BACKGROUND OF THE INVENTION 1. The Field of the Invention The present invention relates to apparatus and methods for the slow release of a medicament, particularly but not exclusively fluoride for the improved treatment and/or prevention of dental caries.

2. The Relevant Technology Dental caries consist of demineralization of a tooth caused by bacteria. In the early stages of caries a white spot develops on the tooth and if the disease is not halted and reversed, the enamel surface breaks down to form a lesion. This can then lead to decay and eventually, a fractured or pitted tooth. It is well known that development of dental caries may be reduced by means of various factors, such as diet and oral hygiene measures, anti-microbial treatments and the provision of fluoride to the teeth. Current methods for administering fluoride include the fluoridation of drinking water, the ingestion of fluoride tablets, the incorporation of fluoride into mouth washes, dentifrices and foods, the topical application of fluoride solutions, gels and varnishes, and recently, the incorporation of fluoride in dental materials and special devices. These have a variable effect on caries which is unpredictable on an individual basis and is dependent on patient compliance in following the prescribed regimen. Evidence supports the concept of frequent applications of relatively low concentrations of fluoride ions for the elimination of caries. A sustained and controlled release delivery system could help to achieve this goal. At least three general approaches have been reported for the application of sustained and controlled slow releasing systems: (1) a sustained release ingested tablet or capsule (Masuhara et al. 1985); (2) incorporation of fluoride into dental cements (McClean & Wilson); and (3) an intra-oral device attached to the teeth (Minth et al. 1983). However, each of these existing technologies has been difficult to use, unpredictable, susceptible to damage, an irritant to surrounding tissue, or unacceptable to the patient. BRIEF SUMMARY OF THE INVENTION In one embodiment, the present invention is directed to a bracket and medicament release device that may be placed in the mouth of a patient. The bracket and device are designed to provide slow release of fluoride or other medicament over a desired period of time. According to one embodiment, the medicament release device includes a medicament-releasing pellet and a bracket. The bracket comprises a base and a socket. The medicament-releasing pellet may have any of various shapes, such as spherical, ellipsoidal, loaf-shaped, bar-shaped, or any other shape that is able to fit within and be held by the bracket socket. It is preferable that the medicament- releasing pellet have a smooth surface and no sharp edges, although this is not required. The pellet may be formed of amorphous or crystalline glass, light or chemically curable resins, thermoplastics, or other material that may be formed into a desirable shape. A medicament (e.g. fluoride) is incorporated into the pellet (e.g., as part of the forming material). One example of a glass material is a phosphorus based fluoride containing glass disclosed in U.S. application Serial No. 10/069,143, which was filed February 14, 2002, and which is incorporated herein by reference. The bracket may be formed of a biocompatible material, for example plastic or a biocompatible metal, such as stainless steel or nickel-titanium. Plastics may be shaped using any known method including thermoplastic molding, thermosetting molding, and the like. When formed of metal, the device may be formed through stamping, cold forming, electro-chemical etching, or any combination thereof. The base of the bracket is sized and configured to be attached to a patient's tooth. The base provides surface area in order to securely bond the bracket to a patient's tooth. According to one embodiment, the base may be flexible so as to better conform to the tooth surface. The base may be transparent or opaque. At least a portion of the base may be perforated. Perforations allow light to pass through to cure a light curable adhesive when the bracket is formed of an opaque material. Perforations also allow the adhesive to flow into the perforations, resulting in a better bond between the bracket and a patient's tooth. According to one embodiment, the socket is sized and configured to receive a correspondingly-shaped medicament-releasing pellet. It may be formed so as to be flexible or rigid, as desired. Preferably, the medicament-releasing pellet fits tightly into the socket so as to minimize space between the pellet and the socket wall. Minimizing this space prevents food, bacteria, and other debris from lodging there and festering. The pellet may be inserted or removed by manipulating the socket with an instrument, such as a dental explorer. The present invention is also directed to a kit for use in placing a