Process for preparation of dental restoration

Abstract

To provide a method for the preparation of a dental restoration.SOLUTION: The invention relates to a method for the preparation of a dental restoration, in which an oxide ceramic material is (a) subjected to at least one heat treatment, and (b) cooled, wherein the cooling comprises (b1) a first cooling step with a cooling rate T1 and (b2) a second cooling step with a cooling rate T2 and wherein the absolute value of the cooling rate T2 is less than the absolute value of the cooling rate T1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a process which allows the production of dental restorations having excellent properties in a short time, starting from an oxide ceramic material. The present invention further relates to the use of an oxide ceramic material for the preparation of dental restorations by the process according to the invention. [Background technology]

[0002] Ceramic materials, such as oxide ceramics, are frequently used to fabricate fully anatomical dental restorations. They offer a high degree of clinical safety, are usually metal-free, can be used for minimally invasive preparation, and are very attractively priced compared to other metal-free restorations. However, the large number of work steps required to fabricate such restorations presents a drawback.

[0003] Restorations are usually milled or ground from a pre-sintered blank, shaded if necessary, sintered densely by heat treatment, and finally further shaded, glazed, and / or finished as required.

[0004] Conventional sintering processes for dental ceramics involve slow heating to a maximum temperature at which the oxide ceramic material used is densely sintered. Due to the low heating rate, the sintering process generally takes more than four hours, which significantly increases the length of the dental ceramic production cycle, especially in tableside procedures.

[0005] The approach of accelerating the sintering process by increasing the heating rate is generally known.

[0006] For example, EP 2098188 describes a dental furnace and a method for sintering dental materials, in which the furnace is heated to a pre-sintering temperature of at least 1000°C at a heating rate of more than 50 K / min in a first heating period.

[0007] EP 2101133 A1 describes a sintering furnace and a process for sintering dental articles, in which the articles are moved along sintering sections and exposed to different temperatures. A high heating rate of 300 K / min or faster can be used in the first section.

[0008] WO 2012 / 057829 describes a process for fast sintering of ceramics using electromagnetic induction or plasma.

[0009] WO 2015 / 091744 describes a process for planning the sintering of dental pre-sintered parts, in which the temperature profile for the heat treatment of the dental pre-sintered part is automatically determined by a computer as a function of the predetermined geometry and material parameters of the dental pre-sintered part to be produced. Heating rates of 100 K / min to 400 K / min are used for sintering the predetermined dental pre-sintered part.

[0010] WO 2015 / 121364 describes a sintering furnace for dental components, which is equipped with a heating device that allows a heating rate of at least 200 K / min in the useful range.

[0011] Sintering of dental materials in an inert gas or in a vacuum is also known in the art.

[0012] WO 2011 / 020688 describes an apparatus for oxygen-free sintering of metals or ceramics in dental technology in an inert gas.

[0013] EP 2 703 760 A1 describes a dental furnace for sintering dentures, the heating chamber of which can be closed by a conventional closing device, e.g. a door, or by attachment with a vacuum vessel, and can be used for normal sintering or vacuum sintering.

[0014] WO 2017 / 189414 describes a method for producing a dental restoration that includes an additional thermal treatment to induce a color change.

[0015] EP 3659548 A1 describes a process for producing dental restorations in which an oxide ceramic material is subjected to at least two heat treatments, the first being carried out at a lower pressure than the second. However, approaches to accelerating the sintering process have resulted in ceramic material properties, especially optical properties, that do not meet the high demands in the dental field. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] European Patent Application Publication No. 2098188 [Patent Document 2] European Patent Application Publication No. 2101133 [Patent Document 3] International Publication No. 2012 / 057829 [Patent Document 4] International Publication No. 2015 / 091744 [Patent Document 5] International Publication No. 2015 / 121364 [Patent Document 6] International Publication No. 2011 / 020688 [Patent Document 7] European Patent Application Publication No. 2703760 [Patent Document 8] International Publication No. 2017 / 189414 [Patent Document 9] European Patent Application Publication No. 3659548 Summary of the Invention [Means for solving the problem]

[0017] The present application is therefore based on the problem of providing a process for preparing dental restorations, which process produces dental restorations in which excellent mechanical, and in particular optical, properties are achievable in a short time by sintering oxide ceramic materials.

