Device for delivery of a tooth whitening agent

A delivery device (12, 140) includes a source (16) of pressurized fluid and a nozzle (24) which defines an outlet (22). A fluid pathway (20) fluidly connects the source of pressurized fluid with the nozzle outlet (22) for delivery of a spray of fluid from the nozzle outlet. A delivery mechanism (14) releases a dose (48) of particles (28) into the fluid pathway from an associated cartridge (32), such that the dose of the particles is carried by the pressurized fluid through the nozzle outlet in the spray. The particles include a dental care agent.

The following relates to the dental cleaning arts, and related arts and more specifically concerns a mechanism and a device for delivering an active agent for dental care, such as a tooth whitening agent for whitening teeth.

Tooth whitening agents are generally hydrogen peroxide-based and the aim is generally to deliver the peroxide to the teeth in a sufficient amount to effect a color change in the surface of the teeth in an acceptable period of time without causing harm to the user. Various methods have been developed for applying tooth whitening agents to the teeth. These include toothpastes, peroxide gel strips, whitening solutions, and mouthwashes. Abrasive toothpastes, while easy to use, are generally ineffective. Peroxide gel strips are somewhat more effective, but entail wearing a plastic strip on the teeth to be treated for an extended period. Mouthwashes, which are solutions of peroxide, can be harmful due to contact of the solution with soft tissues. Dental trays use a high concentration of peroxide solution. As a result, great care is needed to avoid contact of the peroxide with soft tissue. Such methods are therefore best suited to use in a dental surgery.

Another problem with hydrogen peroxide is that it rapidly decomposes and becomes ineffective as a bleaching agent. Recently, methods have been developed for encapsulating carbamide peroxide, a dry source of hydrogen peroxide, which is an adduct of urea and hydrogen peroxide. See, Jing Xue and Zhibing Zhang, “Preparation and characterization of calcium-shellac spheres as a carrier of carbamide peroxide,” J. Microencapsulation, 25(8), p. 523 (2008); and Jing Xue and Zhibing Zhang, “Physical, Structural and Mechanical Characterisation of Calcium-Shellac Microspheres as a Carrier of Carbamide Peroxide,” J. Applied Polymer Science, Vol. 113, p. 1619 (2009).

Such spheres are suggested for being combined in a carrier material, such as a toothpaste or gum. However, moisture in the carrier material may cause the hydrogen peroxide to be released and decompose before the material is used for teeth whitening. Another disadvantage of this method is that the particles cannot be directed to where they are needed, resulting in particle wastage and contact with soft tissue which is undesirable.

A device for delivery of a tooth whitening agent and a cartridge containing encapsulated whitening agent for use therewith are disclosed which can overcome some of the problems with existing delivery systems.

In accordance with one aspect of the invention, a delivery device includes a source of pressurized fluid, a nozzle which defines an outlet, and a fluid pathway which fluidly connects the source of pressurized fluid with the nozzle outlet for delivery of a spray of fluid from the nozzle outlet. A delivery mechanism releases a dose of particles into the fluid pathway from an associated cartridge, such that the dose of the particles is carried by the pressurized fluid through the nozzle outlet in the spray, the particles comprising a dental care agent.

In accordance with another aspect, a method for delivery of particles includes providing a cartridge of particles in a delivery device, the particles comprising a dental care agent. A delivery mechanism is actuated to deliver a dose of the particles from the cartridge to a fluid pathway and cause a flow of pressurized fluid to flow from a source of the pressurized fluid to the dose of particles in the fluid pathway and transport the particles to a nozzle outlet of the delivery device, whereby the particles are ejected from the device in a spray of the pressurized fluid.

In another aspect, a delivery mechanism includes a housing which defines a channel, a fluid pathway, and a slider carried by the housing. The slider is moveable, within the channel, between a first position, in which the slider accepts a dose of particles from an associated cartridge, and a second position, in which the dose of particles is released into the fluid pathway. The housing defines first and second openings to the channel which are closed by the slider when the slider is in the first position, and which are open to the channel when the slider is in the seconds position, wherein in the second position of the slider, the openings define a part of the fluid pathway and the dose of particles is positioned in the second opening.

An advantage of the exemplary delivery device is that particles containing a bleaching agent are maintained in a dry state until needed. Another advantage of the exemplary delivery device is that the particles are directed at the teeth.

