Containers for photocurable materials

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to containers for materials that cure upon exposure to light. The invention is particularly useful for packaging, vials and dispensers for photocurable dental materials such as adhesives and sealants.

[0003] 2. Description of the Related Art

[0004] A variety of materials are known that cure upon exposure to actinic radiation such as light in the visible or ultraviolet spectrum. These materials, also known as photocurable materials, are considered advantageous in that the curing reaction can be initiated when desired by controlling the radiation reaching the material. Photocurable materials are stored in containers that are opaque to the transmission of actinic radiation so that premature curing of the materials is avoided.

[0005] Typical examples of photocurable materials include certain dental adhesives and sealants. In the field of dentistry (including orthodontia, pedodontia, endodontia and other dental specialties) the photocurable material can be placed, for example, in the patient's oral cavity and then manipulated as needed by the practitioner. Once the practitioner is satisfied with the placement of the material, a curing light can be activated in order to harden the material and securely fix it in place.

[0006] Photocurable orthodontic adhesives are a particular advantage to orthodontic practitioners. In orthodontic treatment, tiny slotted appliances known as brackets are often secured by a quantity of photocurable material to the enamel surfaces of the patient's teeth. The use of a photocurable material enables the practitioner to shift the brackets to exact desired positions and orientations on the teeth before the adhesive has hardened.

[0007] Orthodontic brackets serve as a handle to control movement of malpositioned teeth to orthodontically correct positions. During treatment, an archwire is placed in the slots of the brackets and serves as a track to guide movement of the teeth to desired locations.

[0008] In many types of orthodontic treatment, the exact position of the bracket on the corresponding tooth is highly important in order to facilitate moving the teeth to desired positions without the need to place bends or twists in the archwire. As a consequence, the use of a photocurable orthodontic adhesive is highly beneficial in that the practitioner can take as much time as needed to position the brackets in precise, appropriate locations. Once the practitioner is satisfied with the bracket positions, the curing light can be activated to quickly harden the adhesive and secure the brackets in place.

[0009] For many years, orthodontic brackets were prepared for use by applying a small quantity of adhesive to the base of each bracket. Many practitioners used a small spatula to scoop adhesive from a container or mixing pad and then “butter” each bracket base with a portion of the adhesive of the spatula. Other practitioners used a syringe to dispense a small quantity of adhesive directly onto the base of each bracket.

[0010] In recent years, significant advances have occurred in the field of direct bonded dental articles. For example, U.S. Pat. No. 5,015,180 describes in one embodiment an orthodontic bracket and a light curable paste sandwiched between the base of the bracket and a flexible, releasably adhering cover sheet. To bond the bracket to a tooth, the cover sheet is removed from the paste and the bracket base is then applied to the tooth. Such construction represents a time savings for the practitioner because the practitioner need not dispense and apply the adhesive paste to the bracket base before bonding the bracket to the tooth.

[0011] U.S. Pat. No. 4,978,007 describes in one embodiment a substrate having a recess, an orthodontic bracket having an adhesive on an exterior surface, and a release coating sandwiched between the adhesive and the interior surface of the recess. This construction is an advantage because the adhesive is protected in the recess from light, oxygen, water vapor and contaminates. Also, the bracket may be retained in the recess in an upright manner. This upright position facilitates grasping of the sides of the bracket by a placement instrument or other tool when it is necessary to remove the bracket from the recess.

[0012] Other patents that describe adhesive precoated dental appliances include U.S. Pat. Nos. 5,172,809, 5,328,363 and 5,538,129. U.S. Pat. Nos. 5,354,199 and 5,575,645 describe adhesives that are particularly useful for packaged orthodontic appliances.

[0013] Recently, there has been increased interest in broadening the state of the art relating to the adhesive used in adhesive precoated orthodontic appliances. For example, certain practitioners prefer adhesives with different handling characteristics than the adhesives in current popular use. Examples of handling characteristics include viscosity, flow, consistency and other Theological aspects.

[0014] In addition, there has been increased interest in the use of adhesives that change from a noticeable color to a lack of color when curing. Such adhesives, when uncured, are easily observed and thus facilitate clean-up of excess adhesive after the appliance has been positioned on the tooth surface. Once the adhesive has hardened, the color is substantially eliminated, rendering the adhesive more difficult to see and therefore more aesthetic during the course of treatment.

