Dental magnetic attachment and its fixing method including spacer

A dental magnetic attachment having good cushioning properties against a compressing pressure which makes a denture sink appropriately on biting. The dental magnetic attachment embedded in the denture base for holding the denture in the oral cavity by a magnetic attractive force working with the magnetic assembly and a soft magnetic keeper embedded in the top of the root surface includes a magnetic assembly and a cap covering the top of the magnetic assembly. The magnetic assembly has a hollow in the center of its top. The cap with a button is placed on the magnetic assembly, inserting the button into the hollow to contact to its bottom. On biting, the button is compressed, to be deformed with a shorter thickness and at this time a sleeve formed as a body around the core slides down along the side of the magnetic assembly to reduce the thickness of the dental magnetic attachment. This sliding makes the denture sink uniformly and appropriately. The dental magnetic attachment has good cushioning properties and offers a good feeling to a patient when biting with the denture.

TECHNICAL FIELD OF THE INVENTION
 The present invention relates to a dental magnetic attachment which is
 embedded in a denture to stabilize the denture on abutment teeth in the
 oral cavity using magnetic attractive force.
 DESCRIPTION OF THE PRIOR ART
 Up to the present, a dental magnetic attachment which strongly stabilize
 the denture on abutment teeth by magnetic attractive force is well known.
 Its force is acted between a magnetic assembly in a denture and a keeper
 made from a soft magnetic material embedded in a root cap.
 However conventional types of dental magnetic attachment have a week point
 to give damage to an abutment tooth with a keeper when they are applied to
 dentures. Each biting makes nearly equal pressure to any artificial teeth
 of the denture. In the case of free saddle denture shown as FIG. 22, the
 parts on the abutment tooth marked as A shows only small sinking depth of
 about 0.02 mm, on the other hand the parts on gingiva marked as B shows
 large scale sinking depth of about 0.2 mm. It means that the sinking depth
 of the part B is ten times larger than that of the part A. This difference
 about sinking depth between the part A and the part B concentrates the
 biting force on the abutment teeth. This concentration is apt to injure
 the abutment teeth. In some cases the difference makes denture to be
 leaned so that the denture is put out of the place.
 For solving this problem, Japanese Patent application Laid Open(KOKAI)
 No.7-246208 discloses a cushioned type of dental magnetic attachments
 shown in FIG. 23. That has a cap made of an elastic material which is
 attached to the top of the magnetic assembly by self curing adhesive. U.S.
 patent application Ser. No. 4,626,213 discloses another cushioned type of
 dental magnetic attachments shown in FIG. 24. That also has a cap made of
 an plastic material which covers the magnetic assembly with a circular
 side.
 The former patent describes that the magnetic attachment has a cushion
 ability to relief a biting force which is loaded to the denture by means
 of the elasticity of the cap. But shrinking of the cap toward the vertical
 direction is accompanied by extention of the cap toward the traverse
 direction due to the elastic property of the cap material which is
 expressed by the constant of Poisson ratio. Therefore when it is designed
 to get the considerably large shrinking, it must have large extension.
 This large extension makes large stress or gap between the side of the
 magnetic assembly and its periphery. This gap is apt to cause some trouble
 that something such as dregs of food is put into the gap and is rotten in
 it. This elastic motion makes separation or some gap between the magnetic
 assembly and the cap which are attached by self curing adhesive.
 On the contrary when the cap of this type is designed to make the traverse
 extension to be small, vertical shrinking inevitably comes to be small. In
 the case, enough vertical shrinking for practical use is not obtained.
 That is, there remains the large difference of sinking depth between the
 parts on the abutment teeth and the parts on gingiva, which makes the
 denture to be inclined and sometimes to be put out of the place.
 The latter patent describes that the magnetic attachment has a rotary
 ability which is given by the seesaw motion of the cap on the magnetic
 assembly. This motion is made by sliding the cap along the circular side
 of the magnetic assembly. The seesaw motion can solve the problem that
 denture is put out of the place due to leaning the denture But it does not
 show an enough cushion ability to the vertical pressure caused by biting
 force. Because its mechanics can make only small vertical motion between
 the magnetic assembly and the cap. When biting, the pressure is
 concentrated on the abutment teeth to injure them. So it is concluded that
 this type gives not enough solution on the drawback of conventional types
 of magnetic attachment, especially when it is applied to free saddle
 denture.
 THE PROBLEMS TO BE SOLVED BY THE INVENTION
 The first object of the invention is to provide a dental magnetic
 attachment which has a cushion cap for protecting the abutment toeth from
 harmful biting force and for keeping the denture firmly on the abutment
 teeth to be free from shaking or leaning. This cap makes enough sinking
 depth on biting so that there is no concentrration of the biting force on
 the abutment teeth. It is resulted that the denture is free from leaning
 so as to be kept firmly on the keeper embedded into the root cap. Moreover
 it is necessary that this cap is kept as a body with the magnetic
 assembly.
 The second object of the invention is to offer the method and instrument
 for fixing the magnetic assembly with the above mentioned cushion cap to
 the denture.
 When the vertical pressure is loaded on the magnetic attachment, he cap
 placed on the top of the magnetic assembly can slide along the side of the
 magnetic assembly in the vertical direction. If the maximum of the biting
 force is loaded, the cap can sink about 0.20 mm until the front of the
 sleeve reaches to the bottom surface of the magnetic assembly which is
 magnetically attached to the top surface of the keeper. If not loaded, the
 cap is placed on the beginning position. The mechanics which can slide the
 cap about 0.20 mm, needs a space of 0.20 mm in height around the magnetic
 assembly.
 The magnetic assembly with the cap is used to be embedd into the denture.
 As for the setting method, first it is placed in the hollow of the denture
 base made of resin and next is fixed by self curing adhesive. Here since
 controlling the volume of the adhesive at the optimum is difficult, it is
 popular that much volume of the resin more than necessity is used. If the
 volume of resin is less than necessity, enough adhesive strength can not
 be got. In this case, we would meet with a big problem that the magnetic
 assembly will drop out of the denture.
 From above reason, much resin more than necessity is used when the magnetic
 assembly is set. As there is the space around the magnetic assembly for
 sliding, the excess of the self curing adhesive is apt to fill up the
 space. It means that the space for sliding decreases or disappeares.
 The present invention offers the method how to fix the magnetic assembly
 with the cushion cap to the denture together with a spacer to keep the
 above mentioned space.
 SUMMARY OF THE INVENTION
 A dental magnetic attachment disclosed by the present invention is united
 with a magnetic assembly and a cushion cap. The dental magnetic attachment
 which is embedded into the denture retains the denture on the abutment
 teeth by the magnetic force acting between the magnetic assembly and the
 keeper placed on the teeth root. The characteristic of the present
 attachment is that the magnetic assembly is covered with a cap made of
 elastic material and the cap can slide in the vertical direction along the
 side of the magnetic assembly. The cap is designed to hp united with a
 core and a sleeve. The core is placed at the designated distance of about
 0.20 mm over the top of the magnetic assembly. When the biting force is
 loaded, the core is dislocated until touching to the top of the magnetic
 assembly. The sleeve formed around the core can slide down from the
 beginning position to the bottom of magnetic assembly on loading. However
 the sleeve is tightly fit to the magnetic assembly so as not to take off.
