LITHIUM DISILICATE GLASS-CERAMIC WITH HIGH STRENGTH AND HIGH TRANSPARENCY AND PREPARATION METHOD AND USE THEREOF

Abstract

The present disclosure discloses a lithium disilicate glass-ceramic with high strength and high transparency and a preparation method and use thereof. A raw material composition of the lithium disilicate glass-ceramic comprises: 63-75 wt % of SiO.sub.2, 13-18 wt % of Li.sub.2O, 1-6 wt % of Al.sub.2O.sub.3, 1-10 wt % of K.sub.2O, 2-6 wt % of P.sub.2O.sub.5, 0-4 wt % of an additive and 0-10 wt % of a colorant; a main crystal phase of the lithium disilicate glass-ceramic is lithium disilicate crystals, and an impurity phase of the lithium disilicate glass-ceramic is any one or a combination of at least two selected from the group consisting of lithium metasilicate, lithium phosphate and quartz; the lithium disilicate crystal has a size larger than 700 nm and a length-diameter ratio not less than 3.

Claims

1. A lithium disilicate glass-ceramic with high strength and high transparency, wherein a raw material composition of the lithium disilicate glass-ceramic comprises: 63-75 wt % of SiO.sub.2, 13-18 wt % of Li.sub.2O, 1-6 wt % of Al.sub.2O.sub.3, 1-10 wt % of K.sub.2O, 2-6 wt % of P.sub.2, O.sub.5, 0-4 wt % of an additive and 0-10 wt % of a colorant; a main crystal phase of the lithium disilicate glass-ceramic is lithium disilicate crystals, and an impurity phase of the lithium disilicate glass-ceramic is any one or a combination of at least two selected from the group consisting of lithium metasilicate, lithium phosphate and quartz; the lithium disilicate crystal has a size larger than 700 nm and a length-diameter ratio not less than 3.

2. The lithium disilicate glass-ceramic according to claim 1, wherein the raw material composition of the lithium disilicate glass-ceramic comprises: 65-70 wt % of SiO.sub.2, 14-16 wt % of Li.sub.2O, 2-5 wt % of Al.sub.2O.sub.3, 2-8 wt % of K.sub.2O, 3-5 wt % of P.sub.2O.sub.5, 1-3 wt % of an additive and 2-5 wt % of a colorant.

3. The lithium disilicate glass-ceramic according to claim 1, wherein the raw material composition of the lithium disilicate glass-ceramic further comprises any one or a combination of at least two selected from the group consisting of 0-6 wt % of CaO, 0-5 wt % of BaO, 0-10 wt % of B.sub.2O.sub.3 and 0-10 wt % of ZrO.sub.2 or HfO.sub.2, excluding 0 wt % for each.

4. The lithium disilicate glass-ceramic according to claim 1, wherein the additive comprises a monovalent metal oxide and a divalent metal oxide; the monovalent metal oxide comprises any one or a combination of at least two selected from the group consisting of Na.sub.2O, Rb.sub.2O and Cs.sub.2O; the divalent metal oxide comprises any one or a combination of at least two selected from the group consisting of MgO, SrO and ZnO.

5. The lithium disilicate glass-ceramic according to claim 1, wherein the colorant comprises any one or a combination of at least two selected from the group consisting of Fe.sub.2O.sub.3, TiO.sub.2, CeO.sub.2, CuO, Cr.sub.2O.sub.3, MnO, SeO.sub.2, V.sub.2O.sub.5, In.sub.2O.sub.3 and a rare earth oxide; the rare earth oxide comprises any one or a combination of at least two selected from the group consisting of La.sub.2O.sub.3, Nd.sub.2O.sub.3, Tb.sub.2O.sub.3, Pr.sub.6O.sub.11 and Er.sub.2O.sub.3.

6. The lithium disilicate glass-ceramic according to claim 1, wherein the lithium disilicate crystal is fusiform; the lithium disilicate crystal has a microstructure with three-dimensional interweaving and crystal grain interlocking.

