Magnetic denture attachment and method of manufacturing the magnetic structure

Abstract

To provide a thin magnetic attachment having a simple structure and being easy to manufacture, with a thickness of 0.8 mm or less. [Solution] The hole portion of a magnetic stainless steel cap 11 is made into a ring shape, a ring-shaped sintered rare earth magnet 12 is stored inside it, and the hole portion is covered with a ring-shaped shield plate made of 18Cr-8Ni stainless steel with a martensitic structure. The joint portion is laser welded to form a melted and solidified portion and a modified non-magnetic portion, and the magnetization realizes a simple structure consisting of a rare earth sintered magnet and a stainless steel magnet shield plate.

Description

[Technical field]

[0001] The present invention relates to a thin, cap-shaped magnetic denture attachment used in the dental field to maintain and fix dentures by utilizing magnetic attraction. [Background technology]

[0002] In recent years, dentures have begun to be produced using a 3D printer based on the digital data of the design, after the state of the teeth in the oral cavity has been diagnosed using X-ray image analysis equipment and 3D shape measurement. In other words, dentures are changing from precision cast dentures to digital dentures. Magnetic denture attachments are expected to be a retention device for digital dentures. Magnetic dentures include the magnetic dentures shown in FIG. 11 and the magnetic bridge shown in FIG.

[0003] As shown in FIG. 1 of Patent Document 1, a magnetic denture attachment consists of a magnetic structure and a keeper; the magnetic structure is attached inside the denture and the keeper is embedded on the abutment tooth side. The two are attracted to each other by magnetic force via their attracting and attracting surfaces. The combined thickness of the magnetic structure and the keeper is 2 to 4 mm. The magnet is built into the magnetic structure, and anti-corrosion technology for the magnet is disclosed in Patent Document 2.

[0004] In order to manufacture a magnetic bridge by applying it to a crown bridge using a pulp-bearing tooth as an abutment, it is required to make the thickness of the magnetic denture attachment 1 mm or less. As shown in Figure 2, there is a drawback in that the adhesive force is significantly reduced when the thickness is reduced. Measures to solve this drawback are disclosed in Patent Documents 3 and 4. In Patent Document 3, a thin plate type with a thickness of 0.3 to 1 mm has been developed, but this has a structure in which multiple small magnets are placed on the bottom surface of the cap (Fig. 3) and multiple stainless steel and non-magnetic composite magnetic plates are combined and welded together (Fig. 4). However, the complex structure has problems in terms of manufacturability and cost.

[0005] Patent Document 4 discloses that by combining a ring-shaped magnet and a ring-shaped magnetic stainless steel shield plate with a cap (FIG. 5) having a ring-shaped hole in the center, the thickness can be reduced by about 2 / 3, from 1.5 mm to 1.0 mm. In order to form a magnetic circuit, the boundary between the cap and the shield plate needs to be made non-magnetic. The present invention proposes that two non-magnetic rings are inserted in the boundary. However, the complex structure of manufacturing two tiny non-magnetic rings (e.g., outer diameter 1.1 mm × inner diameter 0.5 mm × thickness 0.1 mm), attaching them to the boundary between the cap and the shield plate, and welding and joining the four gaps has problems in terms of manufacturability and cost.

[0006] Furthermore, paragraph 0017 of the specification of Patent Document 4 states that "As an alternative method, the non-magnetic rings 20, 21 can be modified by modifying the magnetic material with a laser or the like, and may be formed by irradiating the outer and inner gap positions with a laser or the like after covering the magnet body 16 with the cover yoke 19," but the cap and shield plate are both magnetic stainless steel with a 19Cr-2Mo-Ti composition, and the welded portion that joins the two is also made of a magnetic material, and no technology is disclosed as to how to modify them to be non-magnetic. It can be said that this description merely points out a future possibility. Therefore, the invention of Patent Document 4 has difficulties in its manufacturing method and is not considered to be practical. In fact, the invention is merely an idea without any specific disclosure, and has not been offered as an actual product.

[0007] Therefore, the present invention simplifies the structure of the magnetic structure of the above-mentioned thin magnetic denture attachment, and realizes a thin magnetic denture attachment that is easy to manufacture and has an adhesive force of 400g to 800g. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-7380 [Patent Document 2] Japanese Patent Application Publication No. 4-227253 [Patent Document 3] Patent No. 7125686 [Patent Document 4] Japanese Patent Application Publication No. 10-127662 [Patent Document 5] Patent No. 7125684 [Non-patent literature]

[0009] [Non-Patent Document 1] Japan Institute of Metals Lecture Abstracts (September 29, 1996, page 408) Summary of the Invention [Problem to be solved by the invention]

[0010] The conventional thin magnetic denture attachments described in Patent Documents 3 and 4 had the disadvantages of being complex in structure, making them difficult to manufacture, and making it difficult to ensure high quality. There were also challenges to commercialization due to their high manufacturing costs. In addition, thin magnetic denture attachments also have thin shield plates, and in order to ensure sufficient strength, the weld depth at the joint between the shield plate and the tip of the cap must be as large as the thickness of the shield plate.This increases the risk of damage to the rare earth sintered magnet due to welding heat, so measures must be taken to prevent this.