 The present attachment with the cushion cap has capability to sink until
 the core would touch to the top of the magnetic assembly due to the biting
 force on biting. Applying the present attachment to the denture, the
 cushion mechanics can make sinking at the parts on the abutment teeth as
 much as that at the parts on the gingiva when biting. Uniformly sinking is
 related that the denture is supported by the abutment teeth and the
 gingiva impartially. In other words the biting force on the denture is
 dispersed to gingiva in stead of concentrating on the abutment teeth, so
 that the abutment teeth is protected from too large biting force. This
 cushion mechanics also makes the seesaw motion of the cap on the contact
 point with the button of the cap and the top of the magnetic assembly as a
 fulcrum by sliding the sleeve along both left and right sides of the
 magnetic assembly in the opposite direction each other when biting.
 The seesaw motion makes the denture not to lean on the abutment teeth and
 prevent the magnetic attachment from lifting up over the keeper. From this
 mechanics, the denture is kept firmly on the gingiva. Moreover when the
 cap moves on each biting, the core of the cap is deformed, but the sleeve
 is not only sliding but also holding the cap tightly fit to the side of
 the magnetic assembly without deformation. The tight contact with them
 keeps the cap to be not removed from the magnetic assembly on each biting.
 A preferable structure of the present magnetic attachment is composed of a
 magnetic assembly which has a hollow on the center of the top surface and
 a cap which has a button on the inner surface of the core of the cap made
 of the elastic material, where the button is inserted in contact with the
 bottom of the hollow. The button offers better cushion property to the
 present magnetic attachment, because it can be elastically compressed more
 than the core. The pressure on biting is concentrated to this button, so
 that it shows large elastic deformation in the hollow. In other words, the
 superior cushion property is obtained by making a proper design of the
 button which is made to determin what kind of the elastic material and how
 size of a button dimension.
 Other merit of this preferable one is that the maximum deformation of the
 button which corresponds to the sinking depth or sliding distance of the
 cap against the magnetic assembly is restricted by the top surface of the
 magnetic assembly. The button cannot deform after reaching to the top
 surface of the magnetic assembly. Therefore the maximum deformation is
 controlled by the gap between the inner surface of the core and the top
 surface of the magnetic assembly on non-loading. The recommendable design
 aboout the gap is that the maximum deformation of the button induced by
 maximum pressure in biting is equal to the gap. This good designated gap
 is useful to prevent the cap from deforming too much in loading more than
 expectation. If not, the cap is damaged by too much deformation and self
 curing adhesive pasted with the cap and the denture base is broken.
 (The method for fixing to the denture)
 As for the method for fixing the present magnetic attachment to the
 denture, conventional method widely used in the dental field is done
 mostly according to that the attacnment is put on the keeper in the teeth
 root, then inserted into the hollow of the denture and after that it is
 fixed to it by self curing adhesive. But it is necessary for getting the
 cushion property to keep the space under the sleeve around the magnetic
 assembly. For keeping the space, a spacer used in the present attachment
 has an inner diameter same to the outer diameter of the magnetic assembly
 and it is inserted into around the magnetic assembly to be set under the
 front of the sleeve of the cap. The magnetic attachment united together
 with thee magnetic assembly ad the spacer is inserted into the hollow of
 the denture, then is fixed by self curing adhesive which cannot enter the
 space because of the spacer, and after that the spacer is removed to make
 the space for sliding. Briefly speaking, this fixing method is
 characterized by using the spacer.
 In the present method as above mentioned, the spacer prevents the excess of
 self curing adhesive existing in the gap between the cap and the denture's
 hollow from entering the space when the magnetic attachment is put into
 the hollow of the denture. The self curing adhesive cannot enter the space
 because the space under the front of the sleeve around the magnetic
 assembly is filled up by the spacer. When the spacer is removed from the
 denture after curing, there remains the space to make it possible to slide
 the cap along the side of the magnetic assembly even if there exists too
 much excess of the adhesive in the gap.
 Therefore the present method makes advantage that the magnetic attachment
 can be firmly fixed to the denture with easy and without fail. It also is
 possible that the space to be necessary for sinking the denture can be
 kept without taking too much care in the fixing procedure.
 There are other methods to make it possible to disappear the spacer. For
 example, there is a chemical method to dissolved it by saliva. But the
 recommendable method is to remove the spacer mechanically after curing.
 This mechanical removing after curing offers some advantages to be done in
 a moment and kept enough space for the denture to sink as much as
 designed.
 (The spacer for fixing to the denture)
 The spacer is used temporally for fixing the present magnetic attachment to
 the denture. The magnetic attachment consists of the magnetic assembly
 retained to the keeper on the abutment teeth by the magnetic force and the
 cap covers the top of the magnetic assembly to make sliding along the side
 of the magnetic assembly. The magnetic attachment with the spacer to be
 set at the position under the front of the sleeve of the cap is put in the
 hollow of the denture where self curing adhesive is filled partially.
 After the magnetic attachment is fixed to the denture by curing, the
 spacer is removed to make the space around the magnetic assembly. Through
 the above procedure, the spacer can offer the function to prevent the
 adhesive from entering the space. Even if there is much excess of the
 adhesive, the space is kept by the spacer.
 A ring shaped spacer is preferable or recommendable because the magnetic
 assembly and the cap are generally cylindrical in shape. The magnetic
 attachment is fixed to the denture in a body with the spacer which is
 attached to the outer side of the magnetic assembly at the position under
 the front of the sleeve. If all of the magnetic assembly, the cap and the
 spacer are axis symmetrical in shape, it is easy to assemble them into one
 with a high accuracy. It means that there is only a little gap between the
 front of sleeve and the top of the spacer, as well as almost no gap
 between the outer side of the disk shaped magnetic assembly and the inner
 side of the ring shaped spacer. It is natural that the too narrow gap
 makes it impossble for the adhesive to enter into the space. In other
 words, the spacer assures to make the space without fail. As a result, the
 space equalto the thickness of the spacer is made around the magnetic
 assembly when the spacer is removed after curing. This space makes it
 possible to slide down the sleeve of the cap along the outer side of the
 magnetic assembly. In the case that the denture may be pressed by less
 than 0.20 mm on biting, the space can make sure that parts of the denture
 on the abutment teeth makes as large sinking as parts on the gingiva does.
 Moreover a simple shape of the spacer is effective in making easily and
 with low cost the denture. As a matter of course there is no need for the
 spacer to make consideration on the up-side-down when using it.
 (Dental magnetic attachment)
 The dental magnetic attachment disclosed in the present invention is
 characterized by the structure of the cap.