[0015] Unfortunately, many of the packages in current use for adhesive precoated orthodontic appliances are not entirely satisfactory for use with some of the new adhesives under consideration as mentioned above. In particular, it has been found that bond strength of the resultant bonded appliance substantially decreases in instances where the appliance and certain adhesives remain in the package for a significant length of time before use. As a result, the useful shelf life of the packaged appliance is adversely affected.

[0016] Unfortunately, an undue decrease in bond strength of orthodontic appliances to tooth enamel is undesirable because of the increased risk that the appliance may spontaneously debond and release from the tooth surface during the course of treatment. In such a circumstance, the patient must return to the orthodontist's office to receive a new appliance before complete treatment is resumed. As can be appreciated, spontaneous debonding of orthodontic appliances is a nuisance to both the practitioner and to the patient that is best avoided if at all possible.

SUMMARY OF THE INVENTION

[0017] The present invention relates to improved containers for photocurable materials that provide excellent protection against degradation of the photocurable materials, even after extended periods of time. The containers of the present invention are particularly useful for protecting dyes that impart a color changing feature to dental adhesives and sealants. The containers of the present invention effectively block the passage of actinic radiation over a broad spectral range and as a result the photocurable material does not prematurely lose color during storage.

[0018] The containers of the present invention comprise a polymer and metallic particles. As an example, the containers may be made of polypropylene that is compounded with aluminum filler or receives an aluminum powder coating. The combination of polymer and metallic particles provides a highly effective block to the passage of actinic radiation to color changing dyes, even though such dyes are known to be highly sensitive to light.

[0019] The containers of the present invention also exhibit good vapor barrier properties. As a result, the Theological characteristics of the photocurable material are less likely to change over extended periods of time. For example, the improved vapor barrier properties of the containers provide substantial protection against degradation of the handling characteristics of orthodontic adhesives so that the adhesive does not prematurely cure or dry or become otherwise unsatisfactory.

[0020] In more detail, one aspect of the present invention is directed toward a packaged article. The article comprises a quantity of photocurable material and a container at least partially surrounding the photocurable material. The container comprises a polymer and metallic particles.

[0021] Another aspect of the invention is also directed to a packaged article. In this aspect, the article includes an orthodontic appliance having a base and a quantity of photocurable dental adhesive received on the base of the appliance. The article also includes a container at least partially surrounding the photocurable adhesive. The container comprises a polymer and metallic particles.

[0022] Additional aspects, features and advantages of the present invention are set out in the detailed description that follows and are illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a fragmentary, side cross-sectional view of a packaged article according to one embodiment of the present invention;

[0024]FIG. 2 is side view in partial cross-section of a packaged article according to another embodiment of the invention;

[0025]FIG. 3 is an enlarged side cross-sectional view of a packaged article according to still another embodiment of the invention;

[0026] FIGS. <b>4</b>-<b>6</b> are graphs of luminous transmission at various wavelengths through walls of certain containers constructed according to the invention;

[0027]FIG. 7 is a graph showing the color stability of certain photocurable adhesives when stored in certain containers constructed in accordance with the invention; and

[0028]FIG. 8 is a graph showing the loss of CPQ in a particular photocurable adhesive when stored in a container of the present invention, in comparison to the loss of CPQ from another adhesive when stored in a container that is not constructed according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] An orthodontic article according to one embodiment of the invention is illustrated in FIG. 1 and is broadly designated by the numeral <b>10</b>. The article <b>10</b> includes an orthodontic appliance such as a bracket <b>12</b>. The bracket <b>12</b> has a base <b>14</b> for directly bonding the bracket <b>12</b> to a patient's tooth structure. Preferably, the base <b>14</b> has a slightly concave shape with a compound contour to precisely match the convex, compound contour of an external tooth surface, although other shapes are also possible.

[0030] The bracket <b>12</b> may be made of any one of a variety of materials, including metals (such as stainless steel), plastic (such as polycarbonate) or ceramic (such as monocrystalline or polycrystalline alumina). If made of plastic or ceramic, the bracket <b>12</b> is preferably transparent or translucent such that the color of the patient's tooth is visible through the bracket <b>12</b>.

[0031] However, other types of appliances may be used with the article <b>10</b> in substitution for the bracket <b>12</b>. For example, the appliance may be an orthodontic buccal tube that is adapted to be secured to one of the patient's molar teeth. As other alternatives, the appliance may be a button, a cleat, a lingual sheath or any other device adapted to be bonded by adhesive directly to the patient's tooth structure.

