Dental bulk block for cutting and its manufacturing method

Abstract

A dental bulk block for cutting is provided, which is a glass ceramic block containing a crystalline phase in an amorphous glass matrix, the crystalline phase being a functionally graded material having a gradient in the size of the crystalline phase with respect to the depth and no interface at the change point of the gradient value of the size of the crystalline phase, and is useful for manufacturing an artificial tooth prosthesis similar to a natural tooth, and thus can shorten the time and process for manufacturing the artificial tooth prosthesis, and can bring about an effect of increasing structural stability in terms of force distribution by functionally grading the mechanical properties.

Description

[Technical field]

[0001] The present invention relates to a dental bulk block for cutting, which is useful for manufacturing artificial teeth similar to the structural characteristics of natural teeth, and a manufacturing method thereof. The present invention is the result of research conducted with the support of the Gangwon Technopark's Material, Parts and Equipment Company Development and Technology Independence Support Project. [Background technology]

[0002] Crown materials are prosthetic materials that repair the damaged dentin and enamel of teeth, and can be classified into inlays, onlays, veneers, crowns, etc., depending on the application site. Crown materials are required to have high aesthetic properties because they are used on the surface of the tooth, and high strength is required to prevent breakage due to wear with the opposing teeth and chipping. Conventional materials used as crown materials include leucite glass-ceramics, reinforced porcelain, and fluorapatite (Ca5(PO4)3F) glass-ceramics, which have excellent aesthetic properties but have the disadvantage of being highly susceptible to breakage due to low strength of 80 to 120 MPa. Therefore, research is currently underway to develop high-strength crown materials made of various materials.

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

[0004] The crystal phase and strength were studied under various crystal nucleation and growth heat treatment conditions using Li2O-Al2O3-SiO2-Li2O-K2O-B2O3-P2O5 system glasses. When the low-temperature lithium metasilicate to high-temperature lithium disilicate crystal phase was shown, the strength was 30~35KPS. This was due to the residual stress caused by the difference in thermal expansion coefficients of the substrate glass, mother glass, Li2SiO5, and Li2SiO3 phases.

[0005] A number of patents have already been published for a material and method for manufacturing an artificial tooth using glass containing lithium disilicate crystals (monolithic dental crown). However, in the known technology, the size of the crystal phase is large and difficult to machine immediately, so in order to process it, a method is used in which a lithium metasilicate crystal phase (machinable crystalline) is formed in the first step, which is then processed, and then a high-strength lithium disilicate crystal phase is formed by heat treatment in the second step. In this case, there is a problem that the dimensional accuracy is reduced due to shrinkage caused by the post-heat treatment process, and a heat treatment process is added. Generally, in the case of prosthetic processing using CAD / CAM, a bulk body is directly processed in the hospital to manufacture a prosthesis, which must be tried on the patient as soon as possible (one-day appointment), so the time delay caused by the heat treatment process causes economic difficulties for patients and users.

[0006] In addition, conventional lithium disilicate glass-ceramic materials have limitations in terms of realizing high light transmittance and opalescence similar to those of natural teeth due to the coarse crystal phase.

[0007] In particular, conventional lithium disilicate crystallized glass materials are made by first creating lithium metasilicate crystallized glass, which is easy to process, and then forming lithium disilicate through a secondary crystallization heat treatment after processing to increase strength. At this time, the size of the crystal phase is approximately 3 μm or more, and in this state, the processability is significantly poor and only the strength aspect is achieved.

[0008] In order to solve these problems, the applicant has proposed a method for manufacturing crystallized glass containing lithium disilicate crystal phase and silicate crystal phase, which has excellent processability by controlling the crystal size through temperature change in the primary heat treatment, and has already received a patent (Korean Patent No. 10-1975548). Specifically, the present invention discloses a method for producing dental crystallized glass containing a silica crystal phase, which comprises a step of subjecting a glass composition containing 60-83% by weight of SiO2, 10-15% by weight of Li2O, 2-6% by weight of P2O5 functioning as a nucleating agent, 1-5% by weight of Al2O3 which increases the glass transition temperature and softening point and promotes the chemical durability of the glass, 0.1-3% by weight of SrO which increases the softening point of the glass, 0.1-2% by weight of ZnO, 1-5% by weight of a colorant, and 2.5-6% by weight of alkali metal oxide Na2O+K2O which increases the thermal expansion coefficient of the glass, to a primary heat treatment at 400°C to 850°C, and a step of subjecting the glass composition to a secondary heat treatment at 780°C to 880°C after the primary heat treatment, in which a nano-sized lithium disilicate crystal phase and a silica crystal phase of 5nm to 2000nm are produced by the primary heat treatment, and the translucency is adjusted by the temperature of the secondary heat treatment.

[0009] On the other hand, as human living standards improve, the demand for aesthetics is also increasing in the field of dentistry. As patients' aesthetic desires gradually increase, much research is being conducted on aesthetic prosthetic restorations using various materials.

[0010] Currently, porcelain is the main esthetic restorative material, and factors that affect the esthetics of porcelain restorations include the tooth's outer shape, surface condition, transparency, and color, among which transparency is particularly important for successful restoration production. Although there has been a great deal of research and development into the mechanical and physical properties of porcelain for such esthetic prostheses, there are still many problems with color matching, and there are many difficulties in clinical and technical aspects regarding color selection of restorations, especially transparency.

[0011] In aesthetic prosthetics, factors that affect aesthetics when restoring teeth include color, tooth shape and size, tooth arrangement and proportional relationship, light, transparency, and restoration design, and it can be said that color and shape are what the eye is most sensitive to. A natural tooth has no single area that is the same color from the neck to the incisal edge. Reflecting this, in recent years, a method for producing artificial teeth that can imitate the deep color of natural teeth using a so-called build-up method has become known.

