Color-masking lithium disilicate glass ceramic and preparation method thereof

Abstract

The invention discloses opaque lithium disilicate glass ceramic and a preparation method thereof, the opaque lithium disilicate glass ceramic is composed of SiO2, K2O, Li2O, Al2O3, P2O5, CeO2, MgO, ZnO and B2O3 as raw materials, the ratio of silicon to lithium is 2.5-2.8, and the mass ratio of SiO2 / (K2O + Li2O) is 3.75-5. The transmittance of the obtained lithium disilicate glass ceramic can be adjusted within 22%-34%, the average value of three-point bending strength is 350-420 MPa, the fracture toughness is 2.5-3.2 MPa.m < 1 / 2 >, the thermal expansion coefficient is (10.6 + / -0.5) * 10 <-6 > / K, the total chromatic aberration delta E value is detected to be smaller than or equal to 1.2 under different background colors through a spectrophotometer, and the lithium disilicate glass ceramic has very high opaque performance, can be matched with the color of adjacent teeth, and is suitable for being used as a dental implant. The method is of great significance in prolonging the service life and improving the aesthetic effect of the prosthesis.

Description

Technical Field

[0001] This invention belongs to the field of glass-ceramic materials, specifically relating to a colorless lithium disilicate glass-ceramic and its preparation method. Background Technology

[0002] In modern dental restoration, the goal is not only to restore the function of damaged or missing teeth, but also to achieve increasingly higher aesthetic standards, with aesthetics even becoming the primary objective in some cases. The transparency of all-ceramic materials is a major aesthetic factor considered by consumers when choosing restorative materials. Transparent / semi-transparent all-ceramic materials can be used for restorations on non-discolored abutments; however, for teeth with varying degrees of discoloration, metal cores and posts, and necrotic teeth, all-ceramic materials with good opacity are required. Therefore, the opacity of all-ceramic restorations is one of the important topics in cosmetic dentistry.

[0003] Lithium disilicate glass-ceramic material is safe, biocompatible, and has high strength. Compared with existing zirconia all-ceramic materials, its strength and hardness are closer to those of natural teeth, so it will not cause secondary wear to healthy natural teeth during long-term wear.

[0004] Patent CN 114524616A achieves the adjustment of the light transmittance of lithium disilicate glass ceramic green bodies by adjusting the isostatic pressure during the preparation of green bodies, as well as adjusting the vacuum degree and sintering number during the sintering of green bodies in a vacuum atmosphere. The light transmittance is between 55% and 62%. Patent CN 113087389A describes a method to adjust the light transmittance of lithium disilicate glass ceramics with the same formulation by controlling the vacuum level during sintering, achieving a minimum transmittance of 31.9%. Patent CN 114716149A relates to a lithium disilicate glass ceramic with gradient transparency and color for dental use, its preparation method and uses. It utilizes millimeter-scale glass powder, through molding and vacuum sintering, without the need for dry pressing and isostatic pressing, to obtain a lithium disilicate glass ceramic with gradient color and transparency. However, glass ceramics prepared by sintering are prone to retaining some pores due to the inherent problems of the sintering process. This can lead to low density or coarse grains, which is not conducive to improving the mechanical properties of glass-ceramics.

[0005] Patent JP 2015-231944A describes a lithium silicate glass combination containing Al2O3 and Li2O, with the ratio of the two contents set at 1:1 to 1.5:1. By utilizing the optical properties of the two crystals, a gradient aesthetic effect can be presented. Patent CN 109592904A describes a high-strength lithium silicate glass composition with high shielding properties, which adjusts the transparency of the glass ceramic by precipitating other secondary crystals in addition to the main crystal.

[0006] Achieving transparency variations through the optical properties of primary and secondary crystals requires precise control of parameters such as sintering temperature and time to ensure uniform growth and distribution of the two crystals. This not only increases the complexity of the preparation process but may also lead to higher production costs. Therefore, it is necessary to develop a color-masking lithium disilicate glass-ceramic that possesses both strong color-masking properties and good mechanical properties to meet the requirements of the restoration for both mechanical performance and aesthetic effects. Summary of the Invention

[0007] The purpose of this invention is to provide a color-masking lithium disilicate glass-ceramic and its preparation method. The glass-ceramic obtained by this invention has lithium disilicate crystals as its main crystalline phase, which not only has strong color-masking properties, but also high three-point bending strength and high fracture toughness. It can also match the color of adjacent teeth, which is of great significance for improving the service life and aesthetic effect of restorations.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: One objective of this invention is to protect a colorless lithium disilicate glass-ceramic. The raw material composition and their weight percentages of the colorless lithium disilicate glass-ceramic, calculated as 100% by weight, are as follows: SiO2 70.01%~78%, K2O 2.0%~6.0%, Li2O 12%~16%, Al2O3 1.0%~4.0%, P2O5 2.8%~6%, CeO2 0.5%~3%, MgO 0.01%~1%, ZnO 0%~2%, B2O3 0.1%~3%, and colorant 0.1%~3%.

