Patent Publication Number: US-2006008761-A1

Title: Dental appliances having separate performance and bonding regions

Description:
BACKGROUND OF THE INVENTION  
      1. The Field of the Invention  
      The present invention relates to dental appliances. More particularly, the present invention is directed to dental appliances having separate performance and bonding regions formed from different materials in order to improve both the performance of the dental appliance and the bond strength to bonding agents.  
      2. The Relevant Technology  
      In the field of dentistry, it is common for dental appliances to be attached to a substrate. For example, orthodontics is a specialized field of dentistry that involves the use of various dental appliances that rely on mechanical forces to urge poorly positioned, or crooked, teeth into correct alignment and orientation. One example is the use of orthodontic brackets, commonly referred to as “braces”, which are used in combination with one or more arch wires. Orthodontic brackets are small slotted bodies configured for direct attachment to a patient&#39;s teeth. Once the brackets are affixed to the patient&#39;s teeth, such as by means of glue, a curved arch wire is inserted into the slot of each bracket. The arch wire acts as a template or track to guide movement of the teeth into proper alignment. Orthodontic brackets can be self-ligating or non-self-ligating. Self-ligating brackets do not require the use of ligatures (i.e., tie wires or elastic bands) to fasten the arch wire to the bracket.  
      Another orthodontic device is a bite ramp, which can be used to correct deep bite. Bite ramps typically include a performance region and a ramp element. The performance region is configured to be attached directly to a patient&#39;s tooth. The ramp element extends from the performance region and contacts the teeth on the opposing dental arch. Ramp elements can be rigidly or flexibly attached to the performance region.  
      Dentistry also uses other dental appliances that need to be securely attached to dental substrates. For example, crowns, bridges and veneers need to be tightly bonded to the tooth to prevent the dental appliance from becoming dislodged therefrom.  
      In view of the foregoing, it would be an improvement in the art to provide dental appliances that are able to readily bond to adhesives and bonding agents use to bond dental appliances to dental substrates (e.g., teeth) without sacrificing desired performance aspects.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention is directed to dental appliances that include separate performance and bonding regions constructed using materials that may advantageously be selected to enhance both performance and bondability, respectively. The performance region advantageously comprises a material, or combination of materials, selected to enhance a desired performance property (e.g., strength, flexibility, bendability, durability, abrasion resistance, rigidity, other mechanical properties, color, shape, other aesthetic features, surface texture, smoothness, plaque resistance, and the like). The bonding region advantageously comprises a material, or combination of materials, selected to be compatible with bonding agents used to bond the dental appliance to a substrate (e.g., a tooth). The bonding region is not itself a bonding agent that bonds to a substrate independently of a separate bonding agent.  
      Examples of dental appliances according to the invention include, but are not limited to, orthodontic brackets, bite ramps, bands, crowns, bridges, and veneers. In a preferred embodiment, the material(s) comprising the bonding regions of such dental appliances will have substantially higher compatibility with bonding agents than the material(s) comprising the performance regions. Similarly, the material(s) within the performance region will preferably exhibit substantially better performance within the desired performance property than the material(s) within the bonding region.  
      Examples of materials that have been found to be especially compatible with bonding agents known in the art, and therefore suitable for use in making the bonding region, include, but are not limited to, less crystalline polyamides, methacrylates, acrylates, polycarbonates, metal oxides, ceramics, and combinations thereof. Examples of metal oxides that can be incorporated into the bonding region include, but are not limited to, alumina, silica, zirconia, and titanium dioxide. Examples of ceramics include metal oxides, metal carbides, and metal nitrides.  
      Examples of materials that have been found to exhibit desired properties within various performance properties include, but are not limited to, a wide variety of polymeric materials (including both thermoset and thermoplastic polymers), metals, metal alloys, ceramics, and combinations thereof. Examples of polymeric materials that can be included in the performance region include, but are not limited to, more crystalline polyamides, acetal polymers, urethanes, polyetherimides, polycarbonates, polysulphones, polyethersulphones, polyethylene terapthalate, polyethylene teraphthalate glycol, acrylics, polyarylether ketones, polyethylene, polypropylene, polyaramides, polyesters, polyarylamides, and combinations thereof. Examples of metals and metal alloys include, but are not limited to, stainless steel, stainless steel alloys, titanium, and nickel-titanium alloys. Examples of ceramics include metal oxides, metal carbides, and metal nitrides.  
      According to one embodiment, the performance and bonding regions may be constructed and situated such that only the bonding region forms a mounting surface that faces the substrate to which the dental appliance is to be bonded. In such cases, the bonding agent will primarily or solely contact the material(s) within the bonding region. According to another embodiment, the bonding region may only form part of the mounting surface facing the substrate to which the dental appliance is to be bonded.  
      The bonding region preferably comprises at least about 25% of the surface area of the mounting surface, more preferably at least about 50% of the mounting surface area, even more preferably at least about 75% of the mounting surface area, and most preferably at least about 90% of the mounting surface area. One of skill in the art may select the proportion of the mounting surface that comprises the bonding region in order to yield a dental appliance that has a desired balance between one or more desired performance properties and bondability to the bonding agent used to bond the dental appliance to a substrate.  
      In order to further improve the bond strength between the dental appliance and a substrate to which it is to be bonded, the mounting surface may include one or more of texture, undercuts, recesses, protrusions, or other mechanical features designed to enhance mechanical interlocking between the bonding agent and the mounting surface, in addition to the aforementioned chemical adhesion.  
      The materials used to form the performance and bonding regions can be formed and/or brought together using any desired process. For example, according to one embodiment, the materials used to form the performance and bonding regions can be co-molded and/or co-extruded together (e.g., using known 2-color molding processes). This process is especially suitable where two or more different polymeric materials or used to form different regions or segments of the dental appliance. In another embodiment, the performance and bonding regions can be formed separately and then joined together using known processes. In the case where a fired ceramic material and/or a molded or stamped metal is used in combination with a polymeric material, the ceramic material or metal will typically be formed or shaped in a separate process, followed by attachment of the polymeric material thereto.  