[0018] According to the present invention, the problem is solved by a process for preparing a dental restoration according to claims 1 to 21. A further subject of the invention is the use of an oxide ceramic material for preparing a dental restoration according to claim 22. The present invention provides, for example, the following items. (Item 1) 1. A method for preparing a dental restoration, comprising: The oxide ceramic material is (a) subjected to at least one heat treatment; (b) cooled, The cooling step comprises: (b1) a first cooling step having a cooling rate T1; (b2) a second cooling step having a cooling rate T2; Including, The method, wherein the absolute value of the cooling rate T2 is less than the absolute value of the cooling rate T1. (Item 2) The cooling step comprises: (b1) a first cooling step having a cooling rate T1; (b2) a second cooling step having a cooling rate T2; (b3) a third cooling step having a cooling rate T3; Including, 10. The method of any one of the preceding items, wherein the absolute value of the cooling rate T2 is smaller than the absolute values ​​of the cooling rate T1 and the cooling rate T3. (Item 3) 8. The method according to any one of the preceding items, wherein step (b2) is carried out at a temperature in the range of 1000°C to 1500°C, preferably in the range of 1100°C to 1400°C, more preferably in the range of 1200°C to 1300°C. (Item 4) 10. The method according to any one of the preceding items, wherein in step (b2) the absolute value of the cooling rate T2 is smaller than 60 K / min, preferably smaller than 50 K / min, more preferably smaller than 40 K / min, even more preferably smaller than 25 K / min, even more preferably smaller than 10 K / min and most preferably smaller than 5 K / min. (Item 5) Item 11. The method of any one of the preceding items, wherein step (b2) is carried out at a substantially constant temperature. (Item 6) 10. The method according to any one of the preceding items, wherein (b2) is carried out for a period of from 1 minute to 20 minutes, preferably from 1 minute to 10 minutes, more preferably from 2 minutes to 8 minutes, particularly preferably from 3 minutes to 7 minutes, and most preferably from 4 minutes to 6 minutes. (Item 7) 10. The method according to claim 1, wherein the absolute value of the cooling rate T1 and / or the absolute value of the cooling rate T3 is at least 40 K / min, preferably at least 50 K / min, particularly preferably at least 60 K / min, in particular in the range from 40 K / min to 200 K / min, preferably from 50 K / min to 100 K / min, particularly preferably from 60 K / min to 80 K / min. (Item 8) 10. The method according to any one of the preceding items, wherein the oxide ceramic material is heated in step (a) to a temperature in the range of from 1100°C to 1700°C, preferably in the range of from 1300°C to 1600°C, more preferably in the range of from 1400°C to 1550°C, especially preferably in the range of from 1450°C to 1500°C, and most preferably at about 1480°C. (Item 9) 10. The method according to any one of the preceding items, wherein the oxide ceramic material is heated in step (a) at a heating rate in the range of 5 K / min to 500 K / min, preferably in the range of 50 K / min to 250 K / min, more preferably in the range of 100 K / min to 200 K / min. (Item 10) 10. The method according to any one of the preceding items, wherein the oxide ceramic material is cooled in step (b) to a temperature in the range of from 20°C to 1300°C, preferably in the range of from 100°C to 1250°C, particularly preferably in the range of from 1000°C to 1200°C. (Item 11) The oxide ceramic material in step (a) is (a1) subjected to a first heat treatment; (a2) subjected to a second heat treatment; 10. The method of any one of the preceding items, wherein the heat treatment in step (a1) is carried out at a lower pressure compared to the heat treatment in step (a2). (Item 12) 10. The method according to any one of the preceding items, wherein the heat treatment in step (a1) is carried out at a pressure of less than 200 mbar, preferably less than 100 mbar, particularly preferably less than 50 mbar, in particular in the range from 0.1 mbar to 200 mbar, preferably in the range from 1 mbar to 150 