Tooth ceramic doped with luminescent material

Abstract

The invention relates to a tooth ceramic based on silicate or zirconium dioxide as a matrix. According to the invention, the tooth ceramic is characterized by a mixture of a cerium-doped LuAG, cerium-doped YAG, and / or a cerium-doped LuYAG garnet which has the following chemical composition: Lu3-aCeaAl5-bGabO12, in which a has a value of 0.003 to 0.075 and b has a value of 0 to 3; the YAG garnet has the following chemical composition: Y3-aCeaAl5-bGabO12, in which a has a value of 0.003 to 0.075 and b has a value of 1 to 3.5; and the LuYAG garnet has the following chemical composition: Y3-a-cLucCeaAl5-bGabO12, in which a has a value of 0.003 to 0.075, b has a value of 1 / 3(3-a-c) to 3.25, and c has a value which is greater than 0.

Description

[0001] Dental ceramics doped with phosphor

[0002] The invention relates to a dental ceramic based on silicate or zirconium dioxide.

[0003] To fabricate a dental prosthesis, whether an inlay, crown, bridge, or implant crown, it is common practice to model the tooth or group of teeth to be replaced manually or with computer assistance in a laboratory and then fabricate the prosthesis from a dental ceramic. The dental ceramic chosen for the prosthesis should, if possible, resemble the appearance of the adjacent natural teeth in the patient's mouth. The appearance of the dental ceramic is subject to several parameters.These parameters include the color in natural light, a possible color gradient from the neck of the tooth to the crown, translucency in the sense of pure light transmission, transparency in the sense of a clear appearance, such as clear glass, colored or white inclusions, such as fine, whitish particles that scatter the light, and finally, reflection in the sense of a wavelength-dependent reflection of the light, as well as the fluorescent behavior of the ceramic. Finally, the gloss and surface roughness of the ceramic also influence the optical appearance and wettability of the dental ceramic. Therefore, the choice of dental ceramic is not just about the color.

[0004] Today, there are well-known dental ceramics available as tooth replacement materials, made from zirconium dioxide, aluminosilicates, or lutetium disilicate (the latter two referred to below as "silicate base"). These inorganic dental ceramics, thanks to appropriate pigmentation, exhibit a color that closely resembles that of a human tooth when illuminated with natural light. To adjust the material properties of dental ceramics as tooth replacement materials, auxiliary substances or additives are added to the dental ceramics used for this purpose. The material properties that can be adjusted in this way affect not only the color, but also the hardness, flexibility, chemical resistance, and abrasiveness of the dental ceramic.

[0005] To produce dental ceramics, the manufacturer delivers ready-made raw material mixtures to a dental laboratory for firing / sintering. The dental laboratory then sinters the dental ceramics in molds created specifically for each patient, strictly adhering to the sintering temperature and sintering time specified by the manufacturer. Typically, fixed temperature programs are implemented as a temperature gradient over time. Depending on the type of dental ceramic, it may also be necessary to perform sintering in a protective gas atmosphere, alternatively in a vacuum, or at least at a pressure significantly lower than atmospheric pressure. Particular attention must be paid to the luminescence behavior of the dental ceramics when manufacturing dental prostheses. For the purposes of this application, "luminescence" refers to the interplay of fluorescence, reflection, and absorption.

[0006] Previously known dental ceramics have the property of displaying a luminescence characteristic mimicking that of a natural tooth in typical black light scenarios. Typical black light scenarios in which a patient may be exposed after receiving their dentures have been discotheques and nightclubs, where black light tubes generate the typical ultraviolet radiation from a specially prepared fluorescent tube. Besides these lighting effects, there are very few other scenarios in which black light from the well-known, dark violet glowing black light tubes is used. The aforementioned black light tubes exhibit a radiation maximum at a wavelength of λ = 365 nm. Further light in the visible range is largely filtered out by the dark violet coloration of the black light tube's glass tube. If the ceramics considered as denture materials are alkali aluminosilicates (e.g.If the yttrium orthosilicates are made of (K,Li)AISi3Os, (K,Li)AISi2Oe, NaAISisOs) or lutetium disilicate (Lu2Si2Oz), all of which are collectively referred to as "silicate-based," they are mixed with cerium-doped or cerium-terbium co-doped yttrium orthosilicate, Y2SiC>5:Ce,(Tb), in quantities of 0.1 to 2 mass% to simulate the luminescence under black light from state-of-the-art black light tubes. Due to the fluorescence of cerium upon excitation with UV light with a wavelength of λ = 365 nm, a dental ceramic is obtained that, when used as a dental prosthesis in a black light scenario, exhibits luminescence similar to that of a natural tooth. A natural tooth exhibits a turquoise to bluish color due to its fluorescence under black light. By additionally incorporating terbium, the emission color of the dental ceramic can be slightly shifted and thus adapted to the patient's individual tooth color.

[0007] A bismuth compound is added to ceramics based on zirconium dioxide (ZrO2; zirconia) during production. Bismuth's fluorescence upon excitation with UV light at a wavelength of 365 nm results in a dental ceramic that, when used as a dental prosthesis, exhibits luminescence similar to that of a natural tooth in a previously described black light scenario.