 The cap is structured by three parts, that is, the core, the sleeve, and
 the button. The core is placed at the designated distance of about 0.20 mm
 over the top of the magnetic assembly. When the biting force is loaded,
 the core sinks until touching to the top of the magnetic assembly. Here it
 is important that the designated distance is proper for sinking of the
 denture.
 The button is put into the hollow on the top of the magnetic assembly to
 keep them contact at the bottom of the hollow. It supports the core over
 the top of the magnetic assembly. It is made of an elastic material and
 designed to get the proper cushion property. When biting, the pressure is
 concentrated on the button so that large deformation is made in the
 vertical direction. The button is deformed not only vertically but also
 horizontally according to the Poisson's ratio of the elastic material of
 the button by the pressure. In order to prevent the horizontal deformation
 from restriction of the periphery, a considerable gap between the top of
 the magnetic assembly and the cap is intended to remain.
 On the other hand, other parts of the cap are free from the pressure, in
 other words, free from deformation. It assures to keep good contact with
 these parts and surrounding because of making no stress in the surface
 with them. If not so, undesirable big stress works on the interface
 between the cap and the magnetic assembly or the cap and the denture base.
 In this case, it is difficult to hold tight contact of their interface.
 By the way, it is noted that there is a special case not to have the
 button, where too soft cushion ability is got.
 The sleeve can slide along the side of the magnetic assembly on loading.
 But it is so tightly fit to the side that the magnetic assembly does not
 take off from the denture in spite of sliding. For producing good tight
 force, the sleeve is made of elastic material having superior elastic
 property. To keep the tight force over a long time, it is important that
 the material has a good wear resistance.
 For making sure to join the cap with the magnetic assembly, it is better
 the the contact surface with the outer side of the magnetic assembly and
 the inner side of the sleeve of the cap become to be arched or tapered
 forward to the bottom of the magnetic assembly. If we try to remove the
 cap from the magnetic assembly, the arched or tapered contact surface
 cause strong resistance to prevent the cap from taking off.
 The attachment must be held in the denture base by self curing adhesive. Tn
 order to prevent the cap from removing, it is desirable that a flange is
 built on the outer side of the sleeve of the cap going to the outer
 direction. The flange can make inroads into the denture base like anchor
 so as to offer strong retention working between the attachment and the
 denture base.
 The cap is made of elastic material. Especially, it is preferable that the
 button is made of a kind of hard resin with a large elastic ratio because
 it shows large deformation under the given pressure. Examples of hard
 resin are polyvinyl acetal and silicon rubber.
 It is possible that the core and the sleeve is made of non-magnetic
 corrosion resistant materials regardless the button is made of hard resin.
 Here non-magnetic corrosion resistant materials for dental use are SUS316
 stainless steel, Ti alloy noble metal and so on.
 One of the reason to need corrosion resistance is that if the sleeve is
 corroded, the corrosion of sleeve makes the sliding face more roughly and
 sliding on the side of the magnetic assembly becomes more resistant. The
 other case to show more cushion property is that the button is made of
 soft resin and other parts is made of hard resin.
 A helper cushion can be inserted into the gap between the magnetic assembly
 and the cap. The effect of the helper cushion is to prevent some alien
 substance from entering the gap. The align substance exsiting in the gap
 makes damage to the cushion ability of the cap. If the helper cushion is
 made of foaming material such as foaming rubber and urethane foam, it
 shows no or little decrease of the cushion ability of the cap even if It
 can fill up the gap perfectly.
 In the case of filling up the gap partially, the helper cushion can be made
 of a kind of elastic material such as silicon rubber. It is useful in
 weakening impact which is concentrated on the button of the cap. Other
 effect is to make is easy for the cap to come back to its original
 position by the restorative power of the material. For this restorative
 power, the helper cushion is applied to the type of the magnetic
 attachment not to have both the button of the cap and the hollow placed on
 the top of the amgnetic assembly.
 The magnetic assembly of the present invention is characterized by the
 hollow on the top of it. Any structure for the magnetic assembly can be
 used for this invention. But in order to make a deep hollow, the magnetic
 assembly with a ring shaped magnet which is covered by a cap yoke
 preparing a projection at the center is advisable. The magnetic assembly
 has been described into details in Japanese Patent Application
 No.8-290775, i.e. Japanese Unexamined Patent Publication (KOKAI)
 No.10-127662. There are two reasons for the structure to offer a good
 cushion property. One is to make a deep hollow around the upper part of
 the projection of the cap yoke at the center with no effect on magnetic
 force. Because only a little magnetic flux flows around the upper side of
 the projection. A long button proportional to the depth of the hollow can
 be applied.
 Another reason is that the ring type can make a thickness of the magnetic
 assembly thinner than that of the cap type without decrease of the
 magnetic force working between the magnetic assembly and the keeper. As
 the total height of the magnetic attachment including the cap and the
 magnetic assembly must be kept less than a critical value requested from a
 view point of clinical application, it is important for getting good
 cushion property that the button of the cap become as thick as possible
 but the magnetic assembly become as thin as possible. It is seen that a
 thick cap or button takes advantage of getting a large elastic deformation
 and offering good cushion.
 As for magnet, it is desirable to use kinds of magnet which have high
 maximum energy product of more than 30 MGOe to get strong magnetic force.
 For example, they are Nd--Fe--B rare earth sintered magnet of more than 40
 MGOe and Sm--Co rare earth sintered magnet of more than 30 MGOe. But rare
 earth magnet is corrosive. In order to protect it against corrosion in the
 oral cavity, the magnet is covered by yokes made of a soft magnetic
 material and sealing cases made of non magnetic material. And the boundary
 lines between them are welded by laser to seal up magnet. By this way, the
 magnet used is perfectly sealed from saliva. Here it is natural that the
 soft magnetic material and the non magnetic material must have good
 corrosion resistance because they are directly exposed in the oral cavity.
 A soft magnetic stainless steel is recommended as yoke material which needs
 good soft magnetic property and high corrosion resistance.
 As above mentioned, the present magnetic attachment consists of the
 magnetic assembly having the hollow on the top face and the cap which is
 compromised from the core, the sleeve, the flange and the button. The
 cushion function of the present magnetic attachment makes advantages as
 follows. Reducing concentration of the pressuLe on the abutment teeth, the
 present magnetic attachment can hold the denture on the teeth root in
 stability not to damage the abutment teeth. It also can solve the problem
 that the denture get out of place because of reducing shaking or rolling
 motion of the denture on biting. Moreover It can use for a long term
 because of not only corrosion resistant materials used but also only a
 little stress loaded on biting. In other words, the pressure is not so
 concentrated on the button to make not plastic deformation but only
 elastic deformation. And other parts are free from the stress.