[0032] An orthodontic adhesive <b>16</b> extends across the base <b>14</b> of the bracket <b>12</b>. The adhesive <b>16</b> has sufficient strength when hardened to secure and retain the bracket <b>12</b> on the patient's tooth structure during the typical course of an orthodontic treatment program. Preferably, the shape of the adhesive <b>16</b> resembles a pillow with four edge sections that are in approximate alignment with the four edge sections of the base <b>14</b>. The adhesive <b>16</b> is also present in sufficient quantity to ensure that all of the space between the base <b>14</b> and the patient's tooth structure is filled with adhesive <b>16</b> once the base <b>14</b> has been forcibly placed onto the tooth structure and the adhesive <b>16</b> has hardened.

[0033] The adhesive <b>16</b> may be any one of a number of commercially available orthodontic adhesives that are useful for direct bonding and that cure upon exposure to actinic radiation such as light in the visible spectrum. Suitable adhesives, include, for example, “Transbond XT” brand adhesive from 3M Unitek and “Light Bond” brand adhesive from Reliance. Additional suitable adhesives are described in applicant's co-pending U.S. patent application Ser. No. ______, entitled “Orthodontic Appliances and Adhesives including an Adhesive on the Base of the Appliance” [attorney docket no. 57757US002] and filed on even date herewith.

[0034] Preferably, the adhesive <b>16</b> includes one or more dyes that change color as the adhesive hardens. For example, the dyes may be selected to impart a color to the adhesive during the time that the adhesive is substantially uncured so that the adhesive may be visually spotted and removed from locations where it is not desired. In general, removal and clean-up of the adhesive is easier when undertaken at a time before the adhesive has hardened.

[0035] The dye preferably bleaches and causes the adhesive to lose its color during curing so that the adhesive is essentially colorless once hardened. The lack of color renders the cured adhesive more difficult to see and consequently provides a more aesthetic appearance in the oral cavity. This lack of color is especially beneficial when the appliance is translucent or transparent and when the color of the patient's tooth is visible through the bracket <b>12</b>.

[0036] Examples of suitable dyes include Rose Bengal, Methylene Violet, Methylene Blue, Fluorescein, Eosin Yellow, Eosin Y, Ethyl Eosin, Eosin bluish, Eosin B, Erythrosin B, Erythrosin Yellowish Blend, Toluidine Blue, 4′,5′-Dibromofluorescein, and combinations thereof. Additional details regarding the dyes are set out in the pending U.S. patent application described above entitled “Orthodontic Appliances and Adhesives including an Adhesive on the Base of the Appliance”.

[0037] The bracket <b>12</b> and the adhesive <b>16</b> are partially surrounded by a container <b>18</b>. The exemplary container <b>18</b> illustrated in FIG. 1 includes an integrally-molded body with internal wall portions that define a recess or well <b>20</b>. The well <b>20</b> includes side walls and a bottom <b>22</b>.

[0038] Optionally, the well <b>20</b> has an oval shape in plan view. As an additional option, the side walls of the well <b>20</b> include horizontally extending recesses for engagement with edge structure of a carrier <b>24</b>. Additional information regarding a suitable carrier <b>24</b> is set out in U.S. Pat. No. 5,328,363 which is incorporated by reference herein.

[0039] Preferably, the bottom <b>22</b> of the well <b>20</b> includes a release substrate having an upper surface with cells, particles, protruding pins, projections or other structure that provides a number of pores at least in areas in contact with the adhesive <b>16</b>. The pores may be separated and spaced from each other in non-communicating relation. Alternatively, the pores may be in communication with each other, either in a reference plane extending along the outermost portion of the upper surface, or in one or more reference planes extending below such upper surface, or in any combination of such planes.

[0040] Preferably, a majority of the volume of the pores does not contain adhesive. More preferably, the pores are substantially free of the adhesive <b>16</b>. Preferably, less than about 50% of the adhesive by weight is within the pores, and more preferably less than about 75% of the adhesive by weight is within the pores. Most preferably, less than about 90% of the adhesive by weight is within the pores. Preferably, at least 50% of the volume of the pores is free of adhesive, and more preferably at least 75% of the volume of the pores is free of adhesive. Most preferably, at least 90% of the volume of the pores is free of adhesive. Such construction facilitates release of the adhesive <b>16</b> from the bottom <b>22</b>.

[0041] The release substrate may be made of any one of a number of materials. In the embodiment illustrated in FIG. 1, the release substrate comprises a polymeric foam <b>25</b> having either an open cellular structure or a closed cellular structure. A closed cell foam is preferred. The foam <b>25</b> is preferably compressible and resilient.

