METAL TO CERAMIC ATTACHMENT IN DENTAL APPLIANCES

Abstract: This invention is directed to a method of attaching a metallic insert to a ceramic orthodontic or dental appliance by an attaching method selected from the group consisting of: (a) soldering with a low melting point solder having a melting point of less than about 500 DEG C, (b) adhering with an adhesive selected from the group consisting of an epoxy, an adhesive which includes 4-methacryloxyethyl trimellitate anhydride (4-META) and combinations thereof, (c) adhering with an adhesive wherein said insert comprises a reactive metal, (d) adhering with an adhesive after coating at least a portion of at least one of the insert and the appliance with a reactive metal or an oxide thereof, and (e) disposing amalgam between the insert and the appliance, and fitting the insert and the appliance together, with the amalgam disposed thereinbetween.

Description: METAL TO CERAMIC ATTACHMENT IN DENTAL APPLIANCES Field of the Invention This invention relates to orthodontic and dental appliances, and, more particularly, to methods of attaching a metallic insert to a ceramic orthodontic or dental appliance. Background of the Invention The use of ceramic in forming orthodontic and dental appliances is well known. Ceramics have been found particularly advantageous because of their aesthetic appeal relative to conventional metallic appliances. However, the physical properties or characteristics of ceramic materials may present several limitations when ceramics are used in orthodontic and dental appliances. For example, ceramic materials typically used are primarily based on aluminum oxide and zirconium oxide, both of which are harder than the metals generally used in orthodontic and dental appliances, and exhibit brittle fracture behavior. This characteristic renders ceramic appliances susceptible to fracture during treatment, which may compromise their function and effectiveness. In addition, the machining operations used to form such appliances typically leave the appliances with a relatively rough exterior surface. This roughness results in a significantly greater coefficient of friction between a ceramic appliance and an orthodontic wire compared with the coefficient of friction between a stainless steel appliance and an orthodontic wire. This increased coefficient of friction may compromise treatment efficiency by preventing the smooth sliding of wire along or through a particular appliance. Furthermore, because ceramic materials generally are harder than the metals used in orthodontic and dental appliances, and because of the surface roughness of ceramic appliances, such appliances tend to cause wear and erosion of the metallic wires which contact the ceramic material, thereby further reducing the efficiency of treatment by altering wire characteristics and dimensions. Various attempts have been made to minimize these limitations of ceramic materials in orthodontic and dental appliances by means such as rounding appliance corners, smoothing the archwire slot area in ceramic brackets, and coating the ceramic appliance with materials having a greater toughness. However, none of these approaches has met with commercial success. More recently, with respect to orthodontic brackets, n has been suggested to position a metallic archwire slot liner into the elongated channel of the bracket body, whereby a metallic orthodontic wire contacts the metallic liner as opposed to the ceramic body portion of the bracket. Specifically, in Reed et al. US Patent No. 5,358,402, it has been suggested that this metallic liner may be positioned in the orthodontic bracket either by brazing or by being formed in situ. With the Reed brazing process, a metal brazing material is dispensed into the elongated channel of the ceramic bracket body and a metallic archwire slot liner is inserted into the channel. After excess brazing material is wiped away, a rectangular mandrel is inserted into the liner to assist in maintaining the archwire slot configuration. The assembly of the bracket body, liner and mandrel is then placed in a furnace and heated to 850 * C in an argon atmosphere for twelve minutes to braze the liner to the ceramic liner before cooling. Alternatively, the bracket body, liner and brazing material may be placed in a furnace at 850 under vacuum for five minutes. Although the brazing process may serve to join the liner and bracket body, it has a significant drawback. The ceramic and metallic materials have very different thermal expansion and contraction properties; and because the brazing process requires such extremely high