Dental bulk block and method for manufacturing the same

Abstract

The crystalline phase is a functionally gradient material that includes at least one lithium silicate-based crystalline phase selected from the group consisting of lithium metasilicate and lithium disilicate and eucryptite, has a gradient in the size of the crystalline phase with respect to depth, and has no interface at the point where the gradient of the size of the crystalline phase changes.The present invention provides a dental bulk block characterized in that when the block is heat-treated at 820°C for 40 minutes, a specific peak of a spodumene crystalline phase appears in a graph of the results of X-ray diffraction analysis, compared to a block heat-treated at 820°C for 2 minutes.

Description

Technical Field

[0001] The present invention is useful for manufacturing artificial teeth similar to the structural characteristics of natural teeth, and particularly relates to a dental bulk block with improved machinability and a method for manufacturing the same.

Background Art

[0002] A crown material means a prosthetic material that repairs the parts corresponding to the dentin and enamel of a damaged tooth, and is classified into inlays, onlays, veneers, crowns, etc. according to the application site. Since the position where the crown material is repaired is the outer surface of the tooth, aesthetic characteristics are highly required, and high strength is required due to wear and chipping with the opposing tooth. Existing materials used for crown materials include leucite glass-ceramics, reinforced porcelain, and fluorapatite (Ca5(PO4)3F) glass-ceramics. These have good aesthetic characteristics, but have the disadvantage of low strength at 80 - 120 MPa and a high possibility of fracture. Therefore, currently, research is underway to develop high-strength crown materials of various materials.

[0003] Lithium silicate glass-ceramics were introduced by Marcus P. Borom and Anna M. Turkalo in 1973 (The Pacific Coast Regional Meeting, The American Ceramic Society, San Francisco, CA, October 31, 1973 (Glass division, No.3-G-73P)).

[0004] The crystallization and crystal growth of various crystal nuclei were studied under different heat treatment conditions using Li2O-Al2O3-SiO2-Li2O-K2O-B2O3-P2O5 system glass. When presenting a high-temperature lithium disilicate crystal phase from a low-temperature lithium metasilicate, it showed a strength of 30-35 KPS, which was due to the residual stress caused by the difference in the thermal expansion coefficients of the base glass, mother glass, Li2SiO5, and Li2SiO3 phases.

[0005] Materials and methods for fabricating artificial teeth (monolithic dental crown) using glass containing lithium disilicate crystals have already been known in many patents. However, in the known technology, the size of the crystal phase is coarsened and it is difficult to machine immediately. For processing, first, a machinable crystalline lithium metasilicate crystal phase is formed and processed, and then, second, heat treatment is performed to form a high-strength lithium disilicate crystal phase. In this case, due to the shrinkage in the post-heat treatment process, the dimensional accuracy is poor, and there is the annoyance of adding a heat treatment process. Generally, in the fabrication of prostheses by CAD / CAM, the bulk body is directly machined in the hospital to fabricate the prosthesis, and this must be promptly tried on the patient (one-day appointment). Therefore, the time delay due to the heat treatment process imposes an economic burden on the patient and the user.

[0006] In addition, existing lithium disilicate crystallized glass materials have limitations in realizing a high light transmittance and opalescence similar to natural teeth due to the coarsened crystal phase.

[0007] In particular, existing lithium disilicate crystallized glass materials manufacture a lithium metasilicate crystallized glass with good workability first for processing, and then form lithium disilicate by crystallization heat treatment after processing to increase the strength. At this time, the size of the crystal phase is about 3 μm or more. In this state, the workability is significantly reduced, and only the strong part can be realized.

[0008] To solve such problems, the applicant of the present application has proposed a method for manufacturing crystallized glass containing a lithium disilicate crystal phase and a silicate crystal phase with excellent workability by adjusting the crystal size with the temperature change of the primary heat treatment, and has already obtained a patent (Korean Patent Registration No. 10-1975548). Specifically, here, 60 to 83% by weight of SiO2, 10 to 15% by weight of Li2O, 2 to 6% by weight of P2O5 serving as a nucleating agent, 1 to 5% by weight of Al2O3 that increases the glass transition temperature and softening point and improves the chemical durability of the glass, 0.1 to 3% by weight of SrO that raises the softening point of the glass, 0.1 to 2% by weight of ZnO, 1 to 5% by weight of a colorant, and 2.5 to 6% by weight of Na2O + K2O which is an alkali metal oxide that increases the thermal expansion coefficient of the glass. A step of performing a primary heat treatment on the glass composition at 400°C to 850°C, and a step of performing a secondary heat treatment at 780 to 880°C after the primary heat treatment, are included. The primary heat treatment generates a nano-sized lithium disilicate crystal phase and a silica crystal phase of 5 to 2000 nm, and the light transmittance is adjusted by the secondary heat treatment temperature. A method for manufacturing dental crystallized glass containing a silica crystal phase is disclosed.

[0009] On the other hand, while the living standards of people are improving, the demand for aesthetics in the dental field is also increasing. As patients' aesthetic desires are gradually rising, many studies have been conducted on aesthetic restorations using various materials.

[0010] Currently, even among the aesthetic restoration materials mainly used, the factors affecting the aesthetics of ceramic restorations include the appearance of teeth, surface condition, transparency, color, etc. Among these, especially transparency can be said to be an important factor for the production of successful restorations. Many studies and developments have been made on the mechanical and physical properties of ceramics for such aesthetic restorations, but there are still many problems regarding color harmony, and there are many difficulties in the selection of the color of restorations, especially regarding transparency, in terms of clinical and technical aspects.

[0011] In aesthetic prosthodontics, factors that affect the aesthetics during tooth restoration include color, tooth shape and size, tooth arrangement and ratio relationship, light transmittance, and the design of restorations. It can be said that what actually appears sensitively to our eyes is color and shape.

[0012] There is not a single part on a natural tooth where the color is the same from the neck of the tooth to the cut.

[0013] Reflecting such points, in recent years, a method of manufacturing artificial teeth that can mimic the deep color of natural teeth using the so-called build-up method is also known.

[0014] The build-up method is a method of forming artificial teeth with color by laminating powders such as porcelain and zirconia and then heat-treating them to embody multiple colors similar to natural teeth. Although it can quite mimic the color of natural teeth, this is a method in which the aesthetics of artificial teeth are determined according to the skilled functions of dental technicians, resulting in reduced reproducibility and inability to manufacture in an immediate manner, which is not advantageous for patients and is difficult to embody by cutting methods such as CAD / CAM processing.

[0015] On the other hand, when manufacturing artificial teeth by a cutting method such as CAD / CAM processing using an existing bulk block, since the bulk block itself is made of a material showing uniform physical properties, the resulting artificial teeth have no choice but to present a single color, different from natural teeth. In particular, when applying artificial teeth made by such a method to anterior teeth, there is no other problem than giving an aesthetically heterogeneous feeling and being inferior in naturalness.