[0012] The build-up method is a method in which porcelain, zirconia, and other powders are layered together to form an artificial tooth with a color tone, and then heat-treated to create a layered color similar to that of natural teeth, and it can closely mimic the color of natural teeth. However, this method has problems in that the aesthetics of the artificial tooth are determined entirely by the skill of the dental technician, so reproducibility is low, it cannot be manufactured in an instantaneous manner, it is not convenient for patients, and it is difficult to achieve with cutting methods such as CAD / CAM.

[0013] Meanwhile, when artificial teeth are manufactured using conventional bulk blocks through cutting methods such as CAD / CAM, the bulk blocks themselves are made of materials with uniform physical properties, so the resulting artificial teeth have to be monochromatic, unlike natural teeth. In particular, artificial teeth manufactured using this method have the problem that they look aesthetically heterogeneous and less natural when applied to front teeth.

[0014] Even with the method for manufacturing crystallized glass described in the above-mentioned patent document 1 (Korean Patent No. 10-1975548) by the applicant, the transparency and workability can be adjusted through a secondary heat treatment process, but the obtained crystallized glass is a block that has the same physical properties, and in order to use it to achieve a deep color similar to that of natural teeth, it is necessary to apply a method of combining multiple results. In other words, it is not easy to immediately realize natural-colored teeth by directly applying cutting processing such as CAD / CAM using the bulk block itself.

[0015] To improve on this issue, the applicant has filed and already received registration for a bulk block that is useful for manufacturing artificial tooth prostheses that resemble natural teeth, thereby shortening the time and process required to manufacture the artificial tooth prostheses, as well as potentially providing the effect of increased structural stability in terms of force distribution through functional grading of mechanical properties (Patent Document 2: Korean Patent No. 10-2246195).

[0016] The present invention aims to provide a gradation bulk block that has improved aesthetics such as transparency and shade, is more similar to natural teeth in terms of physical properties, and has improved machinability compared to such bulk blocks. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Korean Patent No. 10-1975548 [Patent Document 2] Korean Patent No. 10-2246195 [Non-patent literature]

[0018] [Non-Patent Document 1] Marcus P. Borom and Anna M. Turkalo, The Pacific Coast Regional Meeting, The American Ceramic Society, San Francisco, CA, October 31, 1973(Glass division, No.3-G-73P) Summary of the Invention [Problem to be solved by the invention]

[0019] The present invention aims to provide a dental bulk block for cutting, which can be used to manufacture artificial tooth restorative materials that exhibit multi-gradation transparency or physical properties similar to those of natural teeth so that they can be repeatedly and reproducibly by cutting processes such as CAD / CAM without the addition of any other processes.

[0020] In addition, the present invention aims to provide a dental bulk block for cutting processing that can not only shorten the time and process for manufacturing artificial tooth prostheses, but also provide the effect of increased structural stability in terms of force distribution by functionally grading mechanical properties.

[0021] The present invention also aims to provide a method for easily producing a dental bulk block for cutting, which can be used to produce an artificial tooth restorative material that exhibits multi-gradation transparency or physical properties similar to those of natural teeth. Another object of the present invention is to provide a method for easily manufacturing such a dental bulk block into a dental restoration using a processing machine. [Means for solving the problem]

[0022] One embodiment of the present invention provides a dental bulk block for machining, which is a glass ceramic block including a crystalline phase in an amorphous glass matrix, the crystalline phase being a functionally gradient material having a gradient in the size of the crystalline phase with respect to the depth, and no interface at the change point of the gradient value of the size of the crystalline phase. The crystalline phase is a main crystalline phase of lithium disilicate, and additional crystalline phases of at least one selected from cristobalite and tridymite, and lithium phosphate.

[0023] In a preferred embodiment of the present invention, the gradient in size of the main crystal phase may be such that the average grain size is in the range of 0.05 μm to 1.5 μm. A dental bulk block according to an embodiment of the present invention may have a gradient of light transmission with respect to depth. In a preferred embodiment, the gradient of the light transmittance may be within the range of 25 to 40% based on a wavelength of 550 nm. In a preferred embodiment, the gradient of light transmission may vary over depth within a range of less than 0.5 mm. In one preferred embodiment, the gradient of light transmission may vary over depth within 0.31 mm.

[0024] In addition, the dental bulk block according to an embodiment of the present invention is a L based on color difference analysis with respect to depth. * , a * and b * The color deviation (ΔE) value may vary within a range of 0.31 mm relative to the depth. A dental bulk block according to a preferred embodiment may have a crystallinity of 40 to 70%. Furthermore, the dental bulk block according to one embodiment of the present invention may have a gradient of biaxial bending strength with respect to depth. In a preferred embodiment, the gradient of the biaxial bending strength may be in the range of 180 MPa to 420 MPa. A dental bulk block according to one embodiment of the present invention may consist of a continuous glass matrix.

[0025] In a preferred embodiment, the glass matrix contains 65.0 to 73.0 weight% of SiO2, 12.0 to 14.0 weight% of Li2O, 1.5 to 3.0 weight% of Al2O3, 0.12 to 0.22 weight% of ZnO, 2.8 to 3.5 weight% of K2O, 0.3 to 1.0 weight% of Na2O, and 2.0 to 6.0 weight% of P2O, and the molar ratio of Al2O3 / (K2O+ZnO) may satisfy 0.3 to 1.2.

[0026] In another embodiment of the present invention, a method for producing a block having a predetermined shape includes the steps of melting a glass composition containing 65.0 to 73.0% by weight of SiO2, 12.0 to 14.0% by weight of Li2O, 1.5 to 3.0% by weight of Al2O3, 0.12 to 0.22% by weight of ZnO, 2.8 to 3.5% by weight of K2O, 0.3 to 1.0% by weight of Na2O, and 2.0 to 6.0% by weight of P2O5, and a molar ratio of Al2O3 / (K2O+ZnO) satisfies 0.3 to 1.2, forming the glass composition in a mold, cooling the glass composition, and annealing the glass composition at a set rate from 480°C to 280°C for 20 minutes to 2 hours;

[0027] The block is heat-treated at 760 to 880° C. while applying a temperature gradient in the depth direction of the block.