temperatures, the ceramic brackets may tend to develop microcracks as a consequence of the stresses which are created due to the differential thermal expansion/contraction between the metallic archwire slot liner and the ceramic bracket. These microcracks may ultimately lead to fracture of the ceramic appliance. Although the Reed in situ process may not require such severe temperatures, it has limitations of its own in that it requires the use of a metal injection molding machine and process once the ceramic bracket is formed, in order to inject molten metal powder under pressure through a channel in the mold assembly to form the liner. Accordingly, it would be desirable to have an alternative method for attaching a metallic insert to a ceramic orthodontic or dental appliance which does not require exposing the metallic insert and ceramic appliance to extremely high temperatures resulting in stressing and cracking of the appliance due to differential thermal expansion and contraction. It also would be beneficial to have a method which does not require the use of an additional metal injection molding process after having formed the ceramic appliance. Summarv of the Invention The subject matter of this application is related to that of co- pending Patent Application Serial No. , entitled "INSERT FOR REINFORCING AN ORTHODONTIC APPLIANCE AND METHOD OF MAKING SAME", filed simultaneously herewith. The specification of that co- pending application is incorporated herein by reference in its entirety. This invention is directed to a method of attaching a metallic insert to a ceramic orthodontic or dental appliance. One aspect of the invention includes soldering the metallic insert to the ceramic appliance with a low melting point solder having a melting point of less than about 500 "C. Preferably, this method further includes the step of coating at least a portion of at least one of the metallic insert and appliance with a doping material, for example titanium hydrate, prior to the soldering step. Another aspect of the inventive method includes adhering the metallic insert to the appliance with an epoxy, an adhesive including 4- methacryloxyethyl trimellitate anhydride (4-META) or a combination thereof. The method may further include the step of roughening at least a portion of the surface of the metallic insert prior to the adhering step. A further embodiment of the inventive method involves adhering the metallic insert to the orthodontic or dental appliance with an adhesive, with the metallic insert comprising a reactive metal. Preferably, the reactive metal is selected from the group consisting of titanium, aluminum, silicon, beryllium, zirconium, boron, tin, and combinations thereof This method preferably also includes the step of activating the reactive metal, for example by silanation, with the activating step performed before the adhering step. Yet a further embodiment of the method includes coating at least a portion of at least one of the metallic insert and ceramic appliance with a reactive metal or an oxide thereof, and adhering the metallic insert to the ceramic appliance with an adhesive after the coating step. The coating step itself may suitably be performed by a method such as plasma deposition, sputtering, ion beam implantation, chemical vapor deposition, physical vapor deposition, anodization or any combination including these methods. This method also preferably includes the step of activating the reactive metal or oxide thereof, for example by silanation, with the silanation preferably being performed after the coating step and before me adhering step. A further aspect of the inventive method of attaching a metallic insert to a ceramic orthodontic or dental appliance includes disposing an amalgam between the insert and the appliance, and fitting the insert and appliance together with the amalgam disposed therebetween. This inventive method offers several benefits and advantages over existing methods of attaching a metallic insert to an orthodontic or dental appliance. For example, several embodiments of the inventive method discussed above require little to no temperature elevation, thereby avoiding the differential thermal expansion/contraction and concurrent stressing and fracturing problems encountered with the prior art. In addition, the aspect of the invention involving soldering employs a low melting point solder, thereby also avoiding the severe differential thermal expansion/contraction problems found in the prior art brazing method. Also, the method does not require the step of injection molding once the appliance is formed. These