mbar, particularly preferably in the range from 50 mbar to 100 mbar. (Item 13) In step (a2), the oxide ceramic material is further heated and maintained and sintered at a temperature in the range of 1100°C to 1700°C, in particular in the range of 1300°C to 1600°C, preferably in the range of 1400°C to 1550°C, particularly preferably in the range of 1450°C to 1500°C, most preferably at about 1480°C, preferably constant, 8. The method according to any one of the preceding items, wherein the holding is preferably carried out for a period of 1 minute to 60 minutes, more preferably 5 minutes to 30 minutes, even more preferably 10 minutes to 25 minutes, and particularly preferably 15 minutes to 20 minutes. (Item 14) 10. The method according to any one of the preceding items, wherein the heat treatment in step (a2) is carried out at a pressure above 500 mbar, in particular at atmospheric pressure and / or in an oxygen-containing atmosphere, in particular in air, oxygen-enriched air or oxygen. (Item 15) 10. The method according to any one of the preceding items, wherein during step (a2) the oxygen-containing atmosphere, preferably air, oxygen-enriched air or oxygen, is passed through the heating chamber discontinuously or preferably continuously, in particular at a flow rate of 0.1 l / min to 50 l / min, preferably 1 l / min to 10 l / min, particularly preferably 2 l / min to 5 l / min. (Item 16) 10. The method according to any one of the preceding items, wherein the oxidized ceramic material is heated in step (a1) to a temperature that is lower by 0 K to 500 K, in particular by 10 K to 250 K, preferably by 50 K to 150 K, particularly preferably by 75 K to 100 K, compared to the temperature or temperature range at which the oxidized ceramic material is held in step (a2). (Item 17) 10. The method according to any one of the preceding items, wherein the oxide ceramic material is based on zirconia, in particular tetragonal zirconia polycrystalline (TZP). (Item 18) 10. The method according to any one of the preceding items, wherein the zirconium oxide is stabilized with Y2O3, CeO2, MgO and / or CaO, preferably with 2 mol% to 12 mol%, in particular 3 mol% to 6 mol%, of these oxides, based on the amount of zirconium oxide. (Item 19) 10. The method according to any one of the preceding items, wherein the oxide ceramic material is colored and preferably comprises at least two layers, the at least two layers in particular having different colors. (Item 20) 10. The method of any one of the preceding items, wherein the oxide ceramic material comprises at least one color-producing element selected from the group consisting of Fe, Mn, Cr, Pr, Tb, Er, Yb, Ce, Co, Ni, Nd, Cu and Bi, and in particular Fe. (Item 21) 10. The method of any one of the preceding items, wherein the dental restoration is a bridge, inlay, onlay, crown, veneer, facet, or abutment, and preferably comprises two or more parts. (Item 22) 1. Use of an oxide ceramic material for the preparation of a dental restoration, comprising: The oxide ceramic material is (a) subjected to at least one heat treatment; (b) cooled, The cooling step comprises: (b1) a first cooling step having a cooling rate T1; (b2) a second cooling step having a cooling rate T2; Including, The absolute value of the cooling rate T2 is less than the absolute value of the cooling rate T1. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention provides a process for the preparation of a dental restoration, comprising: The oxide ceramic material is (a) subjected to at least one heat treatment; (b) cooled, The cooling step comprises: (b1) a first cooling step with a cooling rate T1; (b2) a second cooling step having a cooling rate T2; For processes in which the absolute value of the cooling rate T2 is less than the absolute value of the cooling rate T1. The process for the preparation of a dental restoration according to the present invention comprises: The oxide ceramic material is (a) subjected to at least one heat treatment; (b) cooled; The cooling step comprises: (b1) a first cooling step with a cooling rate T1; (b2) a second cooling step having a cooling rate T2; The absolute value of the cooling rate T2 is smaller than the absolute value of the cooling rate T1.