[0028] In a preferred embodiment of a method for manufacturing a dental bulk block, the heat treatment step may be performed such that a temperature range of 840 to 880°C is applied to the upper layer of the block and a temperature range of 760 to 800°C is applied to the lower layer of the block.

[0029] In a preferred embodiment, the heat treatment may be performed in a gradient heat treatment furnace at an operating temperature of 900-1100° C. for 1-40 minutes.

[0030] In addition, one embodiment of the present invention provides a method for manufacturing a dental restoration, comprising the steps of: machining the dental bulk block for cutting of the embodiment using a machining machine to manufacture a predetermined dental restoration; and polishing or glazing the dental bulk block. In a method for manufacturing a dental restoration according to a preferred embodiment, glazing can be performed at 730 to 820° C. for 30 seconds to 10 minutes. The glazing within the above range can correspond to normal glazing within a range that does not impair the inherent translucency of the dental restoration obtained from the previous step.

[0031] As another example, glazing can be performed as a step for adjusting the light transmittance of the dental restoration obtained from the previous step to a certain extent according to the needs of the user, and from this perspective, glazing can be used to adjust the light transmittance of the dental restoration processed through heat treatment at least at 825°C. In this case, preferably, glazing can be performed at a temperature of at least 825°C for 1 to 20 minutes. In particular, since the light transmittance decreases from a temperature of 840°C onward, if it is desired to further decrease the light transmittance, the glazing temperature can be further increased so that additional crystallization can be carried out at the same time to a certain extent.

[0032] The bulk block of the present invention can be easily applied to the production of artificial tooth restoration materials having multi-gradation translucency or physical properties similar to those of natural teeth, and has the advantage that it can contribute to simplifying logistics management by allowing users to obtain dental restorations with adjusted translucency through a simple heat treatment method. Effect of the Invention

[0033] The dental bulk block according to the present invention can be easily used to manufacture artificial tooth restorative materials having multi-gradation translucency or physical properties similar to those of natural teeth so that they can be repeatedly reproduced without the addition of other processes through cutting processes such as CAD / CAM, and not only can it shorten the time and process for manufacturing artificial tooth prostheses, but it can also bring about the effect of increased structural stability in terms of force distribution due to the gradient function of mechanical physical properties.Such a dental bulk block has the advantage that it can be manufactured by a simple method of gradient heat treatment using a single glass composition having a specific composition. [Brief description of the drawings]

[0034] [Figure 1] 1 is a graph showing the results of X-ray diffraction analysis of the bulk block of the present invention. [Figure 2a] 1 is a scanning electron microscope (SEM) photograph showing the microstructure and crystal phase size according to depth of a bulk block of the present invention. [Figure 2b] 1 is a scanning electron microscope (SEM) photograph showing the microstructure and crystal phase size according to depth of a bulk block of the present invention. [Figure 2c] 1 is a scanning electron microscope (SEM) photograph showing the microstructure and crystal phase size according to depth of a bulk block of the present invention. [Diagram 3] 1 is a graph showing the visible light transmittance measurement of a sliced ​​test piece having a thickness of 0.31 mm of the bulk block of the present invention. [Figure 4] 1 is a comparative graph of cutting resistance for a bulk block of the present invention. [Diagram 5] FIG. 2 is a schematic diagram showing a method for producing a dental bulk block of the present invention as an example. [Figure 6] 1 is a graph showing the grain size of a main crystalline phase according to depth of a bulk block obtained according to an embodiment of the present invention. [Figure 7] 1 is a graph showing a change in biaxial bending strength according to depth of a bulk block obtained according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The above and further aspects of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention, which are illustrated in the accompanying drawings, in which: FIG. 1 is a block diagram of a method for manufacturing a semiconductor device according to the present invention;

[0036] The dental bulk block for cutting of the present invention is a glass ceramic block containing a crystalline phase in an amorphous glass matrix, the crystalline phase being a functionally gradient material having a gradient in the size of the main crystal phase with respect to depth, and having no interface at the point where the gradient value of the main crystal phase size changes, the main crystal phase being lithium disilicate and the additional crystal phase being at least one selected from cristobalite and tridymite, and lithium phosphate.

[0037] In the above and following description, the term predominant crystalline phase may be defined as a crystalline phase that accounts for at least 80% by weight of all crystalline phases, and the term additional crystalline phase may be defined as the remaining crystalline phase of all crystalline phases that is not the predominant crystalline phase.

[0038] 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 test piece consisting of two polymorphic phases a and b is a is quantitatively expressed by the following Equation 1.

[0039]

number

[0040] This value can be determined by measuring the intensity ratio of the two crystalline phases and obtaining an integer K, which is the absolute intensity ratio I of the two pure polymorphic forms. oa / I ob and is determined by measuring a standard substance. In the above and following descriptions, the term "main crystalline phase" can be defined as being set based on the content calculated by such a method.

[0041] In addition, the meaning of "having a gradient of the main crystal size with respect to the depth" means that when the main crystal phase size is graphed according to the depth of the bulk block, there is a gradient of change in the main crystal phase size, that is, the main crystal phase size is expressed in a gradation form with respect to the depth of the bulk block.

[0042] In addition, the "point of change in the gradient value of the main crystal size" refers to a point where the gradient value of the change in the main crystal size substantially changes when the main crystal size is graphed against the depth of the bulk block. Here, the meaning of "substantially changes" can mean a change as a single numerical value, but it can also include a substantial change in the distribution of the value.

[0043] In addition, the meaning of "there is no interface at the change point of the gradient value of the main crystal phase size" can be interpreted as the absence of a significant boundary surface indicating interlayer separation at the depth point of the bulk block showing the change of the gradient value of the main crystal phase size. In other words, it means that the bulk block has a gradient of the main crystal phase size in a continuous form without an interface with depth.

[0044] On the other hand, the term "functionally gradient material (FGM)" generally refers to a material in which the properties of the constituent materials change continuously from one surface to the other surface. In the present invention, however, the term "functionally gradient material" is used from the viewpoint that, although there is essentially no interface, the properties of the constituent materials change continuously.