and other benefits and advantages will become readily apparent to one of ordinary skill in the art upon reviewing the following detailed description of the invention. Detailed Description of the Invention As used herein, the term "orthodontic or dental appliance" refers to any device which may be adhered directly or indirectly to a tooth surface for the purpose of moving, aligning or fixing the positioning of a tooth or teeth. Non-limiting examples include brackets, buccal tubes and the like. The term "metallic insert" refers to a metallic item of any suitable shape and size which is spatially located on or in the appliance in any position which assists in reinforcing the appliance. In one aspect of the invention, the metallic insert may be attached to the ceramic orthodontic or dental appliance by soldering the insert to the appliance with a low melting point solder having a melting point of less than about 500 'C, and preferably, less than about 300° C. The use of such low melting point solders is highly advantageous, especially because one may avoid the severely elevated temperatures required in brazing, thereby avoiding the ceramic stressing and cracking due to differential thermal expansion and contraction of the different materials. Although any such low melting point solder may be used, suitable solders may include various combinations of metals such as gold, tin and/or gallium. One such low melting point solder includes about 80% gold by weight and about 20% tin by weight, and is commercially available from Wesgo of Belmont, California, under the trade name ATAU- 20SN. When a low melting point solder is used, it is preferred to coat the portions of the insert and appliance to be adhered with a doping material, for example titanium hydrate. A doping material improves the wetability of the insert and appliance surfaces, thereby assisting in forming a better adhesive bond between the solder, insert and appliance. Another aspect of the inventive method includes adhering the metallic insert to the ceramic orthodontic or dental appliance with a moisture- resistant adhesive, such as an epoxy or an adhesive including 4- methacryloxyethyl trimellitate anhydride (4-META). Epoxies and adhesives including 4-META may be used to advantage in attaching an insert to an appliance, especially where the metallic insert is made of a stainless steel, because, unlike many adhesives, these adhesives are capable of adhering not only to reactive metals, but to stainless steels as well. When an epoxy is used, the method preferably includes a step of roughening the portion of the surface of the metallic insert to be adhered to the ceramic appliance. In addition, because many epoxies tend to be relatively thin, it may be advantageous to add a thickener to the epoxy prior to applying the epoxy to the insert or appliance. The thickness of the epoxy may be suitably adjusted by adding fumed silica to the epoxy. It has been found particularly advantageous to add enough fumed silica to the epoxy to give the epoxy a consistency between that of water and a paste. 1 Such a consistency may be achieved with most epoxies by adding approximately 1-5 % fumed silica by weight, and preferably about 3 % fumed silica by weight. The epoxy may be suitably applied by putting the epoxy in a syringe with a fine tip, and subsequently applying the epoxy along the insert surface which is to be contacted with the appliance. The insert and appliance then may be joined together. Although the epoxy will cure at room temperature, the curing time may be accelerated by applying heat. For example, in attaching a metallic archwire slot liner to an archwire slot of a ceramic bracket, it has been found advantageous to place the joined insert and appliance in an oven at a temperature of about 50-60 'C for about one hour. Examples of suitable epoxies include EP30MED and UV10MED, available from Masterbond, Inc. , of Hackensack, New Jersey. In addition, if fumed silica is used to thicken the particular epoxy, fumed silica may be suitably obtained from Degussa of New Jersey, under the trade name AEROSIL R-972. An adhesive including 4-methacryloxyethyl trimellitate anhydride (4-META) also may be used advantageously in attaching a metallic insert to an orthodontic or dental appliance. 