[0020] Surprisingly, it has been found that the process according to the invention makes it possible to sinter oxide ceramics very quickly into dental restorations, which have good mechanical properties and extremely high density, while meeting the high aesthetic demands of dental restorations and mimicking the excellent optical properties of natural dental materials.

[0021] The ceramic oxide material used in step (a) is usually a loosely sintered, in particular a pre-sintered, ceramic oxide material. Typically, the ceramic oxide material used has a relative density in the range of 30 to 90%, in particular in the range of 40 to 80%, preferably in the range of 50 to 70%, in each case based on the true density of the ceramic oxide material.

[0022] The relative density is the ratio of the apparent density of the oxide ceramic material to the true density of the oxide ceramic material.

[0023] The apparent density of an oxide ceramic material is determined by weighing the material and geometrically determining its volume. The density is then calculated using the known formula: Density = weight / volume It is calculated according to

[0024] The determination of the true density of the ceramic oxide material is carried out by grinding the ceramic oxide material to a powder with an average particle size of 10 to 30 μm, in particular 20 μm, and determining the density of the powder by hydrometer. The particle size can be determined, for example, by laser diffraction in accordance with ISO 13320 (2009) on a CILAS® Particle Size Analyzer 1064 by Quantachrome GmbH & Co. KG.

[0025] In a preferred embodiment of the process, the cooling comprises: (b1) a first cooling step having a cooling rate T1; (b2) a second cooling step having a cooling rate T2, and (b3) a third cooling step having a cooling rate T3; The absolute value of the cooling rate T2 is smaller than the absolute values ​​of the cooling rates T1 and T3.

[0026] Furthermore, in the present invention, in step (b2), the absolute value of the cooling rate T2 is preferably smaller than the absolute value of the cooling rate T1, and if necessary, is smaller than the absolute value of the cooling rate T3, and the step is carried out at a temperature in the range of 1000 to 1500°C, preferably 1100 to 1400°C, particularly preferably 1200 to 1300°C.

[0027] Also preferably, in step (b2), the absolute value of the cooling rate T2 is less than 60 K / min, preferably less than 50 K / min, more preferably less than 40 K / min, even more preferably less than 25 K / min, even more preferably less than 10 K / min, and most preferably less than 5 K / min. In a particularly preferred embodiment of the process, step (b2) is carried out at a substantially constant temperature, i.e. the cooling rate T2 is about 0 K / min.

[0028] Step (b2) is in particular carried out for a period of from 1 to 20 minutes, preferably from 1 to 10 minutes, more preferably from 2 to 8 minutes, particularly preferably from 3 to 7 minutes, most preferably from 4 to 6 minutes.

[0029] In the present invention, the absolute value of the cooling rate T2 is smaller than the absolute value of the cooling rate T1, and if necessary, smaller than the absolute value of the cooling rate T3. In a preferred embodiment, the absolute value of the cooling rate T1 is at least 40 K / min, preferably at least 50 K / min, particularly preferably at least 60 K / min, in particular in the range from 40 to 200 K / min, preferably from 50 to 100 K / min, particularly preferably from 60 to 80 K / min. In another preferred embodiment, the absolute value of the cooling rate T3 is at least 40 K / min, preferably at least 50 K / min, particularly preferably at least 60 K / min, in particular in the range from 40 to 200 K / min, preferably from 50 to 100 K / min, particularly preferably from 60 to 80 K / min. In particularly preferred embodiments, the absolute values ​​of the cooling rates T1 and T3 are each at least 40 K / min, preferably at least 50 K / min, particularly preferably at least 60 K / min, in particular in the range from 40 to 200 K / min, preferably from 50 to 100 K / min, particularly preferably from 60 to 80 K / min.

[0030] In step (a), the oxidized ceramic material is preferably heated to a temperature in the range of 1100 to 1700° C., preferably 1300 to 1600° C., more preferably 1400 to 1550° C., particularly preferably 1450 to 1500° C., most preferably about 1480° C. Further preferably, the oxidized ceramic material, after carrying out step (a), has a relative density in the range of 90 to 97%, preferably in the range of 93 to 96%, particularly preferably about 95%, in each case based on the true density of the oxidized ceramic material.

[0031] Preferably, the ceramic oxide material is heated in step (a) at a heating rate ranging from 5 to 500 K / min, preferably from 50 to 250 K / min, particularly preferably from 100 to 200 K / min. In a preferred embodiment, the ceramic oxide material is first heated at a heating rate of from 50 to 500 K / min, preferably from 75 to 250 K / min, particularly preferably from 100 to 200 K / min, to a temperature that is 100 to 800 K, preferably from 300 to 700 K, particularly preferably from 500 to 600 K lower than the maximum temperature reached in step (a), and then further heated at a heating rate of from 5 to 200 K / min, preferably from 10 to 100 K / min, particularly preferably from 25 to 50 K / min.

[0032] In step (b), the oxidized ceramic material is preferably cooled to a temperature in the range of from 20 to 1300° C., preferably from 100 to 1250° C., particularly preferably from 1000 to 1200° C. After reaching such a temperature, the oxidized ceramic material may be removed from the heating chamber.

