Magnetic attachment for artificial tooth

Abstract

To provide a magnetic attachment for an artificial tooth that includes a welding part having an excellent fall prevention force, a high magnetic attraction force, a sufficient magnetic cutout property, and excellent welding strength, and simplifies a process.SOLUTION: A flange having a projection part is provided in a Cr-based magnetic stainless steel cap 1 storing a permanent magnet 2 by cold working of combination of rearward extrusion press work and forward extrusion press work. On an outer surface of a magnetic structure excluding an attraction surface, a metal adhesive is applied to and curing processing is performed on a spiniform uneven surface. A shield plate 3 being a lid of a recessed opening part of the cap 1 includes a 18Cr-8Ni stainless steel magnet in a part 31 other than the outer peripheral part and a non-magnetically modified 18Cr-8Ni stainless steel non-magnetic part in the outer peripheral part 32. A welding part is formed by laser-welding a boundary part of the outer peripheral part 32 formed by the cap 1 and the non-magnetic part of the shield plate 3. A keeper 102 is formed of Cr-based soft magnetic stainless steel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic attachment for dentures that can be used in the dental field to hold and fix dentures by utilizing a strong magnetic attraction force. [Background technology]

[0002] In recent years, dentures have begun to be manufactured using a 3D printer based on the digital data of a computer-designed denture, which is made by using X-ray image analysis equipment and 3D shape measurement to diagnose the state of the teeth in the oral cavity. In other words, dentures are changing from precision cast dentures to digital dentures. Magnetic attachments for magnetic dentures have been used as tooth-friendly retention devices in precision cast dentures, but in the production of digital dentures, they are expected to utilize the self-attracting force of magnets to accurately and stably hold the denture to the abutment teeth. To achieve this, there is a need for increased attractive force.

[0003] Conventionally, examples of magnetic attachments for dentures that utilize magnetic attraction are shown in Figures 11 and 12 of Patent Document 1. According to Figure 11, in order to attach a denture 50, a root plate 62 is embedded in the root 61 of the human tooth, and a keeper 6 is embedded in the root plate 62. The denture 50 consists of a magnetic attachment for dentures 5 arranged opposite the keeper 6, a resin base 63 that encases it, and an enamel artificial tooth 64.

[0004] This device is required to be as small as possible and have as strong an adhesive force as possible. However, a problem arises that a magnetic attachment 5 for dentures that is smaller and has a stronger adhesive force is that it tends to come off from the resin base 63. To address this problem, The following inventions have been disclosed: Patent Document 2 proposes a magnetic attachment having a drum-shaped outer periphery, as shown in FIG. 13, which has improved attractive force and high fall-off prevention capability. Patent Document 3 proposes attaching a flange to the side of the cap, as shown in FIG. Patent document 4 proposes a manufacturing process that improves the adhesion of magnetic structures embedded in dentures using a magnetic structure with a resin layer made of adhesive resin, and reduces the manual work required by dentists and others to prevent them from falling off.

[0005] However, although the drum-shaped magnetic attachment of Patent Document 2 improves the ability to prevent falling off, the drum portion is large, which goes against the goal of miniaturization. The measure of attaching a flange in Patent Document 3 is effective in preventing the cap from falling off, but the attachment position is too high in the outer periphery of the top surface of the cap, which reduces the adhesive force. Similarly, the measure of creating a notch on the side of the cap also has the problem of reducing the adhesive force. The solution in Patent Document 4 involves rough polishing using barrel polishing, so the adhesive resin is applied to the cap surface in a smooth state, and therefore the improvement in adhesion is insufficient. In addition, the method in which dentists sandblast the surface of the cap and then apply metal adhesive with a brush was a measure that was prone to quality variations and left concerns about quality. Furthermore, in Patent Document 5, as shown in Figure 2, by using a stainless steel magnet for the shield plate, the strength of the residual magnetism increases to 800 to 1000 gf, making it possible to achieve an attractive force that is 1.4 times stronger than that of conventional products. Therefore, there has been a demand for measures to prevent falling off while being compact and capable of dealing with strong suction force. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 4-227253 [Patent Document 2] Japanese Patent Application Publication No. 10-127664 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-224109 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-112791 [Patent Document 5] Patent No. 7125684 Summary of the Invention [Problem to be solved by the invention]

