Glass ceramic for dental restoration

Abstract

The invention discloses a glass ceramic for dental restoration, which comprises the following components in percentage by mass: 55-70% of SiO2, 10-30% of Li2O, 3-12% of K2O, 0-3% of Al2O3, 0.1-4% of Na2O, 0.1-3% of B2O3, more than or equal to 6% of nucleating agent, 0.1-5% of CeO2 and 0.1-3% of other pigments, and the sum of the mass fractions of the raw materials is 100%. The glass ceramic is prepared by adopting a melt pouring method, and is directly annealed after being poured without crystallization heat treatment; the restoration body is prepared in a hot die casting mode, no casting channel hole is formed in the contact point of the casting channel and the restoration body, and therefore the requirements for attractiveness, energy consumption reduction and cost reduction can be met.

Description

A glass-ceramic for dental restoration Technical Field

[0001] This invention belongs to the technical field of dental restorative materials, and relates to a glass-ceramic for dental restoration, specifically a lithium silicate glass-ceramic. Background Technology

[0003] Hot-pressed ceramic blocks, or cast porcelain for short, are a new type of castable ceramic material. The hot-pressing process is mature and an important method for preparing all-ceramic restorations. It involves first creating a wax model of the restoration, such as a crown or substructure, which is then embedded and heated in a specialized wax-removal chamber to remove the wax. The finished ceramic block is then melted in a dedicated die-casting furnace and pressure-cast into the model. After cooling, the cast porcelain tooth is obtained. Compared to CAD / CAM-cut ceramics, which have developed in recent years, this method has the advantages of mature technology and high block utilization. However, the use of cast porcelain products relies heavily on the technical skill of the technicians, limiting the application of the blocks. Furthermore, most of the blocks used in China today are still imported, which are expensive. Regardless of whether they are domestically produced or imported, both methods face the problem of casting defects (casting holes) at the junction of the casting channel and the restoration. The formation of casting eyes is mainly due to the directional alignment of crystals. Dental silicate-based glass-ceramics (such as lithium disilicate Li₂Si₂O₅, Li₂O·₂SiO₂) are rod-shaped and, under the influence of the die-casting force field, tend to align along the direction of the force field, i.e., relatively perpendicular to the direction of the restoration (Figure 1). This directional alignment further increases the light transmittance at the casting path location, resulting in a highly transparent casting eye (Figure 2). The presence of casting eyes reduces the aesthetics of the restoration, and for anterior teeth where aesthetics are paramount, die-casting may even be unsuitable. Domestic and international researchers have focused on glass-ceramics with lithium disilicate as the main crystalline phase, but research on hot-die-cast glass ceramics is limited. Patents CN201010604272.4, CN200810226527.0, CN202111331456.2, and CN202210195786.1 use powder pressing to prepare ceramic blocks, while CN202111049540.5 and CN201510304854.3 use melt casting to prepare ceramic blocks. However, these patents focus on cutting the ceramic blocks and do not address the issue of casting defects in the casting process. Therefore, there is an urgent need to develop a glass-ceramic material that can effectively reduce the visibility of casting defects while also reducing energy consumption and costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a glass-ceramic material that is both aesthetically pleasing and reduces energy consumption and costs.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a dental restorative glass-ceramic, the composition of which, by mass fraction, is: SiO2 55%~70%, Li2O 10%~30%, K2O 3~12%, Al2O3 0-3%, Na2O 0.1-4%, B2O3 0.1-3%, nucleating agent ≥6%, CeO2 0.1-5%, and other colorants 0.1-3%, the sum of the mass fractions of the above raw materials being 100%; the glass-ceramic is prepared by melt casting, and after casting, it is directly annealed without crystallization heat treatment to obtain transparent glass or microcrystalline glass; the restoration body prepared by hot pressing of the obtained glass-ceramic has no casting holes at the contact point between the casting channel and the restoration body.

[0006] Preferably, the composition of the glass-ceramic by mass fraction is as follows: SiO2 60%~70%, Li2O 12%~20%, K2O 3~12%, Al2O3 0-3%, Na2O 1-3%, B2O3 0.5-2%, nucleating agent ≥6%, CeO2 1-5%, and other colorants 0.1-3%, the sum of the mass fractions of the above raw materials is 100%.

