Patent Application
20170086947
The present invention relates to orthodontic appliances for use in dental applications and, in particular, to pads for use with orthodontic brackets, orthodontic brackets having pads, and methods of making pads and orthodontic brackets.
Millions of dollars are spent each year to align teeth and/or correct malocclusions. In the field of orthodontics, techniques to correct such problems include attaching orthodontic appliances to the patient's teeth to straighten or correct their alignment relative to one other and to the patient's skeletal structure. To this end, orthodontic appliances, such as brackets, buccal tubes, and the like, are attached to the surfaces of the teeth to transmit corrective forces from an orthodontic archwire or other elastic devices to the teeth.
Of the available orthodontic appliances, clinicians often use orthodontic brackets to correct malocclusions. Typical orthodontic brackets may include a bracket body in which an archwire slot is provided to receive an archwire and may also include tie wings or other ligating structures integral with or secured to the bracket body for use in ligating the archwire to the bracket. Such bracket structure is generally provided with a tooth engaging structure with which the bracket is secured to the tooth surface.
Orthodontic appliances are typically secured to the patient's teeth with an adhesive. The adhesive is generally applied to a tooth, with the orthodontic appliance then being pressed onto the adhesive. Once cured, the adhesive creates a chemical and/or mechanical bond between the adhesive and the tooth and a chemical and/or mechanical bond with structure on the bracket. In a similar fashion, each of a plurality of orthodontic brackets is adhered to a tooth. The brackets may then be coupled together by an archwire to begin treatment.
In this regard, the tooth engaging structure on the bracket often includes a pad that may be either integrally formed with the bracket body or is formed as a separate sheet and then secured to the bracket body. The pad may define a bonding surface and may include specific features to facilitate an adhesive bond to the patient's tooth.
For instance, the bonding surface often includes structural elements, such as a mesh or other highly textured structure that includes undercuts, protrusions, or recesses or a combination of these features. The adhesive may flow in and around these features during affixation of the bracket to the tooth. Once the adhesive hardens or cures, the adhesive provides a mechanical or interlocking bond between the pad and the tooth. Such a bonding surface may be referred to as a “mechanical bonding base.”
In use, orthodontic brackets are subjected to a variety of forces in addition to forces exerted on brackets by archwires. More particularly, when objects, such as food, forcibly contact orthodontic brackets during chewing, the forces are conveyed by the bracket directly to the adhesive bond securing the bracket to the tooth. When the force exceeds the strength of the bond, the bond may fail catastrophically and the bracket may debond from the tooth. Often it is normal mastication that generates forces that debond the brackets from a patient's tooth.
A substantial percentage of brackets debond during treatment. Some studies show that the debond rate may be as high as 10%. With approximately two million orthodontic treatments being started each year in the United States, with each using typically twenty brackets per case, and with treatment lasting on the average about two years, a substantial number of failures (approximately forty million) may be expected to occur each year. Each orthodontist may therefore expect, on average, about four hundred bracket debonds per year. At a cost of $75 per debond, the lost time and money may be about $30,000 per year. Accordingly, bracket debond is a major loss of revenue for the orthodontist.
To address debonding, there have been attempts at toughening the bond between the appliance and the tooth. For example, uniform size particles have been used to provide a larger contact surface for bonding to the adhesive to generate a better bond. Wire meshes between the base portion of the bracket and points of attachment on the tooth have been developed. The wire mesh has a plurality of openings through which the adhesive passes to allow for a more reliable mechanical bond between the adhesive and the mesh. Still other structures include foils or plates having a photoetched surface, and a layer of mesh material diffusion bonded to the photoetched surface. The photoetched surface provides a secondary bond interlock, while the mesh provides a primary bond interlock, thereby increasing the strength of the bond between the bonding pad attached to a bracket and the tooth.
While prior art orthodontic appliances have improved bonding, such improvements are not without drawbacks. Strengthening the bond can have deleterious effects. With a stronger bond between the bracket and the tooth, the adhesive-interface may be significantly stronger. Debonding the bracket may tear a portion of the enamel from the tooth. As a result, a strong bond may make it difficult for a clinician to remove a bracket without damaging the tooth. Torn enamel not only causes pain to the patient, but also requires a repair which is both inconvenient and costly.
Consequently, there have also been attempts to develop orthodontic appliances designed to eliminate tooth enamel damage during debonding. This includes a flexible bonding pad or base for an orthodontic ceramic bracket. With this pad or base, the clinician applies a force, (i.e., with dental pliers) that buckles or flexes the pad and breaks the bond between the base and the adhesive. Removal of the bracket is therefore accomplished at forces substantially below forces sufficient to fracture the bracket or tear tooth enamel.