[0007] A conventional measure to prevent the cap from falling off is to provide a flange (also called a collar) or a notch on the side of the cap by cutting. However, when trying to provide sufficient fall-off prevention with notches, there is a drawback in that the magnetic flux flow inside the cap is disrupted, reducing the adhesive force, as shown in Figure 3. Also, given the relationship between the resin in the resin base and the resin inside the notch, the fall-off prevention force is lower than with the protrusion method described below. The larger the projection (flange) is, the more effective it is, but increasing the maximum diameter of the attachment makes it difficult to embed it in the denture and makes the denture more susceptible to damage. Since the anti-fall function weakens when the length below the projection is short, the projection has traditionally been positioned to match the top surface of the attachment. However, this has the drawback of disrupting the flow of magnetic flux, generating a magnetic vortex at the base of the projection, which reduces the adhesive force, as shown in Figure 4. An object of the present invention is to provide a flanged magnetic attachment for dentures that has a function of preventing dislodging and that suppresses a decrease in adhesive force. The inventors of the present invention have disclosed in Japanese Patent No. 7125684 an invention which has a welded joint with high attractive force, sufficient magnetic blocking properties and excellent weld strength, and which also simplifies the manufacturing process. The present application is an improvement on that invention and solves the problems of the present invention by reference thereto. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into the shape, position and size of the flange portion, as well as the manufacturing method thereof, in a magnetic structure that generates a strong magnetic attraction force and that does not disrupt the flow of magnetic flux from the composite magnet. By making the flow of magnetic flux as shown in Figure 5, it is possible to rectify the flow and prevent disturbances such as the generation of magnetic flux vortices. The magnetic flux from the composite magnet, which is made up of a permanent magnet and a stainless steel magnet, flows diffusely from the center to the periphery at the top of the cap (corresponding to the bottom of the cap), and flows from the top to the bottom on the side of the cap. The flow of magnetic flux that has flowed to the periphery is then received by the curved surface at the top of the side of the cap, and the flow is smoothly rectified, preventing vortices and disturbances from occurring inside the flange. One way to achieve this is to guide the flow of magnetic flux by using an inclined surface at the top end of the cap that slopes downward in an R-shape toward the outside.Furthermore, by making the material structure of the flange portion that has the inclined surface at the top end of the cap that slopes downward in an R-shape toward the outside smooth fibrous structure, magnetic flux can flow along the fibrous structure. In other words, the cross section of the outer periphery of the flange is fan-shaped, and the R-shape of the fan is made up of fibrous tissue that is about 1 / 4 the size of an annual ring, and from the bottom of the flange to the side of the cap, there is a small inverted R-shaped fibrous tissue.

[0009] The flange's upper end extends outward from the upper end of the cap, gradually descending in an inclined plane. The flange's lower end (bottom surface) is located at approximately the same position as the inner bottom surface of the cap in Figure 5, and is flat. Next, the width of the flange, in other words, the protrusion from the side of the cap, is preferably 0.1 mm to 0.25 mm. If the protrusion is less than 0.1 mm, the anti-fall-off force cannot be ensured. Conversely, if it exceeds 0.25 mm, the anti-fall-off force will be improved, but the attachment will not be made smaller.

[0010] Furthermore, in order to achieve a magnetic attraction force of 1000 gf when combining a permanent magnet and a stainless steel magnet, as shown in Figure 2, we came up with the idea of ​​making the surface of the magnetic structure a spiky, uneven surface consisting of triangular pyramidal peaks with the same depth and width, and then applying a strong metal adhesive with a thickness of 20 μm or less onto this uneven surface and curing it. [Effects of the Invention]

[0011] The present invention provides a magnetic attachment for dentures with a strong anti-fall function, taking advantage of the high attractive force achieved by a composite magnet consisting of a permanent magnet and a Cr-Ni stainless steel magnet used in the shield plate, thereby making it possible to fully utilize the benefits of the high attractive force. It also simplifies the manufacturing process and enables the welds to be strengthened. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view of a magnetic attachment for dentures. [Figure 2] FIG. 1 is a diagram showing the relationship between the magnetic adsorptive force and the remanence of a Cr—Ni stainless steel magnet. [Figure 3] FIG. 10 is a diagram showing disturbance of magnetic flux during cutting (machining). [Figure 4] FIG. 10 is a diagram showing the disturbance of magnetic flux in a flange (machined). [Figure 5] FIG. 10 is a diagram showing the flow of rectified magnetic flux in a flange (cold worked) having an inclined surface with an R shape. [Figure 6] (a) A diagram showing the protrusion formed by backward extrusion press processing and the fibrous structure that follows the shape of the protrusion, (b) the flange formed by forward extrusion press processing and its fibrous structure, and (c) a crack in the corner of the bottom surface of the cap caused by excessive forward extrusion press processing. [Figure 7] FIG. 10 is a diagram showing a shield plate. [Figure 8] 10A and 10B are diagrams showing an example of a welded portion of a magnetic structure. [Figure 9] 10A and 10B are diagrams showing other examples of welded portions of the magnetic structure. [Figure 10] This is an SEM photograph of the surface of a magnet structure that has been given a spiky, uneven surface by shot blasting. [Figure 11] FIG. 1 is a diagram illustrating a conventional denture. [Figure 12] FIG. 1 is a diagram showing a cross section of a conventional magnetic attachment for dentures. [Figure 13]FIG. 10 is a diagram showing a cross section of a conventional magnetic attachment for dentures with a drum shape. [Figure 14] FIG. 10 is a diagram showing a cross section of a conventional flanged magnetic attachment for dentures. BEST MODE FOR CARRYING OUT THE INVENTION

