Dental block and method of manufacturing the same

Abstract

Disclosed is a glass-ceramic block containing a crystal phase in a non-crystalline glass matrix, a main crystal phase of the crystal phase including lithium pyrosilicate, an additional crystal phase including eucryptite, a gradient of the main crystal phase size with respect to the depth, a functionally graded material in which the value of the gradient of the main crystal phase size changes without an interface, a dental block required for cutting processing, which can be effectively used to manufacture artificial tooth restorations similar in aesthetics to natural teeth, and which, due to the inclusion of the additional crystal phase such as eucryptite, can be easily manufactured into artificial tooth restorations by mechanical processing compared to a phase including only lithium pyrosilicate, thereby not only shortening the manufacturing time but also increasing the structural stability in terms of force dispersion through functional grading of mechanical properties.

Description

TECHNICAL FIELD

[0001] The present invention relates to a dental block and a method of manufacturing the same, the block being used to manufacture artificial teeth similar to natural tooth structure, and the method improving machinability, in particular. BACKGROUND

[0002] A dental crown material is a restorative material for repairing a damaged portion corresponding to tooth dentin and enamel. The dental crown material can be classified into an inlay, an onlay, a veneer, and a crown according to the site of application. The site of application of the dental crown material is the outer surface of a tooth, and thus the dental crown material requires high aesthetic properties. In addition, the dental crown material requires high strength to prevent chipping due to abrasion or chipping of an opposing tooth. A conventional dental crown material includes leucite glass-ceramics, tempered porcelain, or fluorapatite (Ca5(PO4)3F) glass-ceramics. These materials have excellent aesthetic properties, but have a disadvantage of low strength of 80 to 120 MPa, which can cause chipping. Thus, research is being conducted to develop a high-strength dental crown material.

[0003] A lithium silicate glass-ceramic was introduced 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 crystalline phase and strength of a Li2O-Al2O3-SiO2-Li2O-K2O-B2O3-P2O5-based glass were investigated according to various nucleation and growth heat treatment conditions. The apparent strength of the lithium silicate glass-ceramic was 30 to 35 KPS from a low-temperature lithium metasilicate phase to a high-temperature pyrosilicate phase, and the cause thereof was residual stress due to a difference in thermal expansion coefficient between a matrix glass, a parent glass, a Li2SiO5 phase, and a Li2SiO3 phase.

[0005] Materials and methods for making artificial teeth using a glass containing lithium pyrosilicate crystals (monolithic dental crown) have been disclosed in various patents. However, the known technology is problematic in that the crystal phase is relatively coarse, making it difficult to directly machine the same, and in that the machining is first performed using a lithium metasilicate crystal phase (machinable crystalline) and then a secondary heat treatment is performed after machining, and then a high-strength lithium pyrosilicate crystal phase is formed, at which time shrinkage occurs due to the post-heat treatment process, accuracy is reduced, and the heat treatment process is complicated. In general, restoration machining using CAD / CAM is performed by directly machining a block in a hospital and making a restoration, and the patient is treated in the shortest time (one-day appointment), so when the time is delayed due to the heat treatment process, it causes economic difficulties for the patient and the user.

[0006] The existing lithium pyrosilicate glass-ceramic material is problematic in that the crystal phase is coarse, and the light transmittance or opalescence thereof cannot reach a high level similar to that of a natural tooth.

[0007] In particular, the existing lithium pyrosilicate glass-ceramic material is problematic in that, in order to be machined, a lithium metasilicate glass-ceramic having good machinability is first manufactured, and then a lithium pyrosilicate is formed by a secondary crystallization heat treatment after machining to increase the strength, at which time the size of the crystal phase is about 3 μm or more, and in this state, the machinability is significantly reduced, and only the strength is increased.

[0008] To solve these problems, the present applicant has proposed a method of manufacturing a microcrystalline glass containing a lithium pyrosilicate crystal phase and a silicate crystal phase having good workability by changing the temperature of the first heat treatment, and has obtained a patent (Korean Patent Registration No. 10-1975548). Specifically, a method of manufacturing a dental microcrystalline glass containing a silicate crystal phase is disclosed, which is characterized by including: a step of performing a first heat treatment on a glass composition containing SiO2 60 to 83 weight percent, Li2O 10 to 15 weight percent, P2O5 2 to 6 weight percent to function as a nucleating agent, Al2O3 1 to 5 to increase the glass transition temperature and the glass softening point and to enhance the chemical durability of the glass, SrO 0.1 to 3 weight percent to increase the softening point of the glass, ZnO 0.1 to 2 weight percent, a colorant 1 to 5 weight percent, and an alkali metal oxide, i.e., Na2O + K2O 2.5 to 6 weight percent, to increase the coefficient of thermal expansion of the glass at a temperature of 400°C to 850°C; and a step of performing a second heat treatment at a temperature of 780°C to 880°C after the first heat treatment. A lithium pyrosilicate crystal phase and a silica crystal phase of a nanometer size of 5 nm to 2000 nm are generated through the first heat treatment, and the light transmittance is adjusted by the temperature of the second heat treatment.

[0009] In addition, as people's living standards improve, the demand for aesthetics in the field of dentistry is gradually increasing, and not only the aesthetic requirements of patients are increasing, but research on aesthetic restoration using various materials is also increasing.

[0010] The main aesthetic restoration materials currently used include the shape, surface state, transparency, color tone, etc. of the tooth, among which the transparency is an important factor for successful restoration. Although many studies have been conducted on the mechanical and physical properties of these aesthetic restoration ceramics and have made progress, there are still many problems in the coordination of color tone, and the selection of color tone, especially transparency, of the restoration is still difficult from a clinical and technical point of view.

[0011] In aesthetic restoration, the main factors affecting the aesthetics when restoring teeth are color, tooth shape and size, tooth arrangement state and ratio, light, permeability, restoration design, etc., and in fact, color and shape are the most sensitive to our visual perception.

[0012] Natural teeth are not the same color from the neck to the incision.

[0013] According to these characteristics, a method of manufacturing artificial teeth that mimic the deep color of natural teeth using a so-called construction method has recently been disclosed.

