Note: Descriptions are shown in the official language in which they were submitted.
- ~2~3~397
The invention relates to a method of producing oxide ceramic
dental prostheses such as inlays, crowns or other parts, in a
single operation by sintering a mixture of oxide ceramic
particles, binders and/or mixing fluids.
In dentistry there are a large number of available materials
for fillings and prosthesis parts. Amalgams are widely used as
filling materials, since they are easy to work and have
advantageous abrasion properties in the molar region. The
color is a disadvantage, however, since it is different from
teeth. Also amalgams have acquired a bad reputation owing to ~-
their mercury content.
"Composites" are more complicated to process, of limited
durability, and their long-term properties are little known.
They are used mainly in the front-tooth region, since they can
very easily be given a tooth-like color.
Cast gold fillings and other gold castings are very complicated
to manufacture and the material is very expensive. The
metallic color is often disturbing, although ceramic facing is
possible in some cases. ~`~
Ceramic inlays meet many requirements regarding durability and
color. They are usually complicated to manufacture, however,
and the same applies to manufacture of crowns and other
prosthesis parts. Usually the ceramic materials, consisting of -
oxide ceramic powders, binders and mixing fluids, are sintered
on a refractory stump material at temperatures of 1100 to
1200C to obtain the required strength. In order to compensate
for the shrinkage during sintering and the resulting inaccurate
fit, the ceramic
materials are sintered in layers in a number of firing
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operations. The stump material is accurately matched to the
sintered-on ceramics, in an attempt to reduce the changes in
dimensions caused by shrinkage. In this process, the stump
material has to be mechanically removed after firing, which may
damage the s`intered members.
According to EP laid-open specification 240 643, for example,
dental prosthesis parts are produced by building up layers of a
ceramic slip and water on a stump model. The layers are
sintered at about 1100C without substantial shrinkage. Any
remaining pores are filled with a glass material.
EP-PS 214 341 discloses manufacture of metal prosthesis parts,
using noble metals which can contain ceramics and glass. A
slip is agitated with water and the resulting green compacts
are sintered. The size of the noble metal particles is chosen
so that shrinkage during sintering is at a minimum. Ceramic
parts cannot be produced by this method.
The invention provides a method of manufacturing oxide ceramic ;~
dental prostheses such as inlays, crowns or other parts by ---
sintering a mixture of oxide ceramic particles, binders and/or
mixing fluids, so as to obtain parts with an accurate fit in a - -
single operation and without using stump models. -
-~
More particularly, according to the invention particles of
easily oxidizable metals, metal suboxides and/or metal - -~
hydrides, the stable oxides of which must have a tooth-like
coloring, are added to the ceramic particles, green compacts ---
having the desired final dimensions are moulded from the
mixture, sintering i5 brought about in a supply of air or
oxygen, and the ratio by weight of metal, metal suboxide and/or -
metal hydride particles to ceramic particles is chosen so that
the shrinkage in the ceramic particles during sintering is
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3 93 169 DT
compensated by the increase in volume of the metal, metal
suboxide and/or metal hydride particles during oxidation.
Preferably, the metal particles are powdered titanium,
5 zirconium and/or aluminium. The oxides of these metals are
white or have a tooth-like colour. The metal suboxides can
e.g. be titanium dioxide or zirconium dioxide, and the metal
hydrides can e.g. be titanium hydride or zirconium hydride,
the oxides of which are likewise white or tooth-coloured.
10 The only metals, suboxides or metal hydrides which can be
used are those which form stable oxides at the sintering
temperature of about 1300C in air or oxygen, with increase
in volume. The required ratio by weight of metal particles
to ceramic particles must be determined by preliminary
15 tests.
The binder systems and/or mixing fluid are used mainly for
moulding the green compacts, but can also be components of
the ceramics, if they contain inorganic components. --
20 Preferably the binders are waxes or methacrylates, which
burn without leaving a residue, or silicons, which when `
heated form silicon dioxides absorbed by the ceramic, or
inorganic phosphates which serve as sintering aids.
