Bimodal crystal lithium disilicate glass-ceramics, preparation method and application thereof

Abstract

This invention discloses a bimodal grain lithium disilicate glass-ceramic, its preparation method, and its applications. Through a three-step synergistic process involving low-temperature heat treatment, microwave heating treatment, and high-temperature heat treatment, the homogeneous grains are self-toughened by the selective heating characteristics of microwaves, eliminating the need for the introduction of external reinforcing phases and precisely controlling grain growth and phase transformation. The resulting glass-ceramic exhibits a bimodal grain size distribution structure. Large grains enhance toughness through a fiber-like toughening mechanism, while small grains achieve fine-grain strengthening. Its fracture toughness is (3.8±0.15)~(4.42±0.19) MPa·m. 1 / 2 It exhibits a flexural strength ≥400MPa, along with good transparency and machinability. This process is simple, controllable, and easily industrialized. Applying it to dental restorative materials can address the shortcomings of existing materials, meet clinical needs, and contribute to the domestic production of dental restorative materials.

Description

Technical Field

[0001] This invention belongs to the field of microcrystalline glass preparation technology, specifically to a bimodal grain lithium disilicate microcrystalline glass, its preparation method and application, which is applicable to the preparation and application of dental restorative materials. Background Technology

[0002] Lithium disilicate glass-ceramic, a high-quality inorganic dental restorative material that has emerged in recent years, is primarily used in the field of dental restoration. When teeth are damaged due to factors such as disease, accidental injury, or aging, appropriate restorative materials are needed for treatment. Lithium disilicate glass-ceramic boasts multiple advantages, including moderate strength, a translucent, jade-like appearance, and excellent machinability. It is unlikely to cause secondary damage to healthy teeth after restoration and is highly compatible with CAD / CAM (computer-aided design and manufacturing) dental processing systems, making it one of the preferred materials for clinical restoration. However, the current market supply of this material is highly dependent on imports, with a low level of domestic production, leading to continuously rising market prices and limiting its wider clinical application.

[0003] While lithium disilicate glass-ceramics offer significant advantages in dental restorations, their inherent lack of toughness is a prominent issue. Due to this insufficient toughness, restorations made from them are prone to chipping, cracking, and other failures after 4 to 10 years of use, significantly shortening their lifespan and impacting restorative outcomes. Furthermore, low domestic production rates result in high market prices, making them unaffordable for many patients and medical institutions, further limiting the widespread clinical application of lithium disilicate glass-ceramics.

[0004] To address the insufficient toughness of lithium disilicate glass-ceramics, various toughening methods have been proposed in existing technologies. Chemical tempering enhances toughness by improving the material's fracture strength, but it easily damages the stress-reinforcing layer during restoration processing and poses a potential risk of stress layer failure under long-term chewing loads. Particle / fiber toughening methods incorporating external reinforcing phases such as ZrO2 (zirconia) and LiNbO3 (lithium niobate) can improve toughness, but the refractive index mismatch between the reinforcing phase and the lithium disilicate matrix causes additional light scattering, significantly reducing the material's translucency and violating the aesthetic requirements of dental restorations. Traditional heat treatment autologous toughening methods have limited toughening effects, and improper control of heat treatment parameters can easily lead to a decrease in material strength. Furthermore, the method of artificially preparing large-sized lithium disilicate grains and then incorporating them into the matrix not only suffers from poor operational reliability and stability but also faces difficulties in industrialization.