[0014] The so-called build-up method is a method of forming artificial teeth by layering a powder such as porcelain or zirconia, coloring the same, and then heat-treating the same to achieve a color similar to that of natural teeth. The color of natural teeth is imitated, but the appearance of artificial teeth is determined by the skill of a technician, and thus the reproducibility is low, and the artificial teeth cannot be manufactured by an instant method. Also, it is difficult to manufacture the artificial teeth by a cutting process such as CAD / CAM.

[0015] On the other hand, when artificial teeth are manufactured by a cutting process such as CAD / CAM using a conventional block, the block itself is formed of a material having uniform physical properties, and thus the artificial teeth manufactured by the block have a single color, and thus are different from natural teeth. In particular, when the artificial teeth manufactured by the method are used in the front teeth, the appearance thereof is not harmonious, and thus the artificial teeth have an unnatural feeling.

[0016] Although the transparency and processability can be adjusted by a secondary heat treatment process in the microcrystalline glass manufacturing method according to Korean Patent No. 10-1975548 of the present applicant, the microcrystalline glass obtained thereby has the same physical properties as those of the block itself, and thus it is difficult to obtain a deep color of natural teeth by using the block itself.

[0017] In order to solve the above problems, the present applicant has previously applied for a dental block capable of manufacturing artificial teeth having a color similar to that of natural teeth, and thus capable of shortening the manufacturing time and process of artificial teeth, and increasing the structural stability by the functional gradient of mechanical properties (Korean Patent No. 10-2246195).

[0018] The present application provides a gradient block capable of improving the aesthetic appearance of a block, and particularly improving the machining efficiency. SUMMARY

[0019] TECHNICAL PROBLEM

[0020] The present application provides a dental block capable of manufacturing artificial teeth having a color similar to that of natural teeth by a cutting process such as CAD / CAM without an additional process, and having a multi-gradation transmittance and physical properties similar to those of natural teeth.

[0021] The present invention aims at improving machinability, and provides a dental block required for cutting processing of an artificial tooth restoration material manufacturing that can shorten the manufacturing time and process of the artificial tooth restoration body, and is gradient-functionalized in mechanical and physical properties, and increases structural stability in terms of power dispersion.

[0022] The present invention aims at providing a simple manufacturing method of a dental block required for cutting processing of an artificial tooth restoration material manufacturing that can embody a multi-stage matching permeability similar to a natural tooth, or even physical properties.

[0023] The present invention aims at providing a method that can easily manufacture such a dental block into a tooth restoration body using a processing mechanism.

[0024] Technical Solution

[0025] According to an embodiment of the present invention, a glass-ceramic block containing a crystalline phase in a glass matrix that is not a crystal, a main crystalline phase of the crystalline phase includes lithium metasilicate, and an additional crystalline phase includes eucryptite; a gradient of a main crystalline phase size with respect to a depth, a gradient value of the main crystalline phase size changes at a location where there is no interface of a functionally gradient material, i.e., a dental block is provided.

[0026] According to a preferred embodiment of the present invention, the gradient of the main crystalline phase size is in a range of 0.02 μm to 1.5 μm in average particle diameter.

[0027] According to the dental block of the preferred embodiment, the light transmittance has a gradient along the depth.

[0028] According to the preferred embodiment, the gradient of the light transmittance is in a range of 22 to 35% based on a 550 nm wavelength.

[0029] According to the preferred embodiment, the gradient of the light transmittance also changes in a range of 0.5 mm or less along the depth.

[0030] According to the dental block of an embodiment of the present invention, a gradient of L * , a * , and b * values according to a color difference analysis along the depth, and a color deviation (ΔE) value also changes in a range of 1.5 mm along the depth.

[0031] According to the dental block of an embodiment of the present invention, a crystallization degree is 40 to 80%.

[0032] According to a specific embodiment of the dental block, the lithium pyrosilicate crystal phase comprises 50 to 90 vol.%, and the lithium feldspar crystal phase comprises 10 to 40 vol.%, based on the volume of the bulk crystal phase. According to another embodiment, it can also include a lithium phosphate crystal phase of up to 5 vol.%.

[0033] According to an embodiment of the dental block of the present application, the gradient of the bending strength is applied according to the depth.

[0034] According to a preferred embodiment, the gradient of the bending strength is in the range of 210 MPa to 510 MPa.

[0035] According to an embodiment of the dental block of the present application, the glass matrix is formed in a continuous form.

[0036] According to a preferred embodiment, the glass matrix comprises SiO2 69.0 to 78.0 wt%, Li2O 12.0 to 14.0 wt%, Al2O3 5.5 to 10 wt%, ZnO 0.21 to 0.6 wt%, K2O 2.0 to 3.5 wt%, Na2O 0.3 to 1.0 wt%, SrO 0.1 to 0.5 wt%, CaO 0.3 to 1.0 wt%, La2O3 0.1 to 2.0 wt%, and P2O5 2.0 to 6.0 wt%, and the molar ratio of Al2O3 / (K2O+ZnO) satisfies 1.2 to 2.2.

[0037] According to another embodiment of the present application, there is provided a method of manufacturing a dental block, comprising: a step of manufacturing a block having a predetermined shape, which comprises: melting a glass composition comprising SiO2 69.0 to 78.0 wt%, Li2O 12.0 to 14.0 wt%, Al2O3 5.5 to 10 wt%, ZnO 0.21 to 0.6 wt%, K2O 2.0 to 3.5 wt%, Na2O 0.3 to 1.0 wt%, SrO 0.1 to 0.5 wt%, CaO 0.3 to 1.0 wt%, La2O3 0.1 to 2.0 wt%, and P2O5 2.0 to 6.0 wt%, and the molar ratio of Al2O3 / (K2O+ZnO) satisfies 1.2 to 2.2, and then shaping and cooling in a mold, and then slowly annealing at a predetermined rate for 20 minutes to 2 hours from 480°C to 250°C;

[0038] The block is heat-treated at a temperature range of 740 to 850°C, and a temperature gradient is applied along the depth direction of the block.

[0039] According to the manufacturing method of the dental block according to the preferred embodiment, in the step of performing the heat treatment, the upper layer of the block is subjected to the heat treatment at a temperature range of 800 to 850°C, and the lower layer of the block is subjected to the heat treatment at a temperature range of 740 to 760°C.