[0016] Even with the method for manufacturing crystallized glass described in Patent Document 1 by the aforementioned applicant: Korean Patent Registration No. 10-1975548, although the transparency and workability can be adjusted by the secondary heat treatment process, the obtained crystallized glass is also such that each block itself has the same physical properties. To embody a deep color like that of natural teeth using this, it is necessary to apply a method of combining a plurality of resultant products. In other words, it was not easy to directly apply the bulk block itself to cutting processes such as CAD / CAM processing to immediately embody natural-colored teeth.

[0017] To improve such a point, the applicant has already received a patent registration for a bulk block that is useful for manufacturing artificial tooth prostheses similar to natural teeth, which can not only shorten the time and processes involved in manufacturing artificial dental prostheses, but also bring about the effect of increased structural stability in terms of force dispersion due to the gradient functionalization of mechanical physical properties (Patent Document 2: Korean Patent Registration No. 10-2246195).

[0018] The present invention was devised to provide a gradation bulk block with improved aesthetics and particularly improved machinability for such a bulk block.

Prior Art Documents

Patent Documents

[0019]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0020]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0021] An object of the present invention is to be used in the production of an artificial tooth restoration material that exhibits multi-gradation permeability or physical properties similar to natural teeth with repeatable reproducibility without adding further processes such as cutting by CAD / CAM, etc., and to provide a dental bulk block.

[0022] Another object of the present invention is to improve machinability, not only shorten the time and processes required for fabricating artificial tooth prostheses, but also bring about an effect of increased structural stability in terms of force dispersion due to the gradient function of mechanical physical properties, and to provide a dental bulk block.

[0023] Another object of the present invention is to provide a method for easily manufacturing a dental bulk block that can be used in the production of an artificial tooth restoration material that exhibits multi-gradation permeability or physical properties similar to natural teeth.

[0024] Another object of the present invention is to provide a method for easily manufacturing a tooth restoration from such a dental bulk block using a processing machine.

Means for Solving the Problems

[0025] One embodiment of the present invention is a glass-ceramic block containing a crystalline phase in an amorphous glass matrix. The crystalline phase includes at least one lithium silicate-based crystalline phase selected from the group consisting of lithium metasilicate and lithium disilicate and eucryptite, has a gradient in the size of the crystalline phase with respect to depth, and is a gradient functional material in which there is no interface at the gradient change point of the size of the crystalline phase. When the block is heat-treated at 820°C for 40 minutes, a characteristic peak of a spodumene crystalline phase appears in the graph of the X-ray diffraction analysis results as compared with the block heat-treated at 820°C for 2 minutes, and a dental bulk block is provided.

[0026] In a preferred embodiment of the present invention, the gradient in the size of the crystalline phase can be such that the average particle size is in the range of 0.05 μm to 1.0 μm based on the lithium silicate-based crystalline phase, and the average particle size is in the range of 1.0 μm to 4.0 μm based on the eucryptite crystalline phase.

[0027] Also, the dental bulk block according to one embodiment of the present invention can have a gradient in light transmittance with respect to depth.

[0028] In a preferred embodiment, the gradient in light transmittance may be in the range of 25 to 40% based on a wavelength of 550 nm.

[0029] In a preferred embodiment, the gradient in light transmittance may change within a range of 0.5 mm or less with respect to depth.

[0030] Also, the dental bulk block according to one embodiment of the present invention has gradients in L*, a*, and b* values by color difference analysis with respect to depth, and the color deviation ΔE value may change within a range of 1.5 mm with respect to depth.

[0031] The dental bulk block according to a preferred embodiment can have a crystallinity of 40 to 70%.

[0032] In a dental bulk block according to a specific embodiment, the crystalline phase may include a lithium silicate-based crystalline phase in the range of 40 to 60% by volume and a eucryptite crystalline phase in the range of 40 to 60% by volume based on the volume of the total crystalline phase.

[0033] Also, the dental bulk block according to an embodiment of the present invention can have a bending strength gradient with respect to depth.

[0034] In a preferred embodiment, the bending strength gradient may be within the range of 220 MPa to 350 MPa.

[0035] The dental bulk block according to an embodiment of the present invention may be composed of a continuous glass matrix.

[0036] In a preferred embodiment, the glass matrix contains 63.0 to 74% by weight of SiO2, 11.0 to 13.7% by weight of Li2O, 6 to 9% by weight of Al2O3, 1.5 to 3.5% by weight of K2O, and 2.0 to 4.0% by weight of P2O5, and the molar ratio of SiO2 / (Li2O + Al2O3) can satisfy 2.10 to 2.90. In particular, as a lithium silicate-based crystalline phase, in one embodiment including both lithium metasilicate and lithium disilicate, the glass matrix may have a molar ratio of SiO2 / Li2O of 2.20 to 2.59. As another embodiment, in one embodiment including only a lithium disilicate crystalline phase as the lithium silicate-based crystalline phase, the molar ratio of SiO2 / Li2O can be 2.60 to 3.00.

[0037] In another embodiment of the present invention, a glass composition containing 63.0 to 74 wt% of SiO2, 11.0 to 13.7 wt% of Li2O, 6 to 9 wt% of Al2O3, 1.5 to 3.5 wt% of K2O, and 2.0 to 4.0 wt% of P2O5, and having a molar ratio of SiO2 / (Li2O + Al2O3) satisfying 2.10 to 2.90 is melted, molded and cooled in a mold, and annealed at a set rate between 480 °C and 250 °C for 20 minutes to 2 hours, thereby producing a block of a predetermined shape, and heat-treating the block in a gradient heat treatment furnace at a temperature range of 850 to 1,000 °C to provide a temperature gradient in the depth direction of the block for heat treatment. A method for manufacturing a dental bulk block is provided.

[0038] In a manufacturing method according to an embodiment of the present invention, in one embodiment in which both lithium metasilicate and lithium disilicate are included as lithium silicate-based crystal phases, the glass composition may have a molar ratio of SiO2 / Li2O of 2.20 to 2.59. As another embodiment, in one embodiment for including only a lithium disilicate crystal phase as the lithium silicate-based crystal phase, the glass composition may have a molar ratio of SiO2 / Li2O of 2.60 to 3.00.

[0039] In a manufacturing method according to a preferred embodiment, the heat treatment step can be performed by heating to the maximum temperature at a heating rate of 30 °C / min to 110 °C / min and holding for 1 minute to 5 minutes at the maximum temperature.

[0040] Another embodiment of the present invention provides a method for manufacturing a dental restoration, including manufacturing a predetermined dental restoration by processing a dental bulk block for cutting in the above-described embodiment using a processing machine, and polishing or glazing the dental restoration.

[0041] In a method for manufacturing a dental restoration according to a preferred embodiment, glazing is performed at 730 to 820 °C for 30 seconds to 10 minutes.

[0042] Such glazing can be performed so that the biaxial flexural strength of the dental restoration has a gradient of 300 to 380 MPa.

[0043] In the method for manufacturing a dental restoration according to another embodiment, glazing can be performed for the purpose of adjusting the translucency of the processed dental restoration by heat treatment at at least 825°C.

[0044] Such glazing according to one embodiment can be performed at a temperature of at least 825°C for 1 to 10 minutes. Specifically, glazing can be performed so that the biaxial flexural strength has a gradient of 350 to 400 MPa.

