Description

CERAMIC COPING FOR PROSTHESIS

Technical Field

[1] The present invention relates to a dental coping made of ceramic material.

Generally, it is particularly important in tooth restoration to manufacture a prosthesis that corresponds to the tooth shape of a subject and to precisely position the prosthesis. For this purpose, the tooth shape of a subject is formed with impression material to make a precise tooth model. The model is used to make a highly precise prosthesis for actual implantation. Impression taking is carried out by covering a coping with impression material and then separating the impression material from the coping. According to the present invention, the coping is manufactured using ceramic material, such as alumina or zirconia, as a starting material, in which a frit containing lanthanum series elements is added to the starting material. Accordingly, the use of the dental coping made of ceramic material according to the present invention makes it possible to manufacture an artificial tooth, which is almost impossible to differentiate from a natural tooth with respect to shape and color, because it has original dental aesthetics that could not be expressed through the use of an existing metal coping. Background Art

[2] Generally, a process of restoring teeth using artificial teeth is performed by implanting an implant into an alveolar bond for osteointegration, joining an abutment to the implant, and then covering the abutment with a crown. The implant is generally called a "fixture" and is implanted into an alveolar bone portion, from which a tooth is missing, so as to act as the root of an artificial tooth. Also, the abutment is attached to the alveolar bone at the gums and acts to connect the implant to a tooth.

[3] The artificial tooth thus completed has advantages in that it can be independently implanted, does not damage the surrounding teeth, and has excellent prosthetic stability and aesthetics.

[4] First, a groove corresponding to the dimensions of the implant is formed in the alveolar bone through drilling and tapping processes, and a fixture mount is attached to the top of the implant. The implant and the fixture mount are embedded in the alveolar bone using a surgical hand-piece, and then the fixture mount is removed from the implant. Then, a cover screw is attached to the top of the implant to seal the implant, thus completing the primary surgery.

[5] The cover screw functions to prevent bacteria and foreign matter remaining in the mouth from entering the implant during the osteointegration period of the implant. Although the osteointegration period of the implant varies depending on the bone

quality of a patient and the implantation location of the implant, it is generally between 3 months and 6 months.

[6] Then, the gum is opened through secondary surgery to expose the cover screw.

Then, the osteointegration of the implant is confirmed and the cover screw is removed. For the formation of an aesthetic gum, a healing abutment is attached to the top of the implant, followed by waiting for a time period of 2-3 weeks. Finally, after the formation of the aesthetic gum is confirmed, the healing abutment is removed and an impression coping is attached to the top of the implant in order to make a prosthesis. Then, an alginate impression material is used to take a preliminary impression in the oral cavity, and the impression coping is removed. Then, an abutment is attached to the top of the implant, and a prosthesis is fixed to the abutment, thus completing an artificial tooth.

[7] Herein, the prior coping is generally made of metal. The prior tooth restoration method comprises a process of attaching a crown to the metal coping, and then, if necessary, a process of depositing tin on the crown to form an oxide layer in order to increase the binding force with ceramic material, which is the material for an artificial tooth. Such processes include many steps, and thus process complexity is recognized as a problem.

[8] Also, when this method is used, metal can enter between the tooth and the ceramic material. Thus, there is a problem in that the color of the metal can be seen from the outside even when the tooth is subsequently restored, and the metal color can become darker due to chemical modification of the metal with the passage of time. To prevent these problems, a masking color is used, but it also makes the color of ceramic material turbid with the passage of time, and the metal color also has an effect on the gums, such that the gums appear black. Accordingly, when a metal component is not interposed between the tooth and the ceramic material and when even the coping is made of ceramic material, the above-described problem related to the expression of unfavorable colors is naturally solved, and the resulting coping can be evaluated as an excellent prosthesis, which can easily achieve aesthetics, which is the most important criterion for artificial teeth.

[9] However, when a coping made of ceramic material is used, there is a problem in that it is likely to be broken or damaged due to the characteristic brittleness of ceramic material. To overcome this problem, there have been efforts to use ceramic materials having excellent strength or toughness, typical examples of which include alumina, zirconia and the like. However, alumina, zirconia and the like do not completely overcome the brittleness problem either, and must be sintered at high temperatures in order to ensure sufficient strength, resulting in an increase in process cost. Thus, there are still limitations on the complete substitution of metal copings with ceramic

copings.

Disclosure of Invention

Technical Problem

[10] The present invention has been made in order to solve the above-described problems occurring in the prior art, and it is an object of the present invention to increase the strength of a ceramic coping manufactured from a green body made of ceramic material, either by adding frit to the coping or impregnating the frit into the coping, so as to create a stress difference between the ceramic material and the frit component.