[0040] According to the preferred embodiment, the step of performing the heat treatment is performed for 1 minute to 40 minutes at an operating temperature of 800 to 1,000°C in a gradient heat treatment furnace.

[0041] According to an embodiment of the present application, there is provided a manufacturing method of a dental restoration, comprising: a step of processing the dental block according to the embodiment by using a processing machine, thereby manufacturing a predetermined dental restoration; and a step of polishing or glazing the dental restoration.

[0042] According to the manufacturing method of the dental restoration according to the preferred embodiment, the glazing is performed at a temperature of 730 to 820°C for 30 seconds to 10 minutes.

[0043] According to another preferred embodiment of the manufacturing method of the dental restoration, the glazing is performed by heat treatment at a temperature of at least 825°C, thereby adjusting the light transmittance of the processed dental restoration. Preferably, the glazing is performed at a temperature of at least 825°C for 1 minute to 20 minutes.

[0044] Advantages

[0045] The dental block according to the present application has the advantages that, by cutting processing using CAD / CAM or the like, the manufacturing of artificial dental restoration materials having multi-gradation light transmittance similar to natural teeth and even physical properties with reproducibility can be performed without increasing other processes, the manufacturing time and processes of the artificial dental restoration can be shortened, and the gradient functionalization of mechanical physical properties increases the structural stability in terms of the dispersion of forces. The dental block can be manufactured by a simple method of gradient heat treatment using a glass composition having a specific combination. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a graph of the X-ray diffraction results of the block according to the present application;

[0047] Figure 2 is a photograph of a scanning electron microscope (SEM) showing the microstructure and the crystal phase size at different depths of the block according to the present application;

[0048] Figure 3is a visual light transmittance measurement chart for a 1.5 mm thick sliced specimen of the block of the present application;

[0049] Figure 4 is a cutting resistance comparison chart for the block of the present application;

[0050] Figure 5 is a mode chart showing a method of manufacturing a dental block of the present application as an example;

[0051] Figure 6 is a chart showing the primary crystal phase particle size at different depths of the block obtained according to an embodiment of the present application;

[0052] Figure 7 is a chart showing the biaxial flexure strength variation at different depths of the block obtained according to an embodiment of the present application. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present application will be described in detail below with reference to the accompanying drawings of the embodiments of the present application. The described embodiments are part of the embodiments of the present application, but not all the embodiments. The embodiments facilitate understanding and reproduction by those of ordinary skill in the art.

[0054] The dental block of the present application is a glass-ceramic block containing a crystal phase in an amorphous glass matrix, including a primary crystal phase of lithium pyrosilicate, eucryptite as an additional crystal phase, a functionally graded material having a gradient of the primary crystal phase size with respect to the depth, and the gradient value change site is free of interfaces.

[0055] According to the above and below descriptions, the term definition of the primary crystal phase is at least 50 weight percent of the crystal phase in the overall crystal phase, and the additional crystal phase is defined as the remaining crystal phase other than the primary crystal phase in the overall crystal phase.

[0056] The content of the crystal phase can be calculated by X-ray diffraction. As an example, the ratio Fa of the crystal phase a in a specimen consisting of two polymorphs a and b can be quantitatively represented by the following Formula 1.

[0057] <Formula 1>

[0058]

[0059] The value can be obtained by measuring the intensity ratio of the two crystal phases and obtaining an integer K. K is the absolute intensity ratio I oa / I ob， It is obtained by measuring a standard substance.

[0060] According to the above and below descriptions, the term "main crystal phase" can be defined as follows: the main crystal phase is set based on the content calculated by the above methods.

[0061] The "gradient of the main crystal phase size with respect to the depth" means that the main crystal phase size along the depth of the block is shown in a graph, and the change in the main crystal phase size has a gradient. Further, it means that the main crystal phase size is shown in a gradual manner with respect to the depth of the block.

[0062] The "point of change in the gradient value of the main crystal phase size" refers to a point at which the gradient value of the change in the main crystal phase size actually changes when the main crystal phase size along the depth of the block is presented in a graph. The term "actually changes" herein means that a single data can represent a change, but can also include an actual change according to the distribution of the value.

[0063] The "point of change in the gradient value of the main crystal phase size does not have an interface" means that there is no significant boundary interface that presents an interlayer separation at a point of the depth of the block at which the gradient value of the main crystal phase size changes. Further, the block has a gradient of the main crystal phase size in a continuous manner without an interface along the depth.

[0064] In addition, the "functionally gradient material (FGM)" refers to a material in which the properties of the constituent materials continuously change from one surface to the other. In the present invention, there is actually no interface, but the properties of the constituent materials continuously change, and thus the expression "functionally gradient material" is used.

[0065] According to the above and below descriptions, the block has no limitation in shape, and as an example, can include blocks having various shapes such as a block shape, a disc shape, an ingot shape, a cylindrical shape, etc.

[0066] According to the block of the present invention, the main crystal phase includes lithium pyrosilicate, and includes lepidolite as an additional crystal phase, and can include lithium phosphate as another additional crystal phase.

[0067] The X-ray diffraction (XRD) analysis result graph of the block according to a preferred embodiment of the present invention is shown in FIG. 1. Figure 1

[0068] Figure 1 In the present invention, the dental block according to an embodiment has a main crystal phase of lithium pyrosilicate. In addition, as an additional crystal phase, main peaks appear at 2θ = 19.8, 25.7 (degrees), etc., which can be explained as lepidolite (beta-eucryptite, JCPDS #12-0709).

[0069] ​The dental block of one embodiment of the present application disclosed herein is a lithium phosphate (JCPDS #15-0760, main peaks at 2θ = 22.3, 23.1) as an additional crystal phase in addition to eucryptite, which has main peaks at 2θ = 22.18, 22.9 (degrees).

[0070] According to the above and below descriptions, the XRD analysis is understood as a result of analysis by an X-ray diffractometer (D / MAX-2500, Rigaku, Japan; Cu Kα (40 kV, 60 mA), scanning speed: 6° / minute, 2θ: 10-60 (degrees), Rigaku, Japan).