[0042] Preferably, the pores of the release substrate have a diameter that is mostly, if not entirely, within the range of about 0.001 in. (0.02 mm) to about 0.01 in. (0.2 mm). The pore size is ascertained by determining its diameter in a reference plane parallel to the plane of the upper surface of the release substrate or foam <b>25</b>. If the pore does not present a circular shape in that reference plane, the pore size is determined by calculating the diameter of a circle presenting an area that is equal to the area of that pore in the same reference plane.

[0043] Particularly preferred materials for the foam <b>25</b> include polyolefin foams such as polyethylene foams, polybutylene foams and polypropylene foams, or blends of the foregoing. Polyvinyl chloride foams, polyurethane foams and foam copolymers may also be employed. Examples of suitable foams include Minicel brand foams (such as series M200, M300 and T300) from Voltek. Optionally, an outer layer of cells of the foam may be heated to “seal” or shrink the size of the pores by reducing the pore diameter and/or by reducing the pore depth in directions perpendicular to the plane of its exterior, upper surface.

[0044] Additional information regarding the release substrate can be found in U.S. Pat. No. 6,183,249 which is incorporated by reference herein. Optionally, and as described in that reference, the release substrate may be integral with the bottom <b>22</b>. In that instance, the pores may be made using a microreplication technique such as the methods disclosed in U.S. Pat. Nos. 5,152,917 and 5,500,273, both of which are expressly incorporated by reference herein.

[0045] The container <b>18</b> including the well <b>20</b> with the bottom <b>22</b> is made of a material that comprises a polymer and metallic particle. Examples of suitable polymers include polypropylene, polypropylene copolymer, polyethylene, polyethylene copolymer, cyclo-olefin-copolymer, acrylonitrile-based copolymer, polyvinyl chloride, polyvinylidene chloride and polyamide. Blends and laminates of those polymers are also possible.

[0046] Suitable metallic particles include aluminum, copper, steel, gold, silver, nickel, brass, iron, zinc and alloys of the foregoing. The particles may have a variety of shapes including flakes, powders, fibers, spheres, rods and combinations of the foregoing. Optionally, the particles are metallized particles having an inorganic core, such as glass bubbles, glass fibers or glass spheres. Metallized particles having an organic core are also possible.

[0047] Preferably, the metallic powder has a size in the range of about 0.01 micron to about 50 microns, and more preferably in the range of about 1 micron to about 30 microns. An example of suitable metallic particles is aluminum flakes having an average diameter of 15 microns.

[0048] Preferably, the ratio of polymer to metallic powder in the mixture is about 0.1% to about 40% by weight, and more preferably in the range of about 1% to about 25% by weight.

[0049] Optionally, the metallic particles are mixed with the polymer and the resulting mixture is then molded into the shape of the container <b>18</b> shown in FIG. 1. As another option, the metallic particles and polymer may be mixed together and then extruded or molded into the shape of a sheet which is subsequently formed into the shape of the container <b>18</b> shown in FIG. 1. The sheet material may be formed to the desired shape by any suitable forming operation such as vacuum-forming. Other suitable manufacturing methods are described in U.S. Pat. No. 5,738,816 which is expressly incorporated by reference herein.

[0050] As another option, the container <b>18</b> may be manufactured by applying one or more layers of metallic particles to a sheet of polymer. For example, a thin layer of aluminum powder may be vacuum-deposited onto one or both sides of a sheet of polypropylene. As a further option, the polypropylene may be formed or molded into the desired shape of the container <b>18</b> before the aluminum is applied to the inside of the well <b>20</b>, the outside of the well <b>20</b> or both.

[0051] Preferably, the material of the container <b>18</b> is substantially opaque to the transmission of light in the range of about 400 nanometers to about 600 nanometers. This range is satisfactory for blocking passage of light that might otherwise be absorbed by the light sensitive dyes mentioned above. However, broader ranges are also possible and may be desired when the adhesive 16 contains components that are sensitive to radiation outside of the range identified above.

[0052] Preferably, the material of the container 18 is compatible with a variety of compounds used in photocurable compositions including the photocurable orthodontic adhesives set out above. For example, the polymer preferably does not adsorb or absorb the CPQ or resin components of the adhesive to any significant degree. As a result, the adhesive remains “fresh” and has a relatively long shelf life until such time as the container is opened.

[0053] Advantageously, the metallic particles impart an aesthetic appearance to the container <b>18</b> by providing a shiny, metallic-looking quality. Optionally, other colorants can be added to give variations in the hue, tint or shade. For example, titanium dioxide and ultramarine blue colorants can be added as desired to provide a metallic blue appearance. In addition, the metallic particles impart an antistatic property to the container <b>18</b>.