[0007] Furthermore, the nucleating agent is composed of phosphorus pentoxide and zirconium oxide, wherein the P / Zr atomic ratio is greater than 1.

[0008] Furthermore, the preparation of the glass ceramic includes the following steps: (1) mixing the raw materials evenly, and then melting them after calcining and decomposing the gas; (2) stirring the melted glass thoroughly to make the glass liquid clear and homogenized; (3) casting the homogenized glass liquid into a preheated mold for annealing treatment to obtain the finished product.

[0009] Furthermore, the melting temperature in step (1) is 1300~1500℃, and the holding time is 0.5-4 hours.

[0010] Furthermore, the annealing temperature in step (3) is 350~550℃, and the holding time is 30~120 minutes. Preferably, the annealing temperature is 400~500℃, and the holding time is 30~60 minutes.

[0011] The significant advantages of this invention are: (1) The glass-ceramic obtained by this invention is transparent glass or microcrystalline glass before hot die casting. In this state, the softening temperature of the glass-ceramic is low, and it has excellent fluidity, which can greatly reduce the problems of incomplete die casting and thin edges during the use of the cast ceramic. At the same time, the in-situ precipitation and growth of crystals during the die casting process requires time and a large amount of heat, so that the crystals do not have enough time and heat to oriented and align, which can greatly reduce or even eliminate the casting holes caused by oriented alignment.

[0012] (2) The glass-ceramic formulation of the present invention has a high nucleating agent content (≥6%). ​​The high nucleating agent content enables the ceramic block to precipitate a large amount of crystals rapidly during the die casting process. The large amount of crystal precipitation can form an interlocking structure, which is well matched with the direct pressing in the glass state and slows down the directional alignment of crystals.

[0013] (3) The glass ceramic of the present invention is prepared by melt casting and is directly annealed after casting without crystallization heat treatment. Compared with the traditional melt casting process which requires 1 to 2 heat treatments after molding, it can save 1 to 2 processes, which is simple and energy-saving; compared with the powder pressing process, it does not require crushing, sieving, powder pressing, sintering and other processes, which is simpler, more convenient and energy-saving.

[0014] In summary, this invention solves the problem of casting defects in hot-pressed restorations by using a method that combines high-content nucleating agents with direct pressing in a glass / microcrystalline glass state. This reduces the probability of incomplete casting and incomplete edges, further improves the aesthetics of hot-pressed restorations, and expands the range of restorations to which they are applicable. Attached Figure Description

[0015] Figure 1 shows a sample image (a) and an electron microscope image (b) of the glass-ceramic restoration prepared in the example.

[0016] Figure 2 shows a sample image (a) and an electron microscope image (b) of the glass-ceramic restoration prepared in Comparative Example 1.

[0017] Figure 3 shows a sample of the glass-ceramic restoration prepared in Comparative Example 2.

[0018] Figure 4 shows a sample of the glass-ceramic restoration prepared in Comparative Example 3. Detailed Implementation

[0019] A type of glass-ceramic for dental restoration, comprising the following components by mass fraction: 55%~70% SiO2, 10%~30% Li2O, 3~12% K2O, 0.3% Al2O3, 0.1-4% Na2O, 0.1-3% B2O3, nucleating agent ≥6%, CeO2 0.1-5%, and other colorants 0.1-3%, the sum of the mass fractions of the above raw materials being 100%.

[0020] The nucleating agent is composed of phosphorus pentoxide and zirconium oxide, wherein the P / Zr atomic ratio is greater than 1.

[0021] The preparation of the glass ceramic includes the following steps: (1) Mix the required raw materials evenly, calcine at 850℃ for 30 minutes to decompose the gas, and then heat and melt at 1300~1500℃ for 0.5-4 hours; (2) Stir the melted glass liquid thoroughly to make the glass liquid clear and homogenized; (3) Pour the homogenized glass liquid into a preheated mold and heat and anneal at 350~550℃ for 30~60 minutes to obtain the finished product.

[0022] 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.