[0005] Existing toughening technologies all have significant limitations and cannot effectively solve the problem of insufficient toughness in lithium disilicate glass-ceramics. Chemical tempering and the introduction of external reinforcing phases carry the risks of stress layer failure and reduced light transmittance, respectively. Traditional heat treatment-based self-toughening and artificial preparation of large-size grains offer limited toughening effects and are difficult to industrialize. Therefore, developing a preparation process that does not introduce heterogeneous phases, does not reduce material transparency and processability, and can significantly improve the toughness of lithium disilicate glass-ceramics is particularly urgent. This will be a key breakthrough in promoting the domestic production of this material and facilitating its widespread clinical application. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a bimodal lithium disilicate microcrystalline glass, its preparation method, and its application. By utilizing a self-toughening strategy of microwave heating treatment, a microstructure with a bimodal grain size distribution is constructed. Without introducing heterogeneous phases or changing the basic chemical composition, the mechanical properties of the lithium disilicate microcrystalline glass are significantly improved, while also taking into account the optical transparency and clinical machinability of the material, thus achieving high performance and domestic production of dental restorative materials.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing bimodal grain lithium disilicate microcrystalline glass, the specific steps of which include: Low-temperature heat treatment was performed on transparent hard glass containing lithium disilicate to obtain a glass-ceramic precursor containing lithium metasilicate crystal nuclei. Microwave heating treatment was performed on a glass-ceramic precursor containing lithium metasilicate crystal nuclei to obtain glass-ceramic containing large-sized lithium metasilicate grains. High-temperature heat treatment was performed on glass-ceramics containing large-sized lithium metasilicate grains to obtain glass-ceramics with bimodal grain size distribution of lithium disilicate.

[0008] Furthermore, the low-temperature heat treatment temperature is 50°C to 80°C higher than the glass transition temperature of transparent hard glass containing lithium disilicate, and the holding time is 2 to 4 hours.

[0009] Furthermore, the microwave heating treatment uses 2.45GHz frequency band pulsed microwaves, with a microwave power of 500W~1000W, a single heating time of 0.3min~2min, and a pulse cycle of 30~50 times.

[0010] Furthermore, the high-temperature heat treatment temperature is 815℃~885℃, and the holding time is 2h~6h.

[0011] The present invention also provides a bimodal lithium disilicate glass crystal, which is prepared by the above-mentioned method for preparing a bimodal lithium disilicate glass crystal.

[0012] Furthermore, the microcrystalline glass has a bimodal grain size distribution structure, comprising long rod-shaped lithium disilicate large grains with a size greater than 10 μm and rice-grain-shaped lithium disilicate small grains with a size less than 2 μm.

[0013] Furthermore, the fracture toughness of the bimodal grain lithium disilicate glass-ceramic is (3.8 ± 0.15) MPa·m. 1 / 2 ~(4.42±0.19)MPa·m 1 / 2 Flexural strength ≥400MPa.

[0014] This invention also provides an application of bimodal lithium disilicate microcrystalline glass as a dental restorative material.

[0015] The present invention also provides a dental restorative material, wherein the raw material of the dental restorative material includes the above-mentioned bimodal lithium disilicate microcrystalline glass.

[0016] Furthermore, the visible light transmittance of the bimodal grain lithium disilicate microcrystalline glass is 16%~22%.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides a method for preparing bimodal lithium disilicate microcrystalline glass, constructing a three-step synergistic and progressive process system of low-temperature heat treatment, microwave heating treatment, and high-temperature heat treatment. This process system precisely matches the phase transition evolution mechanism of lithium disilicate crystals, and can effectively construct a scientifically controllable crystal nucleation, growth, and phase transition path, as follows: Through the first step of the low-temperature heat treatment process, uniform precipitation of lithium metasilicate crystal nuclei can be achieved in the glass system, providing a stable precursor basis for the subsequent directional growth of grains, effectively avoiding technical problems such as subsequent grain size disorder and performance fluctuation caused by uneven distribution of crystal nuclei; the second step... The microwave heating process leverages the difference in dielectric loss between lithium metasilicate crystals and the glass phase to selectively apply microwave energy. This drives only the localized rapid heating of lithium metasilicate grains to complete their growth, while the glass phase remains at a low temperature with no new crystal nuclei generated. This ensures the controllable growth of large-sized lithium metasilicate grains, providing crucial technical support for subsequent homogeneous grain self-toughening. The third step, high-temperature heat treatment, precisely induces a controllable regression phase transition in large-sized lithium metasilicate, achieving a directional conversion from lithium metasilicate to lithium disilicate. This ultimately results in the stable fabrication of lithium disilicate glass-ceramics with a bimodal grain size distribution. This fabrication process is logically rigorous and highly controllable, eliminating the need for complex post-processing steps. It effectively solves the technical bottlenecks of precise grain size control and insufficient mechanical properties in existing lithium disilicate glass-ceramics, while avoiding problems such as decreased material transparency and deteriorated processability caused by the introduction of external reinforcing phases. This lays a solid technological foundation for the subsequent fabrication of high-strength, high-toughness lithium disilicate glass-ceramics with excellent optical properties. Meanwhile, the process has the advantages of being easy to operate and highly repeatable, making it easy to achieve large-scale industrial production, which is of great significance for promoting the domestic substitution of lithium disilicate dental restorative materials.

