Magnetic denture attachment and method of manufacturing the magnetic structure

Abstract

To provide a thin magnetic attachment having a simple structure and easy manufacturing, with a thickness of 0.8 mm or less. [Solution] The hole portion of the magnetic stainless steel cap 11 is made ring-shaped, and a ring-shaped rare earth sintered magnet 12 is placed inside it. It is then covered with a ring-shaped shield plate made of 18Cr-8Ni stainless steel with a martensitic structure. The joint is laser welded to form a molten and solidified portion and a modified non-magnetic portion, and the magnet is then magnetized to achieve 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 manufactured using a 3D printer based on the digital data of a denture design, which is created by computerizing the dental alignment 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 the retention devices for digital dentures. Magnetic dentures include the magnetic dentures shown in FIG. 11 and the magnetic bridge shown in FIG.

[0003] As shown in Figure 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 in 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 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 fabricate a magnetic bridge for use in a crown bridge using a pulp-containing tooth as an abutment, the thickness of the magnetic denture attachment must be 1 mm or less. As shown in Figure 2, there is a drawback in that the adhesive force decreases significantly 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 several small magnets are placed on the bottom of the cap (Fig. 3) and a composite magnetic plate made of several stainless steel and non-magnetic parts is welded together (Fig. 4). However, the complex structure has drawbacks 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 (Figure 5) having a ring-shaped hole in the center, the thickness can be reduced by approximately two-thirds, from 1.5 mm to 1.0 mm. To form a magnetic circuit, the boundary between the cap and the shield plate must be made nonmagnetic. The present invention proposes inserting two nonmagnetic rings into the boundary. However, this complex structure, which requires fabricating two tiny nonmagnetic 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, presents challenges in terms of manufacturability and cost.

[0006] Furthermore, paragraph 0017 of the specification of Patent Document 4 states, "As an alternative method, the non-magnetic rings 20, 21 can be modified by modifying the magnetic material using a laser or other means. Therefore, they may be formed by irradiating the outer and inner gaps with a laser or other means after the magnet body 16 is covered with the cover yoke 19." However, both the cap and the shield plate are made of magnetic stainless steel with a 19Cr-2Mo-Ti composition, and the welded portion joining the two is also made of a magnetic material, and no technology is disclosed as to how to modify them to make them non-magnetic. This description can be said to merely point out a future possibility. Therefore, the invention of Patent Document 4 has difficulties in the manufacturing method and is considered to be impractical. In fact, the invention is merely an idea without any specific disclosure, and furthermore, it 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, thereby realizing 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. In addition, the manufacturing costs were high, making them difficult to commercialize. Furthermore, thin magnetic denture attachments also have thinner shield plates, and in order to ensure sufficient strength, the welding 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 to prevent this are necessary.

[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 simplifying the structure by eliminating the non-magnetic ring. However, while we considered using a shield plate made of a composite magnetic material consisting of a stainless steel magnet and a non-magnetic material, as disclosed in Figure 3 of Patent Document 5, it was extremely difficult to make a small portion of the inner periphery of the ring non-magnetic by finely adjusting the amount of heat. Therefore, we decided to simplify the structure by considering a method of using a shield plate made of only a stainless steel magnet, replacing the peripheral portion with a composite magnetic material that has been made non-magnetic. [Means for solving the problem]

[0012] After extensive research into the relationship between adhesive force and thickness, the inventors first incorporated a ring-shaped sintered rare earth magnet into a cap with a ring-shaped hole in the center (Figure 5), then enclosed the rare earth sintered magnet in a ring-shaped shield plate made of stainless steel, and then welded and joined the boundary between the shield plate and the hole in the cap. They discovered that there are conditions under which the area near the weld can be made nonmagnetic simply by laser welding. These conditions are: the penetration depth of the laser weld must match the thickness of the shield plate, ensuring maximum penetration and joint strength, while at the same time forming a nonmagnetic portion in the heat-affected zone around the solidified area using large amounts of laser welding heat. A gap must be provided between the magnet and the shield plate to prevent damage to the magnet from the laser heat. A prototype magnetic 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 4 mm diameter prototype was investigated. As a result, as shown in Fig. 8, it was confirmed that in the case of the round type, reducing the height to 0.6 mm reduces the adhesive force by as much as 40%, but in the case of the ring type, reducing the thickness to 0.6 mm only reduces the adhesive force by around 10%.

