Abstract:
An indirect bonding tray for orthodontic bonding procedures has moisture control structure that is located next to the patient&#39;s teeth when the tray is placed over the patient&#39;s dental arch. The moisture control structure tends to draw moisture away from the adhesive used to bond the appliances to the teeth. As a consequence, the probability that the resulting bond between the appliances and the teeth is adversely affected by the presence of moisture, blood or other fluids in the patient&#39;s mouth is decreased.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention broadly relates to orthodontic indirect bonding procedures for affixing orthodontic appliances to the patient&#39;s teeth. More particularly, the present invention is directed towards apparatus and methods for controlling moisture such as saliva during indirect bonding procedures. 
     2. Description of the Related Art 
     Orthodontic treatment involves movement of malpositioned teeth to desired locations in the oral cavity. Orthodontic treatment can improve the patient&#39;s facial appearance, especially in instances where the teeth are noticeably crooked or where the jaws are out of alignment with each other. Orthodontic treatment can also enhance the function of the teeth by providing better occlusion during mastication. 
     One common type of orthodontic treatment involves the use of tiny, slotted appliances known as brackets. The brackets are fixed to the patient&#39;s teeth and an archwire is placed in the slot of each bracket. The archwire forms a track to guide movement of teeth to desired locations. 
     The ends of orthodontic archwires are often connected to small appliances known as buccal tubes that are, in turn, secured to the patient&#39;s molar teeth. In many instances, a set of brackets, buccal tubes and an archwire is provided for each of the patient&#39;s upper and lower dental arches. The brackets, buccal tubes and archwires are commonly referred to collectively as “braces”. 
     In general, orthodontic appliances that are adapted to be adhesively bonded to the patient&#39;s teeth are placed and connected to the teeth by either one of two procedures: A direct bonding procedure, or an indirect bonding procedure. In the direct bonding procedure, the appliance is grasped with a pair of tweezers or other hand instrument and placed by the practitioner on the surface of the tooth in its desired location, using a quantity of adhesive to fix the appliance to the tooth. In the indirect bonding procedure, a transfer tray is constructed with wall sections having a shape that matches the configuration of at least part of the patient&#39;s dental arch, and a set of appliances such as orthodontic brackets are releasably connected to the tray at certain, predetermined locations. After an adhesive is applied to the base of each appliance, the tray is placed over the patient&#39;s teeth and remains in place until such time as the adhesive has hardened. Next, the tray is detached from the teeth as well as from the appliances, with the result that all of the appliances previously connected to the tray are now bonded to the respective teeth at their intended, predetermined locations. 
     Indirect bonding techniques offer a number of advantages over direct bonding techniques. For example, it is possible with indirect bonding techniques to bond a plurality of appliances to a patient&#39;s dental arch simultaneously, thereby avoiding the need to bond each appliance in individual fashion. In addition, the transfer tray helps to locate the appliances in their proper, intended positions such that adjustment of each appliance on the surface of the tooth before bonding is avoided. The increased accuracy of the appliances that is often afforded by indirect bonding procedures helps ensure that the patient&#39;s teeth are moved to their proper, intended positions at the conclusion of treatment. 
     The control of moisture during a bonding procedure is often deemed important, since the presence of moisture can adversely affect the resultant bond strength between the appliance and the tooth. If, for example, the appliance inadvertently detaches from the tooth during the course of treatment, the patient must often return to the practitioner&#39;s office for rebonding of the appliance or replacement of the appliance before full treatment can resume. Obviously, unintentional debonding of orthodontic appliances is a nuisance to both the practitioner and to the patient that is best avoided if at all possible. 
     In the past, a variety of methods were used to reduce the presence of moisture in the patient&#39;s oral cavity during orthodontic bonding procedures. For example, some practitioners use absorbent articles such as cotton rolls to absorb saliva and/or blood along with cheek retractors to help keep the mouth tissue in an open, stationary position. Other practitioners use suction devices such as Nola brand dry field cheek retractors that have suction tubing for drawing fluids out of the oral cavity. Other practitioners have proposed the use of an anti-sialagogue, a drug that can be used to dry the salivary glands during a bonding procedure. 