dental bracket designed to receive a medicament-releasing pellet onto a tooth of a patient. According to one embodiment, the kit includes a medicament-releasing pellet, a dental bracket having a base and a socket designed to receive the pellet, and a placement device. The placement device includes a body sized and configured to be at least partially inserted into a person's mouth. The placement device further includes a protrusion disposed on the body sized and configured so as to releasably attach to the socket of the dental bracket. The placement device of the kit is used to position the dental bracket on a tooth of a patient before bonding. According to one embodiment, the body of the placement device comprises an elongate handle, and the protrusion is located near an end of the handle. According to one embodiment, the protrusion is male so as to mate within a correspondingly-sized and shaped female socket of a dental bracket. The male protrusion may have any of various shapes corresponding to the shape of the medicament-releasing pellet to be received by the dental bracket socket. For example, the male protrusion may be spherical, ellipsoidal, loaf-shaped, bar-shaped, or any other shape. According to another embodiment, the protrusion includes a female cavity capable of receiving the socket of the dental bracket. As mentioned above, the socket of the dental bracket may be one of various shapes configured to receive a medicament-releasing pellet that may be spherical, ellipsoidal, loaf-shaped, bar- shaped, or any other shape. In this embodiment, the female cavity of the protrusion has a shape and size configured to receive the correspondingly shaped socket. The placement device may be formed of any biocompatible material, such as a biocompatible metal {e.g., stainless steel or nickel-titanium) or plastic. According to one embodiment, at least a portion of the placement device may be formed of a transparent plastic material. Forming at least a portion of the placement device from a transparent material allows the dental practitioner to light cure an adhesive resin while using the placement device to hold the dental bracket against a patient's tooth in the position desired. According to one embodiment, the placement device may be attachable to a dental curing light. Such an embodiment may provide additional convenience and ease of use when using the placement device to place a dental bracket and bonding the bracket to a patient's tooth with a light curable adhesive resin. These and other benefits, 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 In order that the manner in which the above recited and other benefits, advantages and features of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore 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: Figure IA is a perspective view of an exemplary dental bracket shown with a medicament-releasing pellet, which together comprise a medicament release device; Figure IB is a perspective view of the exemplary medicament release device of Figure IA but with the medicament-releasing pellet inserted and held within a socket of the dental bracket; Figures 2-4 are perspective views of various alternative exemplary medicament release devices having differently-shaped medicament releasing pellets and correspondingly sized sockets; Figure 5 is a perspective view of an exemplary kit for use in placing a dental bracket to receive a medicament-releasing pellet onto a tooth; Figure 6A is a perspective view of an exemplary placement device; Figure 6B is a perspective view of the placement device of Figure 6A holding the dental bracket of Figure IA; Figure 6C is a perspective view of an alternative placement device and dental bracket; Figure 6D is a perspective view of an alternative placement device and dental bracket; Figure 6E is a perspective view of an alternative placement device and dental bracket; Figure 7 is a perspective view of an alternative kit for use in placing a dental bracket to receive a medicament-releasing pellet onto a tooth; Figure 8A is a perspective view of an alternative pellet bracket placement device; Figure 8B is a perspective view of the placement device of Figure 8A holding the dental bracket of Figure IA; Figure 9 is a perspective view of an alternative placement device comprising a lens attachment for a dental curing light; and Figures 10 and 11 illustrate the dental bracket of Figure IA being positioned and bonded to a patient's tooth using the placement device illustrated in Figure 6A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction A detailed description of the invention will now be provided with specific reference to Figures illustrating preferred embodiments of the invention. It will be appreciated that like structures will be provided with like reference designations. To provide context for interpreting the scope of the invention, certain terms used throughout the