[0013] A first embodiment of the present invention is as follows. The magnetic attachment for dentures of the present invention comprises: A magnetic attachment for dentures comprising a magnetic structure to be placed on a denture and a keeper made of a soft magnetic material to be placed on an abutment tooth, wherein the magnetic structure and the keeper are configured to be attracted to each other by self-attraction due to magnetic force when an attracting surface of the magnetic structure and an attractable surface of the keeper are brought into contact with each other, the magnetic structure has a cup-like shape with an opening, and the bottom and side surfaces of the magnetic structure are made of a cap made of Cr-based magnetic stainless steel, a permanent magnet housed in a recess of the cap, and a shield plate that covers the opening of the cap; The magnetic structure has a cylindrical shape with a diameter of 1.5 to 5 mm and a height of 0.8 to 2 mm, The permanent magnet has a maximum energy product of 45 MGOe to 55 MGOe, a coercive force of 10 kOe to 20 kOe, and is formed into a disk shape with a thickness of 0.5 mm to 1.6 mm and an outer diameter of 1.2 mm to 4.6 mm, the cap has a flange portion consisting of a protrusion of 0.1 mm to 0.25 mm on a side surface on the upper end side that does not abut against the keeper, and the side surface portion has a parallel fibrous structure along the side surface and a hardness of Hv220 to Hv300; The flange portion has an R-shaped inclined surface that slopes downward outward on the upper end side of the cap, and is made of a semicircular arc-shaped fiber structure, the shield plate has an outer periphery made of non-magnetic Cr-Ni stainless steel, and the other part is made of a Cr-Ni stainless steel magnet having a fibrous structure in the thickness direction, The Cr-Ni stainless steel magnet has magnetic properties in a saturated magnetized state of 8,000 G to 12,000 G of saturation magnetization, 100 Oe to 200 Oe of coercive force, an anisotropic magnetic field of 800 G or more, and 6,000 G to 10,000 G of residual magnetism, a boundary between the outermost end of the cap side surface and the shield plate is joined by welding, and the suction surface including the welded portion is smoothed; The keeper is characterized by being disk-shaped and made of Cr-based soft magnetic stainless steel, and having a smoothed attracting surface. This makes it possible to obtain a magnetic attachment for magnetic dentures that has a high magnetic attraction force and can prevent it from falling off the denture.

[0014] The outer peripheral side of the cap is characterized by having a metal adhesive coating of 20 μm or less in thickness on a spiky uneven surface consisting of triangular pyramidal peaks with the same depth and width. This makes it possible to prevent the magnetic attachment for dentures, which has a higher magnetic attraction force, from falling off.

[0015] A second embodiment of the present invention is as follows. The method for manufacturing the magnetic structure of the magnetic attachment for dentures of the present invention comprises the steps of: (1) First, in the manufacture of the three components that make up the magnet structure, namely the cap with a flange on the upper side made of Cr-based magnetic stainless steel, the permanent magnet made of a disc-shaped rare earth sintered magnet, and the shield plate, which is the base material for the disc-shaped stainless steel magnet, Step a) The cap is made by cold-pressing a Cr-based magnetic stainless steel plate into a disk shape; Step b) Next, a cap is formed by backward extrusion press working, and a protrusion of 0.1 mm to 0.25 mm is protruded from the side surface of the upper end of the cap, and a fibrous structure is formed on the upper end of the cap, with an R-shaped inclined surface processed outward and following the shape of the protrusion; Step c) further includes forming a flange portion by flattening the lower surface of the protrusion by forward extrusion press processing, the flange portion having a semicircular arc-shaped fiber structure; In addition, due to the backward extrusion press process and the forward extrusion press process, the side surface of the cap is made of a parallel fibrous structure along the side surface, The hardness is Hv220 to Hv300. Step d) the shield plate is made of a Cr-Ni non-magnetic stainless steel base material, which is cold drawn by 50% or more to induce transformation of 80% or more of the austenite structure to martensite, and then machined into ring slices to form a disk-shaped shield plate with a thickness of 0.1 mm to 0.2 mm and an outer diameter of 1.2 mm to 4.6 mm. The outer periphery of this shield plate is laser heated to be non-magnetically modified back to Cr-Ni non-magnetic stainless steel consisting of an austenite phase, thereby forming a composite shield plate in which the center of the disk is made of stainless steel magnetic material and the outer periphery is non-magnetic. Step e) forming the permanent magnet into a disk shape having a maximum energy product of 45 MGOe to 55 MGOe, a coercive force of 10 KOe to 20 KOe, a thickness of 0.5 mm to 1.6 mm, and an outer diameter of 1.2 mm to 4.6 mm; (2) Next, in assembling the magnetic structure consisting of the three parts of the cap, the composite shield plate, and the permanent magnet, Step f) inserting the permanent magnet into the hole of the cap, covering it with the composite shield plate, and assembling the three parts; Step g) welding the boundary between the cap and the shield plate; (3) Then, in the surface treatment, magnetization and inspection of the assembled magnetic structure, Step h) shot-blasting the magnet structure, applying a metal adhesive thereto, and then curing the metal adhesive; Step i) polishing the attracting surface of the magnetic structure to make it smooth; Step j) applying a magnetic field of 2 T or more in the height direction to magnetize the magnetic structure; Step k) inspecting the attraction force between the magnet structure and the keeper; The method is characterized by comprising the steps of: This makes it possible to simplify the process while maintaining the function of preventing falling off by changing from the conventional cutting process to press processing.

[0016] In step d), the outer periphery of the shield plate may be made non-magnetic by high-frequency heating. Furthermore, in step d), only the shield plate may be formed, and in (2) the shield plate, cap, and permanent magnet may be assembled, and the outer periphery of the shield plate may be demagnetized by the laser welding heat at the same time as laser welding the boundary between the cap and shield plate. This laser welding non-magnetic modification technology simplifies the process by eliminating the need for laser heating or high-frequency heating to form the composite shield plate.

[0017] The magnetic attachment for a denture and the method for manufacturing the magnetic attachment for a denture will be described with reference to FIGS. As shown in Figure 1, the denture magnetic attachment 10 is composed of a magnetic structure 101 and a keeper 102. The magnetic structure 101 is placed on the denture base 63 and exerts a magnetic attraction force. The keeper, on the other hand, is made of a soft magnetic material and is placed on the abutment. The relationship between the two is such that an attracting surface is provided on the magnetic structure, and an attracted surface is provided on the keeper, and when the attracting surface and the attracted surface are brought into contact, they attract each other by the magnetic attraction force. Furthermore, as shown in Figure 11, in order to prevent the magnetic structure 5 from falling off the denture base 63 due to the magnetic attraction force of both, the magnetic structure 5 is shaped so that a flange 11 consisting of a protrusion is provided on the magnetic structure 101, and on the surfaces of the magnetic structure 101 except for the attraction surface, a metal adhesive is applied to the uneven surface formed by shot blasting and then cured. This will be explained in detail below.