     The control of moisture during an indirect bonding procedure is often considered more challenging than controlling moisture during a direct bonding procedure. For one thing, in an indirect bonding procedure, it is important to simultaneously keep multiple bond sites dry. In addition, many indirect bonding trays have interior wall sections that closely fit the patient&#39;s teeth, and consequently tend to spread moisture over relatively large portions of the tooth surface as the tray is placed onto the dental arch. 
     SUMMARY OF THE INVENTION 
     The present invention relates to improved apparatus and methods for controlling moisture during orthodontic indirect bonding procedures. In particular, the present invention concerns an indirect bonding tray having structure attached to the tray for reducing moisture on the patient&#39;s tooth surfaces. As a result, the probability of a compromised adhesive bond and subsequent inadvertent detachment of the appliances during the course of treatment due to bond failure is reduced. 
     In more detail, the present invention in one aspect relates to apparatus for indirect bonding of orthodontic appliances. The apparatus includes a tray having a channel for receiving a patient&#39;s dental arch, and the channel includes an outer edge. A number of orthodontic appliances are detachably connected to the tray, and the appliances are located along a path in the channel. The apparatus also includes an elongated moisture control structure extending between the path of the appliances and the outer edge for reducing moisture in the channel in an area between the path and the outer edge. 
     Another aspect of the present invention is also directed toward an apparatus for indirect bonding of orthodontic appliances. In this aspect, the apparatus includes a tray having a channel for receiving a patient&#39;s dental arch, and a number of orthodontic appliances are detachably connected to the tray and located in the channel. A manifold is connected to the tray and includes an inlet spaced from the appliances. A source of potential is coupled to the manifold for drawing moisture through the inlet. 
     Another aspect of the present invention relates to a method for controlling moisture during orthodontic indirect bonding procedures. The method comprises: 
     detachably connecting a number of orthodontic appliances to a channel of an indirect bonding tray; 
     coupling moisture control structure to the tray; and 
     placing the tray over the patient&#39;s dental arch such that the moisture control structure is located next to the patient&#39;s teeth in an area between the appliances and the patient&#39;s gingiva. 
     These and other aspects of the invention are described in more detail in the paragraphs that follow and are illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  is a perspective view of an apparatus for indirect bonding of orthodontic appliances constructed in accordance with one embodiment of the invention; 
         FIG. 2  is an enlarged side cross-sectional view of the apparatus depicted in  FIG. 1 ; 
         FIG. 2A  is an enlarged side cross-sectional view of part of a moisture control structure of the apparatus shown in  FIGS. 1-2 ; 
         FIG. 3  is a front elevational view of the apparatus shown in  FIGS. 1 and 2  along with a schematic depiction of a source of vacuum; 
         FIG. 4  is a side cross-sectional view in somewhat smaller scale illustrating the apparatus of  FIGS. 1-3  as it appears when placed over the teeth of a dental arch; 
         FIG. 5  is a view somewhat similar to  FIG. 2  but showing an apparatus for indirect bonding according to another embodiment of the invention; 
         FIG. 6  is a view somewhat similar to  FIG. 2  but showing an apparatus for indirect bonding according to yet another embodiment of the invention; 
         FIG. 7  is a view somewhat similar to  FIG. 2  but showing an apparatus for indirect bonding according to still another embodiment of the invention; and 
         FIG. 8  is a view somewhat similar to  FIG. 2  but showing an apparatus for indirect bonding according to an additional embodiment of the invention. 
     
    
    
     DEFINITIONS 
     “Mesial” means in a direction toward the center of the patient&#39;s curved dental arch. 
     “Distal” means in a direction away from the center of the patient&#39;s curved dental arch. 
     “Occlusal” means in a direction toward the outer tips of the patient&#39;s teeth. 
     “Gingival” means in a direction toward the patient&#39;s gums or gingiva. 
     “Facial” means in a direction toward the patient&#39;s cheeks or lips. 