[0023] A method for preparing a glass ceramic for dental restoration includes the following steps: (1) Weigh the corresponding raw materials (including oxides, carbides or other forms of salts of the corresponding components) according to the component ratio in Table 1, calcine them at 850°C for 30 minutes to decompose the gas, and then heat and melt them at 1500°C for 2 hours; (2) Stir the melted glass liquid thoroughly to make the glass liquid clear and homogenized; (3) Pour the homogenized glass liquid into a preheated mold and heat and anneal it at 400°C for 30 minutes to remove stress, thereby obtaining the transparent glass ceramic block corresponding to the example and comparative example.

[0024] Table 1. Composition of Glass-Ceramic Materials for Dental Restoration (by weight)

[0025] The transparent glass-ceramic blocks prepared in Examples 1 and 3 were directly die-cast (die-casting temperature was 910℃, time was 15min) to obtain glass-ceramic restorations; the transparent glass-ceramic blocks prepared in Comparative Example 2 were die-cast under the same conditions after being kept at 550℃, 650℃ and 820℃ for 60min each, according to conventional processes, to obtain glass-ceramic restorations.

[0026] Figures 1-4 show sample images of the glass-ceramic restorations prepared in the examples and comparative examples. As can be seen from the figures, the glass-ceramic restorations prepared in the examples have a natural transition of casting channels with virtually no casting eye (a), and the crystal structure under electron microscopy shows no obvious directional alignment trend (b); the glass-ceramic restorations prepared in Comparative Example 1 have prominent casting channels (a), and the crystal directional alignment is obvious under electron microscopy (b); the glass-ceramic restorations prepared in Comparative Example 2 have slight casting eye traces; the glass-ceramic restorations prepared in Comparative Example 3 have no casting eye, but due to the high phosphorus pentoxide content, the transparency is significantly reduced, resulting in a whitening appearance after die casting.

[0027] The strength test was conducted according to the three-point bending test method in standard GB30367. The samples prepared in the examples and comparative examples were tested using a 1.2×4×20mm spline. The test results are shown in Table 2.

[0028] Table 2

[0029] As shown in Table 2, the strength of the glass-ceramic material restoration prepared in Comparative Example 1 is lower than that of the other examples. This is because it has less nucleating agent, making it difficult to form sufficient crystals in a short time without heat treatment. The glass-ceramic material restoration prepared in Comparative Example 3 has more nucleating agent, resulting in finer grains and thus a slight decrease in its strength. The measured strengths of the glass-ceramic material restorations prepared in the examples and Comparative Example 2 are similar, with no statistically significant difference, proving that direct annealing after casting does not affect the mechanical properties of the material.

[0030] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A glass-ceramic material for dental restoration, characterized in that, The composition of the glass-ceramic, by mass fraction, is as follows: SiO2 55%~70%, Li2O 10%~30%, K2O 3~12%, Al2O3 0-3%, Na2O 0.1-4%, B2O3 0.1-3%, nucleating agent ≥6%, CeO2 0.1-5%, and other colorants 0.1-3%, with the sum of the mass fractions of the above raw materials being 100%. The glass-ceramic is prepared by melt casting, and after casting, it is directly annealed without crystallization heat treatment to obtain transparent glass or microcrystalline glass. The resulting glass-ceramic is used to prepare the restoration body by hot pressing, and there are no casting holes at the contact points between the casting channel and the restoration body.

2. The dental restorative glass-ceramic according to claim 1, characterized in that, The nucleating agent is composed of phosphorus pentoxide and zirconium oxide, wherein the P / Zr atomic ratio is greater than 1.

3. The dental restorative glass-ceramic according to claim 1, characterized in that, The preparation of the glass ceramic includes the following steps: (1) mixing the raw materials evenly, and then melting them after calcining and decomposing the gas; (2) stirring the melted glass thoroughly to make the glass liquid clear and homogenized; (3) casting the homogenized glass liquid into a preheated mold for annealing treatment to obtain the finished product.

4. The dental restorative glass-ceramic according to claim 3, characterized in that, The melting temperature in step (1) is 1300~1500℃, and the holding time is 0.5-4 hours.

5. The dental restorative glass-ceramic according to claim 3, characterized in that, The annealing temperature in step (3) is 350~550℃, and the holding time is 30~120 minutes.

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