[0054] The article <b>10</b> also includes a cover <b>26</b> that is connected to the container <b>18</b>. In FIG. 1, the cover <b>26</b> is shown in a closed configuration. The cover <b>26</b> may be opened by grasping a tab <b>28</b> of the cover <b>26</b> and pulling the same away from the container <b>18</b>, preferably in a swinging, hinge-like manner so that a portion of the cover <b>26</b> remote from the tab <b>28</b> remains secured to the flange of the container <b>18</b>.

[0055] The cover <b>26</b> may be made of any material that is substantially opaque to the transmission of actinic radiation so that the adhesive <b>16</b> does not prematurely cure. Examples of suitable materials for the cover <b>26</b> include laminates of aluminum foil and polymers. For example, the laminate may comprise a layer of polyethyleneterephthalate, adhesive, aluminum foil, adhesive and oriented polypropylene.

[0056] The cover <b>26</b> is releasably connected to the flange of the container <b>18</b> by heat seal that extends along the flange and surrounds the upper opening of the well <b>20</b>. In the lidding identified above, the heat seal is established by a heated platen that softens the polypropylene for bonding the lidding to the flange of the container <b>18</b>. Alternatively, a layer of adhesive (such as the adhesive <b>30</b>) could be provided.

[0057] As yet another option, the article <b>10</b> may be constructed by omitting the bracket <b>12</b> and providing only the container <b>18</b> and the adhesive <b>14</b>. In such a construction, the adhesive <b>14</b> is preferably a “single-dose” of adhesive of a quantity that is suitable for use with a single orthodontic appliance such as a bracket. The well of the container may contain one single dose or a number of single-dose quantities that are spaced apart from each other.

[0058] A packaged article <b>10</b><i>a </i>in accordance with another embodiment of the invention is illustrated in FIG. 2. In this example, the article <b>10</b><i>a </i>is a syringe that comprises a container <b>18</b><i>a</i>. The container <b>18</b><i>a </i>includes an elongated cylindrical housing <b>32</b><i>a </i>with inner walls that define a chamber <b>34</b><i>a. </i>

[0059] The housing <b>32</b><i>a </i>includes a forward nozzle <b>36</b><i>a </i>having a slightly tapered, frustroconical external surface. The nozzle <b>36</b><i>a </i>includes a passage that extends from the chamber <b>34</b><i>a </i>to a discharge opening that is located on the front end of the nozzle <b>36</b><i>a. </i>

[0060] The syringe also includes a plunger <b>38</b><i>a </i>that is slidable within the housing <b>32</b><i>a</i>. The plunger <b>38</b><i>a </i>includes a front piston <b>40</b><i>a </i>that slidably engages the cylindrical inner walls of the chamber <b>34</b><i>a</i>. The plunger <b>38</b><i>a </i>also includes a rear, somewhat “T”-shaped handle <b>42</b><i>a </i>for facilitating advancement of the plunger <b>38</b><i>a. </i>

[0061] A quantity of a photocurable material <b>16</b><i>a </i>is received in the chamber <b>34</b><i>a</i>. The photocurable material <b>16</b><i>a </i>may be the same as the orthodontic adhesive described above. Alternatively, the photocurable material <b>16</b><i>a </i>may be another type of material such as a bonding agent used in other branches of dentistry or a bonding agent used in non-dental applications such as medical, household and industrial applications.

[0062] Although not shown in the drawings, the article <b>10</b><i>a </i>preferably initially includes a cap that is releasably connected to the nozzle <b>36</b><i>a </i>for protecting the photocurable material <b>16</b><i>a </i>until needed for use. As an additional option, the article <b>10</b><i>a </i>may include a dispensing tip that is adapted for detachable coupling to the nozzle <b>36</b><i>a </i>after the cap, if any, has been removed. An example of a suitable dispensing tip is described in U.S. Pat. No. 6,238,212 which is incorporated by reference herein.

[0063] The container <b>18</b><i>a </i>including the housing <b>32</b><i>a </i>is made of a material that comprises a polymer and metallic particles, such as the materials described above in connection with the container <b>18</b>. Optionally, all of the components of the article <b>10</b><i>a </i>(such as the plunger <b>38</b><i>a</i>) are made of the same material to provide a uniform appearance. Such construction ensures that the passage of actinic radiation to the photocurable material <b>16</b><i>a </i>in the chamber <b>34</b><i>a </i>is substantially blocked without adversely affecting the characteristics (such as the bond strength) of the same.