 (The method and the spacer for fixing the present magnetic attachment to
 the denture base)
 There are two important requirements on the method and the spacer for
 fixing the present magnetic attachment to the denture base. One is that
 the sliding faces are free from a smudge of self-curing adhesive to be
 kept clean. Because the sleeve of the cap slides in contact with its inner
 face and the outer side of the magnetic attachment. Another is that the
 enough space is kept to make it possible to slide the front of the sleeve
 down. These requirements are satisfied with taking proper size in
 relationship with the spacer and the sleeve as follows.
 First point is that the top face of the spacer is in direct contact with
 the front of the sleeve so as to prevent self curing adhesive from
 entering the boundary.
 Second point is that the spacer is wider than the front of the sleeve. If
 not so, resin used for the denture base goes to the space made by the
 spacer from outer side and makes a resin overhang. This overhang obstructs
 the move of the front of the sleeve.
 Third point is that a thickness of the spacer is equal to the sliding
 distance. If the thickness is less than the sliding distance, the front of
 the sleeve makes contact to the keeper on the root cap and is compressed
 to cause undesirable deformation which separates the outer side of the
 sleeve from the denture base made of resin.

NAME OF THE T ACCORDING TO THE SIGN IN THE DRAWING
 1: denture
 11: artificial tooth
 12: denture base
 10: hollow of the denture base
 13: self curing adhesive
 2: dental magnetic attachment
 21, 21',21", 21A: magnetic assembly
 210: hollow of the magnetic assembly
 21a: contact surface
 21b: side of the magnetic assembly
 21c: top of the magnetic assembly
 24: ring shaped magnet
 24': disk shaped magnet
 25: cap yoke (made of the soft magnetic material)
 26: ring shaped bottom yoke(made of the soft magnetic material)
 26', 26", 26B: sealing ring made of the nonmagnetic material
 26A: disk shaped bottom yoke(made of the soft magnetic material)
 27: seat shaped magnet
 27': intermediate yoke
 27": outer yoke
 28: sealing case
 22, 22', 22", 22A, 22B: cap
 221: core
 222: sleeve
 223: button
 224: flange
 226, 226': cap cover made of hard resin
 227, 227': button made of soft resin button made of soft resin
 23: spacer for setting
 3: root cap
 31: post of the root cap,
 32, 32': keeper(made of the soft magnetic material)
 4: foam insert cushion
 4', 4": elastic insert cushion
 M: magnetic flux,
 T: abutment tooth
 F: gingiva
 S: space
 DESCRIPTION OF THE PREFFERED EMBODIMENTS
 Nine kinds of embodiments according to the present invention is described
 with reference to FIG. 1 to FIG. 24.
 First Embodiment
 (The construction of the first example of the magnetic attachment)
 The first example as shown in FIG. 4 is comprised with a magnetic assembly
 21, a keeper 3 and a cushion cap 22. The magnetic assembly is covered by
 the cap 22 on the top side of it and they are unified mechanically to one.
 They are put into the base 12 of the denture 1. The keeper 3 is put on the
 teeth root T. The magnetic assembly 2 and the keeper 3 is attracted with a
 magnetic force.
 Here the magnetic assembly 21 is compromised with a ring shaped magnet 24,
 a cap yoke 25 showing a complicated shape and a disk yoke 26. The magnet
 24 is surrounded by the cap yoke 25 and the disk yoke 26 in the manner
 that a hole of the magnet 24 is filled up by the cap yoke 25. They forms a
 magnetic circuit to connect the magnet 24 with the keeper 32 to make a
 strong attractive force. Here it is important to insulate the disk yoke 26
 from the cap yoke 25 magnetically. The inner sealing ring 26' and the
 outer sealing ring 26" are parts for magnetic insulation which prevent the
 disk yoke 26 from connecting magnetically with the cap yoke 25.
 As seen in FIG. 4 the contact surface 21a is divided to five concentric
 circles of bottom faces of five parts which is a center of the cap yoke
 25, a inner sealing ring 26', the disk yoke 26, a outer sealing ring 26"
 and the outside of the cap yoke 25 in turn from the inner side to the
 outer side. There is formed four contact boundaries of the center of the
 cap yoke 25 and the inner sealing ring 26', the inner sealing ring 26' and
 the disk yoke 26, the disk yoke 26 and the outer sealing ring 26", the
 outer sealing ring 26" and the outside of the cap yoke 25 which are welded
 by laser or electric beam respectively to have been in a body. The welded
 contact surface 21a can protect the ring shaped magnet 24 from saliva
 perfectly. This welded contact surface 21a also prevents the ring shaped
 magnet 24 from falling off from the magnetic assembly 21 when the magnetic
 assembly 21 is taken off the keeper 32. Because the magnet is firmly
 stored in the magnetic assembly 21 by means of welding.
 After welding, the welded contact surface 21a is polished to a flat surface
 like a mirror. As a result it can attach to the keeper 32 with no gap so
 as to create strong attractive force between the magnetic assembly 21 and
 the keeper 32 placed on the root cap 3. By the strong force, the denture 1
 can be held stably on the abutment teeth in the oral cavity
 The most advantage for the above mentioned magnetic assembly 21 is that it
 can furnish a deep hollow 210 on the top of the cap yoke 25 without the
 decrease of the magnetic attractive force because only a little magnetic
 flux flow around the center part of the top of the magnetic assembly 21c
 in this magnetic circuit using the ring shaped magnet 24.
 The cap 22 is made of a hard resin in a body which consists of a core 221
 and a sleeve 222 as two region. The core 221 is placed at the designated
 distance, for example about 0.20 mm, over the top of the magnetic assembly
 21. When the biting force is loaded, the core is dislocated until touching
 to the top of the magnetic assembly 21c. The sleeve 222 formed around the
 core is tightly fit to the side of the magnetic assembly 21b in the
 condition that it can slide but does not take off.
 The present magnetic attachment is an assembly with the cap 22 and the
 magnetic assembly 21. For assembling, the cap 22 is placed on the top of
 the magnetic assembly setting a button 223 into the hollow 210, and then
 is pressed under a given pressure to become one. The side of the magnetic
 assembly is shaped round. The middle part of the side has a maximum
 diameter and the upper part of side is tapered to become smaller in
 diameter going near the top. When pressed, the magnetic assembly 21 can be
 inserted easily into the cap 22. This round shaped side is favorable for
 inserting the magnetic assembly into the cap 22 under the given pressure,
 so that it is furnished in every examples.
 It is noted that the given pressure for inserting is set much larger than
 the magnetic attractive force working between the magnetic assembly and
 the keeper 32. Therefore when the magnetic assembly is taken apart from
 the keeper 32 by the same force to the magnetic attractive force, the
 magnetic assembly is not taken off from the cap 22.