[0011] The present invention is based on Patent Document 4, in which the rare earth sintered magnet to be placed in the magnetic structure is ring-shaped, and uses a stainless steel magnet to increase the adsorptive force by about 50%, while at the same time simplifying the structure by eliminating the non-magnetic ring. However, while we considered using a shield plate made of a stainless steel magnet and a nonmagnetic composite magnetic material as disclosed in Figure 3 of Patent Document 5, it was extremely difficult to make a small portion of the inner circumference of the ring nonmagnetic by delicately adjusting the amount of heat. Therefore, we decided to simplify the structure by considering a method of using a shield plate made only of stainless steel magnets instead of a composite magnetic material whose periphery has been made nonmagnetic. [Means for solving the problem]

[0012] As a result of intensive research into the relationship between the attraction force and thickness, the inventors first incorporated a ring-shaped sintered rare earth magnet into a cap (Fig. 5) with a ring-shaped hole in the center, sealed the rare earth sintered magnet with a ring-shaped shield plate made of stainless steel magnet, and welded and joined the boundary between the shield plate and the hole of the cap. In this case, they discovered that there are conditions that can make the vicinity of the welded part nonmagnetic just by laser welding. The conditions are to make the penetration amount of the laser welded part equal to the thickness of the shield plate, to ensure the maximum penetration amount and to ensure the joint strength, and at the same time, to form a nonmagnetic part in the heat-affected part around the solidified part with large laser welding heat. The condition is to provide a gap between the magnet and the shield plate to prevent the magnet from being damaged by the laser heat. A prototype magnet structure was then created. A cross-section of the prototype is shown in Fig. 6, and the shield plate is shown in Fig. 7. The relationship between the adhesive force and thickness of a prototype with a diameter of 4 mm was investigated. As a result, as shown in Fig. 8, it was confirmed that in the case of the round type, the adhesive force decreases by 40% when the height is reduced to 0.6 mm, but in the case of the ring type, the adhesive force only decreases by about 10% even when the thickness is reduced to 0.6 mm.

[0013] Secondly, when a Cr-Ni stainless steel magnet is used as the material for the shield plate, as shown in Fig. 8, it was found that the adhesive force is greater when a Cr-Ni stainless steel magnet is used than when magnetic stainless steel is used, and that the adhesive force increases in proportion to the strength of the residual magnetism of the stainless steel magnet.

[0014] Thirdly, regarding the manufacturing method of ring-shaped rare earth sintered magnets, Patent Document 4 discloses a ring magnet with a thickness of 0.4 mm, but within the scope of the inventors' investigation, ring magnets with a thickness of less than 0.5 mm have not been manufactured, and no manufacturing method for such magnets has been disclosed. Therefore, the inventors produced disk-shaped rare earth sintered magnets with a thickness of less than 0.5 mm and investigated drilling holes alone, but found that the thinner the magnets, the more likely they were to be damaged or chipped, making them impossible to machine. Therefore, they devised a new method of roughly machining holes by electric discharge machining, removing the heat-induced machining-affected layer by grinding and polishing with a drill, and at the same time improving the hole accuracy, which made it possible to machine the ring magnets required for this invention. Additionally, to prevent damage caused by welding heat during assembly of the magnet structure, the corners of the ring magnet facing the shield plate are rounded to provide a specified gap between the corners and the shield plate.

[0015] The configuration of the thin magnetic denture attachment based on the above discoveries and inventions is as follows. A magnetic denture attachment consists of a magnetic structure that is placed on the denture and a keeper made of a soft magnetic material that is placed on the abutment tooth, and is configured so that when the attracting surface of the magnetic structure and the attractable surface of the keeper are brought into contact with each other, the two are attracted to each other by the self-attracting force caused by magnetic force. The magnet structure includes a cap, a rare earth sintered magnet, and a shield plate. The cap is a disk-shaped cap made of Cr-based magnetic stainless steel, and has a cylinder in the center and a ring-shaped hole having an opening on the outer periphery of the cylinder. The rare earth sintered magnet is a thin ring-shaped magnet with rounded corners on the inside and outside of the bottom surface of the ring. It is placed in the hole of the cap. and a gap of 10 μm or more in the height direction of the rare earth sintered magnet and 100 μm or more in the radial direction is provided between the corner portion of the rare earth sintered magnet and the shield plate, The shield plate has a thin ring shape and is composed of a core portion and a boundary portion between the core portion and a cap. The core is made of a Cr-Ni stainless steel magnet with a two-phase structure consisting of 60% or more martensite and 40% or less austenite. The boundary portion is composed of a molten and solidified portion by laser welding and a modified non-magnetic portion by the heat effect of laser welding. The depth of the molten solidified portion is the same as the thickness of the shield plate. The attraction surface of the magnetic structure including the molten and solidified portion is smoothed, It has an adsorption force of over 400gf.