[0064] An article <b>10</b><i>b </i>according to another embodiment of the invention is illustrated in FIG. 3. In this embodiment, the article <b>10</b><i>b </i>is a capsule or cartridge that includes a container <b>18</b><i>b </i>having a chamber <b>34</b><i>b</i>. The article <b>10</b><i>b </i>also includes a piston <b>44</b><i>b </i>that is movable in the chamber <b>34</b><i>b. </i>

[0065] The container <b>18</b><i>b </i>includes a front nozzle <b>36</b><i>b </i>with an outlet opening. The outlet opening is in communication with the chamber <b>34</b><i>b</i>. Optionally, and as shown in the drawings, a cap <b>38</b><i>b </i>is slidably received on the nozzle <b>36</b><i>b </i>and is removed when desired for a dispensing operation.

[0066] A quantity of photocurable material <b>16</b><i>b </i>is received in the chamber <b>34</b><i>b</i>. Examples of suitable photocurable materials <b>16</b><i>b </i>include the photocurable materials mentioned above.

[0067] In use, the article <b>10</b><i>b </i>is placed in a hand-held applicator, such as those applicators that are well known in the dental field. An example of a suitable applicator is no. 5706SD from 3M Company. A suitable applicator is described and illustrated in U.S. Pat. No. 6,095,814 which is incorporated by reference herein.

[0068] During a dispensing operation, a lever of the applicator is moved to advance a plunger that bears against the rear end of the piston <b>44</b><i>b</i>. Continued advancement of the lever moves the piston <b>44</b><i>b </i>forwardly in a direction toward the nozzle <b>36</b><i>b</i>. This movement exerts a pressure on the photocurable material <b>16</b><i>b </i>that is sufficient to direct the material <b>16</b><i>b </i>through the outlet opening of the nozzle <b>36</b><i>b </i>and toward its intended application site.

[0069] The container <b>18</b><i>b </i>is made of a material that comprises a polymer and metallic particles, such as the materials described above in connection with the containers <b>18</b> and <b>18</b><i>a</i>. As a result, the photocurable material <b>16</b><i>b </i>can be safely stored for extended periods of time within the chamber <b>34</b><i>b </i>without undue hardening or substantial degradation of properties.

[0070] The containers described above are representative of suitable constructions that are possible in accordance with the principles of the present invention. A number of other constructions are also possible, including containers that are similar to those known in the art. The containers described above are provided only as examples, and skilled artisans will be able to design arid construct a variety of other types of containers suitable for particular needs.

EXAMPLES

[0071] Sample articles were constructed according to the exemplary article <b>10</b> shown in FIG. 1. Three types of containers made of a mixture of polymer and metallic particles were injection molded. The wall thickness at the bottom of the container was 0.05 in. (1.3 mm) and was 0.035 in. (0.9 mm) in areas of the flange and the sidewall surrounding the well. The compositions of the three types of containers are set out in Table I. <tables id="TABLE-US-00001" num="1"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="4"><colspec colname="OFFSET" colwidth="70PT" align="left" /><colspec colname="1" colwidth="49PT" align="center" /><colspec colname="2" colwidth="49PT" align="center" /><colspec colname="3" colwidth="49PT" align="center" /><thead><row>&lt;entry /&gt;<entry namest="OFFSET" nameend="3" align="center">TABLE I</entry></row><row>&lt;entry /&gt;&lt;entry /&gt;</row><row>&lt;entry /&gt;<entry namest="OFFSET" nameend="3" align="center" rowsep="1" /></row><row>&lt;entry /&gt;<entry>Container “A”</entry><entry>Container “B”</entry><entry>Container “C”</entry></row><row>&lt;entry /&gt;<entry>1.6% powder</entry><entry>3.0% powder</entry><entry>5.6% powder</entry></row><row>&lt;entry /&gt;<entry namest="OFFSET" nameend="3" align="center" rowsep="1" /></row></thead><tbody valign="top"><row>&lt;entry /&gt;</row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="4"><colspec colname="1" colwidth="70PT" align="left" /><colspec colname="2" colwidth="49PT" align="char" char="." /><colspec colname="3" colwidth="49PT" align="char" char="." /><colspec colname="4" colwidth="49PT" align="char" char="." /><tbody valign="top"><row><entry>Sodium</entry><entry>0.08</entry><entry>0.16</entry><entry>0.30</entry></row><row><entry>Aluminosulphosilicate</entry></row><row><entry>(ultramarine blue)</entry></row><row><entry>Aluminum Powder</entry><entry>0.42</entry><entry>0.82</entry><entry>1.52</entry></row><row><entry>Mica/Titanium</entry><entry>1.06</entry><entry>2.04</entry><entry>3.80</entry></row><row><entry>Dioxide</entry></row><row><entry>Salt of Stearic Acid</entry><entry>0.21</entry><entry>0.41</entry><entry>0.76</entry></row><row><entry>(zinc salt)</entry></row><row><entry>Polypropylene</entry><entry>98.22</entry><entry>96.57</entry><entry>93.62</entry></row><row><entry namest="1" nameend="4" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

