United States Patent:  5,998,431

Assignee:  Gillette Canada Inc. (Kirkland, CA)

Filed: April 16, 1998

A sustained-release matrix for dental application includes either an anti-microbial agent or a colorant that is released from the matrix when the matrix contacts water. The preferred matrices include a water-soluble polymer and a water-insoluble support resin.

SUMMARY OF THE INVENTION

The invention features sustained-release matrices that are particularly suited for use with toothbrushes. The matrices can include an anti-microbial agent that is released over time when the matrices are exposed to water. The matrices may also include a colorant and a water-leachable substance that is released over time when the matrices are exposed to water to cause the matrix to change color.

In one aspect the invention features an oral brush that includes a sustained-release matrix made from a support resin, a water-soluble substance (preferably a water-soluble polymer), and an anti-microbial agent. When the matrix contacts water, the water-soluble substance dissolves, causing the release of the anti-microbial agent.

An oral brush, as used herein, is any brush that includes a handle and a head attached to a brush designed for insertion into the mouth. The brush portion preferably is made from the common bristles found in toothbrushes, but can also be designed for massaging the gums rather than the teeth. For example, Kaminski et al., U.S. Ser. No. 07/724,129, which was filed on Jul. 1, 1991, is assigned to the same assignee as the present application and is hereby incorporated by reference, describes an interdental foam brush in which the brush portion is made of a soft polyurethane foam.

A support resin, as used herein, is an essentially water-insoluble polymer that provides structural integrity to the matrix as the other components of the matrix--the water-soluble polymer and anti-microbial agent--dissolve or leach out. A further description of what constitutes a support resin is included in the Other Embodiments section. Preferably, the polymer used as the support resin should have a low processing temperature (less than 130^oC.) so that it can be readily combined with anti-microbial agents that are unstable at high temperature. Also, the polymer should not become brittle as the other components dissolve or leach out, so that the matrix does not break apart readily when handled.

Preferred polymers for the support resin include polystyrene, polyurethane, ethylene vinyl acetate, polyethylene, styrene/rubber, and ethylene/propylene. The more preferred support resin is an ethylene vinyl acetate polymer. Most preferably the ethylene vinyl acetate polymer includes between 5% and 50% vinyl acetate, and has a softening point of between 100^oC. and 35^oC., respectively.

A water-soluble substance, as used herein, is a substance that is sufficiently soluble in water that it will dissolve out of the matrix during contact with water to form channels in the matrix through which the anti-microbial agent will leach into the water. A further description of what constitutes a water-soluble substance is provided in the Other Embodiments section.

The preferred water-soluble substances are polymers. The preferred polymers are starches, polyvinyl alcohols, polyethylene oxides, hydroxyalkyl starches, hydroxyethyl and hydroxypropyl celluloses, and gelatins. The most preferred are polyethylene oxides, most preferably a Polyox having a molecular weight of between 100,000 and 5,000,000.

An anti-microbial agent is a substance that kills bacteria. The preferred anti-microbial agent for use in the matrix is chlorhexidine, most preferably the digluconate salt thereof; the hydrochloride and diacetate salts of chlorhexidine can also be used. Other anti-microbial agents that can be included in the matrix include tetracycline (and other antibiotics), and domiphen bromide.

Preferably, the matrix is a flat template having a thickness of up to 4 mm and is attached to the head of the body at the base of the bristles. The preferred templates have a surface area of at least 0.01 in², more preferably at least about 0.1 in². Most preferably, the template has the same surface area as the toothbrush head (minus the bristles). In this position the template is exposed to water when the brush is rinsed and to saliva when it is inserted into the mouth, and can supply the anti-microbial agent to the bristles for self-sterilization and to the mouth to kill bacteria. The matrix can also be attached to any other part of the brush (e.g., the back of the brush head or at the junction of the brush head and handle), provided that the part of the brush it is attached to is sufficiently close to the head end that it typically is inserted into the mouth during use.

In other preferred embodiments, the matrix includes two layers, joined together. By "two layers", it is meant that one section of the template has a different composition than a second section. The first outer layer includes a support resin or a water-soluble polymer, and an anti-microbial agent; the second inner layer includes the support resin. Significantly, the first layer can include a large quantity of anti-microbial agent because the layer includes less (or none) of the support resin, yet the layer is stable because the co-extruded second layer provides the necessary support. The second layer may also include, optionally, some water-soluble polymer and/or anti-microbial agent.

The invention features, in another aspect, an oral brush that includes a template including a water-soluble polymer and an anti-microbial agent.

The invention features, in another aspect, a matrix including ethylene vinyl acetate, polyethylene oxide, and an anti-microbial agent such as chlorhexidine. The matrix can be sized, shaped, and otherwise designed for short or long term placement at some point in the mouth. The matrix can also be designed as a template for inclusion on a toothbrush, or can be used to coat dental floss, or other dental instrument(s).

The matrices of the invention provide a controlled release of an anti-microbial agent into the mouth. When included on a toothbrush, the matrix repeatedly supplies controlled dosages of the agent to kill bacteria in the mouth and on the bristles of the brush. The matrices are easy to manufacture, and their composition, shape and thickness can be adjusted to provide the best properties for the intended use. For example, the amount and type of polyethylene oxide in the preferred embodiment can be modified so that the viscosity of the released polymer in solution is less than the viscosity of the saliva in the mouth.

Another aspect of the invention features a wear-indicator oral brush that includes a matrix containing a colorant (e.g., a dye) and a water-leachable substance that is released from the matrix when the oral brush is used to cause the matrix to change color after repeated (at least 5) typical uses. The preferred matrix is a template that includes two co-extruded or co-molded layers. The outer layer, which contacts water and saliva during brushing, preferably includes the water-leachable substance, which can be, for example, a water-soluble polymer like polyethylene oxide, or the colorant itself, or a combination of the two. The second, inner, layer preferably includes a support resin, and can also include a colorant (e.g, TiO.sub.2) that provides the template with a different color, or shade of color, than the colorant included in the outer layer. The first layer preferably also includes a support resin, although less than the amount included in the second layer, and also can include an anti-microbial agent.

The oral brushes having a matrix including a colorant, i.e., pigment or dye, provide a means to monitor the degree of wear of the brush. Where the water-leachable substance includes the colorant, over time as the brush is used the colorant is released, causing the matrix to change color. In those embodiments in which the colorant is not water-leachable and thus is not released from the matrix, typically the portion of the template including a water-leachable substance dissolves away through repeated use of the brush to expose the section of the matrix that includes the colorant, providing an indication of wear. The amounts and types of colorant in the matrix can be adjusted so that the color of the matrix changes after the number of uses through which a typical brush should be used. When the colored matrix also includes an anti-microbial agent, the change of colorant can be designed to correspond with the depletion of the agent in the matrix.

Claim 1 of 13 Claims

1. A color-changing matrix comprising two joined layers being co-extruded or co-injection molded and comprising an outer layer comprising a water-soluble polymer and a first colorant, and an inner layer comprising a water-insoluble polymer and a second colorant different from said first colorant.

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