 A preferable structure of the present magnetic attachment is composed of
 the magnetic assembly has a hollow on the center of the top surface. On
 the other hand the cap 22 has a button 223 on the inner surface of the
 core 221 which is inserted in contact with the bottom of the hollow. On
 non-loading, there remains a proper gap S between the top of the magnetic
 assembly 21a and the core 221. The button 223 is attached to the top of
 the magnetic assembly 21c in the condition that they are contact only at
 the center point of the bottom of the hollow 210 together and there are
 some space around the button 223, that is, between the button 223 and the
 hollow 210 except the center point. This space is enough large to allow
 the button 223 to deform in the horizontal direction when the button 223
 is compressed by the pressure in biting. On the other hand the cap 22 is
 not deformed in the horizontal direction. Because it is nearly free from
 the pressure. Most of the pressure is concentrated on the button 223.
 When the biting force is loaded, the sleeve 222 slides along the side of
 the magnetic assembly 21b and the core 221 approaches to the top of the
 magnetic assembly 21c through the space(S). But the space(S) is designed
 to be not less than the maximum distance for sinking of the denture, so
 the core 221 can go down at most until touching to the top of the magnetic
 assembly. In this manner, the cap 22 which is made of hard resin is free
 from the pressure so that it is not deformed in the horizontal direction
 as well as in the vertical direction.
 It means that the cap 22 can be kept good contact with a hollow10 of the
 denture base 12 by self curing resin as shown in FIG. 2, because no stress
 occurs on the interface with them.
 A flange 224 is built on the outer side of the sleeve 222 going to the
 outer direction. It can make inroads into the denture base 12 like anchor
 so that the attachment 2 is held firmly in the denture base 12. Even if
 separation is made partially on the interface with them, the anchor effect
 prevents the attachment 2 from taking off the denture base 12.
 It is seen in FIG. 5 and 6 that on biting, the biting pressure makes the
 cap 22 of the magnetic attachment 2 slide and approach to the magnetic
 assembly 21. So that the denture base 12 sinks into the gingiva(F). On the
 contrary, when the biting force is released, the elasticity of the
 gingiva(F) makes the righting moment for lifting up the denture 12. The
 moment makes the cap 22 to slide reversely along the magnetic assembly 21
 and to return back to the beginning position.
 As shown in FIG. 1, the side 21b of the magnetic assembly 21 is arched or
 tapered forward to the contact surface 21a. It is pressed against the
 inner side of the sleeve 222. Removing the cap 22 from the magnetic
 assembly 21, the arched or tapered contact surface causes a strong
 resistance to prevent the cap 22 from taking off.
 Here the magnetic assembly 21 is compromised with the ring shaped magnet
 24, the cap yoke 25, the disk yoke 26 and two sealing ring 26' 26". They
 forms a magnetic circuit to connect the magnet 24 with the keeper 32 in
 which two sealing ring insulate the disk yoke 26 from the cap yoke 25
 magnetically. The ring shaped magnet 24 is made of Nd--Fe--B rare earth
 sintered magnet of more than 40 MGOe. Both the cap yoke 25 and the disk
 yoke 26 are made of a soft magnetic stainless steel. Both the sealing
 rings 26',26" are made of a non magnetic stainless steel.
 The cap 22 is made of polyvinyl acetal resin or hard polyoxymethylene
 resin.
 Hereafter the effect of the first example is described. FIG. 4 shows a
 cross section of the denturel with the present magnetic attachment 2
 placed on an abutment tooth in a oral cavity. The denture 1 consists of
 plural artificial teeth 11, a denture base 12 and the present magnetic
 attachment 2 which is put in a hollow 10 of the denture base 12 and is
 cemented by a self curing resin. A flange 224 which is built on the outer
 side of the sleeve 224 going to the outer direction can prevents the
 attachment 2 from taking off the denture base 12. Because it makes inroads
 into the denture base like anchor. The cap 22 is assemblyd firmly with the
 magnetic attachment 21.
 The magnetic attachment 2 is attached to the keeper 32 bedded into the root
 cap 3 in the abutment toothT by the magnetic attractive force, so that the
 denture base 12 is kept in the oral cavity.
 On biting, the present magnetic attachment 2 shows a large shrinking due to
 the elastic deformation of the button 223 on which the biting force makes
 a concentration. In other words, the present magnetic attachment 2 put in
 the denture 1 has a superior cushion property.
 At this time, the cap 22 except the button 223 is hardly deformed, so as to
 give no cyclic mechanical stress to the contact surface with the cap 22
 and the magnetic assembly 21 as well as the cap 22 and the denture base
 12. As a result, these contacts shows good endurance. There is no trouble
 to take the magnetic assembly 21 off from the denture base 12 and to
 remove the cap 22 from the magnetic assembly 21.
 This cushion property of the present magnetic attachment 2 can absorb the
 cyclic pressure so as to prevent the denturel from shaking. Speaking in
 details, the shaking motion occurs by large difference of the displacement
 between the part on the abutment teeth and the part on the gingiva. This
 cushion property makes to sink the part on the abutment toothT by same
 degrees to the part on the gingiva so that a little difference of the
 displacement is made to prevent the denturel from shaking.
 The cap 22 can make seesaw motion or lean on the magnetic assembly 21
 within the limit of elastic deformation of the sleeve against the side 21b
 of the magnetic assembly 21. If it has a round shape, the angle of the
 lean or seesaw motion may become to be large. This property of the cap 22
 makes it possible to lean the denture base 12 to a given degree, with
 keeping the magnetic assembly contact on the keeper 32. Even if the
 denture lean under normal conditions there is no trouble that the denture
 1 remove from oral cavity.
 Summing up the above effect of the present magnetic attachment 2 is as
 follows. On biting, the denture 1 having the present magnetic attachment 2
 tends to sink uniformly on the abutment teeth(T) for the cushion property.
 Uniformly sinking makes no concentration of the pressure on the abutment
 teeth(T). It means that the abutment teeth(T)is kept to be in a good
 condition. This cushion property also restrains shaking of the denture 1
 on the abutment teeth(T). And it also can lean the denture 1 on the
 abutment teeth(T) keeping contact with the magnetic asembly 21 and the
 keeper 32. That is, it offers a merit to hold the denture 1 firmly in oral
 cavity due to the cushion property as well as the strong magnetic
 attractive force. Moreover, It is important that the magnetic attachment 2
 is made of corrosion resistant materials to get a long life in use
 (The method for fixing to the denture)
 The method for fixing the present magnetic attachment 2 to the denture 1
 consists of three steps named as setting step, fixing step and removing
 step in turn. The first setting step is for setting the present magnetic
 attachment 2 into the hollow 10 of the denture 1 shown in FIG. 2. The
 second fixing step is for fixing them by self curing adhesive and the
 third removing step is for removing a spacer 23.
 A spacer 23 for fixing the denture 1 which is a ring in shape is used
 temporally to keep the space under the sleeve around the magnetic
 assembly. It is assemblyd with the magnetic assembly 21 to be set under
 the sleeve 222 in FIG. 3. The magnetic attachment 2 together with the
 spacer 23 is inserted into the hollow 10 of the denturel, then fixed by
 self curing adhesive. At this time the spacer 23 prevent the self curing
 adhesive from entering the space.
