Fluorescein-doped dental ceramic

Abstract

The invention relates to a dental ceramic based on silicate or zirconium dioxide as a matrix. The dental ceramic is characterized according to the invention 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: Lu 3-a Ce a Al 5-b Ga b O 12 , where a takes a value of 0.003 <= a < 0.024 and b a value of 0 to 3, the YAG garnet takes on the following chemical composition: Y 3-a Ce a Al 5-b Ga b O 12 , where a takes a value of 0.003 <= a < 0.024 and b a value of 1 to 3.5, and the LuYAG garnet takes the following chemical composition: Y 3-a-c Lu c Ge a Al 5-b Ga b O 12 , where a takes a value of 0.003 <= a < 0.024, b a value of ⅓(3-ac) to 3.25 and c a value greater than 0.

Description

[0001] The invention relates to a dental ceramic based on silicate or zirconium dioxide.

[0002] To fabricate a dental prosthesis, whether an inlay, crown, bridge, or implant crown, it is standard practice to model the prosthesis for the tooth or group of teeth to be replaced manually or using computer-aided design in a dental laboratory and to manufacture the prosthesis from dental ceramic. The dental ceramic chosen for the prosthesis should, if possible, closely 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, any color gradient from the neck to the crown, translucency (measured by light transmission), transparency (measured by a clear appearance, similar to clear glass), colored or white inclusions (such as fine, whitish particles that scatter light), reflection (measured by wavelength), and the ceramic's fluorescent properties. Finally, the ceramic's gloss and surface roughness also influence its optical appearance and wettability. Therefore, choosing the right dental ceramic depends on more than just color.

[0003] Currently, there are well-known dental ceramics used as dental restoration materials, made from zirconium dioxide, aluminosilicates, or lutetium disilicate (the latter two referred to collectively as "silicate-based"). These inorganic dental ceramics, through appropriate pigmentation, exhibit a coloration that closely resembles that of a human tooth under natural light. To adjust the material properties of dental ceramics used as restorations, auxiliary substances or additives are mixed into the ceramics. The resulting adjustable material properties affect not only the color but also the hardness, flexibility, chemical resistance, and abrasiveness of the dental ceramic.

[0004] To produce dental ceramics, the manufacturer delivers ready-to-use raw material mixtures to a dental laboratory for firing / sintering. The dental laboratory then sinters the dental ceramic in patient-specific molds, strictly adhering to the sintering temperature and duration specified by the manufacturer. This typically involves following predefined temperature programs as a temperature profile over time. Depending on the type of dental ceramic, it may also be necessary to perform sintering in a protective gas atmosphere, or alternatively under vacuum, or at least at a significantly lower pressure than atmospheric pressure. Particular attention must be paid to the luminescence behavior of the dental ceramic when manufacturing a dental prosthesis. In the context of this application, "luminescence" refers to the interplay of fluorescence, reflection, and absorption.

[0005] Previously known dental ceramics exhibit a luminescence property similar to that of a natural tooth under typical black light conditions. Typical black light scenarios in which a patient might be present after receiving the dental prosthesis have been discotheques and nightclubs, where black light tubes generate the characteristic ultraviolet radiation from a specially prepared fluorescent tube. Aside from these lighting effects, there are very few other scenarios in which black light from the familiar, dark violet-glowing black light tubes is used. The aforementioned black light tubes have a radiation maximum at a wavelength of λ = 365 nm. Further light in the visible range is largely filtered out by the dark violet tint of the black light tube's glass.

[0006] If the ceramics under consideration as dental restoration materials are alkali aluminosilicates (e.g., (K,Li)AlSi3O8, (K,Li)AlSi2O6, NaAlSi3O8) or lutetium disilicate (Lu2Si2O7), all grouped under "silicate-based," they are, according to current technology, doped with cerium-doped or cerium-terbium-co-doped yttrium orthosilicate, Y2SiO5:Ce,(Tb), in an amount of 0.1 wt% to 2 wt% to simulate luminescence under black light from black light tubes. Due to the fluorescence of cerium when excited with UV light at a wavelength λ = 365 nm, a dental ceramic is obtained that, when used as a dental restoration in a black light scenario, exhibits luminescence behavior similar to a natural tooth. Under black light, a natural tooth displays a turquoise to bluish color due to its fluorescence.By additionally incorporating terbium, the emission color of the dental ceramic can be slightly shifted and thus adapted to the individual tooth color of the patient.

[0007] Zirconium dioxide (ZrO2; zirconia) ceramics are manufactured with a bismuth compound. The fluorescence of bismuth when excited with UV light at a wavelength of λ = 365 nm results in a dental ceramic that, when used as a dental prosthesis in a previously described black light scenario, exhibits luminescence behavior similar to a natural tooth.

