Abstract:
An adhesive for bonding items includes magnetic particles dispersed therein. Removal is enhanced by applying varying magnetic fields near the adhesive. Magnetic locking elements are biased to engage a catch portion. Removal is effected by urging the magnetic elements out of the catch portion by application of magnetic fields of opposite polarity.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to methods, compounds and devices for adhering items together and more specifically, to adhesive and removal methods and apparatus for securing and removing secured items such that they are removed through the application of magnetic fields. 
     Throughout daily life, there are many occasions requiring that two or more items be secured to one another. For example, in the field of dentistry, there are several ways to permanently secure prosthodontics such that they maintain a proper spatial relationship to either part of an existing tooth or a dental implant. A more commonly employed technique involves the use of some form of dental cement placed between the tooth or implant and the prosthodontic device. Dental cement chemistry is a complex science and the actual method of “affixation” varies. In some types of dental cement, the cement flows into surfaces characterized by micro roughness on the items being cemented. These micro rough surfaces hold onto the cement once the cement has set, thus holding the items together. 
     While these cements allow for a firm bond, removing the cemented prosthodontics can be difficult, time consuming, and uncomfortable for both the patient and the dentist. Additionally, physical forces generated in conventional removal processes can damage the underlying tooth or implant. For this reason many affixed prosthodontic devices are infrequently removed for examination, except when dental problems arise. 
     In the field of prosthodontics, it has been known to employ magnets for securing items together. However, this use of magnetism has hereto been restricted to applications involving affixation between two prosthodontic devices such as an implant and a crown, bridge, or denture. One problem with prior magnetic affixation, typically using a magnet and a ferromagnetic material to which the magnet holds (or another magnet), is the lack of holding power to prevent relative movement between the affixed components. U.S. Pat. No. 4,693,686 (Sendax) incorporates pairs of magnets with one magnet positioned within an implant and the other magnet positioned within a prosthodontic device. The attractive forces between these magnets secure the prosthodontics. U.S. Pat. No. 4,214,366 (Laban), U.S. Pat. No. 5,788,493 (Tanaka et al), U.S. Pat. No. 5,678,998 (Honkura et al), U.S. Pat. No. 5,611,689 (Stemmann), and U.S. Pat. No. 4,997,372 (Shiner et al) all use variations in design of similar concepts. Other patents such as U.S. Pat. No. 5,636,990 (Stemmann), U.S. Pat. No. 5,254,006 (Yamada), and U.S. Pat. No. 5,013,243 (Tanaka et al) function in similar ways, but use the attractive forces between a single magnet and a ferromagnetic material to secure prosthodontic devices in position. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method, compound and apparatus for securing two items together and magnetically assisted separation of the secured items. An adhesive with magnetic particles therein is employed to secure two items together, and, should it be desired to separate the secured items, applied magnetic fields are used to assist in the removal or separation of the secured items. In this manner, the affixation strength of conventional methods is maintained yet removal is considerably simplified, with less potential for damage to the underlying structures of the secured items. 
     In a particular embodiment, the method, adhesive compound and apparatus are employed in the field of affixing prosthodontic devices by applying a layer of dental cement between the two surfaces of the mating devices. Accordingly, an embodiment of the invention comprises a cement that contains magnetic particles, suitably homogeneously interspersed within the cement. A feature of this embodiment is the ability of the cement to be broken up by the “shaking” of the magnetic particles in response to the application of an alternating electromagnetic field. 
     In another aspect of the invention, outwardly biased arms in a first portion engage corresponding catches in a second portion. The arms include magnetic portions thereon, whereby application of magnetic fields of proper polarity will urge the arms inwardly against the bias, and out of the catch portions, to enable separation of the first and second portions. However, in absense of the proper magnetic fields, the items are held together. 
     Accordingly, it is an object of the present invention to provide an improved adhesive for adhering items together. 
     It is a further object of the present invention to provide an improved an improved adhesive enabling easier separation of secured items when desired. 
     It is another object of the present invention to provide an improved adhesive for securing prosthodontic devices that enables easier removal. 
     Another object of the invention is to provide and improved apparatus for affixing prosthodontic devices together. 
     It is a further object of the present invention to rovide an improved apparatus and method for removing prosthodontic devices. 
     It is yet another object of the present invention to provide an improved magnetic apparatus and method that enables quick and simple separating of prosthodontic devices. 