[0016] Here, the magnetic structure is preferably thin, with a diameter of 2.0 mm to 4.5 mm and a thickness of 0.3 to 1 mm. Furthermore, the Cr-Ni stainless steel magnet preferably has a saturation magnetization of 12 kG or more, a coercive force of 50 to 200 Oe, and a residual magnetism of 6 kG or more.

[0017] A method for manufacturing a magnetic structure for a magnetic denture attachment, comprising the steps of: (1) First, the three components that make up the magnet structure are a cap with a protrusion in the center of the hole made of Cr-based magnetic stainless steel, a ring-shaped rare earth sintered magnet, and a shield plate, which is the base material for the ring-shaped stainless steel magnet shield plate. The process is as follows: Step a) The cap is formed by punching and drawing a Cr-based magnetic stainless steel plate in a cold forging press into a concave shape with a protrusion in the center of the hole. Step b) The shield plate is made of Cr-Ni non-magnetic stainless steel bar as the base material. Cold working rate of 50% or more is added After inducing transformation of at least 60% of the austenite structure into martensite, the material is subjected to tension heat treatment and then machined into a ring shape. Alternatively, a Cr-Ni non-magnetic stainless steel plate may be used as the base material, which is then subjected to martensite-induced transformation by cold working, and after tension heat treatment, the plate may be punched out to produce a ring-shaped shield plate. Step c) The rare earth sintered magnet is formed by drilling a hole with an inner diameter of 0.5 mm to 2 mm in the center of a disk-shaped magnet with a thickness of 0.2 mm to 0.49 mm and an outer diameter of 1.6 mm to 4 mm by electrical discharge machining, and then finishing the hole with a drill, and the inner and outer corners of the ring magnet are polished to form a ring shape with R sections. (2) Next, the magnetic structure consisting of the cap, the shield plate, and the rare earth sintered magnet is assembled. The process is as follows: Step d) Insert a rare earth sintered magnet into the hole in the cap, cover it with a shield plate, and assemble the three parts. Step e) Laser weld the two joints between the cap and the shield plate. of The molten and solidified part formed during the welding process forms a micromagnetic part containing a small amount of δ ferrite, and the heat-affected part of the laser welding on the shield plate side forms a modified non-magnetic part. Step f) polishing the suction surface including the laser welded portion to make it smooth; (3) Then, in magnetizing the assembled magnetic structure, Step g) applying a magnetic field of 2 T to 4 T to magnetize the magnetic structure; The method for producing a magnetic structure is characterized by comprising the steps of: Effect of the Invention

[0018] The present invention relates to a thin magnetic denture attachment that is simple in structure, inexpensive, and has a high magnetic attraction. It is expected to be useful in the production of removable magnetic crowns and bridges using pulp-bearing teeth as abutment teeth. [Brief description of the drawings]

[0019] [Figure 1] 1A to 1C are diagrams showing the structure of a conventional magnetic denture attachment. [Diagram 2] A diagram showing the relationship between magnetic attraction force and thickness of a conventional magnetic denture attachment. [Diagram 3] FIG. 2 is a top view of a conventional thin magnetic denture attachment cap (four magnet type). [Figure 4]FIG. 1 is a cross-sectional view of a conventional low-profile magnetic denture attachment. [Diagram 5] 1 is a diagram showing the structure of a cap of the present invention. [Figure 6] FIG. 1 is a diagram showing a cross-sectional structure of a magnetic structure according to the present invention; [Figure 7] 1A is a bottom view of a shield plate of a magnet structure according to the present invention, and FIG. 1B is a cross-sectional view of the shield plate. [Figure 8] FIG. 13 is a diagram showing the relationship between thickness and adhesive force of the ring magnet of the present invention. [Figure 9] FIG. 2 is a diagram showing the relationship between residual magnetism and adhesive force of the stainless steel magnet of the present invention. [Figure 10] FIG. 2 is a diagram showing a ring-shaped shield plate of the present invention. [Figure 11] 13 is a diagram showing the boundaries of laser welding between the inner and outer ends of the shield plate and the tip of the cap. FIG. [Figure 12] FIG. 13 illustrates the use of a magnetic denture attachment as a retention device. [Figure 13] This is a diagram showing the thinness of a magnetic denture attachment for a magnetic bridge that uses pulp-containing teeth as abutment teeth. BEST MODE FOR CARRYING OUT THEINVENTION

[0020] A first embodiment of the present invention is as follows. The magnetic denture attachment of the present invention comprises: A magnetic denture attachment comprising a magnetic structure disposed on a denture and a keeper made of a soft magnetic material disposed on an abutment tooth, the magnetic structure and the keeper being configured to attract each other by self-attraction force 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 magnet structure includes a cap, a rare earth sintered magnet, and a shield plate; The cap is made of Cr-based magnetic stainless steel and has a disk shape, a cylinder in the center, and a ring-shaped hole having an opening on the outer periphery of the cylinder. the rare earth sintered magnet is a thin ring-shaped magnet with inner and outer corners of the lower surface of the ring having rounded corners, and is housed in the hole of the cap; and a gap of 10 μm or more in a height direction of the rare earth sintered magnet and 100 μm or more in a radial direction is provided between the corner portion of the rare earth sintered magnet and the shield plate. the shield plate has a thin ring shape and is composed of a core portion and a boundary portion between the core portion and the cap; the core portion is made of a Cr-Ni stainless steel magnet having a two-phase structure of 60% or more martensite and 40% or less austenite, The boundary portion is composed of a molten and solidified portion by laser welding and a modified non-magnetic portion by the heat effect of laser welding, The depth of the molten solidification portion is the same as the thickness of the shield plate, The attraction surface of the magnetic structure including the molten solidified portion is smoothed, The keeper is made of Cr-based stainless steel and has a smoothed adsorption surface. It is characterized by having an adhesive force of 400gf or more.