[0008] The replacement of fluorescent tubes, a lighting technology now considered outdated, with light-emitting diodes (LEDs) has changed the typical light color and excitation wavelength of "blacklights." Instead of a radiation maximum of λ = 365 nm, typical LEDs used to create a fluorescence effect exhibit a radiation maximum shifted to longer wavelengths, ranging from 395 nm to 415 nm. These LEDs, also known as blacklight LEDs, are not only used in nightclubs but have a wide variety of applications. Some of these applications include: illuminating products on a retail surface to give them a particularly high-contrast appearance, illuminating fresh meat to give it a special, intense color, and using them in flower shops to make the blossoms appear especially vibrant.It is also common practice in supermarkets to illuminate the food section with cold light, which is further enhanced by a fluorescent component from blacklight LEDs, while the non-food section is typically illuminated with warm light that does not contain any fluorescent components. Other scenarios where blacklight LEDs are used include cinema lighting and, increasingly, the lighting of restrooms in public buildings and underpasses. The blue to violet light is intended to make drug abuse with injectable drugs more difficult because the blue color of human veins is very hard to see under blue light against white skin. These blacklight LEDs, or "purple LEDs," are also used wherever fluorescence plays a role, for example, as an optical brightener.

[0009] When a patient's dental prosthesis, made with conventional dental ceramics, is illuminated with the light of a commonly used black light LED, a difference in the fluorescence behavior of the natural tooth becomes apparent compared to that of the prosthesis. 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 dental materials require adequate fluorescence to mimic the optical appearance of natural teeth. The presentation further explained that colored zirconia materials [Note: referring to ceramics based on zirconium dioxide (ZrO2), not zirconia (Zr[SiO4])] do not exhibit this property.The materials tested in the presentation exhibit different wavelengths for their excitation maxima: Lava Esthetic Zirconia at λ = 310 nm, human dentin at λ = 340 nm, e.max® Press at λ = 360 nm, e.max® Glaze Paste Flu at λ = 350 nm, and Lava Ultimate at λ = 320 nm and 380 nm. The fluorescence intensities of the presented materials differ from one another and depend on the light source, particularly evident 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 method for manufacturing high-density, low-defect sintered components and a corresponding ceramic component. The disclosed method includes the use of these high-density, low-defect ceramics in, among other applications, dentistry. This document mentions various ceramic types without specifying their properties. One of the ceramics is designated as type A3B2[RO4]3, where B and R can be identical. With identical B and R, the chemical formula simplifies to A3B5O. 12 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 zirconia-sintered bodies with a fluorescent agent. The object 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 with regard to new LEDs emitting a different blue light than that of traditional fluorescent tubes is not addressed at all. YAG:Cer is only mentioned as an example of a 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 therein.

[0013] In severe cases, dental prostheses can appear dark and dull, giving the impression of a dead and internally rotten tooth. Although this is only a cosmetic flaw, this unnatural appearance of the prosthesis can be very bothersome and completely unacceptable to the patient, because the supposedly dead and internally rotten tooth creates an unattractive and unhealthy image.

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

[0015] A logical solution would be to add pigments to the dental ceramic as phosphors, specifically those that are excitable in the wavelength range of light between λ = 395 nm and λ = 415 nm. The pigment should only minimally alter the color of the dental ceramic under natural light. Furthermore, the translucency of the existing dental ceramic should not be changed, and no microcrystalline domains of such size should form during firing / sintering that they would give the dental ceramic, as a dental restoration material, the appearance of glass that has become "cloudy," so that the desired dental ceramic does not exhibit any unwanted cloudiness. Unlike crystals with a regular lattice structure and glasses, which are solidified liquids, ceramics are solids that contain crystalline domains.When microcrystalline domains form, boundary layers can develop that are colored and / or opaque, or the refractive index can differ significantly from that of the surrounding material. Both boundary layer formation and the difference in refractive index can lead to optical defects that produce the haze effect. Since the enamel of natural teeth is crystal clear to slightly cloudy, the effect caused by pigmentation should not affect the existing haze in a way that is visible to the human eye.

[0016] Europium(II) compounds are known as phosphors for LEDs, capable of excitation at wavelengths above 390 nm. Depending on the host grating, such Eu(II) phosphors can emit over a broad emission range. Doping the Eu(II) phosphors with additional rare-earth metal ions allows for precise adjustment of the perceived color, which can be mapped to the chromaticity diagram of the CIE standard colorimetric system. An example of this is BaSi₂N₂O₂:Eu 2+ , (Ba,Sr)2[SiO4]:Eu 2+ , Ba3MgSi2O8:Eu 2+ and Sr6B[PO4]5:Eu 2+ However, when these color-adjustable phosphors were used as additives in a known dental ceramic for dental restorations, it was found that these phosphors lost their fluorescent properties during sintering into the aforementioned dental ceramics. This application suggests that an oxidation of europium from Eu(II) to Eu(III) occurs during sintering.