[0072] A section of foam material was placed in the bottom of each well of each container. The foam was made from sections that were cut from Minicel brand foam no. M200, 0.030 inch (0.76 mm) thick.

[0073] An adhesive precoated orthodontic bracket was placed in each container. The brackets were twin metal brackets with a mesh base (no. 017-401, “Victory Series” brand miniature twin brackets, upper left central, with mesh base, from 3M Unitek Corporation). Each of the brackets was precoated with a photocurable orthodontic adhesive having one of the compositions set out in Table II. <tables id="TABLE-US-00002" num="2"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="4"><colspec colname="OFFSET" colwidth="49PT" align="left" /><colspec colname="1" colwidth="63PT" align="center" /><colspec colname="2" colwidth="49PT" align="center" /><colspec colname="3" colwidth="56PT" align="center" /><thead><row>&lt;entry /&gt;<entry namest="OFFSET" nameend="3" align="center">TABLE II</entry></row><row>&lt;entry /&gt;&lt;entry /&gt;</row><row>&lt;entry /&gt;<entry namest="OFFSET" nameend="3" align="center" rowsep="1" /></row><row>&lt;entry /&gt;<entry>Adhesive “L”</entry><entry>Adhesive “M”</entry><entry>Adhesive “N⇄</entry></row><row>&lt;entry /&gt;<entry namest="OFFSET" nameend="3" align="center" rowsep="1" /></row></thead><tbody valign="top"><row>&lt;entry /&gt;</row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="4"><colspec colname="1" colwidth="49PT" align="left" /><colspec colname="2" colwidth="63PT" align="char" char="." /><colspec colname="3" colwidth="49PT" align="char" char="." /><colspec colname="4" colwidth="56PT" align="char" char="." /><tbody valign="top"><row><entry>CPQ</entry><entry>0.038</entry><entry>0.043</entry><entry>0.065</entry></row><row><entry>BHT</entry><entry>0.094</entry><entry>0.107</entry><entry>0.027</entry></row><row><entry>EDMAB</entry><entry>0.234</entry><entry>0.269</entry><entry>0.264</entry></row><row><entry>DPI</entry><entry>0.141</entry><entry>0.161</entry><entry>0.042</entry></row><row><entry>EYB</entry><entry>0.0038</entry><entry>0.0043</entry><entry>0.011</entry></row><row><entry>BisGMA</entry><entry>1.07</entry><entry>1.22</entry><entry>7.29</entry></row><row><entry>PEG400DMA</entry><entry>9.64</entry><entry>11.06</entry><entry>8.86</entry></row><row><entry>CDMA</entry><entry>7.53</entry><entry>8.62</entry><entry>4.43</entry></row><row><entry>Filler 1</entry><entry>40.0</entry><entry>38.6</entry><entry>39.0</entry></row><row><entry>Filler 2</entry><entry>40.0</entry><entry>38.6</entry><entry>39.0</entry></row><row><entry>Filler 3</entry><entry>1.30</entry><entry>1.26</entry><entry>0.99</entry></row><row><entry namest="1" nameend="4" align="center" rowsep="1" /></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row><row><entry namest="1" nameend="4" align="left">&lt;!--footnotes removed--&gt;</entry></row></tbody></tgroup></table></tables>

[0074] For purposes of comparison, a number of containers were also molded and identified as control containers. These containers consisted of 99% polypropylene and 1% carbon black. The carbon black was “Omnicolor” brand pigment, no. UN0055, from Clariant, Masterbatches Division, of Muttenz, Switzerland.

[0075] The total luminous transmission of light in the ultraviolet and visible spectrum was measured through the side walls of empty containers “A”, “B” and “C” as identified above. Light transmission was determined according to ASTM methods E903 and E891, using a Perkin-Elmer Lambda 19 Spectrophotometer fitted with a RSA-PE-19A integrating sphere accessory.