7. The lithium disilicate glass-ceramic according to claim 1, wherein a light transmittance of a sample of the lithium disilicate glass-ceramic with a thickness of 1 mm at 550 nm is within a range of 10%-40%, provided that the lithium disilicate crystal has a size larger than 700 nm and smaller than 1200 nm and a length-diameter ratio within a range of 3-5.

8. The lithium disilicate glass-ceramic according to claim 1, wherein a light transmittance of a sample of the lithium disilicate glass-ceramic with a thickness of 1 mm at 550 nm is within a range of 40%-80%, provided that the lithium disilicate crystal has a size not smaller than 1200 nm and a length-diameter ratio not less than 5.

9. A method for preparing the lithium disilicate glass-ceramic according to claim 1, comprising: (1) mixing raw materials of the lithium disilicate glass-ceramic in proportion, followed by melting to obtain a basic glass liquid; and (2) subjecting the basic glass liquid obtained in step (1) to a molding annealing treatment and a heat treatment in sequence to obtain the lithium disilicate glass-ceramic.

10. The method according to claim 9, wherein in step (1), the mixing is performed on a mixer; in step (1), the mixing is performed for 30-300 min.

11. The method according to claim 9, wherein in step (1), the melting is performed at a temperature within a range of 1300-1600? C.; in step (1), the melting is performed for 1-10 h.

12. The method according to claim 9, wherein in step (2), the molding annealing treatment comprises: pouring the basic glass liquid into a mold for annealing to obtain a substrate glass; the mold is preheated to a temperature within a range of 200-500? C.; the annealing is performed for 0.1-24 h; after the molding annealing treatment, the treated substrate glass is cooled to room temperature.

13. The method according to claim 9, wherein the heat treatment comprises at least a first heat treatment and a last heat treatment; the first heat treatment is performed at a temperature within a range of 500-600? C.; the first heat treatment is performed for 60-240 min; the last heat treatment is performed at a temperature within a range of 800-860? C.; the last heat treatment is performed for 1-30 min.

14. The method according to claim 13, wherein the heat treatment further comprises an intermediate heat treatment; the intermediate heat treatment is performed at a temperature within a range of 600-700? C.; the intermediate heat treatment is performed for 30-240 min.

15. The method according to claim 13, wherein the substrate glass or an intermediate product before the last heat treatment is subjected to CAD/CAM machining to be formed into the shape of a tooth to be repaired.

16. The method according to claim 13, wherein the substrate glass or an intermediate product before the last heat treatment is formed into the shape of a tooth to be repaired by a hot pressing process or a lost wax process.

17. A method for using the lithium disilicate glass-ceramic according to claim 1, wherein the lithium disilicate glass-ceramic is used for making an oral restoration.

18. The method according to claim 17, wherein the oral restoration comprises any one of dental veneers, inlays, onlays, abutment teeth, single crowns, anterior multi-unit pontic and posterior multi-unit pontic.

19. The lithium disilicate glass-ceramic according to claim 3, wherein the raw material composition of the lithium disilicate glass-ceramic comprises: 65-70 wt % of SiO.sub.2, 14-16 wt % of Li.sub.2O, 2-5 wt % of Al.sub.2O.sub.3, 2-8 wt % of K.sub.2O, 3-5 wt % of P.sub.2, O.sub.5, 1-3 wt % of an additive and 2-5 wt % of a colorant.

20. The lithium disilicate glass-ceramic according to claim 6, wherein the raw material composition of the lithium disilicate glass-ceramic comprises: 65-70 wt % of SiO.sub.2, 14-16 wt % of Li.sub.2O, 2-5 wt % of Al.sub.2O.sub.3, 2-8 wt % of K.sub.2O, 3-5 wt % of P.sub.2O.sub.5, 1-3 wt % of an additive and 2-5 wt % of a colorant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG. 1 shows a Differential Scanning Calorimetry (DSC) diagram of the lithium disilicate glass-ceramic provided in Example 1 of the present disclosure.

