~M MM M h !f~!-a rfh h hh h O N ~OO h ~Oh h
4. MM M M M N'nMM M M h hM M M M MM M N N M~O~''iN M M
~
NO O M OO O ~r ~DM h th!r~1~ON O ~~~~oN ~oh
O O ~
OO O h O ~,O a0 ~ ~OO aC O O O OO O ~~~'OO O ~iO O
N ~~ " cc" ~w aoso:...w o~ w ~~.~ -,~,~ ~ ......,w w
. . ~ ~ .
O
~O U1O N QvOW h h O o000h N U1~ ~~t~Oo0a Na h N U1
~ ~ ~
N ~M O M M NN NN ~i~ ~,~~ M ~i~ri~~M ~~N N N~~~'~ N ~-i
w~,w w w ww w~.nr w , w..-.~ w ~~.w w ~ r~ Ov~~
~ '. ~ ~
O
~
O ~M ~ M N C~ OO O h O OM N M N NN M O C MO <f-C M M
~ ~ ~ a
U ~ ~~ ~ t rtViv ~v v ~i~ vv v ~ e~:~:a:tr:viVi~iv ~-i~;v ~
r
N hr f , h Mh oo.a a a Nh c ~ h h~,h p '.co ~o~ h x
~ ~e ~ ~ t ~
H . r~:: M Os;C o'.D ;;W ,:p W OWo wc O ~i~.iOC ~.O o s
p ~ ~o ~ o t Cs ~ ~~ o i
o
h C h ~h hh h h h ho ~;h ~;hh o O C ~h ~ C h h
~ ~ ~
N
~'N ' ' '''~ ~a ~ ~ NN N
~ ~ ~ '
" ' . ~ ~,~.~ -.~. ~.N N N N N N
~ ' ' '
<IMG>
CA 02351193 2001-06-21
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For their preparation, a corresponding amount of suitable
oxides, carbonates and fluorides was melted to produce a
starting glass each time in a platinum/rhodium crucible at
a temperature of 1500°C to 1550°C for a homogenization time
of 1 h. The glass melt was quenched in water, and the
granulate formed from the starting glass was dried and
ground to an average particle size of less than 90 ~,m,
relative to a number of particles.
Subsequently, the granulate or the obtained powder of the
starting glass was subjected to a single- or multi-stage
thermal treatment for 30 minutes to 6 hours at more than
500°C and up to 900°C, whereupon the corresponding glass
ceramic formed.
For some of the glass ceramics, selected properties are
listed in Table II which have been measured in test pieces
made from the respective glass ceramic. Furthermore,
details concerning the specifically selected thermal
treatment of the starting glass are found in Table II under
Thermal treatment" .
CA 02351193 2001-06-21
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p V
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5 h r~.N ~OO Wh h
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U
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0 00 0 0 0 g0 0
~ ~~ ~.~
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~o~n n n n t~n n
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00 0
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s ~ ~'~ V'~ N ~
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CA 02351193 2001-06-21
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The "firing temperature on crown" denotes the temperature
at which the glass ceramic was able to be sintered onto a
crown framework made from glass ceramic material.
The examples illustrate how glass ceramics with different
properties can be obtained by changing the chemical
composition.
Measurement of the coefficient of expansion a
To measure the linear thermal coefficient of expansion a,
a rod-shaped green body was prepared from powder of the
respective glass ceramic, 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 respectively stated firing
temperature for the preparation of the test pieces.
Subsequently a glaze firing was carried out without vacuum
at a ffinal temperature which. was 20°C higher and with a
holding time of 1 minute. The linear thermal coefficient of
expansion was measured on 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 glass ceramics used in the dental field, as
these are permanently exposed 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 ceramic powder
with an average particle size of 90 ~,m. The powder was
maintained at the sintering temperature for 1 minute. Then
the small test plates were treated for 16 hours with 4
vol.-o aqueous acetic acid at 80°C, and finally the loss of
CA 02351193 2001-06-21
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weight which had occurred, relative to the surface of the
small plates, was determined as a measure of the acid
resistance.