[0021] Also, magnetic denture attachments are as follows: The magnet structure is characterized by being in the form of a thin plate having a diameter of 2.0 mm to 4.5 mm and a thickness of 0.3 mm to 0.8 mm.

[0022] Also, magnetic denture attachments are as follows: The composition of Cr-Ni stainless steel magnets is at least 18-20% Cr, 8%-10% Ni, and preferably 0.1%-3% Mo. The magnetic properties are characterized by a saturation magnetization of 12 kG or more, a coercive force of 50 Oe-200 Oe, and a residual magnetism of 6 kG or more.

[0023] Also, magnetic denture attachments are as follows: The cap has an attracted surface with a hardness of Hv200 or more, and the keeper has a thickness of 0.05 mm to 0.4 mm, a diameter of 2.0 mm to 4.5 mm, and a attracted surface with a hardness of Hv200 or more.

[0024] A manufacturing method of the magnetic structure according to the second embodiment is as follows. (1) First, in the manufacture of the three components that make up the magnet structure, the cap with a protrusion in the center of the hole made of Cr-based magnetic stainless steel, the rare earth sintered magnet made of a ring-shaped rare earth sintered magnet, and the shield plate, which is the base material for the ring-shaped stainless steel magnet shield plate, Step a) The cap is formed by punching and drawing a Cr-based magnetic stainless steel plate with a cold forging press to form a concave shape with a protrusion in the center of the hole, Step b) The shield plate is made of a Cr-Ni non-magnetic stainless steel as a base material, Cold working rate of 50% or more is added After inducing transformation of 60% or more of the austenite structure into martensite, the material is subjected to tension heat treatment and then machined into a ring shape. Step c) the rare earth sintered magnet is formed into a ring shape by drilling a hole with an inner diameter of 0.5 mm to 2 mm in the center of a disk-shaped magnet having a thickness of 0.2 mm to 0.49 mm and an outer diameter of 1.6 mm to 4 mm by electrical discharge machining, and then finishing the hole with a drill, and the inner and outer corners of the ring magnet are polished to form R-shaped portions; (2) Next, in assembling the magnetic structure consisting of the three components of the cap, the shield plate, and the rare earth sintered magnet, Step d) inserting the rare earth sintered magnet into the hole of the cap, covering it with the shield plate, and assembling the three parts; Step e) Laser welding the two joints between the cap and the shield plate. of The molten and solidified part formed during the welding process forms a micromagnetic part containing a small amount of δ ferrite, and the heat-affected part of the laser welding on the shield plate side forms a modified non-magnetic part. Step f) polishing the suction surface including the laser welded portion to make it smooth; (3) Then, in magnetizing the assembled magnetic structure, Step g) applying a magnetic field of 2 T to 4 T to magnetize the magnetic structure; The present invention is characterized by comprising the steps of:

[0025] The embodiment will be described in detail below with reference to FIGS. 5 to 7, 10 and 11. FIG. <Structure and function of magnetic denture attachments> As shown in Fig. 6, the magnetic denture attachment 1 is composed of a magnetic structure 1a and a keeper 1b. The magnetic structure 1a is disposed on the denture base and exerts a magnetic attraction force. On the other hand, the keeper 1b is made of a soft magnetic material and disposed on the abutment. The relationship between the two is such that an attracting surface 130 is provided on the magnetic structure 1a on the one hand, and an attracted surface 140 is provided on the keeper 1b on the other hand, and the attracting surface 130 and the attracted surface 140 are abutted against each other and are attracted to each other by the magnetic attraction force.

[0026] <Magnetic structure 1a> As shown in FIG. 6 and an enlarged view in FIG. 11, the magnetic structure 1a comprises a cap 11 made of Cr-based magnetic stainless steel, a rare earth sintered magnet 12, and a shield plate 13 made of a magnetized stainless steel magnet 132, a micromagnetic portion 131a which is a weld solidification portion, and a modified nonmagnetic portion 131b which is a heat-affected portion of the weld.

[0027] <Cap 11> Cap 11 is made of Cr-based magnetic stainless steel, as shown in Fig. 5. It is shaped like a cup (cylindrical) consisting of a small container with a circular shallow hole, with a cylinder 111 in the center of the bottom of the cup, a ring-shaped hole 11H on the outer periphery of cylinder 111, and a ring-shaped opening between the outer periphery of the cylinder and the inner periphery of the cup (hereinafter referred to as the predetermined shape). Furthermore, a flange of 0.1 mm to 0.2 mm may be attached to the side of the cap to prevent the magnetic structure from falling off the denture during use. The circular cap, the ring-shaped hole, the rare earth sintered magnet, and the shield plate may be elliptical, flat, or rectangular.