[0033] In a further embodiment, particularly preferred is the process wherein the oxidized ceramic material in step (a) is (a1) subjected to a first heat treatment; (a2) subjected to a second heat treatment; The heat treatment in step (a1) is carried out at a lower pressure than the heat treatment in step (a2).

[0034] Preferably, the heat treatment in step (a1) is carried out at a pressure below 200 mbar, preferably below 100 mbar, particularly preferably below 50 mbar, in particular at a pressure in the range from 0.1 to 200 mbar, preferably in the range from 1 to 150 mbar, particularly preferably in the range from 50 to 100 mbar.

[0035] Before starting to heat the oxidized ceramic material, the pressure can be set to atmospheric pressure. Alternatively, before the pressure defined in step (a) is adjusted, the oxidized ceramic material can first be heated to a temperature above room temperature. This temperature is preferably in the range of 20 to 500°C, in particular in the range of 25 to 100°C.

[0036] In step (a2), the ceramic oxide material is preferably further heated and held, preferably at a constant temperature in the range of 1100 to 1700°C, particularly 1300 to 1600°C, preferably 1400 to 1550°C, more preferably 1450 to 1500°C, and most preferably sintered at about 1480°C. Preferably, the further heating is carried out at a heating rate of 5 to 200 kJ / min, particularly 10 to 100 kJ / min, preferably 25 to 50 kJ / min. Preferably, the holding time is 1 to 60 minutes, particularly 5 to 30 minutes, preferably 10 to 25 minutes, and particularly preferably 15 to 20 minutes. After holding at the corresponding temperature, the ceramic oxide material is generally densely sintered. Thereafter, the ceramic oxide material preferably has a relative density of at least 97%, particularly at least 98%, preferably at least 99%, and most preferably at least 99.5%, in each case based on the true density of the ceramic oxide material.

[0037] Preferably, the heating treatment in step (a2) is carried out at a pressure greater than 500 mbar, in particular at atmospheric pressure.

[0038] Preferably, the heating treatment in step (a2) is carried out in an oxygen-containing atmosphere. In particular, air, oxygen-enriched air and oxygen may be considered as oxygen-containing atmospheres. To establish such an atmosphere, the heating chamber used for the heating treatment is filled with air and / or oxygen. In a preferred embodiment, the oxygen-containing atmosphere, preferably air, oxygen-enriched air or oxygen, is passed discontinuously or preferably continuously through the heating chamber used for the heating treatment during step (2), in particular at a flow rate of 0.1 to 50 l / min, preferably 1 to 10 l / min, particularly preferably 2 to 5 l / min.

[0039] Also preferably, in step (a1) the oxidized ceramic material is heated to a temperature that is 0 to 500 K, in particular 10 to 250 K, preferably 50 to 150 K, more preferably 75 to 100 K lower than the temperature or temperature range at which the oxidized ceramic material is held in step (a2).

[0040] Preferably, the oxide ceramic material obtained by the process according to the invention has a number-average particle size ranging from 1 nm to 1000 nm, in particular from 10 nm to 800 nm, preferably from 100 nm to 600 nm. The number-average particle size can be determined in particular by the line intersection method according to DIN EN 623-3 or ASTM E 112, and the determined value is used for conversion to the true number-average particle size in the three-dimensional microstructure by multiplying by the proportionality constant, which is 1.56, according to M.I. Mendelson, J. Am. Ceram. Soc. 1969, 52(8), 443-446.

[0041] The process according to the present invention is suitable for a variety of ceramic oxide materials. Ceramic oxide materials are ceramic materials based on oxides that are usually highly crystalline and contain, at most, a very small proportion of glass phase. Typical ceramic oxide materials are ZrO2, Al2O3, TiO2, MgO, mixtures thereof, solid solution systems, or composites thereof, particularly ZrO2 / Al2O3 (ZTA), Al2O3 / ZrO2 (ATZ), or ZrO2 / spinel, with the spinel preferably being Sr-spinel, Mg-spinel, La-spinel, and / or Ce-spinel. Ceramic oxide materials based on ZrO2 and / or Al2O3 are suitable for the present invention.