Advantages of the Invention

[0045] The dental bulk block according to the present invention can be easily used for manufacturing an artificial dental restoration material that has multi-gradation translucency or physical properties similar to natural teeth, with good repeatability and without adding further processes by cutting such as CAD / CAM. It can not only shorten the time and processes involved in fabricating artificial dental prostheses, but also bring about the effect of increased structural stability in terms of force dispersion due to the gradient functionality of mechanical physical properties. Such a dental bulk block has the advantage of being manufacturable by a simple method of gradient heat treatment using a single glass composition having a specific composition.

Brief Description of the Drawings

[0046]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8a

Figure 8b

Mode for Carrying Out the Invention

[0047] The foregoing and further aspects of the present invention will become more apparent from the preferred embodiments described with reference to the accompanying drawings. Hereinafter, it will be described in detail so that those skilled in the art can easily understand and reproduce according to such embodiments of the present invention.

[0048] One embodiment of the present invention is a glass-ceramic block containing a crystal phase in an amorphous glass matrix, the crystal phase including at least one lithium silicate-based crystal phase selected from the group consisting of lithium metasilicate and lithium disilicate and eucryptite, having a gradient of the size of the crystal phase with respect to depth, and being a gradient functional material in which no interface exists at the gradient change point of the size of the crystal phase. When the block is heat-treated at 820°C for 40 minutes, it is confirmed from the results of X-ray diffraction analysis that a specific peak identified as a spodumene crystal phase appears as compared with the block heat-treated at 820°C for 2 minutes. A dental bulk block having such a feature is provided.

[0049] It can be said that such a feature is the result of a phase transition from eucryptite to spodumene crystal phase due to the movement of Si ions accompanying the increase in heat treatment time.

[0050] In the above and following descriptions, the meaning of "having a gradient in the size of the crystal phase with respect to depth" means that when graphing the size of the crystal phase according to the depth of the bulk block, there is a gradient in the change of the size of the crystal phase when comparing based on the same crystal phase. That is, it means that the size appears in a gradation form with respect to the same crystal phase with respect to the depth of the bulk block.

[0051] Also, the "gradient change point of the size of the crystal phase" refers to the point at which the value of the gradient of the change in the size of the crystal phase substantially changes when graphing the size of the crystal phase according to the depth of the bulk block and using the same crystal phase as a reference. Here, the meaning of "substantially changes" can mean a mere numerical change, but of course, it can also include those with a substantial change in light of the distribution of the values.

[0052] Also, the meaning of "there is no interface at the gradient change point of the size of the crystal phase" can be interpreted as meaning that there is no significant interfacial surface indicating delamination at the depth position of the bulk block showing the change in the gradient value of the size of the crystal phase when using the same crystal phase as a reference. That is, it means that the bulk block has a gradient in the size of the crystal phase in a continuous form without an interface according to the depth.

[0053] On the other hand, "Functionally Gradient Material (FGM)" refers to a material in which the properties of the constituent materials change continuously from one surface to another surface. In the present invention, although there is substantially no interface, the expression of functionally gradient material is borrowed in that the properties of the constituent materials change continuously.

[0054] In the above and following descriptions, the bulk block is not limited in its shape. As an example, it can of course include bulk bodies in various forms such as block type, disk type, ingot type, cylinder type, etc.

[0055] The bulk block according to the present invention contains at least one lithium silicate-based crystal phase selected from the group consisting of lithium metasilicate and lithium disilicate, and eucryptite. It can contain lithium phosphate as another additional crystal phase.

[0056] The XRD analysis result graph for the bulk block according to a preferred embodiment may be the same as that shown in FIG. 1.

[0057] In the case of FIG. 1(a), it is a bulk block in which both lithium metasilicate and lithium disilicate exist as the lithium silicate-based crystal phase, and eucryptite is included as another crystal phase. In the case of (b), it shows a bulk block that contains only lithium disilicate as the lithium silicate-based crystal phase and eucryptite as another crystalline phase.

[0058] FIG. 1 shows that the dental bulk block according to an embodiment of the present invention contains a lithium metasilicate or lithium disilicate crystal phase, and main peaks appear at 2θ = 19.7, 25.7, 48.5 (°), etc., which can be interpreted as eucryptite (beta-eucryptite, JCPDS #12-0709).

[0059] In the dental bulk block according to an embodiment of the present invention disclosed herein, in addition to eucryptite, main peaks appear at 2θ = 22.18, 22.9 (°) as an additional crystal phase, so this can be defined as lithium phosphate (JCPDS #15-0760, main peaks at 2θ = 22.3, 23.1).

[0060] In the above and the following descriptions, it should be understood that the XRD analysis is the result of analysis using an X-ray diffractometer (D / MAX-2500, manufactured by Rigaku, Japan; Cu Kα (40 kV, 60 mA), scanning speed: 6° / min, 2θ: 10 - 60 (°), manufactured by Rigaku, Japan).

[0061] Eucryptite is a lithium aluminum silicate crystal phase represented by the general formula LiAlSiO4, and compared with other LAS crystal phases such as spodumene (LiAlSi2O6), orthoclase (LiAlSi3O8), petalite (LiAlSi4O8), and virgilite (LiAlSi5O 12 ), the crystal is weak and has the property of low cutting resistance against machining tools due to residual stress. When such a crystal phase is included, when only lithium disilicate is present, a lower tool wear rate can be shown. When such tool resistance is lowered, the cutting efficiency can be improved, not only minimizing the consumption of milling tools, but also minimizing chipping (damage phenomenon) generated during machining.

[0062] A method for more easily identifying a dental bulk block according to an embodiment of the present invention has the characteristic that when the block is heat-treated at 820°C for 40 minutes, a specific peak of the spodumene crystal phase appears in the result graph of X-ray diffraction analysis compared with the block heat-treated at 820°C for 2 minutes. That is, when heat treatment is performed for 2 minutes even under the same heat treatment temperature condition of 820°C, there is no specific change in the crystal phase composition, but when heat treatment is performed for 40 minutes, the movement of SiO2 in the glass matrix becomes smooth, and eucryptite, which is a LAS crystal phase with less SiO2, exhibits the property of phase-transitioning to spodumene, which is a LAS crystal phase with increased SiO2.

[0063] In the above and following descriptions, heat-treating the block at 820°C specifically means heating a bulk block with a specification of 10×10×1.5 mm using the equipment of a dental porcelain furnace (CS, manufactured by Ivoclarvivadent) at a rate of 45°C / min and heat-treating it at a maximum temperature of 820°C. When the heat treatment time is 40 minutes, the holding time at the maximum temperature is 40 minutes, and when the heat treatment time is 2 minutes, the holding time at the maximum temperature is defined as 2 minutes.

[0064] This can be understood as a characteristic manifested by the phase transformation of Si ions and the like in the glass moving more actively and farther while the heat treatment time increases from 2 minutes to 40 minutes at the highest heat treatment temperature, resulting in more SiO2 being bonded to form LiAlSi2O6 (spodumene) than LiAlSiO4 (eucryptite). This characteristic can also be understood as evidence against the dental bulk block according to the present invention containing eucryptite as a crystal phase.