While there have been attempts to address debonding of brackets while eliminating damage to the patient's teeth there remains a need to provide a bonding pad, an orthodontic bracket, or other appliance for attachment to a tooth that does not debond during normal mastication but may be intentionally debonded without damaging the patient's teeth.
The present invention overcomes the foregoing and other shortcomings and drawbacks of orthodontic brackets heretofore known for use in orthodontic treatment. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention. In accordance with the principles of the present invention, a pad is provided for use with an orthodontic bracket that includes a porous superelastic metal structure. The porous superelastic metal structure is configured to receive an adhesive for bonding the orthodontic bracket to a tooth.
In one embodiment, the porous superelastic metal structure is a wafer and is impregnated with the adhesive prior to bonding the orthodontic bracket to the tooth.
In one embodiment, the orthodontic bracket includes a bracket body and the porous superelastic metal structure forms a bonding portion that is coupled to the bracket body and that defines a bonding surface. The bonding surface receives the adhesive.
In one embodiment, the porous superelastic metal structure defines a pore volume that is substantially uniformly distributed through the thickness of the bonding portion.
In one embodiment, the porous superelastic metal structure defines a pore volume in which a volume fraction of porosity at a location proximate the bracket body is different from a volume fraction of porosity at a location proximate the bonding surface.
In one embodiment, the pad further includes an attachment portion for attaching the bonding portion to the bracket body. The attachment portion is substantially solid. In one embodiment, the attachment portion is made of a metal that is different from the metal of the porous superelastic metal structure. In one embodiment, the attachment portion is made of a metal that differs from the metal of the bracket body.
In one embodiment, the bracket body and the porous superelastic metal structure are integrally formed.
According to one aspect of the present invention, in one embodiment, an orthodontic bracket includes a bracket body, and a pad extending from the bracket body and including a porous superelastic metal wafer. The wafer is impregnated with the adhesive prior to bonding the orthodontic bracket to the tooth.
In one embodiment, the bracket body and the pad are integrally formed.
In one embodiment, the porous superelastic metal structure forms a bonding portion that is coupled to the bracket body and defines a bonding surface that is configured to receive the adhesive.
In one embodiment, the pad further includes an attachment portion for attaching the bonding portion to the bracket body. The attachment portion is substantially solid.
According to one aspect of the present invention, a method for making a pad for an orthodontic bracket includes fabricating a porous superelastic metal structure for placement between the orthodontic bracket and a tooth. The porous superelastic metal structure is configured to receive an adhesive for bonding the porous superelastic metal structure to the tooth.
In one embodiment, the orthodontic bracket includes a bracket body and the porous superelastic metal structure forms a bonding portion. The method further includes fabricating an attachment portion that is to be coupled to the body portion and to the bracket body.
In one embodiment, fabricating the attachment portion includes closing off porosity on one side of the bonding portion by spraying molten metal or tack welding a sheet of metal to one side of the bonding portion.
In one embodiment, fabricating the porous superelastic metal structure includes producing a gradient in a volume fraction of porosity in the porous superelastic metal structure with the highest volume fraction of porosity at one surface.
In one embodiment, fabricating the porous superelastic metal structure includes mixing a nickel-containing powder and a titanium-containing powder, pressing the mixture to form a green body, and igniting a reaction between the nickel-containing powder and the titanium-containing powder in the green body.
In one embodiment, fabricating the porous superelastic metal structure includes mixing a powder of a superelastic metal and a powder of a polymeric binder, placing the mixture in a polymeric precursor foam, and sintering the superelastic metal particles.
In one embodiment, fabricating the porous superelastic metal structure includes vapor depositing a superelastic metal on a prefabricated carbon skeleton.
In one embodiment, fabricating the porous superelastic metal structure includes melting a composition from which the superelastic metal forms upon cooling, mixing a filler material in the melt, pouring the mixture of melted metal and filler into a mold, cooling the mixture, and removing the filler.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the brief description given above and the detailed description given below, serve to explain various aspects of the invention.
With reference now generally to
As is known, superelastic metals exhibit large elastic deformation (and recovery) when subjected to a threshold loading. This deformation absorbs energy. The layer of superelastic metal, even though at least partially porous, will absorb more energy from impact and other forces occasionally experienced during orthodontic treatment. Energy absorption in or around the pad 14 reduces the likelihood that forces on the bracket body 12 are transferred directly to the adhesive bond between the tooth (not shown) and the bracket 10. The bracket 10 is thus less likely to be broken loose from the tooth. By way of example, NiTi may act as a shock absorber. More specifically, NiTi may elastically strain near 6 to 8%. Thus, a pad of NiTi may deform significantly before the bond between the pad 14 and the tooth surface is significantly stressed by the external force.