[0017] When using barium silicon dioxide nitride (BaSi2N2O2:Eu 2+ In the case of the use of europium(II) as a phosphor in dental ceramics for dental restorations, it was further observed that an excessively strong milky turbidity appeared in the sintered ceramic, giving the ceramic the appearance of "blind" glass. Known europium(II) compounds therefore do not survive the sintering process for the production of the ceramic dental restorations, and the Eu(II)-based phosphors become spectroscopically inactive in the compounds tested here.

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

[0019] The object of the invention is therefore to provide a dental ceramic as a dental prosthesis material which, even when excited with light in the range of λ = 395 nm up to light with a wavelength of λ = 415 nm, exhibits an appearance like a natural tooth. The comparison "like a natural tooth" is to be made based on average human color perception and on average human color discrimination. This color perception and color discrimination were empirically determined by David Lewis McAdams in 1942 through investigations on the CIE standard colorimetric diagram and quantified by the so-called McAdams ellipses as an entry in the CIE standard colorimetric diagram.

[0020] The problem underlying the invention is solved by a ceramic having the features according to claim 1. Further advantageous embodiments are specified in the dependent claims 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: Lu 3-a Ce a Al 5-b Ga b O 12 , where a takes a value of 0.003 <= a < 0.024 and b a value of 0 to 3, the YAG garnet takes on the following chemical composition: Y 3-a Ce a Al 5-b Ga b O 12 , where a takes a value of 0.003 <= a < 0.024 and b a value of 1 to 3.5, and the LuYAG garnet takes the following chemical composition: Y 3-a-c Lu c Ce a Al 5-b Ga b O 12, where a takes a value of 0.003 ≤ a < 0.024, b a value of ⅓(3-ac) to 3.25, and c a value greater than 0. These garnets are known and commercially available as cerium-doped lutetium and / or yttrium aluminum garnets (LuAG:Ce, YAG:Ce, Lu / YAG:Ce). The garnet contained in dental ceramics can be pure cerium-doped yttrium garnet, a mixture of pure cerium-doped yttrium garnet and pure cerium-doped lutetium garnet, or 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. Additional rare-earth metal ions, such as Gd, can also be present. 3+These components are incorporated into the garnet. While they do not have a beneficial effect in terms of the invention, they do not preclude its realization. The garnets, acting as phosphors, have the property of exhibiting emission in the greenish to yellow range when excited, which is colloquially referred to as "neon green" or "neon yellow." The emission intensity when excited with light at a wavelength of λ = 400 nm is only about 10% to 15% of the emission intensity maximum. To mimic the natural luminescence behavior of a natural tooth, this group of substances initially appears unsuitable due to the color of the emission and the weak emission when excited with light in the wavelength range of λ = 400 nm. A natural tooth fluoresces with a blue-green to bluish color, not yellowish.The addition of a phosphor that fluoresces in the greenish to yellow range would, at first glance, seem unsuitable for solving the problem of the invention. Surprisingly, however, it has been shown that when sintered with a silicate-based or zirconia-based dental ceramic raw material, this group of substances results in a luminescence behavior that is very similar to that of a natural tooth—so similar, in fact, that the color perception of an average observer can no longer distinguish the luminescence color of the ceramic according to the invention as a dental prosthesis from the luminescence color of a natural tooth.

[0022] As an example of a ceramic according to the invention for use as a dental restoration 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 under vacuum for 14 minutes with 100% furnace closure, held for 3 minutes, then cooled to 500 °C with 75% furnace closure, finally removed and allowed to cool to room temperature).A concentration of 0.5% by mass of phosphor, based on the total mass, was used. The following dental ceramics were obtained: Zusammense then (Y / Lu) 3-a What a Al 5-b Ga b OF 12 Color point emission of phosphor when excited with light of wavelength λ = 395 nm *Ceramic composition Color point of ceramics when excited with light of wavelength λ = 395 nm Nr. Y / Lu a b CIE-X CIE-Y Matrix % / Fluorescent % CIE-X CIE-Y 1 Lu 0,024 2,625 0,1931 0,4219 99,5% / 0,5% 0,1838 0,1203 2 Lu 0,045 2,5 0,2125 0,4613 99,5% / 0,5% 0,1897 0,1659 3 Lu 0,045 1,75 0,2425 0,5137 99,5% / 0,5% 0,1903 0,1198 4 Lu 0,045 1,25 0,2712 0,5412 99,5% / 0,5% 0,1888 0,0926 5 Lu 0,063 1 0,2945 0,5593 99,5% / 0,5% 0,1883 0,0795 6 Lu 0,075 1 0,3157 0,5556 99,5% / 0,5% 0,1982 0,1180 7 Y 0,066 2,5 0,32548 0,56463 99,5% / 0,5% 0,2319 0,2345 8 Lu 0,03 0 0,3260 0,5147 99,5% / 0,5% 0,1868 0,0620 9 Y 0,09 0 0,45334 0,47855 99,5% / 0,5% 0,2030 0,0807 *Mixing ratio given in mass %