The examples illustrate how glass ceramics with different
properties can be obtained by changing the chemical
composition.
Example 32
This example describes the use of a mixture of the apatite
glass ceramic according to the invention according to
example 29 together with a potassium-zinc-silicate glass as
a coating material for ceramic suprastructures and thus its
usability for the preparation of all-ceramic dental
products.
The potassium-zinc-silicate gl-ass used had the composition
-o
(in wt. %)
Si02 65.2; LizO 4.2; K20 14.8; Zn0 12.8; Mg0 0.6; Zr02 1.9;
CeOz 0 . 5 .
For the preparation of this potassium-zinc-silicate glass,
a corresponding amount of starting materials was melted 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 starting glass was dried and ground to an average
particle size of less than 90 ~,m.
To obtain a coating material in which sintering temperature
and coefficients of expansion are suitably set, 50 wt.-% of
the apatite glass ceramic according to the invention were
mixed with 50 wt.-o of the glass in the form of powders
with an average particle size of less than 90 ~.m.
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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 min at 840°C. For the test
piece thus obtained, a thermal coefficient of expansion of
9. 96 x 10 6K 1 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 is
shown that the sintering-on of the mixture was already
possible at a temperature of only 730°C. Overall, all-
ceramic dental products such as 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
stability.
;.
Example 33
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.-% HZSO4 for
10 minutes in an ultrasound bath and then sand-blasted with
A1Z03 at a jet pressure of 1.5 bar. A dental material was
then sintered on, this being a mixture of the glass ceramic
No. 2 according to the invention and a potassium-zinc-
silicate glass. The potassium-zinc-silicate glass used had
the composition (in wt.-%):
CA 02351193 2001-06-21
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Si02 : 64 . 0 ; Li20 : 4 . 0 ; Kz0 : 12 . 6 ; Zn0 : 12 . 4 ; A1203 : 3 . 2 ;
Zr02
3.8.
For the preparation of this potassium-zinc-silicate glass,
a corresponding amount of starting materials was melted 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
was dried and ground to an average particle size of less
than 9 0 ~,m .
To obtain a coating material in which sintering temperature
and coefficient of expansion are suitably set, 50 wt.-% of
the apatite glass ceramic according to the invention were
mixed with 50 wt.-°s of the potassium-zinc-silicate glass 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 10-6K-1. .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 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 products.
The veneer furthermore showed a very good translucency,
which is an extremely important property in this form of
dental restoration.
Example 34
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
CA 02351193 2001-06-21
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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 . - % HZSO4 in an ultrasound bath for 10 minutes
and subsequently sand-blasted with A1203 at a jet pressure
of 1.5 bar. Then a dental material was sintered on which
consisted of the apatite glass ceramic No. 28 according-to
the invention and a potassium-zinc-silicate glass. The
potassium-zinc-silicate glass used had the composition (in
-o
wt. %y
SiOz : 65 . 2 ; Li20 : 4 . 2 ; K20 : 14 . 8 ; ZnO: 12 . 8 ; Mg0 : 0 . 6 ; ZrOz
1.9; Ce02: 0.5.
For the preparation of this potassium-zinc-silicate glass,
a corresponding amount of starting materials was melted 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.
To obtain a coating material in which sintering temperature
and coefficient of expansion are suitably set, 50 wt.-% of
the apatite glass ceramic according to the invention were
mixed with 50 wt.-% of the potassium-zinc-silicate glass in
the form of powders with an average particle size of less
than 90 Vim. The thermal coefficient of expansion of this
dental material was 10. 0 x 10-6K 1. 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 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 front tooth bridge showed a homogenous bond
betweer~ lithium disilicate framework and sintering
material. No cracks or faults formed in the bridge, due to
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the matched thermal coefficient of expansion, the low
sintering temperature and the chemical compatibility
between the individual components.