[0062] FIG. 2 shows a micro-morphology image of the lithium disilicate glass-ceramic provided in Example 1 of the present disclosure.

[0063] FIG. 3 shows a length size distribution diagram of the lithium disilicate crystals in the lithium disilicate glass-ceramic provided in Example 1 of the present disclosure.

[0064] FIG. 4 shows a width size distribution diagram of the lithium disilicate crystals in the lithium disilicate glass-ceramic provided in Example 1 of the present disclosure.

[0065] FIG. 5 shows an X-ray diffraction pattern (XRD) of the lithium disilicate glass-ceramic provided in Example 1 of the present disclosure.

[0066] FIG. 6 shows a light transmittance curve diagram of the lithium disilicate glass-ceramic provided in Example 1 of the present disclosure for visible light within a range of 400-900 nm.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0067] In order to better illustrate the present disclosure and to facilitate understanding of the technical solutions of the present disclosure, the present disclosure will be further described in detail below. However, the following embodiments are merely simple examples of the present disclosure without representing or limiting the protection scope of the present disclosure, and the protection scope of the present disclosure is subject to the claims.

[0068] The typical but non-restrictive examples of the present disclosure are as follows.

[0069] The raw material compositions of lithium disilicate glass-ceramics prepared according to the following examples and comparative example are shown in Table 1, in which the content of each component is represented as mass percentage.

TABLE-US-00001 TABLE 1 Raw material proportions in Examples 1-6 Example Example Example Example Example Example 1 2 3 4 5 6 SiO.sub.2 67.5 69 70 64.5 72 70 Li.sub.2O 14.7 16.7 13.4 15.5 13 14 K.sub.2O 4.2 3.2 6.1 5.7 3 3.4 Al.sub.2O.sub.3 3.7 3.3 4.8 5.0 4 3.5 P.sub.2O.sub.5 3.3 4.2 2.9 4.4 5 4.8 Rb.sub.2O 0.3 0.6 0.5 1.2 0.8 1.0 MgO 1.0 0.4 0.6 0.5 CaO 0.4 0.3 0.2 Fe.sub.2O.sub.3 1.75 1.2 0.4 0.8 1.6 1.2 Tb.sub.2O.sub.3 2.7 0.3 0.8 1.0 0.4 1.9 La.sub.2O.sub.3 0.45 0.3 0.2 0.4 0.2 ZnO.sub.2 0.8 1.0

Example 1

[0070] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency, and the preparation method was performed by the following steps: [0071] (1) Raw materials of a lithium disilicate glass-ceramic were placed into a mixer in proportion, mixed for 40 min, then placed in a platinum crucible and melted at 1450? C. for 5 h; after the components were evenly distributed and the bubbles escaped completely, a basic glass liquid was obtained. [0072] (2) The basic glass liquid obtained in step (1) was poured into a mold at 420? C. for annealing for 10 h, and then naturally cooled to room temperature, obtaining a substrate glass.

[0073] The substrate glass was heated to 520? C., held for 130 min and naturally cooled to room temperature, followed by being heated to 660? C., held for 150 min and naturally cooled to room temperature; subsequently, the obtained intermediate product was processed into the shape of the tooth to be repaired by CAD/CAM machining, and then the surface was ground and polished; finally, the processed sample was placed in a high-temperature electric furnace and held at 840? C. for 2 min, obtaining a lithium disilicate glass-ceramic with Li.sub.2Si.sub.2O.sub.5 crystals as the main crystal phase and Li.sub.2SiO.sub.3 and Li.sub.3PO.sub.4 as the impurity phase.

[0074] The lithium disilicate glass-ceramic obtained as described above was characterized. The DSC diagram is shown in FIG. 1. The micro-morphology image is shown in FIG. 2. The length size distribution diagram of the lithium disilicate crystals is shown in FIG. 3. The width size distribution diagram of the lithium disilicate crystals is shown in FIG. 4. The XRD diagram of the lithium disilicate glass-ceramic is shown in FIG. 5. The light transmittance curve diagram of the lithium disilicate glass-ceramic for visible light within a range of 400 nm to 900 nm is shown in FIG. 6.