[0023] The surprising result is that the yellow-green to yellowish fluorescent garnets, when used as phosphors, tend to exhibit a luminescence best described as bluish when sintered with commercially available raw material for dental ceramics. The unexcited dental ceramic has a color that is only marginally different in daylight compared to dental ceramics without the aforementioned garnets as phosphors. The translucency is undisturbed. The surface of the dental ceramic has a clear layer. A similar opacity is observed as in dental ceramics manufactured according to the state of the art. Since the opacity of the dental ceramic cannot be quantified by a single parameter, as in a nephelometric measurement, only an optical comparison with reference dental ceramics, such as those found in [reference missing], remains. Fig.Figure 9 illustrates this. Testing the fluorescent color of sintered dental ceramics using garnets as phosphors shows a mimicry of fluorescence to a degree comparable to the color discrimination of an average person, as characterized by McAdams. The fluorescence of natural teeth presumably varies with the degree of fluoridation from fluoride treatment. Depending on age and duration of fluoride treatment, the fluorescence is more or less pronounced. Teeth exposed to higher levels of fluoride during preschool age naturally exhibit more pronounced fluorescence than adult teeth that were fluoridated later in life through dental treatment, when the teeth were already fully erupted and their enamel already showed initial discoloration.The tooth color of teeth demineralized by sugar and phosphoric acid-containing soft drinks, colloquially known as "chalky teeth", can also be imitated with the dental ceramics presented here, which contain the aforementioned phosphors.

[0024] 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. Dental ceramic mixtures containing the aforementioned garnets as phosphors have proven to be comparable to natural teeth in terms of fluorescence, exhibiting the following garnet concentrations as phosphors: between 0.2 wt% and 3 wt%, preferably between 0.3 wt% and 1.0 wt%, and particularly preferably 0.5 wt% with a tolerance of 0.1 wt%.

[0025] Good results can be achieved with a sintering temperature of 750°C to 1,000°C when sintering the dental ceramic, preferably between 850°C and 980°C, particularly preferably between 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.

[0026] It is advantageous to sinter dental ceramics in a protective atmosphere of nitrogen and / or argon to prevent oxidation of the garnets used as phosphors. Alternatively, sintering under a dynamic vacuum is possible, or at least at a pressure below 20 hPa.

[0027] To avoid the formation of undesirably large microcrystalline phases of phosphor in dental ceramics during sintering, or microcrystalline phases that become visible through boundary layer formation, it is advantageous if the grain size of the garnet as phosphor in the raw material mixture is between 1 µm and 20 µm, preferably between 4 µm and 8 µm with a tolerance of 1 µm.

[0028] 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 alter the color. The advantage of gallium is that it is considerably cheaper on the market than scandium.

[0029] The invention is explained in more detail with reference to the following figures. They show: Fig. 1. A sketch of a tooth front under different lighting scenarios, Fig.2 a CIE diagram according to CIE 1931 with McAdams ellipses drawn in, which delineate places of equal color perception, Fig. 3 a CIE diagram according to CIE 1931 with color coordinates of dental ceramics which, according to the invention, have different garnets as illuminants, when excited with light with a wavelength of 395 nm, Fig. 4. A close-up of a section of the diagram in Fig. 3, Fig. 5 a CIE diagram according to CIE 1931 with color coordinates of dental ceramics which, according to the invention, have different garnets as illuminants, when excited with light with a wavelength of 405 nm, Fig. 6. A close-up of a section of the diagram in Fig. 5, Fig.7 A CIE diagram according to CIE 1931 with color coordinates of dental ceramics which, according to the invention, have different garnets as illuminants when excited with light with a wavelength of 415 nm, Fig. 8 a close-up of a section of the diagram in Fig. 7, Fig. 9 a turbidity experiment.