25 The mixing fluids are preferably water or polyalcohols, and
the ceramic fillers are mainly metal oxides, silicon oxide
and/or silicates.
The method yields very accurately-fitting oxide ceramic
30 dental prostheses with relatively low effort, compared with
the previously-known processes. The resulting parts are
tightly sintered and consequently have high mechanical
~trength. They are tooth-coloured, but the aesthetic effect
can be further improved by colouring or glazing by firing.
The basic features of the method accoxding to the invention
will now be described ~7ith reference to titanium, but the
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description is similarly valid for the other aforementioned
metals and/or their compounds.
Titanium powder, when heated in air, reacts at relatively low
temperatures with oxygen to form titanium oxide. The oxidation
process can be controlled so that oxygen is absorbed gradually
an~ there is no overheating by the reaction, which is normally
strongly exothermic. The conversion to oxide is accompanied by
considerable increase in volume of about 78.3%, owing to the
increase in mass and the difference between the density of
titanium and titanium oxide. In the case of a porous moulding,
the inner pores are substantially closed. The moulding can be
further compacted by additional heating. The normal shrinkage
during sintering is compensated by the oxide formation. If a ~
mixture of titanium powder and metal oxides, such as Tio2, ZrO2 --
alkaline earth-metal oxides or compounds thereof, is adjusted --
to the expected shrinkage, the result can be a tightly sintered -~
moulding which has high strength and a tooth-like color and, - -
after the sintering process, has exactly the same dimensions as - ~-
the green compact.
The following examples will illustrate the method according to ~ ~;
the invention in greater detail:
1. The following raw materials were mixed in a kneader at
about 160C to form a plastic material: ~
36.4% titanium powder, average particle size 7 ~m; --
27.3% magnesium titanate, average particle size 2 ~m;
27.3% zirconium oxide, average particle size 1 ~m, and
9.0% wax
The desired mouldings, e.g. inlays, onlays and crowns, --~
in the form of green compacts were produced, using -
suitable moulds, from the resulting material, which was
plastic at elevated temperature. In a program-
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5 93 169 DT
controlled firing process, the wax was first burnt out
at a heating rate of about 0.5C/min up to a
temperature of 370C. The result was a dimensionally
stable blank with a green density of about 70 vol.%.
During subsequent heating at the rate of about 2C/min
to about 1300C in air, the remaining pores were
gradually closed by the titanium oxide which formed.
At a temperature of about 1300C, the moulding was
sintered to its final density in 3 hours. After
cooling to room temperature, the sintered product had
exactly the starting dimensions of the moulding. ~ ,
2. The following raw materials were homogeneously mixed in -- :
a kneader to form a plastic material~
58% titanium powder, average particle size 7 ~m; ~-
13% titanium dioxide, average particle size 2 ~m; ~-
10% magnesium oxide, average particle size 8 ~m and
21~ methacrylate ~--
The desired moulded members, e.g. inlays, onlays and -~
crowns, were produced from the resulting material,
using suitable moulds.
After the binder had set, the methacrylate was first
burnt out in a program-controlled firing process
similar to Bxample 1. The result was a dimensionally
stable blank having a green density of about 68 vol.%.
During further heating the remaining pores weré
gradually closed by the titanium oxide which formed.
At a temperature of about 1300C the moulded member was
sintered to its final density for 3 hours. After
cooling to room temperature the sintered product had
exactly the starting dimensions of the moulded member.
3. A powder mixture of 50% titanium powder, 33% magnesium
oxide and 17% ammonium dihydrogen phosphate was mixed
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6 93 169 DT
with water on a glass plate to obtain a homogeneous
paste and the desired moulded member was produced,
using suitable moulds.