[0075] It may be seen from FIG. 1 that the glass transition temperature Tg of the sample is 485? C., which means that the formation of a large amount of crystal nuclei in the glass matrix is promoted effectively only at a heat treatment temperature higher than 485? C. 628? C. corresponds to the exothermic peak at which lithium metasilicate crystals are formed. 802? C. corresponds to the exothermic peak at which lithium disilicate crystals are formed. 959? C. corresponds to the softening point of the glass-ceramic, which indicates that the sample is prone to softening and deformation at a temperature higher than this.

[0076] It may be seen from FIG. 2 that the micro-morphology of the sample is fusiform and is distributed in the mechanism of three-dimensional interweaving and crystal grain interlocking. It may be further known from Table 3 that the fusiform lithium disilicate has a crystal size of 1080 nm and a length-diameter ratio of 4.7. A relatively high length-diameter ratio is conducive to the interweaving among the crystal grains, by which the three-point bending strength of the glass-ceramic is effectively improved to 580 MPa. In addition, the fracture mode of lithium disilicate glass-ceramics is intergranular fracture, and a relatively high length-diameter ratio can extend the path of crack propagation effectively, thereby dissipating the driving force of crack propagation and effectively improving the fracture toughness of the lithium disilicate glass-ceramic to 3.62 MPa.Math.m.sup.1/2, which meets the requirements of the international standard IS06872 for using as a three-unit pontic for posterior teeth.

[0077] It may be seen from FIG. 3 and FIG. 4 that the lithium disilicate crystals have an average length of 1.08 m and an average width of 0.23 m.

[0078] It may be seen from FIG. 5 that the main crystal phase of the sample is lithium disilicate (Li.sub.2Si.sub.2O.sub.5) and impurity phases are lithium metasilicate (Li.sub.2SiO.sub.3) and lithium phosphate (Li.sub.3PO.sub.4).

[0079] It may be seen from FIG. 6 that the optical transmittance of the lithium disilicate glass-ceramic sample with a thickness of 1 mm at 550 nm is 20.11%, well meeting the requirements for a high light transmittance of dental restoration materials clinically (a sample with a thickness of 1 mm has an optical transmittance of 20-55% at a wavelength of 550 nm).

Example 2

[0080] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency, and the preparation method was performed by the following steps: [0081] (1) Raw materials of a lithium disilicate glass-ceramic were placed into a mixer in proportion, mixed for 30 min, then placed in a platinum crucible and melted at 1450? C. for 3 h; after the components were evenly distributed and the bubbles escaped completely, a basic glass liquid was obtained. [0082] (2) The basic glass liquid obtained in step (1) was poured into a mold at 400? C. for annealing for 3 h, and then naturally cooled to room temperature, obtaining a substrate glass.

[0083] The substrate glass was heated to 550? C., held for 100 min and naturally cooled to room temperature, followed by being heated to 660? C., held for 180 min and naturally cooled to room temperature; subsequently, the obtained intermediate product was processed into the shape of the tooth to be repaired by CAD/CAM machining, and then the surface was ground and polished; finally, the processed sample was placed in a high-temperature electric furnace and held at 840? C. for 6 min, obtaining a lithium disilicate glass-ceramic with Li.sub.2Si.sub.2O.sub.5 crystals as the main crystal phase and Li.sub.2SiO.sub.3 as the impurity phase.

Example 3

[0084] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency, and the preparation method was performed by the following steps: [0085] (1) Raw materials of a lithium disilicate glass-ceramic were placed into a mixer in proportion, mixed for 60 min, then placed in a platinum crucible and melted at 1450? C. for 5 h; after the components were evenly distributed and the bubbles escaped completely, a basic glass liquid was obtained. [0086] (2) The basic glass liquid obtained in step (1) was poured into a mold at 450? C. for annealing for 2 h, and then naturally cooled to room temperature, obtaining a substrate glass.