[0009] SiO2 and Li2O are the main raw materials for forming the glass-ceramic lithium disilicate crystalline phase; P2O5 is a nucleating agent; Al2O3 is mainly used to reduce the crystallization tendency and rate of glass, increase the glass transition temperature and softening point of glass ceramics, and improve the chemical stability of glass ceramics. B2O3 is mainly used to improve the network structure of glass and also as a flux.

[0010] MgO is used to improve the chemical stability and mechanical strength of glass, control viscosity and crystallization tendency, improve melting performance, and reduce the coefficient of thermal expansion.

[0011] In addition to acting as a flux, alkali metal oxides can also alter the transparency of glass and ceramics.

[0012] ZnO can act as a flux, facilitate glass network breakage, improve crystallization ability, enhance glass alkali resistance, and regulate the glass transition temperature and softening point of glass ceramics.

[0013] Preferably, the raw material composition and their weight percentages of the opaque lithium disilicate glass ceramic, based on a total weight percentage of 100%, are as follows: SiO2 70.01%~76%, K2O 2.0%~6.0%, Li2O 12.5%~16.0%, Al2O3 1.7%~4.0%, P2O5 2.9%~5.6%, CeO2 0.5%~2.8%, MgO 0.01%~1%, ZnO 0%~2%, B2O3 0.1%~3%, and colorant 0.1%~3%.

[0014] Furthermore, the main crystalline phase of the opaque lithium disilicate glass ceramic is lithium disilicate crystal, which does not contain zirconium oxide, and has a silicon-to-lithium ratio of 2.5 to 2.8 and a SiO2 / (K2O+Li2O) mass ratio of 3.75 to 5.

[0015] Furthermore, the colorant includes V2O5, Tb4O7, Er2O3, Fe2O3, Eu2O3, and Pr6O. 11 At least one of MnO2 and TiO2.

[0016] The second objective of this invention is to protect the lithium disilicate glass-ceramic to meet at least one of the following indicators: (1) The average value of the three-point bending strength is 350MPa~420MPa; (2) Transmittance is 22%~34%; (3) The total color difference (ΔE value) detected by a spectrophotometer under different background colors is ≤1.2; (4) Fracture toughness is 2.5~3.2 MPa·m 1 / 2 ; (5) The coefficient of thermal expansion is (10.6±0.5)×10 -6 / K.

[0017] The method for preparing the color-masking lithium disilicate glass ceramic includes the following steps: 1) Weigh the raw materials according to the required components, then mix, melt, and shape the raw materials to make glass blocks; 2) The obtained glass block is subjected to annealing, nucleation treatment, first heat treatment and crystallization heat treatment to obtain the lithium disilicate glass ceramic.

[0018] Furthermore, the melting temperature is 1400℃~1600℃ and the time is 60min~300min.

[0019] Furthermore, the annealing temperature is 380℃~420℃ and the time is 30min~90min.

[0020] Furthermore, the nucleation treatment is performed at a temperature of 430℃ to 600℃ for a time of 30 min to 360 min.

[0021] Furthermore, the temperature of the first heat treatment is 610℃~730℃, and the time is 30min~120min.

[0022] Furthermore, the temperature of the crystallization heat treatment is 800℃~880℃, and the time is 1min~20min.