     The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a magnified cross section of two items secured together by a magnetic adhesive according to the present invention; 
     FIG. 2 is an enlarged cross section of a magnetic adhesive removable bonding system according to the present invention, as applied to a prosthodontic device; 
     FIG. 3 is a cross sectional diagram of a locked spring loaded magnetic lock according to the present invention; 
     FIG. 4 is a cross sectional diagram of a disengaged spring loaded magnetic lock according to the present invention; 
     FIG. 5 is a cross sectional diagram of a locked spring loaded magnetic lock system according to the present invention, as applied to the field of prosthodontics; and 
     FIG. 6 is a cross sectional diagram of a disengaged spring loaded magnetic lock system of FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a schematic representation of a magnified cross section of two items  14  and  14 ′ that are to be secured together, a magnetic adhesive  10  is provided that includes plural magnetic particles  12  therewithin. Suitably, the magnetic particles are substantially homogeneously dispersed throughout the adhesive and are sufficiently small as to not substantially deteriorate the holding properties of the adhesive. The adhesive  10  is placed between surfaces of the two items  14  and  14 ′, and holds them together (once the adhesive cures). 
     The introduction of the magnetic particles  12  gives the magnetic adhesive  10  several desirable characteristics. For example, an improved removal method is thereby enabled to be employed. Referring still to FIG. 1, should it be desired to separate the items  14  and  14 ′, a magnetic field  16  is provided in close proximity to the magnetic adhesive. The magnetic particles  12  will try to align their polarities, as shown by the movement arrows  18 , with the polarities  20  of applied magnetic field  16 . The applied magnetic field  16  polarity  20  is then suitably continually alternated in a rapid sequence, wherein the magnetic particles  12  within the magnetic adhesive  10  will attempt to vibrate in response to the alternating field, assisting in breaking the bond of the magnetic adhesive  10  and enabling separation of the mating surfaces  14  and  14 ′. 
     While the adhesive in accordance with the present invention can be employed in many situations, preferred mbodiments of the present invention comprise adhesives, apparatus and methods for securing and removing prosthodontics. Accordingly, another embodiment of the invention is a of dental cement that contains substantially homogeneously interspersed magnetic particles  12  therein. 
     Having employed the inventive cement to attach a prosthodontic device, the removal method differs from the prior art. Referring to FIG. 2, a cross section of a magnetic adhesive removable bonding system according to the present invention, as applied to a prosthodontic device, a prosthodontic device, such as a crown  22 , is cemented into position on a base  23  (which may comprise an original tooth portion that has been reshaped to receive the crown, for example) using magnetic dental cement  24 . The dental cement  24  comprises plural magnetic particles  12  therein in accordance with the embodiment of cement  10  illustrated in FIG.  1 . The crown is thereby securely held in place. 
     However, if it should become necessary to remove the crown, an extraction tool  26  is provided, comprising first and second magnetic field generators  32  and  33 , suitably positioned on opposing sides of the crown. A vibrator  30  is optionally provided, and in the illustrated embodiment, is positioned at the top of the crown. An electrical source  28  is provided and drives the magnetic field generators, suitably to generate alternating magnetic fields. To accomplish removal of the crown, extraction tool  26  is placed near or clamped onto the prosthodontic device  22  such that magnetic field generators  32  and  33  are positioned on opposing sides of the crown and alternating electromagnetic fields are produced by operation of the electrical source  28  as applied to the magnetic field enerators. Then, in the case of employing optional ibrator  30 , the crown  22  is physically agitated by ibrator  30 . While the removal device is operating, a twisting motion is applied by the dentist. The alternating electromagnetic fields urge the magnetic particles to move back and forth within the cement and, coupled with the vibration and twisting, will encourage the magnetic dental cement  24  to break apart. 
     A specific example of the extraction tool  26  comprises a wishbone shaped device that attaches to the prosthodontics and vibrates while alternating the polarity of the magnetic fields. The elements can suitably be incorporated into dental pliers so that the dentist can simultaneously apply the alternating magnetic fields and grip and pull on the crown or other prosthodontic device. 
     This embodiment allows for easier removal of prosthodontics and is less likely to cause physical damage. The magnetic particles may also strengthen the cement in a manner similar to that of steel rebar in concrete. 
     Referring to FIG.  3  and FIG. 4, which comprise cross sectional diagrams of an engaged and disengaged spring loaded magnetic lock mechanism according to the present invention, spring loaded magnetic lock  46  comprises a fixed component  34  housing magnetic arms  40  within internal recesses  48 . Springs  42  are situated in the internal recess  48  between the innermost surfaces of the internal recesses  48  and the magnetic arms  40  so as to apply pressure forcing the magnetic arms  40  out of the internal recesses  48 . In the locked position as illustrated in FIG. 3, magnetic arms  40  are forced by the bias of springs  42  into recesses  38  of a removable component  36 . The shape of magnetic arms  40  conform and mate to the shape of recesses  38  of the removable component  36 , thus preventing any movement of removable component  36  with respect to fixed component  34 . 