As used herein the terms “upper” and “lower,” and the like, are made with reference to the position of the device or part thereof as shown in the referenced drawing and it is to be appreciated that in use the device may assume different positions.

With reference toFIG. 1, a schematic cross sectional view of a delivery system10is shown. The delivery system10includes a delivery device12which includes a particle delivery mechanism14. The device12includes a source16of a pressurized delivery fluid, which may be carried by a body portion18of the device12. A pathway20fluidly connects the source16of pressurized fluid with an outlet22of a nozzle24. While the exemplary source16includes a fan for delivery of pressurized air, in other embodiments, a pressurized container of gas or a spring loaded piston system may be used as the fluid source. Typically, the nozzle outlet will be 0.5-2 mm in diameter. This enables delivery of a spray26of the pressurized fluid, together with particles28(not to scale) from the nozzle outlet22. The particle-containing spray26is applied to the teeth30of a person or other dentate animal. A cartridge32of particles is received in the delivery device12. The cartridge defines a reservoir34which contains a large number of the particles28to be dispensed in small doses into the pathway20. In operation, a dose of particles28(e.g., microparticles) is carried from the cartridge32by the pressurized delivery fluid and through the nozzle outlet22. The cartridge can be made from a plastic material, such as a polycarbonate, although other materials can be used.

The exemplary particles28include a dental care agent. The dental care agent can include a tooth whitening agent, such as a bleaching agent, and/or other dental care agents, such as fluoride (e.g., NaF), antibiotics, remineralization agents, or pain relief agents (KNO3), combinations thereof and the like. While particular reference is made herein to tooth whitening using peroxide-based dental care agents, it is to be appreciated that other applications and/or dental care agents are also contemplated.

As illustrated inFIGS. 2 and 3, the particle delivery mechanism14is configured for supplying particles28from the cartridge into the pathway20in controlled amounts. The exemplary delivery mechanism includes a slider40which is carried by a housing42. The slider40is traversed, along a channel44within the housing, in the direction of arrow A from a first position, shown inFIG. 2, to a second position, shown inFIG. 3. The slider cooperates with the housing to define an upwardly open cavity46, which is sized to receive a small dose48of the particles28from the cartridge32when the slider is in the first position. In general, each dose48is only a small proportion of the particles contained in the cartridge, such as 10% of the particles, or less, at least initially. The cartridge32defines a suitably positioned opening50in an end wall52, which is sized to allow particles to drop into the cavity46, or to be forced into the cavity under pressure. In particular, the cavity46includes an open, first end54, adjacent the cartridge, and a second opposed end56, which is closed, in this first position of the slider, by the housing42. In this position of the slider40, access to the pathway20is closed by the slider40, so the particles in the reservoir34and cavity46do not come into contact with pressurized fluid, which may contain water droplets in one embodiment.

As illustrated inFIG. 3, the housing42and the slider40cooperate, in this position, to define a portion of the pathway20whereby pressurized fluid flows through the housing and carries the particles out of the cavity into the nozzle24.

An actuator mechanism60for the slider40may include a drive motor, or the like, which drives the slider in the direction of arrow A. Mechanism60is illustrated figuratively by an arrow inFIG. 2. A button62(FIG. 1) may be provided on the device for activating the actuator mechanism60and optionally also the source of fluid.

As illustrated inFIG. 3, the housing42and the slider40cooperate, in this second slider position, to define a portion of the pathway20whereby pressurized fluid flows through the housing and carries the particles out of the cavity into the nozzle24.

An actuator mechanism60for the slider40may include a drive motor, or the like, which drives the slider in the direction of arrow A. Mechanism60is illustrated figuratively by an arrow inFIG. 2. A button62(FIG. 1) may be provided on the device for activating the actuator mechanism60and optionally also the source of fluid.

Upon activation of the device10, e.g., by pressing button62, air or other pressurized fluid is forced through the mechanism14and at the same time the slider is moved laterally to take the dose of particles from the cavity under the reservoir34to an ejection point64where the air flow takes the particles into the exit nozzle24. In one embodiment, a baffle66is positioned in the exit nozzle24. The exemplary baffle is defined by bends in the pathway which created surfaces68which are angled to the fluid flow. These angled surfaces68cause the particles to impact upon a hard surface and this causes them to rupture so that when they adhere to the tooth, they can disperse their dental care agent (e.g. hydrogen peroxide) load in a reasonable time. As will be appreciated, other types of baffles, such as walls extending into a generally straight passage which are configured to intercept the fluid flow are also contemplated. After actuation and release of the particles the slider moves back to its position with the cavity under the reservoir and is refilled with a new dose of particles. In this way, the particles in the reservoir remain dry and do not come into contact with the fluid. The dry storage avoids degradation of the peroxide or other dental care agent in the particles over time.