[0023] In lithium silicate glass ceramics, zirconium oxide is generally used as a nucleating agent to form nucleation sites, inhibiting grain growth and thus improving the transparency of the glass ceramic. However, this also increases the melting temperature of the glass ceramic. This invention does not contain zirconium oxide, lowering the melting temperature and saving energy. Moreover, during crystallization, grain growth forms a rod-shaped interlocking structure, which reduces transparency while increasing the sample's strength. By increasing the silicon-to-lithium ratio in the formulation, the stability of the glass ceramic can be improved. Furthermore, in addition to the main crystalline phase of lithium disilicate, a small amount of residual quartz phase remains in the glass ceramic. This residual quartz phase increases compressive stress, further improving the three-point bending strength, and slightly reduces transmittance, thus achieving the purpose of masking the sample while increasing strength. In addition to acting as a flux, potassium oxide in the formulation can dissolve some silicon dioxide and alumina to form a glassy phase, thereby altering the transparency of the glass ceramic. By controlling the mass ratio of silicon dioxide to the sum of potassium oxide and lithium oxide, specifically, when the mass ratio of silicon dioxide to the sum of potassium oxide and lithium oxide is <3.75, the glass phase increases, transparency increases, and the occlusive property decreases; when the mass ratio is >5, the alkali metal content is low, the melting temperature increases, and energy is wasted. Therefore, this invention obtains a glass-ceramic with lithium disilicate crystals as the main crystalline phase, exhibiting strong occlusive property and high three-point bending strength, by controlling the crystalline phase, glass phase, the content of each component, and the heat treatment regime.

[0024] The significant advantages of this invention are: 1) The lithium disilicate glass ceramic obtained by this invention has high three-point bending strength and fracture toughness, and strong color-masking performance. It has a strong color-masking effect on abutment teeth with mild, moderate and severe discoloration. Therefore, it can be used for abutment teeth with different degrees of discoloration, metal core posts and necrotic pulp teeth restoration, such as in-coronation restorations, inlays, high inlays, veneers, etc., which is of great significance for improving the service life and aesthetic effect of restorations.

[0025] 2) The occlusive lithium disilicate glass ceramic of this invention can replace the occlusive porcelain layer or even the body porcelain layer and be used directly as the occlusive porcelain, which greatly reduces the preparation process of traditional dental restorations that require occlusion, saving a lot of manpower, material resources and time costs; at the same time, it avoids the phenomenon of porcelain peeling, chipping and cracking during use, which greatly reduces the cost of remaking the restoration, which is conducive to expanding the clinical application of lithium disilicate glass ceramics and has great significance in the field of dental restoration.

[0026] 3) The lithium disilicate glass ceramic of the present invention has strong machinability and can cut edges with a thickness of 0.2 mm with good edge integrity; 4) The production process of lithium disilicate glass ceramic of the present invention is simple, has a high controllability coefficient, and has good prospects for industrial application. Attached Figure Description

[0027] Figure 1 The image shows the XRD pattern of the opaque lithium disilicate glass-ceramic prepared in Example 1. As can be seen from the image, the main crystalline phase of the obtained glass-ceramic is lithium disilicate, with a small amount of residual quartz phase.

[0028] Figure 2 The graph shows the thermal expansion curve of the opaque lithium disilicate glass-ceramic prepared in Example 2. As can be seen from the graph, the coefficient of thermal expansion of the obtained glass-ceramic is 10.6 × 10⁻⁶ °C between 27 °C and 500 °C. -6 / K, which matches the coefficient of thermal expansion of the porcelain powder and glaze.

[0029] Figure 3 The image shows the edge integrity of the 0.2mm surface of the opaque lithium disilicate glass-ceramic prepared in Example 4. As can be seen from the image, the edge integrity is good at 0.2mm, indicating that the provided opaque lithium disilicate glass-ceramic has strong machinability. Detailed Implementation

[0030] A type of opaque lithium disilicate glass-ceramic, with the following raw material composition and weight percentages as a total of 100%: SiO2 70.01%~78%, K2O 2.0%~6.0%, Li2O 12%~16%, Al2O3 1.0%~4.0%, P2O5 2.8%~6%, CeO2 0.5%~3%, MgO 0.01%~1%, ZnO 0%~2%, B2O3 0.1%~3%, and colorant 0.1%~3%; and the silicon-to-lithium ratio is 2.5~2.8, and the SiO2 / (K2O+Li2O) mass ratio is 3.75~5.

[0031] Furthermore, the colorant includes V2O5, Tb4O7, Er2O3, Fe2O3, Eu2O3, and Pr6O. 11 At least one of MnO2 and TiO2.

[0032] The method for preparing the color-masking lithium disilicate glass ceramic includes the following steps: 1) Weigh the raw materials according to the required components, ball mill and mix the raw materials evenly, degas them, and then place them in a high-temperature furnace and melt them at 1400℃~1600℃ for 60min~300min to make glass melt; 2) After the molten glass is melted evenly, it is poured into the required mold and demolded to obtain a transparent glass block; 2) The obtained glass block is annealed at 380℃~420℃ for 30min~90min, then nucleated at 430℃~600℃ for 30min~360min, then subjected to a first heat treatment at 610℃~730℃ for 30min~120min, and then subjected to a crystallization heat treatment at 800℃~880℃ for 1min~20min to obtain the lithium disilicate glass ceramic.