[0018] Furthermore, this invention limits the low-temperature heat treatment temperature to 50°C~80°C above the glass transition temperature and the holding time to 2h~4h. This ensures uniform precipitation of lithium metasilicate nuclei within the glass system, effectively avoiding the formation of coarse impurity crystals. This provides a uniform and stable precursor foundation for the directional growth of large-sized lithium metasilicate grains in the subsequent microwave heating stage, ensuring the stability and repeatability of the entire process. This invention specifies that the microwave heating treatment uses 2.45GHz pulsed microwaves with specific power, single heating time, and pulse cycle number. Utilizing the difference in dielectric loss between lithium metasilicate and the glass phase, selective microwave heating is achieved, driving only localized rapid heating and growth of lithium metasilicate grains. The glass phase remains at a low temperature without new nuclei formation, thus ensuring that lithium metasilicate grains can grow to a larger size. Size is crucial for the subsequent formation of large-sized lithium disilicate grains and the self-toughening of homogeneous grains, while avoiding interference from impurities and improving the stability of material performance. This invention limits the high-temperature heat treatment temperature to 815~885℃ and the holding time to 2~6h, which can precisely induce a controllable retrograde phase transformation of large-sized lithium metasilicate, ensuring that it reacts fully with the silicon dioxide in the remaining glass to generate the target crystalline phase of lithium disilicate in situ, while simultaneously precipitating fine grains, successfully constructing a bimodal grain size distribution structure. This parameter range can take into account both the sufficiency of phase transformation and the controllability of grain size, avoiding problems such as impurity formation and unqualified grain size caused by excessively high or low temperatures, further ensuring that the final prepared microcrystalline glass has a uniform microstructure and that its mechanical and optical properties meet the design standards.

[0019] The bimodal lithium disilicate microcrystalline glass prepared by this invention does not require the introduction of external reinforcing phases or change the basic chemical composition of lithium disilicate. It achieves self-toughening of homogeneous grains, which significantly improves the mechanical properties of the material while taking into account its optical transparency and clinical machinability. It solves the problem of the difficulty in balancing mechanical properties and transparency in existing lithium disilicate microcrystalline glass, and can meet the high-performance requirements of dental restorative materials, thus promoting the domestic substitution of dental restorative materials.

[0020] Furthermore, this invention clarifies that the microcrystalline glass has a bimodal grain size distribution structure with large rod-shaped lithium disilicate grains larger than 10 μm and small rice-grain-shaped lithium disilicate grains smaller than 2 μm. The large rod-shaped grains can improve the material's toughness through fiber-like toughening mechanisms such as crack bridging, pull-out, and deflection, while the small grains can achieve fine-grain strengthening to improve the material's strength. The synergistic effect of these two structures significantly improves the overall mechanical properties of the microcrystalline glass, reduces the probability of chipping and cracking in dental restorations, and extends the material's service life. Simultaneously, both types of grains are homogeneous and have no refractive index difference with the glass matrix, ensuring good optical properties. The fracture toughness of the bimodal lithium disilicate microcrystalline glass of this invention is (3.8±0.15)~(4.42±0.19) MPa·m. 1 / 2With a bending strength ≥400MPa, the material's high-performance indicators are clearly defined. Compared with existing lithium disilicate microcrystalline glass, its mechanical properties are significantly improved. It can effectively resist external impacts during dental restoration and use, greatly reduce the risk of restoration failure, improve safety and durability, and fully meet the clinical mechanical requirements for dental restorations. This material also has excellent mechanical and optical properties.