[11] Another object of the present invention is to improve process economy by finely controlling the component and content of the frit so as to enable the resulting coping to ensure at least the same strength or toughness as those of the prior products, which are calcined at a relatively high temperature, even though the inventive coping is calcined at a relatively low temperature.

[12] Still another object of the present invention is to minimize the breakdown of a coping by interposing wax and a die hardener between a model for manufacturing the coping and a green body for forming the coping so as to produce a coping shape having the same the shape as the model, and also enable the coping to be easily separated from the model by heat treatment.

[13] Further another object of the present invention is to manufacture a coping having excellent quality in a simple way through a simple process of model-wax-coping.

Technical Solution

[14] To achieve the above objects, according to one aspect of the present invention, there is provided a slurry for ceramic copings, which is prepared by mixing at least one material selected from among alumina (Al O ) and zirconia (ZrO ) with lanthanum oxide (La O ) and silica (SiO ) and adding a solvent to the mixture.

[15] The mixing ratio between alumina or zirconia, lanthanum and silica is preferably in the range of 1 : 1.2 : 2 to 1 : 2 : 3.

[16] Also, the mixture preferably further contains at least one material selected from the group consisting of boron oxide (B O ), calcium oxide (CaO), tin oxide (TiO ), selenium oxide (CeO ), magnesium oxide (MgO), yttria (Y O ) and iron oxide (Fe O ).

[17] According to another aspect of the present invention, there is provided a slurry for ceramic coping, comprising 15-35 wt% of lanthanum oxide (La O ), 10-25 wt% of silicon dioxide (SiO ), 10-25 wt% of aluminum oxide (Al O ), 5-20 wt% of boron oxide (B O ), 5-20 wt% of calcium oxide (CaO), 0-10 wt% of zirconia (ZrO ), 0-10 wt% of tin oxide (TiO ), 0-15 wt% of selenium oxide (CeO ) and 0-5 wt% of iron oxide (Fe O ).

[18] The slurry for ceramic copings preferably further comprises 0-10 wt% of magnesium oxide (MgO) and 0-10 wt% of yttria (Y O ).

[19] According to still another aspect of the present invention, there is provided a ceramic coping prepared from said slurry for ceramic copings and having a strength higher than 6000 MPa.

[20] According to yet another aspect of the present invention, there is provided a method for manufacturing a ceramic coping, the method comprising the steps of: preparing a green body, made of alumina or zirconia; calcining the green body to form a ceramic coping; and immersing the ceramic coping in a melt containing a mixture of lanthanum oxide (La O ) and silica (SiO ), so as to allow the melt to penetrate into the ceramic coping.

[21] The melt preferably further contains at least one material selected from the group consisting of boron oxide (B O ), calcium oxide (CaO), tin oxide (TiO ), selenium oxide (CeO ), magnesium oxide (MgO), yttria (Y O ) and iron oxide (Fe O ).

[22] According to yet still another aspect of the present invention, there is provided a method for manufacturing a ceramic coping, the method comprising the steps of: applying a die hardener on the margin of a model for manufacturing a coping; applying wax on the model; reapplying the die hardener on the wax-applied model; covering the reapplied model with alumina or zirconia; and heating the covered model and then separating said alumina or zirconia from the heated model.

[23] The thickness of the wax applied on the central lower portion of the model is preferably less than the thickness of the wax applied on the central upper portion of the model.

[24] The thickness of the wax applied on the model is preferably 0.01-0.06 mm.

[25] Said alumina or zirconia is preferably in a slurry state, and is further mixed with lanthanum oxide (La O ) and silica (SiO ).

2 3 2

[26] The mixture preferably further contains at least one material selected from the group consisting of boron oxide (B O ), calcium oxide (CaO), tin oxide (TiO ), selenium oxide (CeO ), magnesium oxide (MgO), yttria (Y O ) and iron oxide (Fe O ).

[27] The method preferably further comprises a step of immersing the heated and separated alumina or zirconia in a melt containing a mixture of lanthanum oxide (La O ) and silica (SiO ), so as to allow the melt to penetrate into said alumina or zirconia.

[28] The melt preferably further contains at least one material selected from the group consisting of boron oxide (B O ), calcium oxide (CaO), tin oxide (TiO ), selenium oxide (CeO ), magnesium oxide (MgO), yttria (Y O ) and iron oxide (Fe O ).

Advantageous Effects

[29] A ceramic coping according to the present invention shows relatively high strength

values, even though it is heat-treated in the same temperature range as the prior coping. Thus, it can greatly reduce some of the total costs of processes, and when it is applied as a product in practice, it will show high durability.