[0033] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0034] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0035] A method for preparing a colorless lithium disilicate glass-ceramic is as follows: (1) Weigh each raw material (analytical grade) according to the components in Table 1. Potassium oxide and lithium oxide are introduced by potassium carbonate and lithium carbonate respectively, phosphorus pentoxide is introduced by ammonium dihydrogen phosphate, boron oxide is introduced by boric acid, and the remaining raw materials are silicon dioxide, aluminum oxide, cerium oxide, magnesium oxide and zinc oxide. (2) Ball mill each raw material from step (1) for 8 hours to mix them evenly, and then degas them in a muffle furnace; (3) Place the mixed material from step (2) into a high-temperature melting furnace and melt it at 1500°C for 2 hours; (4) Cast the molten material obtained in step (3) into a mold and demold it; (5) Anneal the glass block obtained from demolding in step (4) at 420°C for 0.5 h; (6) Nucleate the material after annealing in step (5) at 520°C for 1 hour; (7) Heat-treat the material after nucleation in step (6) at 630°C for 0.5 h; (8) The material after heat treatment in step (7) is crystallized at 850°C for 7 min to obtain lithium disilicate glass ceramic.

[0036] Table 1. Mass percentage of each component in lithium disilicate glass ceramic (%)

[0037] Test experiment: 1. Three-point bending strength and fracture toughness (1) Average value of three-point bending strength: tested according to GB30367-2025; (2) Fracture toughness: Tested according to the single-edge V-notch beam (SEVNB) method.

[0038] Table 2. Three-point bending strength and fracture toughness values ​​of different samples

[0039] As shown in Table 2, the opaque lithium disilicate glass-ceramics prepared in the examples and comparative examples all exhibit high three-point bending strength and fracture toughness.

[0040] 2. Test method for shading performance Haze refers to the cloud-like or cloudy appearance of a transparent or translucent material's interior or surface due to light diffusion. It is expressed as the percentage of diffused luminous flux to luminous flux transmitted through the material. Higher haze indicates decreased transparency. Transmittance, on the other hand, is the percentage of luminous flux that passes through a transparent or translucent material relative to its incident luminous flux; it is an indicator of a material's ability to allow light to pass through. A material's opacity is a result of both its haze and transmittance.

[0041] Transparency parameters are commonly expressed as TP (Translucency Parameter). TP represents the color difference between a material of uniform thickness and a standard black and standard white background. The calculation formula is as follows: the smaller the TP value, the lower the light transmittance of the material and the better its color-blocking ability; conversely, the higher the light transmittance of the material, the worse its color-blocking ability. , Where L, a, and b represent the chromaticity values ​​of the object's color, which are the color space coordinates of the sample color; L B a B b B L represents the chromaticity value of the sample against a standard black background. W a W b W This represents the chromaticity value of the sample against a standard white background.

[0042] Under glass-ceramic fixation conditions, the thicker the ceramic slab, the stronger its opacity. However, the thicker the ceramic slab, the thicker the abutment tooth needs to be. This study measured the TP value and opacity against different backgrounds using 1mm thick samples. The specific procedure was as follows: a transmittance meter was used to measure the haze transmittance of the 1.0mm sample, and a spectrophotometer was used to measure and calculate the TP of glass-ceramic specimens of the same thickness (1.0mm). Using A2 color (natural normal dentin) as a control group, the Lab values ​​of glass-ceramic samples of the same thickness (1.0mm) were measured under A3, C4, titanium alloy, and cobalt-chromium alloy backgrounds. The total color difference (ΔE value) between each specimen under A2 background and other backgrounds was calculated using the following formula to clarify the transparency parameters of the samples and their opacity against different background colors. The A3 background simulates dark dentin, and the C4 background simulates fluorosis-affected dentin; titanium alloy and cobalt-chromium alloy respectively simulate the clinical application of titanium abutments and metal core posts for restoration; the A3 / C4 color blocks, titanium alloy, and cobalt-chromium alloy have a diameter of 8mm and a thickness of 4mm. , When the △E value is less than 1.2, it indicates that the ceramic tile has excellent color-blocking ability; 1.2 < ΔE value < 2.7, indicating that the ceramic tile has a certain ability to cover the color, but cannot completely cover the background color; When the △E value is greater than 2.7, it indicates that the porcelain tile has very poor color-blocking ability.