[0065] This can be confirmed from the result graph of the X-ray diffraction analysis in FIG. 2. FIG. 2(a) is for the product obtained by heat-treating the bulk block according to an embodiment of the present invention (specifically, the bulk block shown in FIG. 1(a) or (b)) at 820°C for 2 minutes, and FIG. 2(b) is for the product obtained by heat-treating the bulk block according to an embodiment of the present invention (specifically, the bulk block shown in FIG. 1(a) or (b)) at 820°C for 40 minutes.

[0066] In the case of the result graph shown in FIG. 2(b), compared with the result graph shown in FIG. 2(a), it can be seen that there is a specific peak identified as the spodumene crystal phase. In particular, it can be confirmed that the specific peak identified as the eucryptite crystal phase disappears and a specific peak identified as the spodumene crystal phase is shown.

[0067] Such a characteristic can predict that the bulk block according to the present invention can show changes in physical properties such as strength under specific conditions in the reheat-treatment method that can be additionally performed by users such as dental laboratories and dental hospitals in the manufacture of dental restorations, and it can be predicted that it is necessary to set conditions considering the change in the crystal phase.

[0068] Such a crystal phase that constitutes the bulk block of the present invention can be formed into crystal particles, which can variously embody mechanical properties and light transmissibility while showing various sizes and size distributions according to temperature.

[0069] In addition, by having a gradient of the size of the crystal phase with respect to depth, the bulk block can embody a gradation of light transmittance and mechanical properties with respect to depth. Furthermore, since there is no interface at the gradient change point of the size of the crystal phase, it is possible to solve the problem of layer separation occurring during cutting without requiring processing by interlayer bonding. Furthermore, it is possible to provide an artificial dental prosthesis with increased structural stability from the viewpoint of force dispersion due to such gradient functionalization.

[0070] Such a gradient of the size of the crystal phase in the bulk block of the present invention can be embodied within a range where the average particle size is within the range of 0.05 μm to 1.0 μm based on the lithium silicate-based crystal phase and within the range of 1.0 μm to 4.0 μm based on the eucryptite crystal phase.

[0071] As an example, FIG. 3 shows scanning electron microscope (SEM) photographs of the dental bulk block of the present invention. Six SEM photographs are shown for a specimen sliced to a thickness of 1.5 mm for one block, which are arranged in the depth direction and are illustrated by being roughly classified into those from the Cervical to the Incisal direction for convenience in consideration of the application. Specifically, starting from the SEM photograph of the upper layer part of the block (the part corresponding to the cervical at a depth of 1.5 mm) in the upper left of FIG. 3, the cross-section corresponding to 1.5 mm in the depth direction was observed, and finally the lowermost layer part of the block (the part corresponding to the Incisal) was observed.

[0072] The average particle size of the crystal phase particles can be derived through the SEM photographs obtained in this way. Specifically, a straight line is drawn diagonally or randomly on the SEM photograph, and the number of crystal phases through which the straight line passes is divided by the length of the straight line, taking into account the magnification, and can be obtained according to the linear cutting method.

[0073] In the above and following descriptions, the size of the crystal phase should be understood as being calculated by such a method.

[0074] The bulk block of the present invention, as a gradient functional material, is applied to machining such as cutting, for example, CAD / CAM machining, etc. under the same processing conditions as such a gradient functional material. Considering machinability, it can exhibit permeability that can be used clinically, such as a restorative material for artificial teeth. Therefore, the lithium silicate-based crystal phase preferably has an average particle size in the range of 0.05 μm to 1.0 μm, and eucryptite preferably has an average particle size in the range of 1.0 μm to 4.0 μm. In particular, eucryptite is a porous crystal phase in which the outer shape of its particles is in the form of dendritic protrusions (dendrites), and it can be predicted that such a morphology can increase machinability more.

[0075] The dental bulk block of the present invention has a gradient of light transmittance with respect to depth by having a gradient of the size of the crystal phase as described above.

[0076] In particular, when considering the range of the average particle size in the gradient of the size of the crystal phase described above, the gradient of the light transmittance may be within the range of 25 to 45% based on a wavelength of 550 nm.

[0077] In the above and following descriptions, the light transmittance was measured using an ultraviolet-visible spectrophotometer (UV-2401PC, manufactured by Shimadzu Corporation, Japan).

[0078] As described above, since there is no interface at the gradient change point of the size of the crystal phase in the dental bulk block of the present invention, it can be confirmed that the gradient of the light transmittance changes within a range of 0.5 mm or less with respect to depth and also changes within a range of 1.5 mm with respect to depth substantially.

[0079] To measure the light transmittance of the dental bulk block according to the present invention by gradient position, after cutting about 1.5 mm in the depth direction where the transparency decreases, the surface of the specimen was cleaned thoroughly with ethanol and measured using an ultraviolet-visible spectrophotometer (UV-2401PC, manufactured by Shimadzu Corporation, Japan). At this time, the measurement wavelength range was 300 to 800 nm, and the slit width was 2.0 nm. From the results in Figure 4, it can be confirmed that there is a difference in transmittance for the 1.5-mm-thick slice specimens.

[0080] Such results were shown in conjunction from Incisal to Cervical so as to correspond to the specimens shown in the scanning electron micrograph of Figure 3.

[0081] In Figure 3, each sample corresponds to the specimen by depth in Table 1 below.

[0082]

Table 1

[0083] Such results seem to mean that the light transmittance value changes even within a 1.5-mm range with respect to the depth, that is, the inclination of the transmittance appears even at such a thickness. This can be said to be a result clearly showing that the dental bulk block of the present invention is a gradient functional material. Also, since the position corresponding to the occlusal part is processed to the thickest thickness when making a prosthesis such as a crown, it can be predicted that an aesthetically favorable light transmittance can be exhibited even within such a thickness range.

[0084] In another aspect, since the dental bulk block of the present invention also has a gradient in shade, specifically, it has gradients of L*, a*, and b* values by color difference analysis with respect to the depth. As described above, since there is no interface at the gradient change point of the crystal phase size in the dental bulk block of the present invention, it can be confirmed that the color deviation ΔE value changes even within a 1.5-mm range with respect to the depth.

[0085] Color standardization is required for the accurate measurement, transmission, and reproduction of colors, and thus color systems were devised. Many color systems have been proposed, and among them, the CIE L*a*b color space defined by the International Commission on Illumination (CIE) in 1976 is the most widely used to date. Here, L* indicates lightness, and a* and b* indicate chromaticity coordinates. In the coordinates, the lighter the color, the larger the L* value, and the darker the color, the smaller the L* value. +a* means red, -a means green, +b means yellow, and -b means blue.