     “Lingual” means in a direction toward the patient&#39;s tongue. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An apparatus for indirect bonding of orthodontic appliances according to one embodiment of the invention is illustrated in  FIGS. 1-4  and is broadly designated by the numeral  10 . The apparatus  10  includes a tray  12  having a channel  14  for receiving a patient&#39;s dental arch. In the exemplary tray  12  shown in the drawings, the channel  14  is adapted to receive a patient&#39;s lower dental arch, although it should be understood in this regard that as an alternative the tray  12  may be constructed to receive the patient&#39;s upper dental arch. 
     The tray  12  may be constructed according to any one of a variety of known techniques. In the example shown in  FIGS. 1-4 , the tray  12  includes an outer shell  16  that is relatively stiff and an inner section of matrix material  18  that is relatively flexible. A suitable material for the shell  16  is a sheet of polycarbonate such as Makrolon brand material from Bayer or Lexan brand polycarbonate from GE having a thickness of 0.06 in. (1.5 mm). Other materials, such as polyethyleneterephthalate (“PET”), polyethyleneterephthalate glycol (“PETG”) may also be used. 
     Preferably, the matrix material  18  has a relatively low viscosity before hardening so that intimate contact between the matrix material  18  and orthodontic appliances received in the channel  14  is assured. In this manner, the matrix material  18  is able to substantially penetrate in various recesses, cavities and other structural features of each appliance so that a secure connection between the appliance and the matrix material  18  can be established. An example of a suitable matrix material having a relatively low viscosity before curing is a silicone material such as “RTV615” silicone material from General Electric. 
     The matrix material  18  preferably has a viscosity before curing that is less than about 60,000 cp. More preferably, the matrix material  18  has a viscosity before curing that is less than about 25,000 cp. Most preferably, the matrix material has a viscosity that is less than about 8,000 cp. Once hardened, the matrix material  18  has a Shore A hardness that is in the range of about 10 to about 80, more preferably in the range of about 30 to about 60 and most preferably in the range of about 40 to about 50. 
     Alternatively, the matrix material  18  may comprise a dental impression material or a bite registration material. Suitable materials include polyvinylsiloxane impression material, such as Memosil 2 brand vinyl polysiloxane material from Heraeus Kulzer Inc., or Peppermint Snap brand clear bite registration material from Discus Dental. Another suitable matrix material is Affinity Crystal brand silicone impression material from Clinician&#39;s Choice Dental Products, Inc. If a light-curable adhesive is to be subsequently used for bonding the appliances to the patient&#39;s teeth, the matrix material  18  is preferably optically clear and transmits actinic radiation without substantial absorption once hardened. 
     Preferably, the inner surface of the matrix material  18  that faces the channel  14  has contours that precisely match the contours of the individual teeth of the patient, as well as an overall configuration that matches the orientation of each tooth relative to other teeth in the same dental arch when the teeth are in their initial maloccluded condition at the beginning of treatment. As a result, when the tray  12  is placed over the patient&#39;s dental arch, the channel  14  of the tray  12  provides a mating fit with the patient&#39;s teeth such that little, if any, tolerance or “slop” is present and relative movement between the tray and the dental arch is substantially hindered. 
     The apparatus  10  also includes a number of orthodontic appliances  20  that are detachably connected to the tray  12 . In  FIGS. 2 and 4 , the exemplary orthodontic appliance  20  is an orthodontic bracket, although other appliances are also possible. Examples of other suitable appliances include buccal tubes, buttons, formed “bumps” made, e.g., of composite material, or any other metal or non-metal “handle” or other structure connected to the teeth that provides an attachment point for a force member such as a wire, aligner tray, polymeric strip, elastomeric band or chain, or any combination of the foregoing. If desired, appliances may be omitted for some of the teeth in the dental arch such as molar teeth or teeth that have only partially erupted. 
     The exemplary appliance  20  as shown in  FIGS. 2 and 4  includes a base  22  that is connected to a base flange  24 . The appliance  20  also has a body  26  that extends outwardly from the base flange  24 . A pair of tiewings  28  is connected to the body  26 , and an archwire slot  30  extends through a space between the tiewings  28 . 
     The base flange  24 , the body  26  and the tiewings  28  may be made of any one of a number of materials suitable for use in the oral cavity and having sufficient strength to withstand the correction forces applied during treatment. Suitable materials include, for example, metallic materials (such as stainless steel), ceramic materials (such as monocrystalline or polycrystalline alumina) and plastic materials (such as fiber-reinforced polycarbonate). Optionally, the base flange  24 , the body  26  and the tiewings  28  are integrally made as a unitary component. 