[0043] Table 3. TP values ​​of different samples and their ΔE values ​​under different background conditions.

[0044] As can be seen from the table above, the haze and transmittance of the lithium disilicate glass ceramic prepared in the examples are lower than (97, 34), and its ΔE is less than or equal to 1.2 under different backgrounds, indicating that it has extremely strong opacity and is an ideal opacity-masking restorative material. It can be used for restorations of teeth with different degrees of discoloration, metal cores and posts, and teeth with dead pulp. The transmittance of the lithium disilicate glass ceramic prepared in Comparative Example 1 exceeds 35%, and the sample only has extremely strong opacity for dark dentin. It only has a certain opacity for fluorosis, titanium abutments, and metal post restorations, but cannot cover the background color. The transmittance of the lithium disilicate glass ceramic prepared in Comparative Examples 2 and 3 are 39.3 and 40.2, respectively. Their opacity for all background colors is very weak, and they basically cannot cover the background color.

[0045] 3. Edge integrity test: SK-5D digital dental cutting machine, test the veneer integrity with an edge of 0.2mm.

[0046] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A colorless lithium disilicate glass-ceramic, characterized in that, The raw material composition and weight percentage of the opaque lithium disilicate glass ceramic, calculated as follows (sum of weight percentages as 100%), are: SiO2 70.01%~78%, K2O 2.0%~6.0%, Li2O 12%~16%, Al2O3 1.0%~4.0%, P2O5 2.8%~6%, CeO2 0.5%~3%, MgO 0.01%~1%, ZnO 0%~2%, B2O3 0.1%~3%, and colorant 0.1%~3%; and the silicon-to-lithium ratio is 2.5~2.8, and the SiO2 / (K2O+Li2O) mass ratio is 3.75~5.

2. The opaque lithium disilicate glass-ceramic according to claim 1, characterized in that, The raw material composition and weight percentage of the opaque lithium disilicate glass ceramic, calculated as follows (sum of weight percentages as 100%), are: SiO2 70.01%~76%, K2O 2.0%~6.0%, Li2O 12.5%~16.0%, Al2O3 1.7%~4.0%, P2O5 2.9%~5.6%, CeO2 0.5%~2.8%, MgO 0.01%~1%, ZnO 0%~2%, B2O3 0.1%~3%, and colorant 0.1%~3%; and the silicon-to-lithium ratio is 2.5~2.8, and the SiO2 / (K2O+Li2O) mass ratio is 3.75~5.

3. The opaque lithium disilicate glass-ceramic according to claim 1 or 2, characterized in that, The colorants include V2O5, Tb4O7, Er2O3, Fe2O3, Eu2O3, and Pr6O. 11 At least one of MnO2 and TiO2.

4. The opaque lithium disilicate glass-ceramic according to claim 1 or 2, characterized in that, The lithium disilicate glass-ceramic meets at least one of the following properties: (1) The average value of the three-point bending strength is 350MPa~420MPa; (2) Transmittance is 22%~34%; (3) Fracture toughness is 2.5~3.2 MPa·m 1 / 2 ; (4) The coefficient of thermal expansion is (10.6±0.5)×10 -6 / K.

5. A method for preparing opaque lithium disilicate glass-ceramic as described in claim 1, characterized in that, Includes the following steps: 1) Weigh the raw materials according to the required components, then mix, melt, and shape the raw materials to make glass blocks; 2) The obtained glass block is subjected to annealing, nucleation treatment, first heat treatment and crystallization heat treatment to obtain the lithium disilicate glass ceramic.

6. The method for preparing opaque lithium disilicate glass-ceramic according to claim 5, characterized in that, The annealing temperature is 380℃~420℃ and the time is 30min~90min.

7. The method for preparing opaque lithium disilicate glass-ceramic according to claim 5, characterized in that, The nucleation treatment is performed at a temperature of 430℃ to 600℃ for a time of 30 min to 360 min.

8. The method for preparing opaque lithium disilicate glass-ceramic according to claim 5, characterized in that, The temperature of the first heat treatment is 610℃~730℃, and the time is 30min~120min.

9. The method for preparing opaque lithium disilicate glass-ceramic according to claim 5, characterized in that, The temperature of the crystallization heat treatment is 800℃~880℃, and the time is 1min~20min.

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