[0086] In order to measure the color of the dental bulk block according to the present invention by gradient position, after cutting so as to be about 1.5 mm in the depth direction in which the transparency decreases, the surface of the specimen was thoroughly cleaned using ethanol and analyzed using an ultraviolet-visible spectrophotometer (UV-2401PC, manufactured by Shimadzu Corporation, Japan). At this time, the measurement wavelength range was 380 to 780 nm, and the slit width was 2.0 nm. After setting a baseline using a standard reference sample, the reflectance of the specimen was measured, and the L*a*b* color system was obtained. The measured L*a*b* values were repeated three times to reduce errors, and then the average value was used. The color difference ΔE was obtained using these three values. If the ΔE value of both specimens is 0, it means there is no color difference. A value corresponding to 0 to 2 means there is a very slight difference. Values of 2 to 4 mean that the color difference is noticeable. Values of 4 to 6 mean that the color difference is appreciable. Values of 6 to 12 mean that the color difference is much. Values of 12 or more mean that the color difference is very much.

[0087] Regarding the dental bulk block having the characteristics as shown in FIGS. 1 to 3, for a 1.5-mm thick slice specimen, the chromatic aberration ΔE with respect to depth being 1.3 to 1.6 can be confirmed from the results in Table 2 below. Such results mean that within a 1.5-mm range with respect to depth, the ΔE value of the color deviation changes, that is, a gradient shade with different colors appears even at such a thickness. This can be said to be a result clearly indicating that the dental bulk block of the present invention is a gradient functional material in other aspects.

[0088]

Table 2

[0089] Furthermore, the dental bulk block of the present invention has a gradient of flexural strength according to depth. In particular, considering the range of the average particle size in the gradient of the size of the crystal phase described above, the gradient of the flexural strength may be within the range of 220 MPa to 350 MPa. In addition, the dental bulk block of the present invention can embody a functional gradient of various physical properties as described above, and considering workability, preferably, the crystallinity can be 40 to 70%.

[0090] In the above and the following descriptions, the "crystallinity" can be defined as the ratio of the crystal phase to the amorphous glass matrix, which can be determined by various methods. In one embodiment of the present invention, it is a value automatically calculated using an X-ray diffractometer.

[0091] Such a dental bulk block of the present invention is a glass-ceramic in which a crystal phase is precipitated in a continuous amorphous glass matrix, and has a crystal phase containing at least one selected from the group consisting of lithium metasilicate and lithium disilicate, and eucryptite, and has a gradient of the size of the crystal phase with respect to depth, and a gradient functional material in which no interface exists at the gradient change point of the size of the crystal phase can be obtained.

[0092] In particular, the crystalline phase preferably contains 40 to 60% by volume of a lithium silicate-based crystalline phase and 40 to 60% by volume of an eucryptite crystalline phase based on the volume of the total crystalline phase. In addition, when lithium phosphate is contained as a further crystalline phase, its content preferably does not exceed 5% by volume at most.

[0093] Generally, the content of the crystalline phase can be calculated by X-ray diffraction analysis. As an example, the ratio F of the crystalline phase a in a sample having two polymorphs a and b a is quantitatively represented by the following formula (1).

[0094]

Equation

[0095] This value can be obtained by measuring the intensity ratio of the two crystalline phases and obtaining the constant K. K is the absolute intensity ratio I of two pure polymorphs oa / I ob and is determined by measuring a standard substance.

[0096] The eucryptite crystalline phase can play a role in improving the machinability of the glass ceramic containing the lithium silicate-based crystalline phase as described above. However, if its content increases excessively, the strength may be reduced. Therefore, considering the processability and strength, the content of eucryptite in the crystalline phase is preferably 40 to 60% by volume based on the total volume of the crystalline phase.

[0097] In the above and the following descriptions, the term "continuous glass matrix" can be defined as a glass matrix in which there is no interlayer interface and the composition constituting the glass matrix is the same throughout the entire block.

[0098] A preferred glass matrix specifically contains 63.0 to 74 wt% of SiO₂, 11.0 to 13.7 wt% of Li₂O, 6 to 9 wt% of Al₂O₃, 1.5 to 3.5 wt% of K₂O, and 2.0 to 4.0 wt% of P₂O₅, and the molar ratio of SiO₂ / (Li₂O + Al₂O₃) can satisfy 2.10 to 2.90.

[0099] In addition, it goes without saying that in addition to the main components of the glass, 0.5 to 1.0 wt% of ZnO, 0.1 to 2.0 wt% of CaO, and 0.2 to 2.5 of Na₂O may be further contained.

[0100] In addition to this, since the lithium silicate-based crystal phase can be controlled according to the molar ratio of SiO₂ / Li₂O, as an example, within the range where the molar ratio of SiO₂ / Li₂O is 2.20 to 2.59, both the lithium disilicate crystal phase and the lithium metasilicate crystal phase may precipitate, and when the molar ratio of SiO₂ / Li₂O is 2.60 to 3.00, only the lithium disilicate crystal phase can precipitate in a lithium silicate-based crystalline form.

[0101] When the molar ratio of SiO₂ / Li₂O exceeds 3.00, rather than eucryptite as the LAS-based crystal phase, it is not desirable in that spodumene, orthoclase, petalite, virgilite, etc. containing a large amount of SiO₂ can be formed together with lithium disilicate.

[0102] In order to generate crystallization, the glass composition precipitates a crystal phase in an amorphous glass matrix through heat treatment for crystal nucleation and crystal growth. The above-mentioned glass matrix corresponds to a temperature range of 500°C to 850°C at which crystal nucleation and growth occur. That is, crystal nucleation starts to form from a minimum of 500°C and crystal growth is carried out while raising the temperature. This crystal growth shows the lowest light transmittance when used as an artificial tooth at a maximum of 850°C. That is, the light transmittance gradually decreases from the crystal growth temperature to a maximum of 850°C. When paying attention to such crystal growth, if this can be realized in one block, it will be possible to imitate the multi gradation of natural teeth.

[0103] Natural teeth not only have different light transmittances for each individual tooth, but also for all teeth. If such a change in light transmittance due to heat treatment temperature can be embodied in a single bulk block, the gradation of natural teeth can be sufficiently realized.

[0104] From such a perspective, the present invention includes melting a glass composition containing 63.0 to 74 wt% of SiO2, 11.0 to 13.7 wt% of Li2O, 6 to 9 wt% of Al2O3, 1.5 to 3.5 wt% of K2O, and 2.0 to 4.0 wt% of P2O5, molding and cooling it in a mold, and annealing it at a set speed for 20 minutes to 2 hours at 480°C to 250°C, including the step of producing a block of a predetermined shape, and heat-treating the block in a stepwise heat treatment furnace within a temperature range of 850 to 1,000°C to provide a temperature gradient in the depth direction of the block for heat treatment, and provides a method for manufacturing a dental bulk block.

[0105] As described above, in addition to the main glass components described above, the glass composition can of course additionally contain 0.5 to 1.0 wt% of ZnO, 0.1 to 2.0 wt% of CaO, and 0.2 to 2.5 of Na2O.

[0106] In addition, since the lithium silicate-based crystal phase can be controlled according to the molar ratio of SiO2 / Li2O, for example, within a range where the molar ratio of SiO2 / Li2O is 2.20 to 2.59, both the lithium disilicate crystal phase and the lithium metasilicate crystal phase may precipitate together. When the molar ratio of SiO2 / Li2O is 2.60 to 3.00, only the lithium disilicate crystal phase can precipitate in a lithium silicate-based crystalline form.