Turning toFIG. 4, which shows an enlarged view of the mechanism14and cartridge32, the slider has a length/between its first and second ends. The slider40has a generally uniform cross section of height s, over most of its length l. The length l is generally greater than the cross sectional height s and width. The cross section corresponds, in dimension, to the cross section of the channel44. The cross section of the slider is only slightly smaller than that of the channel, to allow the slider to move within it, while engaging the channel walls snugly. In one embodiment, the cross section is rectangular, although in other embodiments another polygonal shape or a circular cross section is also contemplated. The channel has a length L which is greater than the length l of the slider.

In the illustrated embodiment, the housing42includes upper and lower parallel, planar walls70,72, which define the height h of the channel44therebetween. As will be appreciated, the housing42also defines end walls at ends of the channel, and side walls (not shown), which connect the planar walls70,72and which define the width of the channel therebetween. In use, the upper wall70of the housing engages the cartridge32and/or is fixed in position, relative to the cartridge. A first pair of opposed openings74,76is defined in the upper and lower walls70,72, respectively, upstream of the reservoir34, and a second pair of opposed openings78,80is defined in the upper and lower walls70,72, downstream of the reservoir. The openings76,80are connected by a portion82of the pathway20, which may be defined by a sealed enclosure84connected with the lower wall72of the housing. In the slider first position, the openings74,76and76,80(or at least one of each pair) are closed to the pathway20/pathway portion82by the slider40. In this position, the cavity46is located intermediate the first pair and the second pair of openings. As the slider40begins to move into the position shown inFIG. 3, a first fluid passageway P1is created between the openings74,76. Specifically, these openings are now aligned with a gap85which has been created between the slider first end and an end wall of the housing. The pressurized fluid can enter the enclosure84through the passageway creating a pressurized pathway potion82. At this time, the second pair of openings is still closed by the slider. When the slider reaches the position inFIG. 3, a second passageway P2is created through the openings78,80. Specifically, these openings are now aligned with cavity openings54,56. P2is thus created slightly after the creation of the first passageway P1. The pressure from within the enclosure82acting on the opening80forces the particles28out of the opening78. After releasing the dose of particles, the slider is returned to the first position, and the process can be repeated.

The slider40and housing42can be formed form any suitably rigid material, such as metal or plastic. The slider can be substantially solid, with the cavity46defined by a bore through the slider.

With continued reference toFIG. 4, the exemplary cartridge34includes upper and lower end walls86,50that are connected with and spaced by cylindrical side wall88. The illustrated cartridge is frustoconical in shape, although cylindrical or other regular polygons are also contemplated. In one embodiment the end wall86is flexible, allowing it to assume a concave shape under an external pressure, thereby putting pressure on the particles in the reservoir and forcing them towards the opening50.

The cartridge32may be from 0.01-2 cm in height h and/or width (average diameter) w, such as from 0.05-0.5 cm in height and/or width.

The cartridge32can be a removable cartridge which is fitted into the body18of the device through a suitably positioned opening90in the body. The opening90may be thereafter closed by a closure member92, such as a door, which holds the cartridge in position on the mechanism. For example, a biasing member94, such as a spring, is connected with an inner surface of the closure member to press the cartridge32into engagement with the upper wall of the housing. A guide member96, such as an annulus, guides the cartridge into the correct position during closing of the door, and may grip the cartridge. The guide member may be mounted to the housing wall70and serve as a receptacle for the cartridge.

As shown inFIG. 4, the cartridge32may be sealed against ingress of moisture, during storage with a seal98. The seal98covers the opening50in the cartridge. The seal may be a frangible membrane formed from plastic and/or metal foil, for example, which can be broken to expose the cartridge opening. In one embodiment, the device includes a cutting member, such as a sharp edged ring, which automatically breaks the membrane as the cartridge is inserted in the device. In another embodiment, the cartridge may be fitted with a pull-off or breakable seal or the like which the user removes/breaks just prior to use.

