CA2128397A1

CA2128397A1 - Method of producing oxide ceramic dental prostheses

Info

Publication number: CA2128397A1
Application number: CA002128397A
Authority: CA
Inventors: Hans Hermann Beyer; Peter Biberbach
Original assignee: Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 1993-07-21
Filing date: 1994-07-20
Publication date: 1995-01-22
Also published as: JPH0751294A; AU6861794A; ZA945346B; EP0635256A1; IL110387A0; DE4324438A1; BR9402877A

Abstract

Abstract In order to produce oxide ceramic dental prostheses with an accurate fit in a single operation, the mixture of ceramic particles, binders and/or mixing fluids must be prevented from shrinking during sintering. This is done by adding particles of easily oxidizable metals, metal suboxides and/or metal hydrides, which absorb oxygen and increase in volume during sistering and compensate for the shrinkage during sintering, if the mixture is in the right proportions.

Description

- ~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 l Y~f~, ' ,' ,'" ; ; i., ,~, ~,:~" , ~, , , , ~ ",,, " , , ~ ,; " . - , ,, ~

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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-f -~ Z~83~3~

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 ~,,, ,. ""~ ,s~ ,-",, ,;;' ;~ "
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39~7 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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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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Claims

1. A method for producing oxide ceramic dental prostheses in a single operation by sintering a mixture of oxide ceramic particles, and binders or mixing fluids or a mixture thereof, characterized in that particles of easily oxidizable metals, metal suboxides, metal hydrides or a mixture thereof, 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 is brought about in a supply of air or oxygen, and the ratio by weight of metal, metal suboxide, metal hydride or mixture thereof particles to ceramic particles is chosen so that the shrinkage in the ceramic particles during sintering is compensated by the increase in volume of the metal, metal suboxide, metal hydride or mixture thereof particles during oxidation.

2. A method according to claim 1, characterized in that the metal particles are powdered titanium, zirconium, aluminum or a mixture thereof.

3. A method according to claim 2, characterized in that the binders are selected from waxes, methacrylates, silicons, inorganic phosphates and mixtures thereof, the mixing fluids are water or polyalcohols, and the ceramic fillers are selected from metal oxides, silicon oxide, silicates and a mixture thereof.

4. A dental prostheses produced by the method of claim 1, 2 or 3.

5. A dental prostheses according to claim 4, selected from an inlay, an onlay and a crown.