Orthodontic Bracket and Associated Fabricating Method

This invention relates to an orthodontic bracket for securing an arch wire or other orthodontic appliances to the tooth of a patient, and an associated bracket fabricating method. In this particular invention the bracket generally comprises a body fabricated of a high strength polymer (plastic), preferably, filled with a colloidal oxide filler, fibers and/or whiskers.

In the orthodontic art, it is a common practice to place metal, plastic or ceramic brackets upon the teeth in order that an arch wire can be stretched across these brackets for the purpose of properly positioning the teeth. These brackets must have the strength to withstand high pressure when wires are stretched across them. However, the bracket's composition must be susceptible to mechanical (or chemical) bonding to the tooth. Another aspect which must be considered is the aesthetic durability of the bracket.

The original orthodontic brackets were based on metal bands, which were wrapped around the tooth. These were extremely unaesthetic and presented difficulty in the mechanics of moving the tooth into proper position. In addition, these orthodontic appliances were extremely labor intensive and often caused damage to the tooth due to difficulty (or impossibility) of maintaining proper dental hygiene.

A second generation of orthodontic brackets were based on a smaller metal bracket which could be affixed directly to the face of the tooth. These brackets were affixed by mechanical bonding between the etched enamel of the tooth and the interlocking grid structure on the bonding surface of the bracket. While more aesthetic than bands, these metal brackets were still quite unaesthetic. Also, these metal brackets could be difficult to bond to the tooth due to the need to entirely fill the grid structure of the bonding surface of the bracket with adhesive. In addition, these metal brackets were expensive to manufacture due to the complexity of the manufacturing process.

A third generation of orthodontic brackets was the lingual device which was affixed to the back side of the tooth. While this method was more aesthetic than previous ones, it presented difficulties in bonding and practice.

A fourth generation of orthodontic brackets was the plastic bracket. While being moderately aesthetic and inexpensive, these brackets would stain and thereby depreciate the aesthetic quality of the brackets. In addition, the plastic composition did not provide adequate stiffness and often resulted in the plastic bracket detaching from the tooth due to the inability of the bracket to hold the adhesive in place. Also, due to its lack of stiffness, treatment was restricted to cases requiring minimal mechanical treatment.

A fifth generation of orthodontic devices was the ceramic bracket. While this bracket was translucent and thereby very aesthetic, the ceramic composition produced a brittle structure. This bracket was also very abrasive to opposing and impinging teeth as well as the arch wire. In addition, the ceramic bracket was difficult to remove, often resulting in damage to the tooth enamel.

Certain related devices, compositions, and methods are disclosed in U.S. Pat. Nos. 3,895,445; 4,435,160; 4,695,251; and 4,772,325.

Accordingly, it is an object of the present invention to provide a plastic/composite orthodontic bracket which is essentially color neutral and thereby aesthetic due to the transparent (or translucent) properties of the constituents.

It is also an object of the present invention to provide an orthodontic bracket which will not stain, even with exposure to foods and drinks, including coffee, cigarettes, juices, etc.

It is a further object of the invention to provide an orthodontic bracket which is chemically bondable to an etched tooth or enamel surface using standard orthodontic adhesives which are designed to chemically adhere to an etched tooth or enamel surface.

It is a further object of the invention to provide an orthodontic bracket which is stiffer and stronger than other plastic brackets.

It is yet another object of the invention to provide an orthodontic bracket which is both tough with respect to the mechanical stresses and wear of the arch wire dynamics and also non-abrasive when in contact with adjacent and/or impinging teeth.

It is a further object of the invention to provide an orthodontic bracket which is formed by injection or compression molding and is curable by heat, chemical reaction or microwave or other electro-magnetic radiation.

Yet another object of the present invention is to provide an orthodontic bracket which is inexpensive to manufacture.

Other object and advantages will be accomplished by the present invention which provides an orthodontic bracket for securing orthodontic appliances to a tooth, and an associated bracket fabricating method. The orthodontic bracket comprises a bracket body made of a high strength, thermal, chemical or electromagnetic radiation cured polymer containing organic or inorganic fillers typically being, but not limited to colloidal oxides and inorganic fibers and/or whiskers to add strength and stiffness to the body. The body can also be coated with a protective coating to resist staining and/or abrasion. In various embodiments of the inventions, the coating includes an organo-functional silane layer and/or a high strength plastic stain and abrasion resistant coating. Generally, the method of the present invention includes the steps of filling the plastic fabricating material with the oxide filler and/or reinforcing fibers or whiskers, and then molding the bracket into the desired configuration. The body can then be cured using heat, chemical reactions or electro-magnetic radiation. The cured bracket can then be coated with an organo-functional silane or coated with an abrasion and stain resistant coating.