Further, the strength of the bond between the orthodontic bracket 10 and the tooth may be in the range in which when the clinician intentionally debonds the orthodontic bracket 10 at the end of treatment, the patient's teeth are not damaged. Advantageously, dental assemblies according to the present invention may show improved bond strength.
To these and other ends and with reference to
With continued reference to
The orthodontic bracket 10, unless otherwise indicated, is described herein using a reference frame attached to a labial surface of an anterior tooth on the lower jaw. Consequently, as used herein, terms such as labial, lingual, mesial, distal, occlusal, and gingival used to describe bracket 10 are relative to the chosen reference frame. The embodiments of the invention, however, are not limited to the chosen reference frame and descriptive terms, as the orthodontic bracket 10 may be used on other teeth and in other orientations within the oral cavity. For example, the bracket 10 may also be coupled to the lingual surface of the tooth and be within the scope of the invention. Those of ordinary skill in the art will recognize that the descriptive terms used herein may not directly apply when there is a change in reference frame. Nevertheless, embodiments of the invention are intended to be independent of location and orientation within the oral cavity and the relative terms used to describe embodiments of the orthodontic bracket are to merely provide a clear description of the embodiments in the drawings. As such, the relative terms labial, lingual, mesial, distal, occlusal, and gingival are in no way limiting the invention to a particular location or orientation.
When mounted to the labial surface of a tooth (not shown) carried on the patient's lower jaw and with reference specifically to
In one embodiment shown in
The pad 14 has a bonding surface 40 that may be contoured to match the surface of the tooth and may define a peripheral surface or edge 42 that defines a bonding area. As is described below, in embodiments of the invention, at least a portion of the bonding surface 40 is defined by a bonding portion 44 that includes a porous superelastic metal structure having open pores that penetrate into the pad 14. Thus, when the orthodontic bracket 10 is adhesively secured to a tooth, the adhesive may cover the bonding area and extend beyond the edge 42 while penetrating into the pores of the porous superelastic metal structure. That is, the adhesive penetrates into the bonding portion 44. Once cured, the adhesive provides a mechanical interlock between the orthodontic bracket 10 and the tooth.
Further in this regard, the porosity extends into the pad 14 and may be referred to as apparent porosity in which the pores are open to the bonding surface 40 and so fluids, such as, an adhesive, may penetrate into the pores. Apparent porosity may be referred to as open porosity. By contrast, embodiments of the present invention may exclude closed porosity in which pores are closed off from, or not connected to, a surface though limited amounts of closed porosity may be tolerated. The porous structure may comprise a solid volume of superelastic metal with pores defining an open volume in the pad 14. It will be appreciated that the open porosity may be in any form but may include individual pockets that are isolated from one another by regions of metal. The pockets may not be isolated but may interconnect to form networks of channels within the pad 14. The porosity may be a combination of interconnected channels and isolated pores or pockets.
With reference to
In one embodiment, the pore volume 50 fraction may be constant throughout the pad 14. In this regard, the bonding portion 44 may include an evenly distributed ratio of solid volume 52 to pore volume 50 through the thickness of the pad 14. Other distributions and ratios are possible. For example, the pore volume 50 may not be evenly distributed through the porous structure 48. In one specific example, the pore volume 50 may be highest at regions proximate the bonding surface 40 and may then decrease in a direction toward the bracket body 12. In another example, the bonding portion 44 may include more than one layer of material. A layer of solid superelastic metal may be coupled to a porous layer of superelastic metal. In this way, the bonding portion 44 includes two discrete layers of metal that are bonded together. In this embodiment, there may be a boundary between the solid metal and the porous metal. This two-layered body may then be coupled to the bracket body 12 with the porous layer defining the bonding surface 40.
Rather than two discrete layers, in one embodiment and with reference to
Exemplary microstructures, including porosity, for the pad 14 are shown in
In an exemplary embodiment, individual pores of the pore volume 50 may have similar pore diameters as the pores of tooth enamel. By way of example and without limitation, the pore diameter may be about 5 μm. Moreover, the depth of the pore volume 50 from the bonding surface 40 may vary. In one embodiment, the pore volume 50 may extend to a depth of a few tens of microns up to a depth of about 250 μm. In view of the similarity between the porosity found in enamel and the porosity formed in the superelastic metal pad, it is believed that the bond strength with an appropriate adhesive will be around 40 MPa.