[0045] In the above and following description, the bulk block is not limited in shape and may include bulk bodies of various shapes, such as, for example, a block shape, a disk shape, an ingot shape, a cylinder shape, etc.

[0046] The bulk block according to the present invention has a main crystalline phase of lithium disilicate and additional crystalline phases of at least one selected from cristobalite and tridymite, and lithium phosphate, and does not contain any other crystalline phases other than lithium disilicate, at least one selected from cristobalite and tridymite, and lithium phosphate. The XRD analysis result graph of the bulk block according to a preferred embodiment is shown in FIG.

[0047] In Fig. 1, the main crystalline phase of the dental bulk block according to the embodiment of the present invention is lithium disilicate. An additional crystalline phase has a main peak at 2θ = 21.7 (degrees), which can be interpreted as cristobalite (JCPDS #39-1425, main peak at 2θ = 21.83 (degrees)) or tridymite (JCPDS #01-0378, 2θ = 21.76 (degrees)), which is a homogeneous heteromorphic form of SiO2. Another additional crystalline phase has a main peak at 2θ = 22.18, 22.9 (degrees), which can be defined as lithium phosphate (JCPDS #15-0760, main peak at 2θ = 22.3, 23.1).

[0048] The XRD analyses in the above and following descriptions will be understood as results of analysis using an X-ray diffraction analyzer (D / MAX-2500, Rigaku, Japan; Cu Kα (40 kV, 60 mA), scanning speed: 6° / min, 2θ: 10 to 70 (degrees), Rigaku, Japan).

[0049] Such a crystalline phase can be formed into microcrystals, which can exhibit various sizes and size distributions depending on the temperature, and thus have the property of realizing a variety of mechanical properties and optical transparency.

[0050] In addition, by having a gradient in the size of the main crystal phase with respect to the depth, the bulk block can realize a gradation in translucency and mechanical properties with respect to the depth. Moreover, since there is no interface at the change point of the gradient value of the size of the main crystal phase, processing by interlayer bonding is not required, and the problem of layer separation during cutting can be eliminated. In addition, such functional gradation can provide an artificial tooth prosthesis with increased structural stability in terms of force distribution. In such a bulk block of the present invention, the gradient of the main crystal phase size can be realized within the average grain size range of 0.05 μm to 1.5 μm.

[0051] As an example, Fig. 2 shows scanning electron microscope (SEM) photographs of a dental bulk block of the present invention, with Fig. 2a showing the low temperature part (bottom of the block), Fig. 2b showing the medium temperature part, and Fig. 2c showing the high temperature part (upper layer of the block) of the gradient heat treated block. Specifically, Fig. 2a shows an SEM photograph of the lower layer part of the block (depth 20 mm), Fig. 2b shows an SEM photograph of the middle part of the block (depth 10 mm), and Fig. 2c shows an SEM photograph of the upper layer part of the block (depth 0.5 mm).

[0052] From the SEM photograph obtained in this manner, the average size of the crystalline phase particles can be derived. Specifically, the average size can be calculated by the linear intercept method, by drawing diagonal lines or random straight lines on the SEM photograph, dividing the number of crystalline phases through which the lines pass by the length of the lines and taking into account the magnification. In the above and following description, it is understood that the sizes of the crystalline phases are calculated according to such methods.

[0053] The bulk block of the present invention is a functionally gradient material, and from the viewpoint of considering machinability when such a functionally gradient material is applied to cutting processes, for example, CAD / CAM processing, under the same processing conditions, and of being able to express permeability that can be used in clinical applications, such as artificial tooth repair materials, it is preferable that the gradient of the main crystal phase size is within the range of 0.05 μm to 1.5 μm in average particle size.

[0054] The dental bulk block of the present invention has a gradient in the size of the main crystal phase as described above, and therefore has a gradient in light transmittance with respect to depth. In particular, considering the range of average grain size in the above-mentioned gradient of crystal size, the gradient of light transmittance may be within the range of 25 to 40% based on a wavelength of 550 nm. In the above and following descriptions, the light transmittance was measured using a UV-visible spectrometer (UV-2401PC, Shimadzu Corporation, Japan).

[0055] As described above, the dental bulk block of the present invention does not have an interface at the point where the gradient value of the main crystal phase size changes, and from this perspective, it can be confirmed that the gradient of light transmittance changes within a range of 0.5 mm relative to the depth, and also changes substantially within a range of 0.31 mm relative to the depth.

[0056] In order to measure the light transmittance at each gradient position for the dental bulk block according to the present invention, the specimen was cut at about 0.31 mm in the depth direction where the transparency decreases, and the surface of the specimen was wiped clean with ethanol and measured using a UV-visible spectrometer (UV-2401PC, Shimadzu Corporation, Japan). At this time, the measurement wavelength range was 300-800 nm, and the slit width was 2.0 nm. It can be seen from the results in Figure 3 that there is a difference in transmittance for the sliced ​​specimen with a thickness of 0.31 mm.

[0057] In FIG. 3, each test piece corresponds to a test piece classified by depth in Table 1 below.

[0058] [Table 1]

[0059] These results show that the light transmittance value changes even within a range of 0.31 mm relative to the depth, that is, gradient transmittance appears even at this thickness. This result clearly shows that the dental bulk block of the present invention is a functionally gradient material. In addition, these transmittance results show that it is possible to provide artificial teeth that are excellent in aesthetics and have appropriate hiding power.

[0060] In another embodiment, the dental bulk block of the present invention has a gradient in shade, so that the L by color difference analysis with respect to depth can be obtained. * , a * and b * As described above, in the dental bulk block of the present invention, there is no interface at the change point of the gradient value of the main crystal phase size, so from this perspective, it can be confirmed that the color deviation (ΔE) value changes even within a range of 0.31 mm relative to the depth.