[0028] The magnetic properties of Cr-based magnetic stainless steel are a magnetic permeability of about 2000 and a saturation magnetic capacity Bs of about 116 kG. It is preferable to increase the magnetic permeability and saturation magnetic capacity by reducing the amount of Cr and Mo, within the range that does not impair corrosion resistance, and thereby improve the magnetic attraction force.

[0029] The Cr stainless steel cap is made by punching out a soft magnetic Cr stainless steel plate such as 18Cr stainless steel or 18Cr-2Mo stainless steel into a specified shape, and then drawing it to create a cylindrical container. It is preferable to use it as is, with a hardness of Hv200 or more. It is also possible to use it after heat treatment.

[0030] <Rare earth sintered magnet 12> The rare earth sintered magnet 12 is preferably a rare earth sintered magnet such as an Nd-Fe-B sintered magnet (Nd magnet). It is shaped like a thin ring plate with rounded corners. The outer shape is a disk-shaped magnet with a thickness of 0.2mm to 0.49mm and an outer diameter of 1.6mm to 4mm, and a hole with an inner diameter of 0.5mm to 2mm is drilled by electric discharge machining in the center of the magnet, and then the hole is finished by grinding and polishing with a drill, and the corners of the lower surface of the ring, i.e., the surface that comes into contact with the shield plate, are rounded to form a ring magnet. This is because it becomes easier to store the cap 11 in the hole portion 11H.

[0031] As shown in FIG. 11, the predetermined R shape of the ring magnet is a round shape that can secure a gap of 10 μm or more in the height direction of the rare earth sintered magnet 12 and 100 μm or more in the radial direction. The height direction of the rare earth sintered magnet 12 is set to 10 μm or more in consideration of a non-contact and constant gap between the upper end of the molten solidified portion 131a (molten portion) and the rare earth sintered magnet 12, and the radial direction of the rare earth sintered magnet 12 is set to 100 μm or more in consideration of the width of the molten solidified portion 131a (molten portion) and the modified nonmagnetic portion 131b (a portion affected by heat high enough to be modified). If the size of the rare earth sintered magnet 12 is reduced by increasing the gap, the adhesive force is reduced, so the upper limits of the gap are set to about 20 μm and about 200 μm, respectively. This makes it possible to prevent the adhesive force from being reduced due to the thermal effect on the rare earth sintered magnet 12 when forming the molten solidified portion 131a and the modified nonmagnetic portion 131b by laser welding.

[0032] For Nd magnets, the larger the maximum energy product, the better, with a BHmax of 40 to 55 MGOe. A BHmax of less than 40 MGOe will not provide sufficient magnetic attraction. The upper limit for a general-purpose Nd magnet is BHmax 55 MGOe. The coercive force should be 10 kOe to 20 kOe. If the coercive force is less than 10 kOe, sufficient magnetic attraction will not be obtained. If it is more than 20 kOe, the magnetic field strength required for magnetization will be too large, making magnetization difficult.

[0033] <Shield Plate 13> As shown in FIG. 7, the shield plate 13 has a thin ring shape and is made up of a core portion (132) and a boundary portion (131a+131b) between the core portion and a cap. The core portion is made of a Cr-Ni stainless steel magnet 132 having a two-phase structure of 60% or more of a martensite structure and 40% or less of an austenite structure.

[0034] The boundary portion (consisting of 131a and 131b) consists of two parts: a ring-shaped joint between the outer periphery of the ring-shaped core portion 132 and the inner periphery of the tip of the cap 11, and a ring-shaped joint between the inner periphery of the core portion 132 and the outer periphery of the tip of the cylinder 111 of the cap 11.

[0035] The boundary is formed by the junction of the Cr-based magnetic stainless steel of the cap 11 (two places at the inner periphery of the tip and the outer periphery of the cylinder 111) and the Cr-Ni-based stainless steel of the shield plate 131 (13a) which is made of a two-phase structure of 60% or more martensite and 40% or less austenite, which is melted and mixed by laser welding, and then cooled to form a molten solidified portion 131a made of a micromagnetic portion in which a small amount of δ ferrite has precipitated. Due to the influence of the large welding heat from this laser welding, the vicinity of the laser weld is transformed from a two-phase structure of 60% or more martensite and 40% or less austenite to a 100% austenite structure, and a modified nonmagnetic portion 131b which is nonmagnetic is formed.

[0036] The core portion 132 made of Cr-Ni stainless steel magnet protects the rare earth sintered magnet 12 from the corrosive environment, and also improves the attractive force by forming a composite magnet with the rare earth sintered magnet 12 (12+132). The Cr-Ni stainless steel magnet 132 is magnetized in the thickness direction, and its performance includes a saturation magnetization of 13 kG or more, a coercive force of 50 to 200 Oe, and a residual magnetism of 6 kG or more (Figure 8). In particular, the larger the residual magnetism, the greater the magnetic attractive force, so it is important to ensure that it is 6 kG or more. As a result, the Cr-Ni stainless steel magnet 132 forms a composite magnet together with the rare earth sintered magnet 12 housed in the hole 11H of the cap 11, achieving a large attractive force.