 Briefly speaking, this method to fix the magnetic attachment 2 to the
 denture base 12 is characterized by using the spacer 23.
 The first step for setting the present magnetic attachment 2 into the
 hollow 10 of the denture 1 with self during adhesive is shown in FIG. 2.
 In FIG. 2 is shown the denture 1 which is comprised with the denture base
 12 made of resin (polymethylene methacrylate) and artificial teethll made
 of resin (polymethylene methacrylate). FIG. 2-1 shows the hollow 10 of the
 denture base 12. FIG. 2--2 shows that self curing adhesive 13 (acrylic
 resin)is varnished on an inner side of the hollow 10.
 FIG. 2-3 shows that the magnetic attachment 2 which is assemblyd with the
 spacer 23 is placed on the keeper 32 to be strongly attached together by
 the magnetic attractive force.
 Next is about the second step for fixing them by self curing adhesive. FIG.
 2-4 shows the magnetic attachment 2 fixed with the denture 1 by self
 curing resin. As soon as self curing resin is varnished, a dentist must
 insert the magnetic attachment 2 into the hollow 10 of the denture 1 in
 oral cavity. For a while the magnetic attachment 2 with the spacer 23 is
 fixed there by self curing adhesive. The spacer 23 is put at the position
 under the sleeve 222 around the magnetic assembly 21. After it is removed,
 the place becomes the space which makes it possible to slide the cap 22
 along the side 21b of the magnetic assembly. The spacer 23 fills up the
 space, so that it is effective for preventing the self curing adhesive
 from entering into the space. In other words, first a dentist continues to
 press the denture 1 in several minute in oral cavity of a patient. For a
 wile the self curing resin on the whole surface of the cap 22 become
 soldering or curing by itself. At last the magnetic attachment 2 is firmly
 fixed in the hollow 10 of the denture base 12.
 When there is the excess of the self curing adhesive, it is going out from
 the space with the cap and the hollow of the denture base. The spacer 23
 prevent the excess of the self curing adhesive from entering the space at
 the front of the sleeve. Even if there is too much excess of the adhesive,
 there remains the space to make it possible to slide the cap along the
 side of the magnetic assembly.
 Last, the third step for removing a spacer 23 is shown using FIG. 2-5.
 After the second step, the denturel is taken off from the oral cavity of
 the patient and then the spacer 23 is removed from the denture base 12
 with a pair of tweezers. After the sapcer 23 is removed, the space is made
 at the former position of the spacer 23. And an enough space for the
 sliding of the sleeve 222 is kept.
 Therefore the cap 22 can slide down along the side 21b of the magnetic
 assembly 21 by a distance equal to the thickness of the space and give a
 good cushion property to the denture having the present magnetic
 attachment 2. This cushion property offer advantages to protect the
 abutment teeth(T) from the harmful pressure and hold the denture 1 stable
 in oral cavity.
 (Effects of the fixing method of the First Embodiment)
 The above mentioned method is useful for making sure to fix the magnetic
 attachment 2 in the denture base 12 by enough volume of self curing
 adhesive. Moreover the method offers other advantages to keep the space
 needed for the chusion property on biting without a considerable training
 and a troublesome adjustment to remove excess of the adhesive.
 (Dimensions and materials of the spacer of the First Embodiment)
 The spacer has a inner diameter of 0.2 mm plus the outer diameter of the
 and a thickness nearly equal to the maximum stroke of sinking. That is,
 the denturel cannot sink more than the thickness of the spacer 23. The
 spacer is made of any material but a harmful one against a human body, and
 it is better that the material can take off easily from the self curing
 adhesive and it has a moderate hardness.
 The ring shaped spacer of an example, in a case of 3.9 mm in a outer
 diameter of the magnetic assembly 21 and 0.2 mm in the maximum depth of
 sinking, has a inner diameter of 4.1 mm, a outer diameter of 5.0 mm and a
 thickness of 0.2 mm, and it is made of aluminum.
 The ring shaped spacer of the second example, in a case of 3.4 mm in a
 outer diameter of the magnetic assembly 21 and 0.1 mm in the maximum depth
 of sinking, has a inner diameter of 3.6 mm, a outer diameter of 4.6 mm and
 a thickness of 0.1 mm, and it is made of SUS304 stainless steel.
 The ring shaped spacer of the third example, in a case of 4.4 mm in a outer
 diameter of the magnetic assembly 21 and 0.4 mm in the maximum depth of
 sinking, has a inner diameter of 4.6 mm, a outer diameter of 6.0 mm and a
 thickness of 0.4 mm, and it is made of hard rubber.
 (The first modified fixing method)
 There are some modified spacer to make it possible to disappear the spacer.
 If a proper material of the spacer 23 is used, it is possible to skip the
 third step for removing the spacer 23. Supposing the material is readily
 soluble or is sublimated in oral cavity without ill effects against a
 human body, the sacer 23 disappears by itself.
 (The second modified fixing method)
 If necessary, we can operate the fixing procedure outside oral cavity in
 stead of operating in oral cavity. The method is done with a procedure as
 follows.
 First, the model for the maxilla is maae through molding in the oral cavity
 of a patient. Next, the magnetic attachments are put on certain places of
 the model. Then, hollows 10 of the denture basel2 are made opposite to the
 places for setting the magnetic attachments. After that, the adhesive 13
 is varnished on the inner side of the hollow 10. As soon as possible, the
 denturel is placed on the model for the magnetic attachment 2 is fixed to
 the hollow of the denture. After curing, the denture takes off from the
 model. last, the spacer 23 is removed to make the space for the denturel
 to sink.
 The merits operating in the outside are that both dentists and technicians
 can operate it very easily, and a physical or mental pain of a patient
 decreases considerably. Of course, there is a demerit that molding
 procedure needs some time. In addition, the outside operating method is
 applied with a self curing adhesive 13 having a high curing temperature.
 (The third modified fixing method)
 There are some modified method that the self curing adhesive does not
 varnish on the hollows.
 For example, it is possible that the self curing adhesive 13 will be put on
 the top of the magnetic attachment which is set on the keeper 32. In this
 case, covering with the denture makes the adhesive 13 spread into the
 hollow 10 all over.
 For other example, the top of the cap 22 in the magnetic attachment is
 coated with the self curing adhesive 13, cooled in the refrigerator and so
 on. After it is inserted into the hollow 10 of the denture base 12, the
 self curing adhesive 13 is warmed to go into a liquid state. Then, the
 adhesive 13 which is a kind of therm setting resin, is cured to fix the
 magnetic attachment 2 to the denture 1.
 For special example, a mother resin is varnished either on the top of the
 cap 22 of the magnetic attachment 2 or on the inner surface of the hollow
 10 of the denture base 12. On the other surface, a cure accelerator is
 varnished. When the denture base 12 is placed on the magnetic attachment 2
 with the spacer 23, both resins are mixed to start curing.