[0061] Color standardization was necessary for accurate measurement, transmission, and reproduction of colors, and this led to the creation of color systems. Many color systems have been proposed, and the most widely used to date is the CIE L system, established by the International Commission on Illumination (CIE) in 1976. * a * b * CIELAB color space, where L * indicates the brightness (lightness), and a * and b * In the coordinates, L * Increasing the value indicates a brighter color, decreasing the value indicates a darker color, and +a * is red, -a* is green, +b * is yellow, -b * means blue, respectively.

[0062] In order to measure the color at each gradient position in the dental bulk block according to the present invention, the dental bulk block was cut in the depth direction where the transparency decreases by about 0.31 mm, and the surface of the test piece was wiped clean with ethanol and analyzed using a UV-visible spectrometer (UV-2401PC, Shimadzu Corporation, Japan). At this time, the measurement wavelength range was 380 to 780 nm, and the slit width was 2.0 nm. A baseline was set using a reference sample, and the reflectance of the test piece was measured to obtain the L * a * b * The measured L * a * b * The values ​​were repeated three times to reduce error, and the average value was used. Using these three values, ΔE, which indicates color difference, was calculated. A ΔE value of 0 for the two test pieces means there is no color difference, and a value between 0 and 2 means there is a very slight color difference. A value between 2 and 4 means that the color difference is perceptible, and a value between 4 and 6 means that the color difference is easily (appreciable). A value between 6 and 12 means that the color difference is much, and a value above 12 means that the color difference is very much.

[0063] The glass ceramic block includes a crystalline phase in an amorphous glass matrix as shown in FIG. 1 and FIG. 2, and the crystalline phase is a functionally gradient material having a gradient of the main crystal size with respect to the depth and no interface at the gradient value change point of the main crystal size. The results in Table 2 below show that the color deviation ΔE of a sliced ​​specimen having a thickness of 0.31 mm is 3.6 to 5.7 with respect to the depth of the dental bulk block. From these results, it can be seen that the color deviation ΔE value changes even within a range of 0.31 mm with respect to the depth, that is, a gradient shade with different colors appears even at such a thickness. This result clearly shows that the dental bulk block of the present invention is a functionally gradient material in another embodiment.

[0064] [Table 2]

[0065] The dental bulk block of the present invention also has a gradient of biaxial bending strength depending on depth. In particular, when the average grain size range is taken into consideration in the gradient of crystalline size described above, the gradient of biaxial bending strength may be within a range of 180 MPa to 420 MPa. On the other hand, in terms of being able to realize the functional gradient of the various physical properties described above and in consideration of processability, the dental bulk block of the present invention may preferably have a crystallinity of 40 to 70%.

[0066] In the above and following description, "crystallinity" can be defined as the ratio of crystalline phase to amorphous glass matrix, which can be determined by various methods, and in one embodiment of the present invention, is a value calculated automatically via an X-ray diffraction analyzer.

[0067] Such a dental bulk block of the present invention is a glass ceramic in which a crystalline phase is precipitated within a continuous amorphous glass matrix, the main crystalline phase being lithium disilicate, the additional crystalline phase including at least one selected from cristobalite and tridymite and a lithium phosphate crystalline phase, and a gradient function material having a gradient in the size of the main crystalline phase with respect to depth and no interface at the change point of the gradient value of the main crystalline phase size can be obtained.

[0068] In the above and following descriptions, the term "continuous glass matrix" can be defined as a glass matrix having no interlayer interfaces and a composition that constitutes the glass matrix being the same within the entire block.

[0069] A preferred glass matrix specifically contains 65.0 to 73.0 weight% of SiO2, 12.0 to 14.0 weight% of Li2O, 1.5 to 3.0 weight% of Al2O3, 0.12 to 0.22 weight% of ZnO, 2.8 to 3.5 weight% of K2O, 0.3 to 1.0 weight% of Na2O, and 2.0 to 6.0 weight% of P2O, and the molar ratio of Al2O3 / (K2O+ZnO) can satisfy 0.3 to 1.2.

[0070] Glass compositions undergo crystal nucleation and crystal growth heat treatments to precipitate a crystalline phase in an amorphous glass matrix, and the temperature at which crystal growth occurs in the above-mentioned glass matrix corresponds to 760°C to 880°C. That is, crystal nuclei begin to form at least at 490°C, and as the temperature rises, crystal growth occurs, and this crystal growth shows the lowest light transmittance when used as an artificial tooth at a maximum of 880°C. In other words, the light transmittance gradually decreases from the crystal growth temperature to a maximum of 880°C. When focusing on this crystal growth, if it is realized in one bulk block, it can mimic the multi-gradation of natural teeth.

[0071] Natural teeth, not just individual teeth, all have various translucencies, and if such changes in translucency due to heat treatment temperatures can be embodied in one bulk block, it will be possible to fully realize the multi-gradation of natural teeth.

[0072] From this viewpoint, the present invention provides a method for producing a block of a predetermined shape by melting a glass composition containing 65.0 to 73.0% by weight of SiO2, 12.0 to 14.0% by weight of Li2O, 1.5 to 3.0% by weight of Al2O3, 0.12 to 0.22% by weight of ZnO, 2.8 to 3.5% by weight of K2O, 0.3 to 1.0% by weight of Na2O, and 52.0 to 6.0% by weight of P2O, with a molar ratio of Al2O3 / (K2O+ZnO) of 0.3 to 1.2, forming the glass composition in a mold, cooling the glass composition, and annealing the glass composition at a set rate from 480°C to 280°C for 20 minutes to 2 hours.

[0073] The block is heat-treated at a temperature in the range of 760 to 880°C while applying a temperature gradient in the depth direction of the block.

[0074] As described above, the glass composition can exhibit a characteristic in which the light transmittance of the material varies depending on the heat treatment temperature range. When the heat treatment is applied uniformly to the entire block, the material exhibits a constant light transmittance. However, when the heat treatment is applied to the block with a temperature gradient, the material exhibits a multi-gradation of physical properties or light transmittance in one block.