[0030] In Fig.Figure 1 shows a sketch of an anterior tooth with a state-of-the-art dental prosthesis at position 2-1 (according to the dental quadrant system "quadrant position") under different lighting conditions. The anterior tooth in the upper left corner shows the appearance of the teeth under natural or artificial daylight. No difference is discernible to the human eye between the two upper incisors 1-1 and 2-1. In the upper right corner, the same anterior tooth is shown under LED light in the visible range. State-of-the-art dental ceramics, such as the one at position 2-1, are also indistinguishable from the appearance of a natural tooth at position 1-1 under LED light in the visible range, even with human color discrimination. In the lower left corner, the same anterior tooth is sketched under black light from black light tubes.Black light tubes exhibit a radiation maximum at a wavelength of λ = 365 nm and, beyond that, a dark violet light in the visible spectrum. State-of-the-art dental ceramics have fluorescent pigmentations that can be excited by light with a wavelength of λ = 365 nm, making the dental ceramic resemble a natural tooth, including the fluorescence of a natural tooth. The effect of illuminating the same tooth front with a black light LED is shown in an exaggerated form in the lower right corner. Depending on the design, black light LEDs exhibit a radiation maximum at a wavelength of light from λ = 395 to λ = 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 dental prosthesis at position 2-1 appearing undesirably darker than the adjacent teeth.This is precisely the effect that the dental ceramic doped according to the invention is intended to avoid.

[0031] In Fig.Figure 2 shows a CIE diagram according to CIE 1931 with McAdams ellipses plotted on it, where the McAdams ellipses delineate the color points in the CIE standard colorimetric diagram of equal color perception. For the construction of the CIE diagram, please refer to the relevant literature. The McAdams ellipses plotted on the CIE diagram vary in size at different color points. This does not necessarily mean that a larger McAdams ellipse represents a color point with lower human color discrimination, because the larger McAdams ellipses are located in the green region, where the wavelength density of the plot in the CIE standard colorimetric 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 colorimetric diagram is relatively high, which results in smaller McAdams ellipses.The quality of human color discrimination can be more clearly illustrated by reformed CIE diagrams, which are mathematically distorted, as in the CIE-UCS diagram of 1960 or the CIE-LUV diagram of 1976. The white point W is located approximately in the center, from which any boundaries between dominant hues can be drawn. The color gradient within the CIE standard colorimetric diagram is continuous. Nevertheless, human color perception suggests the course of the dashed lines extending radially from the white point as the possible boundary between the hues separated by the dashed lines. The CIE standard colorimetric diagram from 1931 shown here is introduced to demonstrate the color coordinates of the emissions and the dental ceramics doped according to the invention in the following figures.

[0032] In Fig.Figure 3 is a CIE diagram according to CIE 1931 with the color coordinates of dental ceramics shown, wherein the dental ceramics, according to the invention, have different garnets as illuminants; this is shown when excited with light with a wavelength of 395 nm. The CIE standard chromaticity diagram in Fig. 3 is in contrast to the representation in Fig. 2. The diagrams are slightly vertically compressed. However, the content of the CIE diagrams is identical. Instead of McAdams ellipses, this CIE standard phosphor diagram shows nine lines for nine different phosphors. These nine phosphors are characterized as follows: Composition (Y / Lu) 3-a What a the 5-b Ga b A 12 :What Color point emission of phosphor when excited with light of wavelength λ = 395 nm *Ceramic composition Color point of ceramics when excited with light of wavelength λ = 395 nm Nr. Y / L u a b CIE-X CIE-Y Matrix % / Fluorescent % CIE-X CIE-Y 1 Lu 0,024 2,625 0,1931 0,4219 99,5% / 0,5% 0,1838 0,1203 2 Lu 0,045 2,5 0,2125 0,4613 99,5% / 0,5% 0,1897 0,1659 3 Lu 0,045 1,75 0,2425 0,5137 99,5% / 0,5% 0,1903 0,1198 4 Lu 0,045 1,25 0,2712 0,5412 99,5% / 0,5% 0,1888 0,0926 5 Lu 0,063 1 0,2945 0,5593 99,5% / 0,5% 0,1883 0,0795 6 Lu 0,075 1 0,3157 0,3254 0,5556 99,5% / 0,5% 0,1982 0,1180 7 Y 0,066 2,5 8 0,56463 99,5% / 0,5% 0,2319 0,2345 8 Lu 0,03 0 0,3260 0,4533 0,5147 99,5% / 0,5% 0,1868 0,0620 9 Y 0,09 0 4 0,47855 99,5% / 0,5% 0,2030 0,0807 *Mixing ratio given in mass %