[0008] The replacement of fluorescent tubes, now considered obsolete lighting technology, with light-emitting diodes (LEDs), has changed the typical light color and excitation wavelength of "black light" lamps. Instead of a radiation maximum of X = 365 nm, typical LED lamps used to create a fluorescence effect have a radiation maximum shifted to longer wavelengths, from 395 nm to 415 nm. Such LED lamps, also called black light LEDs, are not only used in nightclubs but have a wide variety of applications. Some such applications include: illuminating products in a sales area to give the products a particularly high-contrast surface, illuminating fresh meat to give the meat a special, intense color, or even use in flower shops to make the flowers appear particularly colorful.It is also common practice in supermarkets to illuminate the food section with cold light, which also contains a fluorescent component from black light LEDs. The non-food section, on the other hand, is illuminated with warm light that does not contain fluorescent components. Other scenarios in which black light LEDs are used include cinema lighting and, increasingly, the lighting of restrooms in public buildings and subways. The blue to violet lighting is intended to discourage drug abuse with injection drugs, because the blue color of human veins is very difficult to detect in blue light under white skin. The latter, or "purple LEDs," are also used wherever fluorescence plays a role, for example, as an optical brightener.

[0009] When a patient's dentures made with conventional dental ceramics are illuminated with the light of today's widely used black light LEDs, a difference in the fluorescence behavior of the natural tooth compared to the fluorescence behavior of the dentures becomes apparent. At the 2021 meeting of the International Association for Dental Research, an oral presentation on Wednesday, July 21, 2021, entitled "Dental Materials: Additive Manufacturing of Ceramics," stated that to mimic the visual appearance of natural teeth, dental materials require adequate fluorescence. The presentation further stated that colored zirconia materials [note: this refers to ceramics based on zirconium dioxide (ZrO2) and not zirconium (Zr[SiO4])] do not exhibit this property.The tested materials presented in the lecture have different wavelengths for their excitation maxima: Lava Esthetic Zirconia at X = 310 nm, human dentin at X = 340 nm, e.max® Press at X = 360 nm, e.max® Glaze Paste Flu at X = 350 nm and Lava Ultimate at X = 320 nm and 380 nm. The fluorescence intensities of the presented materials differ from each other and depend on the light source, particularly in the case of Lava Esthetic, where a 368 nm LED produces approximately one-third of the fluorescence intensity achieved with daylight.

[0010] German patent application DE 10 2017 104 166 A1 discloses a process for producing high-density, low-defect sintered components and a corresponding ceramic component. The process disclosed therein encompasses the use of these high-density, low-defect ceramics, among other things, in dentistry. This document lists various ceramic types without specifying their properties. One of the ceramics is of the type AsB2[RO4]3, where B and R can also be identical. With identical B and R, the molecular formula is simplified to A3B5O12. These ceramics could also be cerium-doped. A cerium-doped LuAG garnet is mentioned as an example.

[0011] US patent application US 2021-0102116 A1 discloses zirconium oxide sintered bodies with a fluorescent agent. The aim of the invention disclosed therein is to provide a dental ceramic with a fluorescent agent that excels in both translucency and strength. The fluorescence issue associated with new LEDs with a different blue light than that of conventional fluorescent tubes is not even mentioned. YAG:Cerium is only mentioned as an example as the fluorescent agent.

[0012] US patent application US 2002-0017021 A1 discloses zirconia ceramics doped with 4.5 to 9 mol% yttrium. Yttrium is added to the zirconia base material as salts. The addition of garnet structures is not disclosed there.

[0013] In extreme cases, the denture may appear dark and dull, giving the impression of a dead and internally rotten tooth. While this is only a cosmetic flaw, this unnatural appearance of the denture can be very disturbing and completely unacceptable to the patient, because the seemingly dead and internally rotten tooth creates an unattractive and pathological image of the patient.

[0014] It is therefore desirable to modify known dental ceramics so that they closely resemble the appearance of a natural tooth surface even when illuminated with an LED-typical wavelength of 395 nm < X < 415 nm.

[0015] An obvious solution would be to add pigments as phosphors to the dental ceramic as additives that can be excited in the light wavelength range between X = 395 nm and X = 415 nm. The pigment should only slightly alter the body color of the dental ceramic in natural light. Furthermore, the translucency of the existing dental ceramic should not be altered, and during firing / sintering, no microcrystalline domains should be formed in the dental ceramic on such a scale that they would give the dental ceramic, as a dental restoration, the appearance of what is colloquially known as "blind" glass, thus ensuring that the desired dental ceramic does not exhibit unwanted cloudiness. Unlike crystals with a regular lattice structure and glasses as solidified liquids, ceramics are solids that contain crystalline domains.When microcrystalline domains form, boundary layers can form that are colored and / or opaque, or the refractive index can differ significantly from the rest of the material. Both the formation of interfaces and the difference in refractive index can lead to optical defects that create the clouding effect. Since the enamel of natural teeth is crystal-clear to a certain degree of inherent clouding, the effect of pigmentation should not affect the existing clouding in a way that is visible to humans.

[0016] Europium(II) compounds are known as phosphors in the field of phosphors for LEDs, which can be excited at a wavelength of X > 390 nm. Such Eu(II) phosphors can emit over a wide emission range depending on the host lattice. By doping the Eu(II) phosphors with further ions of the rare earth metals, the perceived color can also be adjusted quite well as a color location in the CIE standard valence diagram as a color map. Examples of this are BaSi2N2C>2:Eu 2+ , (Ba,Sr)2[SiC>4]:Eu 2+ , Ba3MgSi20s:Eu 2+ and SreB[PO4]5:Eu 2+ However, when these color-adjustable phosphors were used as additives in a known dental ceramic used as a tooth replacement material, it was found that these phosphors lost their fluorescent properties upon sintering into the aforementioned dental ceramics. It is assumed in this application that oxidation of the europium from Eu(II) to Eu(III) occurs during sintering.

