Dentistry – Orthodontics – Bracket
Reexamination Certificate
2001-03-05
2002-11-19
Lewis, Ralph A. (Department: 3732)
Dentistry
Orthodontics
Bracket
C433S029000
Reexamination Certificate
active
06482002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention broadly relates to appliances that are used during the course of orthodontic treatment. More particularly, the invention relates to orthodontic appliances such as brackets that are directly bonded to the surfaces of teeth, methods for bonding orthodontic appliances to teeth and methods for making orthodontic appliances.
2. Description of the Related Art
Orthodontic treatment involves the movement of malpositioned teeth to orthodontically correct locations. Orthodontic treatment is often undertaken to improve the patient's facial appearance. In addition, orthodontic treatment when completed can provide improved occlusion and help avoid undue wear on the teeth enamel that might otherwise create additional problems in the future.
One type of common orthodontic treatment includes the use of a set of tiny, slotted appliances known as brackets. Each of the brackets is mounted on an outer surface of the patient's tooth, and an archwire is placed in the slot of each bracket. The archwire forms a track to guide movement of the brackets such that the associated teeth are brought into positions of correct alignment. Ends of the archwire are often received in small molar appliances, also called buccal tubes, that are mounted on molar teeth of each dental arch.
Many commercially available orthodontic appliances are adapted to be directly bonded to the outer surface of the patient's teeth by an orthodontic bonding adhesive. Some types of orthodontic adhesives are initially supplied as two separate components, such as CONCISE brand adhesive from 3M Unitek. As the components are mixed together, the components react with each other to form an adhesive that ultimately hardens and provides sufficient strength to bond the appliance to the tooth.
Two-component orthodontic adhesives have a certain “working time”. During the working time, the practitioner transfers the mixed adhesive to the base of the appliance, places the appliance on the tooth and shifts the appliance as may be needed to a desired position on the tooth, all before the adhesive begins to harden. However, if the working time is too short or if the practitioner is interrupted during the procedure, the practitioner may not have sufficient time to precisely place the appliance in its intended position on the tooth surface. On the other hand, if the working time is too long, there is a risk that the appliance will shift from its intended position before the adhesive hardens. Unintentional appliance movement may occur, for example, if the appliance is bumped or jarred, or if the adhesive has a viscosity that enables the appliance to drift along the surface of the tooth. Unfortunately, appliances that are mispositioned once bonded to the teeth represent a significant nuisance to the practitioner as well as to the patient, especially in instances when the appliance must be removed from the tooth and rebonded at the correct location.
For the reasons set out above, many orthodontic practitioners prefer to use a photopolymerizable adhesive that begins to harden once a source of light is directed toward the adhesive. Photopolymerizable adhesives, also known as light-curable adhesives, are used by many orthodontic practitioners because the length of the working time can be chosen as needed. For example, an appliance with a light-curable adhesive can be carefully placed on the patient's tooth and shifted as desired until such time as the practitioner is satisfied with the position of the appliance. At that time, a source of light is directed toward the adhesive in order to harden the adhesive and quickly fix the appliance to the tooth.
Over the years, many attempts have been made to increase the strength of the bond between orthodontic appliances and the associated teeth. Some brackets, for example, have an outer base surface that is roughened, scribed or dimpled, while other brackets have a base surface that includes one or more layers of irregularly shaped fragments or spherical particles. Such base surfaces present an increased surface area that is available for contact with the adhesive, in order to improve the strength of the bond between the appliance and the tooth.
Additionally, certain orthodontic appliances have bases that present undercut regions to receive the adhesive. Once the adhesive has hardened, the adhesive in the undercut regions forms a mechanical interlock with the appliance. As an example, the bases of some appliances have a fine mesh metal “screen” or pad that becomes embedded in the adhesive and provides a mechanical interlock with the adhesive once the adhesive has hardened. Other appliances, such as that shown in U.S. Design Pat. No. 290,040, have a series of undercut grooves that provide a mechanical interlock with the hardened adhesive. U.S. Pat. Nos. 4,094,068 and 5,435,720 describe appliances having bases with peripheral holes or notches that enable the adhesive to flow through and produce an enlarged head that serves to improve retention of the appliance on the tooth. Orthodontic appliances may also have irregularly-shaped fragments or spherical particles that present undercut regions.
Orthodontic appliances are available in a variety of materials, including metallic materials (such as stainless steel and titanium), plastics (such as filled and/or reinforced polycarbonate) and ceramics (such as monocrystalline and polycrystalline alumina). Some orthodontic practitioners and patients prefer appliances that are made of transparent or translucent materials such as certain plastics and ceramics, because those appliances can blend in with the color of the patient's teeth and as a result are less noticeable in the oral cavity. Some orthodontic appliances, such as those described in applicants U.S. Pat. No. 4,954,080, are made of a polycrystalline alumina material that has sufficient translucency to enable the color of the tooth to be visible through the appliance in order to provide an enhanced aesthetic appearance.
When a photopolymerizable orthodontic adhesive is used in combination with an appliance that is made of a translucent or transparent material, light passing through the appliance can normally reach the underlying adhesive. As a result, the adhesive is usually hardened to a substantial extent under most, if not all, portions of the appliance base. The extent of hardening of the adhesive helps ensure that the appliance does not spontaneously debond from the patient's tooth during the course of orthodontic treatment.
Many practitioners, however, prefer to use orthodontic appliances that are made of materials other than light-transmissive plastic and ceramic materials. For example, a substantial number of orthodontists prefer to use appliances made of stainless steel. Although stainless steel appliances are often not considered aesthetic, many practitioners choose stainless steel appliances because they are relatively inexpensive and yet provide satisfactory control over movement of the associated teeth.
However, stainless steel is an opaque material that blocks passage of light to underlying areas of the appliance base. As a consequence, portions of photopolymerizable adhesive beneath the base may not harden, especially in areas near the center of the base. Often, the practitioner may direct light toward the adhesive along two or more edges of the base of metal appliances or attempt to direct light through the patient's tooth enamel. However, such a practice may not harden all of the adhesive beneath the base to a degree necessary to preclude unintentional debonding of the appliance when the appliance is subjected to a relatively large force.
U.S. Pat. No. 5,711,665, assigned to the assignee of the present invention, describes a method and apparatus for bonding orthodontic appliances to teeth. The appliance includes a base with an opening, and a body with a passage aligned with the opening. The passage in the appliance permits light to reach adhesive beneath a central portion of the appliance base that would
Binder Oscar M.
Georgakis Evangelos G.
Jordan Russell A.
Puttler Oliver L.
3M Innovative Properties Company
Christoff James D.
Lewis Ralph A.
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