[0087] The substrate glass was heated to 570? C., held for 140 min and naturally cooled to room temperature, followed by being heated to 670? C., held for 210 min and naturally cooled to room temperature; subsequently, the obtained intermediate product was processed into the shape of the tooth to be repaired by CAD/CAM machining, and then the surface was ground and polished; finally, the processed sample was placed in a high-temperature electric furnace and held at 830? C. for 10 min, obtaining a lithium disilicate glass-ceramic with Li.sub.2Si.sub.2O.sub.5 crystals as the main crystal phase and Li.sub.2SiO.sub.3 as the impurity phase.

Example 4

[0088] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency, and the preparation method was performed by the following steps: [0089] (1) Raw materials of a lithium disilicate glass-ceramic were placed into a mixer in proportion, mixed for 100 min, then placed in a platinum crucible and melted at 1600? C. for 3 h; after the components were evenly distributed and the bubbles escaped completely, a basic glass liquid was obtained. [0090] (2) The basic glass liquid obtained in step (1) was poured into a mold at 450? C. for annealing for 4 h, and then naturally cooled to room temperature, obtaining a substrate glass.

[0091] The substrate glass was heated to 530? C., held for 120 min and naturally cooled to room temperature, followed by being heated to 630? C., held for 130 min and naturally cooled to room temperature; subsequently, the obtained intermediate product was processed into the shape of the tooth to be repaired by CAD/CAM machining, and then the surface was ground and polished; finally, the processed sample was placed in a high-temperature electric furnace and held at 860? C. for 3 min, obtaining a lithium disilicate glass-ceramic with Li.sub.2Si.sub.2O.sub.5 crystals as the main crystal phase and Li.sub.2SiO.sub.3 and Li.sub.3PO.sub.4 as the impurity phase.

Example 5

[0092] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency, and the preparation method was performed by the following steps: [0093] (1) Raw materials of a lithium disilicate glass-ceramic were placed into a mixer in proportion, mixed for 300 min, then placed in a platinum crucible and melted at 1300? C. for 10 h; after the components were evenly distributed and the bubbles escaped completely, a basic glass liquid was obtained. [0094] (2) The basic glass liquid obtained in step (1) was poured into a mold at 200? C. for annealing for 24 h, and then naturally cooled to room temperature, obtaining a substrate glass.

[0095] The substrate glass was heated to 600? C., held for 60 min and naturally cooled to room temperature, followed by being heated to 700? C., held for 30 min and naturally cooled to room temperature; subsequently, the obtained intermediate product was processed into the shape of the tooth to be repaired by CAD/CAM machining, and then the surface was ground and polished; finally, the processed sample was placed in a high-temperature electric furnace and held at 850? C. for 1 min, obtaining a lithium disilicate glass-ceramic with Li.sub.2Si.sub.2O.sub.5 crystals as the main crystal phase and Li.sub.2SiO.sub.3 as the impurity phase.

Example 6

[0096] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency, and the preparation method was performed by the following steps: [0097] (1) Raw materials of a lithium disilicate glass-ceramic were placed into a mixer in proportion, mixed for 200 min, then placed in a platinum crucible and melted at 1500? C. for 1 h; after the components were evenly distributed and the bubbles escaped completely, a basic glass liquid was obtained. [0098] (2) The basic glass liquid obtained in step (1) was poured into a mold at 500? C. for annealing for 0.1 h, and then naturally cooled to room temperature, obtaining a substrate glass.

[0099] The substrate glass was heated to 500? C., held for 240 min and naturally cooled to room temperature, followed by being heated to 600? C., held for 240 min and naturally cooled to room temperature; subsequently, the obtained intermediate product was processed into the shape of the tooth to be repaired by CAD/CAM machining, and then the surface was ground and polished; finally, the processed sample was placed in a high-temperature electric furnace and held at 800? C. for 30 min, obtaining a lithium disilicate glass-ceramic with Li.sub.2Si.sub.2O.sub.5 crystals as the main crystal phase and Li.sub.2SiO.sub.3 and Li.sub.3PO.sub.4 as the impurity phase.