      According to one embodiment, the performance region of the dental appliance can be formed initially, followed by formation of the bonding region thereto, e.g., by overmolding, mechanical attachment, spraying, dipping, brushing, bonding, or a combination thereof. In the case where the bonding region comprises a polymeric material that is initially in a flowable state, the polymeric material is typically caused to solidify, e.g., by chemical, light or heat curing, cooling, and the like. This procedure may be used, for example, in the case where the performance region comprises a metal or ceramic that is formed using a high temperature molding or firing process and the bonding region comprises a polymeric material that would be destroyed during formation or molding of the ceramic or metal material. It may also be used in the case where a polymeric material used in the formation of the performance region is processed differently than a polymeric material used in the formation of the bonding region.  
      According to another embodiment, the bonding region can be formed initially, followed by formation of the performance region thereto, e.g., by overmolding or mechanical attachment. This procedure may be used, for example, in the case where the bonding region comprises a ceramic material and the performance region comprises a polymeric material or metal that would be destroyed or altered during formation of the ceramic material. It may also be used in the case where a polymeric material used in the formation of the bonding region is processed differently than a polymeric material used in the formation of the performance region.  
      The proportion or ratio between the performance region and bonding region can be selected to impart any desired balance between bondability, on the one hand, and desired performance properties, on the other. According to one embodiment, it may be desirable to minimize the size or proportion of the bonding region to only so much as may be needed to yield a dental appliance having a desired level of bondability to one or more bonding agents. In that way, the desired performance properties can be maximized while still providing a desired level of bondability. Consistent with this, it may be desirable to minimize the thickness of the bonding region and maximize the thickness of the performance region since only the surface of the bonding region chemically interacts with the bonding agent.  
      In general, the performance region preferably comprises at least about 25% by volume of the dental appliance, more preferably at least about 50% by volume of the dental appliance, even more preferably at least about 75% by volume of the dental appliance, and most preferably at least about 90% by volume of the dental appliance. Conversely, the bonding region preferably comprises up to about 75% by volume of the dental appliance, more preferably up to about 50% by volume of the dental appliance, even more preferably up to about 25% by volume of the dental appliance, and most preferably up to about 10% by volume of the dental appliance.  
      It should be understood that each of the performance and bonding regions may comprise a single material or region. Alternatively, one or both of the performance and bonding regions may comprise two or more different types of materials, either blended together and/or that comprise discrete subregions. Moreover, while the performance and bonding regions will generally comprise different materials overall, it is possible for the performance region to include two or more materials, with one or more of the materials being the same as or similar to one or more materials found in the bonding region. Similarly, it is possible for the bonding region to include two or more materials, with one or more of the materials being the same as or similar to one or more materials found in the performance region.  
      These and other advantages and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
       FIG. 1A  shows a perspective view of an exemplary dental appliance according to one embodiment of the invention, illustrating the dental appliance in an open position;  
       FIG. 1B  shows a perspective view of the dental appliance of  FIG. 1A , illustrating the dental appliance in a closed position;  
       FIG. 2A  shows a cross-sectional view of another embodiment of a dental appliance, illustrating the dental appliance in an open position;  
       FIG. 2B  shows a cross-sectional view of the dental appliance of  FIG. 2A , illustrating the dental appliance in a closed position;  
       FIG. 3A  shows a cross-sectional view of another embodiment of a dental appliance, illustrating the dental appliance in an open position;  
       FIG. 3B  shows a cross-sectional view of the dental appliance of  FIG. 3A , illustrating the dental appliance in a closed position;  
       FIG. 4A  shows a cross-sectional view of another embodiment of a dental appliance, illustrating the dental appliance in an open position;  
       FIG. 4B  shows a cross-sectional view of the dental appliance of  FIG. 4A , illustrating the dental appliance in a closed position;  
       FIG. 5A  shows a cross-sectional view of another embodiment of a dental appliance, illustrating the dental appliance in an open position;  
       FIG. 5B  shows a cross-sectional view of the dental appliance of  FIG. 5A , illustrating the dental appliance in a closed position;  
       FIG. 6A  shows a cross-sectional view of another embodiment of a dental appliance, illustrating the dental appliance in an open position;  
       FIG. 6B  shows a cross-sectional view of the dental appliance of  FIG. 6A , illustrating the dental appliance in a closed position;  
       FIG. 7A  shows a cross-sectional view of another embodiment of a dental appliance, illustrating the dental appliance in an open position;  
       FIG. 7B  shows a cross-sectional view of the dental appliance of  FIG. 7A , illustrating the dental appliance in a closed position;  
       FIG. 8  shows a cross-sectional view of the dental appliance of  FIG. 1  applied to a substrate (i.e., a tooth);  
       FIG. 9  shows a cross-sectional view of a conventional dental bracket applied to a substrate (i.e., a band);  
       FIG. 10  shows a perspective view of a dental band applied to a tooth; and  
       FIG. 11  shows a perspective view of a bite ramp applied to a tooth.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention is related to dental appliances having a performance region associated with a bonding region so as to enhance both performance and bondability of the dental appliance, respectively. Generally, the bonding region is associated with the performance region so that the bonding region and/or the performance region forms a mounting surface for bonding to a bonding agent.  
      As used herein, the term “dental appliance” is used to broadly refer to various appliances in dentistry and orthodontics which are bonded at least indirectly to a person&#39;s tooth. Examples of dental appliances include, but are not limited to orthodontic brackets, bands, wires, bite ramps, veneers, crowns, and bridges.  