[0107] When the molar ratio of SiO2 / Li2O exceeds 3.00, it is undesirable in that spodumene, orthoclase, petalite, virgilite, etc., which contain a large amount of SiO2 rather than eucryptite as the LAS-based crystal phase, can be generated together with the lithium disilicate crystal phase.

[0108] According to a preferred embodiment, the heating rate to the maximum temperature in the step of heat-treating in a gradient heat treatment furnace is preferably carried out at a high rate of 30 °C / min to 110 °C / min. When reaching the maximum temperature of 850 to 1,000 °C, it is preferably carried out by holding for a short time of 1 minute to 5 minutes at the maximum temperature.

[0109] Since the mobility of SiO2 changes according to the heat treatment rate, temperature, and holding time, various LAS-based crystal phases can precipitate, and the workability and the like can change according to these crystal phases. The crystal phase of the LAS family suitable for satisfying the workability intended in the present invention is eucryptite. In forming such a crystal phase, suitable heat treatment conditions may be those that rapidly reach the maximum temperature and hold for a short time at the maximum temperature. That is, it can be important in terms of generating eucryptite to perform rapid heat treatment to stop crystal growth into LAS-based crystals in the initial state.

[0110] As described above, the glass composition can exhibit the characteristic that the light transmittance of the material appears differently depending on the heat treatment temperature range. Therefore, when the heat treatment is uniformly applied to the entire block, it exhibits a certain light transmittance, but when the heat treatment is applied to the block with a temperature gradient, multi-gradation of physical properties and light transmittance can be exhibited in one block.

[0111] In the case of a bulk-form block, it is used as a workpiece for machining such as CAD / CAM machining. However, the manufacturing method of the present invention can manufacture a bulk block in which the light transmittance and strength are multi-graded by applying a temperature gradient in the depth direction when heat-treating this block.

[0112] Conventional crystallized glass generally has large crystal sizes, making it difficult to adjust light transmittance, and is also strong in strength and difficult to process. In contrast, in the case of the glass composition adopted in the present invention, it is possible to form fine crystals, which can exhibit various physical properties and light transmittances while showing various sizes and size distributions according to temperature. Therefore, after producing a block from a single glass composition reflecting this point, it is possible to embody a single bulk block such that its mechanical properties and light transmittance are multi-graded by a method of heat-treating it with a temperature gradient applied thereto.

[0113] At this time, the step of heat-treating with a temperature gradient applied in the depth direction of the block means that, of course, a temperature gradient that gradually increases from the lower end to the upper end can be applied in the depth direction of the block, and a temperature gradient in a manner of partially applying a temperature difference is also acceptable. The selection of such a temperature gradient method varies according to the characteristics of the natural teeth of a patient who requires a dental prosthesis, or of course according to the inherent characteristics of the part of the tooth that requires the prosthesis.

[0114] However, considering typical natural teeth, it is preferable to apply a temperature gradient for heat treatment in such a manner that the temperature gradually increases from the lower end to the upper end with respect to the depth of the block.

[0115] When using the heat treatment method of the present invention described above using the glass composition described above, it is possible to mimic the characteristic that the original tooth structure has lower light transmittance at the cervical part and higher light transmittance toward the incisal side. As a result, unlike existing methods, it is not necessary to separately characterize during prosthesis production, so it can be very economically advantageous.

[0116] In addition, with respect to the physical properties of natural teeth, the enamel, which is the surface layer, has high flexural strength, while the dentin inside has weak strength and thus plays a role in absorbing and dispersing external forces. However, in the present invention, since it is possible to obtain a gradient functional material having a gradient in mechanical physical properties, particularly flexural strength, due to differences in the fine structure according to the depth of heat treatment, it is characterized in that it can be reproduced to be similar to the physical property aspect of natural teeth.

[0117] Manufacturing a dental restoration using the dental bulk block obtained by the present invention can be expected to have a remarkable improvement in workability. As a specific example, in one embodiment of the present invention, there is provided a method for manufacturing a dental restoration, including the steps of machining the above-described dental bulk block using a processing machine to manufacture a predetermined dental restoration, and polishing or glazing.

[0118] In the above and following descriptions, it goes without saying that dental restorations include all of crowns, inlays, onlays, veneers, abutments, and the like.

[0119] Here, glazing can be performed at 730 to 820°C for 30 seconds to 10 minutes. In this case, it may be a typical finishing heat treatment step with almost no change in translucency due to heat treatment. Glazing is usually performed within a range that does not change the translucency inherent to the block, and during the glazing heat treatment, the strength can increase while surface microcracks are alleviated (surface healing).

[0120] When the holding time exceeds 20 minutes, spodumene or vermiculite crystals with increased SiO2 can be formed. Therefore, if such a change in the crystal phase is not intended, glazing is preferably performed at 730 to 820°C within 30 seconds to 10 minutes.

[0121] Through glazing under such conditions, due to the effect of alleviating microcracks, the dental restoration can have the gradient of biaxial flexural strength enhanced to 300 to 380 MPa, which can be confirmed from the results of FIG. 8a.

[0122] However, in a specific embodiment, glazing in the method for manufacturing a dental restoration using the bulk block according to the present invention can be used for the purpose of adjusting the translucency of the processed dental restoration by heat treatment at at least 825°C. That is, the bulk block can be processed into a dental restoration, and then glazing can be utilized for the purpose of reducing translucency and adjusting lightness in the final finishing step.

[0123] When manufacturing a dental restoration by machining on the processor or user side using a bulk block, there may be a case where the translucency changes significantly unintentionally. In such a case, for a normal lithium disilicate-based bulk block, the machined bulk block has to be discarded, and after reprocessing a bulk block that satisfies the desired translucency through a predetermined heat treatment again from the bulk block, the process of processing this into a dental restoration has to be gone through again. However, in the case of the bulk block according to the present invention, due to the specific bulk block having a fine crystal phase, the property that the translucency is adjusted by the heat treatment temperature can be exhibited, so reprocessing is not required, and the translucency can be easily adjusted again by going through the step of glazing under predetermined conditions in the final finishing step of the workpiece processed into a dental restoration. Thereby, the colored tooth generated during processing into a dental restoration by glazing can be shielded by a simple method.

[0124] Such glazing in such an application is preferably performed at a temperature of at least 825°C for 30 seconds to 10 minutes. When the holding time is prolonged during such glazing treatment, spodumene or virgilite crystals with increased SiO2 can be formed. Therefore, if such a change in crystal phase is not intended, it is preferable that the glass is performed at at least 825°C within 30 seconds to 10 minutes.

[0125] Through crystal growth by such graining under such conditions, the dental restoration can enhance the gradient of biaxial flexural strength to 350 - 400 MPa, which can be confirmed from the results in Fig. 8b.