[0033] 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 λ = 395 nm, are marked as small black squares directly adjacent to reference symbols 1 to 9. The emission of all phosphors 1 to 9 has a greenish-yellow color, commonly associated with fluorescent paint and 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 the determining factor. Rather, the mixed color of the emission and the reflected light, as perceived by humans, is more significant.Lines extend from the color coordinates of phosphors 1 to 9, leading to the next color coordinate: 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 absorption by the phosphor. Both emission intensity and absorption are material constants. The first two points, 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. To investigate its actual suitability as a dopant for dental ceramics, the respective phosphor must be incorporated into the dental ceramic and sintered with it. The phosphor can change during sintering.It is possible that the phosphor oxidizes or that its molecular / crystalline structure changes upon incorporation into the host lattice of the dental ceramic. The surprising aspect of the present invention is that, with the phosphors presented here, a coloration of the fluorescent dental ceramic can be achieved when excited with light with a wavelength of λ = 395 nm, which is very close to the color of a tooth fluorescent under this excitation. On the line for each of the phosphors 1 to 9, the color locus of the phosphor sintered into each of the dental ceramics 1 to 9 is located as the third point, all of which lie at the apex of the angle indicated by a bold line. There, marked with a star, are the color loci of various natural, fluorescent teeth. Two of the McAdams ellipses from... Fig.Two are also shown there. The very narrow area at the tip of the drawn angle is shown in the next figure as a close-up (A).

[0034] In Fig. Figure 4 is a magnified section of area A from the CIE standard valency diagram in Fig.Figure 3 shows two color locations marked with a star as examples; these correspond to the fluorescence color of a natural tooth when excited with light of a wavelength of 395 nm. Natural teeth exhibit a certain range of fluorescence. This range is caused by potentially varying fluoridation, with the age at which fluoridation occurred and the intensity of fluoridation playing a significant role in the characteristic fluorescence of natural teeth. Other parameters include the thickness of the enamel and the natural color of the tooth, which is determined by its structure. Furthermore, patient-specific organic-biological substances embedded in the dental metal, in this case the dentin and enamel, can fluoresce.All black squares shown in this enlarged section correspond to the color coordinates of the respective phosphor when sintered into the dental ceramic's host lattice at a concentration of 0.5 wt%. The two McAdams ellipses shown here indicate that the nine different phosphors allow for color coordinates of the fluorescence of natural teeth to be set with a color accuracy approaching the color resolution of human color perception. In this diagram, the lines connecting the color coordinates of each phosphor are extended to the common origin at the indicated angle. This origin represents the color coordinate of human color perception under pure excitation light. The color coordinate for phosphor 9, located outside this angle, corresponds to a dental ceramic that appears slightly too violet under this excitation light.This dental ceramic is a YAG garnet without gallium, stoichiometry coefficient is 0, and therefore falls outside the claimed range of the stoichiometry coefficient b and thus exhibits a luminescence that is no longer acceptable for imitating average teeth.

[0035] In Fig. Figure 5 shows a CIE diagram according to CIE 1931 with the color coordinates of dental ceramics plotted on it, wherein the dental ceramics, according to the invention, have different garnets as illuminants; this is shown when excited with light with a wavelength of 405 nm. The CIE standard valence diagram in Fig. 5 is in contrast to the representation in Fig. 2. The diagrams are slightly vertically compressed. However, the content of the CIE diagrams is identical. Instead of McAdams ellipses, this CIE standard phosphor diagram shows nine lines for nine different phosphors. These nine phosphors are characterized as follows: Zusammensetzung (Y / Lu) 3-a This a Al 5-b GabO 12 :This Color point of emission of phosphor when excited with light of wavelength λ = 405 nm *Ceramic composition Color point of ceramics when excited with light of wavelength λ = 405 nm Nr. Y / Lu a b CIE-X CIE-Y Matrix % / Fluorescent % CIE-X CIE-Y 1 Lu 0,024 2,625 0,1917 0,4295 99,5% / 0,5% 0,1879 0,3539 2 Lu 0,045 2,5 0,2101 0,4681 99,5% / 0,5% 0,2048 0,402 3 Lu 0,045 1,75 0,2384 0,519 99,5% / 0,5% 0,2281 0,434 4 Lu 0,045 1,25 0,2655 0,5515 99,5% / 0,5% 0,2468 0,4348 5 Lu 0,063 1 0,2886 0,5683 99,5% / 0,5% 0,2675 0,4608 6 Lu 0,075 1 0,3091 0,5695 99,5% / 0,5% 0,2828 0,4563 7 Y 0,066 2,5 0,3217 0,5684 99,5% / 0,5% 0,309 0,5149 8 Lu 0,03 0 0,3385 0,5757 99,5% / 0,5% 0,2572 0,3002 9 Y 0,09 0 0,4689 0,5097 99,5% / 0,5% 0,3543 0,3179 *Mixing ratio given in mass %