[0018] <Magnet structure 101> The magnetic structure 101 is composed of a permanent magnet 2, a cap 1 with a flange 11 that houses the permanent magnet 2, and a shield plate 3 that covers the opening of the cap. The size is a cylindrical shape with a diameter of 1.5 mm to 5 mm and a height of 0.8 mm to 2 mm. These dimensions are compatible with the shape of the artificial tooth. If it is too large, the denture will be prone to cracking, and if it is too small, it will not have sufficient adhesive strength.

[0019] <Cap 1> The Cr-based magnetic stainless steel cap 1 is produced by cold working a soft magnetic Cr stainless steel plate such as 18Cr stainless steel or 18Cr-2Mo stainless steel as the base material. A disk shape is punched out, and then a combination of backward and forward extrusion press working is used to produce a cylindrical container with a flange 11, a protrusion measuring 0.1 to 0.25 mm in width, on the upper side that does not abut against the keeper.

[0020] Figure 6 shows (a) the protrusion formed by backward extrusion press processing and the fibrous structure that follows the shape of the protrusion, (b) the flange formed by forward extrusion press processing and its fibrous structure, and (c) cracks in the corners of the cap surface caused by excessive forward extrusion press processing. The backward extrusion press process forms the cap, and the material protrudes from the side of the upper end of the cap to form a protrusion, forming a fibrous structure that conforms to the shape of the protrusion. This provides hardness and magnetic attraction, but the lower surface of the protrusion has a smooth rounded R-shape, so despite the presence of the protrusion, it does not provide sufficient anti-fall functionality. To address this issue, a forward extrusion press process is added to flatten the underside of the protrusion, completing the flange.

[0021] The position of the flange portion 11 is such that the upper surface is almost the same as the upper end surface of the cap, and the lower surface is at a position that corresponds to the same thickness from the upper surface as the upper part of cap 1. If the flange portion 11 is pressed too hard during the forward extrusion press process and becomes thinner than the thickness of the upper part of cap 1, cracks are likely to occur in the corners of the bottom surface of the cap, as shown in Figure 6(c). The flange 11 has an R-shaped inclined surface that slopes downward outward on the upper end surface of the cap 1, and its internal structure is made of a semicircular fibrous structure. The lower surface of the flange becomes flat from the end of the R-shaped inclined surface and wraps around to form a small R-shape toward the cylindrical side surface.

[0022] The hardness of the container produced by cold working is hardened to Hv220 to Hv300 due to the fibrous structure. If the hardness is less than Hv220, the portion (ring) that constitutes the adsorption surface at the very edge of the side portion of the cap 1 will not have sufficient polishing resistance and will not have sufficient wear resistance as an adsorption surface after polishing. Furthermore, if the hardness of this portion is too soft compared to the hardness of the martensitic structure of the shield plate, which is Hv350, the outer periphery of this portion (ring) will sag during polishing, making it difficult to form a flat adsorption surface, which is also a factor in reducing the magnetic adsorption force. A hardness of Hv260 to Hv280 is preferable. Its magnetic properties are preferably a coercive force Hc of 50 Oe or less and a Bs of 1.3 T or more, which allows for a sufficient magnetic attraction force to be obtained.

[0023] The flange portion 11 is work-hardened to Hv 250 to 300. If the hardness is less than Hv 220, the magnetic structure 101 is not sufficiently prevented from falling off from the denture base, and if the hardness exceeds Hv 300, the magnetic attraction force decreases. Furthermore, the semicircular fiber structure contributes to rectifying the flow of magnetic flux from the composite magnet in the flange portion 11, which is prone to causing turbulence in the flow within the cap 1, as shown in FIG. The side surface of the cap 1 is made of a parallel fibrous structure along the side surface, which allows the flow of magnetic flux to be smooth.

[0024] <Permanent magnet 2> The permanent magnet 2 is preferably a rare earth magnet such as a Nd-Fe-B magnet (NdFeB magnet). In the case of a NdFeB magnet, the maximum energy product BHmax is preferably as large as possible, so BHmax is set to 45 MGOe to 55 MGOe. If the maximum energy product is less than 45 MGOe, sufficient magnetic adsorption force cannot be obtained. Considering the upper limit of a general-purpose NdFeB magnet, BHmax is set to 55 MGOe. The coercive force iHc is preferably as large as possible, but if it is too large, magnetization becomes difficult. The coercive force iHc is set to 10 kOe to 20 kOe. The size of the permanent magnet housed in the cap <1> is a disk shape with a thickness of 0.5 mm to 1.6 mm and an outer diameter of 1.2 mm to 4.6 mm.

[0025] <Shield plate 3> The shield plate 3 has a disk shape. The outer peripheral portion is non-magnetic <32>, and the portion other than the outer peripheral portion is made of a Cr-Ni-based stainless steel magnet <31>. The Cr-Ni-based stainless steel magnet has a fibrous structure in the thickness direction and is magnetized in that direction. Its performance is such that the saturation magnetization is 8,000 G or more, the coercive force is 100 Oe to 200 Oe, the anisotropy magnetic field is 800 G or more, and the residual magnetism is 6,000 G or more. In particular, the larger the residual magnetism, the more the magnetic adsorption force increases as shown in Fig. 2, so it is important to ensure 6,000 G or more. A composite magnet composed of the Cr-Ni-based stainless steel magnet <31> and the permanent magnet 2 housed in the cap <1> is formed to realize a large magnetic adsorption force. At the same time, the shield plate 3 welds the boundary portion with the cap to protect the permanent magnet 2 from saliva in the oral cavity and corrosion. Further, the non-magnetic portion of the shield plate 3 magnetically blocks the composite magnet and the cap to prevent a decrease in the magnetic adsorption force.