     The base  22  of the appliance  20  is preferably made of a material different than the material comprising the base flange  24 , and has a configuration that matches the configuration of a portion of a patient&#39;s tooth structure. More particularly, the base  22  has a concave contour that is a replica of the convex contour of the portion of the patient&#39;s tooth that represents the ultimate desired location of the appliance  20  on the tooth. Optionally, the concave contour of the base  22  is a compound concave contour (i.e., curved in directions along two mutually perpendicular reference planes). 
     The bonding adhesive  31  may be any orthodontic adhesive suitable for use as an indirect bonding adhesive. Optionally, the adhesive  31  is a two-component adhesive, wherein the first component is Transbond brand XT primer and the second component is Transbond brand Plus self-etching primer, both from 3M Unitek. The first component of such two component adhesive is applied to the base  22  and the second component is applied to the area of each patient&#39;s tooth that is to receive the appliance  20 . 
     Another option is to use a preliminary teeth etching step (such as by exposing the teeth to 37% phosphoric acid or equivalent), followed by applying a suitable chemical curing adhesive. Examples of suitable chemical curing adhesives include Sondhi brand Rapid-Set indirect bonding adhesive and Unite brand adhesive, both from 3M Unitek Corporation. The Sondhi brand adhesive includes two lightly filled resin components that are mixed independently from each other and applied to the teeth and to the appliances respectively. The Unite brand adhesive, on the other hand, includes a mixed resin component and a mixed paste component; the resin component is first applied to both the teeth and the appliances, and then the paste component is applied to the appliances to form a so-called “sandwich” configuration. Another suitable two-component adhesive is Concise brand adhesive, also from 3M Unitek Corporation. The Concise brand adhesive includes a mixed paste component along with a mixed resin component that are placed on the appliances and teeth respectively. Alternatively, a resin-modified glass ionomer cement may be applied. Glass ionomer cements provide an additional advantage in that a separate tooth etching step is unnecessary. 
     Optionally, the bases  22  may be precoated with an orthodontic adhesive by the manufacturer as described in Published U.S. Patent Application No. 2005/0074716-A1. Optionally, the precoated adhesive may have multiple layers and/or be patterned, as described in Published U.S. Patent Application No. 2005/0136370. As an additional option, the adhesive  31  may vary from one appliance  20  to the other as described in Published U.S. Patent Application No. 2005/0133384-A1. 
     The appliances  20  extend along a path  32  that is represented by the dashed line in  FIG. 1 . The path  32  may or may not be a curved line that extends in a reference plane parallel to the patient&#39;s occlusal plane depending on the practitioner&#39;s preferred treatment technique. For example, if the practitioner employs the “straight wire” technique, the path  32  of the appliances  20  may lie in a common place at the conclusion of treatment but typically will not lie in a common plane at the beginning of treatment. 
     The apparatus  10  also includes an elongated moisture control structure  34  (not shown in  FIG. 1 ) that extends between the path  32  of the appliances  20  and an outer edge  36  of the tray  12 . In this embodiment, the moisture control structure  34  includes a film  38  having a plurality of flow channels or passages  40  ( FIG. 2A ). The passages  40  are in communication with a manifold  42  located next to the outer edge  36  of the tray  12 . 
     An enlarged cross-sectional view of the film  38  alone is shown in  FIG. 2A . As illustrated, the film  38  includes a body layer  44  and a structured surface  46  connected to the body layer  44 . The structured surface  46  presents a series of lined V-shaped side walls, which define the passages  40 . Preferably, the passages  40  are arranged in a parallel array, although other configurations are also possible. 
     A cap layer  48  extends over and is coupled to the structured surface  46 . In this embodiment, the cap layer  48  is a non-porous flexible film material that is bonded or otherwise affixed to the structured surface  46 . The passages  40  have open ends that represent a plurality of inlets that are located adjacent the enamel surface of the patient&#39;s tooth and next to the bases  22  of the appliances  20 . 