application will now be defined. As used herein, the term "medicament-releasing pellet" or "pellet" refers to a device for slowly releasing a medicament into the body of a patient. The device may be formed of amorphous or crystalline glass, light or chemically curable resins, thermoplastics, or other materials that may be formed into a desired shape. A medicament (e.g., fluoride) may be incorporated into the forming material. Such a device is capable of slowly releasing the medicament into a patient's body when placed in the patient's mouth. The present invention provides a medicament release device including a dental bracket and medicament releasing pellet intended to be placed in the mouth of a patient. The present invention also provides a kit that may be used for placing a dental bracket and medicament-releasing pellet in the mouth of a patient. The kit includes a medicament-releasing pellet, a bracket designed to receive the pellet, and a placement device having a handle with a protrusion sized and configured so as to be attachable to the socket of the dental bracket. The bracket comprises a base and a socket that is sized and configured to receive and hold a correspondingly-sized and shaped pellet. According to one embodiment, the bracket may be placed in the mouth of a patient as a relatively permanent fixture (e.g., up to 20 years), while the medicament-releasing pellet may be removed and replaced at regular intervals, for example once a year. II. Exemplary Medicament Release Devices Attention is now directed to the drawings. Figures IA and IB illustrate an exemplary medicament release device 100. The device includes a medicament- releasing pellet 102 and a dental bracket 104. The bracket 104 includes a base 106 and a socket 108. The base 106 is configured so as to be attached (e.g., by bonding) to a person's tooth (e.g., molar). The socket 108 is configured to receive and retain at least partially therein medicament-releasing pellet 102. Figure IA is a perspective view illustrating the medicament release device 100 with the pellet 102 separate from the bracket 104, while Figure IB illustrates the same medicament release device 100 with the pellet 102 received and held within the socket 108 of dental bracket 104. The medicament-releasing pellet 102 shown in Figures IA and IB has a spherical shape, although any of various other shapes, such as ellipsoidal, loaf-shaped, bar-shaped, or any other shape may be used. The medicament-releasing pellet 102 contains a medicament (e.g. fluoride) that is slowly released into the patient's body over a period of time. For example, where the medicament is fluoride, it may be slowly released over a period between 6 months and 2 years. The pellet may be formed of amorphous or crystalline glass, light or chemically curable resins, thermoplastics, or other materials. An example of a suitable glass composition is a phosphorus-based, fluoride-containing glass disclosed in U.S. application Serial No. 10/069,143, filed February 14, 2002, and which was previously incorporated by reference. Such glass compositions can be formed into a pellet (e.g., by being fused) and once placed in the patient's mouth, will slowly release the fluoride or other medicament contained in the pellet over time. Thermoplastics or curable resins may be desirable pellet forming materials where the medicament decomposes or is otherwise destroyed at high temperatures such as those that may be required to form a glass. In the case of fluoride, the pellet 102 may be replaced once the concentration of fluoride in the patient's mouth begins to decrease below a desired standard. For example, the pellet may be removed and replaced after a period of as little as 6 months or as long as 2 years. The dental bracket 104 includes a base 106 and a socket 108. Although illustrated without perforations formed in the base 106, perforations may be present or not present, as desired. The base 106 is configured so as to be bonded to the surface of a patient's tooth. The base 106 advantageously provides sufficient surface area for bonding, which results in a strong bond to the patient's tooth. Perforations (not shown) may be included to facilitate bonding of the device 104 as they may be configured to allow adhesive to flow through the perforations, providing a better bond between the device 104 and the patient's tooth. In one embodiment, the bracket 104 may be designed so as to be attached to a patient's tooth for a relatively long period of time. Preferably, the bracket is bonded so as to remain attached to the patient's tooth for up to 5 years, more preferably up to 10 years, and most preferably up to 20 years. According to one embodiment, the base 106 may be bonded to a tooth with a chemical cure or light cure adhesive resin. The socket 108 may have any desired size, shape or configuration in order to receive and at least partially retain therein a medicament-releasing