 Three above modified method can offer same merits as the fixing method for
 the first example.
 (Other modified fixing method)
 This case is related to materials used.
 The artificial teethll can be made of resin and ceramics besides several
 kinds of resin. The denture base 12 can be made of metals such as
 titanium, which is not harmful against a human body except resin. For the
 self curing adhesive, self curing resin 13 except acryloyl and many kinds
 of thermal setting resin are useful.
 These materials can offer same merits as the fixing method for the first
 example.
 (Dimensions of the first example)
 For reference, FIG. 7 shows the detail dimensions of the first example.
 Almost dimensions of the parts can be picked up from this figure, since
 the present magnetic attachment is symmetrical with respect to the center
 axis.
 Second Embodiment
 FIG. 8 shows a cross section of the second example of the magnetic
 attachment in which a helper cushion 4 made of foaming material such as
 foaming rubber and urethane foam is inserted into the gap between the
 magnetic assembly 21 and the cap 22.
 The helper cushion makes the effect to prevent some alien substance from
 entering the gap without reducing the cushion property.
 Third Embodiment
 FIG. 9 shows a cross section of the third example same to the second
 example except the following points. One is that the helper cushion 4' is
 made of elastic rubber such as silicon rubber. The second point is that
 the gap between the magnetic assembly 21 and the cap 22 is filled up
 partially by the helper cushion 4'.
 The helper cushion makes the same effect to the second example and in
 addition, to reduce the impact by elastic compression when the cap 22
 collides against the top of the magnetic assembly 21.
 Fourth Embodiment
 FIG. 10 shows a cross section of the fourth example nearly equal to the
 third example except a thickness of the helper cushion 4". The helper
 cushion 4' is not directly contact to the cap 22 because of a smaller
 thickness than a height of the gap between the magnetic assembly 21 and
 the cap 22.
 The helper cushion 4" makes not only the effect same to the third example,
 but also an improved cushion property. That is, when this magnetic
 attachment 2 is deformed, the first stage of deformation goes smoothly
 through elastic deformation of the button 223 and at the last stage when
 the cap collides against the top of the magnetic assembly, the impact is
 reduced by an elastic compression of the helper cushion 4".
 Fifth Embodiment
 FIG. 11 shows a cross section of the fifth example of the magnetic
 attachment 2 in which a button 223 is made of a hard resin and other parts
 of the cap 22 including the sleeve 222 is made of a corrosion resistant
 non-magnetic material. Here the hard resin used is polyvynyl acetal, and
 the corrosion resistant non-magnetic material used is SUS316 stainless
 steel.
 The fifth example has the good property same to the first example and in
 addition, it has an improved cushion property through an improved elastic
 button 223.
 Sixth Embodiment
 As shown in FIG. 12, the sixth example of the magnetic attachment 2
 consists of a cap 22' covered the magnetic assembly 21' and a magnetic
 assembly 21' attached to a keeper 32 with an attractive magnetic force.
 The magnetic assembly 21' is compromised with a ring shaped magnet 24', a
 cap yoke 25' showing a symmetrical shape with respect to the center axis,
 a disk yoke 26A and a sealing ring 26B. The magnet 24 is surrounded by the
 cap yoke 25' and the disk yoke 26A. They forms a magnetic circuit to
 connect the magnet 24' with the keeper 32 to make a strong attractive
 force.
 Here it is important to insulate the disk yoke 26A from the cap yoke 25'
 magnetically. The sealing ring 26B is a part for magnetic insulation which
 prevent the disk yoke 26 from connecting magnetically with the cap yoke
 25. As seen in FIG. 12 the contact surface 21a is divided to three
 concentric circles of bottom faces of three parts which is the disk yoke
 26A, the sealing ring 26B and the cap yoke 25' in turn from the inner side
 to the outer side.
 There are both contact boundaries the sealing ring 26' with the cap yoke
 25' and the disk yoke 26A respectively which are welded by laser or
 electric beam to have been in a body. The welded contact surface 21a can
 perfectly protect the disk shaped magnet 24' which is corrosive from
 saliva.
 After welding, the welded contact surface 21a is polished to a flat surface
 like a mirror. As a result it can attach to the keeper 32 with no gap so
 as to create strong attractive force between the magnetic assembly 21' and
 the keeper 32 placed on the root cap 3. By the strong force, the denturel
 can be held stably on the abutment teeth(T) in the oral cavity as shown in
 FIG. 4.
 The cap 22 consists of a cap-cover 226 and a soft resin button 227. The
 cap-cover 226 is divided into a core 221 and a cap slleve 222. The soft
 resin button 227 is made of a soft POM(polyoxymethylene resin) which
 offers a good cushion property. On the contrary, the cap-cover 226 is made
 of a hard POM(polyoxymethylene resin).
 The soft resin button 227 is contact to both the cap-cover and the top of
 magnetic assembly. And it lifts up the cap-cover 226 at the designated
 distance (S) over the top 21C of the magnetic assembly 21'. The cap-cover
 226 is formed with a hard resin as a body wihch is comprised of the core
 221 and the cap-slleve 222. The sleeve 222 is tightly fit to the side 21b
 of the magnetic assembly 21' in the condition that it can slide but does
 not take off.
 The side 21b of the magnetic assembly 21 which is contact to the sleeve 222
 is arched or tapered forward to the contact surface 21a. The inner side of
 the sleeve 222 tighten the magnetic assembly 21' strongly. So removing the
 cap 22' from the magnetic assembly 21', the arched or tapered contact
 surface causes a strong resistance so as to prevent the cap 22 from taking
 off.
 The magnetic assembly 21' has a hollow 210 on the center of the top
 surface. On the other hand the cap 22 has the soft resin button 227 which
 is attached to the inner surface of the core 221 and at the same time in
 contact with the bottom of the hollow. On non-loading, there remains a
 proper gap(S) between the top of the magnetic assembly 21c and the core
 221.
 The soft resin button 227 is attached to the top of the magnetic assembly
 21c in the condition that they are contact only at the center point of the
 bottom of the hollow 210 together and there are some space around the
 button 223, that is, between the button 223 and the hollow 210 except the
 center point. This space is enough large to allow the soft resin button
 227 to deform in the horizontal direction when the soft resin button 227
 is compressed by the pressure in biting. On the other hand the cap 22 is
 not deformed in the horizontal direction. Because it is nearly free from
 the pressure. Most of the pressure is concentrated on the button 223.
 When the biting force is loaded, the sleeve 222 slides along the side of
 the magnetic assembly 21b and the core 221 approaches to the top of the
 magnetic assembly 21c through the space(S). But the space(S) is designed
 to be not less than the maximum distance for sinking of the denture, so
 the core 221 can go down at most until touching to the top of the magnetic
 assembly. In this manner, the cap 22' which is made of hard resin is free
 from the pressure so that it is not deformed in the horizontal direction
 as well as in the vertical direction. It means that the cap 22' can be
 kept good contact with a hollow 10 of the denture base 12 by self curing
 resin as shown in FIG. 2, because no stress occurs on the interface with
 them.