     Preferably, the inlets extend continuously along a substantial majority of the length of the channel  14  of the tray  12 , and more preferably along the entire length of the channel  14 . Consequently, oral fluids such as saliva and blood will be drawn through the inlets presented by the passages  40  and into the manifold  42  when a potential source such as a vacuum is applied to the manifold  42 . 
     The manifold  42  includes a plenum that is in fluid communication with open ends of the passages  40  remote from the appliances  20 . As one example, the manifold  42  may comprise plastic tubing with a plurality of openings in communication with ends of the passages  40 . In this embodiment, the manifold  42  extends substantially along the entire length of the outer edge  36  of the tray  12  and is substantially equal in length to the length of the film  38 . 
     As illustrated in  FIG. 3 , an outlet tubing  50  is connected to the manifold  42  in an area near the center of the manifold  42 , which corresponds to a region near the middle of the patient&#39;s dental arch. The tubing  50  has an interior passageway that is in communication with the plenum of the manifold  42 . The passageway of the tubing  50  is also connected to a source of potential such as a source of vacuum  52  that is schematically depicted in  FIG. 3 . 
     “Vacuum”, as used herein, shall mean any air pressure that is less than atmospheric pressure, and does not mean an absolute vacuum. Other potential sources may be used in the present invention instead of or in combination with the source of vacuum  52 . Essentially any manner of causing or encouraging liquid flow through the passages  40  is contemplated in this invention. Examples of potential sources include vacuum pumps, vacuum aspirators, pressure pumps, hydrostatic heads and gravity, and/or any other fluid drive system utilizing the creation of a potential difference that urges the fluid to flow to some extent. 
     Examples of suitable films  38  and methods of making such films are described in U.S. Pat. No. 6,290,685 (Insley et al.), U.S. Pat. No. 6,531,206 (Johnston et al.), U.S. Pat. No. 6,080,243 (Insley et al.) and U.S. Pat. No. 5,728,446 (Johnston et al.). 
     As an alternative construction, the cap layer  48  is replaced by a liquid sorbing layer that is permeable to oral fluids. In this alternative, each passage effectively has an open side that represents an elongated inlet for receiving fluids. As such, a larger area of the tooth surface between the path  32  of the appliances  20  and the outer edge  36  is covered by inlets. Suitable materials for the liquid sorbing layer include non-woven webs, particularly those containing meltblown microfibers and microfiber microwebs. An example of a suitable web material is disclosed in U.S. Pat. No. 4,813,948 to Insley. Preferably, the liquid sorbing layer also can function as a collector or reservoir for liquid before it is drawn into the passages  40 . 
     Suitable methods for making the tray  12  are described in U.S. Pat. No. 7,020,963, published U.S. Patent Application No. 20040219473 and pending U.S. patent application Ser. No. 11/098317, entitled “METHOD OF MAKING INDIRECT BONDING APPARATUS FOR ORTHODONTIC THERAPY”. Preferably, the tray  12  also includes occlusal stops such as described in Pending U.S. patent application Ser. No. 11/098716, entitled “ORTHODONTIC INDIRECT BONDING APPARATUS WITH OCCLUSAL POSITIONING STOP MEMBERS”. 
     As one option to make the apparatus  10 , the shell  16  may be constructed as described in the preceding patent applications by initially placing spacer material over a dental model of the patient&#39;s arch. After the shell  16  is formed, the spacer material is removed from the dental arch model, and the film  38  and manifold  42  are then positioned as desired the arch model using a temporary, releasable adhesive. Next, the outer shell  16  is placed over the dental model, the film  38  and the manifold  42 . Subsequently, uncured matrix material  18  is added to the space between the shell  16  and the model and allowed to cure. 
       FIG. 4  is an illustration showing an exemplary use of the apparatus during an orthodontic bonding procedure. As shown, the tray  12  is placed over the dental arch  54 , causing the base  22  of the appliance  20  to contact the enamel surface of the patient&#39;s tooth  56 . When the tray  12  is positioned in this manner, the inlets of the film  38  are located next to the patient&#39;s tooth surfaces and between the base  22  of the appliances  20  and the patient&#39;s gingiva  58  in order to remove moisture in an area near the adhesive  31  associated with each appliance  20 . 