pellet (e.g., pellet 102). In one embodiment, the socket 108 includes a hollow interior 110 defined by inner surfaces of the socket 108. The hollow interior 110 is advantageously sized and configured to receive at least a portion of a pellet (e.g., pellet 102) in a manner so that the pellet is securely retained by the socket 108. In one embodiment, the socket 108 includes an outer rim 112 having a diameter that is smaller than the diameter of the interior portion 110. This allows the portion of the pellet 102 having the largest diameter to be positioned within the interior portion 110 of the socket in a manner so that the outer rim 112 overhangs the largest diameter portion of the pellet 102. In this way, the outer rim 112 of the socket mechanically retains the pellet 102 at least partially within the interior portion 110 of the socket 108. In the illustrated embodiment, the socket 108 may further include one or more auxiliary holes 114, which can be positioned so as to enable a dental practitioner to pry the medicament-releasing pellet 102 from the socket 108 using a dental explorer or other instrument. The socket 108 may be formed of a rigid or flexible material. A flexible material allows for easier insertion and withdrawal of the pellet 102 from the socket 108. Preferably, the medicament-releasing pellet 102 fits tightly within the interior portion 110 of the socket 108 so as to minimize space between the pellet 102 and the inner wall of socket 108. Minimizing space prevents food, bacteria, or other debris from lodging and festering therein. The dental bracket 100 may be designed so as to permit removal and replacement of the pellet 102 at home or at a dentist's office. According to one embodiment, the base and socket of brackets according to the invention may be formed of a thin, resilient, biocompatible material, for example plastic, stainless steel, or nickel-titanium. A preferred material is a urethane plastic because of its exceptional compatibility with light curable adhesives. When formed of metal, the device may be formed through a combination of stamping and cold forming, while perforations (if present) may be formed by electro-chemical etching. In a preferred embodiment, the base and socket are manufactured as a single piece, although they may be formed as two initially separate pieces and then joined together as desired. Figure 2 illustrates an alternative medicament release device 200 having an ellipsoidal medicament-releasing pellet 202 and a dental bracket 204. Bracket 204 includes a base 206 and a socket 208 that includes an ellipsoidally-shaped outer rim 212 and an interior portion (not visible) that is configured to receive at least partially therein the ellipsoidal pellet 202. Figure 2 illustrates the pellet 202 received within socket 204 and mechanically retained by the outer rim 212. The socket 208 may also include one or more auxiliary holes 214 to enable a dental practitioner to pry the medicament-releasing pellet 202 from the socket 208 using a dental explorer or other instrument. Figure 3 illustrates an alternative medicament release device 300 comprising a bar-shaped medicament-releasing pellet 302 and a dental bracket 304. Bracket 304 includes a base 306 and a socket 308 that includes an outer rim 312 and an interior portion (not visible) that is configured to receive at least partially therein the bar- shaped pellet 302. The socket 308 may also include one or more auxiliary holes 314 to enable a dental practitioner to pry the medicament-releasing pellet 302 from the socket 308 using a dental explorer or other instrument. Figure 4 illustrates another alternative medicament release kit 400 comprising a loaf-shaped medicament-releasing pellet 402 and a dental bracket 404. Bracket 404 includes a base 406 and a socket 408 that includes an outer rim 412 and an interior portion (not visible) configured to receive at least partially therein the loaf-shaped pellet 402. Figure 4 is a perspective view of the device 400 with the pellet 402 received within socket 408. The socket 408 may also include one or more auxiliary holes 414 to enable a dental practitioner to pry the medicament-releasing pellet 402 from the socket 408 using a dental explorer or other instrument. III. Exemplary Kits Figure 5 illustrates an exemplary kit 550. The kit includes a medicament- releasing pellet 502, a bracket 504, and a placement device 516. The bracket 504 includes a base 506 and a socket 508. Exemplary kit 550 may optionally include bonding resin 518 and etch 520. A. Medicament-Releasing Pellet and Bracket As illustrated in Figure 5, the kit 550 may provide the medicament-releasing pellet 502 in a configuration where it is removably attached (e.g., by rubber cement or another adhesive) to the placement device 516. The medicament-releasing pellet 502 seen in Figure 5 has a spherical shape, although any of various other shapes, such as