[0017] When using barium silicon oxide nitride (BaSi2N2O2:Eu 2+ ) as a phosphor for dental ceramics used as a tooth substitute, it was further observed that the sintered ceramic exhibits a much too strong milky turbidity, giving the ceramic the appearance of "blind" glass. Known europium^ ^ compounds thus do not survive the sintering process used to produce the ceramic as a tooth substitute, and the Eu(II)-based phosphors become spectroscopically inactive in the compounds tested here.

[0018] Of all the known phosphors used in white light LEDs and which could in principle be considered as phosphors for use in dental ceramics, it is also known that they have a very intense body colour and are therefore apparently unsuitable for use in white dentures.

[0019] The object of the invention is therefore to provide a dental ceramic as a tooth replacement material that exhibits the appearance of a natural tooth even when stimulated with light in the range of X = 395 nm to light with a wavelength of X = 415 nm. The comparison "like a natural tooth" is to be made based on average human color perception and average human color discrimination. This color perception and color discrimination were empirically determined by David Lewis McAdams in 1942 through studies of the CIE standard valence diagram and quantified using the so-called McAdams ellipses as entries in the CIE standard valence diagram.

[0020] The object underlying the invention is achieved by a ceramic having the features of claim 1. Further advantageous embodiments are specified in the subclaims to claim 1.

[0021] The dental ceramics according to the invention contain special phosphors, namely an admixture of a cerium-doped LuAG, cerium-doped YAG and / or a cerium-doped LuYAG garnet, wherein the LuAG garnet assumes the following chemical composition: Lu3-aCe a Al5-bGabOi2, where a has a value of 0.003 to 0.075 and b has a value of 0 to 3, the YAG garnet has the following chemical composition: Y3- a Ce a Al5-bGabOi2, where a takes a value of 0.003 to 0.075 and b a value of 1 to 3.5, and the LuYAG garnet takes the following chemical composition: Y3- a-c Lu c - Ce a As-bGabOi2, where a has a value of 0.003 to 0.075, b has a value of 1 / s(3- ac) to 3.25 and c assumes a value greater than 0. These garnets are known as cerium-doped lutetium and / or yttrium-aluminum garnets (LuAG:Ce, YAG:Ce, Lu / YAG:Ce) and are available on the market. The garnet contained in the dental ceramic can be present as pure cerium-doped yttrium garnet, as a mixture of pure cerium-doped yttrium garnet and pure cerium-doped lutetium garnet, or as pure cerium-doped lutetium garnet. It is also possible to use cerium-doped mixed garnets in which yttrium (Y) and lutetium (Lu) are present in any ratio. In addition, other rare earth metal ions, such as Gd 3+are incorporated into the garnet. While these do not have an advantageous effect within the meaning of the invention, they do not preclude its implementation. Garnets as phosphors have the property of exhibiting an emission in the perceived greenish to yellow range upon excitation, which is colloquially referred to as "neon green" or "neon yellow." The emission intensity upon excitation with light with a wavelength of 400 nm is only approximately 10% to 15% of the emission intensity maximum. This group of substances initially appears unsuitable for simulating the natural luminescence behavior of a natural tooth due to the color of the emission and the weak emission upon excitation with light in the wavelength range of 400 nm. A natural tooth fluoresces with a blue-green to bluish color, not yellowish.The addition of a phosphor that fluoresces in the perceived greenish to yellow range would, at first glance, seem unsuitable for solving the problem of the invention. Surprisingly, however, it has been shown that this group of substances, when sintered with a silicate-based or zirconia-based dental ceramic raw material powder as a dental prosthetic, results in a luminescence behavior that is very similar to that of a natural tooth. Indeed, it is so similar that the color perception of an average observer can no longer distinguish the luminescence color of the inventive ceramic as a dental prosthetic from the luminescence color of a natural tooth.

[0022] As an example of a ceramic according to the invention as a dental prosthetic material, a commercially available raw material (dental ceramic raw material powder) for sintering the ceramic (VITA VMK Master) is mixed with a garnet as a phosphor with a composition according to the following table. The commercially available dental ceramic in the form of a powder to be sintered is listed in the table as the matrix. This mixture of the dental ceramic powder for sintering and the phosphors listed below was sintered under dynamic vacuum in a furnace (manufacturer: Vita Zahnfabrik H. Rauter GmbH & Co. KG, type: Vita VMK Master (silicate-based). Sintering program: started at 500°C with 25% furnace closure, held for 6 minutes, heated to 950°C in 14 minutes with 100% furnace closure under vacuum, held for 3 minutes, then allowed to cool to 500°C with 75% furnace closure, finally removed and allowed to cool to room temperature).A concentration of 0.5 mass% phosphor was used based on the total mass. The following dental ceramics were obtained:

[0023] Color location Color location

[0024] Emission phosphor ceramic when excited with when excited with Composition light of wavelength *Composition light of wavelength