     Preferably, the source of vacuum  52  is activated before or simultaneously with placement of the apparatus  10  over the dental arch  54 . As a consequence, moisture is drawn away from the adhesive  31  before the adhesive  31  has cured and during the time period that the adhesive  31  is curing. 
     After the adhesive  31  has cured, the apparatus  10  is removed from the patient&#39;s dental arch  54 . Preferably, the shell  16  is first separated from the matrix material  18 , which remains in place over the dental arch  54  along with the appliances  20 . Next, the matrix material  18  is detached from the appliances  20 . A hand instrument such as a scaler may be used to help hold each appliance  20  against the surface of the respective tooth  56  as the matrix material  18  is peeled away from the appliances  20 . However, in instances where a relatively soft matrix material is employed or otherwise readily releases from the appliances  20 , the use of a scaler to help avoid fracturing the fresh adhesive bond is optional. 
     An apparatus  10   a  according to another embodiment of the invention is illustrated in  FIG. 5 . Except as set out in the paragraphs that follow, the apparatus  10   a  is substantially the same as the apparatus  10  described above and consequently a description of the similar aspects need not be repeated. 
     The apparatus  10   a  includes a moisture control structure  34   a  that extends between the path of the appliances and an outer edge  36   a  of a tray  12   a . The moisture control structure  34   a  includes a film  38   a  which is substantially the same as the film  38 . However, in this embodiment the passages of the film  38   a  are in communication with an absorbent material  60   a  that extends along the length of the outer edge  36   a.    
     The absorbent material  60   a  may comprise any material suitable for absorbing oral fluids. Examples of suitable absorbent materials  36   a  include nonwoven materials, solid inorganic oxides that react with water to form the corresponding hydroxides, particularly those of elements in Groups 1-2 and 13-17 of the Periodic Table such as calcium oxide, zeolites that may or may not be in the form of finely divided powders, and cellulose (such as cotton). Preferably, the absorbent material  60   a  is encapsulated to facilitate retention of the absorbed fluids and covered with a section of film that is permeable to oral fluids. 
     As another option, the absorbent material  60   a  may comprise super-absorbent sodium polyacrylate granules that are optionally placed within an absorbent hydrophilic fiber fill. Preferably, the sodium polyacrylate granules and fiber fill are contained within a film that is preferably permeable to oral fluids. The sodium polyacrylate granules may be made in a manner similar to the manufacture of sodium polyacrylate granules that are used in disposable diapers. 
     As another alternative, the absorbent material  60   a  described in connection with the apparatus  10   a  may be placed within the plenum of the manifold  42  of the apparatus  10 , which in turn, is connected by outlet tubing  50  to the source of vacuum  52 . In this manner, the absorbent material  60   a  functions as a reservoir or holding chamber for the fluid that is subsequently drawn through the outlet tubing  50  upon application of sufficient vacuum pressure. 
     An apparatus  10   b  according to another embodiment of the invention is illustrated in  FIG. 6 . The apparatus  10   b  includes a tray  12   b  and a number of appliances  20   b  that are essentially the same as the tray  12  and appliances  20  respectively described above. 
     The apparatus  10   b  also includes an elongated moisture control structure  34   b  in the shape of a strip that extends along the area between the path of the appliances  20   b  and an outer edge  36   b  of the tray  12   b . In this embodiment, the moisture control structure  34   b  comprises absorbent material  60   b , but lacks a film with passages or similar structured structure with fluid flow channels. Instead, the absorbent material  60   b  is exposed along the channel  14   b  of the tray  12   b  for direct contact with the enamel surfaces of the patient&#39;s teeth. 
     The absorbent material  60   b  may comprise any of the absorbent materials  60   a  described above. Preferably, the absorbent material  60   b  comprises super-absorbent sodium polyacrylate granules that are placed within an absorbent hydrophilic fiber fill as described above in connection with the absorbent material  60   a.    