Furthermore, individual pores of the pore volume 50 may be generally aligned with each other. In an exemplary embodiment, the pores may generally be at a right angle to the tooth surface. In one embodiment, the pores may be generally aligned at a 45 degree angle to the tooth surface. This anisotropy in the microstructure may produce different degrees of performance (e.g., elastic modulus) in different directions to address debonding force.
As is described above, the pad 14 is at least partially made of a superelastic metal. By way of example only, not limitation, the superelastic metal may be a nickel-titanium (NiTi) based alloy, a copper-aluminum-manganese (CuAlMn) alloy, a copper-aluminum-beryllium (CuAlBe) alloy, or a copper-aluminum-nickel (CuAlNi) alloy, among others. As is described below, the superelastic metal may be fabricated to have anisotropic properties, particularly with regard to the distribution of the porosity.
In one embodiment, and with reference to
As one alternative, and with reference to
In one embodiment, and with reference to
In one embodiment, the pad 14 may be fabricated using the self-propagating high temperature synthesis process, also known as combustion synthesis. This process utilizes high reaction temperatures (e.g., 1200° C.) and short processing times (e.g., seconds to minutes) resulting in homogeneous alloys of desirable stoichiometry. In an exemplary embodiment in which superelastic metal is formed, fine, high-purity powders of nickel and titanium (for superelastic NiTi) may be mixed in an inert atmosphere at a low pre-heat temperature (e.g., 300° C. to 400° C.) and pressure (e.g., up to 200 MPa) to form a green (i.e., unsintered or unreacted) compact. The green compact may then be sintered by ignition of a self-propagating combustion reaction to produce a solid. A specified maximum pre-heat temperature may be chosen to initiate this reaction, which is highly exothermic.
By this process, the compact is ignited at one end. The reaction proceeds directionally toward the other end to form a solid. By way of example, the reaction equation for NiTi may be shown by Equation 1:
Ni+Ti→NiTi+67 kJ/mol
This reaction may be controlled by, for example, salts or reaction stoichiometry and may result in porous superelastic metal having a desired shape, such as the shape of the pad 14 or, alternatively, the bracket body 12. The pad 14 may include a solid volume of superelastic metal having an interconnected porosity of about 45% to about 65%. The percentage of porosity may depend on factors including compaction pressure and particle size distributions, to name only a few. The porosity may be in the form of isolated pockets or interconnected pockets that form channels. The pockets or channels may have cross sectional dimensions that measure up to 0.5 mm.
In an alternative embodiment, porous superelastic metal may be fabricated using hot isostatic pressing. In this process, for example, elemental powders of Ni and Ti may be pressurized at or near the melt temperatures (e.g., about 1310° C.), which drives the reaction and solidification of the alloy. The atmosphere is controlled due to the combination of high temperature and pressure used in the reaction. The pressure determines the degree of porosity in the pad. As with the embodiment involving combustion synthesis, this reaction may be controlled such that the resultant porous NiTi body has a desired shape.
In an alternative embodiment, superelastic powder may be fused and shaped into a porous body using spark plasma sintering. This process relies upon compression and electrical energy to sinter metallic particles into a solid body. In this regard, a pulsed current is induced through a die (e.g., made of graphite) to heat and drive necking (i.e., sintering) between particles. The quantity and type of porosity may be controlled by the temperature and pressure. In this regard, lower temperatures and pressures may result in increased porosity.
In another exemplary embodiment, a “burn out” process may be used to sinter superelastic metal powder into a porous body with a desired shape. For example, a mixture of NiTi powder and polymeric binder may be poured into a polymeric precursor foam. This loaded foam may then be heated to vaporize the binder and foam and to begin sintering the NiTi powder. The porosity may be generally controlled by the characteristics of the precursor foam. In an exemplary embodiment, the polymeric precursor foam may be shaped to create a porosity gradient (described above) in the pad 14.
Other methods of making porous superelastic metal include various deposition techniques. In one embodiment, for example, a porous NiTi body may be fabricated by depositing NiTi via chemical vapor deposition (CVD) or chemical vapor infiltration (CVI) on a prefabricated carbon skeleton. The carbon skeleton does not form a portion of the porous body. Instead, it is mechanically or chemically removed to leave the deposited NiTi body. In an exemplary embodiment, NiTi vapor may be deposited on a prefabricated carbon skeleton shaped to create a gradient in the porosity.