[0013] Secondly, when a Cr-Ni stainless steel magnet is used as the shield plate material, as shown in Figure 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] Third, 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 alone, but found that the thinner the magnet, the more likely it was to be machined due to breakage and chipping. Therefore, they devised a new method of roughly drilling holes using electric discharge machining, removing the heat-affected layer by grinding and polishing with a drill, while simultaneously improving hole precision, thereby enabling the machining of 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 on the shield plate side 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-attractive force caused by the 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 with 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 housed 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 formed 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 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 consists of a molten and solidified portion due to laser welding and a modified non-magnetic portion due to 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] 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 of a magnetic denture attachment, comprising: (1) First, the three components that make up the magnet structure are manufactured: 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. Step a) The cap is made by stamping and drawing a Cr-based magnetic stainless steel plate in a cold forging press to form a concave shape with a protrusion in the center of the hole. Process b) The shield plate is made from a Cr-Ni non-magnetic stainless steel bar as the base material, which is cold worked by 50% or more to induce transformation of 60% or more of the austenite structure into martensite, then 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, and subjected to martensite-induced transformation by cold working, followed by tension heat treatment, followed by punching 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 using electrical discharge machining, followed by finishing the hole with a drill, and the inner and outer corners of the ring magnet are polished to form a ring shape with rounded sections. (2) Next, the magnetic structure consisting of the cap, shield plate, and rare earth sintered magnet is assembled. Step d) Insert the rare earth sintered magnet into the hole in the cap, cover it with a shield plate, and assemble the three parts. Step e) Laser welding the two joints between the cap and the shield plate, and the molten and solidified portion formed during the laser welding forms a micromagnetic portion containing a trace amount of δ ferrite, and the heat-affected portion of the laser welding on the shield plate side forms a modified non-magnetic 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; The method for manufacturing a magnetic structure is characterized by comprising the steps of: [Effects 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 force. It is expected to be useful in the fabrication of removable magnetic crowns and bridges using pulp-containing teeth as abutment teeth. [Brief explanation of the drawings]

[0019] [Figure 1] 1A and 1B are diagrams showing the structure of a conventional magnetic denture attachment. [Figure 2] FIG. 1 is a diagram showing the relationship between magnetic attraction force and thickness of a conventional magnetic denture attachment. [Figure 3] FIG. 1 is a top view of a conventional thin magnetic denture attachment cap (four magnet type). [Figure 4]1 is a cross-sectional view of a conventional thin magnetic denture attachment. [Figure 5] 1A and 1B are diagrams showing the structure of a cap according to the present invention. [Figure 6] 1 is a diagram showing a cross-sectional structure of a magnetic structure according to the present invention; [Figure 7] 1A is a diagram showing a shield plate of the present invention from the bottom of a magnetic structure, and FIG. 1B is a cross-sectional view of the shield plate. [Figure 8] FIG. 10 is a diagram showing the relationship between thickness and adhesive force of the ring magnet of the present invention. [Figure 9] FIG. 1 is a diagram showing the relationship between residual magnetism and adsorptive force of a stainless steel magnet of the present invention. [Figure 10] 1 is a diagram showing a ring-shaped shield plate of the present invention. [Figure 11] 10 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] 10A-10C illustrate the use of magnetic denture attachments as retention devices. [Figure 13] This is a diagram showing the thinness of a magnetic denture attachment for a magnetic bridge using pulp-containing teeth as abutment teeth. BEST MODE FOR CARRYING OUT THE INVENTION

[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, wherein the magnetic structure and the keeper are configured to attract 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 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 thin and ring-shaped, with inner and outer corners of the lower surface of the ring being rounded, and is housed 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 formed 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 and solidified portion is smoothed, The keeper is made of Cr-based stainless steel, and its adsorption surface is smoothed. It is characterized by having an adsorption force of 400gf or more.

[0021] Also, magnetic denture attachments are as follows: The magnetic structure is characterized by being in the form of a thin plate with 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: Cr-Ni stainless steel magnets have a composition containing at least 18-20% Cr, 8-10% Ni, and preferably 0.1-3% Mo. Their magnetic properties include 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.

[0023] Also, magnetic denture attachments are as follows: The cap has a surface to be attached 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 surface to be attached with a hardness of Hv200 or more.