 A flange 224 is built on the outer side of the sleeve 222 of the cap 22'
 going to the outer direction. It can make inroads into the denture base 12
 like anchor so that the attachment 2 is held firmly in the denture base
 12. Even if separation is made partially on the interface with them, the
 anchor effect prevents the attachment 2 from taking off the denture base
 12.
 Summing up effects of the sixth example is as follows. The sixth example
 has not only the effect same to the first example but also an improved
 cushion property to deform softly against the pressure because the soft
 resin button 227 is made of a soft resin instead of a hard resin. In
 addition, the sixth example offers an possibility to be made more cheap
 than the first example because of the simple structure of the magnetic
 assembly 21'.
 Seventh Embodiment
 FIG. 13 shows a cross section of the seventh example same to the sixth
 example except that a length of the soft resin button 227 of the cap 22"
 is smaller than that of the sixth example. There is a small gap(S) between
 the hollow 210 of the magnetic assembly 21' and this half size one of the
 soft resin button 227 on non-loading.
 Therefore at just moment on loading as shown in FIG. 14, no repulsion force
 due to compression of the soft resin button 227 occurs. It means that the
 denturel is supported only by gingiva(T) even if the part is on the
 abutment teeth. In a very small while, the tip of the soft resin button
 227 is reached to the hollow 210 and after that, repulsion forces
 according to degrees of compression of the soft resin button 227 occur.
 When the maximum of the biting force is loaded, the cap can sink until the
 core 221 will reach to the top surface 21c of the magnetic assembly and
 both surfaces are fully contact as shown in FIG. 15.
 This half size one of the soft resin button 227 makes merits that if a
 biting force is more than a repulsion force of the gingiva, the magnetic
 attachments on the abutment teeth makes some repulsion force to protect
 the gingiva. If a biting force is less than a repulsion force of the
 gingiva, the denture sink uniformly to give a patient a good and soft
 feeling.
 Eighth Embodiment
 FIG. 16 shows a cross section of the eighth example same to the sixth
 example or the seventh example except that it has no soft resin button 227
 of the cap 22A. The cap 22A of the eighth example is comprised only of the
 cap-cover 226 made of a hard POM resin without the button 223.
 The eighth example has not only the effect same to the seventh example as
 shown in FIG. 17 and FIG. 18, but also offers an possibility to be made
 more cheap because the cap 22A is molded at one shot of a hard resin.
 Ninth Embodiment
 The ninth example is very different from those above examples in point of
 the structure of the magnetic assembly 21A shown in FIG. 19. The structure
 changes from a circular to a rectangular in shape. As it is changed, the
 cap 22B is like a rectangular in shape which is not symmetrical with
 respect to the center axis as shown in FIG. 20. But the others of the cap
 22B is same to the cap 22' of the sixth examples. In a similar situation
 the keeper 32' is like a rectangular in shape.
 As shown in FIG. 21, the magnetic assembly 21A exhibits a double sandwich
 structure which consists of an intermediate block-shaped yoke 27', a seat
 shaped magnets 27 and an outer yokes 27" in turn from a center to both
 sides. The magnet is made of a rare earth magnet and these yokes are made
 of a soft magnetic stainless steel. The intermediate block-shaped yoke 27'
 is put between two seat shaped magnets 27 of which same poles, for example
 north poles, are faced each other. A set of the yoke 27' and two magnets
 27 is put between two outer yokes 27", where the opposite face of two
 magnets 27 has same poles, for example south poles.
 Similarly, it is seen from FIG. 21 that the magnetic assembly 21A makes a
 magnetic circuit with the keeper 32' so that a strong attractive magnetic
 force can be got.
 For protecting magnets from corrosion, four faces of each magnet besides
 two contact faces with an intermediate yoke 27' and an outer yokes 27" is
 sealed by thin sealing cases 28 made of a non-magnetic stainless steel.
 Thin sealing cases 28 is laser-welded with both the intermediate yoke 27'
 and the outer yokes 27" so that two seat shaped magnets 27 is perfectly
 sealed. Here it is important to insulate the intermediate yoke 27' from
 the outer yokes 27" magnetically. So the thin sealing cases 28 are made of
 a non-magnetic stainless steel which prevents magnetic connection with
 them.
 For making sure to join the cap 22B with the magnetic assembly 21A, the
 side 21b of the magnetic assembly 21A is tapered forward to the contact
 surface 21a.
 The magnetic assembly 21' has a hollow 210 like a groove on the center of
 the top surface of the intermediate yoke 27. On the other hand a soft
 resin cushion button 227 of the cap 22 is contact with the bottom of the
 hollow in the condition that they are contact only at the center point of
 the bottom of the hollow 210. On non-loading as shown in FIG. 21, there
 remains a proper gap(S) between the top 21c of the magnetic assembly 21A
 and the core 221 of the cap 22B.
 The present example has same cushion mechanics so as to offer the cushion
 property same to that of the seventh example. The present example is fixed
 to the denture base by a similar fixing method same to that of the first
 example which is previously described in details. But the spacer is
 different from that of the first example. That is, it is like a
 rectangular in shape to be fit to the shape of the magnetic assembly 21A.
 However the spacer has the effect same to that of the first example.
 MODIFIED EXAMPLES
 It is possible to design some modified structures of the ninth example
 which show triple or more sandwich structures having several magnets and
 intermediate yokes 27', where two magnets 27 which is faced each other has
 same poles. In this modified structure each magnet is so small as to bring
 only a little magnetic flux from it. These small magnetic circuits are
 made in same number to the number of the magnets. These small magnetic
 circuits make it possible to reduce the height of the magnetic assembly.
 The more are magnets, the thinner becomes the height of the magnetic
 assembly. This modified structure offers a special merit to reduce the
 height of the magnetic assembly.
 ADVANTAGES OF THE PRESENT INVENTION
 The present magnetic attachment having a cushion property gives a good
 solution as follows to the first object mentioned previously.
 On biting, the denturel having the present magnetic attachment tends to
 sink uniformly on the abutment teeth for the cushion property. Uniformly
 sinking makes no concentration of the pressure on the abutment teeth. It
 means that the abutment teeth is kept to be in a good condition. This
 cushion property also restrains shaking of the denture 1 on the abutment
 teeth. And it also can lean the denture 1 on the abutment teeth keeping
 contact with the magnetic assembly and the keeper. That is, it offers a
 merit to hold the denturel firmly in oral cavity due to the cushion
 property as well as the strong magnetic attractive force. Also a solution
 to the second object mentioned previously is made as follows. The fixing
 method of the present invention is useful for making sure to fix the
 magnetic attachment in the denture base by enough volume of self curing
 adhesive. Moreover the method offers another advantage to keep the space
 needed for the chusion property on biting without a considerable training.