[0075] Bulk blocks are used as workpieces for machining such as CAD / CAM processing, but the manufacturing method of the present invention can produce a bulk block with multi-gradation in translucency and strength by applying heat while providing a temperature gradient in the depth direction when heat-treating the block.

[0076] Conventional crystallized glass generally has a large crystal size, making it difficult to adjust the translucency, and is also strong and difficult to process. In contrast, the glass composition used in the present invention can form fine crystals, which can show various sizes and size distributions depending on the temperature, and can show various physical properties and optical translucency. In consideration of this, a block is made from one glass composition, and then it is heat-treated by applying a temperature gradient, so that one bulk block can be embodied to have multi-gradation in mechanical properties and optical translucency.

[0077] In this case, the meaning of "the step of heat treating by applying a temperature gradient in the depth direction of the block" may mean a temperature gradient that increases gradually from the bottom end to the top end in the depth direction of the block, and may also allow a temperature gradient in a manner of partially applying a temperature difference. It goes without saying that the selection of such a temperature gradient method may be changed according to the characteristics of the natural teeth of a patient who requires an artificial tooth prosthesis, or may be variable according to the inherent characteristics of the part of the tooth that requires the prosthesis.

[0078] However, in consideration of conventional natural teeth, it is preferable to perform heat treatment by applying a temperature gradient in a manner such that the temperature gradually increases from the bottom to the top of the block depth.

[0079] As a preferred example, the heat treatment step is performed by applying a temperature range of 840 to 880°C to the upper layer of the block and a temperature range of 760 to 800°C to the lower layer of the block. Due to this temperature gradient, the actual heat treatment step is preferably performed in a gradient heat treatment furnace at an operating temperature of 900 to 1,100°C for 1 to 40 minutes.

[0080] When the above-mentioned glass composition is used and the above-mentioned heat treatment method of the present invention is adopted, it is possible to imitate the characteristic that the translucency of the natural tooth structure is low at the cervical side and increases toward the incisal side. Therefore, unlike the conventional method, there is no need to perform characterization when manufacturing the prosthesis, which is very economically advantageous.

[0081] In addition, the physical properties of natural teeth are such that the enamel, which is the surface layer, has high biaxial bending strength, while the dentin inside it has low strength, and therefore plays a role in absorbing and dispersing external forces. However, in the present invention, it is possible to create a functionally gradient material that has a gradient in mechanical properties, particularly in biaxial bending strength, due to differences in microstructure depending on the depth of heat treatment, and therefore it is possible to reproduce the physical properties of natural teeth very similarly.

[0082] Manufacturing dental restorations using the dental bulk block obtained by the present invention can be expected to achieve significant improvements in terms of processability. As a specific example, in one embodiment of the present invention, a method for manufacturing a dental restoration is provided, which includes a step of processing the above-mentioned dental bulk block using a processing machine to manufacture a predetermined dental restoration, and a step of polishing or glazing. In the above and following description, dental restorations include all crowns, inlays, onlays, veneers, abutments, and the like.

[0083] Here, glazing can be performed at 730 to 820°C for 30 seconds to 10 minutes, which can be a normal finishing heat treatment step that does not change the translucency due to the heat treatment. Glazing is usually performed within a range that does not change the inherent translucency of the bulk block, and during the glazing heat treatment, microcracks on the surface are alleviated (surface healing) and the strength can be increased by 50% or more.

[0084] However, in one specific embodiment, in the method for manufacturing a dental restoration using the bulk block according to the present invention, glazing can be used to adjust the translucency of the processed dental restoration through a heat treatment at least at 825° C. That is, after processing the bulk block to manufacture a dental restoration, glazing can be used to reduce the translucency and adjust the brightness in the final finishing stage.

[0085] When a bulk block is machined by a processor or user to manufacture a dental restoration, the translucency may be unintentionally changed. In such a case, the conventional lithium disilicate bulk block must be discarded, and a bulk block having a desired translucency must be reprocessed by a predetermined heat treatment, and then processed into a dental restoration. However, the bulk block according to the present invention is a specific bulk block having a fine crystal phase, and can exhibit a property of controlling the translucency according to the heat treatment temperature, so that reprocessing is not necessary. The translucency can be easily adjusted again by a process of glazing the processed dental restoration under predetermined conditions at the final finishing stage. This allows colored teeth that occur during processing into a dental restoration by glazing to be easily masked. Glazing for such applications is preferably carried out at a temperature of at least 825° C. for a period of 1 to 20 minutes.

[0086] Characteristically, in the case of the dental bulk block obtained by the present invention, when processing using a processing machine, the resistance generated in the tool during processing can be significantly reduced. As a specific example, a glass ceramic block containing a crystalline phase in an amorphous glass matrix as shown in Figures 1 and 2, in which the crystalline phase is a functionally gradient material in which the main crystalline phase is lithium disilicate, the additional crystalline phase is at least one selected from cristobalite and tridymite and lithium phosphate, the main crystalline phase has a gradient in size, and no interface exists at the change point of the gradient value of the main crystalline phase size, was cut into a size of 12 x 14 x 18 mm and rotated at 250 RPM with a low speed cutting machine (ISOMET low speed saw, Buehler, Germany) and a diamond electroplated wheel (2514485H17, Norton, USA) to measure the cutting time. Using the same method, the cutting times were measured for the most common lithium disilicate block (conventional lithium disilicate) (Rosetta SM, manufactured by HASS Corp), a zirconia reinforced lithium disilicate bulk block (Zirconia reinforced lithium disilicate) (Celtra Duo, manufactured by DentsplySiron), and a lithium aluminosilicate reinforced lithium disilicate bulk block (LAS reinforced lithium disilicate) (Nice, manufactured by Straumann).

[0087] The cutting resistance (%) was calculated from each of the cutting time values ​​thus obtained. Specifically, the cutting time obtained for a general lithium disilicate block was set to 100%, and the cutting time was converted into a relative percentage, which was used to calculate each cutting resistance value.

[0088] The results are shown in Figure 4.