The above mentioned features of the invention will become clearly understood from the following detailed description of the invention read together with the drawings in which:

FIG. 1 illustrates a perspective view of an orthodontic bracket of the present invention;

FIG. 2 illustrates a side elevation view, in section, of an orthodontic bracket of the present invention;

FIG. 3 illustrates a partial side view, in section, of one alternate embodiment of an orthodontic bracket of the present invention diagrammatically depicting the composition of such bracket.

FIG. 4 illustrates a partial side view, in section, of one alternate embodiment of an orthodontic bracket of the present invention diagrammatically depicting the composition of such bracket.

FIG. 5 illustrates a partial side view, in section, of one alternate embodiment of an orthodontic bracket of the present invention diagrammatically depicting the composition of such bracket.

FIG. 6 illustrates a partial side view, in section, of one alternate embodiment of an orthodontic bracket of the present invention diagrammatically depicting the composition of such bracket.

FIG. 7 illustrates a partial side view, in section, of one alternate embodiment of an orthodontic bracket of the present invention diagrammatically depicting the composition of such bracket.

An orthodontic bracket incorporating various features of the present invention is illustrated generally at 10 in FIG. 1. As will be understood by those skilled in the art, the bracket 10 is used for securing an arch wire to the tooth of a patient, the arch wire serving to selectively apply pressure to the tooth to move the tooth to a desired position. Accordingly, the bracket 10 defines a rearward tooth engaging surface 12 and is provided with a forwardly disposed arch wire slot 14 for receiving an arch wire (not shown). Whereas the configuration of the bracket 10 can vary depending upon the particular application, in one embodiment the bracket 10 includes the wing portions 16 which serve as means for attaching elastic bands for purposes of ligation and attachment of other devices as deemed necessary by the orthodontist.

For aesthetic purposes the bracket 10 is preferably translucent, e.g. with 30%-40% visible light transmission, such that the bracket 10 transmits the coloration of the tooth on which it is secured, without the artificial reflectivity of total transparency. However, it will be understood that, if desired, the bracket 10 can be constructed so as to be totally transparent or can be pigmented to match the coloration of the operatively associated tooth.

As illustrated in FIG. 2, the bracket 10 generally comprises a body 18 which is preferably, coated with a stain and/or abrasion resistant coating 20. In the embodiment of FIG. 2, the body 18 is fabricated of a plastic material 22 such as a high strength polycarbonate. One suitable material is the high strength plastic, Lexan. Utilizing such material, the body can be formed by injection or compression molding, or other suitable molding processes as will be discussed further below.

As diagrammatically depicted at 18A in FIG. 3 and 4, in an alternate embodiment the body of the bracket 10 is strengthened and made more rigid by dispersing a particulate oxide filler 24 in the plastic fabricating material 22A. Suitable oxide fillers include, without limitation, alumina (Al.sub.2 O.sub.3), silica, aluminum hydroxide, wollastonite, spinel, and mixtures, thereof. Further, the oxide filler 28 preferably defines sub-micron, colloidal-sized oxides in order to facilitate the compacting of the filler within the resulting matrix, and, thus, reduce irregularities in, and the porosity of, the exterior surface of the body 18A. By reducing the irregularities in, and the porosity of, the exterior surface, the surface is less susceptible to staining.

The concentration of the colloidal oxide filler 28 within the matrix can vary depending upon the strength and rigidity desired. Further, in the preferred embodiment the filler 24 is translucent for purposes of aesthetics, but the light transmitting capacity of the filler can vary as desired. In this regard, it will be recognized that the resulting light transmitting capacity of the body 18A will vary depending upon the light transmitting capacity of the filler 24 and the density of the filler 24 within the polycarbonate matrix. Thus, for example, where a transparent plastic is used for the material 22, the desired translucence of the body 18A can be obtained through use of a filler 24 having a preselected, lesser light transmission capacity at a preselected density.