[0036] In the CIE standard colorimetric 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 λ = 405 nm, are marked as small black squares directly adjacent to reference symbols 1 to 9. The emission of all phosphors 1 to 9 has a greenish-yellow color, commonly associated with fluorescent paint and 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 the determining factor. Rather, the mixed color of the emission and the reflected light, as perceived by humans, is more significant.Lines extend from the color coordinates of phosphors 1 to 9, leading to the next color coordinate: 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 absorption by the phosphor. Both emission intensity and absorption are material constants. The first two points, 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. To investigate its actual suitability as a dopant for dental ceramics, the respective phosphor must be incorporated into the dental ceramic and sintered with it. The phosphor can change during sintering.It is possible that the phosphor oxidizes or that its molecular / crystalline structure changes upon incorporation into the host lattice of the dental ceramic. The surprising aspect of the present invention is that, with the phosphors presented here, a coloration of the fluorescent dental ceramic can be achieved when excited with light at a wavelength of 405 nm, which is very close to the color of a tooth fluorescent under this excitation. On the line for each of the phosphors 1 to 9, the color locus of the phosphor sintered into a dental ceramic is located as the third point; all of these lie at the apex of the angle indicated by a bold line. There, marked with a star, are the color loci of various natural, fluorescent teeth. Two of the McAdams ellipses from... Fig.Two are also shown there. The very narrow area at the tip of the drawn angle is shown in the next figure as a close-up (A).

[0037] Fig. Figure 6 shows a magnified section A from the diagram in Fig.5. As examples, two color points marked with a star correspond to the fluorescence color of a natural tooth when excited with light of a wavelength of 405 nm. Natural teeth exhibit a certain range of fluorescence. This range is caused by fluoridation, with the age at which the fluoridation occurred and its intensity playing a significant role in the characteristic fluorescence of natural teeth. Other parameters include the thickness of the enamel and the tooth's natural color, which is determined by its structure. Organic-biological substances embedded in the dental metal can also fluoresce. All black squares shown in this enlarged section correspond to the color points of the respective phosphor when sintered into the dental ceramic's host lattice at a concentration of 0.5 wt%.The two McAdams ellipses shown here suggest that the nine different phosphors allow for color coordinates of the fluorescence of natural teeth to be adjusted with a color accuracy approaching the color resolution of human color perception. In this diagram, the lines connecting the color coordinates of each phosphor are extended to the common origin at the indicated angle. This origin represents the color coordinate of human color perception for the pure excitation light. The color coordinate for phosphor 9, which lies outside the angle, corresponds to a dental ceramic that appears somewhat too violet in this excitation light. This dental ceramic is a gallium-free YAG garnet with a stoichiometric coefficient of 0, and therefore falls outside the required range of the stoichiometric coefficient b, exhibiting a luminescence that is no longer acceptable for imitating average teeth.

[0038] Fig. Figure 7 shows a CIE diagram according to CIE 1931 with the color coordinates of dental ceramics plotted, wherein the dental ceramics, according to the invention, have different garnets as phosphors; this is shown when excited with light with a wavelength of 415 nm. The CIE standard chromaticity diagram in Fig. 7 is in contrast to the representation in Fig. 2. The diagrams are slightly vertically compressed. However, the content of the CIE diagrams is identical. Instead of McAdams ellipses, this CIE standard phosphor diagram shows nine lines for nine different phosphors. These nine phosphors are characterized as follows: Composition (Y / Lu 3-a What a the 5-b Ga b A 12 :What Color point emission of phosphor when excited with light of wavelength λ = 415 nm *Ceramic composition Color point of ceramics when excited with light of wavelength λ = 415 nm Nr. Y / Lu a b CIE-X CIE-Y Matrix % / Fluorescent % CIE-X CIE-Y 1 Lu 0,024 2,625 0,1901 0,4096 99,5% / 0,5% 0,1857 0,3145 2 Lu 0,045 2,5 0,2077 0,4468 99,5% / 0,5% 0,2004 0,3582 3 Lu 0,045 1,75 0,2349 0,4985 99,5% / 0,5% 0,2214 0,3942 4 Lu 0,045 1,25 0,2606 0,5296 99,5% / 0,5% 0,2375 0,3942 5 Lu 0,063 1 0,2829 0,5511 99,5% / 0,5% 0,2575 0,4264 6 Lu 0,075 1 0,3023 0,5532 99,5% / 0,5% 0,2717 0,4254 7 Y 0,066 2,5 0,3175 0,5579 99,5% / 0,5% 0,2998 0,4844 8 Lu 0,03 0 0,3259 0,5538 99,5% / 0,5% 0,2465 0,2769 9 Y 0,09 0 0,458 0,5102 99,5% / 0,5% 0,3446 0,3104 *Mixing ratio specified *in mass %