4-META is available from the Sun Medical Co. of Kyoto, Japan under the trade name 4-META. A further aspect of the inventive method includes adhering a metallic insert to a ceramic orthodontic or dental appliance with an adhesive, with the metallic insert comprising a reactive metal. Although the reactive metal may be any metal exhibiting reactive properties, preferably the reactive metal is titanium, aluminum, silicon, beryllium, zirconium, boron, tin or a combination thereof. Examples of suitable adhesives include: System One Plus Adhesives available from Ormco of Glendora, California; Transbond and Concise adhesives made by 3M of St. Paul, Minnesota; and adhesives available from Reliance Orthodontic Products, Inc. of Itasca, Illinois. The method preferably further includes the step of activating the reactive metal. The metallic insert may be suitably activated by silanating the reactive metal. Although the invention is not so limited, beneficial results have been achieved using a silanation solution formed with 3-gamma methacryloxypropyl trimethoxy silane. A suitable solution formed with this particular silane may include about 2 gm of the silane, about 84 gm of 99.7% isopropanol, about 8 gm of reagent grade acetic acid and about 7 gm of deionized water. If desired, the method also may include the step of actively reacting the reactive metal with a gas to form an oxide of the reactive metal on the surface of the metallic insert prior to the adhering step. If the metallic insert is exposed to an environment containing oxygen, the insert naturally will form an oxide of the reactive metal on the surface within a matter of seconds. However, if desired, the formation of this oxide may be achieved in an active method step by exposing the insert to a specific gaseous environment. Silanation generally will be used to activate the reactive metal of the metallic insert. However, if desired, in lieu of activating the metallic insert, the ceramic bracket itself may be activated by silanation. Alternatively, both the metallic insert and the ceramic appliance may be activated by silanation. If the ceramic appliance is to be silanated, and that appliance is formed of alumina, it is preferable to coat the ceramic bracket with silica prior to silanation. A further aspect of the invention includes coating at least a portion ' of at least one of the metallic insert and ceramic orthodontic or dental appliance with a reactive metal or an oxide of the reactive metal, and adhering the insert to the appliance with an adhesive after the coating step. In this particular embodiment, the metallic insert need not comprise a reactive metal. Regardless of the particular metal used, however, the embodiment includes coating at least a part of one of the surfaces to be joined with a reactive metal or an oxide of the reactive metal. The coating step preferably is performed by a method such as plasma deposition, sputtering, ion beam implantation, chemical vapor deposition, physical vapor deposition, anodization or the like. Also, the reactive metal preferably is titanium, aluminum, silicon, beryllium, zirconium, boron, tin or a combination thereof. Additionally, the method may include the step of actively reacting the reactive metal with a gas to form an oxide on the surface of the metallic insert. This embodiment also may involve the step of activating the reactive metal or metal oxide as discussed above, for example by silanation. If desired, this silanation step also may be used to activate the ceramic bracket itself. In yet a further aspect of the invention, the metallic insert is attached to the ceramic orthodontic or dental appliance by disposing an amalgam between the insert and the appliance, and fitting the insert and appliance together with the amalgam disposed therebetween. The amalgam may be any suitable dental or orthodontic amalgam, and typically will include metals such as mercury and silver. The method of attaching a metallic insert to a ceramic appliance discussed in the various embodiments presented above, is particularly advantageous over prior art methods. Because the inventive method is performed at ambient temperatures or at a relatively low soldering temperature, the method minimizes the effect and significance of the variation in thermal coefficients of the materials being attached. And by minimizing the effect and significance of this variation, the method minimizes the possibility of creating microcracks or other flaws in the ceramic structure, which otherwise would lead to fracture and ultimate failure of the appliance. While the invention has been described above with regard to several specific embodiments, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention is not limited to the specific details, methods and illustrative examples described herein and departures may be made from such details without departing from the spirit and scope of applicant ' s general inventive concept.

