EP2309947A1

EP2309947A1 - Method for the production of oxide dental ceramics

Info

Publication number: EP2309947A1
Application number: EP09777509A
Authority: EP
Inventors: Jürgen HAUSSELT; Regina Knitter; Hans-Joachim Ritzhaupt-Kleissl; Werner Bauer; Joachim R. Binder; Nadja Schlechtriemen
Original assignee: Karlsruher Institut fuer Technologie KIT
Current assignee: Karlsruher Institut fuer Technologie KIT
Priority date: 2008-08-06
Filing date: 2009-07-29
Publication date: 2011-04-20
Also published as: WO2010015350A1; DE102008036661A1

Abstract

The invention relates to a method for producing oxide dental ceramics, comprising the following steps: a) numeric data of the three-dimensional shape of an oxide dental ceramic article that is to be produced is provided, and the dimensions of the three-dimensional shape are numerically enlarged according to the expected subsequent shrinkage due to sintering; b) a master form of the enlarged three-dimensional shape is produced by means of a generative or abrasive process; c) a female mold is produced by copying the master form, said female mold being designed in such a way as to be made up of at least two parts; d) a feedstock containing an oxide-ceramic powder is introduced into the female mold at a temperature ranging from 60°C to 150°C; e) a cooled molded article is removed from the female mold and is debound, and the debound molded article is finally sintered to obtain a compact oxide dental ceramic article. In said method, no or very little material is wasted. Said method allows very fine edges of crowns and complex geometries to be created. The dental ceramic article can be directly colored in basic tooth colors by adding suitable substances to the feedstock. The number of required apparatuses can be kept low especially when using low-pressure injection molding processes.

Description

Process for the production of oxidic dental ceramics

The invention relates to a process for the production of oxide ceramic dentures.

The present invention is in the field of manufacturing of ceramic dental prostheses from oxide ceramics such as alumina or zirconium dioxide. This Mateπalklasse distinguishes itself from other ke ^¬ ramischen or glass-ceramic materials with high strength and good chemical stability.

A disadvantage of the oxide ceramics is their production via a powder technology molding process and subsequent sintering, which has a shrinkage up to the dense ceramics of up to 50 vol.% Result. Only since the establishment of CAD / CAM technologies is it possible to produce dental prostheses from materials of this class in practice by means of a mathematical correction of the dimensions of the desired shape. An overview of the practical use of CAD / CAM systems can be found in the article Fabric for Machine Helpers, dental dialogue, p. 52, 2005.

However, in practice, the following problems arise when using this method:

In this process, the mold to be produced is milled from an oxide ceramic blank. The erosion used here inevitably leads to a loss of material which, depending on the material composition and size of the denture, can amount to up to 90% by volume. This material is lost because it can not be worked up yet.

During machining of the sintered blank, which is referred to as white machining, breakouts of the mold occur, especially in the case of thin crown margins. The entire production process is expensive in terms of apparatus. Therefore, there are various efforts to develop new methods or methods that are already established in other areas, such as those from DE 197 03 177 Al or from W. Bauer and V. Piotter, Ceramic Journal 56, 2004, 292-297 known powder injection molding or from DE 103 37 688 B3 or H. von Both, M. Dauscher and J. Haußelt, Ceramic Journal 56, 2004, 298-303 known electrophoretic deposition to adapt to the conditions of dental technology, so that these Compared to the CAD / CAM technology characterized by a lower equipment cost and a lower material loss and therefore are particularly cost-effective. However, there always remains the problem of sintering shrinkage, which has so far been solved in different ways.

As known from EP 1 324 962 B1, the use of vibration-free ceramics as thermoplastic compositions has the advantage that no expansion is required for this purpose. Disadvantages of this, however, are the lower strengths of such ceramics and the fact that these are multiphase, opaque materials. In addition, the required oxidation reactions lead to longer process times for larger reactions in reaction sintering.

Electrophoretic deposition (EPD) has hitherto been carried out predominantly for the production of inflation ceramics. In DE 100 499 74 A1, metallic powders are deposited and subsequently oxidized by means of EPD to compensate for the sintering fuming, in which case a subsequent glass infiltration is required to close the resulting pores. In DE 10 2004 018 136 B3 and also in DE 102 32 135 Al, expanding stump materials are used for the production of densely sintered oxide ceramics in order to compensate for the occurring sintering fuming. In principle, with the EPD, due to the process, only uniform layers can be produced; However, no complex geometry, as it represents a dental prosthesis, produce, ie it is always a second-consuming manual reworking required. In Heißgießverfahren for shrinkage compensation, as known from EP 1 346 702 Al, also expanding models are used. For the expansion, however, a time-consuming molding process with a subsequent thermal process is required. In addition, the expanded models (so-called Kappchen) are porous and therefore pose difficulties in their handling.