[0021] Furthermore, this invention applies bimodal lithium disilicate microcrystalline glass to dental restorative materials, fully utilizing its advantages of high strength, high toughness, good optical transparency, and machinability. This adapts to the aesthetic and clinical processing requirements of dental restorations, solving the problems of insufficient mechanical properties, easy chipping, poor transparency, or poor machinability in existing dental restorative materials. It provides a high-performance, highly adaptable new material for dental restorations, promoting the upgrading of dental restoration technology, while also contributing to the localization of dental restorative materials and reducing treatment costs. The raw materials for dental restorative materials include this bimodal lithium disilicate microcrystalline glass, ensuring that the dental restorative materials inherit its high strength and toughness from the raw material level. Its advantages, such as high strength and toughness, good transparency and machinability, ensure that the material performance meets the standards and avoids quality problems of restorations caused by improper raw materials. Moreover, the raw materials can be sourced domestically, reducing production costs and meeting the needs of large-scale clinical applications. The visible light transmittance of bimodal lithium disilicate glass reaches 16%~22%, which can ensure that the material has a good translucent jade-like appearance, matching the optical characteristics of natural teeth, meeting the aesthetic requirements of dental restorations, solving the problems of insufficient transparency and poor aesthetics of existing high-performance dental restoration materials, improving the aesthetics and clinical adaptability of dental restorations, while not affecting the mechanical properties and machinability of the material. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the decomposition of lithium metasilicate crystals. The formation of lithium disilicate crystals involves the self-conversion of lithium metasilicate and the release of Li. + The secondary reaction involves two mechanisms, and the lithium disilicate crystals obtained from the self-transformation can inherit the appearance and morphology of lithium metasilicate crystals.

[0023] Figure 2 This is a schematic diagram of microwave-assisted heating. Under microwave heating, no new crystal nuclei are formed, thus ensuring the full growth of lithium metasilicate crystals, allowing them to grow to a larger size. After the lithium metasilicate crystals decompose, large-sized lithium disilicate crystals are obtained, ultimately achieving the effect of homogeneous grain self-toughening.

[0024] Figure 3 The crystal phase composition of the lithium disilicate microcrystalline glass prepared according to the present invention.

[0025] Figure 4 The microstructure of lithium disilicate glass prepared according to the present invention is shown. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0027] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0028] This invention discloses a microwave-assisted method for preparing bimodal lithium disilicate glass-ceramics. Using transparent hard glass of lithium disilicate as the glass matrix, a self-toughening strategy of microwave heating is employed. Through the controllable growth and retrograde metamorphic phase transformation of lithium metasilicate, a microstructure with a bimodal grain size distribution is constructed, resulting in lithium disilicate glass-ceramics possessing both high toughness and high transparency. The specific method is as follows: 1) A variety of oxide raw materials based on Li2CO3 and SiO2 are mixed evenly to obtain lithium disilicate glass raw material. According to the stoichiometric ratio of lithium disilicate, the molar ratio of Li2O to SiO2 obtained after heat treatment of Li2CO3 is required to be 1:1~1:2. By mass percentage, the mixed raw materials for lithium disilicate glass include 22%~35% Li2CO3, 50%~55% SiO2, and the remainder is one or more composite additives selected from ZrO2, Al2O3, K2O, and P2O5. The total content of additives is 5%~18%, which are used to regulate the crystallization behavior and dielectric properties of the glass without changing the basic phase composition of lithium disilicate.

[0029] 2) Weigh the raw materials according to the proportion and mix them thoroughly to obtain mixture 1. Use anhydrous ethanol to prepare all the raw materials into a slurry. The mass ratio of anhydrous ethanol to mixture 1 is 2.5~2.8:1. 3) After the slurry is ball-milled for 4-6 hours and mixed evenly, it is placed in a drying oven and dried at a drying temperature of 40-75℃. Then, it is kept at 740-955℃ for 2.5 hours to obtain a pre-fired block. The pre-fired block is placed in a high-purity corundum crucible and completely melted in a muffle furnace at 1200-1550℃ to remove air bubbles and obtain clear glass liquid. 3) Pour the clarified glass liquid into a mold, cool and solidify it, and then anneal it to obtain transparent hard glass with lithium disilicate composition; Preferably, the annealing temperature is 450~500℃, and the holding time is 2 hours to eliminate internal stress in the glass and ensure its transparency.