[0071] Eucryptite is an aluminum lithium silicate (LAS) crystal phase expressed by the chemical formula LiAlSiO4, and has a lower cutting resistance to a machining tool due to residual thermal stress, as compared with other LAS series of spodumene (LiAlSi2O6), orthoclase (LiAlSi3O8) or petalite (LiAlSi4O8). If this crystal phase is contained, the tool wear rate is lower as compared with the case where only lithium pyrosilicate is contained, and the tool resistance is further lowered, so that the cutting machining efficiency can be improved, the consumption of a milling tool is minimized, and the occurrence of chipping (tearing phenomenon) during machining is also minimized.

[0072] The characteristics of these crystal phases constituting the block of the present application are that a microcrystal can be formed, and various mechanical properties and light transmissivity can be achieved while exhibiting different sizes and size distributions according to the temperature.

[0073] Further, a gradient of the main crystal phase size with respect to the depth is present, so that the block can achieve a gradual light transmissivity and mechanical properties with respect to the depth. In particular, the change point of the gradient value of the main crystal phase size does not have an interface, so that machining by interlayer bonding is not required, and the problem of layer separation during cutting machining can also be solved. Due to these functional gradientization, a dental prosthesis having increased structural stability in terms of force dispersion can be provided.

[0074] According to the block of the present application described above, the gradient of the main crystal phase size can be achieved in the range of an average particle diameter of 0.02 μm to 1.5 μm.

[0075] As an example, Figure 2 The left side of FIG. 1 shows a scanning electron microscope (SEM) photograph of the lower layer portion (20 mm deep portion) of the block, Figure 2 The left side of FIG. 1 shows a scanning electron microscope (SEM) photograph of the lower layer portion (20 mm deep portion) of the block, Figure 2The center shows a scanning electron micrograph of the middle part of the block (10 mm deep), and the rightmost shows a scanning electron micrograph of the upper part of the block (0.5 mm deep).

[0076] The average size of the crystalline phase particles can be derived from the scanning electron micrograph obtained as described above, specifically, a diagonal line or an arbitrary straight line is drawn on the scanning electron micrograph, the number of crystalline phases through which the straight line passes is divided by the length of the straight line, and then the size of the crystalline phase is determined according to the magnification using the linear intercept method.

[0077] According to the above and below descriptions, it can be understood that the size of the crystalline phase can be calculated using the following method.

[0078] The block of the present application is a functionally graded material, which is suitable for cutting processing such as CAD / CAM processing under the same processing conditions, and therefore the average particle size of the gradient of the main crystalline phase size is preferably in the range of 0.02 μm to 1.5 μm in terms of the machinability and the achievable transmittance of the dental prosthesis material and the like which can be used in clinical practice.

[0079] The dental block of the present application has a gradient of the main crystalline phase size as described above, and therefore has a gradient of light transmittance with respect to the depth.

[0080] In particular, according to the gradient of the crystalline phase size, the gradient of the light transmittance is in the range of 22 to 35% with respect to the wavelength of 550 nm, considering the range of the average particle size.

[0081] According to the above and below descriptions, the light transmittance is measured by an ultraviolet-visible spectrophotometer (UV-2401PC, Shimadzu, Japan).

[0082] As described above, the dental block of the present application has a gradient of the main crystalline phase size, and therefore the gradient of the light transmittance with respect to the depth changes in the range of 0.5 mm or less, and in fact it can be confirmed that it also changes in the range of 1.5 mm with respect to the depth.

[0083] For the dental block of the present application, in order to measure the light transmittance at the inclined position, about 1.5 mm is cut in the direction of the depth of reduced transparency, the surface of the sample is wiped clean with alcohol, and then measured using an ultraviolet-visible spectrophotometer (UV-2401PC, Shimadzu, Japan). At this time, the wavelength range is 300-800 nm, and the slit width is 2.0 nm. Figure 3 As can be seen from the results, there is a difference in the transmittance of the 1.5 mm thick section sample.

[0084] Figure 3 Each of the specimens corresponds to the specimens of different depths of Table 1 below.

[0085] [Table 1]

[0086] Specimen No. Depth (mm) 1 1.5 2 3.0 3 4.5 4 6.0

[0087] This result indicates that the light transmittance also changes in the depth range of 1.5 mm, and further, a transmittance gradient is still exhibited at this thickness. Such a result clearly indicates that the dental block of the present application is indeed a functionally graded material.

[0088] In the case of a restoration such as a crown, the thickness of the position processed as a bridgehead is the thickest, and it is predicted that the light transmittance exhibiting aesthetic prominence is still exhibited in this thickness range.

[0089] On the other hand, the dental block of the present application also has a gradient in coloration, specifically, the gradient value in color difference analysis with respect to depth is L * a * value. As described above, the dental block of the present application is one in which an interface is not present at the site of the gradient value change in the primary crystal phase size, and it can be determined from these aspects that the color deviation (ΔE) also changes in the depth range of 1.5 mm.

[0090] For the correct measurement, transmission and reproduction of color, a corresponding color standard is established, and thus a color system is established. Various color systems have appeared, among which the CIE L*a*b* color space (CIELAB colorspace) defined by the Commission International de l'Eclairage (CIE) in 1976 is the most widely used and has been used until now. Among them, L* indicates lightness, a* and b* indicate chromaticity coordinates. The value of L* in the coordinates increases as the lightness increases and decreases as the lightness decreases, +a* indicates red, -a* indicates grass green, +b* indicates yellow, and -b* indicates blue.

[0091] For color measurement of the dental block of the present application according to the inclination position category, after cutting about 1.5 mm in the depth direction in which the transparency is reduced, the surface of the sample was wiped clean with alcohol, and then analyzed using a UV- visible spectrophotometer (UV-2401PC, Shimadzu, Japan). The measurement wavelength range was 380-780 nm, and the slit width was 2.0 nm. After setting the baseline using a base sample, the reflectance of the sample was measured, and L * a* b * Color system. Measured L * a * b * The values ​​are averaged after three repetitions to reduce error. The ΔE value representing the color difference is calculated using these three values. A ΔE value of 0 for two samples indicates no color difference (equivalent to a value of 0-2 indicating a very slight color difference); a value of 2-4 indicates a noticeable color difference; a value of 4-6 indicates an easily distinguishable color difference; a value of 6-12 indicates a large color difference; and values ​​above 12 indicate a very large color difference.