Other techniques may include traditional casting techniques involving pouring a melt of the superelastic metal over salt in a mold, which is later digested chemically, or by introducing gas to the poured melt to form porosity. In these exemplary embodiments, the porosity may be controlled based on the amount of gas or salt introduced.
In one embodiment, the pad 14 may have a uniform porosity through its thickness. A subsequent thermal spray process may be used to create a gradient in the porosity by capping open pores on one surface. For example, a porous body may be plasma sprayed with another metal (e.g., 316 stainless steel) on one side. The molten or liquid metal droplets fill in or cap a portion of the pore volume 50. Capping or filling in the pores on one surface may create a gradient in the pore volume 50 in the pad 14 by reducing or eliminating porosity on one surface. The degree of penetration of the droplets determines the gradient in the pore volume 50 and may result in a solid mixture of superelastic metal and the sprayed metal at one surface. By way of example, plasma spraying may result in a completely sealed (e.g., solid) side of the pad 14. More than one layer of superelastic metal having varying degrees of porosity may be bonded together to build a gradient of porosity in the bonding portion 44. It should be recognized that there may be other methods to create a gradient in a porous pad. As an alternative, a sheet of metal may be tack welded to one side of the bonding portion 44 to provide a platform by which the bonding portion 44 is attached to the bracket body 12.
Once fabricated as described herein, the pad 14 may then be attached to the bracket body 12, as shown in
With reference to
Whether the adhesive 56 is added manually by the clinician or is injected into the porous structure 48 prior to packaging, the amount of adhesive 56 may be sufficient to essentially fill all of or only a portion of the pore volume 50 of the pad 14. The superelastic metal may be hydrophilic and so advantageously promote the penetration of the adhesive 56 into the pore volume 50 of the bonding portion 44. The adhesive 56 may be photopolymerizable or another polymerizable compound known in the art.
In this regard, the composition contains a photoinitiator that upon irradiation with actinic radiation initiates the polymerization (or hardening) of the composition. Such photopolymerizable compositions can be free-radically polymerizable or cationically polymerizable. Suitable photopolymerizable components that can be used in the compositions as disclosed herein include, for example, epoxy resins (which contain cationically active epoxy groups), vinyl ether resins (which contain cationically active vinyl ether groups), ethylenically unsaturated compounds (which contain free-radically active unsaturated groups, e.g., acrylates and methacrylates), and combinations thereof. Also suitable are polymerizable materials that contain both a cationically active functional group and a free-radically active functional group in a single compound. Examples include epoxy-functional acrylates, epoxy-functional methacrylates, and combinations thereof.
In one embodiment, the porous structure 48 acts as a sponge to hold preloaded adhesive in a targeted location. During installation, the clinician may press the bracket 10 against the tooth. This slight manual pressure on the pad 14 may cause the porous structure 48 to elastically compress. During that compression, a thickness of the porous structure 48 is reduced. This may temporarily reduce the pore volume 50 and cause extrusion of the adhesive 56 from the bonding portion 44. The adhesive 56 may extend outwardly from the pad 14, as is shown in
In one embodiment, and with reference to
With reference now to
With continued reference to
In another aspect of the present invention, the pad 14 may act as a bioreservoir. In this regard, at least a portion of the pore volume 50 may house additives intended to improve the quality of the bonding of the bracket body 12 to the tooth. In an exemplary embodiment, anti-bacterial, anti-staining (cosmetic), bleaching, and/or re-mineralization agents may be incorporated into a dental sealant or resin. The pad 14 may then be impregnated by filling at least a portion of the pore volume 50 with the sealant (not shown). The bioactive agent may slow-release at an effective rate to an area adjacent the tooth surface. The location of the bioactive agents within the pad 14 may be chosen based on the area(s) adjacent the tooth that are most at risk (i.e., areas that are hygienically hindered).
In order to facilitate a more complete understanding of the embodiments of the invention, the following non-limiting example is provided.
A porous NiTi base was bonded to an Ormco Mini-Twin™ bracket. The assembled bracket and pad are shown in
The bracket including the porous NiTi pad was adhered to tooth enamel with a standard Ormco adhesive between a tooth and the pad. The bracket bonded to the tooth is shown in
While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in some detail, it is not the intention of the inventors to restrict or in any way limit the scope of the appended claims to such detail. Thus, additional advantages and modifications will readily appear to those of ordinary skill in the art. The various features of the invention may be used alone or in any combination depending on the needs and preferences of the user.
This application claims priority to U.S. Provisional Patent Application Ser. No. 62/232,079 filed Sep. 24, 2015, the disclosure of which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62232079 | Sep 2015 | US |