[0026] <Manufacturing method of Cr-Ni-based stainless steel magnet> First, as shown in Figure 7(A), the method for manufacturing a Cr-Ni stainless steel plate magnet involves cold drawing an austenitic Cr-Ni stainless steel bar by 50% or more to cause 60% or more martensitic transformation, and then slicing the bar to produce shield plates 311 with a fibrous structure running through the thickness direction. The size of this shield plate 311 is 0.1mm to 0.2mm in thickness and 1.2mm to 4.6mm in outer diameter. Next, the outer periphery of the shield plate 311 made of this semi-hard magnetic material in a martensitic transformation state is laser-heated to perform non-magnetic modification, returning it to austenitic Cr-Ni stainless steel 32. The width is 0.15 mm to 0.3 mm, and the thickness is the same as that of the shield plate, specifically 0.05 mm to 0.20 mm. This produces a composite shield plate 312 whose center is made of semi-hard magnetic material and whose outer periphery is made of non-magnetic material (non-magnetic portion) (Figure 7(B)). The outer periphery of the shield plate 311 may be heated by high frequency heating. The shield plate 311 and composite shield plate 312 are magnetized by applying a magnetic field of 3,000 Oe to 4,000 Oe in the thickness direction of the disk using an electromagnet to form a permanent magnet. Alternatively, the composite shield plate 312 and the NdFeB magnet 2 may be stacked and pulse-magnetized together. The method for manufacturing the plate magnet is not limited to the above method, as long as it is a method that ensures a residual magnetism of 6,000 G or more.

[0027] <Assembly of the magnetic structure 101> A permanent magnet 2 is inserted into a cap 1 made of Cr-based magnetic stainless steel, and a composite shield plate 312 made of Cr-Ni-based non-magnetic stainless steel 32 and Cr-Ni-based semi-hard magnetic stainless steel 311 as a lid is press-fitted into the opening of the cap 1 to assemble the magnetic structure.

[0028] Next, the outer surface of the boundary (joint) between the outermost edge of the side of the Cr-based magnetic stainless steel cap 1 and the ring-shaped Cr-Ni-based stainless steel 32 of the composite shield plate 312 is laser welded. As shown in Figure 8, the weld 33 formed by laser welding is an alloy of the Cr-based magnetic stainless steel 1 and the Cr-Ni-based stainless steel 32, in which a small amount of delta ferrite phase precipitates. Therefore, it is necessary to ensure that the width of the nonmagnetic portion 32 is long enough so that the weld does not extend into the nonmagnetically modified portion. As a result, complete magnetic shielding can be achieved. In this method, the laser welding conditions only need to be considered to ensure joint strength. The boundary between the non-magnetic portion 32 and the Cr-Ni stainless steel magnet 31 is linear on the left and right. The size of the welded portion 33 is 0.1 mm to 0.25 mm wide (0.05 mm to 0.125 mm wide on the shield plate side), and its depth is 50% to 90% of the thickness of the shield plate.

[0029] Furthermore, a permanent magnet 12 is inserted into a cap 11 made of Cr-based magnetic stainless steel, and a shield plate 131 made of Cr-Ni-based semi-hard magnetic stainless steel is press-fitted into the opening of the cap 11 as a lid to assemble the magnetic structure.

[0030] Next, the outermost edge of the side portion of the Cr-based magnetic stainless steel cap 11 is laser welded to the surface side of the boundary (joint) between it and the Cr-Ni-based semi-hard magnetic stainless steel of the shield plate 131. When a composite shield plate is not used, as shown in Fig. 9, the boundary is joined by laser welding, and at the same time, a heat-affected zone 131b caused by the welding heat is demagnetized on the outer periphery of the weld solidification zone 131a on the shield plate 131 side. The boundary between the magnetic material and the non-magnetically modified portion is affected by the rounding of the solidified portion 131a due to welding, forming a rounded heat-affected portion (non-magnetic portion) 131b. The solidified portion 131a is an alloy in which Cr-based magnetic stainless steel 1 and Cr-Ni-based stainless steel are melted together, and although the δ-ferrite phase is precipitated in the solidified portion 131a, the non-magnetic portion 131b formed in the surrounding heat-affected portion ensures complete magnetic isolation. The laser welding conditions are those that ensure joint strength, form a non-magnetic part due to welding heat, and make it possible to avoid thermal damage to the internal magnet due to welding heat transfer (i.e., deterioration of magnetic properties). By adjusting the amount of heat from the laser welding, it is possible to achieve jointing and the formation of a non-magnetic part simultaneously. Specifically, the weld penetration depth is expanded to the full thickness of the shield plate, without damaging the internal magnet, thereby maximizing the heat-affected zone. The size of the welded portion 131a is 0.1 mm to 0.25 mm in width and 90% to 100% of the thickness of the shield plate.