[0025] (Y / Lu)3-aCe a Al5-bGabOi2 ​​= 395 nm stzunq ceramic X = 395 nm

[0026] 'Mixing ratio in mass%

[0027] The surprising result is that the yellow-green to yellowish fluorescent garnets, when sintered with the commercially available raw material for dental ceramics, tend to exhibit a luminescence that can best be described as bluish. The unexcited dental ceramic exhibits a color in daylight that is at most insignificantly different from that of a dental ceramic without the aforementioned garnets as phosphors. The translucency is unimpaired. The surface of the dental ceramic exhibits a clear layer. A similar turbidity can be seen as in dental ceramics manufactured using state-of-the-art technology. Since the turbidity of the dental ceramic cannot be quantified using a single parameter, as with a nephelometric measurement, the only possible method is an optical comparison with reference dental ceramics, as shown in Figure 9.Testing the fluorescent color of sintered dental ceramics with garnets as phosphors shows a mimicking of fluorescence to a degree comparable to the color discrimination ability of an average person, as characterized by McAdams. The fluorescence of natural teeth presumably varies with the degree of fluoridation of the teeth through fluoride treatment. Depending on the age and duration of fluoride treatment, the fluorescence is more or less pronounced. In teeth that were exposed to higher levels of fluoridation during preschool age, the fluorescence is naturally more pronounced than in adult teeth that were fluoridated through dental treatment at a later age, when the teeth were already fully grown and their enamel had already begun to show discoloration.The tooth color of teeth demineralized by soft drinks containing sugar and phosphoric acid, colloquially known as "chalky teeth," can also be imitated with the dental ceramics presented here, which contain the aforementioned luminescent substances.

[0028] Different tooth luminescences can be achieved in two ways: firstly, by varying the concentration of garnet as a phosphor in the dental ceramic matrix, and secondly, by switching to a different type of phosphor. Mixtures of dental ceramics with the above-mentioned garnets as phosphors have been found to be comparable to natural teeth in terms of fluorescence, with the following concentrations of garnets as phosphors: between 0.2 and 3 mass%, preferably between 0.3 and 1.0 mass%, particularly preferably 0.5 mass% with a tolerance of 0.1 mass%.

[0029] Good results can be achieved with a sintering temperature when sintering the dental ceramic of 750°C to 1,000°C, preferably between 850°C and 980°C, particularly preferably 950°C with a tolerance of 5°C over a period of 2 min to 120 min, preferably between 10 min and 60 min with a tolerance of ±1 min.

[0030] It is advantageous if the sintering of the dental ceramic takes place in a protective gas atmosphere of nitrogen and / or argon to avoid oxidation of the garnets as phosphors. Another alternative is sintering under a dynamic vacuum, or at least a pressure below 20 hPa. To avoid the formation of undesirably large microcrystalline phases of phosphor in the dental ceramic during sintering, or microcrystalline phases that become visible due to boundary layer formation, it is advantageous if the grain size of the garnet as phosphor in the raw material mixture is between 1 pm and 20 pm, preferably between 4 pm and 8 pm with a tolerance of 1 pm.

[0031] In the dental ceramic according to the invention, the gallium in the garnet can be partially or completely replaced by scandium. This does not significantly change the color coordinate. The advantage of gallium is that it is significantly cheaper to purchase on the market than scandium.

[0032] The invention is explained in more detail with reference to the following figures. They show:

[0033] Fig. 1 a sketch of a tooth front in different lighting scenarios,

[0034] Fig. 2 a CIE diagram according to CIE 1931 with drawn McAdams ellipses that delimit places of equal color perception,

[0035] Fig. 3 a CIE diagram according to CIE 1931 with marked color locations of dental ceramics, which according to the invention have various garnets as illuminants, when excited with light with a wavelength of 395 nm,

[0036] Fig. 4 is an enlarged section of the diagram in Fig. 3,

[0037] Fig. 5 is a CIE diagram according to CIE 1931 with color coordinates of dental ceramics which, according to the invention, comprise various garnets as illuminants, when excited with light having a wavelength of 405 nm,

[0038] Fig. 6 is an enlarged section of the diagram in Fig. 5,

[0039] Fig. 7 a CIE diagram according to CIE 1931 with marked color locations of dental ceramics, which according to the invention have various garnets as illuminants, when excited with light with a wavelength of 415 nm,

[0040] Fig. 8 is an enlarged section of the diagram in Fig. 7,

[0041] Fig. 9 a turbidity experiment.

[0042] Figure 1 shows a sketch of a tooth anterior with a state-of-the-art denture at position 2-1 (according to the dental quadrant scheme "quadrant position") under different lighting scenarios. The tooth anterior in the upper left corner shows the appearance of the teeth when illuminated with natural or artificial daylight. The human eye cannot discern any difference between the two upper incisors 1-1 and 2-1. In the upper right corner, the same tooth anterior is shown illuminated with LED light in the visual range. State-of-the-art dental ceramics, such as those present at position 2-1, are indistinguishable from the appearance of a natural tooth at position 1-1 using human color discrimination, even with LED light in the visual range. In the lower left corner, the same tooth anterior is sketched when illuminated with black light from black light tubes.Black light tubes exhibit a radiation maximum at a wavelength of X = 365 nm and, above this, a dark violet light in the visual range. State-of-the-art dental ceramics feature fluorescent pigments that can be excited with light of a wavelength of X = 365 nm, making the dental ceramic resemble a natural tooth, including the fluorescence of a natural tooth. The lower right corner shows an exaggerated illustration of the effect of illuminating the same tooth anterior surface with a black light LED. Depending on the design, black light LEDs exhibit a radiation maximum at a light wavelength of X = 395 to X = 415 nm. State-of-the-art dental ceramics do not fluoresce in precisely this wavelength range, or at least not in the same way as a natural tooth. This results in the denture in position 2-1 appearing undesirably darker than the neighboring teeth.It is precisely this effect that is to be avoided with the dental ceramic doped according to the invention.