[0092] As such Figure 1 to Figure 2 The amorphous glass matrix shown contains a glass-ceramic block with crystalline phases. The main crystalline phase includes lithium pyrosilicate, and the supplementary crystalline phase includes nepheline. There is a gradient in the size of the main crystalline phase relative to depth. The gradient values ​​of the main crystalline phases do not change at interface points. This is a functionally graded material, i.e., a dental block. As shown in Table 2 below, on a 1.5 mm thick slice, a color deviation (ΔE) of 1.4–1.6 appears relative to depth. The results described above indicate that the color deviation (ΔE) value varies within the 1.5 mm range relative to depth. Furthermore, it can be considered that different color gradient shades are observed at this thickness. Clearly, this result demonstrates that the dental block of the present invention does indeed belong to a functionally graded material.

[0093] Table 2

[0094] Specimen No. Depth (mm) [[ L * ]]> a * ]]> b * ]]> ΔΕ 1 0.31 69.8 -1.68 9.51 2 0.62 70.50 -1.81 10.80 1.47 3 0.93 71.40 -1.95 12.10 1.58 4 1.24 73.00 -2.10 12.02 1.60

[0095] Furthermore, the dental block of the present invention has a gradient of bending strength along the depth. In particular, regarding the gradient of crystal size mentioned above, the gradient of bending strength can be in the range of 210 MPa to 510 MPa, depending on the range of average grain size.

[0096] On the other hand, the dental block of the present invention is preferably crystallized to a degree of 40 to 80% from the perspective of functional gradients that can achieve the various physical properties described above and from the perspective of processing efficiency.

[0097] In the descriptions described above and below, "degree of crystallinity" refers to the crystallinity ratio of an amorphous glass matrix, and can be achieved by various methods. In one embodiment of the present invention, it is a value automatically calculated by an X-ray diffractometer.

[0098] As described above, the dental block of the present application is a glass-ceramic in which a crystal phase is precipitated in a continuous non-crystalline glass matrix, or a functionally gradient material in which a gradient of the size of the main crystal phase including lithium pyrosilicate, and an additional crystal phase including petalite, is present with respect to the depth, and the value of the gradient of the size of the main crystal phase is changed without the presence of an interface.

[0099] Preferably, the crystal phase is such that the lithium pyrosilicate crystal phase comprises 50 to 90 vol.%, and the additional crystal phase, i.e. the petalite crystal phase, comprises 10 to 40 vol.%, and when lithium phosphate is included as an additional crystal phase, the content thereof is preferably, at most, 5 vol.%.

[0100] The petalite crystal phase is as described above, and has the effect of improving the machinability of the glass-ceramic in which lithium pyrosilicate is the main crystal phase, but if the content thereof is excessively increased, the strength is reduced. Therefore, the content of petalite in the crystal phase is preferably 10 to 40 vol.%, based on the volume of the entire crystal phase, in terms of machinability and strength.

[0101] According to the above and below descriptions, the "continuous glass matrix" means that there is no interlayer interface in the glass matrix, and the composition constituting the glass matrix can be defined as the same throughout the block.

[0102] The preferred glass matrix specifically includes SiO2 69.0 to 78.0 wt%, Li2O 12.0 to 14.0 wt%, Al2O3 5.5 to 10 wt%, ZnO 0.21 to 0.6 wt%, K2O 2.0 to 3.5 wt%, Na2O 0.3 to 1.0 wt%, SrO 0.1 to 0.5 wt%, CaO 0.3 to 1.0 wt%, La2O3 0.1 to 2.0 wt%, and P2O5 2.0 to 6.0 wt%, and the molar ratio of Al2O3 / (K2O+ZnO) can satisfy 1.2 to 2.2.

[0103] The glass composition is such that, for the generation of crystals, a crystal nucleus is generated, and a crystal growth heat treatment is performed to precipitate a crystal phase in the non-crystalline glass matrix, and the above glass matrix is such that the temperature at which the crystal nucleus is generated is 500°C to 850°C. Further, the crystal nucleus is formed from a minimum of 500°C, and as the temperature is increased, the crystal grows, and this crystal growth is such that the lowest light transmission is exhibited at a maximum of 850°C for artificial teeth. Further, the transmission gradually decreases from the temperature at which the crystal grows to a maximum of 850°C, but from the viewpoint of these crystal growths, if this can be achieved in one block, the multi gradation of natural teeth can be simulated.

[0104] Natural teeth are not only a tooth itself, all teeth have various light transmittances, and if these light transmittance changes due to heat treatment temperature are realized on one block, then the multi-gradation of natural teeth can be fully realized.

[0105] From these perspectives, the present application provides a method for manufacturing a dental block, including the steps of melting a glass composition containing SiO2 69.0-78.0 wt%, Li2O 12.0-14.0 wt%, Al2O3 5.5-10 wt%, ZnO 0.21-0.6 wt%, K2O 2.0-3.5 wt%, Na2O 0.3-1.0 wt%, SrO 0.1-0.5 wt%, CaO 0.3-1.0 wt%, La2O3 0.1-2.0 wt%, and P2O5 2.0-6.0 wt%, with a molar ratio of Al2O3 / (K2O+ZnO) satisfying 1.2-2.2, shaping in a mold, and cooling, annealing from 480°C to 250°C at a set speed within 20 minutes to 2 hours to produce a block of a predetermined shape;

[0106] The block is heat treated at a temperature range of 740 to 850°C, and heat treated with a temperature gradient applied with respect to the depth direction of the block.

[0107] As described above, the glass composition can exhibit properties that the light transmittance of the material is differently exhibited depending on the heat treatment temperature range, and if the heat treatment applied to the block is constant, the transmittance exhibits a constant, but if the heat treatment applied to the block has a temperature gradient, the block can exhibit a multi-gradation of physical properties or transmittance.

[0108] The block in the form of a bulk block is used as a workpiece for machining such as CAD / CAM machining, and the manufacturing method of the present application is to heat with a temperature gradient applied with respect to the depth direction when heat treating the block, thereby manufacturing a block body with a multi-gradation of transmittance and strength.