The slider actuator mechanism60may actuate the slider to move in one or both directions. In other embodiments, the slider may be biased to one of the first and second positions by a biasing mechanism102, such as a spring. For example, as shown inFIG. 5, a spring is positioned in the channel44between the slider and an end wall of the housing and contacts the slider at an end104nearest the exit point78. The spring may automatically return the slider to the first position when the actuator mechanism60disengages.

FIGS. 5 and 6show another embodiment of the particle delivery mechanism114, where similar elements are accorded the same numerals and new elements are accorded new numerals. As for the mechanism14ofFIGS. 2-4, the mechanism114is configured for supplying particles28from the cartridge into the pathway20in controlled amounts. The exemplary delivery mechanism includes a slider40which is carried by a housing42. The slider40is traversed, along a channel44within the housing, in the direction of arrow A from a first position, shown inFIG. 5, to a second position, shown inFIG. 6. The slider cooperates with the housing to define an upwardly open cavity46sized to receive a small dose48of the particles28from the cartridge32when the slider is in the first position. The cartridge defines a suitably positioned opening50in an end wall52, which is sized to allow particles to drop into the cavity46, or to be forced into the cavity under pressure. In this position of the slider40, access to the pathway20is closed by the slider40, so the particles in the reservoir34and cavity46do not come into contact with pressurized fluid, which may contain water droplets in one embodiment.

In this embodiment, the delivery mechanism14includes a compression mechanism120which compresses the particles28in the cavity46, causing them to rupture. The exemplary compression mechanism includes a spring122which is mounted, at a first end, to an end wall124of the channel. A plunger126is carried by the other end of the spring. A shaft128of the plunger126is axially mounted through the slider40so as to extend into the cavity46where it terminates in a flange130. As the slider40is moved to the particle release position, the weak spring122is compressed and this enables a small force to be applied to the particles in the dose release section of the device. Upon reaching the release point, all the particles (or at least a proportion of them) are ruptured and released into the exit nozzle. The baffle66may still be employed in this embodiment, as the action of forcing particles28together to rupture them may also cause them to adhere to one another. Therefore, the baffle can serve to separate the particles again.

In use, a user may actuate the slider and pressured fluid several times during a whitening procedure to deliver several bursts of particles to the teeth. On impact with the teeth, particles which have not already ruptured may rupture to release the bleaching agent within them. In other embodiments, the particles may include a release agent which progressively releases the bleaching agent, as described in further detail below.

The exemplary delivery device12can be driven by water or air or both. The delivery fluid can thus be a gas, a liquid, or combination thereof. An exemplary delivery fluid is an atomized liquid in a gas. The liquid can be water or an aqueous solution. The gas can be air, oxygen, carbon dioxide, nitrogen, or the like. In other embodiment the device provides an aerosol of particles in gas only, without liquid.

Various dental devices exist for delivery of fluids to the oral cavity which may be adapted to use for delivery of the capsules28. As examples, delivery devices are disclosed in U.S. Pub. Nos. 2009/0305187; 2010/003520; 2010/0273125; 2010/0273126; 2010/0273127; 2010/0217671; 2011/0207078; 2011/0244418; and WO 2010/055435. Such devices have been particularly useful for cleaning of interproximal spaces. The devices often generate liquid droplets by merging liquid flowing from a reservoir into a fast-moving gas stream, such as provided by a source of compressed gas. The devices are activated by a user operating a button or the like, releasing successive bursts of compressed gas, which results in a high velocity gas stream. When this high velocity gas stream comes into contact with a flow of liquid from the reservoir, liquid droplets are produced.

FIG. 7illustrates another embodiment140of a device for delivery of bleaching agent particles to the teeth in which such a device is adapted for whitening. The device can be similar, in many respects, to that ofFIG. 1, where, similar elements are accorded the same numerals and new elements are accorded new numerals. In this embodiment, the delivery mechanism14,114may form a part of a removable nozzle assembly142which may be interchangeable with a conventional nozzle assembly used for cleaning without particles. As for the device12ofFIG. 1, the device140includes an actuation mechanism62, for causing the device to deliver the high pressure fluid from the fluid source16. Any suitable actuation mechanism may be employed, such as a switch, button, or the like which directly or indirectly (e.g., via an electrical circuit, pump, a syringe with a gear operated plunger, gas cylinder release valve, or the like) causes high pressure fluid (e.g., gas) to be released by the source16. For example, the device140provides pulses of gas and/or liquid at high velocity, each pulse producing sufficient force to dislodge particles from the cavity46and then direct them to the tooth in a manner similar to which an inter-dental cleaning device directs water droplets to the tooth surface. The device shown inFIG. 7uses atomized water in pulses of air, although air jets alone could also be used to dislodge and transport the particles to the tooth surface. By activating the device repeatedly, e.g., via depressing the button62, the device produces many pulses of air/water and accompanying doses of particles from the delivery mechanism14or114.