[0126] Characteristically, in the case of the dental bulk block obtained according to the present invention, when processing using a processing machine, the resistance generated during processing can be significantly reduced. As a specific example, for the dental bulk block (the present invention) having the characteristics shown in Figs. 1 - 3, it was sized to 12×14×18 mm and rotated at 250 RPM using a low-speed cutting machine (ISOMET low speed saw, manufactured by Buehler, Germany) and a diamond electroplated wheel (2514485H17, manufactured by Norton, USA), and the cutting time was measured. Then, in the same manner, the final heat treatment of the most common lithium disilicate-based block (conventional lithium disilicate) (Rosetta SM, manufactured by HASS Corp), the zirconia-reinforced lithium disilicate-based bulk block (zirconia-reinforced lithium disilicate) (Celtra Duo, manufactured by Dentsply Siron), and the lithium aluminosilicate-reinforced lithium disilicate bulk block (LAS reinforced lithium disilicate) (Nice, manufactured by Straumann) were measured for their cutting times.

[0127] When the cutting resistance (cutting resistance, %) was calculated from each of the thus obtained cutting time values, specifically, the cutting time obtained for the normal lithium disilicate block was taken as 100%, and the cutting time was converted as a relative percentage thereto and calculated as each cutting resistance value.

[0128] The results are illustrated in Fig. 5.

[0129] From the results of Fig. 5, the normal lithium disilicate block had the highest cutting resistance, followed by LAS (lithium alumino silicate) crystallized glass and zirconia-reinforced crystallized glass, which had high cutting resistance. In the case of the block according to the present invention, it showed significantly low cutting resistance. Here, regarding the blocks according to the present invention, the results are shown for two types of blocks where the molar ratio of SiO2 / Li2O (abbreviated as S / L) is 2.7 and 2.5, respectively. It was confirmed that even when containing a lithium disilicate crystal phase, it showed significantly low cutting resistance.

[0130] From such results, it can be predicted that in the case of the glass-ceramic block of the present invention, it is the most machinable, and this is due to the inclusion of eucryptite in the LAS-based crystal phase.

[0131] In a specific embodiment of the present invention, first, a glass composition containing 63.0 to 74 wt% of SiO2, 11.0 to 13.7 wt% of Li2O, 6 to 9 wt% of Al2O3, 1.5 to 3.5 wt% of K2O, and 2.0 to 4.0 wt% of P2O5 and having a molar ratio of SiO2 / (Li2O + Al2O3) satisfying 2.10 to 2.90 is weighed and mixed.

[0132] As the glass composition, Li2CO3 may be added instead of Li2O, and carbon dioxide (CO2), which is the carbon (C) component of Li2CO3, will be discharged as a gas in the glass melting process. Also, in the case of alkali oxides, K2CO3 and Na2CO3 may be added instead of K2O and Na2O, respectively, and carbon dioxide (CO2), which is the carbon (C) component of K2CO3 and Na2CO3, will be discharged as a gas in the glass melting process.

[0133] Mixing uses a dry mixing process, and as the dry mixing process, a ball milling process or the like can be used. Specifically explaining the ball milling process, the starting materials are loaded into a ball milling machine, and the ball milling machine is rotated at a constant speed to mechanically pulverize and uniformly mix the starting materials. The balls used in the ball milling machine may be balls made of ceramic materials such as zirconia or alumina, and the sizes of the balls may all be the same, or balls having at least two or more sizes can be used. Considering the size of the target particles, the size of the balls, the milling time, the rotational speed per minute of the ball milling machine, etc. are adjusted. As an example, considering the particle size, the size of the balls can be set in the range of about 1 mm to 30 mm, and the rotational speed of the ball milling machine can be set in the range of about 50 to 500 rpm. The ball milling is preferably carried out for 1 to 48 hours considering the size of the target particles and the like. By the ball milling, the starting materials are pulverized into particles of fine dimensions, have a uniform particle size, and are uniformly mixed.

[0134] Put the mixed starting materials into a melting furnace, and heat the melting furnace containing the starting materials to melt the starting materials. Here, melting means that the starting materials change to a substance state having the viscosity of a liquid state rather than a solid state. The melting furnace preferably consists of a substance having a low contact angle in order to have a high melting point while having a large strength and suppressing the phenomenon of the melt sticking. For this reason, it is preferably a melting furnace made of substances such as platinum (Pt), DLC (diamond-like-carbon), chamotte, etc., or a melting furnace whose surface is coated with a substance such as platinum (Pt) or DLC (diamond-like-carbon).

[0135] Melting is preferably carried out at a normal pressure for 1 to 12 hours at 1,400 to 2,000 °C. If the melting temperature is less than 1,400 °C, there is a risk that the starting materials have not yet melted. If the melting temperature exceeds 2,000 °C, excessive energy consumption is required, which is not economical. Therefore, it is preferable to melt at a temperature within the above-mentioned range. Also, if the melting time is too short, the starting materials may not melt sufficiently. If the melting time is too long, excessive energy consumption is required, which is not economical. The heating rate of the melting furnace is preferably about 5 to 50 °C / min. However, if the heating rate of the heating furnace is too slow, it takes a long time and the productivity is poor. If the heating rate of the melting furnace is too fast, the volatilization amount of the starting materials increases due to a rapid temperature rise, and the physical properties of the crystallized glass may not be good. Therefore, it is preferable to raise the temperature of the melting furnace at a heating rate within the above-mentioned range. Melting is preferably carried out in an oxidizing atmosphere such as oxygen (O2) or air.

[0136] The melt is poured into a mold defined to obtain dental crystallized glass of a desired shape and size. The mold preferably has a high melting point and high strength and is made of a material with a low contact angle in order to suppress the phenomenon of the glass melt sticking. For this purpose, it is made of a material such as graphite or carbon. In order to prevent thermal shock, it is preferably preheated to 200 to 300 °C and the melt is poured into the mold.

[0137] Since the melt placed in the mold is formed and cooled, it is preferable to go through a step of slow cooling (annealing) at a set speed for 20 minutes to 2 hours at 480 °C to 250 °C after the cooling process. Going through such a slow cooling step can reduce the variation in stress within the formed article, preferably making the stress non-existent, and can preferably affect the control of the crystal phase size and the improvement of the uniformity of the crystal distribution in the following crystallization step, thereby finally obtaining the target functional gradient material.

[0138] Here, the set speed is preferably 2.3 to 14 °C / min in terms of sufficient slow cooling being carried out.

[0139] The formed body that has undergone the slow cooling process is transferred to a crystallization heat treatment firing furnace, and nucleation and crystal growth are carried out to produce the target crystallized glass.

[0140] FIG. 6 schematically shows a method of performing crystallization heat treatment by applying a temperature gradient according to the present invention. When performing crystallization heat treatment on a bulk block of a block type or an ingot type, a temperature gradient is applied so that the upper end is heat-treated at a high temperature (High temperature) and the lower end is heat-treated at a low temperature (Low temperature) along the depth direction.

[0141] In the above and the following descriptions, the step of heat treatment with a temperature gradient is not limited to a specific apparatus and method. As an example, it may be performed in a gradient heat treatment furnace (furnace). It is preferably performed by heat treatment in a temperature range of 850 to 1,000 ° C. in the gradient heat treatment furnace (furnace), heating up to the maximum temperature at a heating rate of 30 ° C. / min to 110 ° C. / min, and maintaining for 1 to 5 minutes under the maximum temperature.