Proceeding from this, it is the object of the present invention to propose a method for the production of oxide dental ceramic, which does not have the disadvantages and limitations mentioned.

In particular, a method is to be provided which enables the production of oxidic dental ceramics without material loss or with only a very slight material loss. In addition, this method should offer the possibility of producing complex geometries and very fine crown margins.

This object is achieved by the steps of claim 1. The claims describe advantageous embodiments of the invention.

The present invention achieves the stated object by a process chain which comprises low-pressure injection molding, hot-casting or centrifugal molding as an essential process step. In order to compensate for the sintering shrinkage occurring during sintering, the three-dimensional shape or its negative mold must be made correspondingly larger. For this purpose, it is necessary that the desired shape of the dental ceramic is present as numerical data, for which all methods known from dentistry or dental technology can be used.

A erfmdungsgemaßes method accordingly comprises the following process steps a) to e). Under oxidic dental ceramics are understood in relation to the present invention both dentures and dental fillings. According to step a), numerical data of the three-dimensional shape of the desired oxidic dental ceramic, which are usually present as CAD data, form the starting point for the present production method. The CAD data can be obtained here by means of an impression reduction with subsequent modeling or from an intraoral data acquisition. Subsequently, according to the expected later sintering, the dimensions of the three-dimensional shape are numerically enlarged and are then usually available as CAD data.

Subsequently, according to step b), a master model of the enlarged three-dimensional shape from method step a) is first produced, which preferably consists of plastic, wax or a metal. In particular, generative methods such as 3D printmg or ablation methods such as CAD / CAM are used for this purpose.

In the subsequent step c), a negative mold is now produced from the original model. Here it is crucial that this shape is designed such that it consists of two, three, four or more parts. The negative mold itself is preferably made of a plastic or silicone.

Subsequently, according to step d), a so-called feedstock which contains an oxide-ceramic powder, wax and / or paraffin and optionally further additives is introduced into the negative mold produced according to process step c), which consists of two, three, four or more parts , The introduction is preferably carried out by low-pressure injection molding at a pressure of 0.01 to 10 MPa, preferably from 0.1 to 2 MPa, and at a temperature of 60 ⁰ C to 150 ⁰ C, preferably from 70 ⁰ C to 120 ⁰ C, especially preferably from 80 ⁰ C to 100 ⁰ C. Alternatively, non-pressure casting, hot casting, or Zentnfugalabformung is suitable as a method.

Finally, according to step e), the molding is removed from the negative mold and thermally, chemically and / or supercritically debinded and the debinded molding then sintered to a dense oxide dental ceramic.

The inventive method has in particular the following advantages:

When processing the ceramics, no or only a very small loss of material is produced.

Very fine crown margins and complex geometries can be produced with this method.

A direct coloring of dental ceramic in dental ground clays is possible by suitable additives in the feedstock.

In particular, when using the low pressure injection or hot casting only a small amount of equipment is required.

The invention will be explained in more detail below with reference to exemplary embodiments.

For the determination of the form fidelity and the sintering shrinkage, a simplified geometrically measurable model of a posterior full crown was chosen as the archetype for the two exemplary embodiments.

Embodiment 1

With the dimensions of the original model, a CAD file was generated and milled on this database in a 5-axis Frasmaschme from a plastic blank an oversized original model. Here, the necessary Abkühlschwindmaß (molding temperature-room temperature) and the Sinterschwindmaß of Al ₂ θ ₃ -containing Heißgießmasse total of 13.7% were considered from the outset, which corresponds to a linear magnification of 15.9%.

This master model was instigated with wax wires (diameter 0.5 - 5 mm) in a special holder to later feed the mass into an evacuated cavity and thus a complete fulfillment of the same. The incised model was filled with an addition-curing silicone in such a way that finally a two-part negative form was created. The multi-part nature of the silicone mold facilitated the final formability of the molds. The SiIikon negative mold was preheated after curing and cleaning to a molding temperature of 100 ° C in a specially manufactured multipart and lockable metal capsule. The linear thermal expansion of the silicone was taken into account in the production of the silicone negative mold in such a way that the silicone negative mold was embedded in the metal capsule without stress and deformation at the corresponding molding temperature.

In an evacuable dissolver, 65.0% by volume of aluminum oxide powder in 35.0% by volume of a melt-containing thermoplastic binder mixture were incorporated. The binder mixture contained a mixture of two paraffins in a ratio of 20% by weight to 70% by weight; the 100% by weight supplemental portion formed a dispersing aid.

The rheological behavior of the hot casting composition was characterized by a rheometer using a plate-plate-25 measurement setup. The gap width between the two plates was 0.5 mm; it was controlled shear stress at a regulated peltier temperature of 90 ⁰ C to 3000 Pa measured. The produced hot casting compound had a dynamic viscosity of 6.95 Pas at a shear rate of 100 s ^-1 .