      As used herein, a “substrate” is the object to which the dental appliance is affixed. The substrate depends on the particular dental configuration. For example, in one configuration, an orthodontic bracket could be bonded directly to a person&#39;s tooth. In this case, the orthodontic bracket would be the “dental appliance” and the tooth is the “substrate.” In another configuration, an orthodontic bracket can be bonded to indirectly to a person&#39;s tooth by a band which is placed around the tooth. In this case, the bracket is the “dental appliance” and the band is the “substrate.” However, it is also possible that the band is the “dental appliance” and the tooth is the “substrate.” In other words, it can be important for both the bracket and the band to be tightly bonded to their respective substrates. Thus, the invention contemplates that both dental appliances (i.e., the bracket and the band) can include bonding regions, as will be discussed more fully below.  
      As used herein, the term “performance region” is broadly construed as the portion of the dental appliance which provides a desired performance property. Examples of performance property include, but are not limited to, strength, flexibility, bendability, durability, abrasion resistance, rigidity, other mechanical properties, color, shape, other aesthetic features, surface texture, smoothness, plaque resistance, and the like, or a combination thereof. Thus, the performance region can comprise a material which provides a particular performance property, or combination of performance properties. In one preferred embodiment, the performance region exhibits substantially better performance within the desired performance property than the material(s) within the bonding region.  
      As used herein, the term “bonding region” is broadly construed as the portion of the dental appliance that provides a greater bondability to a bonding agent than the performance region. That is, the material of the bonding region is more compatible with a bonding agent than the material of the performance region. Compatibility of the bonding region may be exhibited in higher chemical bond strength and/or mechanical bond strength with the bonding agent than the performance region. Thus, the bonding region is able to form a high-strength bond with a bonding agent applied to a substrate, ensuring that the dental appliance is tightly bonded to the substrate. The bonding region is not itself a bonding agent that bonds to a substrate independently of a separate bonding agent.  
      In each embodiment, the performance region of the dental appliance is associated with the bonding region. As used herein, the term “associated with” means that the bonding region is in some way joined to the performance region. The bonding region is essentially discrete from the performance region except for the interface therebetween where insignificant mixing may occur. Generally, the bonding region can be considered to form one or more discrete regions and/or layers with the performance region.  
      As used herein, the term “mounting surface” is a portion of the dental appliance that provides a minimum surface area which is sufficient to mount the dental appliance to a substrate. The mounting surface is generally located on one or more sides of the dental appliance. In one embodiment, the mounting surface can be composed of primarily the bonding region. In such cases, the bonding agent will primarily or solely contact the material(s) within the bonding region. In another embodiment, the bonding region may only form part of the mounting surface facing the substrate to which the dental appliance is to be bonded. That is, the bonding region and performance region may combine to form the mounting surface.  
      The bonding region preferably comprises at least about 25% of the surface area of the mounting surface, more preferably at least about 50% of the mounting surface area, even more preferably at least about 75% of the mounting surface area, and most preferably at least about 90% of the mounting surface area. One of skill in the art may select the proportion of the mounting surface that comprises the bonding region in order to yield a dental appliance that has a desired balance between desired performance property and bondability to the bonding agent used to bond the dental appliance to a substrate.  
      In order to further improve the bond strength between the dental appliance and a substrate, the mounting surface may include one or more irregularities including, but not limited to, texture, undercuts, recesses, protrusions, or other mechanical features designed to enhance mechanical interlocking between the bonding agent and the mounting surface, in addition to the aforementioned chemical adhesion. It is also contemplated that the performance region may be associated with the bonding region using any of these irregularities in order to enhance the bonding strength between the performance region and the bonding region.  
      As used herein, the term “bonding agent” refers to any dental adhesive, cement or glue to which the dental appliance may be adhered. The bonding agent is typically applied directly on the substrate or the mounting surface of the dental appliance. The bonding agent reacts with the mounting surface of the dental appliance to form a chemical and/or mechanical bond therebetween. The bonding agent can further solidify during and after mounting the dental appliance to the bonding agent.  
      With these definitions in mind, attention will now turn to describing various embodiments of dental appliances having performance regions and bonding regions. With reference to  FIGS. 1A and 1B , a bracket  10  is illustrated comprising a base  12  and a ligation cover  14  connected thereto. Bracket  10  is broadly categorized as a “self-ligating” bracket, which is herein defined as an orthodontic bracket that does not require the use of ligatures (i.e., ties, wires, elastics) to secure an arch wire thereto. The term “self-ligating bracket” refers to a class of orthodontic brackets that include some sort of ligation cover or clasp which encloses or otherwise retains the arch wire within a slot in the performance region. There are both “passive” and “active” self-ligating orthodontic brackets. The term “passive” bracket refers to brackets that only loosely retain the arch wire therein, such that considerable movement between the arch wire and performance region is possible. The term “active” bracket refers to brackets in which the self-ligating cover or clasp exerts force onto the arch wire, resulting in more precise and controlled tooth movement.  
      The base  12  is the portion of the bracket  10  that is attached or adhered to a substrate. The substrate can be a tooth or a band on the tooth. The base  12  includes an arch wire slot  16  for receiving an arch wire  18  (see  FIGS. 2A and 2B ) therein. Although shown as having a square cross section, the arch wire  18  can have any desired cross section, such as rectangular, circular, oval, and combinations thereof. The arch wire slot  16  can similarly have any desired configuration. The base  12  can also include an auxiliary arch wire slot  17  disposed transversely to arch wire slot  16 . Auxiliary slot  17  may be used in the conventional manner to assist in fixing an arch wire within the arch wire slot  17 , such as by means of wire or elastomeric ligatures.  
      The base  12  can further include peripheral recesses  38  on either side, which can be used to optionally secure the arch wire  18  within the slot  16  using conventional wire or elastomeric ligatures. For example, peripheral recesses  38  can serve as a backup where the ligation cover  14  has been permanently removed or separated from the base  12  (e.g., by severing or tearing). Thus, when the ligation cover  14  is removed, the base  12  may at least approximately resemble a conventional bracket shown in  FIG. 4 .  