[0024] The 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, namely the cap with a protrusion in the center of the hole made of Cr-based magnetic stainless steel, the ring-shaped rare earth sintered magnet made of rare earth sintered magnet, and the shield plate that is the base material for the ring-shaped stainless steel magnet shield plate, Step a) The cap is made by stamping and drawing a Cr-based magnetic stainless steel plate with a cold forging press. The hole is formed in a concave shape with a protrusion in the center, Step b) The shield plate is made of Cr-Ni non-magnetic stainless steel as a base material, and is subjected to a cold treatment of 50% or more. After inducing transformation of 60% or more of the austenite structure to martensite, After heat treatment, it is machined into a ring shape, 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 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 polishing the inner and outer corners of the ring magnet to form a ring shape with rounded portions; (2) Next, in assembling the magnetic structure consisting of the three parts 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, and the molten and solidified portion formed during the laser welding forms a micromagnetic portion containing a trace amount of δ ferrite, and the heat-affected portion of the laser welding on the shield plate side forms a modified non-magnetic 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; The method 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 Figure 6, the magnetic denture attachment 1 is composed of a magnetic structure 1a and a keeper 1b. The magnetic structure 1a is placed on the denture base and exerts magnetic attraction. On the other hand, the keeper 1b is made of a soft magnetic material and placed on the abutment. The relationship between the two is such that the magnetic structure 1a is provided with an attracting surface 130, and the keeper 1b is provided with an attracted surface 140, and when the attracting surface 130 and the attracted surface 140 are brought into contact, they attract each other by magnetic attraction.

[0026] <Magnetic structure 1a> As shown in Figure 6 and the enlarged view in Figure 11, the magnetic structure 1a consists of 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 formed by a shield plate 131, a weakly magnetic portion 131a which is a weld solidification portion, and a modified non-magnetic 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 has a cup shape (cylindrical shape) 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, ring-shaped hole, rare earth sintered magnet, and 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 attractive force by reducing the amount of Cr and Mo, within the range that does not impair corrosion resistance, and thereby increasing the magnetic permeability and saturation magnetic capacity.

[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 predetermined 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 can also be used 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 0.2 mm to 0.49 mm and an outer diameter of 1.6 mm to 4 mm. A hole with an inner diameter of 0.5 mm to 2 mm 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 underside 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 the cap 11 can be easily accommodated in the hole portion 11H.

[0031] As shown in FIG. 11, the predetermined R-shape of the ring magnet is a rounded shape that ensures a gap of at least 10 μm in the height direction and at least 100 μm in the radial direction of the rare earth sintered magnet 12. The height direction of the rare earth sintered magnet 12 is set to at least 10 μm to ensure a certain gap between the upper end of the molten and solidified portion 131a (melted portion) and the rare earth sintered magnet 12, ensuring a non-contact and constant gap. The radial direction of the rare earth sintered magnet 12 is set to at least 100 μm to take into account the widths of the molten and solidified portion 131a (melted portion) and the modified nonmagnetic portion 131b (a zone highly heat-affected enough to be modified). Increasing the gap reduces the size of the rare earth sintered magnet 12, which reduces the adhesive force. Therefore, the upper limits of the gap are set to approximately 20 μm and 200 μm, respectively. This prevents a decrease in adhesive force due to the thermal effect on the rare earth sintered magnet 12 when forming the molten and solidified portion 131a and the modified nonmagnetic portion 131b by laser welding.

[0032] For Nd magnets, the higher 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 10 kOe or less, sufficient magnetic attraction will not be achieved. If it is 20 kOe or more, 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 the cap. The core portion is made of a Cr-Ni stainless steel magnet 132 having a two-phase structure of 60% or more martensite structure and 40% or less 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 at the tip of the cap 11, and a ring-shaped joint between the inner periphery of the core portion 132 and the outer periphery at the tip of the cylinder 111 of the cap 11.

[0035] The boundary is formed by laser welding the Cr-based magnetic stainless steel of the cap 11 (two locations: 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 consisting of 60% or more martensite and 40% or less austenite, and then cooling to form a molten solidified portion 131a consisting of a micromagnetic portion where a small amount of delta 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 consisting of 60% or more martensite and 40% or less austenite to a 100% austenite structure, forming a modified nonmagnetic portion 131b, which is nonmagnetic.

[0036] The core portion 132 made of a Cr-Ni stainless steel magnet protects the rare earth sintered magnet 12 from the corrosive environment, and the composite magnet (12+132) with the rare earth sintered magnet 12 can improve the adsorptive force. The Cr-Ni 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 (Figure 8). In particular, the greater 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, thereby achieving a large adsorptive force.