[0030] 4) A low-temperature heat treatment is performed on transparent hard glass containing lithium disilicate to precipitate lithium metasilicate (Li2SiO3) crystal nuclei, thus obtaining a microcrystalline glass precursor containing lithium metasilicate crystal nuclei. Preferably, low-temperature heat treatment: the temperature is 50~80°C higher than the Tg (glass transition temperature) of the above-mentioned transparent hard glass, and the holding time is 2~4h; to ensure that lithium metasilicate crystal nuclei are uniformly precipitated in the glass without the formation of coarse impurities.

[0031] 5) The precursor of the glass-ceramic containing lithium metasilicate crystal nuclei is placed in a microwave sintering furnace for microwave-assisted heating treatment. By using microwave heating treatment, based on the difference in dielectric loss between the lithium metasilicate crystal and the glass phase, the lithium metasilicate crystal is locally heated and grows rapidly, while the glass phase is kept at a low temperature and no additional crystal nuclei are formed, thus obtaining a glass-ceramic containing large-sized lithium metasilicate grains. Microwave heating treatment: 2.45 GHz pulsed microwaves are used, with a microwave power of 500~1000W, a single heating time of 0.3~2min, and a pulse cycle of 30~50 times; 6) High-temperature heat treatment of glass-ceramics containing large-sized lithium metasilicate grains induces a controllable retrograde metamorphic phase transformation of lithium metasilicate, generating in-situ long rod-shaped lithium disilicate grains larger than 10 μm. Simultaneously, fine lithium disilicate grains smaller than 2 μm precipitate in the glass matrix, resulting in a lithium disilicate glass-ceramic with a bimodal grain size distribution. The fracture toughness of this lithium disilicate glass-ceramic can reach (3.8±0.15)~(4.42±0.19) MPa·m. 1 / 2 Bending strength ≥ 400 MPa, specifically: Preferably, high-temperature heat treatment is performed at a temperature of 815~885℃ for a holding time of 2~6 hours.

[0032] like Figure 1 As shown, lithium disilicate crystals in this invention exhibit two formation mechanisms. Figure 1 (a) is the initial complete lithium metasilicate crystal. Figure 1 (b) shows the decomposition of lithium metasilicate grains, Li+ Diffusion into the silicon-rich region and in-situ formation of lithium disilicate crystal nuclei. Figure 1 (c) Two different morphologies of lithium disilicate crystals were formed after the final phase transition.

[0033] like Figure 2 As shown, compared to the ordinary heating process where the growth of existing grains and the precipitation of a large number of new crystal nuclei occur simultaneously, the present invention uses microwave heating treatment, which only drives the directional growth of existing lithium metasilicate grains, and no additional new crystal nuclei are generated in the glass matrix throughout the process, so as to stably obtain large-sized precursor grains.

[0034] Example 1 This invention prepares high-toughness and high-transparency lithium disilicate microcrystalline glass with coexisting bimodal grains. The method includes melting transparent hard glass with lithium disilicate composition and microwave-assisted heat treatment crystallization of transparent hard glass with lithium disilicate composition to obtain lithium disilicate microcrystalline glass. Specifically, it is carried out according to the following steps: (1) Raw material mixing: Mix Li2CO3, SiO2, Al2O3, ZrO2, K2O and P2O5 evenly to obtain a mixture. The specific raw material ratios are shown in Table 1 below.

[0035] Table 1 shows the mass percentage (wt.%) of each raw material in Example 1.

[0036] (2) All raw materials were prepared into a slurry using anhydrous ethanol, with a mass ratio of anhydrous ethanol to the mixture of 2.8:1. The slurry was ball-milled for 4 hours to mix evenly and then placed in a drying oven at 40°C for drying. It was then kept at 900°C for 2.5 hours to obtain a pre-fired block. The pre-fired block was placed in a high-purity corundum crucible and kept at 1550°C for 3 hours in a muffle furnace to completely melt the raw materials and remove air bubbles, thus obtaining a clear glass melt. The glass melt was quickly poured into a square stainless steel mold, cooled, demolded, and then placed in a muffle furnace at 480°C for annealing for 2 hours. The annealed glass was cut into small pieces of 20×20×1.5mm using a diamond low-speed saw, ground and polished, and then used for later use to obtain a transparent hard glass with lithium disilicate composition.

[0037] (3) Differential scanning calorimetry (DSC) was performed on the transparent hard glass to determine its Tg temperature. In this example, the Tg of the glass was 469℃.