The source16of delivery fluid may include a reservoir144, which holds a supply of water, and a gas source146. The water from the reservoir may be delivered to the pathway by a pump, by aspiration, or other suitable mechanism. The gas source146may include a canister containing a pressurized gas or a mechanism for pressurizing air at atmospheric pressure. Suitable pressurizing mechanisms are disclosed, for example, in U.S. Pub. No. 2011/0244418. As an example, the pressurizing mechanism may include a syringe with a barrel containing air. A plunger, movable within the barrel, is automatically actuated by an associated gear mechanism to reduce the volume inside the syringe barrel and thereby pressurize the air before it is released into the pathway20. Alternatively, the air may be pressurized by a pump148. A tube150carries the air to a mixing zone152. A separate tube154carries water from the water reservoir144to the mixing zone, where it atomizes (forms small droplets) in the air. The illustrated mixing zone152is in the pathway20upstream of the delivery mechanism14, such that a mixture of air and water forces the particles from the cavity36. In other embodiments it is contemplated that the water may mix with the air and particles at a mixing zone downstream of the delivery mechanism, e.g., in the nozzle24.

The pressure of the fluid exiting the nozzle outlet22in the embodiments disclosed herein can be, for example, from 0-20 N/cm2(0-2 Bar), e.g., at least 1 N/cm2. The gas source146may deliver air at a velocity of up to 600 meters per second (m/s), e.g., a velocity of at least 10 or at least 30 m/s, and in some embodiments, up to 200 or 300 m/s. The velocity and size of the water droplets can also vary. For example, the droplets may have a size in the range of 5-500 micrometers, and velocity of, for example, in a range of 10-300 meters m/s.

The device disclosed in WO 2010/055435, for example, can eject water droplets at velocities from 10 to 100 m/s, which is sufficient for delivery of the particles28disclosed herein, although higher or lower velocities may be appropriate in some embodiments. The force exerted on the particles28when impacting a hard surface, such as a tooth, can be estimated based on the average particle size and density. Assuming, for example, a particle size of 20 μm diameter and a density of 1 g/mL, each particle has a mass of approximately 30 nanograms. Taking a velocity of about 50 m/s and a deceleration distance of 10 μm, the force exerted on the particle on impact will be about 7.5 mN. This is generally sufficient to cause the particles to adhere well to the teeth, and in some embodiments, for the particles to rupture.

In some embodiments, the nozzle and/or the fluid source16is configured for providing a higher fluid pressure when the device12,140is used for whitening than when it is used without the whitening particles. In one embodiment, the delivery device12,140has a first nozzle assembly configured for delivery of fluid without the capsules and a second nozzle assembly, interchangeable with the first nozzle assembly, which is specifically adapted to the delivery of the capsules. For example, nozzle assembly142includes an engagement member, such as a threaded cap, which is engageable with a mating engagement member, such as a threaded neck of the body18.

In some embodiments, the device may be configured to provide a first gas flow suited to use of the device12,140in a mode without the particles28and a second gas flow, higher than the first, suited to use of the device12in a mode when the whitening particles are being used. In some embodiments, the change in pressure is achieved through different nozzle designs for the two modes or through the trigger mechanism.

FIG. 8summarizes the exemplary method for delivering the particles28to a hard surface, such as the teeth. The method begins at S100. At S102, a cartridge is loaded into the device12,140. The cartridge32of particles is inserted into the device through the opening90in the body so that the opening50to the reservoir is positioned over the cavity46, in the first position of the slider40, using the guide member96to guide the insertion. In other embodiments, the cartridge of particles is disposable along with the nozzle, and so need not be inserted into the device. The membrane98may be broken during the closing of the door92.

With the slider in the first position, a dose48of particles is received by the delivery mechanism14(S104). The device is actuated at S106. For example, the user actuates the device by pressing the button/trigger62. This generates a pulse of fluid. In particular the device causes a jet of the pressurized fluid to flow through the pathway20towards the pressurization chamber82. (This releases the particles into the fluid flow when the flow path is subsequently completed through the openings78,80.)