     Optionally, the absorbent material  60   b  includes one or more layers of film that surround the sodium polyacrylate granules and absorbent fiber fill. For example, the sodium polyacrylate granules and fiber fill may be surrounded by an inner film layer made of a hydrophilic material that is permeable to moisture and has relatively small openings for the containment of fines. The inner layer may be surrounded by an outer film layer that is made of a moisture permeable hydrophobic material that feels dry to the touch, somewhat similar to the material used in disposable diapers. 
     An apparatus  10   c  for indirect bonding of orthodontic appliances according to another embodiment of the invention is illustrated in  FIG. 7 . The apparatus  10   c  includes a tray  12   c  and a number of appliances  20   c  detachably connected to the tray  12   c . The apparatus  10   c  also includes a moisture control structure  34   c  that extends along a path located on a gingival side of an outer labial, gingival edge  36   c  of the tray  12   c.    
     The moisture control structure  34   c  is similar to the moisture control structure  34   b , in that it includes an absorbent material such as the absorbent materials  60   a ,  60   b  as described above. 
     The moisture control structure  34   c  includes an outer flexible film covering such as the “dry to the touch” moisture permeable hydrophobic film material mentioned above. This outer film covering is connected to matrix material  18   c  of the tray  12   c  by allowing the matrix material  18   c  to contact and penetrate the outer film covering prior to hardening of the matrix material  18   c.    
     The moisture control structure  34   c  is pillow-like and readily deformable. As the apparatus  10   c  is placed over the patient&#39;s dental arch, the moisture control structure  34   c  can change in shape to conform to tooth structure or gingival tissue in areas adjacent the gingival margin. Optionally, the apparatus  10   c  may include moisture control structure  34   b  in addition to the moisture control structure  34   c  if desired. Other aspects of the apparatus  10   c  are essentially the same as described above in connection with the apparatus  10 ,  10   a  and  10   b.    
     As an alternative to the moisture control structure  34   c , or in addition to the moisture control structure  34   c , the apparatus  10   c  includes a moisture control structure  35   c  as shown in  FIG. 7 . The moisture control structure  35   c  extends along the lingual side of the tray  12   c  and along an outer, lingual gingival edge of the tray  12   c , and is particularly useful due to the relatively active nature of the salivary glands that reside under the tongue. As shown in the embodiment illustrated in  FIG. 7 , the moisture control structure  35   c  extends past the outer edge of the tray  12   c  in a direction away from the tray channel. In other aspects, the moisture control structure  35   c  is essentially the same as the moisture control structure  34   c.    
     An apparatus  10   d  according to still another embodiment of the invention is illustrated in  FIG. 8 . The apparatus  10   d  includes a tray  12   d  and a number of appliances  20   d  received in the tray  12   d . The apparatus  10   d  also includes a moisture control structure  34   d  for reducing the amount of moisture that might otherwise be present in areas adjacent the bonding base of the appliances  20   d.    
     In this embodiment, the moisture control structure  34   d  comprises one or more stacks of film  38   d , each of which has a microstructured surface with a plurality of flow channels or passages. Open ends of the passages are located adjacent the base of the appliances  20   d . As one example, each film stack may be made by two to five layers of film. External to the tray  12   d , the film stack is bound together by a length of tubing such as heat shrink tubing  62   d.    
     Although not shown in the drawings, the end of the film stack remote from the appliances  20   d  may be connected to a quantity of absorbent material and/or a source of vacuum as described above. As one example, two film stacks are provided, each of which is located in one of the posterior regions of the tray  12   d . As another alternative, a series of four, five or six film stacks are provided along the length of the tray  12   d  in spaced-apart relation. The film stacks may be connected together to a manifold that, in turn, is connected to absorbent material and/or a source of vacuum. 
     Except as described above, the apparatus  10   d  is essentially the same as the apparatus  10 ,  10   a ,  10   b  and  10   c.    
     A number of other options and alternative constructions are also possible. For example, aspects of the moisture control structures  34   b ,  34   c  may be used in combination with the moisture control structure  34   d  of the apparatus  10   d.    
     All of the patents and patent applications mentioned above are hereby incorporated by reference. The foregoing description is intended to exemplify various aspects of the invention and variations are possible. Consequently, the invention should not be deemed limited to the presently preferred embodiments described above, but instead only by a fair scope of the claims that follow and their equivalents.