[0038] (4) Based on the Tg temperature, the lithium disilicate transparent glass is subjected to stepwise heat treatment and microwave treatment: Low-temperature heat treatment: 520℃ (above Tg 50℃), hold for 2h, uniformly precipitate lithium metasilicate (Li2SiO3) crystal nuclei to obtain a glass-ceramic precursor; Microwave heating treatment: 2.45 GHz pulsed microwave, power 800W, 1 minute for each heating, 40 cycles, to enable local rapid growth of lithium metasilicate crystal nuclei, resulting in large-sized lithium metasilicate grains, with no additional crystallization in the glass matrix; High-temperature heat treatment: 885℃, hold for 2 hours, induce lithium metasilicate to undergo a retrograde phase transformation, generate rod-shaped lithium disilicate large grains in situ, and at the same time precipitate rice-grain-shaped fine grains in the matrix, to obtain bimodal grain lithium disilicate microcrystalline glass.

[0039] The specific effects of this three-step process are as follows: First, in the low-temperature heat treatment stage at 520℃, lithium metasilicate nuclei are uniformly precipitated in the glass, laying the foundation for subsequent grain growth; subsequently, in the microwave heating treatment stage, because the dielectric loss of lithium metasilicate is much higher than that of the glass phase, local rapid heating growth can be achieved, forming rod-shaped lithium metasilicate grains with a length exceeding 20μm; finally, in the high-temperature heat treatment stage at 885℃, lithium metasilicate (Li2SiO3) reacts with silicon dioxide (SiO2) in the remaining glass to generate the target crystalline phase lithium disilicate (Li2Si2O5). Figure 3 As shown, all characteristic peaks in the XRD pattern of the microcrystalline glass prepared by this invention belong to pure-phase lithium disilicate, with no impurity phases formed; as Figure 4 Microscopic scanning morphology revealed a bimodal grain distribution structure within the product, exhibiting both large, long rod-shaped grains and fine, millet-like grains. At this stage, lithium disilicate releases Li through self-conversion and decomposition of lithium metasilicate. + The secondary reaction involves two mechanisms, resulting in the formation of long grains exceeding 10 μm in size and approximately 1 μm in width, exhibiting a good aspect ratio. Small grains, with a length of approximately 2 μm, are also produced. The small grains enhance the glass's strength, while the large grains act like short fibers, providing excellent reinforcement and toughening effects. The synergistic effect of these two processes significantly improves the strength and toughness of the glass-ceramic. After the aforementioned microwave-assisted three-step treatment, the fracture toughness of the prepared lithium disilicate glass-ceramic reaches 4.24 ± 0.21 MPa·m. 1 / 2 The bending strength reaches 420±15MPa, and the visible light transmittance is 22%.

[0040] Example 2 (1) A transparent hard glass with lithium disilicate composition was prepared using the method described in Example 1.

[0041] (2) The Tg of the glass was measured to be 480.3℃.

[0042] (3) Based on the Tg temperature, lithium disilicate transparent glass is subjected to stepwise heat treatment and microwave treatment: Low-temperature heat treatment: 540℃ (above Tg 60℃), hold for 3 hours to precipitate lithium metasilicate crystal nuclei; Microwave heating treatment: 2.45 GHz pulsed microwave, 500W power, 2 min for each heating cycle, 50 cycles, to grow large-sized lithium metasilicate grains; High-temperature heat treatment: 850℃, held for 4 hours, to complete the retrograde metamorphic phase transformation and obtain bimodal grain lithium disilicate microcrystalline glass.

[0043] The lithium disilicate glass-ceramic prepared in this embodiment has a fracture toughness of 4.07 ± 0.13 MPa·m. 1 / 2 The bending strength reaches 410±12 MPa, and the visible light transmittance is 16%, which meets the mechanical and aesthetic requirements of dental restorative materials.

[0044] Example 3 (1) A transparent hard glass with lithium disilicate is prepared by the method described in Example 1, wherein the content of Li2CO3 is 22%, the content of SiO2 is 55%, and the total content of additives is 23%.

[0045] (2) The Tg of the glass was measured to be 475.6℃.