[0043] Figure 2 shows a CIE diagram according to CIE 1931 with drawn McAdams ellipses. The McAdams ellipses delimit the color locations in the CIE standard color intensity diagram of equal color perception. For the structure of the CIE diagram, reference is made to the relevant literature. The McAdams ellipses drawn in the CIE diagram are of different sizes at different color locations. This does not necessarily mean that a larger McAdams ellipse indicates a color location with less human color differentiation power, because the larger McAdams ellipses are located in the green region, where the wavelength density of the plot in the CIE standard color intensity diagram is low. Conversely, smaller McAdams ellipses are located in the dark blue and violet regions. There, the wavelength density of the plot in the CIE standard color intensity diagram is relatively high, which is reflected in smaller McAdams ellipses.The quality of human color differentiation can be more clearly illustrated by reformed CIE diagrams that are mathematically distorted, such as the CIE UCS diagram from 1960 or the CIE LUV diagram from 1976. The white point W is located approximately in the middle, from which any boundaries between dominant colors can be drawn. The color gradient within the CIE standard color intensity diagram is continuous. Nevertheless, human color perception suggests the course of the dashed lines that extend radially from the white point as the possible boundary between the colors separated from one another by the dashed lines. The CIE standard color intensity diagram from 1931 shown here is introduced here to demonstrate the color loci of the emissions and the dental ceramics doped according to the invention in the next figures.

[0044] Figure 3 shows a CIE diagram according to CIE 1931 with the color coordinates of dental ceramics plotted. According to the invention, the dental ceramics comprise various garnets as illuminants; this is when excited with light having a wavelength of 395 nm. The CIE standard valence diagram in Figure 3 is slightly compressed vertically compared to the representation in Figure 2. However, the CIE diagrams are identical in content. Instead of the McAdams ellipses, nine lines for nine different phosphors are plotted in this CIE standard valence diagram. These nine phosphors are characterized as follows:

[0045] Color location Color location

[0046] Emission phosphor ceramic when excited with when excited with Composition light of wavelength *Composition light of wavelength

[0047] (Y / Lu)3-aCe a Al5-bGabOi2:Ce X = 395 nm and ceramic X = 395 nm

[0048] Matrix % /

[0049] No. Y / Lu ab CIE-X CIE-Y Phosphor % CIE-X CIE-Y

[0050] 1 Lu 0.024 2.625 0.1931 0.4219 99.5% / 0.5% 0.1838 0.1203

[0051] 2 Lu 0.045 2.5 0.2125 0.4613 99.5% / 0.5% 0.1897 0.1659

[0052] 3 Lu 0.045 1 .75 0.2425 0.5137 99.5% / 0.5% 0.1903 0.1198

[0053] 4 Lu 0.045 1 .25 0.2712 0.5412 99.5% / 0.5% 0.1888 0.0926

[0054] 5 Lu 0.063 1 0.2945 0.5593 99.5% / 0.5% 0.1883 0.0795

[0055] 6 Lu 0.075 1 0.3157 0.5556 99.5% / 0.5% 0.1982 0.1180

[0056] 7 Y 0.066 2.5 0.32548 0.56463 ​​99.5% / 0.5% 0.2319 0.2345

[0057] 8 Lu 0.03 0 0.3260 0.5147 99.5% / 0.5% 0.1868 0.0620

[0058] 9 Y 0.09 0 0.45334 0.47855 99.5% / 0.5% 0.2030 0.0807

[0059] 'Mixing ratio in mass%

[0060] In the CIE standard valence diagram 1931 shown here, the color coordinates of the pure emission of the phosphors listed in the table above when excited with light of wavelength X = 395 nm are shown as small black squares directly next to the reference numerals 1 to 9. The emission of all phosphors 1 to 9 has a greenish-yellow color, which is popularly associated with fluorescent color and is also often referred to as "neon yellow." This color differs significantly from the color of fluorescent natural teeth. Natural teeth fluoresce in the turquoise to bluish, and depending on perception, even bluish-violet color range. However, the color of the pure emission is not decisive. Rather, the human-perceived mixed color of the emission and the reflected light is more significant.For this purpose, lines 1 to 9 branch off from the color coordinates of the phosphors, leading to the next color coordinate, namely the color coordinate of the mixed light from reflected excitation light and emission light. The color coordinate of this mixed light depends on the emission intensity of the phosphor and also on that of the excitation light reflected after the excitation light has been absorbed by the phosphor. Both emission intensity and absorption are material constants. The first two points, namely the color coordinate of the emission and the color coordinate of the mixed light from emission and reflected excitation light, refer to the pure phosphor. In order to investigate the actual suitability as a dopant for a dental ceramic, the respective phosphor must be introduced into the dental ceramic and sintered with it. The phosphor can change during sintering.It is possible that the phosphor oxidizes or that the molecular / crystalline structure of the phosphor changes when incorporated into the host lattice of the dental ceramic. The surprising thing about the present invention is that with the phosphors presented here, a coloration of the fluorescent dental ceramic, when excited with light with a wavelength of X = 395 nm, can be achieved that is very close to the color of a tooth that fluoresces when excited with this excitation. On the line of each dye 1 to 9, the color coordinate of the phosphor sintered into each dental ceramic 1 to 9 is located as the third point, all of which lie at the apex of the angle drawn with a bold line. There, each marked with a star, are the color coordinates of various natural, fluorescent teeth. Two of the McAdams ellipses from Figure 2 are also shown there.The very narrow area in the area of ​​the apex of the drawn angle is shown in the next figure as enlarged detail A.