Example 7

[0100] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency, and the preparation method was performed by the following steps: [0101] (1) Raw materials of a lithium disilicate glass-ceramic were placed into a mixer in proportion, mixed for 100 min, then placed in a platinum crucible and melted at 1400? C. for 4 h; after the components were evenly distributed and the bubbles escaped completely, a basic glass liquid was obtained. [0102] (2) The basic glass liquid obtained in step (1) was poured into a mold at 450? C. for annealing for 5 h, and then naturally cooled to room temperature, obtaining a substrate glass.

[0103] The substrate glass was heated to 550? C., held for 240 min and naturally cooled to room temperature, subsequently, the obtained intermediate product was processed into the shape of the tooth to be repaired by CAD/CAM machining, and then the surface was ground and polished; finally, the processed sample was placed in a high-temperature electric furnace and held at 800? C. for 30 min, obtaining a lithium disilicate glass-ceramic with Li.sub.2Si.sub.2O.sub.5 crystals as the main crystal phase and Li.sub.2SiO.sub.3 and Li.sub.3PO.sub.4 as the impurity phase.

Example 8

[0104] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency. The raw materials used were the same as those in Example 1. The preparation method referred to that in Example 1, with the only difference in that: in step (2), the first heat treatment of the substrate glass was performed at 450? C.

Example 9

[0105] This example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency. The raw materials used were the same as those in Example 3. The preparation method referred to that in Example 3, with the only difference in that: in step (2), the first heat treatment of the substrate glass was performed at 630? C.

Comparative Example 1

[0106] This comparative example provided a method for preparing a lithium disilicate glass-ceramic with high strength and high transparency. The raw materials used were the same as those in Example 1. The preparation method referred to that in Example 1, with the differences in that: in step (2), the substrate glass was heated to 670? C., held for 180 min and naturally cooled to room temperature; subsequently, the obtained intermediate product was processed into the shape of the tooth to be repaired by CAD/CAM machining, and then the surface was ground and polished; finally, the processed sample was placed in a high-temperature electric furnace and held at 840? C. for 5 min, obtaining a lithium disilicate glass-ceramic with Li.sub.2Si.sub.2O.sub.5 crystals as the main crystal phase and Li.sub.2SiO.sub.3 as the impurity phase.

[0107] Firstly, the substrate glasses and intermediate products during heat treatments obtained in the preparation processes of Examples 1-9 and Comparative Example 1 were subjected to the corresponding phase analysis, and the results are shown in Table 2.

TABLE-US-00002 TABLE 2 Phase analysis of products of Examples 1-9 and Comparative Example 1 Crystal Crystal phase phase T.sub.g T.sub.N t.sub.N T.sub.P1 t.sub.P1 after T.sub.P1 T.sub.P2 t.sub.P2 after T.sub.P2 (? C.) (? C.) (min) (? C.) (min) treatment (? C.) (min) treatment Processibility Example 1 485 520 130 660 150 Li.sub.2SiO.sub.3 840 2 Li.sub.2Si.sub.2O.sub.5 Very Li.sub.2SiO.sub.3 good Li.sub.3PO.sub.4 Example 2 480 550 100 660 180 Li.sub.2SiO.sub.3 840 6 Li.sub.2Si.sub.2O.sub.5 Good Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Example 3 478 570 140 670 210 Li.sub.2SiO.sub.3 830 10 Li.sub.2Si.sub.2O.sub.5 Good Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Example 4 489 530 120 630 130 Li.sub.2SiO.sub.3 860 3 Li.sub.2Si.sub.2O.sub.5 Very Li.sub.2SiO.sub.3 good Li.sub.3PO.sub.4 Example 5 482 600 60 700 30 Li.sub.2SiO.sub.3 850 1 Li.sub.2Si.sub.2O.sub.3 Good Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Example 6 472 500 240 600 240 Li.sub.2SiO.sub.3 800 30 Li.sub.2Si.sub.2O.sub.5 Good Li.sub.2SiO.sub.3 Li.sub.3PO.sub.4 Example 7 486 550 240 Li.sub.2SiO.sub.3 810 30 Li.sub.2Si.sub.2O.sub.5 Good Li.sub.2SiO.sub.3 Example 8 485 450 130 660 150 Li.sub.2SiO.sub.3 840 2 Li.sub.2Si.sub.2O.sub.5 Very Li.sub.2SiO.sub.3 good Li.sub.3PO.sub.4 Example 9 478 630 140 670 210 Li.sub.2SiO.sub.3 830 10 Li.sub.2Si.sub.2O.sub.5 Good Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Comparative 486 670 180 Li.sub.2SiO.sub.3 840 5 Li.sub.2Si.sub.2O.sub.5 Ordinary Example 1 Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3