[0046] (3) Based on the Tg temperature, lithium disilicate transparent glass is subjected to stepwise heat treatment and microwave treatment: Low-temperature heat treatment: 555℃ (above Tg 80℃), hold for 4 hours to precipitate lithium metasilicate crystal nuclei; Microwave heating treatment: 2.45GHz pulsed microwave, power 1000W, single heating 0.3min, 30 cycles, to grow large-sized lithium metasilicate grains; High-temperature heat treatment: 815℃, held for 6 hours, to complete the retrograde metamorphic phase transformation and obtain bimodal lithium disilicate microcrystalline glass.

[0047] The lithium disilicate glass-ceramic prepared in this embodiment has a fracture toughness of 3.95 ± 0.18 MPa·m. 1 / 2 It has a bending strength of 405±10MPa, a visible light transmittance of 18%, is compatible with CAD / CAM dental processing systems, and has good edge integrity after processing with no chipping defects.

[0048] In summary, this invention discloses a microwave-assisted preparation method for bimodal lithium disilicate glass-ceramics, along with its application. Utilizing microwave heating treatment and a controllable retrograde phase transformation of lithium metasilicate, a bimodal grain size distribution microstructure is constructed in situ, achieving self-toughening of the lithium disilicate glass-ceramics. This method eliminates the need for introducing external reinforcing phases, ensuring the material's transparency and processability. The process is simple and controllable, using domestically produced raw materials. The prepared glass-ceramics exhibit excellent mechanical properties, fully meeting the requirements for dental restorations. This promotes the domestic substitution and clinical application of lithium disilicate dental restorative materials and provides new ideas for the toughening design of other glass-ceramics.

[0049] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a bimodal crystalline lithium disilicate glass-ceramic, characterized in that, The specific steps include: Low-temperature heat treatment was performed on transparent hard glass containing lithium disilicate to obtain a glass-ceramic precursor containing lithium metasilicate crystal nuclei. Microwave heating treatment was performed on a glass-ceramic precursor containing lithium metasilicate crystal nuclei to obtain glass-ceramic containing large-sized lithium metasilicate grains. High-temperature heat treatment was performed on glass-ceramics containing large-sized lithium metasilicate grains to obtain glass-ceramics with a bimodal grain size distribution of lithium disilicate.

2. The method for preparing a bimodal lithium disilicate microcrystalline glass according to claim 1, characterized in that, The low-temperature heat treatment temperature is 50℃~80℃ higher than the glass transition temperature of transparent hard glass containing lithium disilicate, and the holding time is 2h~4h.

3. The method for preparing a bimodal lithium disilicate microcrystalline glass according to claim 1, characterized in that, The microwave heating treatment uses 2.45GHz pulsed microwaves with a microwave power of 500W~1000W, a single heating time of 0.3min~2min, and a pulse cycle of 30~50 times.

4. The method for preparing a bimodal lithium disilicate microcrystalline glass according to claim 1, characterized in that, The high-temperature heat treatment temperature is 815℃~885℃, and the holding time is 2h~6h.

5. A bimodal lithium disilicate microcrystalline glass, characterized in that, The glass was prepared using the method described in any one of claims 1 to 4, which is a bimodal lithium disilicate microcrystalline glass.

6. The bimodal lithium disilicate microcrystalline glass according to claim 5, characterized in that, The microcrystalline glass has a bimodal grain size distribution structure, comprising long rod-shaped lithium disilicate large grains with a size greater than 10 μm and rice-grain-shaped lithium disilicate small grains with a size less than 2 μm.

7. The bimodal lithium disilicate microcrystalline glass according to claim 5, characterized in that, The bimodal lithium disilicate crystallite glass-ceramics has a fracture toughness of (3.8±0.15) MPa·m 1 / 2 (4.42±0.19) MPa·m 1 / 2 , and a bending strength of ≥400 MPa.

8. The application of the bimodal grain lithium disilicate microcrystalline glass according to any one of claims 5 to 7 as a dental restorative material.

9. A dental restorative material, characterized in that, The raw material for the dental restorative material includes a bimodal lithium disilicate microcrystalline glass as described in any one of claims 5 to 7.

10. A dental restorative material according to claim 9, characterized in that, The visible light transmittance of the bimodal grain lithium disilicate microcrystalline glass is 16%~22%.

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