[0061] Figure 4 shows an enlarged section of area A from the CIE standard valence diagram in Fig. 3. As examples, two color locations are marked with a star. These correspond to the fluorescence color of a natural tooth when excited with light with a wavelength of 395 nm. Natural teeth display a certain range of fluorescence. This range is caused by possibly varying fluoridation, with the age at fluoridation and the intensity of fluoridation playing a major role in the characteristic fluorescence of natural teeth. Other parameters are the thickness of the enamel and the natural color of the tooth, which is determined by the tooth structure. Organic-biological substances that are individually incorporated into the tooth material, in this case the dentin and enamel, can fluoresce.All of the black squares shown in this enlarged detail correspond to the color coordinates of the respective phosphor when sintered into the host lattice of the dental ceramic at a concentration of 0.5 mass%. The two McAdams ellipses shown here indicate that the nine different phosphors can be used to adjust the color coordinates of the fluorescence of natural teeth with a color accuracy that comes close to the color resolution of human color perception. In this diagram, the lines connecting the color coordinates of each phosphor are continued to the common origin at the angle shown. This origin is the color coordinate of human color perception of the pure excitation light. The color coordinate for phosphor 9, which lies outside the angle, corresponds to a dental ceramic that appears slightly too violet in this excitation light.This dental ceramic is a YAG garnet without gallium, stoichiometry coefficient is 0, and thus falls outside the claimed range of the stoichiometry coefficient b and therefore has a luminescence that is no longer acceptable for imitating average teeth.

[0062] Figure 5 shows a CIE diagram according to CIE 1931 with the color coordinates of dental ceramics plotted. According to the invention, the dental ceramics comprise various garnets as illuminants when excited with light having a wavelength of 405 nm. The CIE standard valence diagram in Figure 5 is slightly compressed vertically compared to the representation in Figure 2. However, the content of the CIE diagrams is identical. Instead of the McAdams ellipses, nine lines for nine different phosphors are plotted in this CIE standard valence diagram. These nine phosphors are characterized as follows: Color coordinates Color coordinates

[0063] Emission phosphor ceramic when excited with light when excited with light

[0064] Composition of the wavelength 'Composition of the wavelength

[0065] (Y / Lu)3- a Ce a Al5-bGabOi2:Ce X = 405 nm Ceramic X = 405 nm

[0066] Matrix % / Luminance

[0067] No. Y / Lu from CIE-X CIE-Y fabric % CIE-X CIE-Y

[0068] 1 Lu 0.024 2.625 0.1917 0.4295 99.5% / 0.5% 0.1879 0.3539

[0069] 2 Lu 0.045 2.5 0.2101 0.4681 99.5% / 0.5% 0.2048 0.402

[0070] 3 Lu 0.045 1 .75 0.2384 0.519 99.5% / 0.5% 0.2281 0.434

[0071] 4 Lu 0.045 1 .25 0.2655 0.5515 99.5% / 0.5% 0.2468 0.4348

[0072] 5 Lu 0.063 1 0.2886 0.5683 99.5% / 0.5% 0.2675 0.4608

[0073] 6 Lu 0.075 1 0.3091 0.5695 99.5% / 0.5% 0.2828 0.4563

[0074] 7 Y 0.066 2.5 0.3217 0.5684 99.5% / 0.5% 0.309 0.5149

[0075] 8 Lu 0.03 0 0.3385 0.5757 99.5% / 0.5% 0.2572 0.3002

[0076] 9 Y 0.09 0 0.4689 0.5097 99.5% / 0.5% 0.3543 0.3179

[0077] 'Mixing ratio in mass%

[0078] In the CIE standard valence diagram 1931 shown here, the color coordinates of the pure emission of the phosphors listed in the table above when excited with light of wavelength X = 405 nm are shown as small, black squares directly next to the reference numerals 1 to 9. The emission of all phosphors 1 to 9 has a greenish-yellow color, popularly associated with fluorescent color and also popularly referred to as "neon yellow." This color differs significantly from the color of fluorescent natural teeth. Natural teeth fluoresce in the turquoise to bluish, and depending on perception, even bluish-violet color range. However, the color of the pure emission is not decisive. Rather, the human-perceived mixed color of the emission and the reflected light is more significant.For this purpose, lines 1 to 9 branch off from the color coordinates of the phosphors, leading to the next color coordinate, namely the color coordinate of the mixed light from reflected excitation light and emission light. The color coordinate of this mixed light depends on the emission intensity of the phosphor and also on that of the excitation light reflected after the excitation light has been absorbed by the phosphor. Both emission intensity and absorption are material constants. The first two points, namely the color coordinate of the emission and the color coordinate of the mixed light from emission and reflected excitation light, refer to the pure phosphor. In order to investigate the actual suitability as a dopant for a dental ceramic, the respective phosphor must be introduced into the dental ceramic and sintered with it. The phosphor can change during sintering.It is possible that the phosphor oxidizes or that the molecular / crystalline structure of the phosphor changes when incorporated into the host lattice of the dental ceramic. The surprising thing about the present invention is that with the phosphors presented here, a coloration of the fluorescent dental ceramic, when excited with light at a wavelength of 405 nm, can be achieved that is very close to the color of a tooth that fluoresces when excited at this wavelength. On the line of each dye 1 to 9, the color coordinate of the phosphor sintered into a dental ceramic is located as the third point; all of these lie at the apex of the angle shown with a bold line. There, each marked with a star, are the color coordinates of various natural, fluorescent teeth. Two of the McAdams ellipses from Figure 2 are also shown there.The very narrow area in the area of ​​the apex of the drawn angle is shown in the next figure as enlarged detail A.