[0109] The existing crystallized glass has coarse crystalline size compared to ordinary crystalline size, it is difficult to adjust the transmittance, the strength is also strong and not easy to process, on the contrary, the glass composition used in the present application can form microcrystals, exhibit various sizes and size distributions according to temperature, and exhibit various physical properties and light transmittance, so that a block is made using one glass composition, and then heat treated by applying a temperature gradient, thereby realizing a bulk block with a multi-gradation of mechanical properties and light transmittance on one bulk block.

[0110] The step of heat-treating by applying a temperature gradient with respect to the depth direction of the block means that a temperature gradient that increases sequentially from the lower end to the upper end with respect to the depth direction of the block can be applied, or a temperature gradient in which a temperature difference is allowed to be set in portions. The selection of this temperature gradient is made in accordance with changes in the natural tooth characteristics of the patient of the artificial tooth restoration, or in accordance with changes in the inherent characteristics possessed by the tooth site of the restoration.

[0111] However, in view of ordinary natural teeth, the preferred temperature gradient for heat-treatment is that a temperature gradient is applied in which the temperature gradually increases from the lower end to the upper end with respect to the depth of the block, and the heat-treatment is preferably performed.

[0112] According to a preferred embodiment, in the step of heat-treatment, the upper portion of the block is applied at a temperature in the range of 800 to 850°C, and the lower portion of the block is applied at a temperature in the range of 740 to 760°C, and the actual step of heat-treatment is performed at an operating temperature of 800 to 1,000°C for a period of 1 minute to 40 minutes in a gradient heat-treatment furnace, for the temperature gradient described above.

[0113] When the above-described glass composition is used in the above-described heat-treatment method of the present application, the structure characteristic of natural teeth in which the transmission of light is low at the tooth neck and increases as the distance from the cingulum decreases can be simulated. Therefore, as in the conventional method, no additional characterizing step is required when the restoration is produced, and thus the present application is very advantageous from an economic standpoint.

[0114] According to the physical properties of natural teeth, the enamel that is the surface layer has a high bending strength, and the dentin inside has a low strength, and thus can function to absorb and disperse forces from the outside, and the present application is characterized in that a functionally gradient material that has a gradient in mechanical properties, particularly bending strength, according to the difference in microstructure along the depth of heat-treatment is used, and thus is very similar to the characteristics of natural teeth.

[0115] A dental restoration is produced using the dental block obtained according to the present application, and is expected to have significantly improved workability, and as a specific example, in one embodiment of the present application, a method for producing a dental restoration is provided, including the steps of: machining the above-described dental block using a machining machine to produce a predetermined dental restoration; and polishing or glazing.

[0116] According to the above and the following description, the dental restoration naturally includes a crown, an inlay, an onlay, a veneer, an abutment, and the like.

[0117] In this case, the glazing is performed at a temperature of 730 to 820°C for 30 seconds to 10 minutes, and can be performed as a general finishing heat treatment step, and after the heat treatment, the transmittance is not substantially changed. The glazing is generally performed within a range in which the inherent transmittance of the block is not changed, and the surface microcracks are healed during the glazing heat treatment, so that the strength is increased by more than 50%.

[0118] However, according to a specific embodiment, in the method of manufacturing a dental restoration using the block of the present application, the glazing is performed by heat treatment at a temperature of at least 825°C, and can be used to adjust the transmittance of the manufactured dental restoration. Further, after the block is manufactured into a dental restoration, the glazing can be used to reduce the transmittance and adjust the brightness in the final finishing step.

[0119] When the block is mechanically machined to manufacture a dental restoration by a machining party or a user party, the transmittance can be unintentionally increased, and in this case, the general lithium pyrosilicate block needs to be reprocessed by discarding the machined block, reprocessing the block by the predetermined heat treatment, and machining the block to have a transmittance that satisfies the requirements, and then machining the block into a dental restoration. However, the block of the present application is a special block having a microcrystalline phase, and can exhibit the characteristic that the transmittance can be adjusted according to the heat treatment temperature, so that the machined block to be machined into a dental restoration does not need to be reprocessed, and the transmittance can be simply adjusted by performing the glazing process in the final finishing step under the predetermined conditions. Further, the colored tooth that occurs during the machining of the dental restoration can be simply masked by the glazing.

[0120] The glazing having this use is, preferably, performed at a temperature of at least 825°C for a time of 1 minute to 20 minutes.

[0121] In particular, the dental block obtained according to the present application is characterized in that, when machined using a machining tool, the resistance occurring on the tool during the machining can be significantly reduced, and according to a specific example, as a lithium pyrosilicate block having a transmittance of 70% or more, the machined block can be machined into a dental restoration having a transmittance of 70% or more. Figure 1 to Figure 2The glass-ceramic block containing a crystalline phase in an amorphous glass matrix, the main crystalline phase of which is lithium pyrosilicate, and the additional crystalline phase of which is petalite, has a gradient of the main crystalline phase size with respect to the depth, and the gradient value of the main crystalline phase size varies without an interface. The functionally gradient material, i.e., the dental block (this invention), has a size of 12 x 14 x 18 mm, and is measured for the cutting time using a slow cutting machine (ISOMET low speed saw, Buehler, Germany) and a plated diamond wheel (2514485H17, Norton, USA) rotating at a speed of 250 RPM. In the same manner, the cutting time is measured for the most common lithium pyrosilicate block (final heat-treated conventional lithium pyrosilicate) (Rosetta SM, a product of HASS Corp), a zirconia-reinforced lithium disilicate block (Celtra Duo, a product of Dentsply Siron), and a lithium alumino silicate-reinforced lithium disilicate block (Nice, a product of Straumann).

[0122] The cutting resistance (%) is calculated based on the cutting time values obtained as described above, and specifically, the cutting time of the conventional lithium pyrosilicate block is taken as 100%, and then the cutting time is converted into a relative percentage to calculate the cutting resistance value.

[0123] The results are shown in Figure 4 .

[0124] According to the results, Figure 4 , the cutting resistance of the conventional lithium pyrosilicate block is the highest, followed by the cutting resistance of the LAS (lithium alumino silicate) crystallized glass and the zirconia-reinforced crystallized glass, and the cutting resistance of the block of the present invention is significantly low. From these results, it can be predicted that the glass-ceramic block of the present invention is the most machinable because it contains the additional crystalline phase, i.e., petalite.