After drying and setting, the mixture was fired in a
program-controlled firing process at a heating-up rate
of about 2C/min, during which ammonia and the water
incorporated during the setting process first
evaporated. The result was a dimensionally stable
blank with a green density of about 70%. During
further heating the remaining pores were gradually --
closed by the titanium oxide which formed. At a ~- :
temperature of about 1300C the moulded member was -- --
sintered to its final density. After cooling to room ~
temperature the sintered product had exactly the - :-
starting dimensions of the moulded member.
4. A mixture of 50% titanium powder, 37% magnesium oxide --
and 13% titanium oxide with water and polyethylene
glycol was mixed on a glass plate to form a homogeneous -
paste and the desired moulded member was produced, ~--
using suitable moulds. After drying and setting, the -
mixture was fired in a program-controlled firing -
process at a heating-up rate of 2C/min, during which -
the water incorporated in the setting process -;-
evaporated first. Subsequently during the process the - ~-
polyethylene glycol was oxidised and the resulting
gases were expelled. The result was a dimensionally
I stable blank with a green density of about 70%. During
further heating the remaining pores were closed by the
titanium oxide which formed. At a temperature of about
1300C the moulding was sintered to its final density.
After cooling to room temperature the sintered product
had exactly the starting dimensions of the moulded
member.
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5. A mixture of 15~ titanium powder, 50~ titanium hydride,
20% magnesium oxide and 15% titanium oxide with water
and polyethylene glycol were mixed on a glass plate
into a homogeneous paste and the desired moulded
members, e.g. inlays, onlays and crowns, were produced
in suitable moulds.
After drying and setting, the mixture was fired in a
program-controlled firing process at a heating-up rate
of about 2C/min, and the water incorporated during the
setting process first evaporated. During the
subsequent process the polyethylene glycol was oxidised
and the resulting gases were expelled. The result was
a dimensionally stable blank with a green density of
about 68 vol.%. During further heating the remaining
pores were gradually closed by the titanium oxide
formed from the titanium and the titanium hydride. At
a temperature of about 1300C the moulded member was
sintered for 3 hours to its final density. After
cooling to room temperature the sintered product had
exactly the starting dimensions of the moulded member.
6. The following raw materials were homogeneously mixed in
a kneader to obtain a plastic material:
59% titanium powder, average particle size 7 ~m,
17% titanium suboxide, average particle size 15 ~m
( Ti2O3 ),
10% magnesium oxide, average particle size 8 ~m and
23% methacrylate.
The desired moulded members, e.g. inlays, onlays and
cro~ms, were produced from the resulting material,
using suitable moulds. A~ter the binder had set, the
methacrylate was first burnt out in a program-
controlled firing process similar to Example 1. The
result was a dimensionally stable blank with a green
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8 93 169 DT
density of about 68% vol.%. During subsequent heating
the remaining pores were gradually closed by the
titanium oxide which formed. At a temperature of about
1300C the moulded member was sintered for 3 hours to
its final density. After cooling to room temperature
the sintered product had exactly the starting
dimensions of the moulded member.
7. The following raw materials were homogeneously mixed in -
a kneader at about 160C to obtain a plastic material: -
':
40% titanium powder, average particle size 7 ~m, --
22% magnesium titanate, average particle size 2 ~m, --
28% aluminium powder, average particle size 13 ~m and -
10% wax.
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The desired moulded members, e.g. inlays, onlays and ~
crowns, were produced in suitable moulds from the ;
resulting material, which was plastic at elevated
temperatures. Firstly the wax was burnt out in a ~ - -
program-controlled firing process at a heating-up rate -~ - -
of about 0.5C/min up to a temperature of 370C. The
result was a dimensionally stable blank with a green --
density of about 67 vol.%. During subsequent heating
at a rate of about 2C/min to about 1500C, the ~-
remaining pores were gradually closed by the titanium
oxide and aluminium oxide which formed. At a
temperature of about 1500C, the moulded member was ~
sintered for 3 hours to its final density. After -;
cooling to room temperature the sintered product had
exactly the starting dimensions of the moulded member.
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