[0079] Figure 6 shows an enlarged section A from the diagram in Fig. 5. As examples, two color locations are marked with a star. These correspond to the fluorescence color of a natural tooth when excited with light with a wavelength of 405 nm. Natural teeth exhibit a certain range of fluorescence. This range is caused by fluoridation, with the age at which fluoridation took place and the intensity of fluoridation playing a major role in the characteristic fluorescence of natural teeth. Other parameters are the thickness of the enamel and the natural color of the tooth, which is determined by the tooth structure. Organic-biological substances enclosed in the tooth metal can fluoresce.All of the black squares shown in this enlarged detail correspond to the color coordinates of the respective phosphor when sintered into the host lattice of the dental ceramic at a concentration of 0.5 mass%. The two McAdams ellipses shown here allow the conclusion that, using the nine different phosphors, the color coordinates of the fluorescence of natural teeth can be adjusted with a color accuracy that comes close to the color resolution of human color perception. In this diagram, the lines connecting the color coordinates of each phosphor are continued to the common origin at the angle shown. This origin is the color coordinate of human color perception of the pure excitation light. The color coordinate for phosphor 9, which lies outside the angle, corresponds to a dental ceramic that appears slightly too violet in this excitation light.This dental ceramic is a YAG garnet without gallium, stoichiometry coefficient is 0, and thus falls outside the claimed range of the stoichiometry coefficient b and therefore has a luminescence that is no longer acceptable for imitating average teeth.

[0080] Figure 7 shows a CIE diagram according to CIE 1931 with color coordinates of dental ceramics. According to the invention, the dental ceramics comprise various garnets as illuminants when excited with light having a wavelength of 415 nm. The CIE standard valence diagram in Figure 7 is slightly compressed vertically compared to the representation in Figure 2. However, the content of the CIE diagrams is identical. Instead of the McAdams ellipses, nine lines for nine different phosphors are plotted in this CIE standard valence diagram. These nine phosphors are characterized as follows:

[0081] Color location Color location

[0082] Emission phosphor ceramic when excited with *Combination with when excited with light

[0083] Composition Light of wavelength Setting of wavelength

[0084] (Y / Lu)3-aCe a Al5-bGabOi2:Ce X = 415 nm Ceramic X = 415 nm

[0085] Matrix % /

[0086] No. Y / Lu ab CIE-X CIE-Y Phosphor % CIE-X CIE-Y

[0087] 1 Lu 0.024 2.625 0.1901 0.4096 99.5% / 0.5% 0.1857 0.3145

[0088] 2 Lu 0.045 2.5 0.2077 0.4468 99.5% / 0.5% 0.2004 0.3582

[0089] 3 Lu 0.045 1 .75 0.2349 0.4985 99.5% / 0.5% 0.2214 0.3942

[0090] 4 Lu 0.045 1 .25 0.2606 0.5296 99.5% / 0.5% 0.2375 0.3942

[0091] 5 Lu 0.063 1 0.2829 0.5511 99.5% / 0.5% 0.2575 0.4264

[0092] 6 Lu 0.075 1 0.3023 0.5532 99.5% / 0.5% 0.2717 0.4254

[0093] 7 Y 0.066 2.5 0.3175 0.5579 99.5% / 0.5% 0.2998 0.4844

[0094] 8 Lu 0.03 0 0.3259 0.5538 99.5% / 0.5% 0.2465 0.2769

[0095] 9 Y 0.09 0 0.458 0.5102 99.5% / 0.5% 0.3446 0.3104

[0096] 'Mixing ratio specification *in mass%

[0097] In the CIE standard valence diagram 1931 shown here, the color coordinates of the pure emission of the phosphors listed in the table above when excited with light of wavelength X = 415 nm are shown as small black squares directly next to the reference numerals 1 to 9. The emission of all phosphors 1 to 9 has a greenish-yellow color, which is popularly associated with fluorescent color and is also often referred to as "neon yellow." This color differs significantly from the color of fluorescent natural teeth. Natural teeth fluoresce in the turquoise to bluish, and depending on perception, even bluish-violet color range. However, the color of the pure emission is not decisive. Rather, the human-perceived mixed color of the emission and the reflected light is more significant.For this purpose, lines 1 to 9 branch off from the color coordinates of the phosphors, leading to the next color coordinate, namely the color coordinate of the mixed light from reflected excitation light and emission light. The color coordinate of this mixed light depends on the emission intensity of the phosphor and also on that of the excitation light reflected after the excitation light has been absorbed by the phosphor. Both emission intensity and absorption are material constants. The first two points, namely the color coordinate of the emission and the color coordinate of the mixed light from emission and reflected excitation light, refer to the pure phosphor. In order to investigate the actual suitability as a dopant for a dental ceramic, the respective phosphor must be introduced into the dental ceramic and sintered with it. The phosphor can change during sintering.It is possible that the phosphor oxidizes or that the molecular / crystalline structure of the phosphor changes when incorporated into the host lattice of the dental ceramic. The surprising thing about the present invention is that with the phosphors presented here, a coloration of the fluorescent dental ceramic, when excited with light at a wavelength of 415 nm, can be achieved that is very close to the color of a tooth that fluorescently emits this excitation. On the line of each dye 1 to 9, the color coordinate of the phosphor sintered into a dental ceramic is located as the third point, all of which lie at the apex of the angle shown with a bold line. There, each marked with a star, are the color coordinates of various natural, fluorescent teeth. Two of the McAdams ellipses from Figure 2 are also shown there.The very narrow area in the area of ​​the apex of the drawn angle is shown in the next figure as enlarged detail A.