[0089] From the results of Fig. 4, the cutting resistance of the general lithium disilicate block was the highest, followed by LAS (lithium alumino silicate) crystallized glass and zirconia reinforced crystallized glass, and the cutting resistance of the block according to the present invention was the lowest. From these results, it can be confirmed that the glass ceramic block according to the present invention is the most machinable.

[0090] In one specific embodiment of the present invention, first, a glass composition containing 65.0 to 73.0 wt% SiO2, 12.0 to 14.0 wt% Li2O, 1.5 to 3.0 wt% Al2O3, 0.12 to 0.22 wt% ZnO, 2.8 to 3.5 wt% K2O, 0.3 to 1.0 wt% Na2O, and 52.0 to 6.0 wt% P2O, with a molar ratio of Al2O3 / (K2O+ZnO) of 0.3 to 1.2, is weighed and mixed.

[0091] When Al2O3 is added to silicate glass, it enters tetrahedral sites and functions as a glass former, increasing viscosity and decreasing ion mobility. In contrast, K2O and ZnO decrease viscosity and increase ion mobility. It can be predicted that the higher the ion mobility, the more cristobalite or tridymite will grow in a preferential orientation. From this perspective, it is preferable for the molar ratio of Al2O3 / (K2O+ZnO) to be 0.3 to 1.2 in order to provide the bulk block of the present invention containing cristobalite or tridymite as an additional crystal phase.

[0092] Li2CO3 can be added to the glass composition instead of Li2O, and carbon dioxide (CO2), which is the carbon (C) component of Li2CO3, is discharged as a gas and escapes during the glass melting process. In addition, K2CO3 and Na2CO3 can be added to the alkali oxide instead of K2O and Na2CO3, respectively, and carbon dioxide (CO2), which is the carbon (C) component of K2CO3 and Na2CO3, is discharged as a gas and escapes during the glass melting process.

[0093] The mixing is performed using a dry mixing process, and the dry mixing process may be a ball milling process. In particular, the starting materials are loaded into a ball milling machine, and the ball milling machine is rotated at a constant speed to mechanically crush the starting materials and mix them uniformly. The balls used in the ball milling machine may be balls made of ceramic materials such as zirconia or alumina, and the balls may all be the same size or may have at least two sizes. The ball size, milling time, and rotation speed of the ball milling machine per minute are adjusted in consideration of the target particle size. For example, the ball size may be set in the range of about 1 mm to 30 mm, and the rotation speed of the ball milling machine may be set in the range of about 50 to 500 rpm in consideration of the particle size. The ball milling is preferably performed for 1 to 48 hours in consideration of the target particle size. By ball milling, the starting materials are crushed into fine particles, have a uniform particle size, and are mixed uniformly at the same time.

[0094] The mixed starting materials are placed in a melting furnace, and the melting furnace containing the starting materials is heated to melt the starting materials. Here, melting means that the starting materials are changed into a viscous material state of a liquid state, not a solid state. The melting furnace is preferably made of a material that has a high melting point, high strength, and a low contact angle to prevent the molten material from sticking together. For this reason, the melting furnace is preferably made of a material such as platinum (Pt), diamond-like carbon (DLC), chamotte, or the like, or the surface of the melting furnace is preferably coated with a material such as platinum (Pt) or diamond-like carbon (DLC).

[0095] The melting is preferably carried out at 1,400 to 2,000°C at normal pressure for 1 to 12 hours. If the melting temperature is less than 1,400°C, the starting materials may not melt, and if the melting temperature exceeds 2,000°C, excessive energy consumption is required, which is not economical, so it is preferable to melt at a temperature in the above-mentioned range. If the melting time is too short, the starting materials may not melt sufficiently, and if the melting time is too long, excessive energy consumption is required, which is not economical. The temperature rise rate of the melting furnace is preferably about 5 to 50°C / min, but if the temperature rise rate of the melting furnace is too slow, it takes a long time and productivity decreases, and if the temperature rise rate of the melting furnace is too fast, the amount of volatilization of the starting materials increases due to a sudden temperature rise, which may result in poor physical properties of the crystallized glass, so it is preferable to raise the temperature of the melting furnace at a temperature rise rate in the above-mentioned range. The melting is preferably carried out in an oxidizing atmosphere such as oxygen (O2) or air.

[0096] The molten material is poured into a predetermined mold to obtain dental crystallized glass of a desired shape and size. The mold is preferably made of a material that has a high melting point, high strength, and a low contact angle to prevent the glass melt from sticking to the mold. For this purpose, the mold is preferably made of a material such as graphite or carbon, and is preheated to 200 to 300°C to prevent thermal shock before pouring the molten material into the mold.

[0097] Since the molten material in the forming mold is formed and cooled, it is preferable to carry out an annealing step at a set rate from 480° C. to 450° C. for 20 minutes to 2 hours after the cooling process.

[0098] Since the molten material in the molding mold is molded and cooled, it is preferable to perform an annealing step at a set rate for 20 minutes to 2 hours from 480°C to 280°C after the cooling process. This annealing step reduces the stress deviation in the molded product, preferably makes it so that there is no stress, and has a favorable effect on the size control of the crystal phase and the improvement of the uniformity of the crystal distribution in the subsequent crystallization step, thereby ultimately obtaining the desired functionally gradient material. The rate set here is preferably 1.6° C. / min to 10° C. / min.

[0099] The molded product thus subjected to the slow cooling process is transferred to a crystallization heat treatment furnace, where nuclei are formed and crystals are grown to produce the desired crystallized glass.

[0100] FIG. 5 is a schematic diagram showing a method of performing crystallization heat treatment by applying a temperature gradient according to the present invention. When performing crystallization heat treatment on a block-type or ingot-type bulk block, a temperature gradient is applied along the depth direction so that a high-temperature heat treatment is performed at the upper end and a low-temperature heat treatment is performed at the lower end.

[0101] In the above and following description, the step of applying a temperature gradient to perform heat treatment is not limited to a specific device or method, but may be performed in a gradient heat treatment furnace, for example. Considering the heat treatment temperature, it is preferable that the operating temperature is 900 to 1,100°C.