[0076] The percent transmission over a range of wavelengths in nanometers is shown in FIGS. 4, 5 and <b>6</b> for containers “A”, “B” and “C” respectively. The data set out in FIGS. <b>4</b>-<b>6</b> show that the luminous transmission in various wavelengths for containers “B” and “C” was significantly less than the luminous transmission in the same wavelengths through container “A”.

Example I

[0077] A number of the orthodontic brackets identified above were coated with a layer of adhesive according to the formulation identified as Adhesive “L” or Adhesive “M” in Table II. The brackets and the adhesive were then placed in each of the three containers identified in Table I. A lidding material was placed over the well of each container to serve as a cover. The lidding was made of a laminate that included a layer of polyester film (12 micron thickness), a layer of adhesive, a layer of aluminum foil (25 micron thickness) and an acrylic-based heat seal coating. The containers were then subjected to continuous fluorescent light (30 watts) at a distance of 18 inches (46 cm).

[0078] For comparison purposes, a number of the “A” containers with the same lidding, brackets and adhesive as mentioned above were kept in dark storage.

[0079] To determine the photostability of the adhesive, the red color of the adhesive was measured using a spectrometer (no. EPP2000C, from StellarNet, Inc.) before and after subjecting the containers with the adhesive to the fluorescent light. The spectrometer was fitted with a fiber optic reflectance probe (R400-7-visNIR), a Toshiba photodiode array, a 25 micron slit and a miniature 5 watt fiber optic vis/NIR light source.

[0080] The procedure was carried out in darkroom conditions so that ambient light did not prematurely fade the samples. A dark scan was taken by covering the probe tip with the non-adhesive side of a section of black electrical tape to set up a background value. The fiber optic probe was positioned one-quarter inch (0.6 cm) away from the surface of a white Halon reflectance standard (RS50). The probe was adjusted so that the axis of the probe was approximately 45 degrees with respect to the surface of the standard. After switching the light source on and adjusting the integration time so that the curve covered 90% of the scale, a reference spectrum was saved.

[0081] The adhesive was pressed into the form of a disk between two sheets of release liner (Scotchpak™ 1022, from 3M Company) using steel shims to set the thickness at 0.01 inch (0.25 mm). With the fiber optic source turned off, the disk was placed on the white reflectance standard while still contained between the two sheets of release liner. The light source was then activated and the spectrometer was used to capture the reflectance spectrum and convert it to L*, a* and b* values. The red color of the adhesive is represented as a*. The results of the experiment are set out in FIG. 7.

[0082] The data in FIG. 7 show that containers “B” and “C” provided excellent color protection for the adhesive and that the red color (a*) did not greatly vary from the red color of the adhesive kept in the container that was retained in a dark environment. However, container “A” provided significantly less protection of the red color over a one month period, and results after three months showed a further significant decrease in protection.

Example II

[0083] A number of the orthodontic brackets mentioned above were coated with a layer of adhesive “L” as identified in Table II. Those brackets with the adhesive were then placed in containers “A” identified in Table I. A lidding material was placed over the well of each container to serve as a cover. The lidding comprised a laminate that included a layer of oriented polyamide (25 micron thickness), a layer of adhesive, a layer of aluminum foil (60 micron thickness), a layer of adhesive, a layer of polyethyleneterephthalate (12 micron thickness), a primer and a modified polypropylene heat seal coating. Those containers were then stored in a dark oven at 40° C.

[0084] A quantity of adhesive “N” from Table II was separated into sections approximately equal in size to the size of the adhesive on the base of the brackets in the preceding paragraph. Those sections of adhesive were then placed in the polypropylene control containers with 1% carbon black as described above.

[0085] A lidding material was placed over the well of each container to serve as a cover. The lidding comprised a laminate that included a layer of polyethyleneterephthalate (12 micron thickness), a layer of aluminum foil (20 micron thickness) and a polypropylene heat seal coating. The containers were also stored in a dark oven at 40° C.

[0086]FIG. 8 is a graph showing the remaining percentage of CPQ in the adhesive over a period of time. The data in FIG. 8 show that the loss of CPQ is significant in the polypropylene control containers containing 1% carbon black. Although the amount of CPQ also declined in the adhesive stored in containers “A”, the loss was not as substantial.

[0087] Significant premature loss of CPQ can lead to reduced bond strength and increase the risk of bond failure. As such, the containers “A” are more satisfactory than the control containers for storage of dental compositions including orthodontic adhesives.