[0125] According to a specific embodiment of the present invention, first, a glass composition containing SiO2 69.0 to 78.0 wt%, Li2O 12.0 to 14.0 wt%, Al2O3 5.5 to 10 wt%, ZnO 0.21 to 0.6 wt%, K2O 2.0 to 3.5 wt%, Na2O 0.3 to 1.0 wt%, SrO 0.1 to 0.5 wt%, CaO 0.3 to 1.0 wt%, La2O3 0.1 to 2.0 wt%, and P2O5 2.0 to 6.0 wt%, and the molar ratio of Al2O3 / (K2O+ZnO) satisfies 1.2 to 2.2 is weighed and mixed.

[0126] Al2O3 added to silicate glass enters a tetrahedral site and functions as a glass former, increasing viscosity and reducing ion mobility. In contrast, K2O and ZnO, CaO, Na2O reduce viscosity and increase ion mobility. It is predicted that the more the ion mobility increases, the more preferentially spodumene will orient and grow. Furthermore, the increase in mobility of ZnO and the like increases ion mobility, and if the SiO2 content is excessive, a minor crystalline phase such as spodumene is precipitated together with the main crystalline phase, i.e., lithium pyrosilicate, in the glass matrix. From these perspectives, a molar ratio of Al2O3 / (K2O+ZnO) of 1.2 to 2.2 is preferable for providing the bulk of the present application that contains spodumene as a supplemental crystalline phase.

[0127] As the glass composition, Li2CO3 can also be added in place of Li2O, and the carbon (C) component of Li2CO3, i.e., carbon dioxide (CO2), is discharged as a gas during the glass melting process. Furthermore, K2CO3, Na2CO3 can also be added to the alkali oxide in place of K2O and Na2O, respectively, and the carbon (C) component of K2CO3, Na2CO3, i.e., carbon dioxide (CO2), is discharged as a gas during the glass melting process.

[0128] Mixing is performed using a dry mixing process, and as the dry mixing process, a ball milling process or the like can be used. The ball milling process is specifically a process in which the starting material is loaded into a ball mill, the ball mill is rotated at a certain speed, and the starting material is mechanically pulverized and uniformly mixed. The balls used in the ball mill can be balls formed of a ceramic material such as zirconia or alumina, and the balls can be all the same size or balls of at least two or more sizes can be used. The size of the balls, the ball milling time, the rotation speed of the ball mill per minute, and the like are adjusted according to the particle size that is the target. As an example, the size of the balls is set to a range of about 1 mm to 30 mm in consideration of the particle size, and the rotation speed of the ball mill can be set to a range of about 50 rpm to 500 rpm. The ball milling is preferably performed for 1 to 48 hours according to the particle size that is the target and the like. The starting material is pulverized into fine particles and uniformly mixed while the particle size is uniform by the ball milling.

[0129] The mixed starting material is put into a melting furnace, and the melting furnace with the starting material is heated to melt the starting material. Here, the melting means that the starting material changes into a liquid state having viscosity, i.e., a non-solid state. The melting furnace is preferably formed of a material having a high melting point and high strength, and for the purpose of suppressing the adhesion of the melt, a material having a small contact angle is preferably used, and for this purpose, a melting furnace formed of platinum (Pt), diamond-like carbon, chamotte, or the like, or a melting furnace having a surface coated with platinum or diamond-like carbon, or the like is preferably used.

[0130] The melting is preferably performed at a temperature of 1,400 to 2,000°C under normal pressure for 1 to 12 hours. When the melting temperature is lower than 1,400°C, the starting material does not sufficiently melt, and when the melting temperature exceeds 2,000°C, the energy consumption is excessively large, and the economy is poor, and thus the melting is preferably performed at a temperature within the above range. Further, when the melting time is too short, the starting material does not sufficiently melt, and when the melting time is too long, the energy consumption is excessively large, and the economy is poor. The temperature increasing rate of the melting furnace is preferably about 5 to 50°C / min, and when the temperature increasing rate of the melting furnace is too slow, the time required is too long, and the productivity is poor, and when the temperature increasing rate of the melting furnace is too fast, the temperature rapidly increases, and the volatilization of the starting material increases, and the properties of the crystallized glass can be poor, and thus the temperature of the melting furnace is preferably increased at a temperature increasing rate within the above range. The melting is preferably performed in an oxidizing atmosphere of oxygen, air, or the like.

[0131] For the purpose of obtaining a tooth crystallized glass having a desired shape and size, the melt is poured into a predetermined molding mold. The molding mold is preferably formed of a material having a high melting point and high strength, and for the purpose of suppressing the adhesion of the glass melt, a material having a small contact angle is preferably used, and for this purpose, a material such as graphite or carbon is preferably used, and for the purpose of preventing thermal shock, the melt is preferably poured into the molding mold after being preheated to 200 to 300°C.

[0132] The melt in the molding mold is molded and cooled, and after the cooling, the melt is preferably slowly annealed at a predetermined rate for a time of 20 minutes to 2 hours from 480°C to 250°C. As described above, by the annealing step, the stress deviation in the molded product is reduced, and preferably, no stress is present, and further, in the subsequent crystallization step, the size control of the crystal phase and the homogeneity of the crystallization distribution are favorably improved, and thus a desired functionally gradient material can be finally obtained.

[0133] Here, the predetermined rate means that the annealing is preferably sufficiently slow at 2.3 to 14°C / min.

[0134] As described above, the shaped article subjected to the slow annealing process is moved to a crystallization heat treatment furnace, and a desired crystallized glass is produced by nucleation and crystalline growth.

[0135] Figure 5 FIG. 6 shows a patterned method of the present application for applying a temperature gradient for crystallization heat treatment, in which a temperature gradient is applied in the depth direction when a bulk crystallization heat treatment is performed on a bulk in the form of a block or an ingot, and a high temperature is applied at the upper end and a low temperature is applied at the lower end.

[0136] According to the above and the following description, the step of applying a temperature gradient for heat treatment is not limited to a specific device and method, but as an example, it can be performed in a gradient heat treatment furnace, and considering the heat treatment temperature, the operation temperature is preferably performed at 900 to 1,100°C.