[0108] In Table 2 above, T.sub.g represents the glass transition temperature; T.sub.N and t.sub.N represent the temperature and time for the first heat treatment, respectively; T.sub.P1 and t.sub.P1 represent the temperature and time for the intermediate heat treatment, respectively; T.sub.P2 and t.sub.P2 represent the temperature and time for the last heat treatment, respectively.

[0109] Secondly, the crystal size, the length-diameter ratio, the light transmittance at 550 nm, the three-point bending strength, the hardness, the fracture toughness and the chemical solubility of the lithium disilicate glass-ceramics as prepared according to Examples 1-9 and Comparative Example 1 were measured. The test methods and conditions were as follows, and the test results are shown in Table 3. [0110] {circle around (1)} The crystal size was measured and counted using Nano Measurer 1.2 software. [0111] {circle around (2)} Light transmittance: the test sample was tested within a wavelength range of 400-900 nm using a spectrophotometer, and had a thickness of 1 mm. [0112] {circle around (3)} Mechanical properties: the three-point bending strength and fracture toughness in the present disclosure were both characterized according to the IS06872:2008 international standard; for the test of three-point bending strength, 15 samples were tested and the average value of the obtained three-point bending strength values was calculated; for the test of fracture toughness, 10 samples were tested by the V notched beam (SEVNB) method to obtain the average value of the fracture toughness of the samples.

[0113] The hardness test in the present disclosure was in accordance with the IS014705:2008 international standard; a Vickers hardness tester was used and a load of 1 kilogram-force (1 kgf) was applied; the test was performed for 15 times to obtain the average value of Vickers hardness of the samples. [0114] {circle around (4)} Chemical solubility: the chemical solubility in the present disclosure was tested and analyzed according to the IS06872:2008 international standard.

TABLE-US-00003 TABLE 3 Performance data of lithium disilicate glass-ceramics prepared in Examples 1-9 and Comparative Example 1 Crystal Length- Light Three-point Fracture Chemical size diameter transmittance bending strength Hardness toughness solubility (nm) ratio (at 550 nm) (MPa) (GPa) (MPa .Math. m.sup.1/2) (?g/cm.sup.2) Example 1 1080 4.7 20.11 580 5.76 3.62 34.4 Example 2 1434 7.1 53.08 750 5.9 5.56 43.6 Example 3 1110 4.8 21.28 595 6.2 3.58 41.3 Example 4 1120 5.3 45.3 630 5.65 4.32 29.3 Example 5 960 3.7 24.5 530 6.02 3.60 40.5 Example 6 1200 4.2 28.7 580 6.32 3.77 38.8 Example 7 920 4.0 26.5 560 5.85 4.02 44.0 Example 8 750 3.2 12 470 6.60 3.52 44.5 Example 9 800 3.8 17 488 6.45 3.60 42.2 Comparative 960 2.6 10 380 6.70 2.37 45.2 Example 1