      Ligation cover  14  is joined to base  12  by a joint element  50 . The ligation cover  14  is formed in a hood-like manner and is integrally connected to the joint element  50  by means of an integral hinge  52 . In a preferred embodiment, the integral hinge  52  comprises an area or region of locally reduced cross-sectional thickness in order to provide increased flexibility in the hinge region. Such a hinge may be referred to as a “film hinge”. The joint element  50  merely acts as a connection between cover  14  and base  12 . A recess  54  is advantageously provided in the outside of the cover  14  so that the joint element  50  and the cover  14  can nest together and form a single, smooth outer surface upon closing or locking the cover  14  with the base  12 .  
      The base  12 , ligation cover  14 , and joint element  50  can either be integrally molded in a single step, so as to yield an integral, one-piece orthodontic bracket, or else an end of the joint element  50  opposite the integral hinge  52  may initially be detached from the base  12  and thereafter attached to the base  12 , e.g., by pushing the end of joint element  50  into a corresponding groove within the base  12  in a form-locking manner. In this way, the ligation cover  14  and joint element  50  are insertably affixed to the base  12 . In either embodiment, a further integral hinge  53 , such as a film hinge, may be provided in the region of attachment between the joint element  50  and the base  12  so that the joint element  50 , and thus also the ligation cover  14 , can be pivoted about the hinge  53  in order to facilitate rotation of the cover  14  over and onto the base  12  during ligation.  
      An exit aperture  56  ( FIG. 1B ) is provided on each side of the ligation cover  14  to allow complete closure of the ligation cover  14  around an arch wire (not shown) placed within the arch wire slot  16 . An insertion slot  58  extending from the exit aperture  56  to a lower edge of the ligation cover  14  permits the passage of the arch wire into and out of each exit aperture  56  during opening and closing of the cover  14 .  
      The ligation cover  14  is the mechanism or means by which an arch wire is ligated or held in place within the arch wire slot. Alignment forces exerted by one or more arch wires to the performance region and/or cover are transferred to the tooth in order to urge the tooth into proper alignment. The self-ligating brackets  10  can include a wide variety of different performance regions and ligation covers having varying mechanical and functional features.  
      For example, in one embodiment of a bracket  10 A shown in  FIGS. 2A and 2B , cover  14  can be attached to base  12  using a spring mechanism. The ligation cover  14  can be generally L-shaped so as to hingedly connect to the base  12  at one end of the “L” (by hinge element  22  discussed below), and overlap and lock around the base  12  at the other end. A plurality of locking notches  32  within a latch member  31  assist in locking the ligation cover  14  over a protrusion  34  within the base  12 . The notches  32  provide a plurality of locking positions, or degrees of closure, of the ligation cover  14  in order to provide the orthodontic practitioner with the ability to apply varying levels of force onto the arch wire  18 . A bearing or holding cam  36  can extend downwardly from the ligation cover  14  and partially into the arch wire slot  16  when the cover  14  is in a closed or locked position ( FIG. 2B ) in order to apply direct pressure to the arch wire  18  and thereby provide active ligation.  
      A hinge element  22  integrally connects the ligation cover  14  to the base  12  and can comprise the same material. The hinge element  22  can be a film hinge. In this way, the ligation cover  14  and base  12  can be molded, such as by injection molding, in a single molding step to yield an integral, one-piece orthodontic bracket  10 A. In this way, the film hinge  22  provides a center point or line of rotation about which the ligation cover  14  can be rotated back and forth between an open position, in which the arch wire slot  16  is completely open ( FIG. 2A ), and a closed or locked position, in which the arch wire slot  16  is completely enclosed in order to provide ligation of an arch wire disposed therein ( FIG. 2B ).  
      A spring element  24  interconnects the ligation cover  14  and the base  12 . The spring element  24  can also comprise the same material as ligation cover  14  and base  12  such that the entire bracket  10 A can be molded as a single piece. The spring element  24  is connected to the performance region by hinge element  26  and to the ligation cover  14  by hinge element  28 . Hinge elements  26  and  28  are also depicted as comprising film hinges of reduced cross-sectional thickness. Nevertheless, the spring element  24  may be attached to the cover  14  and base  12  using any desired hinge or other connection means known in the art. In order for the spring element  24  to lay substantially flush with the ligation cover  14  when the cover is in a closed and locked position, the cover  14  may include a region  30  of reduced cross section into which the spring element  24  can insert itself during closure of the ligation cover  14 . In this way, the ligation cover  14  and spring element  24  yield a smooth, continuous and uniform upper surface when closed. This, in turn, reduces the tendency of food, plaque or other debris to become lodged in the orthodontic bracket  10 A while in use. It also yields a bracket having a minimum of uncomfortable jagged edges compared to conventional brackets.  
      Spring element  24  acts to urge the ligation cover  14  to remain open while in the open position depicted in  FIG. 2A , and to remain closed while in the closed position depicted in  FIG. 2B . Details of how this is accomplished are disclosed in U.S. Pat. No. 6,695,612, filed Aug. 15, 2002, the disclosure of which is hereby incorporated by reference.  
      In bracket  10  and  10 A, the base  12  includes a bonding region  90  in the form of a discrete layer. Note that the term “bottom” is used only to illustrate the location of the bonding region  90  in  FIG. 1A, 1B ,  2 A and  2 B and is not limiting to the invention. When in use, the base  12  is actually turned on its side when being applied to a substrate (see  FIG. 8 ) so that the bonding region  90  is vertical. A performance region  11  is thus defined as the cover  14  and the portion of the base  12  that does not include the bonding region  90 . Methods for forming the performance region and the bonding region will be discussed further below.  