ellipsoidal, loaf-shaped, bar-shaped, or any other shape may be used. Examples of these alternative shapes are illustrated in Figures 2-4. As illustrated in Figure 5, the kit 550 may provide the bracket 504 in a configuration where it is removably attached to the placement device 516. The bracket 504 seen in Figure 5 includes a socket 508 configured to receive a spherical pellet, although as described above, the socket can have other shapes configured to receive pellets of other shapes (e.g., ellipsoidal, loaf-shaped, bar-shaped, or any other shape). Examples of alternative bracket shapes are illustrated in Figures 2-4. B. Exemplary Placement Devices Figure 6A illustrates placement device 516 for placing a dental bracket (e.g., bracket 504) onto the tooth of a patient. Placement device 516 includes a body 522 and a protrusion 524 disposed on the body 522. The body 522 is sized and configured to be at least partially inserted into a person's mouth. The protrusion 524 is sized and configured so as to releasably attach to a socket of a dental bracket used to receive and retain a medicament-releasing pellet. In the illustrated embodiment, body 522 comprises an elongate handle, and the protrusion 524 is formed near an end of the body 522. The protrusion 524 illustrated in Figure 6A is male, and configured to mate within the socket of a dental bracket (e.g., socket 508 of dental bracket 504). The protrusion 524 is configured to have an outside surface configured to mate within the socket of a dental bracket. As mentioned above, sockets may be configured to receive pellets which are spherical, ellipsoidal, loaf-shaped, bar-shaped, or any other shape. Accordingly, the protrusion 524 may be spherical, ellipsoidal, loaf-shaped, bar- shaped, or any other shape that is configured to mate with the socket of the dental bracket. Embodiments of such protrusions are illustrated in Figures 6C-6E. A protrusion which mates within the socket of a dental bracket preferably is used with a dental bracket having a flexible socket. The protrusion 524 may be flexible or rigid, as desired. Figure 6B illustrates device 516 with protrusion 524 mated within socket 508 of dental bracket 504. Figure 6C illustrates a device 516a including a body 522a and a protrusion 524a. Pellet 502a may be provided as attached to the body 522a by rubber cement or other adhesive that allows removal of the pellet when desired. The protrusion 524a is mated within the socket 508a of dental bracket 504a. Protrusion 524a, pellet 502a, and the hollow defined by socket 508a are substantially ellipsoidal. Figure 6D illustrates a device 516b including a body 522b and a protrusion 524b. Pellet 502b may be provided as attached to the body 522b by rubber cement or other adhesive that allows removal of the pellet when desired. The protrusion 524b is mated within the socket 508b of dental bracket 504b. Protrusion 524b, pellet 502b, and the hollow defined by socket 508b are substantially bar-shaped. Figure 6E illustrates a device 516c including a body 522c and a protrusion 524c. Pellet 502c may be provided as attached to the body 522c by rubber cement or other adhesive that allows removal of the pellet when desired. The protrusion 524c is mated within the socket 508c of dental bracket 504c. Protrusion 524c, pellet 502c, and the hollow defined by socket 508c are substantially loaf-shaped. Figure 7 illustrates an alternative kit 550'. Kit 550' includes a medicament- releasing pellet 502, a bracket 504, and an alternative placement device 516'. Device 516' (perhaps more easily seen in Figures 8A-8B) includes a body 522' and a protrusion 524' disposed on body 522' and that is configured so as to releasably attach to a socket of a dental bracket (e.g., socket 508 of dental bracket 504) used to receive and retain a medicament-releasing pellet. The protrusion 524' includes a female cavity 526 that is sized and configured to receive a socket (e.g., socket 508). The cavity 526 may be configured to receive any of the various sockets illustrated in Figures 1A-4, or any other socket. A protrusion 524' which includes a female cavity 526 that receives a socket of a dental bracket preferably may be used with a dental bracket having a rigid socket. The protrusion 524' may be flexible or rigid, as desired. Protrusion 524' may optionally have a plurality of prongs that can be flexed or manipulated, as illustrated in Figures 8A and 8B, making insertion and removal of the dental bracket 504 easier. Figure 8B illustrates device 516' with socket 508 of dental bracket 504 received within cavity 526 of protrusion 524'. The placement device (e.g., device 516, 516a, 516b, 516c or 516') may be formed of any biocompatible material, such as a biocompatible metal (e.g., stainless steel or nickel-titanium) or plastic. According to one embodiment, at least a portion of the placement device is formed of a material transparent to curing light wavelengths. This