[0039] 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 λ = 415 nm, are marked as small black squares directly adjacent to reference symbols 1 to 9. The emission of all phosphors 1 to 9 has a greenish-yellow color, commonly associated with fluorescent paint and 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 the determining factor. Rather, the mixed color of the emission and the reflected light, as perceived by humans, is more significant.Lines extend from the color coordinates of phosphors 1 to 9, leading to the next color coordinate: 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 absorption by the phosphor. Both emission intensity and absorption are material constants. The first two points, 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. To investigate its actual suitability as a dopant for dental ceramics, the respective phosphor must be incorporated into the dental ceramic and sintered with it. The phosphor can change during sintering.It is possible that the phosphor oxidizes or that its molecular / crystalline structure changes upon incorporation into the host lattice of the dental ceramic. The surprising aspect of the present invention is that, with the phosphors presented here, a coloration of the fluorescent dental ceramic can be achieved when excited with light at a wavelength of 415 nm, which is very close to the color of a tooth fluorescent under this excitation. On the line for each of the phosphors 1 to 9, the color locus of the phosphor sintered into a dental ceramic is located as the third point; all of these lie at the apex of the angle indicated by a bold line. There, marked with a star, are the color loci of various natural, fluorescent teeth. Two of the McAdams ellipses from... Fig.Two are also shown there. The very narrow area at the tip of the drawn angle is shown in the next figure as a close-up (A).

[0040] Fig. Figure 8 shows a magnified section A from the diagram in Fig.8. As examples, two color points marked with a star correspond to the fluorescence color of a natural tooth when excited with light of a wavelength of 415 nm. Natural teeth exhibit a certain range of fluorescence. This range is caused by fluoridation, with the age at which the fluoridation occurred and its intensity playing a significant role in the characteristic fluorescence of natural teeth. Other parameters include the thickness of the enamel and the tooth's natural color, which is determined by its structure. Organic-biological substances embedded in the dental metal can also fluoresce. All black squares shown in this enlarged section correspond to the color points of the respective phosphor when that phosphor is sintered into the dental ceramic's host lattice at a concentration of 0.5 wt%.The two McAdams ellipses shown here suggest that the nine different phosphors allow for color coordinates of the fluorescence of natural teeth to be adjusted with a color accuracy approaching the color resolution of human color perception. In this diagram, the lines connecting the color coordinates of each phosphor are extended to the common origin at the indicated angle. This origin represents the color coordinate of human color perception for the pure excitation light. The color coordinate for phosphor 9, which lies outside the angle, corresponds to a dental ceramic that appears somewhat too violet in this excitation light. This dental ceramic is a gallium-free YAG garnet with a stoichiometric coefficient of 0, and therefore falls outside the required range of the stoichiometric coefficient b, exhibiting a luminescence that is no longer acceptable for imitating average teeth.

[0041] In Fig. Figure 9 shows a matrix of ceramic platelets produced according to the sintering process described in Quintessence Dental Technology 2009;35(8):1018-102. The dental ceramics according to the invention exhibit a color and opacity level of 980°C for 6 min and 940°C for 10 min under natural light. REFERENCE MARK LIST A close-up X X-axis in the CIE norm valence diagram Y-axis in the CIE normative valence diagram QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 104 166 A1

[0010] US 2021-0102116 A1

[0011] US 2002-0017021 A1

[0012] Cited non-patent literature

[0000] Meeting of the International Association for Dental Research in 2021

[0009] Lecture on Wednesday, July 21, 2021

[0009] David Lewis McAdams in 1942

[0019]

Claims

[1] Dental ceramics 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 has the following chemical composition: Lu 3-a Ce a Al 5-b Ga b O 12 , where a takes a value of 0.003 <= a < 0.024 and b a value of 0 to 3, the YAG garnet has the following chemical composition: Y 3-a Ce a Al 5-b Ga b O 12 , where a has a value of 0.003 <= a < 0.024 and b has a value of 1 to 3.5, and LuYAG garnet has the following chemical composition: Y 3-a-c Lu c Ge a Al 5-b Ga b O 12, where a takes a value of 0.003 <= a < 0.024, b a value of ⅓(3-ac) to 3.25 and c a value greater than 0. [2] Dental ceramic according to claim 1, characterized by , 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 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. [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 dental ceramics. [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 µm to 20 µm, preferably of 4 µm to 8 µm with a tolerance of ±1 µm. [6] Dental ceramic according to one of claims 1 to 5, characterized by the matrix consists of (K,Li)AlSi3O8, (K,Li)AlSi2O6, NaAlSi3O8 as alkali aluminosilicate and / or Lu2Si2O7 as lutetium disilicate. [7] Dental ceramic according to one of claims 1 to 5, characterized by the matrix consists of ZrO2 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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