At S108, the slider is moved toward the second position and the pressurization chamber82is pressurized by the pulse of fluid. As the slider reaches its second position, adjacent the second ends of the channel, the particles are released into the fluid pathway. As will be appreciated, S106and S108can take place contemporaneously. At S110, particles are ejected from the nozzle strike the teeth and may rupture. The method may return from S108to S104for one or a plurality of repeats of S104-S108. Over a period of minutes or hours, the whitening agent is released and effects a whitening of the teeth. The method ends at S112. The cartridge may be left in the device until it is empty.

The particles adhere to the teeth and may rupture. The whiteness of the particles or other color, can be used as an indicator to enable the user to see where the particles have already been applied. The cartridge can remain in the device for a subsequent bleaching operation at a later time, such as one or more days later, since the remaining particles remain dry in the reservoir.

Particles28of small size adhered to the tooth can be significantly unnoticeable by touch or sight (their color can be white), so are not a nuisance to the wearer. The user may apply the particles before going to bed so that the dental care agent (e.g., peroxide) action on the teeth occurs overnight. Tooth brushing in the morning can remove any particulate remnants. The user may repeat the process, as needed. The device12,140acts to concentrate the particles on the tooth by repeated jets of particles projected onto the front teeth area. This provides a targeted method of peroxide application. Particles that miss the teeth will generally be at low concentrations elsewhere in the mouth. Additionally, as they will likely not have struck a hard surface, they will tend to release peroxide at a rather slow rate. Since the total concentration of peroxide in the particles of each dose48(or even in a set of doses, for example, 2-20 such doses), is controlled and quite small, the method can be considered safe for home use.

In one embodiment, the velocity of the particles28is sufficient to cause them to rupture upon hitting the tooth. In this embodiment, the particles may be of a form that enables them to rupture upon impact. In another embodiment, the particles28have an outer layer which becomes permeable, e.g., thorough dissolution of the layer or components hereof, water absorption by the layer, or the like. The exemplary particles may have a density which is less than that of water, for example, less than 0.9 g/cm3at 25° C.

The exemplary particles28can be dry, solid particles of at least 1μm in diameter on average, and up to about 200μ in diameter, e.g., 10-100 μm in diameter, on average, and in one embodiment, 20-50 μm on average. Each particle28includes a dental bleaching agent (whitening agent) protected by a moisture-resistant material. The bleaching agent may form a core of the particle, which is encapsulated in the moisture-resistant material which forms an outer layer of the particle that surrounds and protects the core from exposure to moisture during storage.

Exemplary bleaching agents are solid at ambient conditions and include carbamide peroxide, which is an adduct of urea and hydrogen peroxide (CH4N2O—H2O2). The material releases hydrogen peroxide on contact with water. Other example bleaching agent sources include alkali metal percarbonates, sodium perborate, potassium persulfate, calcium peroxide, zinc peroxide, magnesium peroxide, strontium peroxide, other hydrogen peroxide complexes, sodium chlorite, combinations thereof, and the like. The particles28can include bleaching agent, e.g., carbamide peroxide, at a concentration of at least 10 wt. %, such as up to about 40 wt. %. For example, at about 20 wt. %. carbamide peroxide, the hydrogen peroxide concentration per particle28is about 6%, which is comparable to whitening strips.

FIGS. 9-11illustrate exemplary particles. As will be appreciated, these drawings are intended to be illustrative only and are not intended to be to scale. The particles can comprise a bleaching agent encapsulated in a shell.

In the particle28A ofFIG. 9, the particle includes a core160formed of a bleaching agent which is encapsulated by a shell162of a carrier material, such as shellac, which ruptures on impact with the teeth. The shell may be entirely formed of shellac or predominantly formed of shellac, e.g., at least 50 wt. %, or at least 80 wt. %, or at least 90 wt. % shellac.

Shellac is a natural, biodegradable and renewable resin of insect origin (Kerria lacca). It consists of a mixture of polyesters including polyhydroxy polycarboxylic esters, lactones and anhydrides and the main acid components are aleuritic acid and terpenic acid. Shellac has the features of low water permeability, and excellent film forming properties. It is enteric and listed as a food additive. Recently, methods to extract and purify shellac have significantly improved the stability of batch-to batch production and the use of an aqueous formulation of shellac (ammonium salt of shellac) has allowed elimination of the use of any organic solvents.