[0037] The molten and solidified portion is formed by laser welding the entire 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 in the mouth and other fluids, thereby preventing 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] <Method of manufacturing stainless steel magnets> The stainless steel magnet is manufactured by cold working a thin austenitic Cr-Ni stainless steel plate to cause 50% or more martensitic transformation, and then punching it into the specified ring shape to produce shield plate 13a, as shown in Figure 10. Alternatively, the austenitic Cr-Ni stainless steel bar is cold worked to cause 50% or more martensitic transformation, drilling a hole in the center of the bar, cutting it, and punching it into the specified ring shape to produce shield plate 13a, 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 with 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 portion of the joint melted by the laser heat becomes a weakly magnetic portion 131a, and the shield side around the molten and solidified portion is thermally affected, and the heat-affected portion of the shield plate 13a undergoes a phase transformation from martensite to austenite, becoming nonmagnetic, and forming a modified nonmagnetic portion 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, and the unevenness of the flat surface is preferably 1 μm or less. In this way, the magnetic structure is completed.

[0041] <Magnetization of magnetic structures> The coercive force of the rare earth sintered magnet 2 incorporated in the magnet structure 1, for example, a Nd magnet, is 10 kOe to 20 kOe. To magnetize this Nd magnet, it is necessary to apply at least a magnetic field equal to or greater than the coercive force, and 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 in the magnet structure of the dental prosthesis 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, a shield plate 131 (excluding 131a and 131b) is 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 prosthesis attachment.

[0042] <Keeper 1b> The keeper 1b is made 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, 1.7 to 24 mm 2 It is preferable to do so. As the keeper, the upper surface, which is the adsorption surface with the magnet structure, is preferably made smooth by polishing, and the unevenness is 1 μm or less. The hardness of the keeper is 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 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. In particular, by increasing the residual magnetism to 6 kG or more, the magnetic attractive 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, improving wear resistance. It was confirmed that the attractive force did not decrease even when the magnetic permeability of the material was reduced from 2000 in the heat-treated state to around 200 by hardening it through cold forming. The reason for this is thought to be that the south and north magnetic poles on the attracting surface of the keeper are very close to each other and the demagnetizing factor is large, so even if the magnetic permeability of the material is reduced from 2000 to 200, the effective permeability remains at around 20. Alternatively, in the case of the magnetic structure of the present invention which uses 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. [Example]

[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, and the magnetic structure 1a consists of a ring-shaped rare earth sintered magnet 12, a cap 11 which is a container having a hole 11H with a protrusion in the center to store 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 magnetic 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 rounded 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. It 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 achieves a large adsorptive 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 non-magnetic. The weld zone 131 protects the rare earth sintered magnet 12 from saliva in the mouth and other substances, protecting it from corrosion. Furthermore, the non-magnetic zone 131b of the shield plate 13 magnetically isolates the composite magnet (12 and 132) from the cap 12, preventing a decrease in 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 over the opening of the recess in the cap 11. The surface of the joint between the Cr-based magnetic stainless steel cap 12 and the 18Cr-8Ni-based stainless steel shield plate is laser welded. The melted and solidified portion becomes a weakly magnetic portion 131a, which is then thermally modified into a modified non-magnetic portion 131b. The width and depth of the melted and solidified portion 131a were 0.15 mm and 0.05 mm, respectively. 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 magnetic structure's attraction surface 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 magnetic structure. 2 Both the magnetic structure and the attracting surface of the keeper were polished to be smooth, with the degree of unevenness set to 1 μm or less. As a result, the same adhesive force of 820 g 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 reduces the thickness of the magnetic denture attachment to 0.8mm or less. This makes it applicable to bridges that use pulp-containing teeth as abutment teeth, and is expected to become more widely used. [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 consisting 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, wherein the magnetic structure and the keeper are configured to attract 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 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, with inner and outer corners of the lower surface of the ring being rounded, and 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 and solidified portion is smoothed, The keeper is made of Cr-based stainless steel, and its adsorption surface is smoothed. 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-like attachment 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 any one of claims 1 to 3, the cap has an adsorbed surface with a hardness 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 of a magnetic denture attachment, comprising: (1) First, in the manufacture of the three components that make up the magnet structure, 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 that is the base material for the ring-shaped stainless steel magnet shield plate, Step a) The cap is made by stamping and drawing a Cr-based magnetic stainless steel plate with a cold forging press. The hole is formed in a concave shape with a protrusion at the center thereof, Step b) the shield plate is made of a Cr-Ni non-magnetic stainless steel base material, and is subjected to cold working of 50% or more to induce transformation of 60% or more of the austenite structure into martensite, followed by tension heat treatment, and then formed into a ring shape by machining; 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 electrical 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 with rounded 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 in 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, and the molten and solidified portion formed during laser welding forms a micromagnetic portion containing a trace 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 weld 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; 1. A method for manufacturing a magnetic structure comprising the steps of:

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