      The bonding region  90  forms a mounting surface  60 . In this embodiment, the mounting surface  60  is comprised solely of the bonding region  90 . As shown in  FIG. 8 , the bracket  10  mounts to a substrate, tooth  99 . Mounting surface  60  is configured to interface between the bracket  10  and a bonding agent  95  placed on the tooth  99 . The bonding agent  95  can be any suitable dental adhesive, cement or glue. Preferably, the bonding region  90  is more compatible and provides a higher-strength bonding interaction with the bonding agent  95  than the performance region  11 .  
      Another configuration for forming bracket  10  is shown in  FIGS. 3A and 3B . The orthodontic bracket  100  has a base  110  to which a ligation cover  112  is hingedly attached. A slot  114  open to the upper side of the base  110  is provided near the center of said base  110  and serves for the insertion of an arch wire  116  therein. An additional arch wire slot  114   a  may also be provided.  
      The ligation cover  112  is hingedly connected to the base  110  by an elongated film hinge  118 . The ligation cover  112  is such that it may be selectively rotated between an open and a closed position relative to the arch wire slot  114 , with the ligation cover  112  maintaining the arch wire  116  within the slot  114  when the ligation cover  112  is in the closed, ligating position. The elongated film hinge  118  preferably has a length and thickness that are selected so that the hinge  118  has a desired level of strength, elasticity, flexibility and toughness. In one embodiment, the elongated film hinge  118  has a thickness of at least about 0.2 mm.  
      The film hinge  118  of this embodiment is designed to bend along substantially its entire length rather than at a single point or line. This helps the hinge resist fatigue or fracture better than film hinges that bend along a single line. In embodiments which include an amorphous polymer, the amorphous component of the blend provides enhanced elasticity, flexibility, and toughness, especially important in the area of the elongated film hinge  118 . Elasticity, flexibility, and toughness help the hinge  118  to not become fatigued or broken after repeated bending.  
      Bracket  100  includes an interactive cam structure  120  with a first curved surface  122  and a second curved surface  124 . The first curved surface  122  interacts with the elongated film hinge  118  to provide a curved surface that helps ensure that the elongated film hinge  118  bends gradually over its entire length rather than abruptly at any specific locale. The second curved surface  122  is curved in such a way so that it interacts with a corresponding wall  125  of the base  110  so to bias the ligation cover  112  toward an open position relative to the base  110  when the ligation cover  112  is in the open position. This improves access to arch wire slot  114 , making insertion or removal of the arch wire  116  easier. The second curved surface  124  may, depending on the shape of the corresponding wall  125  of the base  110 , also act to bias the ligation cover  112  to remain in a closed position when in the closed position relative to the base  110 .  
      An angled keyway  126  is provided near one end of the base  110 . The cover  112  contains a corresponding locking tongue  128  that enables the ligation cover  112  to be selectively locked or unlocked relative to the base  110 . The ligation cover  112  is locked to base  110  (as seen in  FIG. 3B ) by closing the cover  112  so that the locking tongue  128  is inserted into angled keyway  126 .  
      In the event that the arch wire  116  pushes against the cover  112  with sufficient force to cause the cover to bulge upwardly relative to the base  110 , rather than causing the tongue  128  to withdraw from the angled keyway  126 , which could result in undesired disengagement of the cover  112 , the locking tongue  128  is instead pulled more deeply into the angled keyway  126 , thereby tightening the locking mechanism. This provides added safety, and in order to open the cover, the locking tongue  128  is pulled out of angled keyway  126  and over an outer protrusion  129  of the base  110 .  
      Furthermore, a bearing protrusion  130  is provided at the inside and middle of the cover  112  to assist in fixing the arch wire  116  in the slot  114  while the cover  112  is in the closed state ( FIG. 3B ). The bearing protrusion  130  reduces the play in the system by effectively widening the ligation cover  112  in the vicinity of the arch wire slot  114 .  
      Base  110  also includes bonding regions  190  formed on the bottom of the base. The boundaries of the bonding regions  190  and the rest of base  110  can be contiguous. The bonding regions  190  form mounting surfaces  160 . In this embodiment, the bonding regions  190  form substantially all of the surface area of the mounting surfaces  190 . Thus, a significant portion of the bonding regions  190  is available to bond with the bonding agent. A performance region  111  is thus defined as the cover  112  and the portion of the base  110  that does not include the bonding regions  190 . Preferably, the bonding regions  190  are more compatible and provide a higher-strength bonding interaction with a bonding agent than the performance region  111 .  
       FIGS. 4A and 4B  depict an alternative embodiment of an orthodontic bracket  200  according to the invention that does not include a cam structure. Instead, the orthodontic bracket  200  depicted in  FIGS. 4A and 4B  includes a base  210  and a ligation cover  212  attached to the base  210  by means of an elongate film hinge  218 , an angled keyway  226 , a locking tongue  228 , and a bearing protrusion  230 . The base  210  further includes a curved end  232  that acts as a hinge guide in order to cause the elongate film hinge  218  to bend gradually over a significant portion of its entire length. In this way, the curved end  232  of the base  210  can substitute for curved hinge-guiding surface  122  of cam structure  120  of the orthodontic bracket  100  depicted in  FIGS. 3A  and  3 B. Thus, as the ligation cover  212  is moved from an open, non-ligating position ( FIG. 4A ) to a closed, ligating position ( FIG. 4B ), the elongate film hinge  218  at least partially abuts the curved end  232  and bend gradually around the curved end  232  so as to better distribute the bending forces and bending angles along substantially the entire length of the elongate film hinge  218 . Base  210  also includes a bonding region  290  in the form of a discrete layer which forms a mounting surface  260  to increase the bondability of dental appliance  200  to a bonding agent.  