[0042] Particularly suitable are ceramic oxide materials based on zirconium oxide, in particular polycrystalline tetragonal zirconium oxide (TZP), and even more preferred are ceramic oxide materials based on zirconium oxide stabilized with Y2O3, La2O3, CeO2, MgO and / or CaO, preferably in an amount of 2 to 12 mol %, in particular 3 to 6 mol %, of these oxides, based on the zirconium oxide component.

[0043] More preferably, the ceramic oxide material is colored. In the present invention, one or more coloring elements are added to the ceramic oxide material. Examples of suitable coloring elements are Fe, Mn, Cr, Pr, Tb, Er, Yb, Ce, Co, Ni, Nd, Cu, and Bi. Preferably, the ceramic oxide material contains, in particular, Fe. Particularly preferably, the ceramic oxide material contains at least two layers that differ, in particular by their color.

[0044] Within the scope of this application, "color" and "colored" refer to the color, luminosity, and / or translucency of a material.

[0045] "Light transmissivity" is the light transmittance of a material, body, or layer, e.g., the ratio of transmitted light intensity to incident light intensity.

[0046] Colors are characterized by color coordinates L*, a*, and b* in the L*a*b* color space commonly used in the dental industry, or by color codes.

[0047] In the L*a*b color space, the L* value represents the brightness of a color, with values ​​ranging from 0 (black) to 100 (white), the a* value represents the green or red component of the color, with negative values ​​representing green and positive values ​​representing red, and the b* value represents the blue or yellow component of the color, with negative values ​​representing blue and positive values ​​representing yellow. Color differences can be expressed in the L*a*b* color space by the ΔE* value, which is given by the following formula: ΔE*=√((ΔL*) 2 +(Δa*) 2 +(Δb*) 2 ) It is calculated as follows.

[0048] Examples of color codes commonly used in the dental industry are Vitapan classical® and Vita 3D Master® from VITA Zahnfabrik H. Rauter GmbH & Co. KG, and Chromascop® from Ivoclar Vivadent AG. Translucency can be characterized by a contrast value CR, where 0% means completely transparent and 100% means completely opaque.

[0049] Typically, the color coordinates L*, a* and b* are determined according to DIN 5033 and DIN 6174, and the transmittance according to BS 5612. The corresponding measurements can be carried out, in particular, with a spectrophotometer of the type CM-3700d (Konica-Minolta). For this purpose, a specimen is used for the measurement, which is wet-ground on both sides with diamond particles (particle size 15 to 20 μm) to obtain a final specimen thickness of 2.00±0.025 mm.

[0050] Preferably, the mono- or polychromatic dental restorations obtained according to the invention belong to the range of natural tooth colors. Particularly preferably, the dental restorations obtained according to the invention have an L* value in the range of 50 to 100, in particular in the range of 80 to 97, an a* value in the range of -10 to 10, in particular in the range of -1 to 5, an ab* value in the range of 0 to 50, in particular in the range of 1 to 20, and / or a CR value in the range of 50 to 100%, in particular in the range of 75 to 99%.

[0051] The process according to the invention is particularly suitable for the preparation of dental restorations, particularly preferably bridges, inlays, onlays, crowns, veneers, facets and abutments. The process according to the invention is particularly suitable for the preparation of dental restorations, in particular bridges, which comprise two or more parts.

[0052] The present invention further relates to the use of an oxide ceramic material for the preparation of a dental restoration, the oxide ceramic material comprising: (a) subjected to at least one heat treatment; (b) cooled, The cooling step comprises: (b1) a first cooling step having a cooling rate T1, and (b2) A second cooling step with a cooling rate of T2 and the absolute value of the cooling rate T2 is smaller than the absolute value of the cooling rate T1.

[0053] A preferred embodiment of the use has already been described in the process according to the invention.

[0054] The present invention will now be described in detail with reference to the following examples. [Example]

[0055] Examples 1A to 1F Test specimens with a diameter of 24 mm and a height of 2.9 mm were fabricated from a commercially available zirconia-based oxide ceramic material containing 9.23 wt.% Y2O3, 0.045 wt.% Al2O3, and 0.25 wt.% Fe2O3 (Zpex Smile Yellow from Tosoh Co.), and were uniaxially pressed at a pressure of 150 MPa and subjected to heat treatment at 1000 °C for 2 h.