[0137] Through the heat treatment of applying a temperature gradient, a gradient of high transmittance in light transmittance and a gradient of low flexural strength from the high temperature portion to the low temperature portion are exhibited. The reason for this is that the crystal size in the crystallized glass can be adjusted according to the temperature. The crystal phase generated after the heat treatment with a temperature gradient is a main crystal phase including lithium pyrosilicate and an additional crystal phase including petalite, and after generation, can have a size gradient of the main crystal phase with an average particle diameter of 0.02 to 1.5 μm.

[0138] In addition, the results of the particle size analysis of the crystal quality with depth of the bulk obtained according to the present application are shown in FIG. 6. Figure 6 .

[0139] The results of the flexural strength variation measurement with depth of the bulk obtained according to the present application are shown in FIG. 7. Figure 7 .

[0140] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions described in the foregoing examples can still be made, and these modifications or equivalent replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions described in the foregoing examples of the present application.

[0141] Industrial Utilization

[0142] The present application is useful for manufacturing artificial teeth having a structure similar to that of natural teeth, and in particular, a dental bulk having improved machinability and a manufacturing method.

[0143] The dental blocks according to the present application, by cutting processing such as CAD / CAM, can be used for the manufacture of artificial tooth restorative materials having reproducibility of multi-gradation light transmittance similar to natural teeth and even physical properties, without adding other processes, can shorten the production time and processes of artificial tooth restorations, and with gradient functionalization of mechanical physical properties, increase structural stability in terms of dispersion of strength, and these dental blocks can be manufactured by a simple method of gradient heat treatment using a glass composition having a specific combination.

Claims

1. A dental block, characterized by, a glass-ceramic block containing a crystal phase in a glass matrix that is non-crystalline, a main crystal phase of the crystal phase includes lithium pyrosilicate, and an additional crystal phase includes eucryptite; a functionally gradient material having a gradient of a main crystal phase size along a depth, and a value of the gradient of the main crystal phase size is changed at a point where an interface is not present; the glass matrix contains SiO2 69.0 to 78.0 weight percent, Li2O 12.0 to 14.0 weight percent, Al2O3 5.5 to 10 weight percent, ZnO 0.21 to 0.6 weight percent, K2O 2.0 to 3.5 weight percent, Na2O 0.3 to 1.0 weight percent, SrO 0.1 to 0.5 weight percent, CaO 0.3 to 1.0 weight percent, La2O3 0.1 to 2.0 weight percent, and P2O5 2.0 to 6.0 weight percent.

2. The dental block according to claim 1, characterized by, the gradient of the main crystal phase size is an average particle size thereof in a range of 0.02 μm to 1.5 μm.

3. The dental block according to claim 1, characterized by, a light transmittance has a gradient along the depth.

4. The dental block according to claim 3, characterized by, the gradient of the light transmittance is in a range of 22 to 35% based on a wavelength of 550 nm.

5. The dental block according to claim 3, characterized by, the gradient of the light transmittance is also changed in a range of 0.5 mm or less along the depth.

6. The dental block according to claim 1, characterized by, has a gradient of L * , a * and b * values according to the color difference analysis along the depth, the color deviation (ΔΕ) value is also changed within a range of 1.5 mm along the depth.

7. The dental block according to claim 1, characterized by, a crystallization degree is 40 to 80%.

8. The dental block according to claim 1 or claim 7, characterized by, the lithium pyrosilicate crystal phase contains 50 to 90 vol.%, and the eucryptite crystal phase contains 10 to 40 vol.%, based on a volume of the entire crystal phase.

9. The dental block according to claim 1, characterized by, a bending strength has a gradient along the depth.

10. The dental block according to claim 9, characterized by, the gradient of the bending strength is in a range of 210 MPa to 510 MPa.

11. The dental block according to claim 1, characterized by, the dental block is formed with a continuous glass matrix.

12. The dental block according to claim 1 or claim 11, characterized by, a molar ratio of Al2O3 / (K2O+ZnO) in the glass matrix satisfies 1.2 to 2.

2.

13. A method of manufacturing a dental block, characterized by, including: a step of producing a block having a predetermined shape, the step including: melting a glass composition containing SiO2 69.0 to 78.0 weight percent, Li2O 12.0 to 14.0 weight percent, Al2O3 5.5 to 10 weight percent, ZnO 0.21 to 0.6 weight percent, K2O 2.0 to 3.5 weight percent, Na2O 0.3 to 1.0 weight percent, SrO 0.1 to 0.5 weight percent, CaO 0.3 to 1.0 weight percent, La2O3 0.1 to 2.0 weight percent, and P2O5 2.0 to 6.0 weight percent, and a molar ratio of Al2O3 / (K2O+ZnO) satisfying 1.2 to 2.2, and then shaping and cooling in a mold, and then slowly annealing at a predetermined rate within 20 minutes to 2 hours from 480°C to 250°C; a step of heat-treating the block at a temperature range of 740 to 850°C, and applying a temperature gradient along a depth direction of the block to perform the heat-treatment.

14. The method of producing a dental block according to claim 13, wherein in the step of performing the heat-treatment, the upper layer portion of the block is applied at a temperature range of 800 to 850°C, and the lower layer portion of the block is applied at a temperature range of 740 to 760°C.

15. The method of producing a dental block according to claim 13 or claim 14, wherein the heat-treatment step is performed at an operation temperature of 800 to 1000°C for 1 minute to 40 minutes in a gradient heat-treatment furnace.

16. A method of manufacturing a dental restoration, wherein a step of processing the dental block according to claim 1 using a processing machine to produce a predetermined dental restoration; and a step of polishing or glazing the dental restoration.

17. The method of producing a dental restoration according to claim 16, wherein the glazing is performed at a temperature of 730 to 820°C for 30 seconds to 10 minutes.

18. The method of producing a dental restoration according to claim 16, wherein the glazing is performed by heat-treatment at least 825°C to adjust the light transmittance of the processed dental restoration.

19. The method of manufacturing a dental restoration according to claim 18, wherein, the glazing is performed at a temperature of at least 825°C for 1 minute to 20 minutes.

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