For the forming process, the mass was filled into the supply container of an injection facility and kept at a processing temperature of 100 ⁰ C. The required injection pressure was applied to the injection system by means of a hand lever press. Formulation was carried out under vacuum at an injection pressure of 0.49 MPa for 30 seconds and a holding pressure of 0.59 MPa for a further 30 seconds.

The specimen thus prepared was removed from the mold after cooling, thermally debinded at a temperature up to 400 ⁰ C and at 1650 ⁰ C over 3 Sintered for hours. After sintering, the specimen was in

Measure the length and width in each case at 5 positions. The measured values obtained were each averaged and the linear shrinkage between prototype and sintered part was calculated. The measured values determined in this way are listed in Table 1.

Table 1: Average values of the measured dimensions in length and width and resulting linear shrinkage between the prototype and the sintered component of alumina:

Table 1

Dimension dimensions of the original form dimensions of the sintered linear (mean value) component (mean value change)

Length 13, 901 mm 11,997 mm -13.70%

Width 11, 588 mm 9, 986 mm -13.82%

According to Table 1, the observed changes in length were -13.70% and -13.82%, respectively. Thus, the sintering shrinkage from the prototype to the replication is isotropic in terms of length and width. The intended final dimensions of the sintered ceramic crown were achieved.

Embodiment 2:

With the dimensions of the original model, a CAD file was generated and milled on this database in a 5-axis milling machine from a plastic blank, an oversized original model. Here, the necessary Abkühlschwindmaß (molding temperature-room temperature) and the Sinterschwindmaß the Zrθ2 ~ containing Heißgießmasse of a total of 21.0% were taken into account from the outset, which corresponds to a linear magnification of 26.6%.

The preparation of the silicone negative mold was carried out as in Example 1 except that the final preheating temperature of the silicone mold 70 ⁰ C was used instead of 100 ° C. In an evacuable dissolver, 49.4% by volume of a Yttrium partially stabilized zirconium oxide (3 mol% yttrium oxide) were incorporated into a melt-flowable thermoplastic binder mixture. The binder mixture contained at least 90% by weight of paraffin; the 100% by weight supplemental portion formed a dispersing aid.

The rheological behavior of the molding composition was characterized in the same manner as in Example 1. The produced hot casting compound had a dynamic viscosity of 13.9 Pa * s at a shear rate of 100 s ^-1 .

The molding process was carried out as in Example 1.

The specimen thus prepared was removed from the mold after cooling, thermally debinded at a temperature up to 400 ⁰ C and sintered at 1450 ⁰ C for 1 hour. After sintering, the specimen was measured in length and width as in Example 1. The measured values obtained were each averaged and the linear shrinkage between prototype and sintered part was calculated. The measured values determined in this way are listed in Table 2.

Table 2: Average values of the measured dimensions m Long and wide and resulting linear shrinkage between the prototype and the sintered component made of partially stabilized zirconium oxide:

According to Table 2, the observed long-term changes were -20.96% and -20.98%, respectively. Thus, the sintering shrinkage from the original form to Replication in terms of length and width isotropic. The desired

Final dimensions of the sintered ceramic crown were achieved.

Claims

cLAIMS

1. A method for the production of oxide dental ceramic, comprising the steps of a) providing numerical data of the three-dimensional shape of an oxidic dental ceramic and numerically increasing the dimensions of the three-dimensional shape according to the expected subsequent sintering shrinkage, b) producing a master model of the enlarged three-dimensional shape means c) producing a negative mold by copying the master model, wherein the negative mold is designed such that it consists of at least two parts, d) introducing a feedstock containing an oxide ceramic powder into the negative mold at a temperature of 60 ⁰ C to 150 ⁰ C, e) deblocking a cooled molding from the female mold, and debinding final sintering the debindered molding to form a dense oxide ceramic tooth.

2. The method of claim 1, wherein the introduction of the feedstock according to process step d) into the negative mold by means of low-pressure injection molding at a pressure of 0.01 to 10 MPa.

3. The method of claim 1 or 2, wherein the introduction of the feedstock into the negative mold according to process step d) at a pressure of 0.1 to 2 MPa and at a temperature of 70 ⁰ C to 120 ⁰ C.

4. The method of claim 3, wherein the introduction of the feedstock into the negative mold according to process step d) at a temperature of 80 ⁰ C to 100 ⁰ C.

5. The method according to claim 1, wherein the introduction of the feedstock according to process step d) takes place in the negative mold by means of hot casting or Zentrifugalabformung.

6. The method according to any one of claims 1 to 5, wherein the debindering of the molding according to process step e) takes place thermally, chemically or supercritically.