[0115] Examples 1-6 are in accordance with the preparation method of the present disclosure. By means of optimizing the raw material components and adjusting the conditions of each heat treatment, the lithium disilicate glass-ceramic obtained has a light transmittance of 20.11-53.08% at a wavelength of 550 nm. This has fully met the requirements for high light transmittance of dental restoration materials in clinic, since the light transmittance of dental restoration materials is generally required to be maintained between 20-55% (at a wavelength of 550 nm) in clinic. Moreover, the lithium disilicate glass-ceramic obtained has good processability, and may reduce significantly the problems of such as chipping and the great wearing on machine needles during machining. In addition, since the lithium disilicate crystals have a size larger than 1080 nm and a length-diameter ratio more than 4.7, they may well form a microstructure with three-dimensional interweaving and crystal grain interlocking, such that the three-point bending strength of glass-ceramics is maintained at 580-750 MPa, effectively reducing the risk of chipping of the teeth. Furthermore, the lithium disilicate glass-ceramic obtained has a fracture toughness of 3.58-5.56 MPa.Math.m.sup.1/2, a hardness of 5.65-6.32 GPa and a chemical solubility of 29.3-43.6 ?g/cm.sup.2, which meet the requirements for dental materials clinically.

[0116] Example 7 is in accordance with the preparation method of the present disclosure. The lithium disilicate glass-ceramic obtained, although undergoing only two heat treatments, can still have a light transmittance of up to 26.5% at a wavelength of 550 nm and good processability. Meanwhile, the three-point bending strength reaches 560 MPa, the fracture toughness reaches 4.02 MPa.Math.m.sup.1/2, the hardness reaches 5.85 GPa, and the chemical solubility is 44.0 ?g/cm.sup.2, which meet the requirements for dental materials clinically.

[0117] In contrast, in Example 8, the temperature for the first heat treatment is decreased during preparation, and the uniform growth of crystals during the heat treatment processes could not be effectively controlled, resulting in decrease in light transmittance at a wavelength of 550 nm and three-point bending strength of the lithium disilicate glass-ceramic finally obtained. In Example 9, the temperature for the first heat treatment is increased during the preparation, which is not conducive to the control of the crystal size of lithium disilicate, thus leading to decrease in light transmittance at a wavelength of 550 nm and three-point bending strength of the obtained lithium disilicate glass-ceramic likewise.

[0118] The lithium disilicate crystals prepared in Comparative Example 1 have a relatively low length-diameter ratio, which results in failure to form a microstructure with three-dimensional interweaving and crystal grain interlocking, such that the light transmittance at a wavelength of 550 nm of the lithium disilicate glass-ceramic obtained is relatively low, and the three-point bending strength is severely reduced.

[0119] It may be seen from the examples and comparative example as described above that in the lithium disilicate glass-ceramic according to the present disclosure, by means of increasing the size of the lithium disilicate crystals, a microstructure with three-dimensional interweaving and crystal grain interlocking may be well formed on the one hand, such that the lithium disilicate glass-ceramic has a three-point bending strength maintained between 450 and 750 MPa and a fracture toughness higher than 3.5 MPa.Math.m.sup.1/2; the increase in size of the crystals may weaken the scattering effect of the grain boundaries on light on the other hand, such that the light transmittance of a sample with a thickness of 1 mm at 550 nm is adjustable within a range of 10%-80%. The lithium disilicate glass-ceramic truly combines the excellent properties of high strength, high transparency and high fracture toughness, effectively reducing the risk of chipping and simulating the toughness and light transparency of natural teeth well. The size of crystals is adjusted by optimizing the formulation composition and controlling the conditions during the heat treatment. The preparation method has a simple technological process, high economic benefit and desirable industrial application prospect.

[0120] The applicant declares that although the products and the detailed methods of the present disclosure are illustrated through the embodiments above, the present disclosure is not limited to the products and detailed methods as mentioned above, which means the present disclosure does not have to rely on the products and detailed methods above to be implemented. Those skilled in the art should understand that any improvement to the present disclosure, equivalent replacement of the operation in the present disclosure as well as addition of auxiliary operations and selection of specific methods all fall within the protection and disclosure scope of the present disclosure.