Claims: WHAT IS CLAIMED IS: 1. A method of attaching a metallic insert to a ceramic orthodontic or dental appliance, comprising the step of: attaching said metallic insert to said orthodontic or dental appliance by a method selected from the group consisting of: (a) soldering with a low melting point solder having a melting point of less than about 500°C, (b) adhering with an adhesive selected from the group consisting of an epoxy, an adhesive which includes 4-methacryloxyethyl trimellitate anhydride (4-META) and combinations thereof, (c) adhering with an adhesive, wherein said insert comprises a reactive metal, (d) adhering with an adhesive after coating at least a portion of at least one of said insert and said appliance with a reactive metal or an oxide thereof, and (e) disposing amalgam between said insert and said appliance, and fitting said insert and said appliance together, with said amalgam disposed therein between. 2. A method of attaching a metallic insert to a ceramic orthodontic or dental appliance, comprising the step of: soldering said metallic insert to said ceramic orthodontic or dental appliance with a low melting point solder having a melting point of less than about 500°C. 3. The method of claim 2 wherein said low melting point solder has a melting point of less than about 300°C. 4. The method of claim 2 wherein said low melting point solder includes a metal selected from the group consisting of gold, tin, gallium and combinations thereof. 5. The method of claim 2 wherein said low melting point solder includes gold and tin, said gold representing about 80% by weight and said tin representing about 20% by weight. 6. The method of claim 2 further comprising the step of coating at least a portion of at least one of said metallic insert and said ceramic orthodontic or dental appliance with a doping material prior to said soldering step. 7. The method of claim 6 wherein said doping material includes titanium hydrate. 8. A method of attaching a metallic insert to a ceramic orthodontic or dental appliance, comprising the step of: adhering said metallic insert to said ceramic orthodontic or dental appliance with an adhesive selected from the group consisting of an epoxy, an adhesive which includes 4-methacryloxyethyl trimellitate anhydride (4-META) and combinations thereof. 9. The method of claim 8 wherein said metallic insert comprises stainless steel. 10. The method of claim 8 further including the step of roughening at least a portion of the surface of said metallic insert prior to said adhering step. 11. The method of claim 8 further comprising the step of adding a thickener to said epoxy. 12. A method of attaching a metallic insert to a ceramic orthodontic or dental appliance, comprising the step of: Adhering said metallic insert to said ceramic orthodontic or dental appliance with an adhesive, said metallic insert comprising a reactive metal. 13. The method of claim 12 wherein said reactive metal is selected from the group consisting of titanium, aluminum, silicon, beryllium, zirconium, boron, tin and combinations thereof. 14. The method of claim 12 further comprising the step of reacting said reactive metal with a gas to form an oxide of said reactive metal on the surface of said metallic insert prior to said adhering step. 15. The method of claim 12 further comprising the step of activating said reactive metal. 16. The method of claim 15 wherein said activating step includes silanation. 17. The method of claim 16 wherein said silanation is performed before said adhering step. 18. A method of attaching a metallic insert to a ceramic orthodontic or dental appliance, comprising the steps of: coating at least a portion of at least one of said metallic insert and said ceramic orthodontic or dental appliance with a reactive metal or an oxide thereof; and adhering said metallic insert to said ceramic orthodontic or dental appliance with an adhesive after said coating step. 19. The method of claim 18 wherein said coating step is performed by a method selected from the group consisting of plasma deposition, sputtering, ion beam implantation, chemical vapor deposition, physical vapor deposition, anodization and combinations thereof. 20. The method of claim 18 wherein said reactive metal is selected from the group consisting of titanium, aluminum, silicon, beryllium, zirconium, boron, tin and combinations thereof. 21. The method of claim 18 further comprising the step of reacting said reactive metal with a gas to form an oxide of said reactive metal on the G surface or said metallic insert prior to said adhering step. 22. The method of claim 18 further comprising the step of activating said reactive metal or oxide thereof. 23. The method of claim 22 wherein said activating step includes silanation. 5 24. The method of claim 23 wherein said silanation is performed after said coating step and before said adhering step. 25. A method of attaching a metallic insert to a ceramic orthodontic or dental appliance, comprising the steps of: disposing amalgam between said metallic insert and said orthodontic or dental appliance; and fitting said metallic insert and said orthodontic or dental appliance together, with said amalgam disposed thereinbetween. 26. The method of claim 25 wherein said amalgam includes mercury and silver. 27. The orthodontic or dental appliance produced by the method of claim 1. 28. The orthodontic or dental appliance produced by the method of claim 2. 29. The orthodontic or dental appliance produced by the method of claim 8. 30. The orthodontic or dental appliance produced by the method of claim 12. 31. The orthodontic or dental appliance produced by the method of claim 18. 32. The orthodontic or dental appliance produced by the method of claim 25.

Inventors: FARZIN-NIA FARROKH, FARZIN-NIA, FARROKH
Applicants: ORMCO CORP, ORMCO CORPORATION
Application year: 1997
Main classification: C09J5
IPC codes: A61C7, A61K6, C09J4, C09J5, C09J163