As noted above, the colloidal oxide filler 24 is readily compactible so as to reduce the porosity of the exterior surface of the body of the bracket. However, whenever a filler is used in a plastic small pores or capillaries such as those illustrated at 26 in FIG. 3 can form in the exterior surface. If unfilled, these capillaries can fill with foreign matter, resulting in the staining of the exterior surface of the bracket 10. In order to obviate such staining, in the embodiment of FIG. 3, the coating 20A includes a coating of organo-functional silane 28. As illustrated, the silane coating fills the pores and capillaries 26 of the exterior surface of the body 18A and provides a smooth surface which resists staining. The silane coating 28 can be applied, as by dipping, spraying or painting.

Referring now to FIG. 4, in an alternate embodiment the coating 20B comprises a high strength stain and abrasion resistant plastic coating 30, bonded to the body 18B. Particularly suited for this purpose is a silicone or acrylic material which is curable with ultraviolet or other electro-magnetic radiation, by solvent evaporation (drying) or by heat. The plastic coating 30 can be applied to the body 18B by dipping, painting or spraying and serves to provide a smooth abrasion and stain resistant exterior surface.

In the further alternate embodiment illustrated in FIG. 5 it will be noted that the body 18C can also be strengthened by dispersing reinforcing whiskers or fibers 32 in the polycarbonate material 22C. Preferably the fibers 32 are fabricated of glass or ceramic and are translucent. Of course, the fibers 32 can be used without the oxide filler 24C. However, the combination of a colloidal oxide filler 24C and fibers 32 in this matrix is particularly effective in providing a strong durable bracket. In this regard, the colloidal-sized oxides 24C serve to efficiently fill the spaces between the fibers or whiskers 32 firmly locking the fibers 32 in the matrix. Further, organo-functional silanes function as adhesion promoters and can be engineered to have affinities for differing materials so as to aid in the bonding together of such materials. Thus, as illustrated in the preferred embodiment of FIG. 6, the particles of the oxide filler 24D and the fibers or whiskers 32D can be coated with organo-functional silanes 28D to promote the bonding of the filler 24D and the fibers or whiskers 32D with the polycarbonate material 22D. The body 18D can be coated with the abrasion and stain resistant coating 30D. It is also possible to coat the body 18D with the silane 28D and give it a level of stain resistance by sealing the surface. In this case the abrasion and stain resistant coating 30D would not be used.

With respect to FIG. 7, in this embodiment the stain and abrasion resistant coating 30E has been filled with a colloidal oxide filler 24E to strengthen and control translucence of the coating 30E. Of course, the filler 24E can be coated with silane prior to dispersal in the coating and applied to the exterior surface of the body to promote bonding with the coating material. Further, it will be recognized that the filled coating 30E of FIG. 7 can be utilized with an oxide and/or fiber or whisker filled body as discussed above, if desired.

In view of the above, it will be understood by those skilled in the art that the present invention provides an aesthetically desirable, stain and abrasion resistant orthodontic bracket with great advantages over the prior art. Moreover, the bracket can be manufactured cost efficiently. For example, to produce one preferred embodiment, the filler 24 and/or fibers or whiskers 32 are coated with an organo-functional silane 28, and the coated filler 24 and/or fibers or whiskers 32 are dispersed in the plastic matrix material 22 to produce the desired composite material for fabrication of the body 18. Then, utilizing the composite material, the body is formed by injection or compression molding, and the stain and abrasion resistant coating 30 is then applied to the body 18. Of course, as discussed above the coating 30 can be filled with colloidal oxides if desired.

The bracket 10 is chemically bondable to an etched tooth or enamel surface using standard orthodontic adhesives due to the coating of silanes 28 which have a high level of adhesion to the bracket bonding surface due to the presence of silanes, colloidal oxides and inorganic fibers or whiskers which may be silanated or unsilanated themselves. In this regard, as illustrated in FIG. 2, a coating of organo-functional silane 28 can be applied to the tooth engaging surface 12 of the bracket 10 to promote adhesion of the bracket 10 to the tooth. The particular silane utilized will be specific to the adhesive to be used to secure the bracket 10 and specific to the material defining the tooth engaging surface 12.

While a preferred embodiment has been shown and described, it will be understood that there is no intent to limit the invention to such disclosure, but rather it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.