[0102] By the heat treatment with such a temperature gradient, the light transmittance has a gradient at high transmittance and the biaxial bending strength has a gradient at low flexural strength from the high temperature part to the low temperature part. This is because the size of the crystals in the crystallized glass can be adjusted according to the temperature. The crystal phase generated after the heat treatment with a temperature gradient has a main crystal phase of lithium disilicate, and an additional crystal phase of at least one selected from cristobalite and tridymite and lithium phosphate, and can be generated to have a size gradient of the main crystal phase with an average grain size of 0.05μm to 1.5μm at a temperature gradient of 760 to 880℃.

[0103] Meanwhile, the crystalline grain size versus depth for the bulk block obtained according to the present invention was analyzed and is shown in FIG. Furthermore, the change in biaxial bending strength with respect to depth was measured for the bulk block obtained according to the present invention, and the results are shown in FIG.

[0104] While the present invention has been described with reference to one embodiment shown in the drawings, this is by way of example only, and those skilled in the art will recognize that various modifications and equivalent alternative embodiments are possible. [Industrial Applicability]

[0105] The present invention relates to a dental bulk block for machining, which is useful for producing artificial teeth that resemble the structural characteristics of natural teeth, and a method for producing the same.

[0106] The dental bulk block according to the present invention can be easily used to manufacture artificial tooth restorative materials having multi-gradation translucency or physical properties similar to those of natural teeth with high repeatability and reproducibility without the addition of other processes through cutting processes such as CAD / CAM, and not only can it shorten the time and process for manufacturing artificial tooth prostheses, but it can also bring about the effect of increased structural stability in terms of force distribution due to the gradient function of mechanical physical properties.Such a dental bulk block has the advantage that it can be manufactured by a simple method of gradient heat treatment using a single glass composition having a specific composition.

Claims

1. 1. A glass-ceramic block comprising a crystalline phase within an amorphous glass matrix, comprising: The crystalline phase is composed of a main crystalline phase of lithium disilicate, and additional crystalline phases of at least one selected from cristobalite and tridymite, and lithium phosphate; The functionally gradient material has a gradient in the size of the main crystal phase with respect to the depth, and no interface exists at the point where the gradient value of the size of the main crystal phase changes. A dental bulk block for cutting, comprising:

2. The gradient of the main crystal phase size is in the range of 0.05 μm to 1.5 μm in average grain size. A dental bulk block for cutting according to claim 1.

3. Has a gradient of light transmittance with respect to depth A dental bulk block for cutting according to claim 1.

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

5. The gradient of light transmittance changes within a range of 0.5 mm relative to the depth. A dental bulk block for cutting according to claim 3.

6. The gradient of light transmission changes over a range of 0.31 mm relative to the depth. A dental bulk block for cutting according to claim 5.

7. L by color difference analysis for depth ＊ , a ＊ and b ＊ The color deviation (ΔE) value changes even within a range of 0.31 mm relative to the depth. A dental bulk block for cutting according to claim 1.

8. The crystallinity is 40-70%. A dental bulk block for cutting according to claim 1.

9. The biaxial bending strength has a gradient with respect to depth. A dental bulk block for cutting according to claim 1.

10. The gradient of the biaxial bending strength is in the range of 180 MPa to 420 MPa. A dental bulk block for cutting according to claim 9.

11. Dental bulk blocks consist of a continuous glass matrix A dental bulk block for cutting according to claim 1.

12. The glass matrix is ​​SiO ２ 65.0-73.0% by weight, Li ２ O12.0-14.0% by weight, Al ２ O ３ 1.5-3.0% by weight, ZnO 0.12-0.22% by weight, K ２ O2.8-3.5% by weight, Na ２ O 0.3 to 1.0% by weight and P ２ O ５ 2.0 to 6.0 wt. % Al ２ O ３ / (K ２ The molar ratio of ZnO to ZnO is 0.3 to 1.

2. A dental bulk block for cutting according to claim 1 or 11.

13. SiO ２ 65.0-73.0% by weight, Li ２ O12.0-14.0% by weight, Al ２ O ３ 1.5-3.0% by weight, ZnO 0.12-0.22% by weight, K ２ O2.8-3.5% by weight, Na ２ O 0.3 to 1.0% by weight and P ２ O ５ 2.0 to 6.0 wt. % Al ２ O ３ / (K ２ The method includes the steps of melting a glass composition having a molar ratio of 0.3 to 1.2 (ZnO+ZnO), forming the glass composition in a mold, cooling the glass composition, and annealing the glass composition at a set rate from 480° C. to 280° C. for 20 minutes to 2 hours, thereby producing a block of a predetermined shape; The block is heat-treated at a temperature range of 760 to 880° C., and a temperature gradient is applied to the block in the depth direction. A method for manufacturing a dental bulk block for cutting, comprising the steps of:

14. The heat treatment step is performed such that the upper layer of the block is heated at a temperature range of 840 to 880° C. and the lower layer of the block is heated at a temperature range of 760 to 800° C. A method for producing a dental bulk block for cutting according to claim 13.

15. The heat treatment is carried out in a gradient heat treatment furnace at an operating temperature of 900 to 1100° C. for 1 to 40 minutes. A method for producing a dental bulk block for cutting according to claim 13 or 14.

16. A step of manufacturing a predetermined dental restoration by machining the dental bulk block for cutting according to claim 1 using a machining machine; and polishing or glazing the dental restoration. A method for producing a dental restoration comprising the steps of:

17. Glazing is carried out at 730-820°C for 30 seconds to 10 minutes. A method for producing a dental restoration according to claim 16.

18. Glazing is an application for adjusting the translucency of fabricated dental restorations by heat treatment at least 825°C. A method for producing a dental restoration according to claim 16.

19. Glazing is carried out at a temperature of at least 825°C for 1 to 20 minutes. A method for producing a dental restoration according to claim 18.

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