     Referring to FIG. 4, in the unlocked or disengaged position, external magnets  44  are positioned in close proximity to magnetic arms  40  such that their nearest respective magnetic fields have identical polarities. The resultant repelling magnetic field forces magnetic arms  40  inwardly to recesses  48  and out of the recesses  38  of the removable component  36 , thereby freeing removable component  36  and enabling it to be separated from the fixed component  34 . 
     In the preferred version of this embodiment, the fixed component  34  and the removable component  36  are suitably fabricated of non-magnetic materials and the internal recesses  48  are provided, oriented approximately 180° apart. The magnetic arms  40  of the fixed component  34  are also oriented approximately 180° apart. 
     An application of the embodiment of FIGS. 3 and 4 pertains to an improved apparatus and method of affixing and removing prosthodontic devices wherein a spring loaded magnetic lock affixes the prosthodontic device and a magnetic field unlocks the device. Referring to FIG. 5, a cross sectional diagram of a locked spring loaded magnetic lock system according to the present invention, as applied to the field of prosthodontics, in the locked configuration, a prosthodontic device  50  fits over an inner prosthodontic device  47 , which is positioned within the mouth, and may comprise a dental implant, for example, and serves to anchor the mating crown, denture or bridge device  50  (hereinafter referred to as the outer prosthodontic device). The inner prosthodontic device  47  carries the fixed component portions of the spring loaded magnetic lock  46 ′. This inner prosthodontic device  47  may be aligned and attached to a tooth stub, tooth root or implant  52  using conventional dental methods. In the illustrated embodiment, a dental implant is screwed via threaded portion  53  into a tooth base  51 , surrounded by gum  21  The removable component  36 ′ is incorporated as the inner surface of the outer prosthodontic device  50 . In this embodiment, the outer faces  54  of magnetic arms  40 ′ and the body of the inner prosthodontic device  47  are tapered, narrowing from the end nearest the base point illustrated at  56 . The inner surface  58  of the removable prosthodontic device  36  is tapered with a slope matching that of the outer faces  54  of magnetic arms  40  and the body of the inner prosthodontic device  47 , allowing sufficient clearance for the outer prosthodontic device  50  to be slid over and attached to the inner prosthodontic device  47  without the use of magnets to repel magnetic arms  40 ′ back into recesses  38 ′. Once the outer device  50  is slid into position, the springs urge arms  40 ′ outwardly to engage with the recesses in the portion  36 ′. 
     FIG. 6 illustrates a cross sectional diagram of a disengaged spring loaded magnetic lock system according to the present invention, as applied to the field of prosthodontics. The operation of the spring loaded lock  46  is as previously described hereinabove in connection with FIGS. 3 and 4. Magnets  44 ′ are brought in close proximity to magnetic arms  40 ′ thereby magnetically urging the magnetic arms  40 ′ out of recesses  38 ′ and into recesses  48 ′, allowing a suitable clearance for removal of the outer prosthodontic device  50 . Easy removal is thereby enabled, while still provided a secure engagement between the base portion and the crown portion, until removal is desired. 
     Accordingly, this embodiment of the invention comprises a magnetic prosthodontics removal apparatus and method for affixing and removing a prosthodontic device that uses a spring loaded magnetic mechanical lock incorporated into a part of the inner prosthodontic device that remains in the mouth. The mechanical lock has magnetic arms that are normally forced outward by spring pressure such that the arms lock into detents in the outer mating prosthodontic device. The prosthodontic devices are then magnetically separated by forcing the magnetic arms of the locking device inward against the spring tension and out of the detents by the application of a magnetic field of the same polarity. This type of quick release is especially useful to allow for ease of dentist access for performing work on the underlying inner prosthodontic device or replacement of the outer prosthodontic device. 
     Although a number of embodiments described herein are directed towards use in dental applications, in a broader sense the magnetic locking device can be used in numerous other situations requiring mechanical locks. This style of magnetic lock is especially well suited to applications where a key is not desirable or where access to the lock is an issue. The magnetic particles can be interspersed in other cements, glues and adhesives for use of this system outside the field of dentistry. The breakup of bonds in such cements, glues or adhesives may be accomplished by the use of alternating electromagnetic field devices with or without an applied vibration. 
     While plural embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.