       FIGS. 5A and 5B  illustrate an alternative bracket embodiment  300  which is similar to the bracket  100  illustrated in  FIGS. 3A and 3B  in that it includes a base  310 , a ligation cover  312 , a slot  314 , an arch wire  316  (seen in  FIG. 5B ), an angled keyway  326 , a locking tongue  328 , and a bearing protrusion  330 . This example differs from the bracket  100  illustrated in  FIGS. 3A and 3B  in that the hinge  318  is not as elongated as hinge  118 . Bracket  300  may further include additional arch wire slots  333  and  334  for use with additional or alternative arch wires as known in the art.  
      Base  310  includes a plurality of bonding regions  390 . In this embodiment, base  310  includes a plurality of recesses  362  into which are disposed material for the bonding regions  390 . The performance region  311  for this embodiment includes the cover  312  and the portion of base  310  that does not include the bonding regions  390 . Recesses  362  are one example of irregularities in the performance region  310  that can be formed to increase the chemical and mechanical bond between the performance region  311  and the bonding regions  390 .  
      In this embodiment, mounting surface  360  is formed from a combination of the performance region  311  and bonding regions  390  so that the bonding regions  390  form only a percentage of the surface area of the mounting surface  360 . The mounting surface  360  is configured to mount to a substrate wherein the bonding regions  390  are more compatible with the bonding agent than the performance region  311 .  
       FIGS. 6A and 6B  illustrate an alternative bracket  400  including a base  410 , a ligation cover  412 , a slot  414 , an arch wire  416  (seen in  FIG. 6B ), a main film hinge  418 , an angled keyway  426 , a locking tongue  428 , a bearing protrusion  430 , and an additional arch wire slot  433 . This example differs from that illustrated in  FIGS. 5A and 5B  in that it further has a spring element  420  attached at one end of the base  410  by a film hinge  422  and at an opposite end to the ligation cover  412  by a film hinge  424 .  
      Base  410  includes a plurality of bonding regions  490  extending outwardly. The performance region  411  thus includes the cover  412  and the portion of the base  410  that does not include the bonding regions  490 . A mounting surface  460  is formed from bonding regions  490  and from performance region  411 . In this embodiment, the mounting surface  460  is not rectilinear as is the case for  FIGS. 1 through 5 . Rather, the mounting surface  460  includes irregularities to assist the mounting surface in bonding to a substrate. The bonding regions  490  are trapezoidal in shape so that they form undercuts against the performance region  411 . The undercuts can increase the mechanical bonding strength between the mounting surface  460  and a bonding agent. In addition, the undercuts provide increased surface area for chemical bonding to occur between the mounting surface  460  and the bonding agent.  
       FIGS. 7A and 7B  illustrate yet another alternative bracket  500  including a base  510 , a ligation cover  512 , a slot  514 , an arch wire  516 , a pair of angled keyways  526 , a pair of locking tongues  528 , a bearing protrusion  530 , and additional arch wire slots  533  and  534 . This example differs from that illustrated in  FIGS. 1-5  in that it includes no hinge between the base  510  and the cover  512 . The base  510  could be used without the cover  512  as a traditional bracket requiring ligatures. Using the cover  512  results in a self-ligating bracket with a uniform, closed, smooth surface across the top surface of the bracket  500 , which is beneficial for patient comfort and hygiene.  
      Base  510  includes a bonding region  590 . Bonding region  590  forms a mounting surface  560 . In this embodiment, the bonding region  590  forms the entire surface area of the mounting surface  560 . This embodiment illustrates that the performance region  511  and the bonding region  590  can be bonded together at an irregular surface. This can increase the bonding strength between the performance region  511  and the bonding region  590  by increasing both mechanical bonding and chemical bonding therebetween.  
      It will be appreciated that each of brackets  100 ,  200 ,  300 ,  400  and  500  can be disposed on a substrate similar to that shown in  FIG. 8 . In addition, the bonding regions formed on the bases of these brackets forms a high-strength bond with a bonding agent applied to the substrate. Various other self-ligating bracket designs are disclosed in U.S. Pat. No. 6,607,383; U.S. application Ser. No. 09/914,737, filed Aug. 29, 2001, abandoned; and U.S. application Ser. No. 09/953,400, filed Sep. 12, 2001. For purposes of disclosing exemplary orthodontic self-ligating bracket designs, the foregoing U.S. applications and patent are incorporated by reference.  
      While  FIG. 8  illustrates that tooth  99  can be a substrate,  FIG. 9  illustrates that the dental appliance can also be attached to another substrate which is not a tooth. In  FIG. 9 , a conventional bracket  600  is attached to a band  602 . The band  602  is, in turn, attached to a tooth  604 . The bracket  600  includes a base  606  and an arch wire slot  608 . A pair of opposing tie wings  610  is disposed on opposing sides of the base  606 . The tie wings  610  are configured to receive ligatures which secure an arch wire  612  in arch wire slot  608 . Base  606  includes a bonding region  614  forming a mounting surface  660 . The bonding region  614  assists in bonding the bracket  600  to a bonding agent  616  disposed on band  602 . Thus, in this embodiment, the “performance region” is the portion of the base  606  that does not include bonding region  614  and the “substrate” is the band  602 .  
      With reference to  FIG. 9 , however, the band  602  could also be considered to be a “performance region”.  FIG. 9  illustrates that the band  602  includes an outer surface  618  and an inner surface  620 . The inner surface  620  serves as a “mounting surface” for attaching the band  602  to the tooth  604 . The inner surface  602  includes a bonding region  620  applied thereon. The bonding region  620  assists in bonding the performance region  602  to a bonding agent  622  applied to the tooth  604 . Thus, in this case, the “performance region” is the band  602  and the “substrate” is the tooth  604 .  