[0037] The molten and solidified portion is formed by laser welding the entire surface of the joint between the cap 11 and the shield plate 131, eliminating any gaps in the joint and protecting the rare earth sintered magnet 12 from saliva and other fluids in the mouth and from corrosion. Furthermore, since the depth of the molten and solidified portion is the same as the thickness of the shield plate, the bonding strength between the cap 11 and the shield plate 13 is sufficient.

[0038] The depth of the non-magnetic modified portion formed around the molten solidified portion is the same as the thickness of the shield plate, and the modified non-magnetic portion completely magnetically isolates the composite magnet (12+132) from the cap 11, preventing a decrease in the adsorptive force.

[0039] <Manufacturing method of stainless steel magnets> The manufacturing method for stainless steel magnets is to cold work a thin plate of Cr-Ni stainless steel in the austenitic phase to cause 50% or more of martensitic transformation, and then punch out the plate into a specified ring shape to produce shield plate 13a as shown in Figure 10. Alternatively, the manufacturing method is to cold work a thin plate of Cr-Ni stainless steel in the austenitic phase to cause 50% or more of martensitic transformation, drill a hole in the center of the bar, cut it, and punch out the shield plate into a specified ring shape as shown in Figure 10.

[0040] After the rare earth sintered magnet 12 is placed in the hole 11H of the cap 11, the shield plate 13a made of Cr-Ni stainless steel having a martensitic structure is fitted as a lid. Next, the joint between the outer periphery of the cylinder 111 of the cap 11 and the inner periphery of the ring of the shield plate 13a is laser welded, and then the joint between the inner periphery of the tip of the cap 11 and the outer periphery of the ring is laser welded. During these laser welding steps, the molten and solidified part of the joint melted by the laser heat becomes a micromagnetic part 131a, and the shield side around the molten and solidified part is thermally affected, and the heat-affected part of the shield plate 13a becomes austenitic due to phase transformation from martensite structure to nonmagnetic structure, forming modified nonmagnetic part 131b. The size of the molten solidified portion 131a is preferably 0.08 to 0.18 mm in width, and the depth is the same as the thickness of the shield plate, and is preferably 0.03 to 0.10 mm. The welded portion 131a is then polished to a flat surface, the unevenness of which is preferably 1 μm or less. In this way, the magnet structure is completed.

[0041] <Magnetization of magnetic structure> The coercive force of the rare earth sintered magnet 2 incorporated in the magnet structure 1, for example, an Nd magnet, is 10 kOe to 20 kOe. To magnetize this Nd magnet, it is necessary to apply a magnetic field of at least the coercive force or more. Applying a magnetic field that is too high is unnecessary and difficult in terms of equipment. Therefore, usually when the coercive force is 10 kOe, a magnetic field of 1.0 T to 3.0 T is applied. Since the coercive force iHc of the Nd magnet used for the magnet structure of the dental denture attachment is 10 kOe to 20 kOe, a magnetic field of 2 T to 4 T is sufficient for magnetization. However, due to equipment constraints, it should be 4 T or less. Therefore, for this structure, the shield plate 131 (excluding 131a and 131b) is also magnetized together with the Nd magnet in the thickness direction of the magnetic attachment with a magnetic force of 2 T to 4 T, and a composite magnet of the Nd magnet 12 and the stainless steel magnet 132 is used to obtain a predetermined adsorption force for the dental denture attachment.

[0042] <Keeper 1b> The keeper 1b is manufactured by punching a Cr-based soft magnetic stainless steel plate into a predetermined shape and size. In terms of size, the thickness is 0.05 mm to 0.4 mm, the diameter is 2.0 mm to 4.5 mm, and the adsorption area is the same as or slightly wider than the adsorption surface of the magnet structure, which is 1.7 to 24 mm 2 It is preferably set as such. As for the keeper, the upper surface, which is the adsorption surface with the magnet structure, is preferably smoothed by polishing so that the unevenness is 1 μm or less. The hardness of the keeper is preferably Hv200 or more in the cold forming state when used, and Hv200 or less when heat-treated.

[0043] <Size of the magnet structure 1a> The size of the magnet structure is in the shape of a thin plate with a diameter of 2.0 mm to 4.5 mm and a thickness of 0.3 mm to 1.0 mm. These dimensions and shapes are applicable to a bridge with a vital tooth as a abutment tooth.

[0044] <Cr-Ni-based stainless steel magnet> The characteristics of Cr-Ni stainless steel magnets include saturation magnetization of 13 kG or more, coercive force of 50 to 200 Oe, and residual magnetism of 6 kG or more. In particular, by increasing the residual magnetism to 6 kG or more, the magnetic attraction force (adsorption force) can be made stronger.