In one embodiment, particles28A are formed according to the method described in Jing Xue and Zhibing Zhang, “Preparation and characterization of calcium-shellac spheres as a carrier of carbamide peroxide.” In this method, an aqueous formulation of shellac (ammonium salt of shellac) is mixed with carbamide peroxide powder to dissolve the carbamide peroxide. Droplets of the resulting mixture are then dropped from a nozzle into a cross-linking solution comprising calcium chloride in ethanol to form solid particles of calcium shellac with hydrogen peroxide encapsulated. An ice bath can be used to maintain the temperature of the cross-linking solution at 4° C. A coaxial air stream with a flow rate, for example, of 90 liters/hr can be used to pull the liquid stream from the nozzle tip to create droplets and consistent particles. After the extrusion process, the particles formed in the cross-linking solution may be transferred into a stabilization solution of calcium chloride (at 4° C.) to increase the mechanical strength of the particles. The calcium shellac particles with carbamide peroxide encapsulated can be frozen by putting them into a freezer at 25° C. for 1 hr and then dried in a freeze dryer. A vacuum pump is switched on during the freeze drying process, which may be continued for 24 hr. The temperature in the drying chamber can be maintained at 25° C. with the aid of a fan.

In another method, particles28A are formed as described in Jing Xue, Zhibing Zhang. “Physical, Structural, and Mechanical Characterization of Calcium—Shellac Microspheres as a Carrier of Carbamide Peroxide.” In this method, an emulsification-gelation method is used in which calcium chloride powder is dispersed in an oil phase to encapsulate water-soluble carbamide peroxide. The carbamide peroxide is dissolved in shellac solution (ammonium salt of shellac). The mixture of carbamide peroxide and shellac is dispersed in an oil, such as sunflower oil by agitating the mixture, e.g., with a flat-blade disk turbine impeller at an agitation speed of 200 rpm for30min. CaCl2powder is added slowly into the dispersion. Agitation is maintained for another 2 hr. The formed microspheres settling at the bottom of the stirred vessel are then collected, washed with 2% Tween80solution, and dried at room temperature (about 24° C.) for 24 hr by freeze drying, as for the other method.

In other embodiments, the shell can comprise a hydrophobic material which adheres to the teeth, the particles further comprising a release rate modifier in contact with the hydrophobic material, which modifies the rate of release of bleaching agent from the particle. The hydrophobic material can comprise a waxy solid. The release rate modifier can be selected from the group consisting of polyethylene glycol, silica, water-soluble alkali metal salts, and combinations thereof. In the particle28B ofFIG. 10, for example, the particle includes a core166formed of a bleaching agent which is encapsulated in a shell168, formed of the controlled release carrier material. The controlled release carrier material in shell168includes a hydrophobic material, serving as a matrix, such as a wax, and a release rate modifier in contact with, e.g., dispersed in, the hydrophobic material. The particle28B adheres to the tooth and the integrity of the hydrophobic material is disrupted when the release rate modifier comes into contact with water. A ratio of the release rate modifier to hydrophobic material can be tailored to provide a slower or faster release rate of the hydrogen peroxide.

In the particle28C ofFIG. 11, the particle includes a core170formed of a bleaching agent which is encapsulated by a shell172of controlled release carrier material in the form of two layers174,176, the first, inner layer174comprising release rate modifier, and the second, outer layer176comprising hydrophobic material, such as a wax. The integrity of the hydrophobic material is disrupted when the particles collide with the teeth and the release rate modifier is thereby exposed and comes into contact with water. This enables a slow release of the hydrogen peroxide from the core over several hours. A ratio of the release rate modifier to hydrophobic material can be tailored to provide a slower or faster release rate of the hydrogen peroxide.

The hydrophobic material used to form the shell168,172of particles28B and28C may be a waxy solid, i.e., is solid at ambient temperature (25° C.) and may be a solid at higher temperatures. The hydrophobic material may be primarily (greater than 50%) or entirely formed from a waxy solid. Exemplary waxes suitable to use as the hydrophobic material include hydrocarbon waxes, such as paraffin wax, and the like, which are substantially or entirely free of unsaturation. Exemplary paraffin waxes are mixtures of higher alkanes of the general formula CnH2n+2, where typically, 20≦n≦50. They are solid at ambient temperatures and melt-processable.