[30] Also, according to the present invention, the separation between the model and the coping can be made easy by applying a die hardener at two different points of time and applying wax to allow the die hardener and the wax to evaporate by heat treatment. Thus, a change in the shape of the coping is minimized and, at the same time, the inner surface of the coping can become smooth. In addition, the process of the present invention can be carried out in a relatively simple way, leading to a reduction in process time. Mode for the Invention

[31] Hereinafter, the present invention will be described in further detail on the basis of examples.

[32] In the present invention, in order to manufacture a ceramic coping for tooth restoration, a slurry for manufacturing the ceramic coping was first prepared.

[33] The slurry is prepared based on non-glass crystalline powder, which is the parent material of the ceramic coping. Examples of material associated with this powder include alumina, zirconia and the like, but other ceramic materials may also be selected. However, it is preferable to select a white or cream-colored material, because it is to be used as a dental coping.

[34] Alumina or zirconia, as the parent material of the ceramic coping, has strong fracture toughness, but they have a high risk of breakdown from momentarily concentrated stress due to their characteristic brittleness. For this reason, it is not preferable to prepare a compact calcined material using alumina or zirconia as a base. Rather, when a composite is prepared by adding other components to alumina or zirconia, it can show the desired compactness and a strength higher than the desired level, even when it is calcined at a low temperature.

[35] For this purpose, a highly compact coping can be prepared by mixing alumina or zirconia with a mineral material containing glass components, for example, silicate mineral, in an initial stage, to prepare a slurry, and subjecting the slurry to liquid-phase sintering.

[36] However, in addition to the above method, other methods can also be used to prepare a coping. One example thereof may be a method comprising calcining alumina or zirconia at a low temperature to prepare a porous material, applying the surface of the porous material with mineral powder that contains glass components, and then heating the resulting material until the glass is melted, such that the glass components are impregnated into pores formed in the calcined alumina or zirconia material. When

the calcining process is carried out in a vacuum atmosphere, a more preferred impregnation effect can be achieved.

[37] Moreover, the above-described impregnation effect can also be achieved by immersing a low-temperature calcined material of alumina or zirconia in a melt containing glass components so as to allow the glass components to penetrate into the calcined material.

[38] The glass components impregnated to a given depth from the surface of the alumina or zirconia calcined material cause stress at the interface with the non-impregnated alumina or zirconia base. Generally, a reinforcement effect is expressed by the compressive stress caused by the glass components and the tensile stress caused by the alumina or zirconia base.

[39] The preparation of the slurry for ceramic copings according to the present invention is characterized in that selected frit components are used.

[40] The frit components used in the present invention are as follows.

[41] First, lanthanum oxide (La O ) as a lanthanum series material was used.

[42] Lanthanum oxide was used as a material, which could reduce the viscosity of the frit (glass component) to increase the penetration of the frit and could increase the transparency of a coping for aesthetic reasons. Thus, lanthanum oxide functions to facilitate the formation of a matrix by the frit in the alumina or zirconia base and to increase the depth of penetration of the frit melt into the alumina or zirconia base so as to increase the compactness and strength of the frit-applied base.

[43] Also, silica (SiO ) was used as an essential frit component. In addition, at least one component selected from the group consisting of boron oxide (B O ), calcium oxide (CaO), tin oxide (TiO ), selenium oxide (CeO ), magnesium oxide (MgO), yttria (Y O ) and iron oxide (Fe O ) was used.

[44] Herein, iron oxide (Fe O ) is a component that is very stable to sunlight, air, water and heat, and can increase the strength of the frit. Because it is red-brown in color, it is used in small amounts in the present invention.

[45] In order to manufacture a coping from the slurry according to the present invention, alumina was heat-treated at a temperature of 1000-1200 ⁰ C, which is lower than its compacting temperature of 1650 ⁰ C or higher, and alumina powder could be prepared into a porous material into which the melted glass components would easily penetrate, because the crosslinking between the powders was weak. Also, when the slurry contained alumina or zirconia and glass components, it was possible to make the finally formed coping compact due to the formation of a matrix by the melting of the glass components. The tensile strength of the ceramic coping prepared using the slurry was measured as described below for comparison with the prior ceramic coping.

[46] Also, a ceramic green body was heat-treated at said temperature to prepare a

calcined ceramic material, which was then immersed in a frit, which was heat-treated at a temperature similar to said temperature, so as to allow the frit to penetrate into the calcined material. The tensile strength of the calcined ceramic material was measured.