[0098] Figure 8 shows an enlarged section A from the diagram in Fig. 8. As examples, two color locations are marked with a star. These correspond to the fluorescence color of a natural tooth when excited with light with a wavelength of 415 nm. Natural teeth exhibit a certain range of fluorescence. This range is caused by fluoridation, with the age at fluoridation and the intensity of fluoridation playing a major role in the characteristic fluorescence of natural teeth. Other parameters are the thickness of the enamel and the natural color of the tooth, which is determined by the tooth structure. Organic-biological substances enclosed in the tooth metal can fluoresce.All of the black squares shown in this enlarged detail correspond to the color coordinates of the respective phosphor when this respective phosphor is sintered into the host lattice of the dental ceramic at a concentration of 0.5 mass%. The two McAdams ellipses shown here allow us to conclude that, using the nine different phosphors, the color coordinates of the fluorescence of natural teeth can be adjusted with a color accuracy that comes close to the color resolution of human color perception. In this diagram, the lines connecting the color coordinates of each phosphor are continued to the common origin at the angle shown. This origin is the color coordinate of human color perception of the pure excitation light. The color coordinate for phosphor 9, which lies outside the angle, corresponds to a dental ceramic that appears slightly too violet in this excitation light.This dental ceramic is a YAG garnet without gallium, stoichiometry coefficient is 0, and thus falls outside the claimed range of the stoichiometry coefficient b and therefore has a luminescence that is no longer acceptable for imitating average teeth.

[0099] Figure 9 shows a matrix of ceramic platelets produced using the sintering process described in Quintessenz Zahntech 2009;35(8):1018-102. The dental ceramics according to the invention are on the diagonal of 6 min 980°C to 10 min 940°C in terms of color under natural light and degree of opacity.

[0100] LIST OF REFERENCE SYMBOLS

[0101] A Enlarged section Y Y-axis in CIE standard color valence

[0102] X X-axis in the CIE standard colorimetric diagram

Claims

PATENT CLAIMS 1 . Dental ceramic based on silicate or zirconium dioxide as matrix, characterized by an admixture of a cerium-doped LuAG, cerium-doped YAG and / or a cerium-doped LuYAG garnet, wherein the LuAG garnet assumes the following chemical composition: Lu3-aCe a Al5-bGabOi2, where a takes a value of 0.003 to 0.075 and b a value of 0 to 3, the YAG garnet takes the following chemical composition: Y3- a Ce a Al5-bGabOi2, where a takes a value of 0.003 to 0.075 and b a value of 1 to 3.5, and the LuYAG garnet takes the following chemical composition: Y3- a -cLu c Ce a Al5-bGabOi2, where a has a value of 0.003 to 0.075, b has a value of 1 / 3(3-ac) to 3.25 and c takes a value greater than 0.

2. Dental ceramic according to claim 1, characterized in that the concentration of garnet in the host lattice of the dental ceramic is between 0.2 mass% and 3.0 mass%, preferably between 0.3 mass% and 1.0 mass%, particularly preferably 0.5 mass% with a tolerance of ±0.1 mass% 3. Dental ceramic according to one of claims 1 or 2, characterized by a sintering temperature during sintering of the dental ceramic of 750°C to 1,000°C, preferably between 850°C and 980°C, particularly preferably from 950°C with a tolerance of 5°C over a period of 2 min to 120 min, preferably between 10 min and 60 min with a tolerance of ±1 min.

4. Dental ceramic according to one of claims 1 to 3, characterized by sintering in a protective gas atmosphere of nitrogen or argon or under dynamic vacuum during the production of the dental ceramic.

5. Dental ceramic according to one of claims 1 to 4, characterized by a grain size of the garnet in the raw material mixture of 2 pm to 20 pm, preferably of 4 pm to 8 pm with a tolerance of ±1 pm.

6. Dental ceramic according to one of claims 1 to 5, characterized by the matrix consisting of (K,Li)AISi30s, (K,Li)AISi20e, NaAISisOs as alkali aluminosilicate and / or Lu2Si20z as lutetium disilicate.

7. Dental ceramic according to one of claims 1 to 5, characterized by the matrix consisting of ZrC>2 as zirconia.

8. Dental ceramic according to one of claims 1 to 7, characterized by a content of Y2SiO5:Ce(Tb) between 0.1 mass% and 2 mass%.

9. Dental ceramic according to claim 7, characterized by a Bi content between 0.005 mass% and 3 mass%.

10. Dental ceramic according to one of claims 1 to 9, characterized by a partial or complete replacement of gallium (Ga) by scandium (Sc) in the garnet. 11 . Dental ceramic according to one of claims 1 to 10, characterized by doping of the garnet or garnets with Gd 3+ .

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