[0031] <Surface treatment and inspection of magnetic structures> The outer peripheral surface of the cap of the magnetic structure is shot blasted with alumina powder of 50 to 100 μm in size. The crushed particles on the surface of the alumina powder create a spiky, irregular surface with triangular pyramidal peaks of approximately equal depth and width on the outer peripheral surface, as shown in Figure 10. A metal adhesive is applied to this irregular surface and then cured. The Cr-based magnetic stainless steel cap 1, which has a spiky, uneven surface, and the metal adhesive are intricately intertwined to form a strong bond, which creates a strong adhesive force between this metal adhesive and the denture base resin, further improving the ability to prevent it from falling off. The thickness of the metal adhesive is 10 to 20 μm. A thickness of at least 10 μm is required to cover the depth of the spiky irregularities, and a thickness exceeding 20 μm is not preferable in terms of productivity, such as the amount of application, application time, and curing time.

[0032] The attracting surface of the magnetic structure 101 that comes into contact with the keeper 102 is a flat surface. After the above surface treatment, the attracting surface including the welded portion of the magnetic structure is polished to make it a flat surface. The cap formed by cold working had a fibrous structure and, due to work hardening, the hardness of the flange was Hv280. The hardness of the cap end face (the ring that serves as the adsorption surface) was Hv270, and it had good abrasion resistance, with no abrasion damage occurring on the outer periphery of the ring.

[0033] <Creating Keeper 102> The keeper 102 is made by punching out a Cr-based soft magnetic stainless steel plate into a disk shape of a specified size. The attracting surface is also polished to a flat surface. Note that there are various shapes of keepers, including root keepers, but in all cases the upper surface is the attracting surface for the magnetic structure. If the hardness of the attracting surface of the keeper is lower than that of the magnet structure, the Cr-based soft magnetic stainless steel plate may be hardened by cold working before punching. Alternatively, a 3-8 μm thick Cr diffusion layer may be formed on the attracting surface of the keeper to harden it. This improves the wear resistance of the keeper and extends its lifespan.

[0034] <Magnetization of magnetic structures> The permanent magnet 2 incorporated into the magnetic structure 1, for example, the NdFeB magnet used in Example 1, has a coercive force of 11 kOe to 12 kOe. To magnetize this NdFeB magnet, a magnetic field at least equal to the coercive force must be applied; applying a magnetic field that is too high is unnecessary and difficult from an equipment perspective. Therefore, for a magnet with a coercive force of 11 kOe, a magnetic field of 1.1 T to 3.6 T is typically applied. The coercive force iHc of the NdFeB magnet used in the magnetic structure of a denture magnetic attachment is 10 kOe to 20 kOe, so a magnetic field of 2 T or more is sufficient for magnetization. However, due to equipment limitations, the magnetic field should be 4 T or less.

[0035] The test involves joining the attracting surface of the magnetic structure 101 and the attracted surface of the keeper 102 together, and measuring the tensile strength in the vertical direction using a tensile tester to determine the magnetic attracting force. The magnetic attraction force can be 800gf to 1000gf.

[0036] <Fall prevention test> Finally, a fall-off prevention test was conducted. The test method was to embed the magnetic structure 10 of the present invention, which corresponds to the magnetic structure 5, in a temporary denture made of resin, which corresponds to the denture base 63 shown in Fig. 11, and to prepare a tensile jig for fixing the magnetic structure 10. The temporary denture and the tensile jig were pulled by a tensile tester to determine their tensile strength. By providing the flange 11 on the cap 1 of the present invention, the tensile strength of the magnetic structure with a diameter of 4.0 mm and a height of 1.5 mm is 40 to 60 kgf, and by adding a surface treatment, it is 60 kgf to 75 kgf. In comparison, without the flange or surface treatment, it was 15 kgf to 25 kgf. [Example]

[0037] [Example 1] The magnetic attachment for dentures and the method for producing the same according to the present invention will be described with reference to FIGS. As shown in Figure 1, the magnetic attachment 10 for dentures in this example is a magnetic structure 101 consisting of a permanent magnet 2, a cap 1 with a flange 11 that serves as a container for storing the permanent magnet 2, and a shield plate 3 that serves as a lid for the recess opening of the cap 1, together with a keeper 102.

[0038] The configuration of the magnetic structure 101 will be described. The permanent magnet 2 is an NdFeB magnet with a BHmax of 52 MGOe, a coercive force iHc of 11 kOe, and an Ms of 1.33 T. Its size is 3.0 mm in diameter and 0.8 mm in height, with rounded corners. The cap 1 is made of 18Cr-2Mo stainless steel, and has a coercive force Hc of 30 Oe and a saturation magnetic flux density Bs of 16 kG. Its size is 3.8 mm in diameter and 1.3 mm in height.

[0039] The manufacturing method is to cut a 0.3 mm thick 18Cr-2Mo stainless steel plate into a disk shape with a diameter of 6.4 mm. Then, by drawing and extrusion, a cylindrical shape with a diameter of 3.8 mm and a height of 1.3 mm was obtained. It is a container for The cap 1 has a flange 11 on the side of its upper end face, which has a 0.25 mm rounded protrusion. The height of the flange 11 was 0.25 mm, which was the same as the thickness of the bottom of the cylindrical container.

[0040] The shield plate 3 is disc-shaped, with the outer periphery being non-magnetic 32 and the rest being made of 18Cr-8Ni stainless steel magnet 31. The 18Cr-8Ni stainless steel magnet 31 has a fibrous structure in the thickness direction and is magnetized in that direction, with a saturation magnetization of 8,500 G, a coercive force of 150 Oe, an anisotropic magnetic field of 860 G, and a residual magnetism of 6,400 G. The 18Cr-8Ni stainless steel magnet 3 and the permanent magnet 2 housed in the cap 1 form a composite magnet, achieving a large magnetic attraction force. At the same time, the shield plate 3 is welded to the boundary with the cap to protect the NdFeB magnet 2 from saliva in the mouth and other substances, thus preventing corrosion. Furthermore, the non-magnetic part of the shield plate 3 magnetically isolates the composite magnet from the cap 1, preventing a decrease in magnetic attraction force.