[0142] By such heat treatment with a temperature gradient, from the high temperature part to the low temperature part, the light transmittance shows a gradient with a high transmittance (high transmittance), and the flexural strength shows a gradient with a low strength (low flexural strengh). This is because the size of the crystals in the crystallized glass can be adjusted according to the temperature. The crystal phase generated after heat treatment with a temperature gradient includes a lithium silicate-based crystal phase such as lithium metasilicate or lithium disilicate, and eucryptite. A bulk block which is a gradient functional material having an average particle size of the lithium silicate-based crystal phase in the range of 0.05 μm to 1.0 μm and an average particle size of the eucryptite crystal phase in the range of 1.0 μm to 4.0 μm can be manufactured.

[0143] Also, regarding the bulk block obtained by the present invention, the change in flexural strength with respect to the depth is measured and shown in FIG. 7.

[0144] On the other hand, the results of measuring the flexural strength of the product obtained by subjecting such a bulk block to glazing heat treatment at 820°C for 2 minutes are shown in FIG. 8a.

[0145] On the other hand, the results of measuring the flexural strength of the product obtained by subjecting such a bulk block to glazing heat treatment at 840°C for 2 minutes are shown in FIG. 8b.

[0146] As described above, the present invention has been described with reference to one embodiment shown in the drawings, but this is merely exemplary, and those having ordinary knowledge in the technical field can understand that various modifications and equivalent other embodiments are possible hereinafter.

Industrial Applicability

[0147] The present invention relates to a dental bulk block having improved machinability and a method for producing the same, which are useful for producing artificial teeth similar to the structural characteristics of natural teeth.

[0148] The dental bulk block according to the present invention can be easily used for producing an artificial tooth restoration material that exhibits multi-gradation permeability or physical properties similar to natural teeth with repeatable reproducibility without adding further steps by cutting such as CAD / CAM. It can not only shorten the time and steps involved in producing artificial dental prostheses, but also bring about the effect of increasing the structural stability in terms of force dispersion due to the gradient function of mechanical physical properties. Such a dental bulk block has the advantage that it can be produced by a simple method of gradient heat treatment using a single glass composition having a specific composition.

Claims

1. A glass-ceramic block containing a crystal phase in an amorphous glass matrix, wherein the crystal phase includes at least one lithium silicate-based crystal phase selected from the group consisting of lithium metasilicate and lithium disilicate and eucryptite, which is a gradient functional material having a gradient in the size of the crystal phase with respect to depth and having no interface at the gradient change point of the size of the crystal phase, when the block is heat-treated at 820 °C for 40 minutes, a specific peak of the spodumene crystal phase appears in the graph of the X-ray diffraction analysis results as compared with the block heat-treated at 820 °C for 2 minutes, the crystal phase is contained in a range of 40 to 60% by volume of the lithium silicate-based crystal phase and 40 to 60% by volume of the eucryptite crystal phase based on the total volume of the crystal phase characterized in that it is a dental bulk block.

2. The gradient of the size of the crystal phase is such that the average particle size thereof is in the range of 0.05 μm to 1.0 μm based on the lithium silicate-based crystal phase and the average particle size thereof is in the range of 1.0 μm to 4.0 μm based on the eucryptite crystal phase The dental bulk block according to Claim 1.

3. having a gradient in light transmittance with respect to depth The dental bulk block according to Claim 1.

4. The gradient of the light transmittance is in the range of 25 to 40% based on a wavelength of 550 nm The dental bulk block according to Claim 3.

5. The gradient of the light transmittance varies within a range of 0.5 mm or less with respect to depth The dental bulk block according to Claim 3.

6. having a gradient in L*, a*, and b* values by color difference analysis with respect to depth and having a color deviation (ΔE) value that changes even within a range of 1.5 mm with respect to depth The dental bulk block according to Claim 1.

7. The crystallinity is 40 to 70% The dental bulk block according to Claim 1.

8. having a gradient in flexural strength with respect to depth The dental bulk block according to Claim 1.

9. The gradient of the flexural strength is in the range of 220 MPa to 350 MPa The dental bulk block according to Claim 8.

10. The dental bulk block is made of a continuous glass matrix The dental bulk block according to Claim 1.

11. The glass matrix contains 63.0 to 74 wt% of SiO₂, 11.0 to 13.7 wt% of Li₂O, 6 to 9 wt% of Al₂O₃, 1.5 to 3.5 wt% of K₂O, and 2.0 to 4.0 wt% of P₂O₅, and the molar ratio of SiO₂ / (Li₂O + Al₂O₃) satisfies 2.10 to 2.

90. The dental bulk block according to claim 1 or 10.

12. The glass matrix has a molar ratio of SiO₂ / Li₂O of 2.20 to 2.

59. The dental bulk block according to claim 1 or 10.

13. The glass matrix has a molar ratio of SiO₂ / Li₂O of 2.60 to 3.

00. The dental bulk block according to claim 1 or 10.

14. A step of producing a block of a predetermined shape by melting a glass composition containing 63.0 to 74 wt% of SiO₂, 11.0 to 13.7 wt% of Li₂O, 6 to 9 wt% of Al₂O₃, 1.5 to 3.5 wt% of K₂O, and 2.0 to 4.0 wt% of P₂O₅, and having a molar ratio of SiO₂ / (Li₂O + Al₂O₃) satisfying 2.10 to 2.90, molding and cooling in a mold, and annealing at a set speed for 20 minutes to 2 hours at 480 °C to 250 °C, Heat-treating the block in a gradient heat treatment furnace at a temperature range of 850 to 1,000 °C to apply a temperature gradient in the depth direction of the block and heat-treat it. A method for manufacturing a dental bulk block, characterized by the above.

15. The glass composition has a molar ratio of SiO₂ / Li₂O of 2.20 to 2.

59. The method for manufacturing a dental bulk block according to claim 14.

16. The glass composition has a molar ratio of SiO₂ / Li₂O of 2.60 to 3.

00. The method for manufacturing a dental bulk block according to claim 14.

17. The heat treatment step is performed by heating to the maximum temperature at a heating rate of 30 °C / min to 110 °C / min and holding for 1 minute to 5 minutes at the maximum temperature. The method for manufacturing a dental bulk block according to claim 14.

18. A step of manufacturing a predetermined dental restoration by processing the dental bulk block for cutting according to claim 1 using a processing machine, And a step of polishing or glazing the dental restoration. A method for manufacturing a dental restoration, characterized by the above.

19. Glazing is performed at 730 to 820 °C for 30 seconds to 10 minutes The method for manufacturing a dental restoration according to claim 18

20. Glazing is performed so as to have a gradient of biaxial flexural strength of 300 to 380 MPa The method for manufacturing a dental restoration according to claim 18 or 19

21. Glazing is for the use of adjusting the translucency of the processed dental restoration by heat treatment at at least 825 °C The method for manufacturing a dental restoration according to claim 18

22. Glazing is performed at a temperature of at least 825 °C for 1 minute to 10 minutes The method for manufacturing a dental restoration according to claim 18

23. Glazing is performed so as to have a gradient of biaxial flexural strength of 350 to 400 MPa The method for manufacturing a dental restoration according to any one of claims 18, 21, and 22

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