The release rate modifier used for forming the shell168,172of particles28B and28C may be a material which is insoluble or substantially insoluble in the hydrophobic material such that it forms discrete regions where it is of high concentration in the hydrophobic material (or a separate layer174). The discrete regions have an average size of, for example, 0.1-100 nm, e.g., 0.5-20 nm.

The release rate modifier may be more hydrophilic than the hydrophobic material. Exemplary release rate modifiers include hydrophilic organic polymers which are capable of hydrogen bonding and that are solid at ambient temperatures (25° C.), and hydrophilic and/or water soluble powders. The release rate modifier may be present in the microparticles in a total concentration of from 0.001 wt. % to 30 wt. %. Examples of hydrophilic powders include anhydrous inorganic particles, such as silicon dioxide, e.g., hydrophilic silica and silica nanopowders. Exemplary water-soluble powders include water-soluble acids and salts thereof, such as anhydrous phosphate salts, e.g., sodium polyphosphate, sodium tripolyphosphate, sodium pyrophosphate; anhydrous citric acid and salts thereof, such as alkali metals salts, e.g., sodium citrate; anhydrous sodium sulfate, anhydrous magnesium salts, such as magnesium sulfate and magnesium chloride. Combinations of such release agents may be employed. The hydrophilic and/or water soluble powders, such as silica, may have an average size of, for example, 1-100 nanometers (nm), e.g., 5-20 nm. Hydrophilic fumed silica may be obtained under the tradename AEROSIL™ from Evonik Industries with a specific surface area (measured by the BET method) in the range of 90-300 m2/g. As an example, AEROSIL™ 200 has a specific surface area of 200 m2/g.

Hydrophilic organic polymers which are useful as release rate modifiers include polyalkylene glycols, such as polyethylene glycol and polypropylene glycol, and esters thereof, polyamide compounds (e.g., polyvinylpyrrolidone), poly(vinyl acetate), poly(vinyl alcohol), poly(acrylic acid), polyacrylamide, polyoxylglycerides, such as lauroyl, oleoyl, and stearoyl polyoxylglycerides, which are mixtures of monoesters, diesters, and triesters of glycerol and monoesters and diesters of polyethylene glycols (e.g., lauroyl macrogolglycerides), and ethylene oxide derivatives thereof, poloxamers, which are triblock copolymers having a central hydrophobic block of poly(propylene oxide) and two side blocks of poly(ethylene oxide) (e.g., poloxamer 188, which has a melting point 52° C.), and derivatives thereof, and mixtures thereof. The hydrophilic polymer can have a weight average molecular weight of at least 300.

Exemplary polyethylene glycols (PEG) for the release rate modifier have a molecular weight of 300 daltons to 50,000 daltons, e.g., 600-35000, or 1000 to 5,000 daltons. As examples PEG 1000 (melting point 37-40° C.), PEG 1500 (melting point 44-48° C.), PEG 2000 (melting point 49-52° C.), combinations thereof, and the like may be used.

A ratio of the hydrophobic material to release rate modifier in the particles may be, for example, from 1:99 to 99:1, expressed by weight, such as from 5:95 to 95:5 or from 10:90 to 90:10. For example, the ratio of hydrophobic material:release rate modifier may be about 30:70 to 70:30, for example, in the case of PEG. For hydrophilic and/or water soluble powders, the ratio may be higher, such as at least about 85:15.

The particles of types28A, B, and C generally have a low water content, such as less than 5 wt. %, or less than 1 wt. %, or less than 0.2 wt. % of the particles is made up of water.

The particles of types28A, B, and C may be used separately or combined in a container34.

The microparticles28can be formed by a variety of methods including spray cooling, precipitation, and the like. Spray cooling/chilling methods can be used where the molten hydrophobic material containing the core material is sprayed into a cold chamber or onto a cooled surface and allowed to solidify. For example, small particles of carbamide peroxide, or other bleaching agent, are combined with a molten mixture of wax and release rate modifier, e.g., PEG. The mixture is sprayed through a nozzle into a fluid at a sufficiently low temperature to solidify the mixture as microparticles. For example, carbon dioxide at low temperature may be used as the cooling fluid. Other encapsulation techniques are disclosed in MICROENCAPSULATION: Methods and Industrial Applications, Edited by Benita and Simon (Marcel Dekker, Inc., 1996).