[47] Table 1 below shows the measurement results for the tensile strength of the prior coping, prepared by mixing alumina with frit, and the tensile strength of the inventive copings calcined at various temperatures. As can be seen in Table 1 below, the calcined materials according to the present invention showed an increase of about 98-130 MPa in strength compared to the prior alumina coping.

[48] Herein, test conditions and the specification of specimens used in the test are as follows:

[49] Material measured: alumina [50] Measurement temperature: 25 ⁰ C [51] Strength measured: tensile strength [52] Measurement instrument: Universal tester for the measurement of tensile strength [53] Falling speed of load: 20 sec/cm [54] Specimen length: 0.42 cm [55] Specimen thickness: 0.10 cm [56] Table 1

[57] Also, ceramic copings were manufactured by preparing a calcined material of alumina and allowing the frit components of the present invention to penetrate into the ceramic copings. The tensile strength of the ceramic copings was measured and compared with the prior alumina/frit coping. The measurement results are shown in Table 2 below.

[58] The measurement of tensile strength was carried out in the same conditions as those for the specimens in Table 1. [59] Table 2 below shows measurement results for the tensile strength of the prior coping, which was prepared by allowing frit to penetrate into alumina, and the tensile strength of the inventive copings, which were prepared by calcining the green bodies at various temperatures and allowing frit components to penetrate into alumina. As can be seen in Table 2 below, the calcined materials according to the present invention showed an increase in strength of about 115-124 MPa compared to the prior alumina coping.

[60] Table 2

[61] Accordingly, it can be seen that the ceramic coping according to the present invention shows relatively high strength values, even though it is heat-treated in the same temperature range as the prior coping. Thus, it can greatly reduce the expenditure of costs which can be calculated in processes, and when it is used in an actual product, it will show high durability.

[62] Moreover, the present invention provides a method capable of manufacturing a coping in a simple manner, the method comprising molding a coping using wax, and heat-treating impurities, such as wax and a die hardener, to evaporate these impurities.

[63] Herein, the wax is applied on the surface shape of a model for manufacturing a coping, and thus can make the same shape as the shape of the model. Also, because the wax can prevent the model from coming into direct contact with the material of the coping, the model and the coping can be easily separated. In addition, because the wax is an organic material that can be thermally treated at low temperatures, it can be easily evaporated by heat treatment. That is, the wax is volatilized by heat treatment, making the separation between the coping and the mold easy.

[64] Although wax is used herein, any material other than wax may be used in the present invention, as long as it can be formed into the shape of the coping, and can also be evaporated by heat treatment, making it possible to achieve easy separation between the model and the coping.

[65] Also, in the present invention, the die hardener is used at two different points of time. The die hardener is an organic material comprising 2-butanone, methyl methacrylate and a resin co-polymer.

[66] However, the die hardener may also be applied only after the application of the wax, without being applied before the application of the wax.

[67] Herein, the die hardener, when it is applied at a first point in time, hardens the model made of soft material, so as to make it easy to handle the model and prevent the shape of the model from being readily deformed. Also, because the surface of the die hardener, which is dried after application, is smooth, it can serve to maintain the shape of the coping such that it corresponds to the mold.

[68] Also, if the wax surface is not smooth in a process of applying the wax, it can be maintained smooth by applying the die hardener, thus smoothing the inner surface of the finally manufactured coping.

[69] Moreover, the thickness of the wax applied can be made thicker on the central lower portion of the coping than on the central upper portion. This is because the

central lower portion of the coping should be formed thicker, such that, when the coping is separated from the mold, the breakdown of the coping can be reduced.

[70] However, the central lower portion of the coping does not necessarily need to be thicker, and there may also be no difference in thickness between the central upper portion and the central lower portion, as long as these portions have a thickness of 0.1-0.6 mm. Industrial Applicability

[71] As described above, according to the present invention, the strength of the ceramic coating can be increased by manufacturing a coping from a ceramic green body and either adding frit to the coping or impregnating the frit into the coping so as to create a stress difference between the ceramic material and the frit component.

[72] Also, according to the present invention, process economy can be improved by finely controlling the components and contents of the frit so as to enable the resulting coping to ensure at least the same strength or toughness as the prior products, which are calcined at a relatively high temperature, even though the inventive coping is calcined at a relatively low temperature.

[73] Furthermore, according to the present invention, the breakdown of the coping can be minimized by interposing wax and a die hardener between a model for manufacturing the coping and a green body for forming the coping so as to produce a coping shape having the same the shape as the model, and also enable the coping to be easily separated from the model by heat treatment.

[74] In addition, according to the present invention, a coping having excellent quality can be manufactured in a simple way through a simple process of model- wax-coping.