[0041] The NdFeB magnet 2 is inserted into the cap 1, and then the composite shield plate that serves as the lid is press-fitted into the recessed opening of the cap 1. The surface side of the joint between the 18Cr-2Mo magnetic stainless steel cap 1 and the ring-shaped 18Cr-8Ni stainless steel 32 of the composite shield plate is laser-welded. The weld 33 has a width of 0.3 mm and a depth of 0.08 mm. The magnet structure 101 was magnetized by applying a magnetic field of 2.5 T.

[0042] Next, the keeper 102 is made of 18Cr-2Mo stainless steel, and has a coercive force of 11 kOe and a saturation magnetic flux density Bs of 16 kG.

[0043] A comparative test of magnetic attraction was conducted between a denture magnetic attachment consisting of a Cr-Ni stainless steel magnet and a flanged cap made of Cr-based magnetic stainless steel of the present invention, and a conventional denture magnetic attachment consisting of a soft magnetic stainless steel cap and seal plate. Both have the same size and permanent magnet, and the only difference is whether they are magnet-type or soft magnetic stainless steel-type. As a result, the magnetic attraction force of the magnetic attachment for dentures of the present invention was 920 gf, a 53% improvement in comparison to 600 gf for conventional magnetic attachments for dentures. In addition, in the anti-drop test, the tensile strength was 55 kgf, a significant improvement over the conventional product's 23 kgf.

[0044] [Example 2] In Example 1, assembly and laser welding were carried out using a shield plate instead of the composite shield plate. The properties were equivalent to those of Example 1.

[0045] The cap 1 of Example 2 was subjected to a surface treatment. 70μm alumina powder is ejected at a pressure of 4kgf / mm 2 The specimen was shot blasted for 10 seconds at 1000 W. The specimen was then immersed in a metal adhesive to a thickness of 12 μm and cured by air drying. As a result, in the drop prevention test, the tensile strength was improved to 62 kgf. [Industrial Applicability]

[0046] By using a composite magnet, this invention enables magnetic attachments for dentures to have a magnetic attraction force that is 1.4 times stronger than conventional products, and can be used without falling off the dentures, and is expected to become widely used. [Explanation of symbols]

[0047] 10: Magnetic attachment 101: Magnet structure 102;Keeper 1. Cap (flanged cap) 2. Permanent magnet 3; Shield plate 31: Cr-Ni stainless steel magnet (except for outer periphery) 32: Cr-Ni stainless steel non-magnetic part (outer periphery) 33: Welded section 301; Semi-hard magnetic material 311;Shield Plate 312;Composite Shield Plate 11. Cap (flanged cap) 12. Permanent magnet 131: Semi-hard magnetic material (shield plate) 131a: Welded part (solidified part) 131b; Heat affected zone (non-magnetic zone)

Claims

1. A magnetic attachment for dentures comprising a magnetic structure to be placed on a denture and a keeper made of a soft magnetic material to be placed on an abutment tooth, wherein the magnetic structure and the keeper are configured to be attracted to each other by self-attraction due to magnetic force when an attracting surface of the magnetic structure and an attractable surface of the keeper are brought into contact with each other, the magnetic structure has a cup-like shape with an opening, and the bottom and side surfaces of the magnetic structure are made of Cr-based magnetic stainless steel, and the magnetic structure comprises a cap, a permanent magnet housed in a recess of the cap, and a shield plate that covers the opening of the cap; The magnetic structure has a cylindrical shape with a diameter of 1.5 mm to 5 mm and a height of 0.8 mm to 2 mm, The permanent magnet is formed into a disk shape having a maximum energy product of 45 MGOe to 55 MGOe, a coercive force of 10 kOe to 20 kOe, a thickness of 0.5 mm to 1.6 mm, and an outer diameter of 1.2 mm to 4.6 mm, the cap has a flange portion consisting of a protrusion of 0.1 mm to 0.25 mm on a side surface on the upper end side that does not abut against the keeper, the side surface portion having a parallel fibrous structure along the side surface and a hardness of Hv220 to Hv300; the flange portion has an R-shaped inclined surface that slopes downward outward on the upper end side of the cap, and is made of a semicircular arc-shaped fiber structure; the shield plate has an outer periphery made of non-magnetic Cr-Ni stainless steel, and the rest of the outer periphery made of a Cr-Ni stainless steel magnet having a fibrous structure in the thickness direction, The Cr-Ni stainless steel magnet has the following magnetic properties when saturated: a saturation magnetization of 8,000 to 12,000 G, a coercive force of 100 Oe to 200 Oe, an anisotropic magnetic field of 800 G or more, and a residual magnetism of 6,000 G to 10,000 G; The boundary between the outermost end of the cap side surface and the shield plate is joined by welding, The suction surface, including the welded part, is smoothed. The magnetic attachment for dentures is characterized in that the keeper is disk-shaped and made of Cr-based soft magnetic stainless steel, and has a smoothed adsorption surface.

2. In claim 1, A magnetic attachment for dentures characterized in that the outer side of the cap has a spiky, uneven surface consisting of triangular pyramidal peaks with approximately the same depth and protrusion width, and a metal adhesive coating with a thickness of 20 μm or less.