[0045] <Hardness of Goalkeeper 1b> The hardness of the keeper is increased by cold forming to Hv200 or more to improve wear resistance. It was confirmed that the attractive force does not decrease even when the magnetic permeability of the material is reduced from 2000 in the heat-treated state to about 200 by hardening it through cold forming. The reason for this is thought to be that the magnetic south and north poles of the attracting surface of the keeper are very close to each other and have a large demagnetizing factor, so even if the magnetic permeability of the material is reduced from 2000 to 200, the effective magnetic permeability does not change much, remaining at about 20. Alternatively, in the case of the magnetic structure of the present invention which employs a Cr-Ni stainless steel magnet, it is thought that the attractive force will not be affected even if the magnetomotive force increases and the magnetic resistance of the keeper portion increases slightly. EXAMPLES

[0046] [Example 1] The magnetic denture attachment and its manufacturing method according to the present invention will be described with reference to FIGS. 5, 6, 9 and 10. FIG. The magnetic denture attachment 1 in this example is composed of a magnetic structure 1a and a keeper 1b. The magnetic structure 1a comprises a ring-shaped rare earth sintered magnet 12, a cap 11 which is a container having a hole portion 11H with a protrusion in the center for housing it, and a ring-shaped shield plate 13 which serves as a lid for the recess opening of the cap 11.

[0047] The configuration of the magnet structure 1a will be described. The rare earth sintered magnet 12 is a Nd-based magnet with a BHmax of 52 MGOe, an Ms of 1.33 T, and a coercive force of 12 kOe. Its dimensions are 3.6 mm in diameter, 0.8 mm in inner diameter, and 0.35 mm in thickness, with R parts formed at the corners. The cap 11 is made of 18Cr-2Mo stainless steel, and has a magnetic permeability of 2000 Oe and a saturation magnetic flux density Bs of 16 kG. The cap 11 is cylindrical in shape, with a diameter of 4 mm and a height of 0.6 mm. The manufacturing method is to cold press a 0.2 mm thick 18Cr-2Mo stainless steel plate. The container has a diameter of 4 mm and a hole (hole portion 11H) of 0.4 mm in depth. The cylinder 111 in the center of the hole has a diameter of 0.8 mm and a height of 0.35 mm.

[0048] The shield plate 13 is a ring-shaped thin plate made of an 18Cr-8Ni stainless steel magnet 132. The 18Cr-8Ni stainless steel magnet 132 is magnetized in the thickness direction, and has a saturation magnetization of 13 kG or more, a coercive force of 50 to 200 Oe, and a residual magnetism of 6 kG or more.

[0049] The 18Cr-8Ni stainless steel magnet 132 forms a composite magnet together with the rare earth sintered magnet 12 housed in the cap 11, and realizes a large attractive force.

[0050] At the same time, the ring-shaped shield plate 13 is welded to the boundary with the cap 11, and the weld solidification zone 131a is slightly magnetic with a small amount of δ ferrite precipitated, while the heat-affected zone 131b is nonmagnetic. The weld zone 131 protects the rare earth sintered magnet 12 from saliva in the mouth and protects it from corrosion. Furthermore, the nonmagnetic part 131b of the shield plate 13 magnetically isolates the composite magnet (12 and 132) from the cap 12, preventing a decrease in the magnetic attraction force.

[0051] The rare earth sintered magnet 12 is placed in the hole 11H of the cap 11, and then a ring-shaped shield plate 13a is fitted to the opening of the recess in the cap 11, and the surface side of the joint between the Cr-based magnetic stainless steel cap 12 and the 18Cr-8Ni-based stainless steel shield plate is laser welded. At this time, the melted and solidified portion becomes a weakly magnetic portion 131a, which is modified to a modified non-magnetic portion 131b by the effect of heat. The width of the melted and solidified portion 131a is 0.15 mm, and the depth is 0.05 mm. The assembled magnetic structure was magnetized in a 3T magnetic field.

[0052] Next, the cap 11 was made of 18Cr-2Mo stainless steel, with a magnetic permeability of 2000 and a saturation magnetic flux density Bs of 16 kG. The keeper 1b was also made of 18Cr-2Mo stainless steel, with a magnetic permeability of 1000 and a hardness of Hv230. As a result, the attraction surface of the magnet structure is 12.5 mm 2 An adsorption force of 820 g was obtained.

[0053] [Example 2] In Example 1, the hardness of the cap is Hv270, and at the same time, the hardness of the keeper 1b is Hv270, the thickness is 0.10 mm, and the attraction area is 12.5 mm, the same as the attraction surface of the magnet structure. 2 Both the magnetic structure and the attraction surface of the keeper were smoothed by polishing to reduce the unevenness to 1 μm or less. As a result, an adhesive force of 820 g, the same as that of the magnetic denture attachment of Example 1, was obtained. [Industrial Applicability]

[0054] By using a Cr-Ni stainless steel magnet for the shield plate and a multiple rare earth sintered magnet, the present invention improves the adhesive force to over 400g and enables the thickness of the magnetic denture attachment to be reduced to 0.8mm or less. This makes it applicable to bridges that use pulp teeth as abutments, and is expected to see widespread use. [Explanation of symbols]