      Turning now to  FIG. 10 , the dental appliance could be a bite ramp  700 . Bite ramps typically include a base  702  and a ramp element  704 . The base  702  is sized and configured to bond to the lingual surface of a patient&#39;s front tooth  799  (e.g., an upper or lower incisor and/or canine), while the ramp element  704  is hingedly or bendably adjustable relative to the base  702 . The ramp element  704  provides a ramp structure at a desired angle for engaging the corresponding teeth of the opposite dental arch (e.g., the upper or lower incisors and/or canines) when the patient&#39;s mouth is closed. The engagement between the ramp structure  704  and the corresponding teeth of the opposite dental arch causes the lower jaw to move forward relative to the upper jaw, while also disoccluding the lateral teeth and allowing a new neutral occlusion. The bite ramp  700  may also be used in combination with class II elastics to move the lower jaw forward.  
      In one embodiment, the bite ramp  700  can be adjustable such that the ramp element  704  is selectively adjustable in relation to the base  702 . The bite ramp  700  may further comprise means for locking the ramp element  704  in a desired adjustment angle relative to the base  702 . An example of such a means for locking is a curable resin that is applied to and cured between the base  702  and ramp element  704 . The cured resin locks the ramp element  704  in a desired adjustment angle, and provides a more comfortable surface for the patient&#39;s tongue and soft tissues. In one embodiment, an optional shoe (not shown) may be placed over the ramp element  704 . The lower surface of the shoe provides the ramp element  704  for engaging the corresponding tooth of the opposite dental arch. The upper surface of the shoe provides a smoother surface within the patient&#39;s mouth (e.g., to provide enhanced comfort and/or to help prevent buildup of plaque or other foreign matter). An adjustable bite ramp with an optional shoe is described in more detail in U.S. patent Ser. No. 10/835,963, filed Apr. 30, 2004, the disclosure of which is hereby incorporated by reference. The bite ramp  700  includes a bonding region  790  formed on the base  702  which is configured to bond to a bonding agent  795  disposed on a tooth  799 .  
      It will thus be appreciated that the present invention broadly applies to a wide range of dental appliances in which is it desired to more strongly bond the dental appliance to a substrate.  
      The materials of the performance region and the bonding regions of the dental appliances of the present invention will now be discussed in detail. The performance region advantageously comprises one or more performance properties listed above, and for this reason, can compose a majority of the volume of the dental appliance. However, it is not required that the performance region provide a majority of the volume of the dental appliance. In most embodiments, the performance region exhibits superior performance property than the bonding region.  
      The proportion or ratio between the performance region and bonding region can be selected to impart any desired balance between bondability, on the one hand, and desired performance properties, on the other. According to one embodiment, it may be desirable to minimize the size or proportion of the bonding region to only so much as may be needed to yield a dental appliance having a desired level of bondability to one or more bonding agents. In that way, the desired performance properties can be maximized while still providing a desired level of bondability. Consistent with this, it may be desirable to minimize the thickness of the bonding region and maximize the thickness of the performance region since only the surface of the bonding region chemically interacts with the bonding agent.  
      In general, the performance region preferably comprises at least about 25% by volume of the dental appliance, more preferably at least about 50% by volume of the dental appliance, even more preferably at least about 75% by volume of the dental appliance, and most preferably at least about 90% by volume of the dental appliance. Conversely, the bonding region preferably comprises up to about 75% by volume of the dental appliance, more preferably up to about 50% by volume of the dental appliance, even more preferably up to about 25% by volume of the dental appliance, and most preferably up to about 10% by volume of the dental appliance.  
      Thus, the performance region can be made from any suitable material, or groups of materials, having desired performance properties, such as strength, rigidity, durability, flexibility, resilience, moldability, or machinability. The performance region may comprise a material that is partially or wholly for aesthetic purposes (e.g., color, shape, etc.). Examples of materials that have been found to exhibit desired properties within various performance properties include, but are not limited to, a wide variety of polymeric materials (including both thermoset and thermoplastic polymers), metals, metal alloys, ceramics, and combinations thereof.  
      Suitable polymers broadly include thermoplastic and thermoset materials or those materials which have suitable properties of moldability and hardenability. In general, polymers that result in harder plastics are generally preferred in order to provide a rigid, stable performance region. Of course, virtually any polymer that can safely be employed in a person&#39;s mouth, and that has sufficient strength, toughness and rigidity for use as a performance region, is within the scope of the invention. Softer, more flexible polymers such as polyethylene and polypropylene may be suitably employed in some portions of the dental appliance (e.g., ligation covers), particularly where it is desired for that portion of the dental appliance to have more resiliency or flexibility.  
      Examples of polymeric materials that can be included in the performance region include, but are not limited to, more crystalline polyamides, acetal polymers, urethanes, polyetherimides, polycarbonates, polysulphones, polyethersulphones, polyethylene terapthalate, polyethylene teraphthalate glycol, acrylics, polyarylether ketones, polyethylene, polypropylene, polyaramides, polyesters, polyarylamides, and combinations thereof.  
      In one embodiment, crystalline polymers are desirable to construct the performance region. Crystalline polymers are unique in the sense that they form strong, crystalline bonds. However, because the polymers in crystalline polymers are usually never perfectly aligned, the crystalline polymer also has some slightly amorphous qualities. This results in an extremely strong material which can also be flexible and resilient. Such qualities can be ideal in some dental appliances, for example a self-ligating bracket having a performance region and ligation cover in which the hinge connection between the performance region and ligation cover can experience repeated bending and flexing. In one embodiment, the crystalline polymer may be blended with an amorphous polymer, so as to lend enhanced elasticity, flexibility, and toughness to the hinge connection of the bracket.  
      In addition, crystalline polymers lend increased strength, rigidity and durability, which can be important in the region of the performance region around the arch wire slot(s). Strength, rigidity and durability around the arch wire slots prevents or substantially inhibits deformation that may otherwise result because of the mechanical forces transmitted to the performance region from the arch wire as the teeth are urged into proper alignment. U.S. patent Ser. No. 10/835,959, filed Apr. 30, 2004 discusses embodiments of self-ligating brackets which are constructed of suitable crystalline polymers, which disclosure is hereby incorporated by reference.  