3. 3. The method for manufacturing the magnetic structure of the magnetic attachment for dentures according to claim 2, (1) First, in the manufacture of the three components constituting the magnetic structure, namely, a cap having a flange on the upper side made of Cr-based magnetic stainless steel, a disk-shaped permanent magnet made of rare earth sintered magnet, and a shield plate which is the base material of the disk-shaped stainless steel magnet, Step a) The cap is made by cold-working a Cr-based magnetic stainless steel plate into a disk shape; Step b) Next, a cap is formed by backward extrusion press working, and a protrusion of 0.1 mm to 0.25 mm is protruded from the side surface of the upper end of the cap, and a fibrous texture is formed on the upper end of the cap, the protrusion having an R-shaped inclined surface descending outward, and following the shape of the protrusion; Step c) further includes forming a flange portion by flattening the lower surface of the protrusion by forward extrusion press processing, the flange portion having a semicircular arc-shaped fiber structure; In addition, due to the backward extrusion press process and the forward extrusion press process, the side surface of the cap is made of a parallel fibrous structure along the side surface, The hardness is Hv220 to Hv300, Step d) the shield plate is made of a Cr-Ni non-magnetic stainless steel base material, which is cold drawn by 50% or more to induce transformation of 60% or more of the austenite structure to martensite, and then machined into slices to form disk-shaped shield plates with a thickness of 0.1 mm to 0.2 mm and an outer diameter of 1.2 mm to 4.6 mm. The outer periphery of this shield plate is laser heated to be non-magnetically modified back to Cr-Ni non-magnetic stainless steel consisting of an austenite phase, thereby forming a composite shield plate in which the center of the disk is made of stainless steel magnetic material and the outer periphery is non-magnetic; Step e) The permanent magnet is formed into a disk shape having a maximum energy product of 45 MGOe to 55 MGOe, a coercive force of 10 kOe to 20 kOe, a thickness of 0.5 mm to 1.6 mm, and an outer diameter of 1.2 mm to 4.6 mm; (2) Next, in assembling the magnetic structure consisting of the three parts of the cap, the composite shield plate, and the permanent magnet, Step f) inserting the permanent magnet into the hole of the cap, covering it with the composite shield plate, and assembling the three parts; Step g) laser welding the boundary between the cap and the composite shield plate; (3) Then, in the surface treatment, magnetization, and inspection of the assembled magnetic structure, Step h) shot-blasting the magnet structure, then applying a dental metal adhesive thereto and curing the same; Step i) polishing the attracting surface of the magnetic structure to make it smooth; Step j) applying a magnetic field of 2 T or more in the height direction to magnetize the magnetic structure; Step k) inspecting the attraction force between the magnet structure and the keeper; 1. A method for manufacturing a magnetic structure using a composite shield plate comprising the steps of:

4. A method for manufacturing a magnetic structure for a denture magnetic attachment, comprising: (1) First, in the manufacture of the three components that make up the magnet structure, namely, a cap with a flange on the upper side made of Cr-based magnetic stainless steel, a permanent magnet made of a disc-shaped rare earth sintered magnet, and a shield plate that is the base material for the disc-shaped stainless steel magnet, Step a) The cap is made by cold-working a Cr-based magnetic stainless steel plate into a disk shape; Step b) Next, a cap is formed by backward extrusion press working, and a protrusion of 0.1 mm to 0.25 mm is protruded from the side surface of the upper end of the cap, and a fibrous texture is formed on the upper end of the cap, the protrusion having an R-shaped inclined surface descending outward, and following the shape of the protrusion; Step c) further includes forming a flange portion by flattening the lower surface of the protrusion by forward extrusion press processing, the flange portion having a semicircular arc-shaped fiber structure; In addition, due to the backward extrusion press process and the forward extrusion press process, the side surface of the cap is made of a parallel fibrous structure along the side surface, The hardness is Hv220 to Hv300, Step d) the shield plate is made of a Cr-Ni non-magnetic stainless steel base material, which is cold drawn by 50% or more, and 60% or more of the austenite structure is induced to transform into martensite, and then machined into slices to form a disk-shaped shield plate made of stainless steel magnetic material with a thickness of 0.1 mm to 0.2 mm and an outer diameter of 1.2 mm to 4.6 mm; Step e) The permanent magnet is formed into a disk shape having a maximum energy product of 40 MGOe to 55 MGOe, a coercive force of 10 kOe to 20 kOe, a thickness of 0.5 mm to 1.6 mm, and an outer diameter of 1.2 mm to 4.6 mm; (2) Next, in assembling the magnetic structure consisting of the three parts of the cap, the shield plate, and the permanent magnet, Step f) inserting the permanent magnet into the hole of the cap, covering it with the shield plate, and assembling the three parts; step g) laser welding the boundary between the cap and the shield plate, and modifying the laser welding heat-affected zone on the shield plate side to be nonmagnetic to form a nonmagnetic portion at the boundary; (3) Then, in the surface treatment, magnetization, and inspection of the assembled magnetic structure, Step h) shot-blasting the magnet structure, then applying a metal adhesive thereto and curing the same; Step i) polishing the attracting surface of the magnetic structure to make it smooth; Step j) applying a magnetic field of 2 T or more in the height direction to magnetize the magnetic structure; Step k) inspecting the attraction force between the magnet structure and the keeper; A manufacturing method of a magnetic structure characterized by laser welding non-magnetic modification technology consisting of the steps.

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