[0055] 1;Magnetic denture attachment 1a: Magnet structure 11; Cap 11H: Hole (for storing rare earth sintered magnets) 12: Rare earth sintered magnet 13; Shield plate (composite magnetic material) 13a; Shield plate 130;Adsorption surface 131; Shield plate 131a: Micromagnetic part made of molten solidified part 131b: Modified non-magnetic part consisting of heat-affected zone 131a+131b;Border 132: Cr-Ni stainless steel magnet (core) 1b; Goalkeeper 140;Adsorption surface 2. Magnetic denture attachment (conventional) 2a; Magnet structure 2b; Goalkeeper 3. Thin magnetic denture attachment (conventional) 3a; magnet structure 31; Cap 31H; Multiple holes 32; Multiple rare earth sintered magnets 33;Shield plate 330;Adsorption surface 3b; Goalkeeper 340;Adsorption surface 40: Magnetic denture attachment (conventional) 44;Magnetic attachment 45;keeper 50;Magnetic bridge 51;Magnetic attachment 52; pulped tooth

Claims

1. A magnetic denture attachment comprising a magnetic structure disposed on a denture and a keeper made of a soft magnetic material disposed on an abutment tooth, the magnetic structure and the keeper being configured to attract each other by self-attraction force 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 magnet structure includes a cap, a rare earth sintered magnet, and a shield plate; the cap is a disk-shaped cap made of Cr-based magnetic stainless steel, and has a cylinder in its center and a ring-shaped hole having an opening on the outer periphery of the cylinder; the rare earth sintered magnet is thin and ring-shaped, the inner and outer corners of the lower surface of the ring are rounded, and the magnet is housed in the hole of the cap; and a gap is formed between the corner portion of the rare earth sintered magnet and the shield plate due to the R-shape of the rare earth sintered magnet, the size of the gap being 10 μm or more in the height direction and 100 μm or more in the radial direction, the shield plate has a thin ring shape and is composed of a core portion and a boundary portion between the core portion and the cap; the core portion is made of a Cr-Ni stainless steel magnet having a two-phase structure of 60% or more martensite and 40% or less austenite, The boundary portion is composed of a molten and solidified portion by laser welding and a modified non-magnetic portion by the heat effect of laser welding, The depth of the molten solidification portion is the same as the thickness of the shield plate, The attraction surface of the magnetic structure including the molten solidified portion is smoothed, The keeper is made of Cr-based stainless steel and has a smoothed adsorption surface. A magnetic denture attachment characterized by having an adhesive force of 400 gf or more.

2. In claim 1, The magnetic structure is a thin plate having a diameter of 2.0 mm to 4.5 mm and a thickness of 0.3 mm to 0.8 mm.

3. In claim 1 or 2, The Cr-Ni stainless steel magnet has a composition containing at least 18-20% Cr and 8-10% Ni, and has magnetic properties including a saturation magnetization of 12 kG or more, a coercive force of 50 Oe to 200 Oe, and a residual magnetism of 6 kG or more.

4. In claim 1 or 2, The cap has a hardness of an adsorbed surface of Hv200 or more, The keeper has a thickness of 0.05 mm to 0.4 mm, a diameter of 2.0 mm to 4.5 mm, and a hardness of the attached surface of Hv200 or more.

5. A method for manufacturing a magnetic structure for a magnetic denture attachment, comprising the steps of: (1) First, in the manufacture of the three components constituting the magnet structure, a cap having a protrusion in the center of the hole made of Cr-based magnetic stainless steel, a ring-shaped rare earth sintered magnet, and a shield plate which is the base material of the ring-shaped stainless steel magnet shield plate, Step a) forming the cap into a concave shape having a protrusion at the center of the hole by punching and drawing a Cr-based magnetic stainless steel plate with a cold forging press; Step b) the shield plate is made of a Cr-Ni non-magnetic stainless steel as a base material, and is cold worked to a cold working rate of 50% or more to induce transformation of 60% or more of the austenite structure into martensite, and then is subjected to tension heat treatment, and is then machined into a ring shape; Step c) the rare earth sintered magnet is a disk-shaped magnet having a thickness of 0.2 mm to 0.49 mm and an outer diameter of 1.6 mm to 4 mm, the center of which is drilled by electric discharge machining to have an inner diameter of 0.5 mm to 2 mm, and then a finish hole is drilled using a drill, and the inner and outer corners of the rare earth sintered magnet are polished to form a ring shape consisting of R portions; (2) Next, in assembling the magnetic structure consisting of the three components of the cap, the shield plate, and the rare earth sintered magnet, Step d) inserting the rare earth sintered magnet into the hole of the cap, covering it with the shield plate, and assembling the three parts; Step e) The two joints between the cap and the shield plate are laser welded, and the molten solidified portion formed during the laser welding forms a micromagnetic portion containing a small amount of δ ferrite, and the heat-affected portion of the laser welding on the shield plate side forms a modified nonmagnetic portion; Step f) polishing the suction surface including the laser welded portion to make it smooth; (3) Then, in magnetizing the assembled magnetic structure, Step g) applying a magnetic field of 2 T to 4 T to magnetize the magnetic structure; 2. A method for manufacturing a magnetic structure comprising the steps of:

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