      In some embodiments, the performance region can be made from a single material in a single piece, which may be more cost effective from the standpoint of manufacturing costs, as well as providing greater ease of use. In the case where a more rigid plastic is used (e.g., the base (except for the bonding region)), and a more flexible plastic is used (e.g., the ligation cover), it will typically be advantageous to separately mold the base and ligation cover and then thermally fuse them together to form a single, integrally connected bracket. This procedure is sometimes referred to in the art of molding as “two-color molding”, which refers to the fact that two different plastic materials are molded or fused together to form a single integral, or one-piece, article of manufacture.  
      Plastics and ceramics can be reinforced with suitable materials to strengthen the resulting performance region. For example, reinforcing particles (not shown) or a reinforcement insert (not shown) that is made of metal, ceramic, glass, fibers or a more durable plastic can comport to the performance region greater durability and resistance to wear. Reinforcements can be localized at particular locations where the performance region may experience more stress, for example where it comes into contact with an arch wire. In an exemplary molding process, the base may be molded around a metallic, ceramic, or other reinforcement insert. Alternatively, for reinforcement particles, the plastic precursor can be mixed with reinforcement particles. Other portions of the dental appliance may likewise incorporate a metal feature. For example, the ligation cover can include a metal feature that comes into direct contact with the arch wire to provide greater durability.  
      In one embodiment, the performance region is reinforced with TFG Type 3 glass (“c-glass”) or other appropriate fibers which increases flexibility, toughness, and resilience. These characteristics can be particularly beneficial in dental appliances having a hinge portion (e.g., self-ligating bracket). Reinforcement with c-glass fibers, which are characterized by relatively small diameters, high flexibility, and short fiber length, results in substantial improvement of flexibility, toughness, and resilience as compared to other reinforcement materials. Maintaining flexibility of the polymeric material, while providing increased strength and resistance to creep, is particularly beneficial in the case where an orthodontic bracket includes a living hinge that is expected to flex back and forth several, and often numerous, times during the lifespan of the bracket. U.S. patent Ser. No. 10/835,744, filed Apr. 30, 2004 describes embodiments of self-ligating brackets constructed of a plastic reinforced with c-glass, which disclosure is incorporated by reference.  
      Other reinforcement materials include, but are not limited to, silica, aluminum hydroxide, wollastonite, spinel, titanium dioxide, feldspar, silicas, calcium carbonate, talc, micas, calcium silicates, metals, and combinations or mixtures thereof. Ceramic material can be, but is not limited to, zirconium oxide, aluminum oxide, magnesium oxide and/or silicon oxide or mixtures thereof.  
      Additives which increase the bond between the plastic material and reinforcement material can be used, for example, but not limited to, organo-functional silanes. In addition, the present invention contemplates that performance region can include coating which reduces staining or abrasion.  
      Examples of metals and metal alloys include, but are not limited to, stainless steel, stainless steel alloys, titanium, and nickel-titanium alloys.  
      Examples of ceramics include metal oxides, metal carbides, and metal nitrides.  
      The bonding region is generally more compatible with a bonding agent than the performance region. Generally, the bonding region typically provides less of the volume of the dental appliance. In addition, the bonding region can provide less performance properties than the performance region. Examples of materials that have been found to be especially compatible with bonding agents known in the art, and therefore suitable for use in making the bonding region, include, but are not limited to, less crystalline polyamides, methacrylates, acrylates, polycarbonates, metal oxides, ceramics, and combinations thereof. Examples of metal oxides that can be incorporated into the bonding region include, but are not limited to, alumina, silica, zirconia, and titanium dioxide. Examples of ceramics include metal oxides, metal carbides, and metal nitrides.  
      It should be understood that each of the performance and bonding regions may comprise a single material or region. Alternatively, one or both of the performance and bonding regions may comprise two or more different types of materials, either blended together and/or that comprise discrete subregions. Moreover, while the performance and bonding regions will generally comprise different materials overall, it is possible for the performance region to include two or more materials, with one or more of the materials being the same as or similar to one or more materials found in the bonding region. Similarly, it is possible for the bonding region to include two or more materials, with one or more of the materials being the same as or similar to one or more materials found in the performance region.  
      The materials used to form the performance and bonding regions can be formed and/or brought together using any desired process. For example, according to one embodiment, the materials used to form the performance and bonding regions can be co-molded and/or co-extruded together (e.g., using known 2-color molding processes). This process is especially suitable where two or more different polymeric materials or used to form different regions or segments of the dental appliance.  
      In another embodiment, the performance and bonding regions can be formed separately and then joined together using known processes. In the case where a fired ceramic material and/or a molded or stamped metal is used in combination with a polymeric material, the ceramic material or metal will typically be formed or shaped in a separate process, followed by attachment of the polymeric material thereto.  
      According to one embodiment, the performance region of the dental appliance can be formed initially, followed by formation of the bonding region thereto, e.g., by overmolding, mechanical attachment, spraying, dipping, brushing, bonding, or a combination thereof. In the case where the bonding region comprises a polymeric material that is initially in a flowable state, the polymeric material is typically caused to solidify, e.g., by chemical, light or heat curing, cooling, and the like. This procedure may be used, for example, in the case where the performance region comprises a metal or ceramic that is formed using a high temperature molding or firing process and the bonding region comprises a polymeric material that would be destroyed during formation or molding of the ceramic or metal material. It may also be used in the case where a polymeric material used in the formation of the performance region is processed differently than a polymeric material used in the formation of the bonding region.  
      According to another embodiment, the bonding region can be formed initially, followed by formation of the performance region thereto, e.g., by overmolding or mechanical attachment. This procedure may be used, for example, in the case where the bonding region comprises a ceramic material and the performance region comprises a polymeric material or metal that would be destroyed or altered during formation of the ceramic material. It may also be used in the case where a polymeric material used in the formation of the bonding region is processed differently than a polymeric material used in the formation of the performance region.  
      The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.