allows the user to hold the dental bracket in place and cure a light curable adhesive resin through the transparent portion of the device. Figure 9 illustrates an alternative embodiment of a pellet bracket placement device 616 that is a lens attachment to a dental curing light 628. Placement device 616 includes a body 622 and a protrusion 624 on the body 622 sized and configured so as to be releasably attachable to the socket of a dental bracket used to receive and retain a medicament-releasing pellet. Such a lens attachment 616 may be removably attachable adjacent to a light source of a dental curing light. Light generated by the dental curing light 628 is directed through the body 622, exiting through and around protrusion 624, which is transparent to curing light wavelengths. This allows a dental practitioner to attach the dental bracket to protrusion 624, manipulate the body 622 by manipulating dental curing light 628, and to light cure the dental bracket to the patient's tooth in the location desired. Although protrusion 624 is illustrated as male, a protrusion including a female cavity could alternatively be used. IV. An Exemplary Method of Use The dental bracket and medicament-releasing pellet may be attached to a patient's tooth, as illustrated in Figures 10 and 11. Figure 10 illustrates positioning and attachment of the dental bracket 104 illustrated in Figure IA, although any of the other bracket embodiments may similarly be attached. Prior to placement and bonding of the dental bracket 104, an etch (e.g., etch 520) may be used to prepare the tooth 730 to be bonded to dental bracket 104. The dental bracket is positioned against the tooth as desired by manipulating the placement device (e.g., device 516, 516a, 516b, 516c, or 516'). The bracket 104 may then be bonded to the tooth 730 with any suitable adhesive, e.g., adhesive bonding resin 518. Figure 10 illustrates use of a dental curing light 732 to cure a light curable adhesive resin, bonding the dental bracket 104 to the tooth 730. The adhesive may be chemical cured, light cured, or air cured as desired in order to securely bond the dental bracket 104 to the tooth 730. In one embodiment, the bonding side of the base 106 may have the first part of a two-part chemical cure adhesive resin pre-applied. In another embodiment, the bonding side of base 106 may have a light activated adhesive resin pre-applied. Pre- applying either adhesive aids the dental practitioner in ease of use and placement. With the adhesive in place (whether pre-applied or applied by the dental practitioner), the dental bracket 104 is positioned on the tooth using the placement device. The base 106 provides sufficient surface area for bonding to the tooth 730. According to one embodiment, the base 106 is sufficiently curved and flexible so as to tightly fit the contour of the patient's tooth. The medicament-releasing pellet 102 may be held within the socket 108 by a friction fit by manipulating the socket 108 so as to grip and contact pellet 102 (e.g., the rim 112 retains the pellet 102 at least partially within interior portion 110 (see Figures IA and IB)), or by placing a bead of silicone resin 734 between the socket 108 and the pellet 102. According to one embodiment, the bracket base is bonded to the patient's tooth prior to inserting the medicament-releasing pellet so as to be received by the socket of the bracket. According to another embodiment, for example when using a placement device with a protrusion having a female cavity, the medicament-releasing pellet may be inserted into the socket of the bracket prior to bonding the bracket base to the patient's tooth. As illustrated in Figure 11, it is preferable to bond the dental bracket 104 to the patient's first upper molar, although other positions could be used. In addition, it may sometimes be desirable to install more than one device within the patient's mouth, for example, one dental bracket may be attached to each of the upper and lower first molars. The dental bracket 104 is intended to remain installed in the patient's mouth over a long period of time (e.g., up to 20 years). The medicament-releasing pellet 102 is intended to provide slow release of a medicament (e.g., fluoride) over a period between about 6 months and about 2 years, after which time the pellet may be removed and replaced, either at home or at a dentist's office. Other medicaments may be included within medicament-releasing pellets according to invention in addition to, or instead of, fluoride. Non-limiting examples include antimicrobial agents, anti-tartar agents, anti-plaque agents, anesthetics, desensitizing agents, tooth whitening agents, vitamins, minerals, other nutrients, and/or mouth freshening agents known in the art. It will also be appreciated that the present claimed 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, not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.