[0056] The test specimens were sintered in a sintering furnace with a MoSi heating element. To this end, the test specimens were placed in the heating chamber of the sintering furnace at room temperature, the heating chamber was closed, and a partial vacuum with a final pressure of about 50 to 100 mbar was established in the heating chamber. The test specimens were heated to a temperature of about 900°C at a heating rate of about 130 K / min, then to a temperature of about 1220°C at a heating rate of about 50 K / min, and further to a temperature of about 1400°C at a heating rate of about 10 K / min. After reaching this temperature, the heating chamber was flushed with fresh air. Then, while continuously passing fresh air at a flow rate of about 2.2 L / min, the test specimens were further heated to a temperature of 1480°C at a heating rate of about 10 K / min and held at this temperature for about 17 minutes. The test specimens were then cooled to a temperature T at a cooling rate of about 70 K / min, held at this temperature for a period of t minutes, and further cooled to a temperature of about 1200°C at a cooling rate of about 70 K / min according to Table 1. The heating chamber was then opened. The total duration of the sintering process was 64 to 66 minutes.

[0057] Example 1G (Comparative) Similar to Example 1A, but the specimen was cooled continuously without interruption from 1480° C. to 1200° C. at a cooling rate of about 70 K / min. The total duration of the sintering process was about 60 min.

[0058] Example 1H (Comparative) Similar to Example 1A, but using a slower sintering process. For this purpose, the test specimens were heated to a temperature of about 900°C at a heating rate of about 10 K / min, held at this temperature for 30 minutes, and then heated to about 1500°C at a heating rate of about 3 K / min and held at this temperature for about 120 minutes. The test specimens were then cooled to 900°C at a cooling rate of about 10 K / min and further cooled to 300°C at a cooling rate of about 8 K / min. The heating chamber was then opened. The total duration of the sintering process was about 575 minutes.

[0059] The CR values ​​and color coordinates of the oxide ceramic materials obtained in Examples 1A-H are shown in Table 1. Examples 1A to 1F according to the invention exhibit significantly higher a* and b* values ​​than Example 1G, which was obtained using a fast sintering process, with the a* values ​​consistently in the positive range. As a result, these examples are better suited to mimicking the color characteristics of natural dental materials. Similarly, the sintering process used in Examples 1A to 1F according to the invention is only about one-tenth the duration of the slow sintering process of Example 1H. [Table 1] * (comparison)

Claims

1. 1. A method for preparing a dental restoration, comprising: The oxide ceramic material is (a) subjected to at least one heat treatment; (b) cooled; The cooling step comprises: (b1) a first cooling step having a cooling rate T1; (b2) a second cooling step having a cooling rate T2; Including, The absolute value of the cooling rate T2 is less than the absolute value of the cooling rate T1.

2. The cooling step comprises: (b1) a first cooling step having a cooling rate T1; (b2) a second cooling step having a cooling rate T2; (b3) a third cooling step having a cooling rate T3; Including, The method of claim 1 , wherein the absolute value of the cooling rate T2 is less than the absolute values of the cooling rate T1 and the cooling rate T3.

3. 2. The method of claim 1, wherein step (b2) is carried out at a temperature in the range of 1000°C to 1500°C, preferably in the range of 1100°C to 1400°C, more preferably in the range of 1200°C to 1300°C.

4. 2. The method according to claim 1, wherein in step (b2) the absolute value of the cooling rate T2 is less than 60 K / min, preferably less than 50 K / min, more preferably less than 40 K / min, even more preferably less than 25 K / min, even more preferably less than 10 K / min and most preferably less than 5 K / min.

5. 10. The method of claim 1, wherein step (b2) is carried out at a substantially constant temperature.

6. 2. The method of claim 1, wherein (b2) is carried out for a period of 1 to 20 minutes, preferably 1 to 10 minutes, more preferably 2 to 8 minutes, particularly preferably 3 to 7 minutes, and most preferably 4 to 6 minutes.

7. 2. The method according to claim 1, wherein the absolute value of the cooling rate T1 and / or the absolute value of the cooling rate T3 is at least 40 K / min, preferably at least 50 K / min, particularly preferably at least 60 K / min, in particular in the range from 40 K / min to 200 K / min, preferably from 50 K / min to 100 K / min, particularly preferably from 60 K / min to 80 K / min.

8. 2. The method of claim 1, wherein the oxide ceramic material is heated in step (a) to a temperature in the range of from 1100°C to 1700°C, preferably in the range of from 1300°C to 1600°C, more preferably in the range of from 1400°C to 1550°C, particularly preferably in the range of from 1450°C to 1500°C, and most preferably at about 1480°C.

9. 2. The method of claim 1, wherein the oxide ceramic material is heated in step (a) at a heating rate in the range of 5 K / min to 500 K / min, preferably in the range of 50 K / min to 250 K / min, more preferably in the range of 100 K / min to 200 K / min.

10. 2. The method according to claim 1, wherein the oxide ceramic material is cooled in step (b) to a temperature in the range of from 20°C to 1300°C, preferably in the range of from 100°C to 1250°C, particularly preferably in the range of from 1000°C to 1200°C.

11. The oxide ceramic material in step (a) is (a1) subjected to a first heat treatment; (a2) subjected to a second heat treatment; 11. The method of claim 1, wherein the heat treatment in step (a1) is carried out at a lower pressure than the heat treatment in step (a2).

12. 12. The method according to claim 11, wherein the heat treatment in step (a1) is carried out at a pressure of less than 200 mbar, preferably less than 100 mbar, particularly preferably less than 50 mbar, in particular in the range from 0.1 mbar to 200 mbar, preferably in the range from 1 mbar to 150 mbar, particularly preferably in the range from 50 mbar to 100 mbar.

13. In step (a2), the oxide ceramic material is further heated and maintained and sintered at a temperature in the range of 1100°C to 1700°C, in particular in the range of 1300°C to 1600°C, preferably in the range of 1400°C to 1550°C, particularly preferably in the range of 1450°C to 1500°C, most preferably at about 1480°C, preferably constant, 12. The method according to claim 11, wherein the holding is preferably carried out for 1 to 60 minutes, more preferably 5 to 30 minutes, even more preferably 10 to 25 minutes, and particularly preferably 15 to 20 minutes.

14. 12. The method according to claim 11, wherein the heat treatment in step (a2) is carried out at a pressure above 500 mbar, in particular at atmospheric pressure and / or in an oxygen-containing atmosphere, in particular in air, oxygen-enriched air or oxygen.

15. 15. The method according to claim 14, wherein during step (a2) the oxygen-containing atmosphere, preferably air, oxygen-enriched air or oxygen, is passed discontinuously or preferably continuously through the heating chamber, in particular at a flow rate of 0.1 l / min to 50 l / min, preferably 1 l / min to 10 l / min, particularly preferably 2 l / min to 5 l / min.

16. 12. The method according to claim 11, wherein the oxidized ceramic material is heated in step (a1) to a temperature that is lower by 0 K to 500 K, in particular by 10 K to 250 K, preferably by 50 K to 150 K, particularly preferably by 75 K to 100 K, than the temperature or temperature range at which the oxidized ceramic material is held in step (a2).

17. 11. The method according to any one of claims 1 to 10, wherein the oxide ceramic material is based on zirconia, in particular tetragonal zirconia polycrystal (TZP).

18. The zirconium oxide is Y ２ O ３ , CeO ２ 18. The method according to claim 17, wherein the zirconium oxide is stabilized with MgO and / or CaO, preferably with 2 mol % to 12 mol %, in particular 3 mol % to 6 mol % of these oxides, based on the amount of zirconium oxide.

19. 11. The method according to any one of claims 1 to 10, wherein the oxide ceramic material is colored and preferably comprises at least two layers, said at least two layers having in particular different colors.

20. 11. The method according to any one of claims 1 to 10, wherein the oxide ceramic material comprises at least one chromophoric element selected from the group consisting of Fe, Mn, Cr, Pr, Tb, Er, Yb, Ce, Co, Ni, Nd, Cu and Bi, in particular Fe.

21. 11. The method of any one of claims 1 to 10, wherein the dental restoration is a bridge, inlay, onlay, crown, veneer, facet, or abutment, and preferably comprises two or more parts.

22. 1. Use of an oxide ceramic material for the preparation of a dental restoration, comprising: The oxide ceramic material is (a) subjected to at least one heat treatment; (b) cooled; The cooling step comprises: (b1) a first cooling step having a cooling rate T1; (b2) a second cooling step having a cooling rate T2; Including, The absolute value of the cooling rate T2 is smaller than the absolute value of the cooling rate T1.